Multiconfiguration multihop protocols: a new class of protocols forpacket-switched WDM optical networks

Wavelength-division multiplexing (WDM) local-area networks based on the optical passive-star coupler have traditionally been classified as being either single-hop or multihop. A single-hop network provides a direct connection between the source and the destination of a packet during the packet transfer duration, but may require some amount of coordination between the nodes which may involve tuning of the transmitters or receivers at each node. Since the time required to tune a tunable optical transmitter or receiver may be high, a single-hop network may incur significant overhead. On the other hand, a typical multihop network requires little or no tuning, but a packet may traverse a number of intermediate nodes between the source and destination nodes. Each hop incurs additional queueing delays at each node and also increases the overall load on each link and on the network. In this paper, we propose a new class of multiconfiguration multihop protocols (MMPs) which use tunable transmitters and receivers to cycle through a number of configurations which together make up a multihop logical topology. This class of protocols offers a trade-off between the tuning required in a single-hop network and the number of hops required in a multihop network. We present a generalized framework for comparing the proposed protocols with existing single-hop and multihop protocols, and we show that these protocols may offer significant performance gains for systems with high tuning delays and a limited number of transmitters and receivers at each node     

Capacity regions for wireless ad hoc networks

We define and study capacity regions for wireless ad hoc networks with an arbitrary number of nodes and topology. These regions describe the set of achievable rate combinations between all source-destination pairs in the network under various transmission strategies, such as variable-rate transmission, single-hop or multihop routing, power control, and successive interference cancellation (SIC). Multihop cellular networks and networks with energy constraints are studied as special cases. With slight modifications, the developed formulation can handle node mobility and time-varying flat-fading channels. Numerical results indicate that multihop routing, the ability for concurrent transmissions, and SIC significantly increase the capacity of ad hoc and multihop cellular networks. On the other hand, gains from power control are significant only when variable-rate transmission is not used. Also, time-varying flat-fading and node mobility actually improve the capacity. Finally, multihop routing greatly improves the performance of energy-constraint networks.     

Power allocations in minimum-energy SER-constrained cooperative networks

In this paper, we propose minimum power allocation strategies for repetition-based amplify-and-forward (AF) relaying, given a required symbol error rate (SER) at the destination. We consider the scenario where one source and multiple relays cooperate to transmit messages to the destination. We derive the optimal power allocation strategy for two-hop AF cooperative network that minimizes the total relay power subject to the SER requirement at the destination. Two outstanding features of the proposed schemes are that the power coefficients have a simple solution and are independent of knowledge of instantaneous channel state information (CSI). We further extend the SER constraint minimum power allocation to the case of multibranch, multihop network and derive the closed-form solution for the power control coefficients. For the case of power-limited relays, we propose two iterative algorithms to find the power coefficients for the SER constraint minimum-energy cooperative networks. However, this power minimization strategy does not necessarily maximize the lifetime of battery-limited systems. Thus, we propose two other AF cooperative schemes which consider the residual battery energy, as well as the statistical CSI, for the purpose of lifetime maximization. Simulations show that the proposed minimum power allocation strategies could considerably save the total transmitted power compared to the equal transmit power scheme.     

Throughput-range tradeoff of wireless mesh backhaul networks

Wireless backhaul communication is expected to play a significant role in providing the necessary backhaul resources for future high-rate wireless networks. Mesh networking, in which information is routed from source to destination over multiple wireless links, has potential advantages over traditional single-hop networking, especially for backhaul communication. We develop a linear programming framework for determining optimum routing and scheduling of flows that maximizes throughput in a wireless mesh network and accounts for the effect of interference and variable-rate transmission. We then apply this framework to examine the throughput and range capabilities for providing wireless backhaul to a hexagonal grid of base stations, for both single-hop and multihop transmissions for various network scenarios. We then discuss the application of mesh networking for load balancing of wired backhaul traffic under unequal access traffic conditions. Numerical results show a significant benefit for mesh networking under unbalanced loading.     

A Relay-Aided Media Access (RAMA) Protocol in Multirate Wireless Networks

The IEEE 802.11 standard inherently supports multiple data rates at the physical layer. Various rate adaptation mechanisms have been proposed to exploit this multirate capability by automatically adapting the transmission rate to best utilize the wireless spectrum. This study is primarily motivated by the observation that in a wireless network, a multihop high-rate path can potentially achieve better throughput and delay than using a single-hop low-rate path for transmission. Specifically, this paper introduces a relay-aided media access (RAMA) protocol by taking advantage of the existence of such multihop high-rate links. This is demonstrated by replacing one low-rate link with two high-rate links using a relay node. One of the key novelties in the proposed RAMA protocol is that the transmission from the immediate relay node to the destination node is free of contention. Results from analysis and simulations show that RAMA can significantly improve performances in terms of both throughput and delay.     

Cooperative Communications in Resource-Constrained Wireless Networks

Cooperative communications have been proposed to exploit the spatial diversity gains inherent in multiuser wireless systems without the need of multiple antennas at each node. This is achieved by having the users relay each others messages and thus forming multiple transmission paths to the destination. In resource constrained networks, such as wireless sensor networks, the advantages of cooperation can be further exploited by optimally allocating the energy and bandwidth resources among users based on the available channel state information (CSI) at each node. In the first part of this article, we provide a tutorial survey on various power allocation strategies for cooperative networks based on different cooperation strategies, optimizing criteria, and CSI assumptions. In the second part, we identify the similarities between cooperative networks and several sensor network applications that utilize collaboration among distributed sensors to achieve the system goal. These applications include decentralized detection/estimation and data gathering. The techniques developed in cooperative communications can be used to solve many sensor network problems     

End-to-End Batch Transmission in a Multihop and Multirate Wireless Network: Latency, Reliability, and Throughput Analysis

This paper presents a novel Markov-based model for analyzing the end-to-end transmission of a batch of packets in a multihop wireless network using multirate transmission. The end-to-end reliability of this transmission (in terms of the number of packets delivered to the destination node) is controlled through different types of Automatic Repeat reQuest (ARQ)-based error control mechanisms implemented at each node. For a batch of packets, we derive complete statistics (i.e., probability mass function) for end-to-end latency and the number of packets successfully delivered to the destination node. Typical numerical results obtained from the model are validated by means of simulation. These results reveal the trade-off between end-to-end latency and end-to-end reliability, which would be an important issue in designing and engineering multihop wireless networks. Also, we demonstrate the usefulness of the proposed analytical model in predicting the latency and the reliability performances of TCP (Transmission Control Protocol) in a multihop wireless scenario.     

Routing in Packet-Switching Broadcast Radio Networks

Packet-switching broadcast radio networks are receiving considerable attention as a feasible solution for applications involving fast network deployment requirements, inaccessible physical environments, and mobile communication devices. Such networks also offer economic alternatives to traditional multiplexing schemes for local distribution. Most of the published papers relating to packet-switching broadcast radio networks address the case in which all communication devices are within an effective transmission range of the destination receiver, thus forming a single-hop network in which no packet routing is involved. In this paper, we address multihop networks. The problems encountered in packet transportation are identified and strategies to resolve these are proposed.     

Capacity of practical wireless multihop broadcast networks

In a wireless multihop broadcasting scenario, a number of relay nodes may cooperate the source node in order to improve the capacity of the network. However, the imposition of total energy and maximum hop constraints to this system in a practical setting. In this paper, we study an ad-hoc network with infinitely many nodes and analytically find the number and positions of rebroadcasting relay nodes to achieve the optimal broadcast capacity. The interference due to multiple transmissions in the same geographical area is taken into account. According to the results of this theoretical model, we propose two heuristics, one distributed and one centralized, as suboptimal but practical solutions to the relay selection problem in wireless multihop broadcasting. We discuss the broadcast capacity performances and CSI (channel state information) requirements of these algorithms. The results illustrate that the benefits of peer-assisted broadcasting are more pronounced in the centralized relay selection algorithm when compared to the fully randomized and distributed selection under a realistic system model.     

Energy Planning for Progressive Estimation in Multihop Sensor Networks

Multihop sensor networks where transmissions are conducted between neighboring sensors can be more efficient in energy and spectrum than single-hop sensor networks where transmissions are conducted directly between each sensor and a fusion center. With the knowledge of a routing tree from all sensors to a destination node, we present a digital transmission energy planning algorithm as well as an analog transmission energy planning algorithm for progressive estimation in multihop sensor networks. Unlike many iterative consensus-type algorithms, the proposed progressive estimation algorithms along with their transmission energy planning further reduce the network transmission energy while guaranteeing any pre-specified estimation performance at the destination node within a finite time. We also show that digital transmission is more efficient in transmission energy than analog transmission if the available transmission time-bandwidth product for each link and each observation sample is not too limited.     

基于确定性观测的压缩感知MIMO信道参数反馈

在实际资源受限(带宽受限或功率受限)的无线通信系统中,多径信道具有很强的稀疏特性,如何利用这一特点更加高效地将接收端获得的多径信道状态信息( CSI)进行压缩、反馈,是目前信道状态信息反馈技术的研究热点。针对现有多入多出( MIMO)信道状态信息反馈方法中随机观测矩阵需要较大存储空间的问题,引入了确定性Golay测量矩阵,提出了一种基于确定性观测的压缩感知MIMO多径信道参数反馈方法。在接收端对由信道估计得出的信道状态信息利用确定性Golay测量矩阵进行观测,将较少数目的观测值反馈到发送端,在发送端通过重构算法恢复出完全信道状态信息。仿真实验表明,与随机观测相比,采用确定性Golay观测矩阵的方法虽然需要的观测值数目会有所增加,但所需存储空间远小于随机观测矩阵,且利用确定性观测反馈信道状态信息的重构性能与随机观测矩阵相当。     

Cooperative Strategies and Achievable Rate for Tree Networks With Optimal Spatial Reuse

In this paper, a low-complexity cooperative protocol that significantly increases the average throughput of multihop upstream transmissions for wireless tree networks is developed and analyzed. A system in which transmissions are assigned to nodes in a collision free, spatial time division fashion is considered. The suggested protocol exploits the broadcast nature of wireless networks where the communication channel is shared between multiple adjacent nodes within interference range. For any upstream end-to-end flow in the tree, each intermediate node receives information from both one-hop and two-hop neighbors and transmits only sufficient information such that the next upstream one-hop neighbor will be able to decode the packet. This approach can be viewed as the generalization of the classical three node relay channel for end-to-end flows in which each intermediate node becomes successively source, relay and destination. The achievable rate for any regular tree network is derived and an optimal schedule that realizes this rate in most cases is proposed. Our protocol is shown to dramatically outperform the conventional scheme where intermediate nodes simply forward the packets hop by hop. At high signal-to-noise ratio (SNR), it yields approximately 66% throughput gain for practical scenarios.     

Rateless Coding and Relay Networks

A framework for coding over relay channels using rateless codes is the intersection of two active areas of research in communications; namely relay networks and rateless coding. We demonstrate that there is a very natural and useful fit between these two areas and describe some design challenges and implementation considerations for this framework. The use of relays in wireless communication networks provide a new dimension to the design space of wireless networks that promises enhancements to both the coverage and throughput of the network. In its simplest form, a relay network is a collection of terminals that are able to transmit, receive, and possibly assist the reliable delivery of information from source terminals to destination terminals. Thus, communication of data through a wireless relay network is not required to be direct; it may pass through a number of other terminals, though direct communication from source to destination is not precluded. In fact, it is possible to simultaneously use single-hop, i.e., direct, and multihop communications paths.     

Capacity bounds and power allocation for wireless relay channels

We consider three-node wireless relay channels in a Rayleigh-fading environment. Assuming transmitter channel state information (CSI), we study upper bounds and lower bounds on the outage capacity and the ergodic capacity. Our studies take into account practical constraints on the transmission/reception duplexing at the relay node and on the synchronization between the source node and the relay node. We also explore power allocation. Compared to the direct transmission and traditional multihop protocols, our results reveal that optimum relay channel signaling can significantly outperform multihop protocols, and that power allocation has a significant impact on the performance.     

菱形中继网络中基于叠加训练的信道估计技术研究

针对放大转发(Amplify-and-Forward, AF)模式下的菱形中继网络,为了高效获取级联和单跳链路信道状态信息(Channel State Information, CSI),本文提出基于叠加训练的信道估计方案,以消除多址接入干扰和训练间互干扰为目标,进行最优的多训练序列设计。新方案将中继训练叠加到源训练序列上,通过对中继识别符号以及中继训练组进行联合优化设计,设计了一种基于频域循环移位的正交扩展序列组生成算法。为了消除非高斯复合噪声对单跳信道估计造成的严重干扰,提出了一种中继噪声消除算法。通过两路中继链路获取的信息副本,能够在端节点实现分集合并,有效提高符号检测性能。仿真实验对比了同类型的信道估计方案,分析验证了方案的有效性。      

Multiradio Channel Allocation in Multihop Wireless Networks

Channel allocation was extensively investigated in the framework of cellular networks, but it was rarely studied in the wireless ad hoc networks, especially in the multihop networks. In this paper, we study the competitive multiradio multichannel allocation problem in multihop wireless networks in detail. We first analyze that the static noncooperative game and Nash equilibrium (NE) channel allocation scheme are not suitable for the multihop wireless networks. Thus, we model the channel allocation problem as a hybrid game involving both cooperative game and noncooperative game. Within a communication session, it is cooperative; and among sessions, it is noncooperative. We propose the min-max coalition-proof Nash equilibrium (MMCPNE) channel allocation scheme in the game, which aims to maximize the achieved data rates of communication sessions. We analyze the existence of MMCPNE and prove the necessary conditions for MMCPNE. Furthermore, we propose several algorithms that enable the selfish players to converge to MMCPNE. Simulation results show that MMCPNE outperforms NE and coalition-proof Nash equilibrium (CPNE) schemes in terms of the achieved data rates of multihop sessions and the throughput of whole networks due to cooperation gain.     

A simple void node and loop‐free three‐dimensional routing protocol for multi‐hop wireless networks

Wireless networks are now very essential part for modern ubiquitous communication systems. The design of efficient routing and scheduling techniques for such networks have gained importance to ensure reliable communication. Most of the currently proposed geographic routing protocols are designed for 2D spatial distribution of user nodes, although in many practical scenarios user nodes may be deployed in 3D space also. In this paper, we propose 3D routing protocols for multihop wireless networks that may be implemented in two different ways depending on how the routing paths are computed. When the routing paths to different user nodes from the base station in the wireless network are computed by the base station, we call it centralized protocol (3DMA‐CS). A distributed routing (3DMA‐DS) protocol is implemented when respective routing path of each user node to the base station is computed by the user node. In both of these protocols, the user (base station) selects the relay node to forward packets in the direction of destination, from the set of its neighbours, which makes minimum angle with the reference line drawn from user (base station) to the base station (user), within its transmission range. The proposed protocols are free from looping problem and can solve the void node problem (VNP) of multihop wireless networks. Performance analysis of the proposed protocol is shown by calculating end‐to‐end throughput, average path length, end‐to‐end delay, and energy consumption of each routing path through extensive simulation under different network densities and transmission ranges.     

Handover in multihop cellular networks [Accepted from Open Call]

This article introduces various handover scenarios in multihop cellular networks. In addition, this article presents handover schemes where relay stations are located either inside a cell or on the boundary between two adjacent cells and investigates the effects of the deployment position of relay stations to handover performance. The simulation results show that multihop cellular networks for both deployment scenarios can achieve 90 percent throughput increase over single-hop cellular networks. The results also show that the overall throughput of the multihop cellular networks with relay stations inside a cell is higher than for those with relay stations on the boundary between two adjacent cells, whereas the opposite is observed for the throughput of cell-boundary users. The intercell handover latency in multihop cellular networks is increased by 20 ~ 56 percent compared with that in singlehop cellular networks because of the increased number of handovers and signaling overhead. However, by deploying relay stations on the boundary between two adjacent cells, the service-interruption time caused by inter-cell handover is reduced by 80 percent compared with that of single-hop cellular networks.     

Performance analysis of relative location estimation for multihop wireless sensor networks

In this paper, we present new analytical, simulated, and experimental results on the performance of relative location estimation in multihop wireless sensor networks. With relative location, node locations are estimated based on the collection of peer-to-peer ranges between nodes and their neighbors using a priori knowledge of the location of a small subset of nodes, called reference nodes. This paper establishes that when applying relative location to multihop networks the resulting location accuracy has a fundamental upper bound that is determined by such system parameters as the number of hops and the number of links to the reference nodes. This is in contrast to the case of single-hop or fully connected systems where increasing the node density results in continuously increasing location accuracy. More specifically, in multihop networks for a fixed number of hops, as sensor nodes are added to the network the overall location accuracy improves converging toward a fixed asymptotic value that is determined by the total number of links to the reference nodes, whereas for a fixed number of links to the reference nodes, the location accuracy of a node decreases the greater the number of hops from the reference nodes. Analytical expressions are derived from one-dimensional networks for these fundamental relationships that are also validated in two-dimensional and three-dimensional networks with simulation and UWB measurement results.     

Empirical comparison of MIMO and beamforming schemes for outdoor-indoor scenarios

We present an empirically based comparative study of spectral efficiency for a variety of transmission systems applicable to a fixed or repositionable wireless environment, in the context of Wi-Fi, WiMAX or MuniNet systems. A narrowband 4×4 Multiple Input Multiple Output (MIMO) channel sounder was constructed and a series of outdoor to indoor measurements were carried out, in multiple locations and with different array configurations. The channel measurements were used to compute the efficiency of different systems that could be deployed in such scenarios, ranging from a full MIMO system with perfect Channel State Information (CSI) at both ends to simple diversity schemes such as classical beamforming. We show comparisons of efficiency for the different transmit/receive configurations operating in a representative variety of locations. Our results indicate that for low values of signal to noise ratio (SNR), in the range of 5dB, such as found in strong interference scenarios, simple schemes can achieve median spectral efficiencies as high as 80% of that of MIMO with complete CSI.