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Performance Evaluation of WiMAX/IEEE 802.16 OFDM Physical Layer - page 53 / 107





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5.2 Physical layer performance results

The objective behind simulating the physical layer in Matlab™ was to study BER and BLER performance under different channel conditions and varying parameters that characterize the performance. But, in order to relay on any results from PHY layer simulation we must have some results that can do some validation in terms of general trends. The next section presents a set of scatter plot to identify trends in reception quality as we vary different parameters.

5.2.1 Scatter Plots

Figure 5.1 to 5.7 shows the scatter plots for different coding and modulation schemes as SNR values are changed on SUI­1 channel model. The '+' symbol denotes the transmitted data and the '*' symbol denotes the received data. These plots are obtained by sending the same frame data from transmitter to receiver through the channel repeatedly 1000 times. The input frame was taken from section of IEEE standard 802.16d. But, this does not confirm the presence of all constellation points, as it can be seen from the scatter plot of 64­QAM modulation (Figure. 5.6 and 5.7) where few constellation points are missing.

It can be observed from these plots that spread reduction is taking place with the increasing values of SNR. This scenario validates the implementation of channel model. It is also very important to note that the scatter spread gives a strong hint about the BER/BLER statistics as SNR values are varied.

In Figure 5.8, we have observed the effect of channel model on scatter plot at an SNR of 35 dB. It can be seen that severe variation is introduced in SUI­4,5,6 channel model even at high SNR value. It is clear that equalization is required for those three channel models. Figure 5.9 shows the effect of CP length on scatter plot with fixed SNR value. The differences are clearly visible that the scatter plots are less scattered for higher values of CP length. Because, the capabilities to absorb multipath effects increases with higher value of CP length.


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