Green multi-hop cooperative wireless communication with signal space diversity

The cooperative communication in wireless multi-hop networks is a reliable energy efficient mechanism that mitigates the effects of channel fading and improves the performance and throughput of the systems. In this paper, green cooperative multi-hop scheme is proposed by employing signal space diversity (SSD). The proposed scheme offers a significant improvement in performance of the regenerative multi-hop networks without the requirement of extra bandwidth or power. The expressions for the average end to end bit error probability of the multi-hop networks employing the SSD scheme is derived. The optimal relay location for a better performance and the total energy consumption of the scheme is also probed. The simulation results show that the proposed scheme provides better quality of service and is more energy efficient compared to the conventional decode and forward scheme in single-hop as well as multi-hop situations.     

A cross-layer protocol for exploiting cooperative diversity in multi-hop wireless ad hoc networks

Cooperative communication has emerged to reap the benefits of spatial diversity. To fully exploit cooperative diversity, we propose a medium access control and routing enabled cross-layer cooperative transmission (MACR-CCT) protocol for improving the performance in multi-hop wireless ad hoc networks (MWAN). Different from previous cooperative protocols that determine a receiver in one hop according to a non-cooperative routing protocol first and then select a cooperative relay, MACR-CCT selects the cooperative relay together with the receiver in one hop to exploit fully cooperative diversity, so that the receiver is selected for higher cooperative gain and closer distance to destination, and the relay is selected to achieve the better throughput performance while considering transmission error. Furthermore, considering that there are multiple source–destination pairs in MWAN, MACR-CCT takes interference mitigation into account to further improve network throughput when selecting the cooperative relay. Besides, we propose a theoretical model to analyze the throughput performance. Finally, we take advantage of simulation results to validate the effectiveness of our analytical model and show that our proposed MACR-CCT protocol can significantly outperform existing packet transmission mechanisms in terms of throughput and delay under the multi-hop multi-flow network scenario.     

Efficient broadcasting in multi-hop wireless networks with a realistic physical layer

Almost all existing broadcasting algorithms assume an ideal physical layer, in which a successful transmission is guaranteed if the distance between communicating nodes is less than a certain threshold, e.g., a transmission range. However, wireless communication links normally suffer from the characteristics of realistic physical layer, which significantly reduce the reliability of broadcasting among the nodes. This work addresses the minimal broadcasting problem in multi-hop wireless networks with a realistic physical layer. Given a probability p^*, the problem is to design a distributed broadcasting algorithm such that each node in the network receives the broadcasting packet with probability no less than p^* and the number of retransmissions is minimized. We show that this problem is NP-hard and propose a distributed greedy algorithm which maximizes the gain cost ratio at each node. We prove that the proposed algorithm guarantees that each node receives the broadcasting packet with probability no less than p^*, and analyze upper bound on the number of total retransmissions in the network. Simulation results show that our algorithm can provide near 100% coverage to the wireless network with a realistic physical layer, and reduce the number of retransmissions compared with modified traditional flooding schemes k-Flooding (pure flooding with multiple times) and ACK-Flooding (pure flooding with acknowledgement). We believe our algorithmic solution is efficient and practical for general existing multi-hop wireless networks.     

On the connectivity of wireless multi-hop networks with arbitrary wireless channel models

Considering a wireless multi-hop network where a total of n nodes are randomly, independently and uniformly distributed in a unit square in R² and each node has a uniform transmission power, a fundamental problem is to investigate the connectivity of such networks. In this letter, we prove that the probability of having a connected network and the probability of having no isolated node asymptotically converges to the same value as n goes to infinity for an arbitrary wireless channel model satisfying certain intuitively reasonable conditions.     

Coded diversity for cooperative MISO based wireless sensor networks

Motivated by the recent works on cooperative MIMO, this letter presents a coded diversity based cooperative protocol for wireless sensor networks. In densely deployed sensor networks, nearby nodes form a cluster of virtual antenna array to provide independent fading paths. The source node encodes the information bits with any channel code and forwards a portion of the codeword towards the cooperating nodes. The source and the cooperating nodes transmit different portion of the codeword to achieve a coded diversity at destination. Analysis and simulation show that our proposal can achieve full diversity when code rate is below a certain threshold.     

Distributed space-time-coded protocols for exploiting cooperative diversity in wireless networks

We develop and analyze space-time coded cooperative diversity protocols for combating multipath fading across multiple protocol layers in a wireless network. The protocols exploit spatial diversity available among a collection of distributed terminals that relay messages for one another in such a manner that the destination terminal can average the fading, even though it is unknown a priori which terminals will be involved. In particular, a source initiates transmission to its destination, and many relays potentially receive the transmission. Those terminals that can fully decode the transmission utilize a space-time code to cooperatively relay to the destination. We demonstrate that these protocols achieve full spatial diversity in the number of cooperating terminals, not just the number of decoding relays, and can be used effectively for higher spectral efficiencies than repetition-based schemes. We discuss issues related to space-time code design for these protocols, emphasizing codes that readily allow for appealing distributed versions.     

On the complexity of cooperative peer-to-peer repair for wireless broadcasting

The well-known NAK implosion problem for wireless broadcast can be addressed by leveraging cooperative peer-to-peer connectivity to repair corrupted data. This paper studies the cooperative peer-to-peer repair (CPR) framework for multimedia broadcast. We show that CPR can be formulated as an optimization problem that minimizes the number of iterations it takes to wirelessly disseminate a desired message from peers with the content to peers without it. Complicating the problem are transmission conflicts, where pre-specified sets of links cannot simultaneously transmit due to interference. In this paper, we formalize the CPR minimum delay problem and prove that it is NP-hard     

Relay ordering in a multi-hop cooperative diversity network

In this paper, we first propose an optimum relay ordering algorithm for the multi-branch multi-hop cooperative diversity networks. This optimum algorithm has a high complexity that makes it hard to implement. Therefore, a suboptimum relay ordering algorithm, which considerably reduces the complexity, is then developed. Furthermore, for a cooperative network with two relays, we analytically evaluate the performance of the suboptimum algorithm by using an approximate end-to-end signal-to-noise ratio expression. Specifically, an approximate probability of wrong selection and an approximate expression of the symbol error rate are derived. The analysis and the numerical results demonstrate that the suboptimum algorithm performs very well as the optimum one at a much lower complexity.     

Capacity of FH wireless multi-hop networks

In this article, the capacity of wireless multi-hop networks with the frequency hopping (FH) technique is derived. Different from the previous work based on non- spread spectrum (SS) system, this study is based on frequency hopping spread spectrum (FHSS) and the retransmission mechanism. The analysis results show that the normalized transport capacity decreases as 1/(Mλ) , when the total available frequency band is divided into M sub-bands for frequency hopping and the nodes are randomly distributed in space according to a Poisson point process with intensity λ . In this work, the best transmission range per hop to get the maximum capacity is also derived. Besides, the results summarize how the capacity of FH wireless multihop networks is affected by the outage probability, target signal to interference plus noise ratio (SINR) and other system parameters.     

Segment cooperation communication in multi-hop wireless networks

Cooperative communication could enhance the performance of wireless communications by allowing nodes to cooperate with each other to provide spatial diversity gain. In cooperative communications, rational helper selection is an important issue to obtain good cooperative gain at destinations. There are many works on this topic; however, most of them are based on hop-by-hop model and few works investigate how to select helpers for the nodes in a multi-hop path to optimize the end-to-end performance. The helper selection for one node could affect the helper selection for other nodes on the same route and in turn affect end-to-end performance. In other words, the traditional hop-by-hop helper selection methods could not lead to optimal performance in multi-hop environments. To solve this, this paper firstly defines a novel cooperation mode, named segment cooperation, and deduces the capacity and outage probability of cooperation segment. Then new performance metrics, end-to-end capacity and end-to-end outage probability, are defined to measure the end-to-end performance of multi-hop route. Finally, a segment cooperation method is proposed to maximize these metrics.     

Efficient geocasting with multi-target regions in mobile multi-hop wireless networks

Geocasting, a variation on the notion of multicasting, is a mechanism to deliver messages of interest to all nodes within a certain geographical target region. Although several geocasting protocols have already been proposed for multi-hop wireless networks, most of these algorithms consider a “single” target region only. Here, when more than one target regions need to receive the same geocast messages, multiple transmissions need to be initiated separately by the message source. This causes significant performance degradation due to redundant packet transmissions, and it becomes more severe as the number of target regions increase. To solve this problem, we propose a basic scheme and its variations which utilize the geometric concept of “Fermat point” to determine the optimal junction point among multiple geocast regions from the source node. Our simulation study using ns-2 shows that the proposed schemes can effectively reduce the overhead of message delivery while maintaining a high delivery ratio in mobile multi-hop wireless networks.     

Distributed fault-tolerant topology control in wireless multi-hop networks

In wireless multi-hop and ad-hoc networks, minimizing power consumption and at the same time maintaining desired properties of the network topology is of prime importance. In this work, we present a distributed algorithm for assigning minimum possible power to all the nodes in a static wireless network such that the resultant network topology is k-connected. In this algorithm, a node collects the location and maximum power information from all nodes in its vicinity, and then adjusts the power of these nodes in such a way that it can reach all of them through k optimal vertex-disjoint paths. The algorithm ensures k-connectivity in the final topology provided the topology induced when all nodes transmit with their maximum power is k-connected. We extend our topology control algorithm from static networks to networks having mobile nodes. We present proof of correctness for our algorithm for both static and mobile scenarios, and through extensive simulation we present its behavior.     

Neighbor caching in multi-hop wireless ad hoc networks

We propose a neighbor caching strategy to overcome the overhead of multi-hop wireless communications. Neighbor caching makes a node able to expand its caching storage instantaneously by storing its data in the storage of idle neighbors. We also present the ranking based prediction that selects the most appropriate neighbor which data can be stored in. The ranking based prediction is an adaptive algorithm that adjusts the frequency of neighbor caching and makes neighbor caching flexible according to the idleness of nodes.     

On optimum selection relaying protocols in cooperative wireless networks

In this letter, the outage probabilities of selection relaying protocols are analyzed and compared for cooperative wireless networks. It is assumed that both source and relay use equal allocated time in transmission. Depending on the quality of the source-relay channel, the relay may choose either Decode-and-Forward (DF), Amplify-and-Forward (AF), or Direct-Transmission (DT) to forward signals. It turns out that in terms of outage probability, two selection relaying schemes are better than others: selecting between DF and AF protocols (DF-AF) or selecting between DF and DT protocols (DF-DT). It is shown that with an equal power allocation, both of the DF-AF and DF-DT selection relaying protocols have the same asymptotic outage probability. However, with an optimum power allocation strategy, the DF-AF selection scheme is in general better than the DF-DT selection scheme. Note that the optimum power allocations depend on channel variances, not on instantaneous channel gains. When the quality of the relay-destination link is much better than that of the source-relay link, observed from simulation, the outage probability of the DF-AF selection protocol with its optimum power allocation is 1.5dB better than that of the DF-DT selection with its own optimum power allocation. Extensive simulations are presented to validate the analytical results.     

On enabling cooperative communication and diversity combination in IEEE 802.15.4 wireless networks using off-the-shelf sensor motes

This paper presents the ‘Generalized Poor Man’s SIMO System’ (gPMSS) which combines two approaches, cooperative communication and diversity combination, to reduce packet losses over links in wireless sensor networks. The proposed gPMSS is distinct from previous cooperative communication architectures in wireless sensor networks which rely on a relay channel, and also distinct from implementations in 802.11 networks that require a wired infrastructure or hardware changes for cooperation. gPMSS foregoes the need for any changes to mote hardware and it works within the current IEEE 802.15.4 standard. We describe the gPMSS protocol that governs the cooperation between receivers. Three variants are evaluated including selection diversity, equal gain and maximal ratio combining. First, we demonstrate gPMSS on bit error traces in a fully reproducible manner. This is followed by an implementation of gPMSS in C# on the .NET Micro Framework edition of the recently released Imote2 mote platform. We demonstrate by means of experiments an increase in the packet reception rate from 22–30% to 73–76%, a relative increase of 150–245%. We also analyzed the power consumed by the transmitter per delivered packet and observe a reduction of up to 68%. We also take into account the retry limit of the IEEE 802.15.4 protocol and demonstrate that gPMSS is able to provide 99% packet delivery at the protocol’s default retry parameters against 65–75% without it.     

Efficient delay based scheduling with fairness in multi-hop wireless mesh networks

Some scheduling algorithms have been designed to improve the performance of multi-hop wireless mesh networks (WMNs) recently. However the end-to-end delay is seldom considered as the complexity of multi-hop topology and open wireless shared channel. This article proposes an efficient delay based scheduling algorithm with the concept of buffer-data- hops. Considering the demand satisfaction factor (DSF), the proposed algorithm can also achieve a good fairness performance. Moreover, with the interference-based network model, the scheduling algorithm can maximize the spatial reuse, compared to those graph-based scheduling algorithms. Detailed theoretical analysis shows that the algorithm can minimize the end-to-end delay and make a fair scheduling to all the links.     

Clustering and multi-hop routing with power control in wireless sensor networks

Clustering routing protocols excel in several aspects of wireless sensor networks (WSNs). This article proposes a clustering and multihop routing protocol (CMRP). In CMRP, a node independently makes its decision to compete for becoming a cluster head or join a cluster, according to its residual energy and average broadcast power of all its neighbors. To minimize the power consumption of the cluster head, CMRP sends the data in a power-aware multihop manner to the base station (BS) through a quasi-fixed route (QFR). In addition, CMRP presents a transmission power control algorithm with dynamic intercluster neighbor position estimation (DCNPE) to save energy. Simulation results show that the performance of CMRP is better than the hybrid, energy-efficient, distributed clustering approach (HEED). In the best case, CMRP increases the sensor network lifetime by 150.2%.     

多跳无线网络中一种基于博弈理论的拓扑控制算法

根据博弈论思想为多跳无线网络中的拓扑控制问题设计了一种新颖的收益函数,该收益函数不仅考虑了网络的连接性,而且还考虑了网络的干扰特性和路由性能。理论分析表明,根据此收益函数,网络行为将收敛于一个理想的稳定状态(纳什均衡点),通过最佳响应算法可以求得此稳定状态。     

Flow-balanced routing for multi-hop clustered wireless sensor networks

Power efficiency and coverage preservation are two important performance metrics for a wireless sensor network. However, there is scarcely any protocol to consider them at the same time. In this paper, we propose a flow-balanced routing (FBR) protocol for multi-hop clustered wireless sensor networks that attempts to achieve both power efficiency and coverage preservation. The proposed protocol consists of four algorithms, one each for network clustering, multi-hop backbone construction, flow-balanced transmission, and rerouting. The proposed clustering algorithm groups several sensors into one cluster on the basis of overlapping degrees of sensors. The backbone construction algorithm constructs a novel multi-level backbone, which is not necessarily a tree, using the cluster heads and the sink. Furthermore, the flow-balanced routing algorithm assigns the transferred data over multiple paths from the sensors to the sink in order to equalize the power consumption of sensors. Lastly, the rerouting algorithm reconstructs the network topology only in a place where a head drops out from the backbone due to the head running out of its energy. Two metrics called the network lifetime and the coverage lifetime are used to evaluate the performance of FBR protocol in comparison with previous ones. The simulation results show that FBR yields both much longer lifetime and better coverage preservation than previous protocols. For example, FBR yields more than twice network lifetime and better coverage preservation than a previous efficient protocol, called the coverage-preserving clustering protocol (CPCP) [18], when the first sensor dies and the network coverage is kept at 100%, respectively.