Performance of concatenated LDPC and CCK codes
It can be seen from Figure 3 that the performance of CCK in the fading channel is very poor. When SNR = 32 dB, the BER is approximately 10-4. The reason is because the cross-correlation between the code words in the CCK code set is not very good, especially in the fading environment, the channel interference on the signal seriously deteriorates the cross-correlation between the code words. Therefore, this paper uses the outer cascade LDPC code to correct the demodulation error of CCK and improve the performance gain of CCK.
The system uses (504, 3, 6) regular LDPC codes, the interleaving depth is two coding blocks, and a random interleaver is used. CCK demodulation uses large-number logic soft decision algorithm. The channels are AWGN and Rayleigh fading channels, respectively. The fading channel is 3 paths. The ITU M.1225 standard channel A multipath channel model is used. The system composition is shown in Figure 4.
Figure 4 During the simulation of the simulation system model, it is assumed that the ideal channel is estimated and Rake receiving technology is not used. Figures 5 and 6 show the simulation results of CCK cascaded LDPC outer codes under AWGN and Rayleigh fading channels, respectively. It can be seen that when BER = 10-5, under the AWGN channel, the minimum SNR required by CCK is 9 dB, and the minimum SNR ratio of CCK cascade LDPC is 6 dB, which is improved by 3 dB. Under the Rayleigh channel, when the BER is 10-4, the minimum SNR required by CCK and CCK of the cascade LDPC are 33 dB and 22 dB, respectively, and there is obviously a performance gain of 11 dB. That is, the performance of CCK modulation of concatenated LDPC codes has a significant performance gain compared to CCK modulation alone, and the effect under fading channels is more obvious.
SNB / DB SNB / DB
Figure 5 CCK cascade LDPC performance in AWGN SNR / dB Figure 6 CCK cascade LDPC performance in Rayleigh channel
Whether in AWGN or multipath fading channels, the CCK cascade LDPC structure can obtain a certain performance gain relative to CCK modulation and coding. In the fading channel, the gain is more obvious. When the BER is 10−4, the gain can reach 11 dB. Because LDPC code decoding is relatively simple and can achieve performance close to the Shannon limit, CCK has better performance in a multipath environment. Therefore, in the fourth-generation cellular mobile communication system, LDPC and CCK will be widely used. Especially when using Rake receiving technology, the advantages of CCK will be more obvious, this is our next step.
Analysis of code modulation performance of concatenated LDPC codes and CCK
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