Xiao-Hui Lin

Survey on cooperative strategies for wireless relay channels

Cooperative communication has the potential of providing better throughput and reliability to wireless systems when compared with direct communication. To realise the potential gain, it is important to design cooperative strategies for some representative scenarios. This survey deals with three basic wireless relay channels, namely, the parallel relay channel, the multiple-access relay channel and the broadcast relay channel. For the first channel, which models a single unicast connection, various forwarding strategies are studied. For the second and third channels, which model, respectively, the uplink and downlink scenarios with multiple unicast connections; network codes that exploit the possibility of coding among the connections are studied. The common aim pertaining to the studies of all these three channels is to use the limited radio resource in the most efficient way. Beside the aforementioned conventional works, studies that have state-of-the-art assumptions for relay networks, including outdated channel state information at the transmitter, full duplex relay and practical rateless-coded cooperation, are also extensively reviewed. Copyright

A quantitative comparison of ad hoc routing protocols with and without channel adaptation

To efficiently support tetherless applications in ad hoc wireless mobile computing networks, a judicious ad hoc routing protocol is needed. Much research has been done on designing ad hoc routing protocols and some well-known protocols are also being implemented in practical situations. However; one major imperfection in existing protocols is that the time-varying nature of the wireless channels among the mobile-terminals is ignored; let alone exploited. This could be a severe design drawback because the varying channel quality can lead to very poor overall route quality in turn, resulting in low data throughput. Indeed, better performance could be achieved if a routing protocol dynamically changes the routes according to the channel conditions. In this paper, we first propose two channel adaptive routing protocols which work by using an adaptive channel coding and modulation scheme that allows a mobile terminal to dynamically adjust the data throughput via changing the amount of error protection incorporated. We then present a qualitative and quantitative comparison of the two classes of ad hoc routing protocols. Extensive simulation results indicate that channel adaptive ad hoc routing protocols are more efficient in that shorter delays and higher rates are achieved, at the expense of a higher overhead in route set-up and maintenance.

A multipath ad hoc routing approach to combat wireless link insecurity

As wireless LAN (WLAN) technologies proliferate, it is becoming common that ad hoc networks, in which mobile devices communicate via temporary links, are built using WLAN products. In the IEEE 802.11b standard, the wired equivalent privacy (WEP) scheme is used as the only measure to enhance data confidentiality against eavesdropping. However, owing to well known pitfalls in initialization vector (IV) attachment in the ciphertext, the underlying 40-bit RC4 encryption mechanism in WEP is unsafe regardless of the key size. On the other hand, solutions involving replacement of RC4 by another cipher are not attractive because that may lead to reconstruction of the whole system and result in high cost as well as redevelopment of the products. In order to enhance the security on the existing development efforts, we propose a novel multipath routing approach to combat the link insecurity problem at a higher protocol layer. This approach does not require the application to use sophisticated encryption technologies that may be too heavy burdens for mobile devices. Based on our suggested confidentiality measurement model, we find that our proposed multipath ad hoc routing technique called secure multipath source routing (SMSR), is highly effective.

A genetic algorithm based approach to route selection and capacity flow assignment

In large-scale computer communication networks (e.g. the nowadays Internet), the assignment of link capacity and the selection of routes (or the assignment of flows) are extremely complex network optimization problems. Efficient solutions to these problems are much sought after because such solutions could lead to considerable monetary savings and better utilization of the networks. Unfortunately, as indicated by much prior theoretical research, these problems belong to the class of nonlinear combinatorial optimization problems, which are mostly (if not all) NP-hard problems. Although the traditional Lagrange relaxation and sub-gradient optimization methods can be used for tackling these problems, the results generated by these algorithms are locally optimal instead of globally optimal. In this paper, we propose a genetic algorithm based approach to providing optimized integrated solutions to the route selection and capacity flow assignment problems. With our novel formulation and genetic modeling, the proposed algorithm generates much better solutions than two well known efficient methods in our simulation studies.

RICA: a receiver-initiated approach for channel-adaptive on-demand routing in ad hoc mobile computing networks

To support truly peer-to-peer applications in ad hoc wireless mobile computing networks, a judicious and efficient ad hoc routing protocol is needed. Much research has been done on designing ad hoc routing protocols and some well known protocols are also being implemented in practical situations. However, one major drawback in existing state-of-the-art protocols, such as the AODV routing protocol, is that the time-varying nature of the wireless channels among the mobile terminals is ignored, let alone exploited. This can be a severe design shortcoming because the varying channel quality can lead to very poor overall route quality, in turn result in low data throughput. In this paper, by using a previously proposed adaptive channel coding and modulation scheme which allows a mobile terminal to dynamically adjust the data throughput via changing the amount of error protection incorporated, we devise a new receiver-initiated algorithm for ad hoc routing that dynamically changes the routes according to the channel conditions. Extensive simulation results indicate that our proposed protocol are more efficient in that shorter delays and higher rates are achieved.

Power control approach for IEEE 802.11 ad hoc networks

In packet radio networks, especially an ad hoc wireless network using IEEE 802.11 as the MAC (media access control) protocol, power control is a crucial issue. By using a judicious power control mechanism, co-channel interference can be significantly reduced, thus improving the channel spatial reuse and network capacity. However, efficient power control in an IEEE 802.11 system is very challenging because according to the standard, fixed power is used for transmitting packets, and there is only one channel. In this paper, we propose an enhancement to the standard IEEE 802.11 MAC protocol by improving the handshaking mechanisms and adding one separate power control channel. With the control channel, the receiver notifies its neighbors its noise tolerance. Thus, the neighbors can adjust their transmission power levels to avoid packet collisions at the receiver. Through extensive simulations using NS-2, our proposed power control mechanism is found to be effective in that network throughput can be increased by about 10%, and the battery utilization can also be improved at the same time.

Power control for IEEE 802.11 ad hoc networks: issues and a new algorithm

We propose an enhancement to the original MAC (multiple access control) protocol in the IEEE 802.11 standard by improving the handshake mechanism and adding one more separate power control channel. With the control channel, the receiver notifies its neighbors about the noise tolerance. Thus, the neighbors can adjust their transmission power levels to avoid packet collision at the receiver. Through extensive simulations on the NS-2 platform, our power control mechanism is found to be effective in that network throughput can be increased by about 10%

BGCA: bandwidth guarded channel adaptive routing for ad hoc networks

To support truly peer-to-peer applications in ad hoc wireless networks, a judicious and efficient ad hoc routing protocol is needed. Much research has been done on designing ad hoc routing protocols and some well known protocols are also being implemented in practical situations. However, one major drawback in existing state-of-the-art protocols, such as the AODV (ad hoc on demand distance vector) routing protocol, is that the time-varying nature of the wireless channels among the mobile terminals is ignored, let alone exploited. In this paper, by using a previously proposed adaptive channel coding and modulation scheme which allows a mobile terminal to dynamically adjust the data throughput via changing the amount of error protection incorporated, we devise a new ad hoc routing algorithm that dynamically changes the routes according to the channel conditions. Extensive simulation results indicate that our proposed protocol is more efficient in that shorter delays and higher rates are achieved.

Opportunistic relaying with analogue and digital network coding for two-way parallel relay network

A pair of terminals exchanging information via a layer of parallel relay nodes under slow fading is considered. Two protocols are proposed based on the combination of opportunistic relaying (OR) with analogue network coding (ANC), named ORANC, or with digital network coding (DNC), named ORDNC, respectively. Two schemes/versions of ORDNC, including 2-phase ORDNC (2P-ORDNC) and 3-phase ORDNC (3P-ORDNC) are proposed. Their outage performances are investigated. ORANC and 2P-ORDNC are proved to achieve optimal diversity-multiplexing tradeoff (DMT), whereas 3P-ORDNC is proved to be suboptimal. However, from diversity viewpoint only, all the above schemes are proven to achieve full diversity order. Simulation results verify the analysis, and show that 3P-ORDNC and ORANC shows advantage at low- and high-data rate regions, respectively.

On using game theory to balance energy consumption in heterogeneous wireless sensor networks

In this paper, we consider energy fairness problem in wireless sensor networks. However, the heterogeneous hostile operating conditions - different transmission distances, varying fading environments and distinct remained energy levels, have made energy balancing a highly challenging design issue. To tackle this problem, we model the packet transmission of sensor nodes as a game. By properly designing the utility function, we get the Nash equilibrium, in which, while each node can optimize its own payoff, the global objective - energy balancing can also be achieved. In addition, by imposing penalty mechanism on sensors to punish selfish behaviors, the delivery rate and delay constraints are also satisfied. Through extensive simulations, the proposed game theoretical approach is proved to be effective in that the energy consumption is balanced and the energy resources are efficiently utilized, which can significantly improve the network lifetime.