A fast algebraic codebook search method based on iteration-free pulse replacement is proposed. The method comprises two stages. At the first stage, an initial codevector is determined by the pulse-position likelihood-estimate vector. At the second stage, after computing pulse-contributions for every track, the pulse replacement is performed to maximise the search criterion over all combinations, replacing the pulses of the initial codevector with the most important pulses for every track. Experimental results show that the proposed method is very efficient in terms of computational complexity and speech quality compared to previous pulse replacement methods.

In this letter, we analyze the performance of maximum-ratio combining (MRC) system with channel estimation error for physical layer security. The quantified measure for channel estimation error is the correlation coefficient between the true fading channel coefficients and their estimates. Exact closed-form expressions for secrecy performance including the statistical distribution of the signal-to-noise ratio (SNR), the secrecy outage probability and the secrecy capacity are derived. The analytical results are confirmed by numerical simulations.

This report presents performance evaluation of a prototype of a millimeter-wave-based communication system in tunnel environments. The prototype could give 500 Mbps of data rate throughout 1.1 km on a straight route. The data rate dropped from 500 Mbps to 100 Mbps while a receiver of the prototype passed by 530-m point on a curved route. The results can be used to determine appropriate locations of trackside radio components to achieve enough coverages in a system deployment for railway communication networks.

A simplified soft demapper for non-square quadrature amplitude modulation (QAM) provided by fifth generation of high-speed data-over-cable systems (DOCSIS 3.1) is proposed. By using the geometric tendency of the non-square QAM constellation and “fold-and-overlap” approach, the non-linear log likelihood ratio (LLR) equation based on the max-log maximum a posteriori (MAP) algorithm can be approximated to linear equations. With this approximation, the proposed method can be applied to high-order non-square QAM, up to 8192 QAM, with negligible bit error rate performance degradation under additive white Gaussian noise and multipath flat-fading channels. Computational complexity is reduced by at least 93% compared to the LLR calculation based on the max-log MAP algorithm.

A new carrier frequency acquisition algorithm for high-order QAM systems is proposed. The proposed algorithm is based on a frequency offset estimator combined with previous work that developed an improved phase and frequency detector. Compared with the previous work, the proposed algorithm increases the acquisition speed maximum by six times.