Affine Projection Decoders In Uplink Of MU-MIMO System And Their Performances

To satisfy high-speed transmission requirements of various applications, wirelesscommunication systems with high transmission rate, such as, Multiple-Input, Multiple-Output(MIMO) systems, are urgently required. MIMO is a smart antenna technology that can significantlyincrease transmission rate and improve reliability of wireless systems. For a point-to-point MIMOsystem, extensive research efforts have been made on transmitter and receiver designs. However,for a multiple access MIMO system, study of MIMO transmitter and receiver designs is stillongoing.Consider a multiple access system with K users each having N transmit antennas and areceiver, e.g., Base Station (BS), having M antennas. All users transmit their signals to the BSsimultaneously in the same frequency band. At the BS, signals from all users are mixed up together,and thus, signals from one user become interference to other users. Hence, interference managementis critical to the receiver design, especially, when channel state information is not available attransmitters. For a decoder, two factors: decoding complexity and its performance, are alwaysconcerned. For the performance of a decoder, usually it is evaluated by using a terminology, socalled “diversity order”. Now it shows that, when N1, the diversity order ofMaximum-Likelihood(ML) decoder is and both Zero-Forcing (ZF) and MinimumMean-Square Error (MMSE) decoders have diversity order of M K1. Clearly, the diversityorder of linear decoders is smaller than that of the ML decoder. However, the decoding complexityis also reduced. Thus, these results show that there is a tradeoff between diversity order anddecoding complexity.In the thesis, new decoders, namely affine projection based decoders, are proposed undercondition of M KN. In the proposed scheme, users are divided into several groups. Whensignals from one of them is decoded (users in this group are called as “joint users”), all users inother groups are called as “interference users”. The affine projection based decoder is applied to thereceived signal to remove signals from the interference users. Moreover, the basic transmit-receiveequation after implementing the proposed decoder is the same as the equation of a point-to-pointMIMO system, except the noise part. Hence, any decoding methods used in a point-to-point MIMOsystem can be applied to decode messages of the joint users. Finally, by selecting another group asjoint users and using the same method above, all users’ messages can be decoded out. Performancestudies show that the system with the proposed decoders can achieve a diversity order of(M KN kN)N, for any integer k (1k K), and the decoding complexity is higher than thatof the linear decoders, lower than that of the ML-decoder. Affine projection based user selection decoders are also proposed, which improves the performance of the system, further.The achievable rate region of the proposed decoders is also analyzed. The analysis shows thataffine projection based decoders can achieve the optimal degree of freedom of the system.Moreover, when M goes to infinity, the achievable rate region can approach the capacity regionof the system. Therefore, the proposed decoders are asymptotical optimal when the number of thereceiving antennas goes to infinity.