Linear transceiver design for amplify-and-forward MIMO relay systems under channel uncertainties

Proceedings of the IEEE Wireless Communications and Networking Conference, 2010, p. 1-6In this paper, robust joint design of linear relay precoders and destination equalizers for amplify-and-forward (AF) MIMO relay systems under Gaussian channel uncertainties is investigated. After incorporating the channel uncertainties into the robust design based on the Bayesian framework, a closed-form solution is derived to minimize the mean-square-error (MSE) of the received signal at the destination. The effectiveness of the proposed robust transceiver is verified by simulations. ©2010 IEEE.published_or_final_versionThe IEEE Wireless Communications and Networking Conference (WCNC), Sydney, Australia, 18-21 April 2010. In Proceedings of WCNC, 2010, p. 1-

Exploring centrality for message forwarding in opportunistic networks

In opportunistic networks, centrality characterizes a node's capability to act as a communication hub. In this paper, we provide an in-depth study of choosing effective centrality metrics for message forwarding in bandwidth-limited opportunistic networks. Based on this study, we propose a destination-unaware forwarding algorithm that accounts for the popularity of a node and the contact durations between nodes. We evaluate the algorithm on two experimental human mobility traces. The simulation results show that the proposed algorithm achieves higher system throughput while maintaining a lower forwarding cost compared with several known destination-unaware forwarding schemes. ©2010 IEEE.published_or_final_versionThe 2010 IEEE Conference on Wireless Communications and Networking (WCNC), Sydney, NSW, Australia, 18-21 April 2010. In Proceedings of the IEEE WCNC, 2010, p. 1-

A joint routing and scheduling algorithm for efficient broadcast in wireless mesh networks

With the increasing popularity of wireless mesh networks (WMNs), broadcasting traffic (e.g. IP-TV) will contribute a large portion of network load. In this paper, we consider a multi-channel multi-interface WMN with real time broadcast call arrivals. Aiming at maximizing the call acceptance rate of the network, an efficient broadcast tree construction algorithm, called Schedule-based Greedy Expansion (S-Expand), is designed. Unlike the existing time fraction approach, which focuses on assigning time fractions to tree links to guarantee the existence of a feasible schedule, we follow the approach of joint routing and scheduling. The proposed S-Expand algorithm packs non-interfering transmissions to use the same time slots; this would allow more flexibility in accepting future calls. Simulation results show that S-Expand achieves higher call acceptance rate than the traditional time fraction approach. ©2010 IEEE.published_or_final_versionThe 2010 IEEE Wireless Communications and Networking Conference (WCNC), Sydney, Australia, 18-21 April 2010. In Proceedings of WCNC, 2010, p. 1-

Enhanced variable power broadcasting based on local information in mobile ad hoc networks

Broadcasting in mobile ad hoc networks (MANETs) usually involve fixed transmission power that covers, for example an area within 250 meters. However, it is often unnecessary to broadcast using fixed power because a node that needs to be covered may just be 100 meters away. By reducing the transmission power enough to cover this node, energy expenditure would be reduced, thus, prolonging the lifetime of a battery-powered MANET. Existing works on variable power broadcasting based on local information are effective in achieving this objective. However, they are not optimized and can be improved by dynamically adjusting the transmission power based on where a broadcast message comes from. This paper proposes simple mechanisms based on local knowledge to adjust the transmission power dynamically and incorporates a timer suppression mechanism to further enhance the effectiveness of the protocols in reducing energy expenditure. Results of simulation studies confirm the effectiveness of the proposed enhancements. ©2010 IEEE.published_or_final_versionThe 2010 IEEE Wireless Communications and Networking Conference (WCNC), Sydney, Australia, 18-21 April 2010. In Proceedings of IEEE-WCNC, 2010, p. 1-

On detection algorithms for spurious retransmissions in TCP

In TCP, a spurious packet retransmission can be caused by either spurious timeout (STO) or spurious fast retransmit (SFR). The "lost" packets are unnecessarily retransmitted and the evoked congestion control process causes network underutilization. In this paper, we focus on spurious retransmission detection. We first present a survey on some important and interesting spurious retransmission detection algorithms. Based on the insights obtained, we propose a novel yet simple detection algorithm called split-and-retransmit (SnR). SnR only requires a minor modification to the TCP sender while leaving the receiver intact. The key idea is to split the retransmitted packet into two smaller ones before retransmitting them. As the packet size is different, the ACK triggered will carry different ACK numbers. This allows the sender to easily distinguish between the original transmission and the retransmission of a packet without relying on, e.g., TCP options. We then compare our SnR with STODER, F-RTO and Newreno under both loss-free and lossy network environments. We show that our SnR is resilient to packet loss and yields good performance under various simulation settings. ©2010 IEEE.published_or_final_versionThe 2010 IEEE Wireless Communications and Networking Conference (WCNC), Sydney, Australia, 18-21 April 2010. In Proceedings of WCNC, 2010, p. 1-

Requirement analysis for building practical accident warning systems based on vehicular ad-hoc networks

An Accident Warning System (AWS) is a safety application that provides collision avoidance notifications for next generation vehicles whilst Vehicular Ad-hoc Networks (VANETs) provide the communication functionality to exchange these notifi- cations. Despite much previous research, there is little agreement on the requirements for accident warning systems. In order to build a practical warning system, it is important to ascertain the system requirements, information to be exchanged, and protocols needed for communication between vehicles. This paper presents a practical model of an accident warning system by stipulating the requirements in a realistic manner and thoroughly reviewing previous proposals with a view to identify gaps in this area

Design of a Practical and Compact mm-Wave MIMO System with Optimized Capacity and Phased Arrays

In this paper we evaluate the feasibility of short range outdoor mm-wave MIMO links in the 70 GHz portion of the E-band (71–76 GHz). We use phased arrays in order to strongly reduce the impact of the multipath components, thus making the channel mainly line-of-sight (LOS). We design the array using a simple patch as a single element and simulate the performances for a 200 m link and a MIMO system with equal element spacing at the transmitter and the receiver. Each node of the MIMO system consists of a uniform rectangular array (URA) where the single element is a patch antenna, in order to achieve higher gains and narrow beams. Such configuration is much more compact compared to the antennas currently employed for the same bandwidth. We optimize the interelement distances at the transmitter and the receiver and evaluate the capacity achievable with different array sizes. The results show that, for the proposed link budget, capacity up to 29 bit/s/Hz is achievable at a range of 200 m, with practical dimensions. We also show that the beamforming capabilities make the design much more flexible than the single reflector antenna systems. In the last part of the paper, we verify that our antenna can also operate in rainy conditions and longer ranges