Power Control Approaches In MIMO Mobile Communication Systems

This thesis focuses on the power control approaches in MIMO (Multiple-Input Multiple-Output) mobile communication systems. The power controlled MIMO systems obtain the transmit power which is adaptive to the channel. The transmit power is feedback to the transmitter from the receiver and used to weight the transmit signals.The thesis firstly analyses the substrems' BER (Bit Error Rate) difference of the OSICD (Ordered Succesive Interference Cancellation Detector) and proposes a PAPC (Per-Antenna Power Control) approach based on the criterion minimizing the substream's maximum BER. The PAPC approach improves the worst BER performance among substreams to improve the averaged BER performance, while the information rate and total transmit powe keep constant. The thesis takes the unequal antenna power into consideration in MIMO signal process and proposes a P-OSICD (Power controlled OSICD). Simulation results show that the P-MMSE-OSICD (MMSE: Minimum Mean Square Error) can achieve the comparible BER performance to that of the MLD (Maximum Likelihood Detector) at small feedback overhead and lower compelxity. The calculation complexity addition of the P-MMSE-OSICD compared to MMSE-OSICD is small too.Because the numerical stabability of the OSICD is not good, the thesis studies another MIMO detector as SDFD (Sorted Decision Feedback Detector) with better numerical stabability. However, the BER performance of the SDFD is not good enough for real MIMO systems. Hence, the thesis proposes a PAPC approach to improve the BER performance by minimizing the BLER (BLock Error Rate) of SDFD. The PAPC approach makes the matrix R have equal-diagonal elements and maximizes the lower bound of the free distance at the same time. By the performance analysis, the thesis proves that the PAPC approach is a tradeoff between feedback overhead and detection performance. The thesis also proposes a P-SDFD (Power controlled SDFD) concerning the unequl transmit power among transmit antennas. Simulation results show that the P-SDFD achieves the comparible BER performance to that of the MLD at small feedback overhead and lower complexity, when receive antenna number is larger than transmit antenna number.In MIMO cellular mobile communication systems, CCI (Co-Channel Interference) affects the performance greatly. The thesis proposes a CPC (Centralized Power Control) approach to control the CCI and by so to improve the SIR (Signal to Interference Ratio) outage performance and BER performance. The PAPC approach adjusts each user's total transmit power but keeps queal power levels among antennas of each user. With the fact that signals from multiple transmit antennas are indepedant to each other, a simplified SIR expression and channel matrix expression are derived. The thesis proves that the normalized channel matrix is an irreducible nonnegative matrix. We can obtain the balanced SIR value and the conesponding transmit power by calculation of the eigenvalues and eigenvectors of the normalized channel matrix. SIR balancing maximizes the minimum SIR among users. Simuation results show that the CPC approach can improve the SIR outage probability performance and BER performance.The CPC approach needs to collect channel information of all communication links in the system, which costs much system overhead. The thesis then proposes a DPC (Distributed Power Control) approach to lower the CPC's overhead. The DPC approach only measures the local desired signal power and local SIR. In iteration fashion, the DPC approach can also achieve the SIR balance. The thesis gives DPC algorithm 1 for interference-limitted systems to minimize the averaged SIR outage...