Shaohe Lv

Scheduling in wireless ad hoc networks with successive interference cancellation

Successive interference cancellation (SIC) is an effective way of multipacket reception (MPR) to combat interference in wireless networks. To understand the potential MPR advantages, we study link scheduling in an ad hoc network with SIC at the physical layer. The fact that the links detected sequentially by SIC are correlated at the receiver poses key technical challenges. We characterize the link dependence and propose simultaneity graph (SG) to capture the effect of SIC. Then interference number is defined to measure the interference of a link. We show that scheduling over SG is NP-hard and the maximum interference number bounds the performance of maximal greedy schemes. An independent set based greedy scheme is explored to efficiently construct a maximal feasible schedule. Moreover, with careful selection of link ordering, we present a scheduling scheme that improves the bound. The performance is evaluated by both simulations and measurements in testbed. The throughput gain is on average 40% and up to 120% over IEEE 802.11. The complexity of SG is comparable with that of conflict graph, especially when the network size is not large.

Detecting the Sybil Attack Cooperatively in Wireless Sensor Networks

Sybil attack is a network threat introduced by one or more malicious nodes to declare numerous illegal identifies to confuse or even collapse the network applications. A new detection mechanism, called CRSD, is proposed for static wireless sensor networks, which takes use of the received signal strength (RSS) to infer the distance between two identities and further determines the positions relation of the interesting identities by use of the RSS information from multiple neighbor nodes, e.g., via node cooperation. A Sybil attack is detected when two or more different identities have almost the same position. The analysis and simulation results show that, first, Sybil attack deteriorates the system performance significantly and second, CRSD can detect such attack in most cases, thus protecting the overall performance effectively.

Understanding the Scheduling Performance in Wireless Networks with Successive Interference Cancellation

Successive interference cancellation (SIC) is an effective way of multipacket reception to combat interference in wireless networks. We focus on link scheduling in wireless networks with SIC, and propose a layered protocol model and a layered physical model to characterize the impact of SIC. In both the interference models, we show that several existing scheduling schemes achieve the same order of approximation ratios, independent of whether or not SIC is available. Moreover, the capacity order in a network with SIC is the same as that without SIC. We then examine the impact of SIC from first principles. In both chain and cell topologies, SIC does improve the throughput with a gain between 20 and 100 percent. However, unless SIC is properly characterized, any scheduling scheme cannot effectively utilize the new transmission opportunities. The results indicate the challenge of designing an SIC-aware scheduling scheme, and suggest that the approximation ratio is insufficient to measure the scheduling performance when SIC is available.

Link scheduling in wireless networks with successive interference cancellation

Successive interference cancellation (SIC) is an effective way of multipacket reception (MPR) to combat interference at the physical layer. To understand the potential MPR advantages, we study link scheduling in an ad hoc network with SIC at the physical layer. The fact that the links detected sequentially by SIC are correlated at the receiver poses key technical challenges. A link can be interfered indirectly when the detecting and removing of the correlated signals fail. We characterize the link dependence and propose a simultaneity graph (SG) to capture the effect of SIC. Then interference number is defined to measure the interference of a link. We show that scheduling over SG is NP-hard and the maximum interference number bounds the performance of a maximal greedy scheme. An independent set based greedy scheme is explored to efficiently construct a maximal feasible schedule. Moreover, with careful selection of link ordering, we present a scheduling scheme that improves the bound. The performance is evaluated by both simulations and measurements in a testbed. The throughput gain is on average 40% and up to 120% over IEEE 802.11. The complexity of SG is comparable with that of conflict graph, especially when the network size is not large.

Scheduling under SINR Model in Ad Hoc Networks with Successive Interference Cancellation

Successive interference cancellation (SIC) is an effective way of multipacket reception to combat interference. We study link scheduling under SINR (Signal to Interference Noise Ratio) model in ad hoc networks with SIC at physical layer. The facts that interference is accumulated and the links decoded sequentially by SIC are correlated pose key technical challenges. We propose conflict set graph (CSG) to characterize the interference and define interference degree to measure the interference of a link. As scheduling over CSG is NP-hard, independent set based greedy scheme is explored to efficiently construct maximal feasible schedule. The performance is evaluated by simulations. As compared to the simple greedy method [1], the throughput gain is on average 30% and up to 60%.

3D pipeline contention: Asymmetric full duplex in wireless networks

Coordination among users is an indispensable part in wireless networks for efficient medium access. Alone with the rapid increase of transmission rate, however, coordination time becomes insufferable. We present AFD, namely asymmetric full duplex, to achieve high coordination efficiency at nearly zero overhead. In AFD, channel contention is performed simultaneously with data transmission. We propose a 3D pipeline contention scheme where the contention process is divided into several parallel stages and executed in a pipelined manner in a 3D domain specified by time, frequency and spatial antenna. To mitigate the interference between the data packet and the contention signal, we adopt a singleton PN sequence as a contention pilot. AFD provides a novel network-scale full duplex capability. The performance is evaluated by both simulations and measurements in a testbed. AFD outperforms IEEE 802.11 significantly, i.e., the Jains fairness index is around 0.95 with a throughput gain up to 120%.

Maximizing Capacity in the SINR Model in Wireless Networks with Successive Interference Cancellation

Successive interference cancellation (SIC) is an effective way of multipacket reception to combat interference. We consider the problem of maximizing the number of successful transmissions based on the physical model in wireless networks with SIC at the physical layer. We propose weighted simultaneity graph to characterize the sequential detection nature of SIC and the accumulative effect of multiple interfering signals. A context-aware metric, transmission price, is defined to measure the interference of a link set. As maximizing the number of supported links is NP-hard, a greedy scheme is proposed to efficiently construct a near-optimal maximal feasible set of links. We show that the approximation performance is bounded by the transmission price of the constructed link set. The performance of the proposed scheme is further verified by simulation.

On the rate adaptation for IEEE 802.11 wireless networks

Rate adaptation (RA) is a mechanism to choose transmission rate based on the dynamic channel quality in wireless networks. This paper studied the adaptation algorithm run solely at the sender-side in IEEE 802.11 networks. The key insight is the inference discrepancy in inferring the relative order of transmission rates with respect to the expected performance, which indicates that one cannot always reach the correct order based solely on the channel state information collected by the sender itself. The consequence is wrong rate decision and significant performance loss. Therefore, we present a new RA structure to mitigate such effect by using a novel component, rate testing. Further, by employing the active measurement, a lightweight and effective testing mechanism, SFB, short frame burst, is proposed to detect and filter out the unsuitable transmission rate. Finally, an active measurement-based rate adaptation mechanism (AMRA) is designed and implemented. The experimental results show that AMRA outperforms many other well-known RA solutions in most scenarios.

A performance study of CSMA in wireless networks with successive interference cancellation

Successive interference cancellation (SIC) is an effective way of multipacket reception to combat interference. As conventional CSMA (Carrier Sense Multiple Access) is designed for single packet reception, it is unclear whether or not CSMA performs well to exploit the SIC capability. In this paper, we analyze the performance of a simple CSMA protocol in a network with SIC. For a given link, we derive the residing areas of an interfering node when simultaneous transmission is allowed and when the interference is harmful, respectively. We show that, though SIC provides many new transmission opportunities, CSMA cannot effectively exploit them. There is a fundamental tradeoff in a CSMA protocol between exploiting the transmission opportunities from SIC and capturing the harmful interference. In many cases, when CSMA achieves its best performance, almost all new transmission opportunities are not exploited. It is therefore very necessary to design a new distributed access protocol in wireless networks with SIC.

Efficiently monitoring link bandwidth in IP networks

Link bandwidth utilization is obviously critical for numerous network management tasks. Using the flow-conservation law, we could reduce the number of activated monitor agents. The problem of efficiently monitoring link-bandwidth based on flow-conservation law could be reduced to weak vertex cover problem, which is NP-hard. In this paper, we demonstrate an approximation preserving reduction from the vertex cover problem to weak vertex cover problem. Due to this reduction, it follows that it is very difficult to get an approximation algorithm with approximation ratio lower than 2 for weak vertex cover problem. Using the primal-dual method, we give an approximation algorithm with approximation ratio 2 to solve the problem. The effectiveness of our monitoring algorithm is validated by simulations evaluation over a wide range of network topologies. We also demonstrate the problem of weak vertex cover with blackout vertices could be reduce to weak vertex cover problem. Hence we could use the approximation algorithms for weak vertex cover problem to solve the problem of weak vertex cover with blackout vertices.