Information Theoretic Considerations for Simple, Multiple Access Cellular Communication Channels

A simple idealized linear uplink cellular multiple access communication model, where only adjacent cell interference is present and all signals may experience fading is considered in terms of Shannon theoretic arguments. We address the case of practical importance where the cell-site receiver processes only the signals received at this cell-site and where the actively interfering users assigned to other cells (but not those within the cell) are interpreted as Gaussian noise. It is assumed that the cell-site receiver (but not users' transmitters) is aware of the instantaneous signal-to-noise ratios for all users assigned to that cell. We focus on the effect of fading and inter-cell interference and also provide a general formulation for an achievable rate region. The features of TDMA and wide-band (WB) intra-cell multiple access techniques are examined as well as the role of (optimized) inter-cell fractional time-sharing protocol. With no fading, orthogonality within the cell is optimal (not unique however) with or without inter-cell interference. When fading is present and inter-cell interference is not dominant, WB intra-cell access is found advantageous due to an inherent fading averaging effect. This conclusion may reverse when inter-cell interference takes place and exceeds a given threshold: and then intra-cell orthogonal signalling (TDMA) is preferable. This is also the case where fading is assumed to affect only the transmitters in other cells, modelling an idealized situation with genie-aided unpenalized instantaneous power control within the cell. With inter-cell interference present, it is demonstrated that fractional inter-cell time sharing may prove beneficial. Extensions of the results to planar cellular configurations, macro or micro two fold diversity and random number of users are referenced.