Uplink capacity of a variable density cellular system with multicell processing

In this work we investigate the information theoretic capacity of the uplink of a cellular system. Assuming centralised processing for all base stations, we consider a power-law path loss model along with variable cell size (variable density of Base Stations) and we formulate an average path-loss approximation. Considering a realistic Rician flat fading environment, the analytical result for the per-cell capacity is derived for a large number of users distributed over each cell. We extend this general approach to model the uplink of sectorized cellular system. To this end, we assume that the user terminals are served by perfectly directional receiver antennas, dividing the cell coverage area into perfectly non-interfering sectors. We show how the capacity is increased (due to degrees of freedom gain) in comparison to the single receiving antenna system and we investigate the asymptotic behaviour when the number of sectors grows large. We further extend the analysis to find the capacity when the multiple antennas used for each Base Station are omnidirectional and uncorrelated (power gain on top of degrees of freedom gain). We validate the numerical solutions with Monte Carlo simulations for random fading realizations and we interpret the results for the real-world systems

Transmit Power Formulation for Relay-Enhanced UMTS Using Simulation and Theory

Applying relaying concept to a universal mobile telecommunications system (UMTS) mobile network is not a new idea, and many systems employing relaying capabilities have been suggested. The power control (PC), which is an important aspect of UMTS, can be applied in such a mobile system, either in a centralised or a distributed fashion. An increase in the system capacity is expected, when utilised in all system links, single-hop (SH) and multi-hop. This is because the PC allocates, to the transmitters, the minimum powers which satisfy the link quality criteria. In this paper we formulate the transmit powers of a relaying system. We then compare, in an example, the power convergence of an iterative PC to the solution provided by the suggested equations. The assumptions, which facilitate rendering the formulations to a linear set of equations, are analysed

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

Spectral Efficiency of Variable Density Cellular Systems with Realistic System Models

In the information-theoretic literature, multicell joint processing has been shown to produce high spectral efficiencies. However, the majority of existing results employ simplified models and normalized variables and in addition they consider only the sum-rate capacity, neglecting the individual user rates. In this paper, we investigate a realistic cellular model which incorporates flat fading, path loss and distributed users. Furthermore, the presented results are produced by varying the cell density of the cellular system, while practical values are used for system parameters, such as users per cell, transmitted power, path loss exponent. What is more, we study the effect of sum-rate maximization on the fairness of user rate distribution by comparing channel-dependent and random user orderings within the joint encoding/decoding process

On the Capacity of Variable Density Cellular Systems under Multicell Decoding

The majority of multicell-decoding cellular models preserve a fundamental assumption which has initially appeared in Wyner’s model, namely the collocation of User Terminals (UTs). Although this assumption produces more tractable mathematical models, it is unrealistic w.r.t. current practical cellular systems. In this paper, we alleviate this assumption by assuming uniformly distributed UTs. The model under investigation is the uplink channel of a planar cellular array in the presence of power-law path loss and flat fading. In this context, we employ a free probability approach to evaluate the effect of UT distribution on the optimal sum-rate capacity of a variable-density cellular system