Portfolio Optimization in Traffic Offloading: Concept, Model, and Algorithms

Due to explosive growth of mobile data over the overburdened cellular network, opportunistic offloading is proposed to transmit the traffic originally transmitted through infrastructure network to delay-tolerant device-to-device networks at the edge of mobile networks. Existing offloading schemes mainly focus on selecting a subset of mobile nodes to work as offloadees, who first download the contents through the infrastructure, and then transmit them to subscriber nodes. However, when there is large amount of contents to be offloaded, and if all contents are disseminated through only one fixed set of offloadees every time, it may result in the risk of extreme cases that only extremely few nodes received the content, even if the expectation is large. This is like putting all of your eggs in one basket. To deal with this problem, we introduce an economic concept, conditional value at risk (CVaR) to measure the risk in offloadee set selection. CVaR is a widely used risk assessment measure for investments, which provides a unified and comprehensive risk evaluation framework for complex investment portfolio. We propose an algorithm to compute a portfolio over multiple offloadee sets with a guarantee on CVaR. Moreover, we prove the feasibility of our methodology from the mathematical point of view. Extensive evaluations with real-world traces show that our proposed offloading scheme can obtain a portfolio with significantly better CVaR, i.e., 91.53 percent performance gain at most, compared with the state-of-the-art solutions.