[Show abstract][Hide abstract] ABSTRACT: This paper proposes a TDMA-based medium access control protocol which enables cooperative communications in multi-hop wireless mesh networks. According to the proposed scheme, each router at the two-hop neighbourhood of each other is allocated to a specific time slot for accommodating either direct or cooperative transmissions in a coordinated manner, controlled by mini-slots which are part of the time slot. Benefiting from the elaborate mini-slot design, channel resources are fairly and efficiently allocated to each router so that no handshake is needed prior to each packet transmission. By providing access priority to cooperative transmission through an optimal relay which is determined by combined instantaneous relay channel conditions, higher system throughput can be achieved. To analyze the performance of the proposed cooperative protocol a Markov chain is introduced to model the behavior of the protocol. Simulation results demonstrate that the proposed MAC scheme can improve not only the one-hop transmission throughput but also the end-to-end throughput significantly. Moreover, the throughput performance of the proposed scheme is robust as packet size varies.
International journal of Computer Networks & Communications. 09/2011; 3(5).
[Show abstract][Hide abstract] ABSTRACT: Ubiquitous and pervasive computing and networking are envisaged as part of the future 5G wireless communication landscape
where devices which are multi-hops away from each other are connected in a cooperative way. In this paper, we investigate
a challenging case in cooperative communications where source and destination are two-hops away from each other. From the
perspective of MAC design, we propose a novel MAC protocol which enables two-hop cooperative communications by involving one
or more one-hop neighbors of both source and destination as the relays for cooperative communication. To do so, a concept
referred to as Multiple Relay Points (MRPs) has been introduced and the MRPs are selected by jointly considering the link
quality of both hops. In addition to employing a static scheme which always uses a fixed number of relays for cooperative
communication, we have also proposed an adaptive scheme which can optimally adjust the number of relays flexibly according
to channel conditions. Through performance evaluation and comparison with the original IEEE 802.11 based scheme, we demonstrate
that more reliable communications, reduced transmission power and significant throughput improvement can be achieved by using
our two-hop cooperative MAC protocol, especially when operated in the adaptive mode.
Keywords5G–Two-hop cooperative communication–MAC protocol–Relay selection
Wireless Personal Communications 04/2011; 57(3):351-363. · 0.43 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: To reduce energy consumption in wireless sensor networks, the concept of duty cycle is used in many MAC protocols. Although these protocols provide efficient energy-conservation solutions, they cannot resolve the energy hole problem in a multi-hop network, where a few nodes near the sink must relay the packets from the rest of the network, and consequently exhaust their batteries earlier. The previously proposed REACT forwarding protocol triggers the cooperation of several nodes to extend transmission range and hop over the highly burdened node, thereby allowing it to save its energy and extend the lifetime of the network. However, the previous work lacked a MAC protocol with a duty cycle. In this paper, we propose a novel cooperative duty cycle MAC (CDC-MAC) protocol, by employing a wake-up rendezvous selection scheme for multiple sensor nodes to exchange messages and a cooperator recruiting mechanism that favors nodes with more residual energy than the highly burdened node. Simulation results demonstrate that CDC-MAC can prolong the entire network longevity efficiently in comparison with another duty cycle MAC protocol, OC-MAC.
MILITARY COMMUNICATIONS CONFERENCE, 2011 - MILCOM 2011; 01/2011
[Show abstract][Hide abstract] ABSTRACT: In this paper, we propose a novel adaptive cooperative MAC mechanism that is specifically designed for two-hop cooperative communications where source and destination cannot hear each other directly. The proposed scheme employs an efficient adaptive relay selection algorithm such that the number of relay nodes is optimized for each cooperative transmission to maximize cooperation benefits and effectively avoid potential collisions with other transmissions. In order to determine the optimal number of relays we apply a training sequence in Hello message exchange, which provides us with a channel status indicator combining both bit-level and flow-level information. Numerical results show that compared with the original 802.11-based scheme and the static cooperative scheme, reliable transmission, reduced power consumption and significant throughput improvement have been achieved by using our two-hop adaptive cooperative MAC mechanism.
Proceedings of the 15th IEEE Symposium on Computers and Communications, ISCC 2010, Riccione, Italy, June 22-25, 2010; 01/2010
[Show abstract][Hide abstract] ABSTRACT: Cooperative communication has emerged as a promising technique to enhance system performance in wireless networks. This paper proposes a contention-based cooperative multiple medium access control protocol by means of multiple retransmissions of the same packet from different relay nodes. The proposed scheme exploits cooperative communication capability not only from time diversity derived from multiple temporal transmissions but also spatial diversity derived from distributed multiple relays. A Markov chain is introduced to analyze the throughput performance of the proposed cooperative scheme. The performance evaluation of the protocol is validated and compared with non-cooperative ARQ protocol in error-prone channels.
Proceedings of the 6th International Wireless Communications and Mobile Computing Conference, IWCMC 2010, Caen, France, June 28 - July 2, 2010; 01/2010
[Show abstract][Hide abstract] ABSTRACT: Cooperative communication has been recently proposed as a powerful means to improve network performance in wireless networks. However, most existing work focuses solely on one-hop source-destination cooperation. In this paper, we propose a novel cooperative MAC mechanism that is specially designed for two-hop cooperation communications where the source node and the destination node cannot hear each other directly. In this case, cooperative communication is operated in a two-hop manner and transmit-diversity is achieved by the reception of the same data packet forwarded through multiple relays towards a single destination. The proposed scheme employs an efficient relay selection algorithm to maximize cooperation benefits and can avoid collision effectively. Numerical results show that compared with the original non-cooperative protocol, significant throughput improvement and access delay reduction have been achieved with our two-hop cooperative MAC mechanism.
Wireless and Mobile Computing, Networking and Communications, 2009. WIMOB 2009. IEEE International Conference on; 11/2009
[Show abstract][Hide abstract] ABSTRACT: Wireless mesh networks are expected to play an important role in the next-generation wireless communication systems as it can provide wide coverage and scalable broadband Internet access services. However, as more traffic is injected into the network it may lead to throughput degradation, packet loss and longer transmission delay. In this paper, we argue that network performance can be improved by cross-layer design over multiple layers and load balancing based on service types. Correspondingly, a novel traffic splitting policy which can potentially utilize diverse paths for transmitting traffic flows of different service types from the same router has been proposed and investigated. Such a policy is able to balance traffic load, ideally aggregate capacities across multiple paths and leverage diversity among the paths to achieve low packet loss and more stable throughput.
Wireless Conference, 2009. EW 2009. European; 06/2009
[Show abstract][Hide abstract] ABSTRACT: Wireless mesh networks will play an important role in the next-generation wireless communication systems as it can provide wide coverage and scalable broadband Internet access services. However, congestion in such networks may lead to throughput degradation, packet loss and longer transmission delay. Therefore, routing and traffic forwarding schemes which are aware of the congestion status of a wireless network can efficiently improve network performance. In this paper, we propose a new congestion-aware routing scheme which may direct different paths for different services types, according to network congestion status. The goal of this routing scheme is to use traffic load metric for choosing a high throughput path for each mesh client towards the most appropriate Internet gateway so that load balancing is achieved among gateways. Simulations based on ns2 are conducted in order to evaluate the performance of the proposed scheme, considering both UDP and TCP traffic classes. We observe that the proposed scheme outperforms the legacy routing scheme in the simulated scenarios.
Wireless Communication Systems. 2008. ISWCS '08. IEEE International Symposium on; 11/2008
[Show abstract][Hide abstract] ABSTRACT: The aim of IP Multimedia Subsystem (IMS) is not only to realize the convergence of the fixed or mobile networks at network
level, but also to establish a uni-platform for providing services, no matter which access technology is used. However, due
to limited protocol support and the other limitation of device capabilities, a majority of legacy devices (e.g. mobile phone,
PDA, laptop, etc) today and in the near future lack coherent support for those services. In this paper, we propose a browser-based
Thin Client IMS System Architecture to support non-IMS Client devices. The main issues considered in the paper include security,
provisioning, identity management, Thin Client Inter-working, IMS Inter-working and device management. We also build the prototype
to validate the design concept.