A novel practical codebook-precoding multiple-input multiple-output（MIMO） system based on signal space diversity（SSD） with the minimum mean squared error（MMSE）receiver is proposed.This scheme utilizes rotation modulation and space-time-frequency component interleaving.A novel precoding matrix selection criterion to maximize the average signal to interference plus noise ratio（SINR） is also put forward for the proposed scheme,which has a larger average mutual information（AMI）.Based on the AMI- maximization criterion,the optimal rotation angles for the proposed system are also investigated.The new scheme can make full use of space-time-frequency diversity and signal space diversity,and exhibit high spectral efficiency and high reliability in fading channels.Simulation results show that the proposed scheme greatly outperforms the conventional bit- interleaved coded modulation（BICM） MIMO-orthogonal frequency division multiplexing（OFDM） scheme without SSD,which is up to4.5 dB signal-to-noise ratio（SNR） gain.
对超奈奎斯特(faster than Nyquist,FTN)和奈奎斯特系统的频谱效率进行了对比分析。在绝对带宽的前提下,首先证明了基于根升余弦函数脉冲的单载波FTN可达速率大于奈奎斯特可达速率,并推导了有子载波间干扰的多载波FTN的频谱效率公式。本文证明了单载波FTN的频谱效率大于奈奎斯特系统的频谱效率,并且证明了单载波FTN的频谱效率随着滚降因子的减小而增大。基于频谱效率公式和数值仿真,本文给出了多载波FTN对于不同滚降因子的最优子载波间隔。结果表明,即使存在子载波间干扰,基于最优子载波间隔的多载波FTN频谱效率也高于正交系统(奈奎斯特)的频谱效率。
The 16-ary quadrature amplitude modulation （16QAM） is a high spectral efficient scheme for high-speed transmission systems. To remove the phase ambiguity in the coherent detection system, differential-encoded 16QAM （DE-16QAM） is usually used, however, it will cause performance degradation about 3 dB as compared to the conventional 16QAM. To overcome the performance loss, a serial concatenated system with outer low density parity check （LDPC） codes and inner DE-16QAM is proposed. At the receiver, joint iterative differential demodulation and decoding （ID） is carried out to approach the maximum likelihood performance. Moreover, a genetic evolution algorithm based on the extrinsic information transfer chart is proposed to optimize the degree distribution of the outer LDPC codes. Both theoretical analyses and simulation results indicate that this algorithm not only compensates the performance loss, but also obtains a significant performance gain, which is up to 1 dB as compared to the conventional non-DE-16QAM.
The research and application of wireless local area networks （WLAN） technology are in a stage of rapid development. It has been one of research focuses of the wireless communications field. Through the use of enhanced single-user （SU）/multi-user （MU） multiple input multiple output （MIMO）-orthogonal frequency division multiplexing （OFDM） technology, the next generation WLAN IEEE 802.1 lac dramatically increases the throughput. An improved MIMO-OFDM scheme based on modulation diversity is proposed for the next generation WLAN. It uses two-dimensional modulation diversity to the current IEEE 802.11ac transmission scheme. Through the space-time-frequency component inter- leaver and the rotational modulation, the proposed scheme ex- hibits high spectral efficiency and low error rate in fading channels. The simulation results show that the proposed scheme significantly outperforms the SU/MU MIMO-OFDM scheme in the current IEEE 802.11 ac standard, which is up to 5 dB.
