Trade-Off Between Frequency Diversity Gain and Frequency-Selective Scheduling Gain in OFDMA Systems with Spatial Diversity

OFDMA systems inherently take advantages of both frequency diversity gain and frequency-selective scheduling gain. The former is achieved by allocating a user the subcarriers widely scattered over an entire frequency band, while the latter is achieved by allocating a user the subcarriers consecutively located within a subband of a limited bandwidth which is the most favorable to the user among many subbands in the entire frequency band. In this letter, the effect of user mobility is quantitatively investigated in relation to a trade-off between the frequency diversity gain and the frequency-selective scheduling gain in OFDMA systems. As a performance measure, outage capacity is considered. Also studied is how the spatial diversity resulting from multiple antenna techniques and the outage probability affect the dependence of the performance trade-off on the user mobility.