Energy-Delay Tradeoff and Dynamic Sleep Switching for Bluetooth-Like Body-Area Sensor Networks

Wireless technology enables novel approaches to healthcare, in particular the remote monitoring of vital signs and other parameters indicative of people's health. This paper considers a system scenario relevant to such applications, where a smart-phone acts as a data-collecting hub, gathering data from a number of wireless-capable body sensors, and relaying them to a healthcare provider host through standard existing cellular networks. Delay of critical data and sensors' energy efficiency are both relevant and conflicting issues. Therefore, it is important to operate the wireless body-area sensor network at some desired point close to the optimal energy-delay tradeoff curve. This tradeoff curve is a function of the employed physical-layer protocol: in particular, it depends on the multiple-access scheme and on the coding and modulation schemes available. In this work, we consider a protocol closely inspired by the widely-used Bluetooth standard. First, we consider the calculation of the minimum energy function, i.e., the minimum sum energy per symbol that guarantees the stability of all transmission queues in the network. Then, we apply the general theory developed by Neely to develop a dynamic scheduling policy that approaches the optimal energy-delay tradeoff for the network at hand. Finally, we examine the queue dynamics and propose a novel policy that adaptively switches between connected and disconnected (sleeping) modes. We demonstrate that the proposed policy can achieve significant gains in the realistic case where the control "NULL" packets necessary to maintain the connection alive, have a non-zero energy cost, and the data arrival statistics corresponding to the sensed physical process are bursty.Comment: Extended version (with proofs details in the Appendix) of a paper accepted for publication on the IEEE Transactions on Communication

Delay Tolerant Networking over the Metropolitan Public Transportation

We discuss MDTN: a delay tolerant application platform built on top of the Public Transportation System (PTS) and able to provide service access while exploiting opportunistic connectivity. Our solution adopts a carrier-based approach where buses act as data collectors for user requests requiring Internet access. Simulations based on real maps and PTS routes with state-of-the-art routing protocols demonstrate that MDTN represents a viable solution for elastic nonreal-time service delivery. Nevertheless, performance indexes of the considered routing policies show that there is no golden rule for optimal performance and a tailored routing strategy is required for each specific case

TOWARD LAYERLESS COOPERATION AND RATE CONTROL IN WIRELESS MULTI-ACCESS CHANNELS

In wireless networks, a transmitted message may successfully reach multiple nodes simultaneously, which is referred to as the Wireless Multicast Advantage. As such, intermediate nodes have the ability to capture the message and then contribute to the communication toward the ultimate destination by cooperatively relaying the received message. This enables cooperative communication, which has been shown to counteract the effects of fading and attenuation in wireless networks. There has been a great deal of work addressing cooperative methods and their resulting benefits, but most of the work to date has focused on physical-layer techniques and on information-theoretic considerations. While compatible with these, the main thrust of this dissertation is to explore a new approach by implementing cooperation at the network layer. First, we illustrate the idea in a multi-hop multi-access wireless network, in which a set of source users generate packets to deliver to a common destination. An opportunistic and dynamic cooperation protocol is proposed at the network level, where users with a better channel to the destination have the capability and option to relay packets from users that are farther afield. The proposed mode of cooperation protocol is new and relies on MAC/Network-level of relaying, but also takes into account physical-layer parameters that determine successful reception at the destination and/or the relay. We explicitly characterize the stable throughput and average delay performance. Our analysis reveals that cooperation at the network layer leads to substantial performance gains for both performance metrics. Next, on top of the network-layer cooperation, we investigate enhanced cooperative techniques that exploit more sophisticated physical-layer properties. Specifically, we consider dynamic decode-and-forward, superposition coding, and multipacket reception capability, and we quantify the extent to which the enhancement techniques can further improve the stable throughput region. Then we revert back to the two-user multi-access channel with single-packet reception, which has been extensively studied in the case of no cooperation. After cooperation is permitted between the two users, we revisit the relationship between the stability region and the throughput region under both scheduled access and random access schemes. Finally, we shift our focus from the packet-level to bit-level multi-access channels. By exploiting the bit-nature of a packet, we create a bridge between traditional physical-layer-based transmission rates and classical MAC/Network-layer-based throughput rates. We first obtain the closed form of the stability region in bits/slot. Then, as a separate, but related issue, we look at the minimum delivery time policy; for any initial queue size vector, the optimal policy that empties all bits in the system within the shortest time is characterized