Gaussian Cellular Multiple Access Channel Research Articles

Hadamard upper bound on optimum joint decoding capacity of Wyner Gaussian cellular MAC

This article presents an original analytical expression for an upper bound on the optimum joint decoding capacity of Wyner circular Gaussian cellular multiple access channel (C-GCMAC) for uniformly distributed mobile terminals (MTs). This upper bound is referred to as Hadamard upper bound (HUB) and is a novel application of the Hadamard inequality established by exploiting the Hadamard operation between the channel fading matrix G and the channel path gain matrix Ω. This article demonstrates that the actual capacity converges to the theoretical upper bound under the constraints like low signal-to-noise ratios and limiting channel path gain among the MTs and the respective base station of interest. In order to determine the usefulness of the HUB, the behavior of the theoretical upper bound is critically observed specially when the inter-cell and the intra-cell time sharing schemes are employed. In this context, we derive an analytical form of HUB by employing an approximation approach based on the estimation of probability density function of trace of Hadamard product of two matrices, i.e., G and Ω. A closed form of expression has been derived to capture the effect of the MT distribution on the optimum joint decoding capacity of C-GCMAC. This article demonstrates that the analytical HUB based on the proposed approximation approach converges to the theoretical upper bound results in the medium to high signal to noise ratio regime and shows a reasonably tighter bound on optimum joint decoding capacity of Wyner GCMAC.

Information theoretic capacity of cellular multiple access channel with shadow fading

In this paper, we extend the well-known model for the Gaussian Cellular Multiple Access Channel originally presented by Wyner. The first extension to the model incorporates the distance-dependent path loss (maintaining a close relevance to path loss values in real world cellular systems) experienced by the users distributed in a planar cellular array. The density of base stations and hence the cell sizes are variable. In the context of a Hyper-receiver joint decoder, an expression for the information theoretic capacity is obtained assuming a large number of users in each cell. The model is further extended to incorporate the log-normal shadow fading variations, ensuring that the shadowing models are fairly comparable to the free space model. Using these fair models the effect of the shadow fading standard deviation on the information theoretic capacity of the cellular system is quantified. It is observed that a higher standard deviation results in lower capacity if the mean path loss is appropriately adjusted in order to model the mean loss due to the physical obstacles causing the shadow fading. The results validate that larger cell sizes and a higher standard deviation of shadowing (with appropriately adjusted mean path loss) results in lower spectral efficiency.

Capacity of the Multiple Spot Beam Satellite Channel With Rician Fading

In this correspondence, the uplink of a multibeam satellite system with Rician fading is analyzed under the framework of Wyner's Gaussian cellular multiple access channel. In this framework the received signal at a given multibeam antenna is the sum of signals transmitted by users within that beam's cell area plus a factor 0 les alpha les 1 times the sum of the signals transmitted by users from adjacent cells plus ambient Gaussian noise. Both one-dimensional (1-D) linear, and 2-D hexagonal cellular arrangements are considered. In addition, we consider a modified version of the 1-D linear arrangement whereby users from cells further than adjacent cells contribute to intercell interference. It is assumed that the distance between the antenna elements is small compared to the distance between a user and the satellite. Thus when fading is present, a particular user's fading coefficient is the same at each multibeam antenna. This is the fundamental difference between the multibeam satellite fading channel and the terrestrial cellular fading channel, in which each user experiences independent fading at each base station. Using a Haar measure approximation we derive closed form approximations for the capacity of the satellite fading channel for the scenarios when optimal joint decoding and linear minimum mean square error filtering is employed at the ground station. These approximations are shown to be in close agreement to Monte Carlo simulation results for large dimensional systems. It is shown that fading causes a loss in capacity compared to the nonfading channel. Furthermore, at high signal-to-noise ratio (SNR) this loss is independent of the intercell interference and topology of the system, but is dependent on the distribution of the fading coefficients and the number of users per beam.