An Efficient Diversity Exploitation in Multiuser Time-Varying Frequency-Selective Fading Channels

Diversity exploitation is a proven efficient means for addressing detrimental effects of wireless channel fadings. User channelization, where the frequency and time resources are structured into several user channels, can substantially help to capture the diversity, but it has not been well investigated. In this paper, we develop theoretical formulation of optimal resource structures under different performance metrics and then analyze them in frequency-selective time-varying channels. We propose a simplified system model which maintains the main features, and based on which, we develop a new practical approach of user channelization or user resource structuring which captures better diversity for OFDMA systems in multiuser time-varying frequency-selective fading channels. In contrast to the existing user resource structures where relative locations of the resources in the time-frequency grid remain the same throughout the transmission frame, the proposed resource structures evolve within the frame to enjoy better diversity gain. Example designs of the proposed evolving structures are presented from the 3GPP LTE perspective. Simulations done under LTE system environments validate that the proposed practical approach can obtain a near-optimal structure design, and provide significant performance advantage over the existing structures at the mobile speeds ranging from 3 km/h to 350 km/h.