Hybrid Strategies for Link Adaptation Exploiting Several Degrees of Freedom in OFDM Based Broadband Wireless Systems

In orthogonal frequency division multiplexing (OFDM) systems, there are several degrees of freedom in time and frequency domain, such as, sub-band size, forward error control coding (FEC) rate, modulation order, power level, modulation adaptation interval, coding rate adaptation interval and power adaptation interval, which can be exploited for link adaptation to achieve high spectral efficiency. The variable channel parameters such as delay spread, Doppler frequency spread, average signal to noise ratio and instantaneous channel gains influence the link adaptation parameters. Optimal adaptation of the link parameters based on the channel conditions would lead to highly complex systems with high overhead. Hybrid strategies to vary the adaptation rates to tradeoff achievable efficiency and complexity are presented in this work.