The Two-Tap Input-Erasure Gaussian Channel and its Application to Cellular Communications

TL;DR

This paper introduces the two-tap input-erasure Gaussian channel model, demonstrating its equivalence to output-erasure channels, and applies it to analyze joint multicell processing benefits in cellular uplinks with shadowing and user activity.

Contribution

It presents a novel input-erasure channel model, derives an achievable rate expression, and applies it to cellular communication scenarios with shadowing and dynamic user activity.

Findings

Input-erasure and output-erasure channels are equivalent for i.i.d. inputs.

Achievable rate expressed as an infinite sum for two-tap FIR filters.

Optimal multicell processing improves capacity under shadowing and user activity.

Abstract

This paper considers the input-erasure Gaussian channel. In contrast to the output-erasure channel where erasures are applied to the output of a linear time-invariant (LTI) system, here erasures, known to the receiver, are applied to the inputs of the LTI system. Focusing on the case where the input symbols are independent and identically distributed (i.i.d)., it is shown that the two channels (input- and output-erasure) are equivalent. Furthermore, assuming that the LTI system consists of a two-tap finite impulse response (FIR) filter, and using simple properties of tri-diagonal matrices, an achievable rate expression is presented in the form of an infinite sum. The results are then used to study the benefits of joint multicell processing (MCP) over single-cell processing (SCP) in a simple linear cellular uplink, where each mobile terminal is received by only the two nearby base-stations (BSs). Specifically, the analysis accounts for ergodic shadowing that simultaneously blocks the mobile terminal (MT) signal from being received by the two BS. It is shown that the resulting ergodic per-cell capacity with optimal MCP is equivalent to that of the two-tap input-erasure channel. Finally, the same cellular uplink is addressed by accounting for dynamic user activity, which is modelled by assuming that each MT is randomly selected to be active or to remain silent throughout the whole transmission block. For this alternative model, a similar equivalence results to the input-erasure channel are reported.