MIMO Precoding Codebook Design With Low Cost And Codebook Selection

With the development of communication technologies,and the increase of high data rate requirement for users,the very high speed wireless communication is becoming the main communication type.Among that,the very high throughput wireless local area network(VHT-WLAN)has witnessed rapid growth with its advantages of high data rate,low cost and convenience.The VHT-WLAN systems represented by IEEE802.11ac,always apply a transmission scheme of Multiple-Input Multiple-Output and Orthogonal Frequency Division Multiplexing(MIMO-OFDM).IEEE802.11ac system is equipped with multiple antennas and multiple spatial data streams.Research and practices show that,the precoding scheme in IEEE802.11ac systems produces large quantity of feedback cost and provides low quantization accuracy of channel information.It cannot apply to the next generation VHT-WLAN system which will have more transmit antennas and data streams.To deal with the above problems,the precoding in VHT-WLAN systems based on IEEE802.11ac protocol is studied in this thesis.Firstly,the channel model of IEEE802.11ac is analyzed,as well as several existing precoding schemes.Simulation is also performed to validate the improved scheme.Then the author investigates the advantages of precoding based on codebook applying to VHT-WLAN systems with multiple data streams,and proposes a low-cost codebook design method for multiple-antenna multiple-stream systems,which is called matrix Linde-Buzo-Gray(LBG)algorithm.Based on that,the initial codebook generation method is been researched.By theoretical analysis and simulation validation,the proposed codebook design algorithm in this thesis could obtain the same quantization accuracy with the current precoding scheme consuming 30%feedback overhead.After that,the codeword selection algorithm is researched.Different existing algorithms are verified by theoretical analysis and simulation.Then the most appropriate codeword selection algorithm for the proposed codebook design algorithm is identified.In addition,the proposed codebook design algorithm needs large quantity of codewords when applied to the multi-antenna multi-stream system.So,this thesis proposes a non-ergodic codeword selection algorithm based on binary search tree to decrease the search complexity.Simulation results show that the codeword selection algorithm could also simplify the codeword search process in the precoding system with the complexity of O(log n).