Adaptive Power Allocation for Limited Feedback Multi-Antenna Transmissions

This paper addresses the problem of optimizing the adaptive power allocation for data transmission over wireless communication fading channels using multiple transmit antennas with band-limited feedback channel. The objective of the optimization is to minimize the bit error rate (BER) subject to constraint on the average transmitted power. The chosen multi-antenna transmission scheme is the transmit antenna selection, which requires limited number of feedback bits. The adaptive power allocation is chosen to have finite levels of allocated power so that the system will still require limited number of feedback bits when the proposed adaptive power allocation scheme is combined. The allocated power of each level will be optimally determined. This has to be done with regarding to the employment of antenna selection. In order to achieve this goal, the formula of the BER of the system using transmit antenna selection scheme as a function of allocated power level is first derived. Then, the obtained formula is solved for optimal allocated power of each level. The obtained results shows that the advantageous features of two different techniques, namely antenna selection and the adaptive power allocation, can be combined effectively to combat fading using limited feedback information. Numerical results of the systems with 2-transmit and 3-transmit antenna are used here to demonstrate that substantial BER performance improvement can be achieved by using even only a few power adaptation levels.