6.1 Conclusion
In this thesis, we first presented the ranging techniques for IEEE 802.16e OFDMA PHY, analyzed and verified them by floating-point simulation. Second, we modified them to point version and compare the difference of performance between floating-point and fixed-point versions. Finally, we implemented them on TI’s digital signal processor.
We mainly discussed the periodic ranging process and presented several analysis and simulations. We employ the frequency domain reception algorithm because it is less complex.
We find that the frequency offset which was within the range of [-0.1,0.1] did not cause an effect on the performance in evidence. Thus, we ignore the estimation of frequency offset and focus on the tasks of ranging code detection and timing offset estimation. We provide some simple analysis of our algorithm. The nonzero cross-correlation values of ranging codes had some effect on the analysis and we took them into account. Then, we considered two code detection methods [6], did some floating-point simulation and concluded that method-1 is a better choice. In addition, we discussed the costs of missed detection and false alarm and used them to determine the detection thresholds. Under our algorithm and detection thresholds, the average required numbers of ranging retransmission are 0.0488 and 0.4002
for AWGN channel with 3 ranging users and SNR=3 dB and SUI-3 channel with 3 ranging users and SNR=5 dB, respectively. Each retransmission causes increased latency which is 5 ms in our system.
Finally, we modified the program to fixed-point version. Simulation results showed that all curves of fixed-point simulations are very close to that of floating-point simulations. Then we employed some optimization techniques to accelerate functions of ranging as fast as we can. Finally, some clock cycles simulation results were provided to show that the ranging task can achieve real-time requirements.
6.2 Future Work
There are several possible extension for our study:
• In this thesis, we only discussed periodic ranging. It is possible to includes bandwidth request and handover ranging into our study.
• We only provided analysis of successful detection rate of the algorithm. Some analysis of the performance of timing offset estimation can also be considered.
• The analysis were done for single-user case. More complex analysis in multi-user case can be further considered.
• Analysis of detection method 1.
• Design of better ranging methods.
• Try to develop frequency offset estimation algorithms. It may improve the ranging performance although the improvement is small.
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