Abstract-There is a growing interest in exploiting interference (rather than avoiding it) to increase network throughput. In particular, the so-called successive interference cancellation (SIC) scheme appears very promising, due to its ability to enable concurrent receptions from multiple transmitters as well as inter ference rejection. Although SIC has been extensively studied as a physical layer technology, its research and advances in the context of multi-hop wireless network remain limited. In this paper, we try to answer the following fundamental questions. What are the limitations of SIC? How to overcome such limitations? How to optimize the interaction between SIC and interference avoidance? How to incorporate multiple layers (physical, link, and network) in an optimization framework? We find that SIC alone is not adequate to handle interference in a multi-hop wireless network, and advocate the use of joint SIC and interference avoidance. To optimize a joint scheme, we propose a cross-layer optimization framework that incorporates variables at physical, link, and network layers. This is the first work that combines successive interference cancellation and interference avoidance in multi-hop wireless network. We use numerical results to affirm the validity of our optimization framework and give insights on how SIC and interference avoidance can complement each other in an optimal manner. Interference is widely regarded as the fundamental imped iment to throughput performance in wireless networks. In networking community, a natural and main stream approach to handle interference is to employ certain interference avoidance scheme, which can be done either through deterministic re source allocation (e.g., TDMA, FDMA, or CDMA) or random access based schemes (e.g., CSMA, CSMAlCA). The essence of an interference avoidance scheme is to remove any overlap among the transmitting signals (the root of interference). Although easy to understand and simple to implement, an interference avoidance scheme, in general, cannot offer a per formance close to network information theoretical limit [25] . Recently, there is a growing interest in exploiting interfer ence (rather than avoiding it) to increase network throughput (see Section II for related work). In essence, such an interfer ence exploitation approach allows overlap among transmitting signals and relies on some advanced decoding schemes to re move interference. In particular, the so-called successive inter ference cancellation (SIC) scheme appears very promising [1], [3] , [7] , [9] , [15], [28] and has already attracted development efforts from industry (e.g., QUALCOMM's CSM6850 chipset for cellular base station [18] ). Under SIC, a receiver attempts to decode concurrent signals from multiple transmitters suc cessively, starting from the strongest signal. If the strongest signal can be decoded, it will be subtracted from the aggregate signal so that the SINR (signal-to-interference-and-noise-ratio) for the remaining signals can be improved. Then the SIC receiver continues to decode the second strongest signal and so forth, until all signals are decoded, or terminates if the signal is no longer decodable (see Section III for more details). Although SIC has been extensively studied as a physical layer technology, its limitation and optimal application in the context of multi-hop wireless network remain limited. In this paper, we will try to answer the following fundamental questions. • What are the limitations of SIC? How to overcome such limitations? • How to develop an optimization framework for optimal interaction between SIC and interference avoidance? How to incorporate variables from multiple layers (physical, link, and network) into such an optimization framework? We take a formal optimization approach to address these fundamental questions. We find that the limitations of SIC come from its stringent constraints when decoding multiple signals. Specifically, in order to decode aggregate signals successively, an SIC receiver must meet a series of SINR constraints for its received signal powers. Further, due to these constraints, there exists a decoding limit for SIC in its abilities for concurrent receptions or interference rejection. As a result, SIC alone is inadequate to handle all concurrent interference in a multi-user wireless network. Interestingly, the limitations of SIC can be compensated precisely by the traditional interference avoidance scheme. Therefore, we advocate a joint interference exploitation and interference avoidance approach, which combines the best of both worlds while remove each other ' s pitfalls. We believe such a joint approach is most efficient to handle interference in a multi-hop wireless network. Although the need of such a joint approach is easy to understand, a number of new technical challenges arise in the context of a multi-hop network. This is particularly true when our optimization space encompasses physical layer SIC, link layer scheduling, and network layer flow routing. We address these new challenges by developing a formal optimization framework, with cross-layer formulation of physical, link, and 978-1-4673-0775-8/12/$31.00 ©2012 IEEE 424 network layers. This new optimIzation framework offers a holistic design space to squeeze the most out of interference and lay a mathematical foundation for the modeling and analy sis of a joint interference exploitation and avoidance scheme in a multi-hop wireless network. To the best of our knowledge, this is the first effort toward this direction. To demonstrate the practical utility of our optimization framework, we con duct a case study on maximizing network throughput. Our numerical results affirm the efficacy of this framework and give us insights on how SIC should optimally interact with an interference avoidance scheme. The rest of this paper is organized as follows. Section IT presents related work on interference exploitation. Section III offers a primer on SIC and illustrates its benefits. In Sec tion IV, we discuss some inherent limitations of SIC. In Section V, we advocate a joint interference exploitation and avoidance approach to overcome these limitations. In Sec tion VI, we develop mathematical models for constraints under such a scheme. In Section VII, we develop a formal optimization framework for joint interference exploitation avoidance scheme. In Section VIII, we apply our optimization framework on a case study and present some numerical results. Section IX concludes this paper. [27] , which all aim to enable a receiver to decode multiple signals at the same time, and reject interference from other unintended transmitters. A recent review on how to apply interference cancellation for cellular systems was given in [1], which positioned SIC as one of the most promising techniques to mitigate interference due to its simplicity and effectiveness. Note that the SIC considered in this paper differs from some new interference cancellation schemes such as analog network coding [13] and ZigZag decoding [17] . Both were proposed to resolve packet collisions, and they require knowledge of some bits in one of the collision packets. SIC also differs from smart antenna-based interference cancellation schemes, such as Zero-Forcing Beam Forming (ZFBF) problem, the authors considered fixed routes in the network (e.g., based on shortest path), and subsequently developed a greedy heuristic scheduling algorithm based on conflict set graph. Link scheduling problem for wireless networks with SIC was also studied in [16] , but the aggregate interference effect of the practical SINR model was not considered. In [7] , Gelal et at. proposed a topology control framework to exploit SIC. They studied how to divide a network topology into a minimum number of sub-topologies where the set of links in each sub-topology can be active at the same time. In [28] , Weber et at. studied asymptotic transmission capacity of one hop ad hoc networks with SIC under a simplified model where all signals from transmitters within a specific radius can all be successfully decoded. More realistic SIC model for asymptotic transmission capacity was later explored by Blomer and Jindal in [3]. We also notice a recent paper [21] [21] shows that their SIC scheme did not fully exploit the benefits of SIC. They only considered a simple network with two links. They compared the completion time required to transmit one packet on both links with and without SIC. When without SIC, the two links transmits data sequentially and the completion time is the sum of the time used on both links. With SIC, the two links can transmit data simultaneously and the completion time was defined as the maximum time used by these two links. We argue that such a comparison is not quite fair, as the link that finishes its transmission first can start to transmit other packets instead of being idle. To date, results on how to apply SIC in a multi-hop network remain very limited, particularly those results based on a formal optimization framework that explores the interaction of interference exploitation and cancellation. This is the focus of this paper.
In the work by Jiang et al., REF the authors designed an optimal algorithm for multi-hop ad hoc networks with SIC.
Squeezing the most out of interference: An optimization framework for joint interference exploitation and avoidance
2012 Proceedings IEEE INFOCOM
2012 Proceedings IEEE INFOCOM
Computer Science