Shlomo Shamai

Sum Rate Characterisation of Joint Multiple Cell-Site Processing

The sum-rate capacity of a simple cellular system model is considered, considering the uplink and downlink channels, while addressing both non-fading and flat-fading channels. We address a simple Wyner-like multi-cell model, where the system cells are arranged on a circle, assuming the cell-sites are located at the boundaries of the cells. For the uplink channel, analytical expressions for the sum-rate capacities are derived for intra-cell TDMA scheduling, and a "Wide-Band" (WB) scheme (where all users are active simultaneously utilizing all bandwidth for coding). Assuming individual per-cell power constraints and using the Lagrangian uplink-downlink duality principle, an analytical expression for the sum-rate capacity of the downlink channel is derived for non-fading channels, and shown to coincide with the corresponding uplink result. Introducing Rayleigh fading, lower and upper bounds on the average per-cell sum-rate capacity are evaluated. The bounds exhibit an O(ln K) multi-user diversity factor for a  large number of users per-cell K>>1, in addition to the array diversity gain. Joint multi-cell processing is shown to eliminate out-of-cell interference, which is traditionally considered to be a limiting factor in high-rate reliable communications. Implications of restricted multi-cell processing are also discussed.

Joint work with Oren Somekh and Benjamin Zaidel, EE Dept. Technion, Haifa, Israel..