Asynchronous multicarrier multiple access: Optimal and sub-optimal detection and decoding
Andrea M. Tonello · Bell Labs Technical Journal · 2003
In this paper, we describe multicarrier multiple access architectures that are based on combining filtered multicarrier modulation with multiplexing of sub-carriers across distinct users. These architectures can be deployed for both uplink and downlink wireless communications. We focus on the more critical uplink where multiple users share an asynchronous channel. Signals belonging to distinct users experience time and carrier frequency asynchronism and propagate through independent frequency-selective fading channels. In such a scenario the receiver sees intersymbol interference, intercarrier interference, and multiple access interference components that are a function of the propagation conditions, the design of the sub-channel transmit filters, and the tone allocation strategy. We formulate the optimal multicarrier multiuser detector that yields minimum probability of error. Then, we devise sub-optimal (simplified) detection approaches. These detectors are soft-in soft-out modules that can be concatenated with the channel decoders when the users' information signals are channel encoded. In such a case, practical decoding can be performed by the iterative concatenation of multicarrier detection and decoding (turbo multiuser decoding).