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Link Adaptive In MIMO-OFDM Systems

Posted on:2007-05-18Degree:MasterType:Thesis
Country:ChinaCandidate:Y JiaFull Text:PDF
GTID:2178360182477833Subject:Communication and Information System
Abstract/Summary:PDF Full Text Request
High-speed wireless data transmission requires robust and spectrally efficient communication techniques. When the channel can be estimated and this estimate is sent back to the transmitter, the transmission scheme can be adapted relatively to the channel characteristics. Most modulation and coding techniques do not adapt to fading conditions. These non-adaptive methods require a fixed link margin to maintain acceptable performance when the channel quality is poor. Thus, these systems are effectively designed for the worst channel conditions, resulting in insufficient utilization of the whole channel capacity. Adapting to the signal fading allows the channel to be used more efficiently since power and rate can be allocated to take advantage of favorable channel conditions.In this paper, a variable-rate and variable-power MQAM and MPSK modulation scheme based on perfect CSI for high-speed data transmission in MIMO-OFDM systems over frequency selective fading channels was proposed. The author first reviewed results for the"water-filling"power allocation scheme of MIMO systems with channel side information, where the maximum capacity is achieved using adaptive transmission techniques. The OFDM technique can change the frequency selective fading channel to the flat fading channel. According to that, the paper then derived the performance results of the system using the new adaptive algorithm in each sub-channel to achieve the maximum sub-channel capacity in frequency selective fading channel. This results furthermore verifies that the new algorithm can improve the frequency efficiency of MIMO-OFDM systems.Then the author compared the new algorithm with the uniform allocating algorithm and the channel reversing algorithm, analyzed their advantages and disadvantages. By comparing the three algorithms in conditions of different number of sub-carriers (N = 40, 80, 200, 400) and different target BER ( 10-7 ,10-6 ,10-5 ,10-4 ,10-3 ,10-2 ) respectively, the author obtained that the new algorithm had much better performance than the other two.Because of the delay of the feedback channel and the limitation of channel estimation, it is very difficult to obtain the perfect CSI. So the research of the adaptive bit-power allocation algorithm in partial CSI systems is valuable for practical work. Focusing on this reason, the author derived a mathematic model for channel estimation...
Keywords/Search Tags:MIMO-OFDM, Link Adaptive, adaptive power, adaptive modulation, Partial CSI, Water-filling
PDF Full Text Request
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