On the encoding rate and modulation adaptation design for MIMO CSIT links with

For slow fading channels, the MIMO performance is limited by packet outage even if powerful component codes are used at the transmitter. It is well-known that MIMO links in slow fading channels can benefit significantly through rate and power adaptations when there is knowledge of channel state information at the transmitter (CSIT). However, practical MIMO transmitter can only support finite combinations of the channel encoding rates and modulation constellation levels due to the finite number of bits allocated in the control overhead (embedded in the packet transmission) to inform the receiver of the current transmission mode. As a result of this practical limitation, there are several design issues concerning MIMO adaptation design. In this paper, we shall address various practical MIMO adaptation design issues such as how many different transmission modes are needed, how to determine the specific channel encoding rates and modulation constellation levels for each transmission modes as well as how to choose select a transmission mode for the current packet transmission given a particular CSIT. We propose a systematic design framework to address the MIMO adaptation design based on information theoretical framework. We assume time division duplex (TDD) systems with quasi-static fading channels where packet outage is an important concern with imperfect CSIT. The design problem is cast into an optimization problem similar to the classical vector quantization problem with a modified distortion measure. As an illustration, we apply the design framework to a 2 times 2 MIMO link and compare the goodput performance with the optimal performance predicted by the theory. We found that the goodput performance of the MIMO link predicted by the theoretical framework matches the actual performance closely