Scientific Journal of Impact Factor (SJIF): 4.72 International Journal of Advance Engineering and Research Development Volume 4, Issue 2, February -2017 e-issn (O): 2348-4470 p-issn (P): 2348-6406 Analysis Of MIMO OFDM Based Wimax System With LPDC Er.Gurpinder singh 1, Er. Manpreet Kaushal 2 1 Department of Electronics And Communication,Asra College of Engg. & Technology, 2 Department of Electronics And Communication,Asra College of Engg. & Technology, Abstract OFDM is stated as Orthogonal Frequency Division Multiplexing. It is a technology used in wireless communication for achieving more reliable and effective communication. It supports multicarrier modulation and has the characteristic of flexibility. The OFDM has various advantages but fails at the point of BER(Bit Error Rate). To decrease the BER of OFDM system various techniques have been developed. The objective behind this study is to reduce the BER in OFDM-MIMO system. The step taken towards accomplishment of the objective by using the coding schemes like the PN and Alamouti STBC codes. The modulation schemes uses in this paper are BPSK,QPSK and QAM16. The result section explores the proficiency of the proposed work over Keywords- OFDM-MIMO, Alamouti STBC, Modulations, Binary Phase Shift Key, Quadrature Phase Shift Key, Quadrature Amplitude Modulation I. INTRODUCTION With the evolution in communication technology, needs of the users are also increasing day by day. So the plenty of the work had been done and still going on in order to fulfill the various need of the consumers or users. The issue regarding the data transfer at high rates with high quality is still in pipeline. Over a decade many researchers focused on MIMO (Multiple Input Multiple Output) is a solution which enables the data to travel at high rates with wider bandwidth but still not able to work efficiently. Hence the solution is to combine the OFDM and MIMO in order to get more reliable and high quality of data transmission. OFDM was collaborated with MIMO with the intention of removing the backlogs of OFDM system and to increase the overall efficiency of both OFDM and MIMO. OFDM is a technology which is meant for 4G implementations. It is a wireless broadband technology with high bandwidth normally up to 20MHz. Thus it supports greater than 1Gbps data transfer rate. In modulation, Information is mapped onto the variation in frequency, Phase and amplitude of a signal. Multiplexing is used for allocating the users in given bandwidth. OFDM is an approach which is the mixture of modulation and multiplexing.. In this the resources are shareable i.e. shared by the data sources. It uses modulation techniques. OFDM is a digital multicarrier modulation scheme which enhances the single sub carrier modulation by using the concept of multiple subcarriers within the same individual channel. It follows the concept of FDM. In this various stream of information are added to the various channels which have parallel frequency. Features of OFDM: Less sensitive to time synchronization errors. Provides the SFN i.e. Single Frequency Network. Robust against fading and ISI i.e. Inter Symbol Interference. MIMO stands for Multiple Input and Multiple Output. MIMO system has many advantages as compare to single to single antenna communication. It is used as transmission and receiver equipment for wireless radio communication. It include multiple transmitter and receiver antenna. Multiple antennas cause Variation in data rate. MIMO has two features: @IJAERD-2017, All rights Reserved 223
Spatial Diversity: In this, same information is transferred over the independent fading channels to oppose fading. Spatial multiplexing- In this, each spatial channel carries independent information thereby, increasing data rate of system. II. MODULATION SCHEME Modulation is a process of varying one or more characteristics of periodic waveform known as carrier signals along with modulating signals that consists information to be transmitted. Classifications are as follows; ASK (Amplitude Shift Keying) FSK (Frequency Shift Keying ) PSK (Phase Shift Keying) BPSK (Binary PSK) QPSK (Quadrature PSK) DPSK (Differential PSK) QAM (Quadrature amplitude modulation) ASK: In this, strength of carrier signals differentiate for represent the binary 1 or 0. Both frequency and phase does not varies while amplitude not varies constantly and one of the amplitude is not zero normally. FSK: In this, frequency signals are variable signals to represent the binary 1 or 0. Amplitude and phase remains same at the time of each bit interval. PSK: In this, Phase of carrier signals varies to represent the binary. Amplitude and phase remains constant during every interval. DPSK: It conveys data by changing the phase of carrier wave. BPSK: It is a simplest form of PSK. In this, two phases are used and both of those phases are separated by 180 o. It is also known as 2-PSK. The general form of equation is given by: S n (t) = 2E b T b cos 2πf c t + π 1 n, n = 0,1 (1) QPSK: It uses four points on the constellation diagram. It can encode two bits per symbol. The following equation is used for QPSK modulation: δ n t = 2E s cos (2πf T c t + 2π 1 π ), n = 1,2,3,4) (2) s 4 QAM: In this, there are two signals with the same frequency and different phase by 90 o. One signal is known as I signal and second signal is known as Q signal mathematically. Sine and Cosine waves are used to represent the signals. III. CODE SCHEMES STBC CODES STBC stands for Space Time Block Coding. STBC is used to transfer the multiple copies of data to more than one antenna. It is used in Wireless communication for replicating and transmitting the data at more than one receiver s end. It also makes the reliable data transmission. Sometimes data to be transferred gets corrupted with the effect of reflection, refraction or scattering. Sometimes some data also gets altered with the intrusion of thermal noise which affects the quality of data at the @IJAERD-2017, All rights Reserved 224
receiver side. This problem results that there is a scope of being able to use more than one received copies to correctly decode the received signal. STBC helps to fabricate the more accurate information from received signals by combining them together IV. PROBLEM FORMULATION The major aim of wireless data transmission is to send the data with high speed and with fewer errors to a very long distance. Orthogonal frequency-division multiplexing (OFDM) is a method of encoding digital data on multiple carrier frequencies. OFDM has developed a popular scheme for wideband digital communication, used in applications such as; digital television and audio broadcasting, DSL Internet access, wireless networks, power line networks, and 4G mobile communications. The high BER of the system was the major problem of the system. In traditional systems the LDPC codes were used for encoding and decoding. The major problem with the LDPC coding was that, it was slow channel coding. Due to this slow channel coding there are lot of variation in the signal that give rise to higher BER. Along with this the STE (space, time encoder) coding scheme was used. The results achieved by using these methods were not efficient. The BER of the system was more. So there is need to design a system in which the BER performance of the system is improved. Along with this, the traditionally used method needs to be replaced, so that the efficient system is designed. V. PROPOSED WORK Earlier OFDM method was used, but it has various disadvantages; high BER of the system. To overcome the problem, various coding algorithm were used. The algorithm like LDPC, STE (space time encoder) codes were used for improving the efficiency or other multiple access technique was used. The major problem of using LDPC was delay module of the channel was not considerd. By studying the various problems of the system, a new system is being proposed in this work. The existing LDPC codes were replaced by the TFT (Time frequency Training). The main benefit of using the TFT (Time frequency Training) is that, delay module was considered. It helps in fast channel coding that is the major requirement of the communication that the data is sent with high speed. In addition to this the BER of the system is also improved. Along with this, the STE (space time encoder) codes are replaced by the Alamouti STBC code. The STBC (Space-Time Block Code) is used which is multi input multi user code to improve the reliability of data transfer. This code is used as it reduces BER (Bit Error Rate). So in this proposed work the BER of the system is improved by using this hybrid system in which the TFT codes and Alamouti STBC code scheme is introduced. VI. METHODOLOGY The working of the proposed work can be explained in a flow as shown in the following diagram: STEP 1: First step is to generate the data bits randomly. This block creates the serial binary formatted data that that will be further converted to the parallel format by serial to parallel converter. These generated bits will be used for further processing. STEP 2: In next step the data bits are passed to the TFT (Time frequency Training) module since TFT works upon the basis of both time and frequency. STEP 3: After applying TFT the bits are transferred for modulation. Modulation is done by applying most prominent modulation schemes such as BPSK, QPSK and 16QAM. STEP 4: The output of the modulation will be provided as an input to the next block to apply Alamouti STBC code. As it transmits the multiple replicas of data over a single antenna. After this the inverse FFT and Cyclic Prefix is added to the data and then transferred to the receiver. STEP 5: In this step the receiver receives the data and FFT is applied to the data along with the removal of Cyclic Prefix. STEP 6: After this the Alamouti STBC code will applied to the data sequence. STEP 7: The modulated signals are demodulated by using the similar demodulation schemes. And then the TFT will process the demodulated signals and hence the receiver reached to the final data. STEP 8: Last step is to calculate that the received signals are how much reliable with respect to the transmitted signals by calculating the Bit Error Rate of the Signals. The following diagram explains the proposed work in a flow: @IJAERD-2017, All rights Reserved 225
Data Bits BER calculation Time frequency Training Time frequency Training Modulation (BPSK, QPSK, 16 QAM) Demodulation (BPSK, QPSK, 16 QAM) Almouti STBC code Almouti STBC code IFFT + CP IFFT + CP FFT - CP FFT - CP VII. RESULTS AND DISCUSSIONS This Section explores the implementation of the proposed work in the form of results. The results evaluation is done in the form of BER i.e. Bit Error Rate defines the bit wise error in the signals. Figure3 Graph of BER with implementation of BPSK-LDPC and BPSK-PN sequences @IJAERD-2017, All rights Reserved 226
Figure4 Graph of BER with implementation of QPSK-LDPC and QPSK-PN sequences Figure5 Graph of BER with implementation of QAM-LDPC and QAM-PN sequences Figure6 Comparison graph on the basis of BPSK, QPSK and QAM16 The Figure2 shows the comparison of BER in case of BPSK-LDPC and BPSK-PN sequences. From the graph(figure2) it is clear that the BER of BPSK-PN is minimum as compare to BPSK-LDPC. In figure3 there is a comparison on the basis of QPSK-LDPC and QPSK-PN the graph makes it clear that the QPSK-PN is better than the other one as it has least value of BER. @IJAERD-2017, All rights Reserved 227
The figure4 explores the comparison graph between QAM16-LDPC and QAM16-PN and it reveals that the QAM16-PN has lesser value of BER in contrast of QAM16-LDPC. The figure2,3,4 explains the results on the behalf of individual modulation schemes along with coding sequences. But the figure6 draws a comparison graph which compares the three of the modulation scheme on a single screen or graph. From this figure it is observed that the BPSK modulation outperforms QPSK and QAM16. VIII. CONCLUSION AND FUTURE SCOPE A coded modulation scheme for the Wimax PHY layer with Time Frequency Training was presented. The approach is pragmatic but quite effective for bandwidth efficient transmission, because only one encoder and one decoder are employed and it does not require interleavers. This is an advantage over other coded modulation schemes for reducing the associated complexity. It is difficult to analytically evaluate TFT, so BER graph analysis is used to investigate and discussed their performances. Inspite of the fact that higher order modulations are able to offer a faster data rates and better spectral inefficiency for the advanced communication systems, these schemes suffers comparatively less delay. This was evident from the BER performance. For future reference more modulation codes can be used for improving BER performance in OFDM-MIMO systems. References [1] H. Bolcskei On the capacity of OFDM-based spatial multiplexing systems IEEE, Vol 50, Issue: 2, Pp- 225 234. [2] Jiang Liu Design and Performance Evaluation of OFDM Based Wireless Services Employing Radio over Optical Wireless Link International Journal of Wireless & Mobile Networks (IJWMN) Vol. 3, No. 5, October 2011,Pp 173-184. [3] Mohsin Khan, A review paper on: the PAPR analysis of orthogonal frequency division multiplexing (OFDM) International Journal of Mobile Network Communications & Telemat, Feb 2014, Vol. 4 Issue 1, [4] Taewon Hwang OFDM and Its Wireless Applications: A Survey IEEE Transactions on Vehicular Technology, Volume: 58, Issue: 4, Pp 1673-1694 [5] Md. Mejbaul Haque Performance Analysis of MIMO-OFDM for 4G Wireless Systems under Rayleigh Fading Channel International Journal of Multimedia and Ubiquitous Engineering Vol. 8, No. 1, January, 2013,Pp 29-40 [6] Gordon L. Stüber, Broadband MIMO-OFDM Wireless Communications IEEE, VOL. 92, NO. 2, February 2004 Pp 271-294 [7] M.S. Chavan, Multipath Fading Channel Modeling and Performance Comparison of Wireless Channel Models International Journal of Electronics and Communication Engineering..Vol 4, Number 2 (2011), pp. 189-203 [8] Youjian Liu, (2004), On the Design of MIMO Block-Fading Channels With Feedback-Link Capacity Constraint IEEE, Vol 52,No,2004 Pp 62-70 [9] Ruchin Mangla Performance Comparison Of MIMO-OFDM Transceiver Wireless Communication System Using QAM And QPSK Modulation Schemes, IJAEST, Vol. 1, No. 2, pp. 66-72. [10] Lavish Kansal (2012), BER Analysis Of MIMO-OFDM System Using OSTBC Code Structure For M-PSK Under Different Fading Channels, IJSER, Vol. 2, No. 11 [11] Niharika Sethy (2013) BER Analysis Of MIMO-OFDM System In Different Fading Channel, IJAIEM, Vol. 2, No. 4, pp. 405-409, April 2013 [12] C.Nithiya (January 2013) Error Control And Performance Analysis Of MIMO-OFDM Over Fading Channels, [13] Nisha Achra (May 2013) Performance Analysis Of MIMO OFDM System For Different Modulation Schemes Under Various Fading Channels, IJARCCE, Vol. 2, No. 5, Pp. 2098-2103 [14] Vibha Rao (May 2014) Performance Analysis Of MIMO-OFDM For Multiple Antennas, IJAREEIE, Vol. 3, No. 5, pp. 9349-9355 [15] Vishal Sharma BER Analysis Of MIMO-OFDM System Using Various Modulation Schemes, International Conference on Communication, Computing & Systems, pp. 192-195 [16] Parul Wadhwa (2013) BER Analysis & Comparison Of Different Equalization Techniques For MIMO-OFDM System, IJARCSSE, Vol. 3, No. 6, pp. 1682-1688. @IJAERD-2017, All rights Reserved 228
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