Shannon-theoretic considerations for a Gaussian cellular TDMA multiple-access channel with fading

Shannon-theoretic limits on the achievable throughput for a simple cellular multiple-access system (referred to as Wyner´s (1994) model) in the presence of fading are presented. In this model, which is modified to account for flat fading, the received signal at a given cell-site is the sum of the faded signals transmitted from all users within that cell, plus an attenuation factor α ∈ [0,1] times the sum of the faded signals received from the adjacent cells, accompanied with an additive Gaussian noise. Although this simple model is scarcely realistic, it serves as a simple tractable model which provides considerable insight into complex and intractable real-world cellular communication systems. We assume a hyper (super)-receiver, jointly decoding all the users, using the received signals from all the active cell-sites. The hyper-receiver is assumed to be aware of the codebooks and realizations of the fading processes of each user. We consider the intra-cell time division multiple access (TDMA) protocol which is known to be equivalent to the optimal protocol under the average power constraint in the absence of fading. We are interested in the maximum reliably transmitted equal rate (system throughput per user). Bounds on this rate are found by incorporating information-theoretic inequalities and the Tchebycheff-Markov moment bounding technique. We observe the rather surprising result that flat fading (Rayleigh) may increase the maximum equal rate for a certain range of α and signal to noise ratio (SNR) in comparison to the non-faded case