Lightweight Self-Organizing Reconfiguration of Opportunistic Infrastructure-Mode WiFi Networks

Daniel J. Dubois¹ Yosuke Bando^1,2 Konosuke Watanabe^1,2 Henry Holtzman¹
¹MIT Media Lab ²TOSHIBA Corporation

The purpose of this work is to provide a method for exploiting pervasive wireless communication capabilities that are often underutilized on smart devices (e.g., phones, tablets, cameras, TVs, etc.) in an opportunistic and collaborative way. This goal can be accomplished by sharing device resources using their built-in WiFi adapter. In this paper we explain why the standard ad-hoc mode for building mobile peer-to-peer networks is not always the best choice and we propose an alternative self-organizing approach in which an opportunistic infrastructure-mode WiFi network is built. The particularity of this network is that each device can either be an access point or a client and change its role and wireless channel over time. This contribution advances the state of the art by using a context-aware approach that considers actual frequency allocation to other devices and monitored traffic. We finally show that our approach increases the average speed for delivering messages to a level that in several situations outperforms previous work in the area, as well as a simple single-channel ad-hoc WiFi network.

Paper (1MB, PDF):
Proceedings of the IEEE International Conference on Self-Adaptive and Self-Organizing Systems, pp. 247-256, 2013.

In forming opportunistic mobile ad-hoc networks, we propose to use infrastructure-mode WiFi instead of ad-hoc mode because:
- The infrastructure mode is available on many current mobile devices while the ad-hoc mode is not.
- It supports multiple channels (radio frequency bands), which can be used to reduce signal interference.

Algorithm:

In the infrastructure mode, each node may be an access point (AP) or a client. Nodes can still form ad-hoc networks by having each client opportunistically connect to one of its nearby APs. Unlike in the ad-hoc mode, however, nodes need to choose their roles to maximize communication, and changing roles incurs overhead. On the other hand, APs can choose their channels to avoid interference.

The proposed algorithm is excuted at each node based only on locally available information. It chooses AP/client roles, frequency (channel) when it has chosen to be an AP, and an AP to connect to among its nearby APs when it has chosen to be a client.

Result:
Performance of the proposed algorithm, along with the (single-channel) ad-hoc mode and the previous work called WiFi-Opp, was measured and compared using the ONE opportunistic network simulator. A crowded room was simulated.


	The proposed algorithm outperforms the ad-hoc mode because it uses multiple (3 in this experiment) channels. WiFi-Opp also performs better than the ad-hoc but not to the extent achieved by the proposed algorithm, as it does not involve adaptive channel or AP selection.

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