Anthony Lo

A flexible quality of service model for mobile ad-hoc networks

Quality of service (QoS) support in mobile ad-hoc networks (MANETs) is a challenging task. Most of the proposals in the literature only address certain aspects of the QoS support, e.g., QoS routing, QoS medium access control (MAC) and resource reservation. However, none of them proposes a QoS model for MANETs. Meanwhile, two QoS models have been proposed for the Internet, viz., the integrated services (IntServ) model and the differentiated services (DiffServ) model, but these models are aimed for wired networks. In this paper, we propose a flexible QoS model for MANETs (FQMM) which considers the characteristics of MANETs and combines the high quality QoS of IntServ and service differentiation of Diff-Serv. Salient features of FQMM include: dynamics roles of nodes, hybrid provisioning and adaptive conditioning. Preliminary simulation results show that FQMM achieves better performance in terms of throughput and service differentiation than the best-effort model.

A cellular-centric service architecture for machine-to-machine (M2M) communications

A machine-to-machine (M2M) communications system is a large-scale network with diverse applications and a massive number of interconnected heterogeneous machines (e.g., sensors, vending machines and vehicles). Cellular wireless technologies will be a potential candidate for providing the last mile M2M connectivity. Thus, the Third Generation Partnership Project (3GPP) and IEEE 802.16p, have both specified an overall cellular M2M reference architecture. The European Telecommunications Standards Institute (ETSI), in contrast, has defined a service- oriented M2M architecture. This article reviews and compares the three architectures. As a result, the 3GPP and 802.16p M2M architectures, which are functionally equivalent, complement the ETSI one. Therefore, we propose to combine the ETSI and 3GPP architectures, yielding a cellular-centric M2M service architecture. Our proposed architecture advocates the use of M2M relay nodes as a data concentrator. The M2M relay implements a tunnel-based aggregation scheme which coalesces data from several machines destined to the same tunnel exit-point. The aggregation scheme is also employed at the M2M gateway and the cellular base station. Numerical results show a significant reduction in protocol overheads as compared to not using aggregation at the expense of packet delay. However, the delay rapidly decreases with increasing machine density.

WAKE: Key management scheme for wide-area measurement systems in smart grid

A wide-area measurement system (WAMS) is a system that provides a time-synchronized view of electrical conditions over a large geographical area, thereby enhancing the situational awareness of the energy management system of a power grid. With this enhanced situational awareness, utilities would be able to react promptly to contingencies, and prevent large-scale blackouts. To secure WAMS communications, we propose WAMS key management (WAKE), a comprehensive key management scheme targeting a concrete set of security objectives derived from NISTs security impact level ratings. For security objectives involving unicast, WAKE employs industry- standard security protocols. For security objectives involving multicast, we show the scheme standardized by the IEC is inadequate, and identify multicast authentication as a requirement. We investigate two recent multicast authentication schemes designed for power grid communications: TV-HORS and tunable signing and verification (TSV), which supposedly improves on TV-HORS. We show that TSV is vulnerable, and propose a patched version of TSV called TSV+. Systematic comparison of TV-HORS and TSV+ shows that TV-HORS provides significantly more efficient signing and verification for the same security level at the expense of signature size. Consequently, TV-HORS is chosen as part of WAKE for multicast authentication.

Multi-hop relay architectures for 3GPP LTE-advanced

The next-generation wireless network is envisaged to incorporate multi-hop ad hoc characteristics into cellular network infrastructure. Multi-hop communication is viewed as an annexe to the cellular network infrastructure in order to increase coverage and capacity. Currently, the Third Generation Partnership Project (3GPP) is investigating multi-hop functionality as one technical component for LTE-Advanced. LTE-Advanced is the evolution of Long-Term Evolution (LTE). Even though multi-hop communication research has been ongoing for the past decades, research work on multi-hop cellular network is premature. This paper serves to provide a comprehensive review on state-of-the-art relaying strategies for LTE-Advanced. Two relaying strategies, namely amplify-and-forward and decode-and-forward are discussed. The relaying strategies are qualitatively compared against a set of criteria. The main conclusion drawn from the review is that each relaying strategy has its benefits and limitations. Thus, LTE-Advanced could deploy a mixture of amplify-and-forward and decode-and-forward relays depending on the needs and scenarios. We also discuss a new problem facing conventional channel-dependent scheduling mechanisms in LTE-Advanced with multi-hop links. Consequently, we propose a multi-hop aware channel-dependent scheduling mechanism to ameliorate the problem.

On service prioritization in mobile ad-hoc networks

The aim of service prioritization is to give resource priority to certain traffic types. For example, the voice service can have higher priority than the data service, Web surfing can have higher priority than FTP and e-mail applications, or some users can have higher priority than others. This paper investigates the performance of service prioritization in mobile ad-hoc networks (MANETs). Two schemes, priority buffer management and priority scheduling, are applied to realize service prioritization and three service profiles are discussed as well as simulation results are presented to show that the priority schemes work well with TCP traffic but not with constant bit rate (CBR) traffic. Besides this, the priority scheduling scheme outperforms the priority buffer management scheme in terms of average end-to-end delay of TCP packets and average throughput of TCP sessions.

EUROPCOM - An Ultra-WideBand (UWB)-Based Ad Hoc Network for Emergency Applications

The Information Society Technologies (IST) EUROPCOM project designs and develops an Ultra-WideBand (UWB)-based ad hoc network for search and rescue operations in disaster zones, especially indoors. The primary application of the EUROPCOM system is to provide position tracking of rescue personnel within the disaster zone. Currently no such technologies or systems exist, which can provide the envisaged functionality. The paper presents the network architecture that was proposed in the EUROPCOM project. The network architecture defines new physical entities and includes a complete protocol stack - from the physical layer up to the application layer. Each protocol layer was tailor-made to the operational constraints and requirements of the EUROPCOM system. The resulting protocol layers are lightweight, self- adaptive, bandwidth- and energy-efficient.

Evaluation of MPEG-4 video streaming over UMTS/WCDNL4, dedicated channels

Universal mobile telecommunications system (UMTS) is a third-generation mobile communication system that supports wireless wideband multimedia communications. This paper investigates the performance of streaming MPEG-4 video over UMTS dedicated channels with varying channel conditions. In order to evaluate the performance, simulation models for UMTS and MPEG-4 were developed. Simulation results show that UMTS radio control link (RLC) protocol operating in the acknowledged mode outperforms the unacknowledged mode. The latter mode provides timely delivery but no error recovery. The acknowledged mode can deliver acceptable video quality for RLC block error rates up to 40% utilizing a pre-decoder buffer. We also discover that RLC block size can affect the video quality with a larger RLC block size attaining better quality. However, the optimum RLC block size is dependent on the encoded video frame size and the channel bit rate. Therefore, the RLC block size can be tuned to a proper value given the encoded video frame size and channel bit rate.

Performance of in-band full-duplex Amplify-and-Forward and Decode-and-Forward relays with spatial diversity for next-generation wireless broadband

Advanced relaying technologies are part of the next-generation wireless broadband network architecture. In this paper, we derive the average capacity expressions of in-band full-duplex relays operating in the Amplify-and-Forward (AF) and the Decode-and-Forward (DF) modes in the present of spatial diversity. The capacity of the in-band full-duplex AF and DF relays is compared with the half-duplex AF and DF relays. Our numerical results indicate that the capacity obtained by full-duplex relays in AF and DF is superior to half-duplex AF and DF relays. It is interesting to observe that full-duplex relays in AF and DF deliver approximately equal performance. The performance of full-duplex and half-duplex DF relay is more sensitive to the relay link than full-duplex and half-duplex AF.

Experimental studies of the ZigBee frequency agility mechanism in home area networks

A normal home environment consists of various wireless technologies, in particular WiFi and ZigBee, which usually operate in the ISM 2.4-GHz band. In addition, some of the home appliances (e.g., a microwave oven) may operate in this crowded ISM band. WiFi-based, ZigBee-based devices and home appliances operating at the same frequency and physical space can cause harmful interference to one another, particularly to ZigBee technology. Therefore, the ZigBee Frequency Agility mechanism is introduced by the ZigBee Alliance to ZigBee networks for resolving such harmful interference. In this paper, we experimentally study the performance of the ZigBee Frequency Agility mechanism using a home area network (HAN) testbed. The measurement results show that this mechanism can effectively overcome interference caused by WiFi-based devices. However, in the extreme case, when all the channels are occupied, the mechanism is not effective as expected. In addition, it is observed that the response time for the ZigBee Frequency Agility mechanism to perform channel switching is depending on packet-error-rate (PER) and send-packet-counter thresholds. Low thresholds can reduce channel-switching time but increases signaling overhead. Thus, in order to obtain optimum performance, self-adaptive PER and send-packet-counter thresholds based on interference level are desired rather than static ones.

Efficient In-Band Spectrum Sensing Using Swarm Intelligence for Cognitive Radio Network

Spectrum sensing mechanisms enable cognitive radio networks to detect primary users (Upsi) and utilize spectrum holes for secondary user (SU) transmission. However, precise PU detection leads to longer sensing time and lower achievable throughput. In this paper, we propose a particle swarm optimization (PSO)-based scheme for an in-band local spectrum sensing to address the tradeoff between sensing time and throughput. Using methodological analysis, a fast convergence PSO (FC-PSO) scheme is derived by implementing a distribution-based stopping criterion subject to detection performance, optimization time, and SU gain. At the target probability of detection of at least 90%, the results show significant improvements of ~45% for sensing time, 70% for the probability of false alarm, and 12% for achievable throughput compared with nonoptimal sensing scheme at signal-to-noise ratio of 0 dB. FC-PSO also outperforms other optimization schemes in terms of convergence speed. The proposed scheme is proved to be an energy-efficient solution for practical implementation as it outperforms the other algorithms in terms of lower computational complexity as well as providing the best tradeoff values in meeting the objective function of sufficient opportunistic access for an SU under optimized sensing time for maximized throughput, while providing high protection to the PU.