UNIVERSITY OF SUSSEX

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1 UNIVERSITY OF SUSSEX OFDMA in 4G Mobile Communications Candidate Number: Supervisor: Dr. Falah Ali Submitted for the degree of MSc. in Digital Communication Systems School of Engineering and Informatics Department of Engineering and Design Word count: 11840

2 DECLARATION I hereby certify that the attached dissertation is my own work, except where specifically indicated in the text. I have identified my resources and in particular I have put in quotation marks any passages, identifying their origins. I also declare that this dissertation has not been submitted, either in the same or different form, to this or any other University for a degree. Fanny Flores September 2015 II

3 LIST OF CONTENTS DECLARATION... II LIST OF CONTENTS... III LIST OF FIGURES... V LIST OF TABLES... VII LIST OF ABBREVIATIONS... VIII ACKNOWLEDGEMENTS... XI SUMMARY... XII 1 CHAPTER 1: INTRODUCTION AIMS, WORK AND ACHIEVEMENTS MOBILE COMMUNICATIONS EVOLUTION LTE-A OVERVIEW Architecture and Protocol stack Uplink and Downlink Operation Frame Structures Resource Block in OFDMA and SC-FDMA Bandwidth Management Carrier Aggregation Spectrum Sharing Enhanced MIMO OFDMA and SC-FDMA Parameters DOWNLINK PHYSICAL CHANNELS AND SIGNALS Downlink Physical Channels Signals IFFT AND FFT IMPORTANCE LTE-A PERFORMANCE SOFTWARE SIMULATION PACKAGE CHAPTER 2: DESIGN OFDMA BLOCK DIAGRAM SC-FDMA BLOCK DIAGRAM PARAMETERES OFDMA 2 USERS (AWGN) OFDMA 5 USERS (AWGN) OFDMA 2 USERS (AWGN + Rayleigh Fading) OFDMA 5 USERS (AWGN + Rayleigh Fading) III

4 2.8 SC-FDMA 2 USERS (AWGN) CHAPTER 3: SIMULATION SETTINGS OFDMA 2 USERS (AWGN) Transmitter Channel Receiver OFDMA 5 USERS (AWGN) Transmitter Channel Receiver OFDMA 2 USERS (AWGN + Rayleigh Fading) Transmitter Channel Receiver OFDMA 5 USERS (AWGN + Rayleigh Fading) Transmitter Channel Receiver SC-FDMA 2 USERS (AWGN) Transmitter Channel Receiver CHAPTER 4: RESULTS AND ANAYLIS OFDMA 2 USERS (AWGN) OFDMA 5 USERS (AWGN) BER RESULTS PAPR RESULTS CHAPTER 5: CHALLENGES AND DESIGN IMPROVEMTS CHALLENGES IMPROVEMENTS CHAPTER 5: CONCLUSIONSGN IMPROVEMTS CONCLUSIONS FUTURE WORK REFERENCES APPENDIX A... A IV

5 LIST OF FIGURES Figure 1.1.: Global mobile-cellular subscriptions [1]... 2 Figure 1.2: LTE-Advanced E-UTRAN architecture [6]... 5 Figure 1.3: Protocol Stack [6]... 6 Figure 1.4: FDM vs. OFDM [7]... 7 Figure 1.5: OFDM vs. OFDMA [7]... 8 Figure 1.6: OFDMA vs. SC-FDMA in Time and Frequency domains [8]... 9 Figure 1.7: Frame structure type 1 [9] Figure 1.8: Frame structure type 2 [9] Figure 1.9: Resource grid [9], [10] Figure 1.10: Channel bandwidth [11] Figure 1.11: FDD and TDD in CA [12] Figure 1.12: Carrier Aggregation modes [6] Figure 1.13: Spectrum sharing scenarios [6] Figure 1.14: Base station radiation pattern [6] Figure 1.15: LTE-A main MIMO modes [6] Figure 1.16: Cyclic Prefix [13] Figure 1.17: Overview of physical channel processing [9] Figure 1.18: Uplink vs. Downlink Reference signals allocation [14] Figure 1.19: Mapping of downlink reference signals [9] Figure 1.20: IFFT and FFT [15] Figure 1.21: SC-FDMA vs. OFDMA performance with QPSK [16] Figure 1.22: PAPR comparison for OFDMA and SC-FDMA [17] Figure 1.23: Simulink Library Figure 1.24: Simulink Library Browser Figure 1.25: Simulink New Model Figure 1.26: Adding blocks and connecting Figure 2.1: OFDMA Transmission and Reception model [18] Figure 2.2: SC-FDMA Transmission and Reception model [18] Figure 2.3: OFDMA 2 Users Design Figure 2.4: OFDMA 2 Users (AWGN) Diagram Figure 2.5: OFDMA 5 Users Design Figure 2.6: OFDMA 5 Users (AWGN) Diagram Figure 2.7: OFDMA 2 Users (AWGN + Rayleigh Fading) Diagram Figure 2.8: OFDMA 5 Users (AWGN + Rayleigh Fading) Diagram Figure 2.9: SC-FDMA 2 Users Design Figure 2.10: SC-FDMA 2 Users Diagram Figure 3.1: OFDMA 2 Users Transmitter Figure 3.2: Source Block Parameters (OFDMA 2 users) Figure 3.3: Integer to Bit Converter / Bit to Integer Converter Figure 3.4: Rectangular QAM Modulator Figure 3.5: Zero constant vectors (OFDMA 2 Users) V

6 Figure 3.6: Extension of zeros (OFDMA 2 Users) Figure 3.7: Vectors Addition (OFDMA 2 Users) Figure 3.8: Multiport Selector Figure 3.9: Null subcarriers constants Figure 3.10: Reference signals constant Figure 3.11: Matrix concatenate (OFDMA) Figure 3.12: IFFT (OFDMA) Figure 3.13: Cyclic Prefix Addition Figure 3.14: Channel (AWGN) Figure 3.15: AWGN Channel (OFDMA 2 Users) Figure 3.16: OFDMA 2 Users Receiver Figure 3.17: Cyclic Prefix Removal Figure 3.18: FFT (OFDMA) Figure 3.19: Frame Conversion Figure 3.20: Null subcarriers removal Figure 3.21: Reference signals removal Figure 3.22: Reference signals terminator Figure 3.23: Users data separation (OFDMA 2 Users) Figure 3.24: Rectangular QAM Demodulator Figure 3.25: Error Rate Calculation Figure 3.26: OFDMA 5 Users Transmitter Figure 3.27: Source Block Parameters (OFDMA 5 users) Figure 3.28: Zero constant vectors (OFDMA 5 Users) Figure 3.29: Vectors Addition (OFDMA 5 Users) Figure 3.30: Receiver (OFDMA 5 Users) Figure 3.31: Users data separation (OFDMA 5 Users) Figure 3.32: Channel (AWGN + Rayleigh Fading) Figure 3.33: AWGN Channel (OFDMA 5 Users) Figure 3.34 AWGN Channel (OFDMA 5 Users) Figure 3.35: SC-FDMA 2 Users Transmitter Figure 3.36: FFT (SC-FDMA Transmitter) Figure 3.37: Multiport Selector (SC-FDMA) Figure 3.38: Null subcarriers constants (SC-FDMA) Figure 3.39: Matrix Concatenate (SC-FDMA) Figure 3.40: SC-FDMA 2 Users Receiver Figure 3.41: Null subcarriers removal (SC-FDMA) Figure 3.42: IFFT Figure 4.1: TX and RX Integer data (2 Users) Eb/No=30dB (a), 43dB (b), 80dB (c) Figure 4.2: Error rate, Errors and Comparisons (2 Users) Eb/No=30dB (a), 43dB (b), 80dB (c) Figure 4.3: Modulated TX Data (User 1 of 2) Figure 4.4: Modulated RX Data (User 1) Eb/No=30dB (a), 43dB (b) and 80dB (c) Figure 4.5: Modulated TX Data (User 2 of 2) Figure 4.6: Modulated RX Data (User 2) Eb/No=30dB (a), 43dB (b) and 80dB (c) VI

7 Figure 4.7: Transmitted signal Figure 4.8: Received signal Eb/No=30dB (a), 43dB (b) and 80dB(c) Figure 4.9: TX and RX Integer data (5 Users) Eb/No=30dB (a), 43dB (b), 80dB (c) Figure 4.10: Error rate, Errors and Comparisons (5 Users) Eb/No=30dB (a), 43dB (b), 80dB (c) Figure 4.11: Modulated TX Data (User 1 of 5) Figure 4.12: Modulated RX Data (User 1 of 5) Eb/No=30dB (a), 43dB (b), 80dB (c) Figure 4.13: Modulated TX Data (User 2 of 5) Figure 4.14: Modulated RX Data (User 2 of 5) Eb/No=30dB (a), 43dB (b), 80dB (c) Figure 4.15: Modulated TX Data (User 3 of 5) Figure 4.16: Modulated RX Data (User 3 of 5) Eb/No=30dB (a), 43dB (b), 80dB (c) Figure 4.17: Modulated TX Data (User 4 of 5) Figure 4.18: Modulated RX Data (User 4 of 5) Eb/No=30dB (a), 43dB (b), 80dB (c) Figure 4.19: Modulated TX Data (User 5 of 5) Figure 4.20: Modulated RX Data (User 5 of 5) Eb/No=30dB (a), 43dB (b), 80dB (c) Figure 4.21: Transmitted signal (5 Users) Figure 4.22: Received signal (5 Users) Eb/No=30dB (a), 43dB (b), 80dB (c) Figure 4.23: BER Curves for 2 and 5 Users (AWGN) Figure 4.24: BER Curves for 2 Users (a), and 5 Users (b) (AWGN vs. AWGN + Fading) Figure 4.26: PAPR for 2 Users OFDMA (a) vs. SC-FDMA (b) (AWGN) Figure 4.27: OFDMA Design Proposal Figure 4.28: OFDMA Diagram Proposal LIST OF TABLES Table 1.1: 3GPP Releases Summary [3]... 3 Table 1.2: SC-FDMA RB parameters [9] Table 1.3: OFDMA RB parameters [9] Table 1.4: 3GPP LTE-A OFDMA Parameters [10] Table 1.5: Number of OFDM symbols used for PDCCH [9] Table 1.6: Targets for LTE-Advanced as set by 3GPP [5] Table 2.1: Simulation Parameters VII

8 LIST OF ABBREVIATIONS ITU 1G 2G 3G 4G D-AMPS GSM GPRS EV-DO 3GPP LTE LTE-A UE EPS EPC E-UTRAN E-UTRA RAN enodeb / Enb MME S-GW P-GW/ PDN-GW PDCP RLC MAC PHY RRC NAS AS International Telecommunication Union First Generation Second Generation Third Generation Fourth Generation Digital Advanced Mobile Phone System Global System for Mobile Communications General Packet Radio Service Evolution Data Optimized Third Generation Partnership Project Long Term Evolution Long Term Evolution Advanced User Equipment Evolved Packet System Evolved Packet Core Evolved Universal Terrestrial Radio Access Network Evolved Universal Terrestrial Radio Access Radio Access Network Enhanced Node B Mobility Management Entity Serving Gateway Packet Data Network Gateway Packet Data Convergence Protocol Radio Link Control Medium Access Control Physical layer Radio Resource Control Non-Access Stratum Access Stratum VIII

9 ARQ HARQ PDU TDMA CDMA FDMA SC-FDMA OFDMA FDM OFDM PAPR ISI ICI TDD FDD MIMO SU-MIMO MU-MIMO RB UL N symb Automatic Repeat request Hybrid Automatic Repeat request Packet Data Unit Time Division Multiple Access Code Division Multiple Access Frequency Division Multiple Access Single Carrier Frequency Division Multiple Access Orthogonal Frequency Division Multiple Access Frequency Division Multiplexing Orthogonal Frequency Division Multiplexing Peak to Average Power Ratio Inter Symbol Interference Inter Carrier Interference Time Division Duplexing Frequency Division Duplexing Multiple Input Multiple Output Single-User Multiple Input Multiple Output Multi-User Multiple Input Multiple Output Resource Block Number of SC-FDMA symbols in an uplink slot DL N symb Number of OFDMA symbols in a downlink slot N sc RB CP CA BER FER SNR QPSK QAM Resource block size in the frequency domain, expressed as a number of subcarriers Cyclic Prefix Carrier Aggregation Bit Error Rate Frame Error Rate Signal to Noise Ratio Quadrature Phase Shift Keying Quadrature Amplitude Modulation IX

10 MBSFN PDSCH PBCH PMCH PCFICH PDCCH PHICH CRS DM-RS PRS CSI-RS ACK NACK FFT IFFT AWGN TX RX Multicast-Broadcast Single-Frequency Network Physical Downlink Shared Channel Physical Broadcast Channel Physical Multicast Channel Physical Control Format Indicator Channel Physical Downlink Control Channel Physical Hybrid ARQ Indicator Channel Cell-specific Reference Signals Demodulation Reference Signals Positioning Reference Signals Channel State Information Reference Signal Acknowledgement Negative Acknowledgement Fast Fourier Transform Inverse Fast Fourier Transform Additive White Gaussian Noise Transmitter Receiver X

11 ACKNOWLEDGEMENTS I wish to extend my gratitude to the government of Ecuador and to the University of Sussex for this opportunity. I would also like to thank my supervisor Dr Falah Ali for his accurate guide, encouragement and advice. I would like to take this opportunity to thank my loving parents, Juan and Fanny, without whom, I would not be able to reach this achievement in my career. Thanks for their constant support and for being my endless inspiration. Thanks to my siblings, Juan and Evelyn for supporting me during this process. Finally, I would like to thank Antonio for his unconditional support and love despite distance. XI

12 SUMMARY This project analyzes, designs and simulates OFDMA in 4G Mobile Communications. The analysis and designs are based on ETSI TS V technical specification, defined by 3GPP. The simulations have been developed with Simulink of Matlab R2014a. Chapter 1, Introduction, includes a recapitulation of the evolution that mobile communications has had. Besides, it contains a review of the concepts defined by 3GPP for LTE-A; including uplink and downlink, frame structures, resources, parameters. Chapter 2, Design, presents block diagrams and the LTE-A parameters that have been considered for the design. This chapter is organized in five sections, each with a different scenario. The number of users and the introduction of fading has been considered to create the scenarios. At the end, the corresponding designs of OFDMA symbol and Simulink diagrams are presented. Chapter 3, Simulation Settings, describes the settings of each block used in Simulink. This Chapter consists of five sections, presenting the settings of each scenario described in Chapter 2. The analysis is based on transmitter, channel and receiver. Chapter 4, Results and Analysis, studies the results obtained in simulations. The transmitted and received integer data are shown; as well as the Error rate, errors and the number of comparisons made by the corresponding blocks. Also, the modulated transmitted and received data and signals are compared. This Chapter also analyses BER curves, and compares PAPR for SC-FDMA and OFDMA. Chapter 5, Challenges and Design Improvements includes some challenges that LTE-A faces. Finally, the suppression of reference signals is assessed and suggested as a possible improvement. At last, Chapter 6 Conclusions and Future work presents the conclusions of the investigation, analysis, design and simulation carried out in this project. It also contains topics of interest for future study. XII

13 1 CHAPTER 1: INTRODUCTION CHAPTER 1 INTRODUCTION 1.1 AIMS, WORK AND ACHIEVEMENTS This project aims to investigate, design, simulate, analyze results and suggest possible improvements related to OFDMA in LTE-A. Initially, research and investigation were necessary in order to learn and understand LTE- A technical specifications. Besides, the review of previous research was useful. Once the standard was analyzed, the design of OFDMA was carried out. Then, the design was deployed in Simulink with the aid of previous simulations to have some guide about the blocks that execute the required functions. The results of different scenarios were analyzed to finally suggest possible improvements. Some achievements of this project include satisfactory simulations, confirming appropriate designs. Also, the results that were obtained confirm what theory and LTE-A standard denote. Furthermore, improvements to the current standard were presented based on the results. 1.2 MOBILE COMMUNICATIONS EVOLUTION According to the ITU, the number of mobile cellular subscriptions has exponentially increased from 962 million in 2001 to 7,085 million in 2015, which means that 96,8 of 100 inhabitants are currently subscripted to the service [1], as shown in Figure 1.1. MSc. in Digital Communication Systems Page 1 of 95 Candidate Number:

14 Mobile-celullar subscriptions (millions) Per 100 inhabitants This accelerated growth has been the result of the mobile communications evolution in the last years. As a matter of fact, four generations of mobile communications have been developed since the 80 s to current days. 7,000 Global mobile-cellular subscriptions, total and per 100 inhabitants, ,000 5,000 Subscriptions (in millions) Per 100 inhabitants , , , , * Note: * Estimate Source: ITU World Telecommunication /ICT Indicators database 0 Figure 1.1.: Global mobile-cellular subscriptions [1] The first generation (1G) was based on analog technology, and its mobiles had limited functions, as well as considerable size and weight. The multiple access method used by 1G was FDMA, supporting one user per channel transmitting at the same time. The second generation (2G) introduced digital technology, and it was based on the following standards: D-AMPS, GSM and GPRS. TDMA was used in this generation, supporting multiple users per channel, but transmitting one at a time. Then, 3G was characterized for introducing CDMA; hence, multiple users with different codes share the channel while transmitting at the same time. Furthermore, EV-DO allowed the MSc. in Digital Communication Systems Page 2 of 95 Candidate Number:

15 transmission of larger packets, while technologies as Carrier Aggregation increased transmission data rates. In order to normalize 3G, seven telecommunications standard development organizations created the 3GPP [2]. Finally, 4G was introduced by 3GPP as LTE in Release 8 and LTE-A in Release 10. The purpose of this last generation is to reach very high data rates to satisfy users increasing requirements associated with web applications and the Internet, in general. New technologies as carrier aggregation and MIMO are the basis of LTE-A for higher data rates and spectral efficiency. LTE-A has defined SC-FDMA as the access technique used in the uplink, and OFDMA in the downlink. Table 1.1 shows a summary of the 3GPP releases from 2003 and their main characteristics. PARAMETER WCDMA HSPA HSDPA LTE HSPA+ LTE (UMTS) / HSUPA ADVANCED Max downlink speed (bps) 384 k 14 M 28 M 100 M 1 G Max uplink speed (bps) 128 k 5.7 M 11 M 50 M 500 M Latency round trip time 150 ms 100 ms 50 ms Less than Less than 5 10 ms ms 3GPP releases Rel 99/4 Rel 5/6 Rel 7 Rel 8 Rel 10 Access methodology CDMA CDMA CDMA OFDMA / OFDMA / SC-FDMA SC-FDMA Table 1.1: 3GPP Releases Summary [3] 1.3 LTE-A OVERVIEW LTE-A is the last generation of mobile communications, characterized by its high network capacity, high data rate and a myriad of available services. Its technical specification has been published by the 3GPP. MSc. in Digital Communication Systems Page 3 of 95 Candidate Number:

16 When comparing 3G and LTE-A, one of the main differences between both generations is the downlink rate. Indeed, it is possible to reach 1 Gbps in LTE-A, while in 3G it was possible to reach only 20 Mbps [4]. Moreover, the difference in the uplink rate is also considerable with up to 500 Mbps in LTE-A and 10 Mbps in 3G. [4], [5] This considerable increase in rate has been necessary to offer new services and applications that require more resources and are not tolerant to delays; for instance, multimedia, mobile TV, real time audio and video. Another reason by which it is possible to use these new services and applications is the reduction of latency round trip time in LTE-A, which is less than 5 ms. Furthermore, due to the increase of mobile service subscriptions worldwide, LTE-A is based on a higher network capacity; thus, it is possible to have more calls per cell at the same time. LTE-A supports up to 8 downlink transmit antennas and up to 4 uplink transmit antennas Architecture and Protocol stack As part of the technical specifications, 3GPP has defined the next generation network, including its main components: EPC, E-UTRAN and E-UTRA. They correspond to the core network, radio access network and air interface, respectively. The EPS is responsible for IP connection between a UE and an external packet data network using E-UTRAN [6]. Figure 1.2 presents the network architecture of E-UTRAN for LTE-A. The enb is a logical element, which is the main component in the E-UTRAN architecture. It provides the air interface with user and control plane protocols towards the UE. X2 is the interface interconnecting the enbs. MSc. in Digital Communication Systems Page 4 of 95 Candidate Number:

17 Figure 1.2: LTE-Advanced E-UTRAN architecture [6] The HeNB is an enb of low cost used to improve indoor coverage. The HeNB could be directly connected to the EPC or through a gateway if more HeNB have to be connected. Relay nodes are used for performance enhancement, increased coverage and higher data rates. The MME is a control plane element used for roaming, handling idle state mobility, selecting the S-GW and P-GW nodes and executing security tasks, including authentication and authorization. The S-GW, which is connected to the E-UTRAN through the S1-U interface, is the termination of the EPC. This element performs packet routing, packet forwarding, interoperator charging and it is also in change of mobility. The node that assigns an IP address to the UE is the P-GW. It also contributes with secure connection between UEs though IPSec tunnels. MSc. in Digital Communication Systems Page 5 of 95 Candidate Number:

18 As mentioned before, the protocol stack encloses User and Control planes. Figure 1.3 provides an overview of the protocol stack. The user and control planes consist of PDCP, RLC, MAC and PHY protocols; additionally, the control plane includes RRC protocols. Figure 1.3: Protocol Stack [6] (NAS) layer protocols exclusively belong to MME. Some of their functions include, registration, authentication, location and connection management between UE and the core network. (AS) layer protocols are exclusive of enb. To start, RRC establishes, maintains and releases RRC connections. Others of its functions include mobility, key, QoS and reporting management. Second, the PDCP compresses headers, duplicates detection and ciphers data. Third, some of the functions that RLC has include error detection and correction by using ARQ, segmentation and in-sequence delivery. Fourth, the MAC protocols functions include MSc. in Digital Communication Systems Page 6 of 95 Candidate Number:

19 multiplexing and demultiplexing of PDUs, scheduling, error correction through HARQ, priorization and padding Uplink and Downlink Operation Before defining SC-FDMA and OFDMA, it is convenient to review the differences between FDM, OFDM and OFDMA. Figure 1.4 shows FDM and OFDM multiplexing techniques; both allocate users in different frequency slots. OFDM achieves spectral efficiency by using orthogonal carriers. Due to orthogonality, interference is minimized. Figure 1.4: FDM vs. OFDM [7] OFDMA is considered as an extension of OFDM, in which multiple users share resources efficiently. In fact, in OFDM each user is assigned all the subcarriers during a subframe, where a subframe is a number of OFDM symbols; while in OFDMA, more than one user is assigned multiple subcarriers during the same subframe; thus, there is an efficient resource sharing, as shown in Figure 1.5. MSc. in Digital Communication Systems Page 7 of 95 Candidate Number:

20 Figure 1.5: OFDM vs. OFDMA [7] LTE defines SC-FDMA for the uplink and OFDMA for the downlink. In fact, the main reason by which SC-FDMA is used in the uplink. This multiple access methodology has lower PAPR than OFDMA; therefore, in general it is possible to require lower power levels. Indeed, as that power is provided by the user equipment in the uplink, it is ideal to minimize it in order to use limited transmit power devices. OFDMA is used in the downlink with the purpose of exploiting efficiently the frequency resource by orthogonally accommodating multiple subcarriers in a given band. As shown in Figure 1.6, OFDMA has lower sensitivity to ISI due to the fact that all the subcarriers at a time belong to the same symbol, unlike SC-FDMA. Hence, OFDMA is more scalable and suitable to manage different users data at the same time. Furthermore, OFDMA provides immunity to multi path and frequency selective fading. First, in the case of the downlink (OFDMA), sub-carriers duration is longer than in the SC- FDMA case, according to the Time axis in this figure. Also, each sub-carrier in OFDMA is modulated by different data symbols; hence modulation and symbols have also considerable time duration. MSc. in Digital Communication Systems Page 8 of 95 Candidate Number:

21 Figure 1.6: OFDMA vs. SC-FDMA in Time and Frequency domains [8] Second, SC-FDMA is used in the uplink; this multiple access technique is actually a multicarrier method, but all the sub-carriers in a block are modulated with the same data. As shown in Figure 1.6, in SC-FDMA all the sub-carriers of the same colour are modulated with the same data, and their duration is shorter than in the OFDMA case; thus, symbols in SC-FDMA are also shorter than in OFDMA Frame Structures TDD and FDD are supported by LTE-A, which defines two different frame types based on TDD and FDD. Frame Type 1 is used in FDD. As shown in Figure 1.7, frame type 1 lasts 10 ms., and it consists of 10 subframes, each lasts 1 ms. Besides, each subframe consists of 2 slots, the duration of each slot is 0.5 ms. Half duplex and full duplex are supported in FDD. MSc. in Digital Communication Systems Page 9 of 95 Candidate Number:

22 Figure 1.7: Frame structure type 1 [9] Figure 1.8 shows frame type 2, which is used in TDD and its duration is also 10 ms. and consists of 10 subrames. Each subframe has also 2 slots. The difference with frame type 1 is that subframes in frame type 2 have reserved fixed positions for uplink, downlink and special data. Figure 1.8: Frame structure type 2 [9] Resource Block in OFDMA and SC-FDMA UL According to 3GPP, a physical RB is defined as N symb RB UL x N sc resource elements (N symb consecutive SC-FDMA symbols in an uplink slot in the time domain and N sc RB consecutive DL subcarriers in the frequency domain) [9]. An RB is also defined for the downlink as N symb x RB DL N sc resource elements (N symb consecutive OFDMA symbols in a downlink slot in the time RB UL domain and N sc consecutive subcarriers in the frequency domain) [9]. N symb, N RB DL sc, N symb MSc. in Digital Communication Systems Page 10 of 95 Candidate Number:

23 and N sc RB are given by Tables 1.2 and 1.3. For SC-FDMA and OFDMA, the resource block occupies 180 KHz in the frequency domain. CONFIGURATION NRB sc UL N symb CONFIGURATION NRB sc DL N symb Normal Cyclic Prefix 12 7 Extended Cyclic Prefix 12 6 Normal Cyclic Prefix Extended Cyclic Prefix f = 15kHz 7 12 f = 15kHz 6 f = 7.5kHz 24 3 Table 1.2: SC-FDMA RB parameters [9] Table 1.3: OFDMA RB parameters [9] DL The number of N RB depends on the downlink bandwidth arranged in the cell; such that N min,dl RB N DL RB N max.dl RB, where N min,dl RB = 6 and N max.dl RB = 110. Also, the number of symbols in a slot is configured depending on the CP length. [9] Figure 1.9 shows the relationship between a slot, a resource block, resource elements and symbols. In this example, the slot consists of 7 symbols in the time domain. The resource block consists also of 7 symbols in the time domain and 12 subcarriers in the frequency domain. Each element of the resource block is called resource element. Appendix A shows an OFDMA full frame, in which the horizontal and vertical axis correspond to the time and frequency domain, respectively. As shown, each slot consists of 7 OFDMA symbols, in this case. Besides, each RB contains 12 subcarriers. In this example, there are 180 occupied subcarriers per OFDMA symbol; therefore, each OFDMA symbol has 78 null subcarriers. MSc. in Digital Communication Systems Page 11 of 95 Candidate Number:

24 Figure 1.9: Resource grid [9], [10] An antenna port is defined such that the channel over which a symbol on the antenna port is conveyed can be inferred from the channel over which another symbol on the same antenna port is conveyed. There is one resource grid per antenna port. 1 Also, the possible 1 3GPP. ETSI IS V ( ) Technical Specification. Release 10. France, MSc. in Digital Communication Systems Page 12 of 95 Candidate Number:

25 configurations for cell-specific reference signals are one, two or four antenna ports: p = 0, p {0,1} and p {0,1,2,3}. [9] Port 4 is used to transmit MBSFN reference signals. Ports 5, 7, 8 or one or several of p {7,8,9,10, 11, 12, 13 14} are used for user equipment reference signals. Besides, port 6 is used to transmit positioning reference signals. CSI reference signals are sent through p = 15, p = 15, 16, p = 15,,18 or p = 15,,22. [9] Bandwidth Management LTE-A technical specification is based on the use of bandwidths of up to 100 MHz. The spectrum bands that LTE-A considers include MHz, MHz, MHz, GHz, GHz and GHz [6]. It is advisable to use the lower frequency bands for demands of high mobility, low capacity and long range; while the higher frequency bands for low mobility, high capacity and short range. Channel bandwidth is the width of the channel in frequency as measured from the lowest channel edge to the highest channel edge. 2 As shown in Table 1.4, the number of RB is directly proportional to the channel bandwidth. Figure 1.10 shows the difference between Channel Bandwidth, Transmission Bandwidth Configuration and Transmission Bandwidth. The Transmission Bandwidth Configuration is the maximum number of RB that can be used in a given channel bandwidth with guard band. 2 ANRITSU. LTE Resources Guide Rev Japan, MSc. in Digital Communication Systems Page 13 of 95 Candidate Number:

26 Figure 1.10: Channel bandwidth [11] Carrier Aggregation Along with LTE-A Release 10, component carriers can have different bandwidth, without exceeding 20 MHz. Moreover, it is possible to aggregate up to five component carriers of maximum 20 MHz for transmission in uplink or downlink; thus, bandwidth of up to 100 MHz can be reached with CA. For instance, a 60 MHz system can be deployed with three 20 MHz component carriers, allocated in already exploited bands or in new ones. As a result of MSc. in Digital Communication Systems Page 14 of 95 Candidate Number:

27 bandwidth optimization, it is possible to reach higher data rates, which is perceived by the end user. As shown in Figure 1.11, CA can be deployed with FDD or TDD either in uplink or downlink transmissions. If the deployment uses FDD, one carrier is used for uplink traffic and another for downlink traffic. When TDD is used, only one carrier frequency is required. Figure 1.11: FDD and TDD in CA [12] It is important to consider that in spite of the fact that LTE-A Release 10 terminals are compatible with releases 8 and 9, just release 10 terminals support CA. Due to the fact that there is not a unique standardized schema of bandwidth utilization for providers, there are three different modes of component carriers allocation along the spectrum, as shown in Figure Hence, even in scenarios with complex designs, it would be possible to deploy CA. Firstly, in intra-band contiguous allocation (a), component carriers are allocated contiguously one beside the other in a unique bandwidth range. Second, in intraband non-contiguous allocation (b), some component carriers in the same bandwidth range would be separated of each other. Lastly, inter-band non-contiguous allocation considers no contiguous component carriers in different spectrum bands. MSc. in Digital Communication Systems Page 15 of 95 Candidate Number:

28 Figure 1.12: Carrier Aggregation modes [6] Spectrum Sharing Network and spectrum sharing are supported by 3GPP. When operators share network and spectrum, they reduce initial investment. There are different spectrum sharing scenarios, as presented in Figure1.13. For example, three operators in (a) have their own dedicated spectrum bands, and they are also sharing a specific spectrum band. In (b), the shared spectrum bands are located between the dedicated spectrum bands. Indeed, the center spectrum band belongs to operator 2, and the bands next to it are shared between operator 2 and operator 1 and 3, respectively. Figure 1.13: Spectrum sharing scenarios [6] MSc. in Digital Communication Systems Page 16 of 95 Candidate Number:

29 3GPP suggests operators to keep shared structure when operating in low density areas, while deploy a dedicated structure in high density areas Enhanced MIMO Enhanced MIMO is a technology considered in LTE-A which enhances the spectral efficiency in scenarios with large number of users and high data rates. MIMO is based on the use of multiple antennas at the transmitter and receiver; thus, MIMO properties are applied for both the uplink and the downlink. With the purpose of getting the highest possible gain in the direction of each user, MIMO technology uses SDMA so that it adapts the radiation pattern of the base station to each user, as shown in Figure Therefore, each base station analyzes the CSI of each UE in order to allocate resources. Figure 1.14: Base station radiation pattern [6] LTE-A describes three main MIMO operating modes, as shown in Figure SU-MIMO is based on a single multi antenna transmitter communicating with a single multi antenna receiver. In contrast, MU-MIMO consists of multiple users with one or more antennas MSc. in Digital Communication Systems Page 17 of 95 Candidate Number:

30 communicating with each other. The third mode defined by 3GPP is the Cooperative MIMO, which is suitable for cell-edge users to improve their throughput by working with different base stations at the same time. Figure 1.15: LTE-A main MIMO modes [6] OFDMA and SC-FDMA Parameters As presented previously in Tables 1.2 and 1.3, the CP is an important concept in LTE-A. It is defined as the fragment of the last part of a symbol, which is copied at the beginning of that symbol in order to increase the separation between symbols, minimizing ISI, as shown in Figure1.16. Figure 1.16: Cyclic Prefix [13] MSc. in Digital Communication Systems Page 18 of 95 Candidate Number:

31 According to table 1.3, when normal CP is used, the RB size is 7x12, and the subcarrier spacing is f=15khz; therefore, the bandwidth of an RB is 12x15kHz = 180kHz, as described in section If extended CP is used, the RB size could be 6x12 or 3x24, depending on the f used (15kHz or 7.5kHz); even though, in both cases the bandwidth of an RB is 180kHz. LTE defines different values to design OFDMA symbols, as presented in Table 1.4. The current work will be based on the values marked in red. Chapter 2 will cover the designs and simulations based on these parameters and values. The generation of the SC-FDMA signal is similar to the OFDMA processing using the same parameters shown in Table 1.4. PARAMETER VALUE Channel bandwidth (MHz) Resource Block RB Occupied subcarriers IDFT/FFT size Subcarrier spacing f (khz) 15 or 7.5 CP SIZE 5.21 μs (first symbol of the slot) Normal CP ( f = 15 khz) 4.69 μs (other symbols of the slot) Extended CP ( f = 15 khz) μs Extended CP ( f = 7. 5 khz) μs Table 1.4: 3GPP LTE-A OFDMA Parameters [10] An OFDMA symbol is made up of null subcarriers (guard band and center subcarrier) and data (user data and reference signals). The length of the symbol is equal to the FFT size; such that the occupied subcarriers are part of the RBs, and the remaining subcarriers correspond to the null subcarriers. MSc. in Digital Communication Systems Page 19 of 95 Candidate Number:

32 1.4 DOWNLINK PHYSICAL CHANNELS AND SIGNALS Downlink Physical Channels Six steps are used to define the baseband signal representing a downlink physical channel, as shown in Figure First, the coded bits in each codeword are scrambled. Second, scrambled bits are modulated in order to create complex-valued symbols. Third, the complexvalued modulation symbols are mapped into one or more layers. Fourth, complex-valued modulation symbols on each layer are precoded preparing them to be transmitted on the antenna ports. Fifth, complex-valued modulation symbols for each antenna port are mapped to resource elements. Finally, complex-valued time domain OFDM signal is generated for each antenna port. Figure 1.17: Overview of physical channel processing [9] The group of some resource elements with specific information from higher levels is known as physical channel. There are six different downlink physical channels: PDSCH, PBCH, PMCH, PCFICH, PDCCH and PHICH [9]. The PDSCH transports user data; thus, it supports high data rates. In order to send cell specific identification and access control parameters, PBCH is used. The PMCH transports multimedia information. The PCFICH informs the equipment the number of OFDM symbols (1, 2 or 3) to be used for the PDCCH in a subframe. The PDCCH is in charge of allocating MSc. in Digital Communication Systems Page 20 of 95 Candidate Number:

33 resource scheduling, so its value corresponds to the number of symbols to be used for the PDCCH. Finally, with the purpose of confirming or retransmitting uplink transmissions, the PHICH transmits ACK/NACKs. The PDSCH and PMCH support QPSK, 16QAM and 64QAM modulation; while the PBCH, PCFICH and PDCCH support QPSK. A group of downlink subcarriers supporting PDSCH can be configured as MBSFN subframes. Each subframe has two regions: non-mbsfn region and MBSFN region. The non- MBSFN region contains the first or two first OFDM symbols in an MBSFN subframe; while the MBSFN region contains all the OFDM symbols that are not part of the non-mbsfn region in a MBSFN subframe. Table 1.5 shows the number of OFDM symbols used for PDCCH. SUBFRAME Subframe 1 and 6 for frame structure type 2 MBSFN subframes on a carrier supporting PDSCH, configured with 1 or 2 cell-specific antenna ports MBSFN subframes on a carrier supporting PDSCH, configured with 4 cell-specific antenna ports Subframes on a carrier not supporting PDSCH Non-MBSFN subframes (except subframe 6 for frame structure type 2) configured with positioning reference signals Number of OFDM symbols for PDCCH when N DL RB > 10 Number of OFDM symbols for PDCCH when N DL RB 10 1, 2 2 1, , 2, 3 2, 3 All other cases 1, 2, 3 2, 3, 4 Table 1.5: Number of OFDM symbols used for PDCCH [9] MSc. in Digital Communication Systems Page 21 of 95 Candidate Number:

34 1.4.2 Signals On the other hand, the group of resource elements carrying information that is not originated from higher layers is called downlink physical signal. There are two kinds of downlink physical signals: - Reference signal - Synchronization signal Reference signals are used for channel estimation. They are allocated in the first and fifth symbols if normal CP is used, as shown in Figure 1.18 and Appendix A. In the case of extended CP, reference signals use the first and fourth symbols. One reference signal is transmitted per antenna port. There are five types of downlink reference signals: - CRS - MBSFN - UE-specific reference signals or DM-RS - PRS - CSI-RS Synchronization signals are used for frequency and timing acquirement when user equipment are searching for a cell. They are transmitted on 62 subcarriers of 72 reserved around DC on the sixth and seventh symbols in slots 0 and 10, as shown in Appendix A. They use binary sequences of 31 bits and BPSK modulation. The uplink and downlink reference signals are different, and their transmission allocation is also different. Figure 1.18 shows the pattern for uplink and downlink reference signals. MSc. in Digital Communication Systems Page 22 of 95 Candidate Number:

35 Figure 1.18: Uplink vs. Downlink Reference signals allocation [14] It is clear that there are exclusive symbols within a slot to transmit only reference signals in the uplink; while in the downlink, reference signals and data share a symbol within a slot. It is also clear that the reference signals are not transmitted in all symbols; indeed, only 4 subcarriers are used to transmit reference signals in a RB (7x12) in the downlink. The current work focuses on the downlink (OFDMA); hence, it is important to consider its reference signal allocation pattern, as it will be used during all simulations later. However, the uplink pattern will also be discussed in order to present comparisons between SC-FDMA and OFDMA. The mapping of reference signals depends on the number of antenna ports to be used. Figure 1.19 shows the mapping for one, two and four antenna ports. MSc. in Digital Communication Systems Page 23 of 95 Candidate Number:

36 Figure 1.19: Mapping of downlink reference signals [9] 1.5 IFFT AND FFT IMPORTANCE Unlike TDMA or FDMA, OFDMA and SC-FDMA depend on the time and frequency domains. Therefore, the use of tools that allow the signal conversion from one domain to the other is essential. FFT and IFFT are the tools to accomplish this purpose. Figure 1.20 shows the use of IFFT and FFT. In the downlink (OFDMA), the transmitter executes an IFFT on the frequency domain in order to generate the OFDM symbol in the time domain. Then, the receiver performs an FFT on the OFDM symbol, returning it to the frequency domain. Besides, FFT and IFFT guarantee orthogonal subcarriers because when these operations are performed on each subcarrier, the result for the others is zero. MSc. in Digital Communication Systems Page 24 of 95 Candidate Number:

37 Figure 1.20: IFFT and FFT [15] 1.6 LTE-A PERFORMANCE The targets of LTE-A specified in Release 10, in terms of performance, are presented in Table 1.6. PARAMETER Downlink Uplink Capacity (Mbps) Normalized capacity (bps/hz) Average spectral efficiency (bps/hz/cell) Table 1.6: Targets for LTE-Advanced as set by 3GPP [5] As it noted above, OFDMA is used for the downlink transmission and SC-FDMA for the uplink. Therefore, according to Table 1.6, OFDMA has higher capacity than SC-FDMA; in fact, it corresponds to the double. Likewise, normalized capacity is also higher for OFDMA than for SC-FDMA. Also, the downlink has better average spectral efficiency per cell than the uplink. MSc. in Digital Communication Systems Page 25 of 95 Candidate Number:

38 Another important parameter of performance is the BER, which states how reliable the signal is, in terms of the bits and errors received. Figure 1.21 shows SC-FDMA and OFDMA FER performance studied in a previous research. Figure 1.21: SC-FDMA vs. OFDMA performance with QPSK [16] From the research, some important conclusions were stated. First, OFDMA performance is highly dependent on the coding rate. For instance, without code or with high coding rates, OFDMA performance is poor. Nonetheless, when a strong code is employed; for instance, rate ½, OFDMA recovers performance, surpassing SC-FDMA performance. With regard to the rate capacity, when the number of users is large, the best rate capacity is achieved with adequate SNR values. S/N is the ratio of average signal power to average noise power. While the Eb/No is the ratio of average energy per bit to noise power spectral density 3. 3 Dr Falah Ali. Digital Modulation for Wireless Communications lecture. Mobile Communications module. University of Sussex, Brighton MSc. in Digital Communication Systems Page 26 of 95 Candidate Number:

39 E b = ST b = S = SB N o N o R b N o R b N = SB (1.1) NkR s E s N o = ke b N o (1.2) Formulas 1.1 and 1.2 define the Eb/No ratio in terms of S/N ratio and viceversa, where 3 : E b : Signal Energy per Bit E s : Energy per Symbol, E s = ke b S: Average Signal Power N o : Noise Power Spectral Density T b : Bit Period N 0 = N B R b : Bit Rate, R b = 1 T b N: Noise Power R s : Symbol Rate, R b = kr s B: System Bandwidth k: Number of Bits per symbol Besides, increasing the number of receptor antennas does not increase significantly the general capacity. As stated in section 1.2.1, the power constraints at the user equipment imply the need to use SC-FDMA for the uplink. Figure 1.22 presents a PAPR comparison between OFDMA and SC-FDMA. It is evident that SC-FDMA has lower PAPR; hence, more efficient. In fact, in this case, it is approximately 2dB lower than OFDMA. MSc. in Digital Communication Systems Page 27 of 95 Candidate Number:

40 Figure 1.22: PAPR comparison for OFDMA and SC-FDMA [17] 1.7 SOFTWARE SIMULATION PACKAGE Simulink library of Matlab R2014a has been used for simulations in this project. When opening Matlab, Simulink library is accessible through its button in the Home main menu, as shown in Figure 1.23 or in the Matlab Command Window by entering simulink, Figure 1.23: Simulink Library MSc. in Digital Communication Systems Page 28 of 95 Candidate Number:

41 Simulink library is made up of different intern libraries, as shown in Figure Each library has several blocks with different functions. Moreover, it is possible to search for a specific subsystem or block in the Search toolbox. Figure 1.24: Simulink Library Browser In order to start creating a new Simulink model, select File New Model, as shown in Figure Figure 1.25: Simulink New Model MSc. in Digital Communication Systems Page 29 of 95 Candidate Number:

42 Then, drag the required blocks from the Simulink Library to the model window to add blocks to the model. Connections are established by dragging a wire from an output to an input, as shown in Figure Figure 1.26: Adding blocks and connecting By double clicking on each block, it is possible to configure its settings. Once the model is ready, the Run button starts simulation. MSc. in Digital Communication Systems Page 30 of 95 Candidate Number:

43 2 CHAPTER 2: DESIGN CHAPTER 2 2. DESIGN This chapter includes the design of OFDMA in 4G, using 3GPP technical specification as the main source and basis. As explained in Chapter 1, the multiple access technique used for the uplink in 4G is SC-FDMA and OFDMA is used for the downlink. The purpose of this Chapter focuses on the design of OFDMA, as it is the main topic of this project; however, a simple design on SC-FDMA has also been made for comparison. 2.1 OFDMA BLOCK DIAGRAM Figure 2.1 shows an OFDMA transmitter and receiver model. The main components in the transmitter are the Modulator, the Subcarrier mapping, the IFT block and the addition of the Cyclic Prefix. According to the LTE-A standard, there are three possible modulation schemes in the downlink: QPSK, 16QAM and 64QAM [9], as explained in Chapter 1. Then, the subcarrier mapping is performed considering the Resource Block diagram shown in Figure Also, the channels and signals allocation presented in Appendix A have to be considered in order to map the subcarriers. With regard to the IFT block, it permits the move from the frequency domain to the time domain, which is necessary after the subcarrier mapping and before adding the cyclic prefix, also known as guard interval. Finally, the CP is inserted, according to Table 1.4. MSc. in Digital Communication Systems Page 31 of 95 Candidate Number:

44 Figure 2.1: OFDMA Transmission and Reception model [18] The receiver has four important blocks. The removal of the CP eliminates the information contained in the last part of the OFDMA symbol that was added al the end of the transmitter. The FT, which permits the move from the time domain to the frequency domain, after removing de CP and before the Subcarrier mapping. The subcarrier mapping counteracts its corresponding in the transmitter side, and the demodulator compensates the modulator processing. 2.2 SC-FDMA BLOCK DIAGRAM In spite of the fact that SC-FDMA is beyond the scope of this project, with the purpose of comparing both techniques, its model is presented in Figure 2.2. It is clear that there are two important differences compared to OFDMA. First, there is an FFT block after the modulator in the transmitter. Second, there is an IFT block before the demodulator in the receiver. By adding an FT block between the modulator and the subcarrier mapping in the transmitter, the subcarrier mapping is executed in the frequency domain, modulating all the MSc. in Digital Communication Systems Page 32 of 95 Candidate Number:

45 subcarriers with the same data, unlike OFDMA. Consequently, this action has to be balanced in the receiver with the aid of an IFT block. Figure 2.2: SC-FDMA Transmission and Reception model [18] 2.3 PARAMETERES Five different scenarios have been designed during this project. It has been possible to ascertain the impact of increasing the number of users in OFDMA. Moreover, the impact that fading has on BER in OFDMA. With the intention of comparing transmitted and received signals transmitted through a channel configured with different Eb/No values, different testings have been developed. Also, a comparison between OFDMA and SC-FDMA has been feasible, in terms of PAPR. The diagrams developed in Matlab R2014a Simulink, are based on the block diagrams presented in Figures 2.1 and 2.2. The designs include the simulation of one OFDMA symbol, based on the LTE-A parameters shown in Table 2.1. Due to space limitations on Simulink screen, the design is based on FFT=256, which is the size of the OFDMA symbol. MSc. in Digital Communication Systems Page 33 of 95 Candidate Number:

46 PARAMETER VALUE Resource Block RB 15 RB N sc 12 N symb 7 Maximum occupied subcarriers 180 IFFT/FFT size 256 Normal CP ( f = 15 khz) 5.21 μs (first symbol of the slot) Modulation 16QAM Table 2.1: Simulation Parameters 2.4 OFDMA 2 USERS (AWGN) The following scenario is designed for two users in an AWGN environment. As OFDMA is simulated, which corresponds to the downlink, the transmitters represent the base stations and the receivers represent the final users. The symbol processing design is presented in Figure 2.3, and its corresponding diagram in Figure 2.4. FDD is used in this example, such that 100 of 150 subcarriers are assigned to User 1, and the other 50 to User 2, as shown in Figure 2.3. Consistent with the standard, there are maximum 180 occupied subcarriers; therefore, 30 subcarriers are used for reference signals ( ), which are allocated according to the first symbol of the pattern shown in Figure 1.18 (downlink). Before adding the reference signals and the null subcarriers (not occupied subcarriers) to the frame, it is necessary to join both users data. To achieve this, two vectors of size 150 have been created filling them with the users data and zeros. Then, both vectors are added to have MSc. in Digital Communication Systems Page 34 of 95 Candidate Number:

47 a resulting vector of size 150, the first 100 elements of which correspond to User 1 data, and the last 50 to User 2. As the FFT size to be used is 256, there are 76 null subcarriers ( ), which are considered as guard subcarriers in both sides of the frame and are filled with zeros with the purpose of building the Fourier signal walls. 38 of the 76 subcarriers are allocated as left guard subcarriers, 37 as right guard subcarriers, and 1 remaining subcarrier corresponds to the center subcarrier, which is not transmitted in the downlink [11]. Finally, in order to calculate the number of subcarriers to be added at the begging of the symbol as CP, corresponding to 5.21μs, the following estimations have been considered: 1 slot 0.5 ms [9] As N symb = 7: 1 symb 0.5 ms 7 = μs (FFT Size = 256) 5.21 μs 19 subcarriers At the receiver, the CP is removed, which corresponds to the information of the first 19 subcarriers of the received symbol. Then, the 76 null subcarriers are removed, including the left guard subcarriers, right guard subcarriers and the center subcarrier. After removing the null subcarriers, the 30 reference signals are also removed. Finally, the resulting vector of size 150 is divided into two parts. The first 100 subcarriers correspond to the data that belongs to User 1 and the remaining 50 to User 2. MSc. in Digital Communication Systems Page 35 of 95 Candidate Number:

48 2.5 OFDMA 5 USERS (AWGN) The following scenario is designed for five users in an AWGN environment. The symbol processing design is presented in Figure 2.5, and its corresponding diagram in Figure 2.6. FDD is used in this example, such that 30 of 150 subcarriers are assigned to each user. According to the standard, there are maximum 180 occupied subcarriers; hence, 30 subcarriers are used for reference signals ( ), which are allocated according to the first symbol of the pattern shown in Figure 1.18 (downlink). Before adding the reference signals and the null subcarriers to the frame, it is necessary to join the data of the five users. For this, five vectors of size 150 have been created, and they are filled with the users data and zeros. As it is shown in Figure 2.5, the first vector has user 1 data at the beginning; the second vector has user 2 data from location 31 to 60, etc. The last vector has user 5 data at the end. Then, the five vectors are added to have a resulting vector of size 150, the first 30 elements of which correspond to User 1 data, and the last 30 to User 5. As the FFT size to be used is 256 and there are 180 occupied subcarriers, there are 76 not occupied subcarriers, which are the guard subcarriers and the center subcarrier, as in the scenario presented in numeral Also, the CP estimation is the same as in the previous scenario. At the receiver, as in the last scenario, the CP is removed. Then, the 76 null subcarriers are removed. After this, the 30 reference signals are also removed. Finally, the resulting vector of size 150 is divided into five parts. The first 30 subcarriers correspond to the data that belongs to User 1, the next 30 to User 2, etc. until the last 30 that correspond to User 5. MSc. in Digital Communication Systems Page 36 of 95 Candidate Number:

49 2.6 OFDMA 2 USERS (AWGN + Rayleigh Fading) The design of this scenario is the same as the described in numeral 2.1.1, but including fading. The purpose of designing this scenario is to see the effects of fading on BER curves in an OFDMA scenario for 2 users. The design s diagram is shown in Figure OFDMA 5 USERS (AWGN + Rayleigh Fading) The design of this scenario is the same as the described in numeral 2.1.2, but including fading. The purpose of designing this scenario is to see the effects of fading on BER curves in an OFDMA scenario for 5 users. The design s diagram is shown in Figure SC-FDMA 2 USERS (AWGN) The last design is a SC-FDMA scenario, according to LTE-A parameters. As this simulation corresponds to the uplink, it has to be considered that the transmitters represent users starting communication and the receivers represent base stations that process the users requests. The symbol processing design is presented in Figure 2.9, and its corresponding diagram in Figure The generation of the SC-FDMA signal is similar to the OFDMA signal processing using the same parameters shown in Table 2.1 [10]. Even though, there are some differences to consider. First, reference signals are not transmitted in the following simulation because in SC-FDMA, the first symbol within a slot is used only to transmit data, as shown in Figure 1.18 MSc. in Digital Communication Systems Page 37 of 95 Candidate Number:

50 (uplink). Also, as the center subcarrier is not transmitted only in the downlink, in this case it has to be transmitted. Before adding the null subcarriers, it is necessary to join both users data. To achieve this, two vectors of size 150 have been created filling them with the users data and zeros, as in scenario Then, both vectors are added to have a resulting vector of size 150, the first 100 elements of which correspond to User 1, and the last 50 to User 2. The FFT size is also 256 in this case; though, the number of occupied subcarriers is not considered as the maximum that the standard defines (180). With the purpose of transmitting the same data in the uplink as the transmitted in the downlink in scenario 2.1.1, the occupied subcarriers in the uplink is equal to 150 due to the lack of reference signals in the first symbol of the slot. Thus, there are 106 null subcarriers ( ), 53 of which are allocated as left guard subcarriers and the remaining 53 are the right guard subcarriers. In this case, the center subcarrier is transmitted, for being the uplink, so it is one of the occupied subcarriers. As the FFT and RB sizes are the same as in the other cases, the CP size does not change. At the receiver, firstly, the CP is removed. Then, the 106 null subcarriers are removed. After this, the resulting vector of size 150 is divided into two parts. The first 100 subcarriers correspond to the data that belongs to User 1 and the remaining 50 to User 2. MSc. in Digital Communication Systems Page 38 of 95 Candidate Number:

51 Figure 2.3: OFDMA 2 Users Design Figure 2.4: OFDMA 2 Users (AWGN) Diagram 4 4 Adapted from: [20], [21] and [22]. MSc. in Digital Communication Systems Page 39 of 95 Candidate Number:

52 Figure 2.5: OFDMA 5 Users Design Figure 2.6: OFDMA 5 Users (AWGN) Diagram 5 5 Adapted from: [20], [21] and [22]. MSc. in Digital Communication Systems Page 40 of 95 Candidate Number:

53 Figure 2.7: OFDMA 2 Users (AWGN + Rayleigh Fading) Diagram 6 Figure 2.8: OFDMA 5 Users (AWGN + Rayleigh Fading) Diagram 6 6 Adapted from: [20], [21] and [22]. MSc. in Digital Communication Systems Page 41 of 95 Candidate Number:

54 Figure 2.9: SC-FDMA 2 Users Design Figure 2.10: SC-FDMA 2 Users Diagram 7 7 Adapted from: [20], [21] and [22]. MSc. in Digital Communication Systems Page 42 of 95 Candidate Number:

55 3 CHAPTER 3: SIMULATION SETTINGS CHAPTER 3 3. SIMULATION SETTINGS This chapter describes the parameters configured in each block of Simulink for the different scenarios. 3.1 OFDMA 2 USERS (AWGN) Figures 3.1, 3.14 and 3.16 are extracts of Figure 2.4, and they correspond to the transmitter, channel and receiver Transmitter Figure 3.1: OFDMA 2 Users Transmitter MSc. in Digital Communication Systems Page 43 of 95 Candidate Number:

56 Random Integer (User 1), (User 2): As the modulation scheme to be used is 16QAM, the M-ary number parameter is configured as 16 in both cases. For user 1, 100 samples per frame are generated (a), and 50 samples per frame for user 2 (b). (a) (b) Figure 3.2: Source Block Parameters (OFDMA 2 users) Integer to Bit Converter and Bit to Integer Converter: These blocks are necessary only to obtain the BER calculation. As the source generates integers, it would cause confusion or estimation errors while calculating the BER, which is based on bits; therefore, the change from integer to bit is used. As the parameters of these blocks depend only on the modulation order, they are the same for both users. (a) (b) Figure 3.3: Integer to Bit Converter / Bit to Integer Converter MSc. in Digital Communication Systems Page 44 of 95 Candidate Number:

57 Rectangular QAM Modulator: According to the LTE-A standard, 16QAM modulation has been chosen for both users. Besides, Gray constellation ordering is configured. Figure 3.4: Rectangular QAM Modulator Constants for Zero extension: As explained in Chapter 2, in order to join the data of both users, two vectors of size 150 are created, filling them with data and zeros. The constant created to be used with the data of User 1 is a vector of 50 zeros (b), while the other constant is a vector of 100 zeros (a), and it will be used for User 2 data. (a) (b) Figure 3.5: Zero constant vectors (OFDMA 2 Users) MSc. in Digital Communication Systems Page 45 of 95 Candidate Number:

58 Extension of zeros: Two vectors are created. The first vector contains the 100 samples created by the Random Integer block for User 1 and 50 zeros originated by one of the constant blocks. The second vector is created by 100 zeros originated by the other constant block and at the end by the 50 samples of User 2. Both function blocks have the same configuration, as shown in Figure 3.6. For this, the Vector Concatenate block was used. Figure 3.6: Extension of zeros (OFDMA 2 Users) Addition: The two previous vectors of size 150 are summed up to obtain another vector of size 150, with User 1 data at the beginning and User 2 data at the end of the vector. Figure 3.7: Vectors Addition (OFDMA 2 Users) MSc. in Digital Communication Systems Page 46 of 95 Candidate Number:

59 Multiport Selector: The signal entering into this block is divided into 30 groups; each group contains 5 elements (1:5, 6:10, 11: :150), as shown in the configuration parameter in Figure 3.8. This is to prepare the symbol to introduce the reference signals, according to the pattern of the first OFDMA symbol shown in Figure 1.18 (downlink). Figure 3.8: Multiport Selector Null subcarriers constants: As explained in Chapter 2, 38 subcarriers are used as left guard (a), 37 subcarriers correspond to right guard (b) and one remaining is the central subcarrier (c), which is not transmitted in the downlink, so the design considers to fill the subcarrier with zero. All these constants are configured as 38 (a), 37 (b) and 1 zero (c), respectively, as shown in Figure 3.9. (a) (b) MSc. in Digital Communication Systems Page 47 of 95 Candidate Number:

60 (c) Figure 3.9: Null subcarriers constants Reference signals constant: Thirty reference signals are generated to complete 180 occupied subcarriers. These signals are allocated one by one after each group generated by the Multiport Selector block, according to the pattern shown in Figure To accomplish the scope of this project, the reference signals are set with 1, as shown in Figure 3.10; however, in real scenarios, reference signals contain special information to estimate the channel. Figure 3.10: Reference signals constant MSc. in Digital Communication Systems Page 48 of 95 Candidate Number:

61 Matrix Concatenate: 63 Inputs enter into this block, as shown in Figure First, the left guard subcarriers; second, a reference signal, then the first block of 5 subcarriers from the Multiport selector, then another reference signal, etc. until completing the 63 inputs with the last one, which corresponds to the right guard subcarriers input. Figure 3.11: Matrix concatenate (OFDMA) IFFT: Based on the standard, the FFT length to be used is 256 for this simulation. It is important to note that the FFT length has to be the same as the frame size after the matrix concatenate block. Figure 3.12: IFFT (OFDMA) MSc. in Digital Communication Systems Page 49 of 95 Candidate Number:

62 Add Cyclic Prefix: As described in Chapter 2, the last 19 subcarriers of the OFDMA symbol are copied and inserted at its beginning. As the FFT length is 256, the last 19 subcarriers are from 238 to 256, as presented in Figure After specifying the CP, the remaining symbol has to be transmitted, from 1 to 256. For this, the block Selector was used. Figure 3.13: Cyclic Prefix Addition Channel Figure 3.14: Channel (AWGN) AWGN Channel: First, with the purpose of comparing how the transmitted signal is affected by the Eb/No ratio, three different values have been configured Eb/No = 30 db (a), 43 db (b) and 80 db (c). Then, in order to obtain the BER curve, the Eb/No parameter has been set to Eb/No in general, not a fixed value (d). MSc. in Digital Communication Systems Page 50 of 95 Candidate Number:

63 (a) (b) (c) (d) Figure 3.15: AWGN Channel (OFDMA 2 Users) MSc. in Digital Communication Systems Page 51 of 95 Candidate Number:

64 3.1.3 Receiver Figure 3.16: OFDMA 2 Users Receiver Remove Cyclic Prefix: The Selector block is used to remove the CP. After adding the CP, the frame size is 275 (256+19); hence, in order to remove the CP, only the subcarriers 20 to 275 have to be transmitted, as shown in Figure Figure 3.17: Cyclic Prefix Removal FFT: The FFT length to be used is 256 to contrast the effect of the IFFT block in the transmitter and due to the frame size. MSc. in Digital Communication Systems Page 52 of 95 Candidate Number:

65 Figure 3.18: FFT (OFDMA) Frame Conversion: This block does not make any change to the input, only changes the output sampling mode. In this case, the FFT block allows the change from the time domain to the frequency domain; therefore, before removing the null subcarriers, it is advisable to set the sampling mode to frame based to avoid any mismatch. Figure 3.19: Frame Conversion Remove Null Subcarriers: This Selector block removes the first 38 subcarriers, the center subcarrier and the last 37 subcarriers of the frame; thus, the null subcarriers. MSc. in Digital Communication Systems Page 53 of 95 Candidate Number:

66 Figure 3.20: Null subcarriers removal Remove Reference signals: This Multiport Selector block removes the reference signals. The first output port of the block is configured with all the subcarriers to be transmitted: 2:6 8:12 14:18 20:24.176:180. The second output port is used to send the reference signals to be discarded: 1, 7, 13, 19, Figure 3.21: Reference signals removal Terminator: This block is used to discard the 30 reference signals configured in the second port of the Multiport Selector block. This block does not have parameters to be set; though, it is advisable to terminate the reference signals to avoid any mismatch during simulation. Figure 3.22: Reference signals terminator MSc. in Digital Communication Systems Page 54 of 95 Candidate Number:

67 Separate Users data: This Multiport Selector block is used to separate the frame of size 150 into two streams. The first stream corresponds to the first 100 modulated subcarriers, and the other to the last 50 modulated subcarriers. Figure 3.23: Users data separation (OFDMA 2 Users) Rectangular QAM Demodulator: The setting of both demodulators is the same. As 16QAM was used in modulation during transmission, 16QAM is also used in demodulation during reception. Also, Gray constellation is used, as in modulation. Figure 3.24: Rectangular QAM Demodulator MSc. in Digital Communication Systems Page 55 of 95 Candidate Number:

68 Integer to Bit Converter: The configuration of this block is exactly the same as the Integer to Bit Converter block shown in Figure 3.3 (a). This block is used to avoid conflicts during the Error rate calculation. Error Rate Calculation: The variables maxnumerrs and maxnumbits were defined in the Matlab workspace to stop the simulation. Figure 3.25: Error Rate Calculation 3.2 OFDMA 5 USERS (AWGN) Figures 3.26, 3.14 and 3.30 are extracts of Figure 2.6, and they correspond to the transmitter, channel and receiver. The following description corresponds to the parameters that differ from scenario 1 (OFDMA 2 Users AWGN), so all the blocks that are not described in this section in spite of being in the corresponding diagrams, were configured with the same parameters of scenario 1. MSc. in Digital Communication Systems Page 56 of 95 Candidate Number:

69 3.2.1 Transmitter Figure 3.26: OFDMA 5 Users Transmitter Random Integer (All Users): As the modulation scheme to be used is 16QAM, the M-ary number parameter is 16. For all users, 30 samples per frame are generated in this example; however it is possible to design different sizes per user, as in the previous scenario. Figure 3.27: Source Block Parameters (OFDMA 5 users) MSc. in Digital Communication Systems Page 57 of 95 Candidate Number:

70 Constants for Zero extension: Four constants were included in the design. The first one generates 120 zeros (a), the second 90 (b), the third 60 (c) and the last one generates 30 zeros (d), as shown in Figure (a) (b) (c) (d) Figure 3.28: Zero constant vectors (OFDMA 5 Users) Extension of zeros: Five vectors are created. The first vector for instance, contains the 30 samples created for User 1 by the Random Integer block and 120 zeros originated by one of the constant blocks (a). The generation of the five vectors is shown in Figure 2.5. Two of the three function blocks concatenate 2 inputs, while the remaining three blocks concatenate 3 inputs. MSc. in Digital Communication Systems Page 58 of 95 Candidate Number:

71 Addition: The five vectors of size 150 are summed up to obtain another vector of size 150, with User 1 s data at the beginning and User 5 s data at the end of the resulting vector. Figure 3.29: Vectors Addition (OFDMA 5 Users) Channel The channel configuration is the same as the previous case with 2 Users Receiver Figure 3.30: Receiver (OFDMA 5 Users) Separate Users data: This Multiport Selector block is used to separate the frame of size 150 into five streams, each one of size 30. MSc. in Digital Communication Systems Page 59 of 95 Candidate Number:

72 Figure 3.31: Users data separation (OFDMA 5 Users) 3.3 OFDMA 2 USERS (AWGN + Rayleigh Fading) Figures 3.1, 3.32 and 3.16 are extracts of Figure 2.7, and they correspond to the transmitter, channel and receiver. The following description corresponds to the parameters that differ from scenario 1 (OFDMA 2 Users AWGN), so all the blocks that are not described in this section in spite of being in the corresponding diagrams, were configured with the same parameters of scenario Transmitter The configuration of all the blocks in the transmitter is the same as the described in section MSc. in Digital Communication Systems Page 60 of 95 Candidate Number:

73 3.3.2 Channel Figure 3.32: Channel (AWGN + Rayleigh Fading) AWGN Channel: In order to obtain the BER curve, the Eb/No parameter has been set to Eb/No in general, not a fixed value. Figure 3.33: AWGN Channel (OFDMA 5 Users) Rayleigh Fading: This block is the main component of this design because its purpose is to evaluate the impact of fading in the transmission. The parameters shown in Figure 3.34 were configured. MSc. in Digital Communication Systems Page 61 of 95 Candidate Number:

74 Besides, the Math function (conj) and a product block were used to combine the effect of the fading block with the AWGN block. This part of the design was developed and tested during the Mobile Communications module. Figure 3.34 AWGN Channel (OFDMA 5 Users) Receiver The configuration of all the blocks in the receiver is the same as the described in section 3.4 OFDMA 5 USERS (AWGN + Rayleigh Fading) Figures 3.26, 3.32 and 3.30 are extracts of Figure 2.8, and they correspond to the transmitter, channel and receiver. All the blocks were configured with the same parameters of MSc. in Digital Communication Systems Page 62 of 95 Candidate Number:

75 scenario 2 (OFDMA 5 Users AWGN) in the case of transmitter and receiver, and scenario 3 (OFDMA 2 Users AWGN + Fading) for the channel Transmitter The configuration of all the blocks in the transmitter is the same as the described in section Channel All the channel configuration is the same as the described in section (2 Users AWGN + Fading) Receiver The configuration of all the blocks in the receiver is the same as the described in section 3.5 SC-FDMA 2 USERS (AWGN) Figures 3.35, 3.14 and 3.40 are extracts of Figure 2.10, and they correspond to the transmitter, channel and receiver. The following description corresponds to the parameters that differ from scenario 1 (OFDMA 2 Users AWGN); thus, all the blocks that are not described in this section in spite of being in the corresponding diagrams, were configured with the same parameters of scenario 1. MSc. in Digital Communication Systems Page 63 of 95 Candidate Number:

76 3.5.1 Transmitter Figure 3.35: SC-FDMA 2 Users Transmitter FFT: It is important to note that in previous versions of Simulink, the FFT length must be a power of two. In this case, the signal length entering into the FFT block is 150, which is not a power of two. Hence, it was necessary to use the last version of the software and configure FFT implementation as Auto, which permits to work with any input dimension, as shown in Figure Figure 3.36: FFT (SC-FDMA Transmitter) Multiport Selector: As explained in Chapter 1, Figure 1.6, the first symbol of a SC-FDMA slot does not contain reference signals, so the configuration of this block is simpler than in OFDMA because it is not necessary to create groups of five subcarriers. In fact, it could even MSc. in Digital Communication Systems Page 64 of 95 Candidate Number:

77 be omitted. In this case, it was configured just to show that the data of the users is not divided in groups and is continuously transmitted without interruption. Figure 3.37: Multiport Selector (SC-FDMA) Null subcarriers constants: As explained in Chapter 2, 53 subcarriers are used as left guard and also as right guard. For the uplink, the central subcarrier is transmitted, so in this case there is not a null subcarrier in the center as in OFDMA. These constants are configured as 53 zeros, as shown in Figure Figure 3.38: Null subcarriers constants (SC-FDMA) MSc. in Digital Communication Systems Page 65 of 95 Candidate Number:

78 Matrix Concatenate: There are 4 inputs; two for the null subcarriers and the others for the data subcarriers, as shown in Figure Figure 3.39: Matrix Concatenate (SC-FDMA) Channel The configuration of the channel is the same as case 1 (OFDMA 2 Users AWGN) Receiver Figure 3.40: SC-FDMA 2 Users Receiver Remove Null Subcarriers: This Selector block removes the first and final 53 subcarriers, respectively. MSc. in Digital Communication Systems Page 66 of 95 Candidate Number:

79 Figure 3.41: Null subcarriers removal (SC-FDMA) IFFT: The input length of this block is not a power of two, so it is configured as Auto, and Inherit FFT length from input dimensions, as presented in Figure Figure 3.42: IFFT MSc. in Digital Communication Systems Page 67 of 95 Candidate Number:

80 4 CHAPTER 4: RESULTS AND ANAYLIS CHAPTER 4 4. RESULTS AND ANALYSIS 4.1 OFDMA 2 USERS (AWGN) Figure 4.1 shows a portion of the integer data transmitted by two base stations (TX1 and TX2), and a portion of the integer data received by the corresponding users (RX1 and RX2). Three different values of Eb/No were configured as explained in Chapter 3 Eb/No = 30dB (a), 43dB (b) and 80dB (c). (a) (b) (c) Figure 4.1: TX and RX Integer data (2 Users) Eb/No=30dB (a), 43dB (b), 80dB (c) Twenty samples have been taken of the 100 random integers generated by TX1; as well as 20 samples of the 50 random integers that TX2 generates. In the first case, 30dB (a), RX1 MSc. in Digital Communication Systems Page 68 of 95 Candidate Number:

81 received 2 errors and RX2 received 4 errors. With Eb/No = 43dB (b), both RX1 and RX2 did not receive any error, as in the last case when Eb/No = 80dB (c). Accordingly, as the Signal to Noise ratio Eb/No increases, the number of wrong values or errors decreases. In this case, it was possible to reach no errors from values close to 40dB. Figure 4.2 shows the Error rate, number of errors and number of comparisons that the block made for both users. Three different values of Eb/No have been configured Eb/No = 30dB (a), 43dB (b) and 80dB (c) to have these results. (a) (b) (c) Figure 4.2: Error rate, Errors and Comparisons (2 Users) Eb/No=30dB (a), 43dB (b), 80dB (c) From Figure 4.2, it is clear that User 1 is receiving the double of bits compared to User 2, which is the expected result according to the design. In spite of the fact that both users receive errors when Eb/No=30dB (a), the highest Error rate value corresponds to the user with the lowest amount of information. As obtained in the results of Figure 4.1, for Eb/No=43dB (b) and Eb/No=80dB (c), all the data received is the same as the transmitted for both users, which is confirmed in the results shown in Figure 4.2, where Error rate = 0 and no errors are detected in both cases. MSc. in Digital Communication Systems Page 69 of 95 Candidate Number:

82 Figure 4.3 corresponds to User 1 s transmitted data after being modulated. Indeed, the figure shows data modulated with 16QAM, which corresponds to the modulated selected from the standard. The received data was tested configuring the channel with Eb/No = 30 db (a), 43 db (b) and 80 db (c), and they are presented in Figure 4.4. Figure 4.3: Modulated TX Data (User 1 of 2) (a) (b) (c) Figure 4.4: Modulated RX Data (User 1) Eb/No=30dB (a), 43dB (b) and 80dB (c) Based on the previous results, it was predicted that the received signal would be very different from the transmitted when Eb/No=30dB, as it actually is. In the second case, Eb/No=43dB, even though the symbols are not located exactly at the same position where MSc. in Digital Communication Systems Page 70 of 95 Candidate Number:

83 were transmitted, the receptor is able enough to detect the correct positions due to proximity; thus, no errors were detected in Figures 4.1 (b) and 4.2 (b). Finally, Eb/No=80dB is high enough for the system to receive all the symbols exactly as they were transmitted. The data transmitted to User 2 is shown in Figure 4.5. The received data is shown in Figure 4.6, tested in three different scenarios, as with User 1. Figure 4.5: Modulated TX Data (User 2 of 2) (a) (b) (c) Figure 4.6: Modulated RX Data (User 2) Eb/No=30dB (a), 43dB (b) and 80dB (c) The received modulated signal corresponds to 16QAM. In the first case, Eb/No=30dB (a), it is not possible to distinguish the received symbols; hence, the number of errors was higher MSc. in Digital Communication Systems Page 71 of 95 Candidate Number:

84 in that case. In the other cases, it is possible to distinguish the symbols, especially for the last case, Eb/No=80dB (c), which the received modulated signal is exactly as the transmitted modulated data. The signal transmitted in terms of dbw/hz vs. Hz is shown in Figure 4.7, and Figure 4.8 presents the received signal after passing the channel configured with Eb/No=30dB (a), 43dB (b) and 80dB (c), respectively. Figure 4.7: Transmitted signal (a) (b) (c) Figure 4.8: Received signal Eb/No=30dB (a), 43dB (b) and 80dB(c) MSc. in Digital Communication Systems Page 72 of 95 Candidate Number:

85 As the Eb/No value increases, the received and transmitted signals are more alike. In the first case (a), Eb/No=30dB is not high enough for the system to receive an appropriate signal; in other words, the difference between the transmitted and received signals is the reason by which multiple errors were detected and shown in Figures 4.1 (a) and 4.2 (a). When Eb/No=43dB (b), the received signal is more similar to the transmitted signal than the signal received with Eb/No=30dB; however, they are still not equal. When Eb/No=80dB (c), the transmitted and received signals are equal, and this is confirmed in Figure 4.1 (c) and 4.2 (c), where no errors were detected. 4.2 OFDMA 5 USERS (AWGN) The transmitted and received random integers for 5 users are shown in Figure 4.9. Three different values of Eb/No were also used, as in the previous scenario Eb/No = 30dB, 43dB and 80dB. In this case, the display sample size is 10 integers per user; however, it is important to consider that the total number of integers generated per user is 30, as shown in Figures 2.5 and 2.6. Because of space, only 10 integers of 30 integers per user are considered for analysis. When Eb/No=30dB (a), in a sample of 10 integers, User 1 receives two errors, User 2 does not receive errors, User 3 registers one error, User 4 has two errors and User 5 does not register any error in the first 10 integers. On the other hand, when Eb/No = 43dB (b) and 80dB (c), as in the previous scenario with two users, no errors are received in the first 10 integers. MSc. in Digital Communication Systems Page 73 of 95 Candidate Number:

86 (a) (b) (c) Figure 4.9: TX and RX Integer data (5 Users) Eb/No=30dB (a), 43dB (b), 80dB (c) Figure 4.10 shows the Error rate, number of errors and number of comparisons that the block made. These displays confirm that no errors were detected when Eb/No = 43 (b) and 80dB (c). Additionally, in spite of the fact that the five users receive the same amount of data (30 integers), the number of errors is not the same for each one. Thus, the Error rate values are different. MSc. in Digital Communication Systems Page 74 of 95 Candidate Number:

87 (a) (b) (c) Figure 4.10: Error rate, Errors and Comparisons (5 Users) Eb/No=30dB (a), 43dB (b), 80dB (c) From Figure 4.10, it is clear that when Eb/No=30dB (a), Users 3 and 5 receive the most errors; thus their Error rate are the highest. User 5 receives the lowest amount of errors, so its Error rate is the lowest. When Eb/No=43dB (b), no errors are detected for all the users. Also, when Eb/No=80dB (c) no errors are detected; hence, the Error rate is zero. Figures 4.11 and 4.12 show the transmitted and received modulated data for User 1.. The transmitted signal corresponds to the modulated OFDMA symbol, so it is clear that 16QAM modulation is used, as stated in the standard. With the purpose of comparing the transmitted signal with the received signal, it is useful to see that there is not any sample between 0 and -2 in both axes (Quadrature Amplitude and In-phase Amplitude). Consequently, at the receiver this range in both axes should also be empty of samples. MSc. in Digital Communication Systems Page 75 of 95 Candidate Number:

88 Figure 4.11: Modulated TX Data (User 1 of 5) (a) (b) (c) Figure 4.12: Modulated RX Data (User 1 of 5) Eb/No=30dB (a), 43dB (b), 80dB (c) When Eb/No=80dB (c), it is possible to recover the signal exactly as it was transmitted; however, when Eb/No=43dB (b), the system can recognize the samples and no errors are transmitted. When Eb/No=30dB (a), it is not possible to recover a reliable signal; thus, errors were detected as shown in Figures 4.9 (a) and 4.10 (a) Figures 4.13 and 4.14 show the transmitted and received modulated data for User 2. Again, it is clear that Eb/No=30dB (a) does not permit to receive reliable data. MSc. in Digital Communication Systems Page 76 of 95 Candidate Number:

89 Figure 4.13: Modulated TX Data (User 2 of 5) (a) (b) (c) Figure 4.14: Modulated RX Data (User 2 of 5) Eb/No=30dB (a), 43dB (b), 80dB (c) The received data of User 3 corresponds to Figure 4.16, and the originally transmitted data is shown in Figure The pattern obtained for the previous users, is repeated in this case; hence, Eb/No=30dB (a) has low reliability, when Eb/No=43dB (b) the 16QAM symbols have enough proximity to distinguish the samples and avoid errors, and Eb/No=80dB (c) has the highest reliability. MSc. in Digital Communication Systems Page 77 of 95 Candidate Number:

90 Figure 4.15: Modulated TX Data (User 3 of 5) (a) (b) (c) Figure 4.16: Modulated RX Data (User 3 of 5) Eb/No=30dB (a), 43dB (b), 80dB (c) Figures 4.17 and 4.18 correspond to User 4. The general behavior is repeated for all the users; however, analyzing each sample and comparing with other users, it is clear that samples are not the same for all the users, especially with Eb/No=30dB (a) and Eb/No=43dB (b). MSc. in Digital Communication Systems Page 78 of 95 Candidate Number:

91 Figure 4.17: Modulated TX Data (User 4 of 5) (a) (b) (c) Figure 4.18: Modulated RX Data (User 4 of 5) Eb/No=30dB (a), 43dB (b), 80dB (c) Finally, Figures 4.19 and 4.20 show the transmitted and received modulated data for User 5. In the transmitted signal, there is a square in the constellation without any sample. Comparing the transmitted data with the received, when Eb/No=30dB (a), there is a pair of samples in the square that is supposed to be empty, so this generates the errors and a high Error rate value at the receiver. MSc. in Digital Communication Systems Page 79 of 95 Candidate Number:

92 Figure 4.19: Modulated TX Data (User 5 of 5) (a) (b) (c) Figure 4.20: Modulated RX Data (User 5 of 5) Eb/No=30dB (a), 43dB (b), 80dB (c) Figures 4.21 and 4.22 show the transmitted and received signals, respectively, in terms of dbw/hz vs. Hz. It is evident that the most reliable signal is obtained when Eb/No=80dB (c). The received signal when Eb/No=30dB (a) is considerably different from the transmitted signal. With Eb/No=43dB (b), the received signal is still different than the transmitted, but it is reliable enough to avoid errors, as shown in Figures 4.9 and MSc. in Digital Communication Systems Page 80 of 95 Candidate Number:

93 Figure 4.21: Transmitted signal (5 Users) (a) (b) (c) Figure 4.22: Received signal (5 Users) Eb/No=30dB (a), 43dB (b), 80dB (c) Despite the fact that the second received signal Eb/No=43dB (b) is not exactly the same as the transmitted, it does not register errors for users because the system is able to recognize correctly the 16QAM received symbols, as shown in Figure BER RESULTS The Bit Error Rate (BER) is one of the most important parameters to evaluate performance in digital communications. The BER quantifies the reliability of the entire radio system from bits in to bits out, including the electronics, antennas and signal path between [19]. MSc. in Digital Communication Systems Page 81 of 95 Candidate Number:

94 As two scenarios generating an OFDMA symbol were designed, with two and five users, respectively, the purpose of the following results was comparing the BER curves for both scenarios, shown in Figure Note: User 1 of 2 : User 1 performance of 2 User system, User 1 of 5 : User 1 performance of 5 User system Figure 4.23: BER Curves for 2 and 5 Users (AWGN) There are some aspects to consider in order to analyze Figure First, (User 1 of 2) handles the biggest data size, (User 2 of 2) has a medium size of data and the other users have the lowest data size. Second, the AWGN channel has exactly the same configuration in all the cases. Besides, the ideal condition for a given BER value corresponds to the curves located on the left, so they have the best performance. MSc. in Digital Communication Systems Page 82 of 95 Candidate Number:

95 Based on this, (User 1 of 5) has the best performance because at a certain BER value, its Eb/No corresponding value is the lowest. In other words, the Bit / Error ratio is the same as the other curves in spite of its low Eb/No value, which means that though less ideal environment conditions in terms of noise, it has the same BER performance than other curves related with better environment conditions. Furthermore, it is clear that (User 1 of 2), which is the user receiving the most data, has a good performance at high Eb/No values. Finally, the five users of the second design do not have the same BER curve behavior in spite of receiving the same amount of information. Figure 4.24 shows the BER curves with and without fading for two and five users, respectively. (a) (b) Note: 1 of 2 : User 1 performance of 2 User system, 1 of 5 : User 1 performance of 5 User system Figure 4.24: BER Curves for 2 Users (a), and 5 Users (b) (AWGN vs. AWGN + Fading) MSc. in Digital Communication Systems Page 83 of 95 Candidate Number:

96 In the first case, as stated previously, (User 1 of 2) has better performance than (User 2 of 2) approximately from Eb/No = 13dB onwards. Also, the performance for both users degrades when fading is added to the channel. In the second case, only three of five users have been analyzed to avoid confusion because of the number of curves. The curves corresponding to the scenario without fading have better performance compared to those with fading. Indeed, the user with the best performance in AWGN, has also the best performance in AWGN + Fading. 4.4 PAPR RESULTS The Peak to Average Power Ratio (PAPR) is the key parameter by which SC-FDMA is used in the uplink instead of OFDMA. With the purpose of verifying that the PAPR is in fact lower in SC-FDMA than in OFDMA, the simulation of an SC-FDMA symbol was designed, as shown in the diagram presented in Figure 2.8. The Spectrum Analyzer block was used in simulations to measure the PAPR values of the uplink and downlink, as shown in Figure (a) (b) Figure 4.26: PAPR for 2 Users OFDMA (a) vs. SC-FDMA (b) (AWGN) MSc. in Digital Communication Systems Page 84 of 95 Candidate Number:

97 In the downlink (a), the PAPR is equal to db; while in the uplink (b) it is equal to In other words, in the simulation of SC-FDMA, the PAPR obtained is almost the half of the PAPR corresponding to OFDMA. MSc. in Digital Communication Systems Page 85 of 95 Candidate Number:

98 5 CHAPTER 5: CHALLENGES AND DESIGN IMPROVEMTS CHAPTER 5 5. CHALLENGES AND DESIGN IMPROVEMENTS 5.1 CHALLENGES Despite the efforts of LTE-A to increase the data rate, the excessive growth of users, makes capacity a key requirement. In fact, in order to guarantee coverage, companies opt to install more base stations, antennas and radio links, investing heavily sometimes. In addition, expansion deployment involves other costs such as battery, air conditioning, support, training, and others. On the other hand, high demand is not a constant pattern for 24 hours a day; therefore, high investment is not justified in hours of low usage. As the size of the platform increases, interference becomes more challenging. This directly affects performance. Even with OFDMA in the downlink, it cannot be possible to guarantee perfect orthogonal subcarriers because of the uncertainty of the channel, and with more users it becomes more challenging. Besides OFDMA, LTE-A considers other technologies to deal with the growing capacity requirement, such as MIMO and Carrier Aggregation. However, they are technologies that continues being dependent on spectrum, which is unpredictable, scarce and expensive. Synchronization is another challenge that LTE-A has because of the unpredictable channel and unpredictable demand for resources. In fact, synchronization is essential to avoid interference and minimize errors during transmission. MSc. in Digital Communication Systems Page 86 of 95 Candidate Number:

99 Some user equipment challenges are related to carrier aggregation and MIMO technology. Carrier aggregation could involve a complex radio environment design. Then, MIMO is based on the use of a number of antennas; indeed, up to eight transmitters in downlink, requiring more battery life of devices. SC-FDMA is used in the uplink with the purpose of minimizing PAPR and ensuring longer battery life of devices; however, at the cost of BER. Therefore, as BER could not be affected in the downlink, OFDMA is used instead of SC-FDMA. To sum up, designing a system with an efficient PAPR implies a BER performance decline, and vice versa. 5.2 IMPROVEMENTS One of the most challenging tasks in mobile communications is to deal with the transmission of data and control information without degrading performance, but guaranteeing proper synchronization and use of resources at the same time. However, it is clear that the use of resources to transmit control information during data transmission decreases bandwidth capabilities for users. Thus, a possible improvement is to separate data and control information to be transmitted using different resources. By doing this, spectral efficiency is achieved because all the subcarriers within a symbol transmit only user data. To illustrate, the OFDMA symbol that has been designed and simulated during the current project, has 256 subcarriers, 30 of which are reference signals. Hence, 11.7% of the OFDMA symbol was used to transmit information that does not correspond to user data. MSc. in Digital Communication Systems Page 87 of 95 Candidate Number:

100 This is not so critical in the downlink, as it is in the uplink. As 3 of 14 symbols within a subframe are completely used to transmit control information, 21.4% of the subframe is used to transmit it. Hence, it is a fairly high number considering the excessive cost of bandwidth. Figure 4.27 presents a design in which the reference signals do not occupy the subcarriers of the symbol transmitting user data. Figure 4.28 shows the corresponding diagram. Tough, as their function do not cease to be important and necessary, reference signals should be transmitted, but through a different resource than frequency. Figure 4.27: OFDMA Design Proposal Figure 4.28: OFDMA Diagram Proposal MSc. in Digital Communication Systems Page 88 of 95 Candidate Number: