Adaptive group loading for MIMO OFDM systems

Adaptive Bit Loading (ABL) in Multiple-Input Multiple-Output Orthogonal Frequency-Division Multiplexing (MIMO-OFDM) is most likely used for achieving the desired Bit Error Rate (BER) performance in wireless systems. In this paper, we discuss some of the bit loading algorithms, compare them with respect to their BER performance, and present an effective concise Adaptive Grouped Loading (AGL) algorithm. In particular, we consider the bit loading in near optimal Singular Value Decomposition (SVD) based MIMO-OFDM system. While using SVD based system, the system requires the perfect Channel State Information (CSI) of channel transfer function at the transmitter. This scenario of SVD can be taken as an ideal case for the comparison of loading algorithms and to show the actual enhancement achievable by our AGL algorithm. Irrespective of the CSI requirement imposed by the mode of the system itself, ABL demands high level of feedback requirement. Grouped Loading (GL) would reduce the feedback requirement depending upon the group size. However, this also leads to considerable degradation in BER performance. In our AGL algorithm, a group is formed with a number of consecutive sub-channels belonging to same transmit antenna, with individual gains falling under predefined criteria. Simulation results show that the proposed AGL requires much lesser CSI compared to GL for same BER performance margin.