Cross-layer Interference-aware Routing for Wireless Multi-hop Networks

Cross-layer Interference-aware Routing for Wireless Multi-hop Networks Tamer ElBatt

Timothy Andersen

Information and System Sciences Laboratory HRL Laboratories, LLC Malibu, CA 90265, USA

ABSTRACT In this paper we address the problem of interference-aware routing that tightly couples the design of the lower three layers of the ISO Open Systems Interconnection (OSI) protocol stack. This is primarily motivated by the observation that shortest path routing could potentially lead to degrading the single-hop throughput which constitutes an upper bound on the end-to-end multi-hop throughput. We introduce the concept of set-based routing in an attempt to incorporate interference into the routing decision as well as reduce the problem complexity. Towards this objective, we propose a novel algorithm that takes routing, scheduling and power control decisions for a set of interference-coupled transmitters. Furthermore, we discuss set coordination schemes for combating inter-set interference. Finally, we conduct a simulation study that shows considerable throughput improvement over a reference system that uses minimum hop routing and collision-free scheduling.

Categories and Subject Descriptors C.2.1 [Computer-Communication Networks]: Network Architecture and Design—Wireless Communication

General Terms Algorithms, Performance

Keywords Routing, scheduling, power control, interference, cross-layer design, simulation

1. INTRODUCTION The problem of routing over multi-hop wireless networks has received considerable attention in the literature, primarily, along two thrusts: i) Efficient route discovery/maintenance under mobility conditions and time-varying topologies and ii) Developing link metrics to match a wide variety of performance objectives. Most of the protocols under the former thrust adopt the shortest path (SP) routing criteria widely employed in wireline networks [1]. Under the second thrust, a variety of routing metrics have been introduced for the purposes of energy-efficiency, link stability, minimum delays, etc. Nevertheless, the problem of interference-aware routing

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Dept. of Mathematical Sciences Rensselaer Polytechnic Institute Troy, NY 12180, USA

that tightly couples the MAC and routing decisions has not received adequate attention in the literature. [2] establishes bounds on the optimal throughput of interference-limited wireless multi-hop networks given the existence of an omniscient and omnipotent central entity. However, developing interference-aware routing protocols was left as an open problem. The problem of joint routing, scheduling and power control has been recently addressed in [3, 4, 5]. However, [3] assumes no interference between links in the same neighborhood sharing the same slot. On the other hand, [4] focuses on the simple setting of symmetric one-dimensional multi-hop networks. The work in [5] is the closest to ours, however, it hinges on the Gaussian approximation for interference [6]. This assumption facilitates separating the MAC and routing portions of the problem which considerably simplifies the problem. In this paper, we present a solution to the problem without making any assumptions about the structure of interference known to be non-Gaussian in case of finite number of interferers. This work constitutes a step beyond our earlier work [7] to incorporate the impact of interference in the design of higher layer protocols. Our contribution in this paper is two-fold: i) Introduce a novel hop-by-hop set-based routing concept that incorporates interference into the routing decision of spatially close transmitters and ii) Introduce a joint routing, scheduling and power control (RSP) algorithm that solves the problem within each set. Motivated by the challenge of defining interference-aware link metrics, the complexity of the optimal RSP over the entire network [8] and the negligible interference among spatially far nodes, the solution proceeds through three steps: i) Construct interference-coupled transmitters sets, ii) Resolve intra-set interference via the RSP algorithm and iii) Resolve potential inter-set interference via set coordination. The paper is organized as follows: In section 2, the problem is motivated. In section 3, we highlight the challenges associated with interference-aware routing followed by a detailed description of set-based routing along with the RSP algorithm. The simulation results and discussion are given in section 4. Finally, conclusions are drawn in section 5.

2.

MOTIVATION

In this section, we show that handling MAC and routing decisions in isolation could lead to throughput degradation in wireless multi-hop networks. This is confirmed with the aid of a simple example. Consider a wireless network consisting of 13 stationary nodes with connectivity shown in Figure 1. For this example, we assume time is slotted and the channels are constant over a time slot. Moreover, we assume two source-destination (S-D) pairs (S1 , D1 ) and (S2 , D2 ) with identical traffic demands and there is always a packet in the queue of each source ready for transmission. We compare the average slot throughput and end-to-end (E2E) throughput of three routing policies. The slot throughput is

defined as the average number of successful transmissions per slot. In this section, the E2E throughput is defined as the average number of packets that are successfully transferred from each source to its respective destination over d slots.  



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