Smart Roaming: How Operator Cooperation Can Increase Spectrum Usage Efficiency At practically No Cost

Abstract

We propose Smart Roaming (SR), a cooperation technique between cellular telcos operating in the same region, that enables users to roam for performance reasons (instead of lack of coverage from their operator). Within a region, base-stations of different operators are seldom co-located and even when they are, the sectors are rarely aligned. SR leverages spatial diversity to enhance spectrum usage efficiency, specifically an edge user of an operator might well be a ``good user" for another one. This work answers the following research questions: i) Can significant gain be obtained with SR? ii) What are the factors that affect the gain? iii) How to deal with operator heterogeneity to avoid that a large operator cross subsidizes a smaller one? iv) How to implement SR in an online fashion?

We answer the first three questions by proposing a snapshot model for the downlink that shows that SR can indeed provide significant gain without yielding cross-subsidies if done properly. We then propose two schemes to implement SR online 1) a modification of the scheduler to allow base-stations to discriminate between users of different operators (a necessity to avoid cross-subsidy) jointly with a ``free" user association (UA) whereby each user selects the best base-station irrespective of the operator it belongs to; 2) a controlled UA based on a distributed load sharing algorithm combined with the legacy scheduler. We evaluate these two schemes via extensive simulations based on two traffic scenarios and find gains in efficiency (defined as the per-operator sum-rate) above 25% and better performance for the first scheme. However, the second scheme might be easier to adopt since it does not affect the schedulers.