Hoi-Sheung Wilson So

Comparison of Multichannel MAC Protocols

This paper compares, through analysis and simulation, a number of multichannel MAC protocols. We first classify these protocols into four categories based on their principles of operation: dedicated control channel, common hopping, split phase, and parallel rendezvous protocols. We then examine the effects of the number of channels and devices, channel switching times, and traffic patterns on the throughput and delay of the protocols. Here are some of the conclusions of our study: (1) parallel rendezvous protocols generally perform better than single rendezvous protocols, (2) the dedicated control channel protocol can be a good approach with its simplicity when the number of channels is high and the packets are long, and (3) the split phase protocol is very sensitive to the durations of the control and data phases. Our study focuses on a single collision domain.

Comparison of multi-channel MAC protocols

This paper compares, through analysis and simulation, a number of multichannel MAC protocols for wireless networks. We first classify these protocols into 4 categories based on their principles of operation. We then examine the effects of the number of channels and devices, channel switching times, and traffic patterns on throughput and delay. Our study focuses on a single collision domain.

Performance Analysis of Multichannel Medium Access Control Algorithms for Opportunistic Spectrum Access

In this paper, different control channel (CC) implementations for multichannel medium access control (MAC) algorithms are compared and analyzed in the context of opportunistic spectrum access (OSA) as a function of spectrum-sensing performance and licensed user activity. The analysis is based on a discrete Markov chain model of a subset of representative multichannel OSA MAC classes that incorporates physical layer effects, such as spectrum sensing and fading. The analysis is complemented with extensive simulations. The major observations are given as follows: 1) When the CC is implemented through a dedicated channel, sharing such dedicated channel with the licensed user does not significantly decrease the throughput achieved by the OSA network when the data packet sizes are sufficiently large or the number of considered data channels is small. 2) Hopping OSA MACs, where the CC is spread over all channels, are less susceptible to licensed user activity than those with a dedicated CC (in terms of both average utilization and on/off times). 3) Scanning efficiency has a large impact on the achievable performance of licensed and OSA users for all analyzed protocols. 4) The multiple rendezvous MAC class, which has yet to be proposed in OSA literature, outperforms all the multichannel MAC designs analyzed in this paper.

Network support for mobile multimedia using a self-adaptive distributed proxy

Recent advancements in video and audio codec technologies~(e.g., RealV ideo [18] make multimedia streaming possible across a wide range of network conditions. With an increasing trend of ubiquitous connectivity, more and more areas have overlapping coverage of multiple wired and wireless networks. Because the best network service changes as the user moves, to provide good multimedia application performance, the service needs to adapt to user movement as well as network and computational resource variations. For wireless multimedia applications, one must ensure smooth transitions when network connectivity changes. We argue that network adaptations for multimedia applications should be provided at the application layer with help from proxies in the network. The reasons are ease of programming, ease of deployment, better fault-tolerance, and greater scalability. We propose aself-adaptive distributed proxy systemthat provides streaming multimedia service to mobile wireless clients. Our system intelligently adapts to the real-time network variations and hides handoff artifacts using application protocol specific knowledge whenever possible. It also uses application-independent techniques such as dynamic relocation of transcoders and automatic insertion of forward error correction and compression into the data transcoding path. We advocate a composable, relocatable transcoding data path consisting of a directed acyclic graph ofstrongly-typedoperators to bridge any data format mismatch between the client and the data source. In this paper, we present the design, implementation, and evaluation of our system in the context of streaming video playback involving a series of transcoding proxies and a mobile client.

State of the Art in Opportunistic Spectrum Access Medium Access Control Design

Opportunistic spectrum access (OSA) allows unlicensed secondary networks to share licensed spectrum in space and time, but only when licensed users are not using the spectrum. Thus this novel spectrum management technique started drawing the attention of researchers recently. Although many interesting approaches have been proposed, most techniques are early proposals that often only cover a subset of the problems related to OSA. In this paper, we give an extensive overview of medium access control design challenges specific to OSA, while discussing the main approaches proposed so far in the literature. We give an extensive survey of protocols proposed and discuss which features are not explored yet and which one need to be looked at more carefully.

Design and Analysis of a Cooperative Multichannel MAC Protocol for Heterogeneous Networks

Many incompatible wireless protocols proliferate in unlicensed bands, creating complex coexistence and connectivity problems. If the trend continues, such problems will continue to exist in future unlicensed bands. We take a different approach to spectrum sharing. Instead of proposing a distinct medium-access control (MAC) protocol for each type of application, we propose a family of parameterized MAC protocols called WiFlex, which can be tailored to different application needs, ranging from wireless sensors to media centers. However, these protocols allow communication and spectrum-sharing coordination among different types of devices. We envision this family to be based on a multichannel physical layer. The contributions of this paper include a novel asynchronous split phase (ASP) protocol with dynamic priority support, even in multiple-collision-domain environments. When links are bidirectional, WiFlex resolves the multichannel hidden-node problem, achieving collision-free data exchange in a multihop environment. ASP provides a mechanism for prioritization and fairness. The performance of the protocol is evaluated through analysis and simulation. The coexistence of heterogeneous devices and the support for different applications with high performance are demonstrated.

Comparison of Opportunistic Spectrum Multichannel Medium Access Control Protocols

This work comprehensively compares four possible multichannel medium access control (MAC) approaches for opportunistic spectrum access (OSA). One of important conclusions to be drawn from the analysis is that multichannel OSA MACs that spread both control and data between all available channels, e.g., hopping MACs, perform best among possible OSA MAC implementations when the PU traffic has long ON/OFF periods compared to the time-scale of the SU channel access.

Adaptive Quality of Service for a Mobile Ad Hoc Network

This paper presents a QoS routing system for MANET supporting multiple traffic classes. The system takes into consideration clustering and channel allocation. Simulation experiments show that our algorithms are convergent. The system also yields a higher total throughput compared to the case in which every interface uses the same channel.

A robust acknowledgement scheme for unreliable flows

The increasing presence of UDP traffic in the Internet and the emergence of sensing applications which do not require full reliability motivates the search for a robust acknowledgement scheme for unreliable flows. TCP-styled cumulative ack relies on the eventual retransmission of all lost packets and hence cannot be used for unreliable flows. Our contribution is the design and analysis of a simple, yet robust acknowledgement scheme for unreliable flows. We show that our scheme achieves good performance even when the actual network conditions deviate from the designers estimate. It works in networks having orders of magnitude difference in bandwidth and loss probability, with little variation of overhead and no change to the algorithms.

WiFlex: Multi-Channel Cooperative Protocols for Heterogeneous Wireless Devices

In ISM bands, many wireless protocols proliferate such as 802.11, Bluetooth, and ZigBee. However, these incompatible protocols create complex coexistence and connectivity problems. If the same trend continues, similar interference and performance problems will continue to exist in future unlicensed bands. As new unlicensed bands open up, one can take a different approach to spectrum sharing. Instead of proposing a new MAC protocol for each type of application, we propose a family of parameterized MAC protocols called WiFlex that can tailor to different application needs ranging from wireless sensors to media center. Yet, these protocols within this family are compatible with each other to allow communication and spectrum-sharing coordination among different types of devices. We envision this family to be based on an OFDM-like multichannel physical layer. The contribution of this paper includes the discovery of an asynchronous split phase (ASP) protocol with dynamic priority support. This protocol enables powerful devices to achieve a high throughput and protects low power devices with urgent but only occasional transmissions. It is distributed and data collision-free. Moreover, it can support low delays for real time applications. The performance of the protocols are evaluated using an extension of NS-2. The results demonstrate the coexistence of devices with disparate radio characteristics and the support of applications with different requirements with good performance.