| One of the purposes in wireless communication is to improve the channel capacity and efficiency. When the wireless channel resource is shared by many users, multiuser interference is an important factor which restricts system throughput. Meanwhile, the uncertainty of received signal caused by random wireless channel reduces the transmission reliability. This paper aims at improving the capacity of wireless multiuser communication system, decreasing the bit error rate, and offering a reliable and high-efficient wireless transmission.OFDM is important in the next generation mobile communication system. Combining it with CDMA increases the robustness against frequency selective fading and narrowband interference. This paper proposes the power truncation in multicarrier CDMA systems, when the channel power gain is lower than a certain threshold, corresponding bit is not transmitted. The reason is that bits in deep-fading period are quite likely to be in error, if transmitted would waste the transmission power and produce interference to other users. So truncating it, generating an erasure at the receiver and redistributing the saved power resource will reduce multiuser interference, increase the SINR and improve communication quality. The performance of multiuser truncated system in Rayleigh fading channel is analyzed and simulated. The results demonstrate the performance is improved.Among the remainder subchannels, the best resource allocation scheme is water-filling. But the water-filling scheme is too complex to practice. Based on it, an adaptive feedback resource allocation. scheme in multiuser OFDM systems under time-varying fading channels is discussed. Two adaptive schemes are presented:adjust the power based on the increment between the coherence time and adaptively feedback based on the capacity changement. By simulating the capacity of adaptive scheme presented and the water-filling scheme in multiuser OFDM system, it is proved that the methods can preserve the performance, reduce the system complexity, and improve the system efficiency.Multi-antenna system improves the throughput, provides independent parallel subchannels by using the singular value decomposition. But the transmitter needs to know the accurate channel-state information (CSI), which is hard to implement. The opportunistic beamforming (OBF) system doesn't need perfect channel-state information, also achieves high throughput. To select the random beamfomings, this paper discussed adaptive truncated OBF in Multiuser MISO system. Setting truncated SINR threshold, only when receive SINR is larger than the threshold, the users feed back. The random transmitting beamformings are optimized by truncating the beamfomings which have no feedback. Through analysis and simulation, the optimum truncated thresholds under different condition are found. It's also proved that adaptive opportunistic beamforming can reduce the interference, decrease feedbacks, and enlarge the system throughput. To further reduce feedbacks, adaptive truncated opportunistic beamforming under inquiring feedback strategy is proposed. The base station inquires the users randomly, only when the user is inquired and received SINR is larger than the threshold, the user can feed the SINR back. The base station communicates with user who feeds back first. By analyzing and simulating the performance in rayleigh fading channels, the adaptive truncated opportunistic beamforming system under inquiring feedback strategy is proved can reduce the feedback and improve the throughput when there are a few users.To reduce multiuser interference, multi-antenna receiver based on maximal ratio combining and spatial filtering is proposed, which mitigates both fading and co-channel interferences in the multiuser mobile communication system. The outage probability and BER performance of multi-antenna system in Nakagami-m fading channels with multiuser interference is analyzed and simulated, and the approximate closed-form expressions are derived.
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