Multicast Routing Scheme for Recipient Maximization in Wireless Relay Networks

Multicast routing in wireless networks that possess the wireless multicast advantage could significantly reduce the power and energy consumption. However, this kind of multicast routing that only addresses the transmission radius coverage might not be able to meet the bandwidth requirement of the users. As a result, additional transmissions are required to incur more energy consumption and carbon dioxide emissions that make existing algorithms not applicable to bandwidth constrained applications. In this paper, for the first time, we address the bandwidth aware minimum power multicast routing problem in wireless networks where the objective function is to minimize the total power consumption subject to the users’ bandwidth requirements. This problem is a challenging cross-layer design problem that requires seamless and sophisticated integrated design in the network layer (multicast routing) and physical layer (bandwidth-aware wireless transmission and power control). We first formulate this problem as a mixed integer linear programming problem and then propose a Lagrangian relaxation based algorithm to solve this problem. Numerical results demonstrate that the proposed approach is a sound green networking algorithm that outperforms the existing power efficient multicast routing approaches under all tested cases, especially in large bandwidth request, fine radius granularity, large group size and sparse network.

In this paper, an efficient QoS aware resource allocation algorithm is proposed for wireless relay networks. This algorithm is yielded by considering G/G/1 queue for each subcarrier and using effective capacity concept to model the transmission delay in wireless relay networks. The objective is to minimize the transmission power considering support of QoS parameters. The constant user arrival rate is assumed throughout the paper. An extended Kalman filter also is used to estimate the residual times and vacation times of the relays and subcarriers. Based on the channel state information and queue state information, proposed algorithm assigns proper subcarriers to the relays. Then, the optimum subcarriers and relays are allocated for optimum power efficient transmission to the users.

In conventional digital communication systems, the quality of the received signal does not improve beyond a certain level as the channel quality increases. Such kind of quality saturation effect is caused by the unrecoverable quantization errors produced by source coding. The Hybrid Digital-Analog (HDA) transmission, where the quantization errors are transmitted in an analog mode along with the quantized data in a digital mode, has been recognized as an effective technique to combat the quality saturation effect. In this paper, we introduce HDA transmission in Wireless Relay Networks (WRNs) over Rayleigh slow-fading channels to eliminate the quality saturation effect and achieve graceful improvement for the better channel quality. Our goal is to minimize the end-to-end distortion by optimal power allocation. We note that digital-analog power allocation involved in HDA transmission is coupled with source-relay power allocation in WRNs. Therefore, the joint power allocation problem should be considered. We investigate this problem for two kinds of relays in WRNs, i.e., Amplify-and-Forward (AF) relays and Decode-and-Forward (DF) relays. In the case of AF relays, we find that the joint power problem is concave and thus derive the explicit expressions of the optimal solution. In the case of DF relays, we formulate the joint power allocation problem as a nonlinear fractional programming problem and then propose an efficient algorithm to search the optimal solution. Simulation results show that the proposed joint power allocation schemes outperform existing schemes in terms of end-to-end distortion in both WRNs with AF relays and that with DF relays under various channel conditions.

In this work, we propose using video caching in the wireless relay networks (WRNs) for video on demand (VoD) service. We assume the relay station (RS) of the WRNs is capable of caching a small portion of the ongoing video stream. The cached video data can be used to accommodate new user requests. Previous works on video caching for VoD are in the context of overlay network, where the physical topology is a minor concern. However, in the WMNs, it is crucial for us to take the topology into consideration. Based on the topology, we could minimize the communication cost for a request to join a video multicast. In this way, efficient utilization of video caching in the targeted environment can be achieved. Simulation study verifies the efficiency of the proposed approach.

In this paper, we study the multicast routing problem in ATM networks. The multicast routing problem, also known as the Steiner tree problem, has been well studied in the literature. However, less attention has been made for the definition of link costs and evaluating the performance of multicast routing algorithm from the network revenue point of view. Therefore, in this paper, we first proposed two approaches, namely, the Markov decision process-based (MDP) and maximum free residual capacity-based (MFC) approaches for defining link costs. We then developed three heuristic algorithms for finding near optimal multicast trees. Our simulation results indicate algorithms that estimating link costs based on the MDP approach yield better performance than those that based on the MFC approach. Among the three multicast routing algorithms that use MDP approach for estimating link costs, the algorithm that treats a multicast call as a collection of multiple point-to-point calls yields the worst performance while the algorithm that based on the genetic algorithm yields the best performance.

It has been proved that when the transmit power is sufficiently large distributed space time codes can achieve the maximal diversity order in a wireless relay network. In the previous works, space time codes used in a wireless relay network are limited on unitary space time codes or orthogonal (or quasi- orthogonal) space time codes. In this paper, we apply general multi-layer full-rate space time codes generated by algebraic extension into the wireless relay network. Moreover, the optimal power allocation and the Chernoff upper bound of the pair-wise error probability (PEP) based on the maximum-likelihood (ML) decoding are calculated. Based on this bound, two design criteria of the multi-layer full-rate space time codes are provided.

In this paper we propose a distributed Alamouti-based space-time code (STC) where opportunistic listening of packets from independent sources is exploited. Relays overhear broadcasted packets from multiple sources and acknowledge them dynamically. Acknowledgments are also overheard, allowing thus the relays to know the received packets at their neighbors. At each relay, the overheard data packets are multiplexed for generating in a distributed fashion the Alamouti STC that is broadcasted by the relays. Depending on the overheard packets the two relays may use dynamically the aforementioned multiplexed Alamouti STC scheme, or classic decode-and-forward (DF), or exploit transmit diversity with decode and joint forward (DJF). We perform extensive Monte Carlo simulations for testing the proposed protocol and the Alamouti-based STC under different channel conditions in the studied network topology.

Energy optimization is one of the major issues in the telecommunication field and particularly in wireless networks. This optimization is an essential condition for the ubiquity of wireless and mobile networks. Recent studies show that the Information and Communications Technology sector (ICT) (production, distribution, and use) amounts to 1.4% of overall global CO2e emissions. Almost all works on wireless telecommunication protocols focus on a short term vision of energy consumption consisting of the extension of non-rechargeable battery lifespan, the reduction of the consumed energy amount, or the energy use planning. We discuss how a long-term vision of energy consumption can be conducted by taking into account the device’s state of health and particularly the rechargeable battery status. We discuss how the improvement of the devices lifespan impacts on the network lifespan and the energy consumption in production and distribution phases and hence significantly improves energy efficiency. We illustrate the impact of this new paradigm on the routing problem in wireless sensor networks. We compared the new routing approach with well-known methods in terms of nodes and system lifespan. The obtained results show that consideration of the state of health of batteries extends the system life significantly and improves the success rate of data transmission.

ABSTRACTUser cooperation has evolved as a popular coding technique in wireless relay networks (WRNs). Using the neighboring nodes as relays to establish a communication between a source and a destination achieves an increase of the diversity order. The relay nodes can be seen as a distributed multi‐antenna system, which can be exploited for transmit diversity by using distributed space–time block coding (STBC). In this paper, we investigate the bit error rate (BER) of multi‐hop WRNs employing distributed STBC at the relay nodes. We develop the general model of WRNs using distributed STBC, and we derive the pairwise error probability and an approximation of the BER. We examine the impact of several parameters, such as distributed STBC at the relays, the number of relays, the distances between the nodes, and the channel state information available at the receivers, on the BER performance of the multi‐hop WRN. The obtained results provide guidelines about the expected error performance and the design of channel estimation for these networks. Copyright © 2011 John Wiley & Sons, Ltd.

In wireless relay networks (WRNs), multiple source nodes communicate with a single destination node through a common relay network. Different source nodes may have different error protection or recovery time requirements. In this paper, we focus on unequal error protection (UEP) distributed network coding (DNC) design for WRNs. Specifically, we propose a continuous UEP method based on fountain codes with the objective of satisfying the UEP or unequal recovery time (URT) requirements. Then based upon this UEP method, we develop an adaptive UEP DNC scheme to realize adaptive UEP in WRNs. We analyze the properties of the proposed adaptive UEP DNC scheme and derive the upper and lower bit error rate (BER) bounds for it over Rayleigh fading channels under maximum-likelihood (ML) decoding. Simulation results show that the proposed adaptive UEP DNC scheme has desirable UEP and URT properties. The transmitted data from the source nodes in different protection groups can be recovered successfully under their performance requirements in a shorter time by using the adaptive UEP DNC scheme.

This paper addresses channel state information (CSI) estimation in a wireless relay network, which consists of a base station (BS), a relay station (RS), and a mobile station (MS). We propose a method for the BS to obtain the instantaneous CSIs of the three links (BS-RS, BS-MS, and RS-MS links) with minimized overhead. The CSI availability plays an important role for the BS to adapt its transmission strategies to the given channel conditions. Our proposed method exploits the fact that the link condition between fixed BS and fixed RS tends to be stable, and the frequent CSI update is not necessary for this link. In order for the BS to obtain the CSI of the distant link (i.e. RS-MS link), RS amplifies a pilot signal received from MS with a pre-defined amplification factor, and forwards it to BS. This enables the BS to obtain the CSI of the RS-MS link based on the received pilot signal and pre-knowledge on the CSI of BS-RS link. We show by computer simulation that our proposed method can reduce the required overhead for CSI estimation with little degradation on the accuracy of the obtained CSI.

Because low Earth orbit (LEO) satellites provide short round-trip delay, they are becoming increasingly important for providing real-time applications such as voice and video traffic to global coverage. Multicast communication that simultaneously transmits messages from a source to a group of destination is essential for future LEO satellite networks. The multicast routing problem in terrestrial networks has already been studied extensively in the past. In LEO networks, previous research on the multicast routing only considers the network cost optimization without satisfying the delay requirement. This paper proposes a distributed multicast tree algorithm with sub-optimal network cost under the delay bound in LEO satellite networks. We compare the performance of our MC algorithm when applied to the LEO satellite networks with the periodically time-variant ISL sub-network. The algorithms are judged based on the quality of MC trees it generates and its efficiency in managing the network resources. Simulation results show that our delay-constrained multicast algorithms are capable of fulfilling the delay requirements in LEO satellite networks.

In this paper, we study optimal power control for sequential NOMA in wireless relay networks. When a sequential NOMA scheme is used, in each time slot, the base station uses NOMA in the first phase, while the stronger relay uses NOMA in the second phase. To solve the problem of optimal power control for sequential NOMA, we design the geometric eight-point algorithm based on geometric properties of the non-convex optimization problem. Specifically, the proposed geometric eight-point algorithm adopts parabolas and the geometric classification algorithm to obtain a locally optimal power allocation vector with low computational complexity. Simulation results indicate that the proposed sequential NOMA scheme could increase the spectral efficiency and reduce the relay power consumption for wireless relay networks.

Resource allocation using time division multiple access over wireless relay networks

Network coding has recently been applied to wireless networks and has achieved some initial success. Researches in wireless network coding have been mostly focusing on utilizing the broadcast nature of the wireless networks. In this paper, we propose a novel network coding framework for wireless relay networks that also takes into consideration the fading and error prone nature of the wireless networks. First, we extend the traditional network coding in lossless networks which operates on 0-1 bits, to a new framework which defines network coding on the posterior probability of each bit. This new framework allows an imperfect decode-recode process at a relay node and avoids possible error propagation when a hard decision is made at the relay node. It implicitly integrates decode-and-forward and estimate-and-forward strategies for wireless network coding to address the technical issues of channel fading and transmission errors. The proposed approach is validated through both theoretical analysis and extensive simulations. Both analysis and simulation confirm that this new framework is able to achieve significant gain over traditional network coding. This new framework also enables the introduction of adaptive scheme into network coding. We demonstrate a basic adaptation scheme and present some preliminary experimental results. The proposed adaptive scheme will lay down an essential foundation in this emerging field of wireless network coding in order to address issues related to link heterogeneity.