Multi-hop Transmission In Wireless Networks Research Articles

Distributed Scheduling With Centralized Coordination for Scalable Wireless Mesh Networking

A coordinated carrier sense multiple access (C-CSMA) scheme is developed to schedule packet transmissions in multihop wireless networks. It integrates distributed scheduling and centralized coordination at different time scales. At a small time scale, a distributed scheduling algorithm, which is incorporated into CSMA, runs on each node to determine key parameters for CSMA. These parameters are optimized by ensuring multiple network attributes, i.e., average link date rate, node transmission probability, and the conditional probability of a link being selected for transmission, approaching their corresponding optimal values at a large time scale, e.g., a few seconds. Such optimal values are obtained from a centralized algorithm running on a portal node. The algorithm collects topology, link, and traffic information from the network at a large time scale and determines the attributes above to fulfill the optimal tradeoff between throughput and fairness. Since the distributed algorithm is shepherded by the centralized algorithm, C-CSMA has high scalability: first, it achieves long-term optimal performance with low information collection overhead; second, it schedules packet transmissions in a distributed way and responds quickly to changes in networks. It is proved that network attributes resulting from the distributed scheduling algorithm converge to optimal values provided by the centralized algorithm. Simulation experiments demonstrate that the convergence speed is fast. Moreover, extensive simulation results show that C-CSMA achieves much higher throughput, better fairness, and lower delay than existing scheduling schemes under different carrier sensing thresholds and traffic conditions.

A Novel Relay Selection Scheme Based on Q-Learning in Multi-Hop Wireless Networks

In wireless communication systems, reliability, low latency and power are essential in large scale multi-hop environment. Multi-hop based cooperative communication is an efficient way to achieve goals of wireless networks. This paper proposes a relay selection scheme for reliable transmission by selecting an optimal relay. The proposed scheme uses a signal-to-noise ratio (SNR) based Q-learning relay selection scheme to select an optimal relay in multi-hop transmission. Q-learning consists of an agent, environment, state, action and reward. When the learning is converged, the agent learns the optimal policy which is a rule of the actions that maximize the reward. In other words, the base station (BS) knows the optimal relay to select and transmit the signal. At this time, the cooperative communication scheme used in this paper is a decode-and-forward (DF) scheme in orthogonal frequency division multiplexing (OFDM) system. The Q-learning in the proposed scheme defines an environment to maximize a reward which is defined as SNR. After the learning process, the proposed scheme finds an optimal policy. Furthermore, this paper defines a reward which is based on the SNR. The simulation results show that the proposed scheme has the same bit error rate (BER) performance as the conventional relay selection scheme. However, this paper proposes an advantage of selecting fewer relays than conventional scheme when the target BER is satisfied. This can reduce the latency and the waste of resources. Therefore, the performance of the multi-hop transmission in wireless networks is enhanced.

Toward a Comprehensive Model for Performance Analysis of Opportunistic Routing in Wireless Mesh Networks

Opportunistic routing (OR) is a promising paradigm that has been proposed for wireless mesh networks. This routing paradigm takes advantage of the broadcast nature of the wireless medium to increase the reliability of transmissions in multihop wireless networks. The selection of a set of candidates involves satisfying the basic requirements of the model, in which packets are forwarded toward the destination. In OR, if one of the selected candidates does not receive the packet, another candidate might be able to continue forwarding the packet. The decision of which forwarder to choose is made by coordination between candidates that have successfully received the transmitted packet. In this paper, we propose a discrete-time Markov chain as a general model for OR and demonstrate how it can be used to evaluate the performance of OR protocols. We also review three well-known OR protocols that we have selected as a study case. Our study demonstrates how our model facilitates better understanding of the combination of a number of candidates and retransmissions and their significant contributions to the successful delivery of data packets. Thus, this shows that our model can help in the design of future OR protocols and efficient candidate selection algorithms.

Analytical model of batch flow multihop transmission in wireless networks with channel reservations

The IEEE 802.11s standard of Wi-Fi Mesh networking introduces a novel deterministicchannel access mechanism called MCCA. This mechanism enables stations to reserve certain time intervals for their data transmission. Since each station is informed about the reservations of its neighbor stations, it does not transmit during them, thus leading to less packet losses caused by packet collisions. However, additional packet retransmissions might be required to provide quality of service (QoS) over an imperfect wireless channel. This gives rise to the problem of choosing appropriate MCCA reservation parameters. An analytical model of providing QoS data streaming over a lossy Wi-Fi Mesh network via MCCA was developed. It can be used to find such reservation parameters for which the channel resource consumption is minimal while the QoS requirements are met.

Design of a new scheme for multi-hop wireless networks using decode-and-forward strategy

This paper proposes a Decode-and-Forward (DF) relaying scheme for the multi-hop transmission in wireless networks, where the information generated by an independent source has to be sent to a far destination based on multiple-relay cooperation. The proposed DF scheme blends together convolutional channel coding with linear combination of blocks of data over a finite field using very short block lengths (K=13). We provide an extrinsic information transfer (EXIT) chart analysis to understand the good performance behavior of the proposed scheme when compared with other referenced schemes using much larger block lengths. This fact is corroborated by a set of Monte Carlo simulations. Moreover, the proposed DF scheme is suitable for large multi-hop networks since a negligible performance degradation is obtained when adding more hops.

An Exposed-Terminal-Eliminated Dual-Channel MAC Protocol for Exploiting Concurrent Transmissions in Multihop Wireless Networks

This paper proposes a novel exposed-terminal-eliminated medium access control (ETE-MAC) protocol by combining channel reservation, collision avoidance and concurrent transmissions to improve multi-access performance of the multihop wireless networks. Based on the proposed slot scheduling scheme, each node senses the control channel (CCH) or the data channel (DCH) to accurately determine whether it can send or receive the corresponding packets without collisions. Slot reservation on the CCH can be simultaneously executed with data packet transmissions on the DCH. Therefore, it resolves the hidden-terminal type and the exposed-terminal type problems efficiently, and obtains more spatial reuse of channel resources. Concurrent packet transmissions without extra network overheads are maximized. An analytical model combining Markov model and M/G/1 queuing theory is proposed to analyze its performance. The performance comparison between analysis and simulation shows that the analytical model is highly accurate. Finally, simulation results show that, the proposed protocol obviously outperforms the link-directionality-based dual-channel MAC protocol (DCP) and WiFlex in terms of the network throughput and the average packet delay.

Proteus: Multiflow Diversity Routing for Wireless Networks with Cooperative Transmissions

In this paper, we consider the use of cooperative transmissions in multihop wireless networks to achieve Virtual Multiple Input Single Output (VMISO) links. Specifically, we investigate how the physical layer VMISO benefits translate into network level performance improvements. We show that the improvements are nontrivial (15 to 300 percent depending on the node density) but rely on two crucial algorithmic decisions: the number of cooperating transmitters for each link; and the cooperation strategy used by the transmitters. We explore the tradeoffs in making routing decisions using analytical models and derive the key routing considerations. Finally, we present Proteus, an adaptive diversity routing protocol that includes algorithmic solutions to the above two decision problems and leverages VMISO links in multihop wireless network to achieve performance improvements. We evaluate Proteus using NS2-based simulations with an enhanced physical layer model that accurately captures the effect of VMISO transmissions.

A Classification Framework for Scheduling Algorithms in Wireless Mesh Networks

Scheduling MAC-layer transmissions in multi-hop wireless networks is an active and stimulating area of research. There are several interesting algorithms proposed in the literature in the problem space of scheduling for multi-hop wireless networks, specifically for (a) WiMAX mesh networks, (b) long distance multi-hop WiFi networks, and (c) Vehicular Ad-hoc Networks (VANETs). In general, these algorithms have several dimensions in terms of the assumptions made, the input space considered and the solution space generated. In this context, the goal of this survey is three-fold. Firstly, we classify the scheduling algorithms proposed in the literature based on following parameters: problem setting, problem goal, type of inputs and solution technique. Secondly, we describe different scheduling algorithms based on this classification framework. We specifically cover the state-of-the-art scheduling mechanisms proposed for generic multi-channel, multi-radio wireless mesh networks and in particular scheduling algorithms for WiMAX mesh networks, long distance mesh networks and vehicular ad-hoc networks. We describe scheduling algorithms which consider scheduling data, voice as well as video traffic. Finally, we compare these algorithms based on our classification parameters. We also critique individual mechanisms and point out the practicality and the limitations, wherever applicable. We observe that, the literature in the domain of scheduling for wireless mesh network is quite extensive, in terms of depth as well as breadth. Our classification framework helps in understanding the pros and cons of various aspects of scheduling for wireless multi-hop (popularly known as wireless mesh) networks. We also list desirable properties of any scheduling mechanism and use our classification framework to point out the open research issues in the space of scheduling for wireless mesh networks.

Performance evaluation of split transmission in multihop wireless networks

Multimedia applications in multihop wireless networks have great market potential. Multiple channels and multiple radios are commonly used for exploring multimedia transmissions in multihop wireless networks. Split transmission allows multiple channels attached to different radios simultaneously to be used, and so to achieve a fundamentally improved transmission capacity. The goal of this paper is to present a theoretical background to justify the improved performance of the split transmission. We theoretically study and prove that, by using the split transmission, the worst-case delay is decreased to $\frac{\sigma\rho_{k-1}}{LC_{m-1}C_{k-1}}$ of that without using the split transmission, the average throughput is increased to $\frac{1}{1-\prod_{j=0}^{k-1}\alpha_j}$ of that without using the split transmission, and the average delay jitter is decreased to $\frac{C_{k-1}C_{\rho}}{C_{m-1}[C_{\rho}+L(\rho+C)]}$ of that without using the split transmission. We believe that this is the first attempt to consider split transmission in theory. We also evaluate the performance of the split transmission in ns-2 simulations. The observed results show that the split transmission achieves shorter worst packet delays, higher average throughput, and smaller average delay jitter as compared to the performance achieved without the split transmission.

Exploiting Location Information for Concurrent Transmissions in Multihop Wireless Networks

In a multihop wireless network environment, it has been shown that IEEE 802.11 media access control (MAC) suffers from a low-throughput problem, which is largely due to the inefficiency in carrier sensing and spatial reuse. In this paper, we present a location-assisted MAC protocol that schedules ldquofeasiblerdquo concurrent transmissions in a multihop wireless network. A simple procedure based on location information is adopted in the proposed MAC to validate the feasibility of a concurrent transmission. Our simulation results show that the proposed scheme can effectively increase the throughput and reduce the average end-to-end delay of multihop wireless networks.

On the Optimal Transmission in Multihop Relay Networks over Rayleigh Fading Channels

In this letter we investigate the relaying strategies for multihop transmission in wireless networks over Rayleigh fading channels. Theoretical analysis reveals that equally allocating power among all transmitters and placing relays equidistantly on the line between source and destination are optimal in terms of outage capacity. Then equal time duration for the transmission of each hop is also proved to be optimal. Furthermore, the optimum number of hops is also derived and shown to be inversely proportional to the signal-to-noise ratio (SNR). Numerical simulations agree well with the reported theoretical results.

On Throughput Efficiency of Geographic Opportunistic Routing in Multihop Wireless Networks

Geographic opportunistic routing (GOR) has shown throughput efficiency in coping with unreliable transmissions in multihop wireless networks. The basic idea behind opportunistic routing is to take advantage of the broadcast nature and spacial diversity of the wireless medium by involving multiple neighbors of the sender into the local forwarding, thus improve transmission reliability. The existing GOR schemes typically involve as many as available next-hop neighbors into the local forwarding, and give the nodes closer to the destination higher relay priorities. In this paper, we show that it is not always the optimal way to achieve the best throughput. We introduce a framework to analyze the one-hop throughput of GOR, provide a deeper insight into the trade-off between the benefit (packet advancement and transmission reliability) and cost (medium time delay) associated with the node collaboration, and propose a local metric named expected one-hop throughput (EOT) to balance the benefit and cost. We also identify an upper bound of EOT and its concavity, which indicates that even if the candidate coordination delay were negligible, the throughput gain would become marginal when the number of forwarding candidates increases. Based on the EOT, we also propose a local candidate selection and prioritization algorithm. Simulation results validate our analysis and show that the EOT metric leads to both better one-hop and path throughput than the corresponding pure GOR and geographic routing.

A cross-layer optimization of IEEE 802.11 MAC for wireless multihop networks

Introducing multihop transmission in wireless networks has both pros and cons. It will improve the reliability of each wireless link by reducing the average transmission distance. On the other hand, it will add delay to the end-to-end QoS, which is caused by multiple packet relays. In this letter, we analyze the optimal performance of the IEEE 802.11 based multihop network, by jointly optimizing the carrier-sensing range of CSMA/CA and the target data rate of each wireless link.

A cross-layer optimization of IEEE 802.11 MAC for wireless multihop networks

Introducing multihop transmission in wireless networks has both pros and cons. It will improve the reliability of each wireless link by reducing the average transmission distance. On the other hand, it will add delay to the end-to-end QoS, which is caused by multiple packet relays. In this letter, we analyze the optimal performance of the IEEE 802.11 based multihop network, by jointly optimizing the carrier-sensing range of CSMA/CA and the target data rate of each wireless link.

Cooperative multi-hop transmission in wireless networks

We consider various relaying strategies for wireless networks by comparatively examining direct transmission, conventional relaying, and the novel concepts of cooperative relaying. The latter build...

Cooperative multi-hop transmission in wireless networks

We consider various relaying strategies for wireless networks by comparatively examining direct transmission, conventional relaying, and the novel concepts of cooperative relaying. The latter build on two inherent benefits of relaying systems: the spatial diversity offered by the relay channel, and the ability to exploit the broadcast nature of the wireless medium. Studied cooperative protocols include adaptive decode-and-forward schemes as a simple extension of conventional store-and-forward relaying systems, and more complex decode-and-reencoding schemes that realize distributed coding strategies. We provide a unifying analysis for the tractable two-hop case, before extending the consideration to multi-hop scenarios. The analysis is conducted from the perspective of communication over fading channels under limited bandwidth, energy, and end-to-end delay; main parameters include propagation loss, network geometry, and targeted end-to-end spectral efficiency. Main results indicate that (i) cooperative relaying provides attractive benefits for wireless systems whenever temporal and frequency diversity are scarce or not exploited, (ii) using just two hops is reasonable for many practical scenarios, and (iii) the advantages of the studied relaying schemes decrease for higher desired end-to-end spectral efficiency.