Performance, Evaluation and Enhancement of Some Orthogonal Frequency Division Multiplexing Techniques

Abstract

This research investigates the evaluation of Coded Frequency Division Multiplexing (COFDM) and Dual OFDM performance under wireless transmission system drawbacks. COFDM and DOFDM simulation model have been designed using Matlab & Simulink. Different modulation schemes such as BPSK, QPSK, DQPSK, 8PSK and 16PSK were executed using the model. The model was enhance with different channel estimation techniques such as Combi-type pilot channel estimation techniques with singular value decomposition (SVD) and applying a raised cosine filters in the simulation model. Different types of channel estimation strategies have been studied such as Combtype pilot channel estimation and Block-Type Pilot Channel Estimation. The model system has been enhanced by applying Convolution Encoder and Viterbi Decoder in the system where a good receiving spectrum power was achieved as illustrated in the power spectrum graphs. The evaluation of performance measurements have been considered by comparing their performance effect under different types of modulation schemes. To be able to compare the different modulation schemes there was a need for a simulator that was realistic enough to provide reliable results. Therefore the coded and Dual OFDM simulator were modeled. The signal was subjected to wireless transmission system drawbacks, such as Multiple Path Rayleigh Fading and Additive White Gaussian Noise (AWGN). Different types of performance measurements have been considered such as BER SER E N E N S N b o s o , , / , / & / . These performance measurements have been evaluated and compared with different modulation schemes with and without filtering as illustrated in the graphs. Reed Solomon (RS) Encoder and Decoder were installed in the system. The coding blocks were set with the desirable values of parameters. To fulfill a high signal quality the sample time was set to be 8e-5 v seconds. The dual model (Double error correction, forwarded and afterward) achieved a betters received signal quality when compared with other ones. When applying the capacity rate equations in different modulation scheme with different number of channel bit, different channel capacity were achieved. When using BPSK& QPSK we get Mbps of 8.467, energy to noise ratio of 9dB, Bit Error Rate (BER) of 1e-6.5 and Symbol Error Rate (SER) of 0.499%, 0.751% respectively. When using DBPSK& DQPSK, we get Mbps of 16.934. And we get BER of 1e-3.6, 1e-3 respectively. And we get energy to noise ration of 9 dB, 14dB respectively. Also we get SER of 0.508%, 0.994% respectively. When using 8PSK& 16PSK we get Mbps of 33.868. And BER of 1e-7.25, 1e-5.5 respectively and we get energy to noise ration of 15dB, 18 dB respectively. And we get SER of 0.998% for both of them. Therefore and with reference to the result obtained from calculations and graphs, 8 PSK and 16 PSK achieved a high data rate in high signal to noise ratio but with high bit error rate (BER) and high symbol error rate (SER). BPSK and QPSK achieved a lower data rate in low signal to noise ratio and with low bit error rate and low symbol error rate. DBPSK and DQPSK achieved a higher data rate with high signal to noise ratio, but in low bit error rate and acceptable SER. The simulation indicated that DQPSK yields the best performance therefore we introduced it as the most capable modulation scheme for enhancing OFDM.