SIMULATIVE STUDY (LINK/SYSTEM) OF WCDMA SYSTEMS

on 17 th - 18 th December 2016, in Goa, India. ISBN: 9788193137383 SIMULATIVE STUDY (LINK/SYSTEM) OF WCDMA SYSTEMS Ms.Ishata Bhardwaj Dr.Suyeb Ahmed Khan Mr.Govinda Pathak Prof. H.L Sharma M.Tech Student Associate Professor M.Tech Students Professor ECE Deptt, SSIET Patti ECE Deptt, SSIET Patti ECE Deptt, SSIET Patti SSIET Patti Abstract Simulation plays an important role during all phases of the design and engineering of communications systems, from early stages of conceptual design through the various stages of implementation, testing, and fielding of the system. In this paper we report on performance evaluation of the WCDMA radio interface of UMTS through a detailed link level and system level simulation tool. The motivation is to reproduce a possibly realistic scenario, where detailed behavior of various transmission techniques is modelled and their interaction evidenced in an actually integrated framework. The simulation model has been constructed for the WCDMA system in order to evaluate the performance of multiuser. This model describes multiusers effects and checks the performance parameters in terms of BER using simulink matlab 7.1. The Multiuser effect has been evaluated by Gaussian Approximation in AWGN Channel. 1. Introduction The First Generation (1G) systems are represented by the analog mobile systems designed to carry the voice application traffic. Their subsequent digital counterparts are known as Second Generation (2G) cellular systems. Third generation (3G) systems such as WCDMA, mark a significant leap, both in applications and capacity, from the current second generation standards [1]. Whereas the digital mobile phone systems are optimized for voice communications, 3G communicators are oriented towards data & multimedia service capabilities. 3G systems are currently deployed and their goal is to integrate a wide variety of communication services, multimedia services: voice services and high data services. The most appropriates multiple access technology for 3G wireless system is the Wideband Code Division Multiple Access Technique (WCDMA). The WCDMA technology is developed in order to achieve the technical objectives of IMT- 2000 and was chosen by ETSI as basic radio access technology for the UMT (Universal Mobile Technology System) [2]. The main benefits of a wideband carrier with a higher chip rate are Higher bit rates Spectrum efficiency Better coverage, as the frequency diversity 144 kb/s data rates for full coverage and vehicular mobility 384 kb/s data rate for pedestrian mobility 2 Mb/s data rate for limited coverage and mobility Flexibility Support of packet mode services. 2. WCDMA Key Technical parameters 345

on 17 th - 18 th December 2016, in Goa, India. ISBN: 9788193137383 WCDMA System Parameters Bandwidth Table 1 Key parameters of WCDMA for simulation model 5,10 20 MHz Chip rate (3.84 Mcps)* 2, 4 Bit rate 12.2 kbps (Voice), 64 (Data), 144 Spreading Factor 32, 64 (Multimedia) Link Level Parameter Processing Gain Voice (25, 29, 31 db), Data (19, Number of interfere User 24,28 db), Multimedia (17, 19, 21 db) 1-5 Signal to noise ratio 1-10 Loading Factor 30 % (10 % -90 %) Sectorization 1.5 Bandwidth 75 % Voice Activity 2.66 MUD efficiency Target BER 10-3 Path method Combining Maximum Power at base station 65 % for load, (25%-80 %) for different multipath Maximal ratio Combining 24 dbm Orthogonality factor 0.6 & 0.9 (0.1 0.9) 1 for System Level Parameters Outage Requirement Average Signal To Noise Ratio (E b /N o ) Variance pure orthogonality. 95% satisfied users 6 db Different for variable User The following table (1) shows the key technical features of the WCDMA radio interface [3]: 3. Simulation Set Up All the functions needed in WCDMA systems are included in the simulink MATLAB[4, 5]. Simulink is a suitable tool for the present work due to easy in use, interface to build system block diagram, performing simulations, and analyzing the results [6]. In order to run the simulation, certain things have to be assumed in the model [7,8,9,10] which are as follows. a) Sequence of bit is from exactly coding in WCDMA Scheme. b) Perfect power control is assumed, and each signal is assumed to arrive at the receiver with equal average power. c) The transmitted signal is corrupted by multiple Access Interference (MAI) which is generated in a structured way rather than treating it as Additive White Gaussian Noise (AWGN). d) The transmission medium is only added noise with Desired User at AWGN Channel. e) To illustrate the effect of user interference on system performance, the number of user in the system N increases from 1 to 4. Suppose all users transmit at the same power P and the interference seen by each user with increase proportional to N, and system BER will increase correspondingly. f) The desired Signal and all MAI signals is chip synchronized at the receiver. g) The receiver is a simple correlation receiver. 4.Multi-User Transmitter and Receiver Simulation Model The simulink model has been built for three users as shown in Figure (1) and its sub-block in Figure (2). The multiuser model is classified in two phase. In first phase only single user is accessing the system 346

on 17 th - 18 th December 2016, in Goa, India. ISBN: 9788193137383 without any other interferer user. In the second phase, three users are simultaneously accessing the system. After the simulation model is developed, simulation parameters such as sampling rate, seed random number generators, simulation length and design parameters (such as filter bandwidths, code rates, and signal to noise ratios) are specified. The simulation is than executed for single user. Practically, it is not possible for only single user can access the any wireless system at a time. So it is necessary to consider more users in the system and analyze the performance. Therefore, in second phase, desired user works with two other users. They are spreaded by the same spreading sequence generated by PN sequence but the orthogonality is maintained with OVSF code. The desired user is corrupted by the multiple access interference at the channel. At the transmission medium, two variables are added to the users signal as shown in figure (3). These are db gain and Gaussian noise generator blocks. The db gain, block diagram is used to generate a noise in the transmission medium. In this simulation, the db gain will be adjusted from 0dB to 20dB with 2dB difference. While, the Gaussian noise generator is used to generate a multi-user effect in the transmission medium. Table (2) has shown the different values of variance for Gaussian noise approximation with the amount of users uses the system simultaneously [9].The desired user signal is reconstructed at the receiver. Thus, all the same parameters are given in the receiver section as used in the transmitter section for the desired user. Finally the performance of WCDMA system is calculated in term of Bit Error Rate, measured with the comparison of transmitted data to the receiver data [11-12] Figure 1 Multi-User Transmitter / Receiver block diagram 347

Figure 2 Subsystem Block in Multi-User Simulation Block Users Figure 3 Gaussian Noise with SNR 2 1.67 3 2.43 4 4.09 5 6.67 Table 2 Numbers of users and Variance for Gaussian Noise Variance 10 16.67 15 23.33 5. Observation in Multiuser Simulation Model The scope block in Figure (4) displays its input signal amplitude with respect to the simulation time. This block has multiple axes for PN Sequence, Walsh Code & Spreaded output having common time range and independent of the y axes. If the input signal is continuous than the scope produces a point to point plot and the signal is discrete as in present case, the scope produces a stair step plot. The input bit stream is generated using the rand function. This input sequence simulates the information signal to be sent to the channel for retrieving by the receiver. A 64 by 64 Walsh function matrix is used to generate the walsh codes for the simulations. A user is able to choose any of the 64 walsh codes by entering a number (1-64) in the block parameter of the walsh code. The PN sequence is then XOR with the selected walsh code for the spreading code. This spreading code is further multiplied by the information bit stream for the CDMA spread spectrum. The Bernoulli binary generator generates random binary numbers as an information bit stream of ten bits having unit amplitude using a Bernoulli distribution as shown in Figure (5).The information bearing spreaded signal is then modulated by QPSK in which spreaded signal are converted into a parallel form, and then split into I (odd) and Q (even) streams corresponding to the inphase (I) and quadrature phase (Q) components of the transmitted signal. Each bit of I and Q stream are mapped into a BPSK symbol: a zero into -1 and one into +1, thus the overall modulation scheme becomes QPSK. The symbols of the I and Q branches are then multiplied by a gain factor and spreaded by a code known as orthogonal variable spreading factor (OVSF) code. The different OVSF codes are assigned for different users in order to preserve its orthogonality from the other users present in the same system. Both the channels are modulated on the same carrier frequency (f c ) and have a bit rate of R/2 bits-per second, where R is the data rate. However, the carrier signal in the Q-channel is shifted 348

Proceedings of International Interdisciplinary Conference On Engineering Science & Management Held by 90 to achieve a sine waveform. Then signal uses the downlink scrambling codes for the cell separation and the modulated and scrambled wave. The sequential change in amplitude is shown in Figure (6). The sampling rate is increased by 8 for desired user signal and 4 for other users; in the upsample block. The signal is corrupted by multiple user interference before reaching the channel as shown in Figure (7). The interfering users have different spreading factors in order to maintain theorhtogonality between the users. A white Gaussian Noise is introduced to the signals that pass through AWGN channel and their effect is clearly shown in Figure (8). In the receiver all the same parameters are given as were used in transmitter section of desired signal. The individual effect of each component is shown in Figures (9-10). PN sequence (ms) Figure 6 Subsystem Output Walsh Code sequence Amplitude ) Spreaded Out put sequence Figure 4 Output of PN (ms) Sequence, Walsh Code and XOR Signal (ms) Figure 7 MAI signal introduced with desired User (ms) Figure 5 Information Signal (ms) Figure 8 Signal Corrupted by White Noise from AWGN channel 349

Figure 9 Carrier wave with Desired Signal for Demodulation (ms) Figure 10 Bernoulli (ms) Binary Code with Desired Signal (ms) Figure 11 Reconstruction of Desired Signal with Delay 6. Results and Discussion (read this also) (A) Multiuser Model In this section, simulation results are discussed which has been done in the present work to evaluate the performance of the proposed simulator for WCDMA system. The system performance is analyzed in terms of Bit Error Rate as a function of signal to noise ratio. Bit-error-rate performance is usually depicted on a two-dimensional graph. The Abscissa is the normalized signal-to-noise ratio (SNR) expressed as E b /N 0 : the energy-per-bit divided by the one-sided power spectral density of the noise (expressed in decibels db).the ordinate is the bit-error-rate, a dimensionless quantity, usually expressed in powers of ten. The BER performance of WCDMA System is plotted in Figure (12). The required parameters for this Figure (12) are taken from Table (1). It is observed that the BER is proportional to the access users, i.e, the BER increases is proportional to the user s number. This effect becomes more explicit when the signal to noise ratio is low. Thus, the system capacity is changed from noise limited to interference limited case. It is cleared from Figure (13), that at a particular value of signal to noise ratio i.e. 6 db, BER increases as the number of user increases. In Figure (14) results of this study are compared with the work of [9]. The simulated results in terms of BER are nearly same upto 3dB of signal to noise ratio for the system performance. But deviation occurred at higher values of signal to noise ratio. The other users at the receiver are unable retained their orthogonality and thus act as interference to the desired user. Thus the use of a wider band carrier makes it possible to provide higher transmission rates. It also allows services efficiently to users, even in a situation where lower and higher rate services coexist. 350

BER BER BER Proceedings of International Interdisciplinary Conference On Engineering Science & Management Held 1.00E+00 1.00E-01 1.00E-02 1.00E-03 1.00E-04 1.00E+01 1.00E+00 1.00E-01 1.00E-02 Conclusion: simulated one two user three user 2 4 6 8 10 12 14 16 Eb/No Figure 12 Bit Error Rate vs Signal to Noise Ratio Figure 13 BER vs Number of User for E b/n o of 6 db Presant Study 1.00E+00 1.00E-01 1.00E-02 1.00E-03 2 3 4 5 Numbers of User Eb/No=6dB Hamizi Bin Zamzuri Result 2 4 6 8 10 12 14 Eb/No Figure 14 Comparison of performance of Hamizi Bin zamzuri [9] with the present Result The simulation tool is developed in Matlab using simulink block set and to able to show important information about WCDMA air interference as channels, modulation, codes, mapping and spreading etc. The tool shows how the information moves between the different parts of the system. In present study, simulation tool of communication procedures of WCDMA are presented. The number of display scope has been deployed at different part of the simulation model. So the users can view the sequential order change in the original signal at different part. It improve a past work [9] with the addition of scrambler, various coding, with this, user can see the change in the flow of information signal while the simulation is running. The simulation also includes the effect of Additive White Gaussian Noise and Multiple Access Interference (MAI). Using this simulation, we can estimate the BER as a function of the bit energy to noise spectral density ratio (E b /N o ), the number of interferers (K) and spreading factor. It has been seen that there are two factors that affect to the system performance, which is SNR and Multi-user effect. In SNR, lower the signal received by receiver higher will be the BER produced. While in Multi-user effect case, many users propose the system in the same time will produce higher BER. References 1. Rappaport,T.S (1996), Wireless Communication Principles and Practice, New Jersey, Prentice Hall. 2. Universal Mobile Telecommunications System (UMTS); Selection procedures for the choice of radio transmission technologies of the UMTS", TR 101 112 V3.1.0 (1997-11), UMTS 30.03 version 3.1.0. UMTS30.03. 3. 3GPP Technical Report, Deployment Aspects (Release 5), TR 25.943, V5.1.0, 2002 06. 4. Mathworks. Simulink and Real Workshop at http:/www.mathworks.com/products/. Website, 2006. 5. The Math Works, Inc., Matlab Compiler: The Language of Technical Computing User s Guide. Version 2.0 January 1999. 351

6. Hanselman and B. Littlefield, Mastering MATLAB 5: A Comprehensive Tutorial and Reference, Upper Saddle River, N.J Prentice-Hall, 1998. 7. V. Sundaramurthy. A Software Simulation Testbed for CDMA Wireless Communication Systems. Master s thesis, Rice University, May 1999. 8. Michel C. Jeruchim, Philip Balaban, K. Shanmugan, Simulation of Communication Systems, Modeling, Methodology, and Techniques, 2 nd Academy/plenum Publishers New York 2000. Edition Kluwer 9. Hamizi Bin Zamzuri and Muhammad Bin Ibrahim, Simulation On WCDMA For 3G Mobile Systems, 4 th Nahonal Conference on Telecommunication Technology Proceedmgs, Shah Alam, Malaysla, 0-7803-7773-7/03, IEEE 2003, PP 244-249. 10. William H. Tranter, K Sam Shanmugan, Theodore S. Rappaport, Kurt L. Kosbar, Principles of Communication Systems Simulation, Pearson Education, 2004. 11. Jean-François Frigon et al, Simulation, implementation and performance evaluation of a diversity enabled WCDMA mobile terminal Wireless Personal Comm, Springer, Vol 43, Issue 4, Dec 2007, PP 1101-1112. 12. Panagiotis K. Gkonis et al, An Adaptive Beam- Shaping Strategy for WCDMA Multicellular Networks with NonUniform Traffic Requirements, JOURNAL OF COMMUNICATIONS, VOL. 3, NO. 4, SEPTEMBER 2008, PP 16-25. 352