SUMMARYWe propose that the throughput performance of the DS CDMA unslotted ALOHA system with two user classes is analyzed by the M/M/infinity queueing model without the death rate approximation. The previous scheme uses the M/D/infinity queueing model with the death rate approximation. The new analysis method is simpler than the previous one because four-dimensional summation is replaced by two-dimensional summation in the packet success probability calculation. The speed of new analysis program is 250 times faster than that of the previous one. In the numerical results, we consider the cases when the message arrival rates of the two classes are equal or not equal, and the access control is present or not. It shows that the proposed scheme has more accurate analyzed throughput than the previous one does.
We apply LDPC codes for turbo inter-carrier interference (ICI) cancellation (channel detecting) and decoding in OFDM systems due to mobility of channels. The simulation result shows that the proposed turbo ICI cancellation and sum-product algorithm decoding of LDPC coded OFDM systems can achieve the better error rate performance than turbo ICI cancellation and BCJR decoding of convolutional coded OFDM systems when the codeword length is 816 bits.
In this paper, we study the performance of turbo codes in Poisson optical channels with pulse position modulation (PPM). We conduct simulations because the simulated performance is more accurate than the performance bound obtained by union bounds in previous publications. We modify the iterative decoding algorithm to apply turbo codes to PPM. The simulation results show that the PPM system has significant performance improvements over the system using on-off keying (OOK) modulation. They also show that the turbo-coded PPM system has significant performance degradation in imperfect synchronized situation.
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