A novel differential detection method in frequency domain spread spectrum system, called multicarrier spread spectrum chip-level differential detection (MC-SS-CLDD), is proposed. The moment generating function (MGF) of decision variable and a saddlepoint approximation method are exploited to analyze the BER performance of MC-SS-CLDD. The results of analysis and simulation indicate that, If the coherent bandwidth of channel doesn’t exceed the occupied bandwidth of two subcarriers, MC-SS-CLDD exhibits a better performance to make the system resistant to frequency-selective fading in case of narrower coherent bandwidth of channel.

We explore in this paper one novel deterministic simulation model for downlink multiple-input multiple-output (NIIMO) fading channel in wireless communication. The von Mires function, which characterizes accurately the distribution of non-isotropic scattering around mobile station. is used to deterministic modeling process for both space-time codes (STC) scenario and downlink beam-forming (DBF) scenario. Statistical fading characteristics of the simulated MlMO channel, including level-crossing rate, average duration of fades and envelope crosscorrelation. we studied. The impact of non-isotropic scattering on MIMO-link capacity is also investigated. The numerical results show that existence of non-isotropic scattering degraded ergodic capacity of MlMO channel by IbitlHds in the case of STC scenario. And the maxim5m achievable capacity in the case of DBF scenario is always lower than that of STC scenario because transmit steering vector affected the transmit antenna correlation. The proposed MIMO channel simulation model has P universal structure and requires less parameter measurements. Hence. it can be used effectively for link-level simulation and capacity evaluation in MlMO wireless communication systems.

In this paper, the bit error rate (BER) performance of orthogonal frequency division multiplexing (OFDM) system in multipath fading channels using the frequency domain differential demodulation (FDDD) and time domain differential demodulation (TDDD) is analyzed. The results indicate that in frequency-nonselective fading channel, the BER performance of FDDD is better than that of TDDD. In frequency-selective fading channel, if the time delay doesn’t exceed the guard time, the BER performance of TDDD is not affected by the multipath and time delay, but it will be affected by the Doppler frequency; the BER performance of FDDD is affected by the time delay and the Doppler frequency at the same time. With the increase of Doppler frequency, the BER performance of FDDD is better than that of TDDD demodulation. Index Terms-orthogonal frequency division multiplexing, bit error rate, frequency domain differential demodulation, time domain differential demodulation, Doppler frequency

在采用部分功率训练序列同步的OFDM系统中[1]，训练序列会对OFDM承载用户数据的检测造成严重干扰. 本文针对每个无线分组包中只有一个OFDM符号，即训练序列和用户数据同时在一个OFDM符号时间内发射，提出一种抑制训练序列干扰的方法,在接收机中分离训练序列、OFDM承载的用户数据. 在室内多径衰落信道的条件下，本文分析和仿真了训练序列和OFDM承载用户数据的分离性能，结果表明，分析与仿真结果相近，分离效果明显.