SummaryAlthough establishing correct and efficient routes is an important design issue in mobile ad hoc networks (MANETs), a more challenging goal is to provide energy efficient routes because mobile nodes' operation time is the most critical limiting factor. This article surveys and classifies the energy-aware routing protocols proposed for MANETs. They minimize either the active communication energy required to transmit or receive packets or the inactive energy consumed when a mobile node stays idle but listens to the wireless medium for any possible communication requests from other nodes. Transmission power control approach and load distribution approach belong to the former category, and sleep/power-down mode approach belongs to the latter category. While it is not clear whether any particular algorithm or a class of algorithms is the best for all scenarios, each protocol has definite advantages/disadvantages and is well suited for certain situations. The purpose of this paper is to facilitate the research efforts in combining the existing solutions to offer a more energy efficient routing mechanism.

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In interference-rich and noisy environment, wireless communication is often hampered by unreliable communication links. Recently, there has been active research on cooperative communication that improves the communication reliability by having a collection of radio terminals transmit signals in a cooperative way. This paper proposes a medium access control (MAC) algorithm, called Cooperative Diversity Medium Access Control (CD-MAC), which exploits the cooperative communication capability to provide robust communication in wireless ad hoc networks. In CD-MAC, each terminal proactively selects a relay and lets it transmit simultaneously whenever necessary, mitigating interference from nearby terminals and thus improving the network performance. The proposed CD-MAC algorithm is designed based on the widely adopted IEEE 802.11 MAC for practicality. For accurate evaluation, this study presents and uses a realistic reception model by taking bit error rate (BER), derived from Intersil HFA3861B radio hardware, as well as frame error rate (FER) into consideration. System-level simulation study shows that CD-MAC significantly outperforms the original IEEE 802.11 MAC in terms of packet delivery ratio. Index Terms-Wireless ad hoc network, cooperative diversity, cooperative transmission, relay selection. ).Function (DCF) in IEEE 802.11 standard [6], a node can be regarded as a greedy adversary to other nodes in its proximity as they compete with each other to grab the shared medium, interfere each other's communication, and cause collisions. At the physical layer, a node's data transfer not only provides interference to other nodes depriving their opportunity of using the medium but also incurs energy wastage by rendering them to overhear.Recently, there has been active research in developing cooperative MAC algorithms, where nodes cooperate to accomplish the path-centric medium access rather than hop-centric [2], to salvage a collided packet for each other's behalf at the MAC layer [35], and so on. On the other hand, cooperative communication at the PHY layer attracts a lot of researchers' attention as well [1, 3-5] because it makes communication links more reliable. It refers to scenarios in which distributed radios interact with each other to jointly transmit information in wireless environments [4]. In other words, cooperative communication exploits diversity offered by multiple users, known as cooperative diversity, and improves the bit error rate (BER) dramatically, resulting in more reliable transmission and higher throughput. It is important to note that the primary motivation of cooperative diversity is to improve link reliability over wireless fading channels rather than lengthen the transmission range [3][4][5].There are two types of cooperative diversity algorithms: repetition-based and space-time-coded [13]. The former consists of the sender broadcasting its transmission both to its receiver and potential relays (or partners) and the relays repeating the sender's message individually on orthogonal channels (frequ...

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Recently, researchers have discovered that many of social, natural and biological networks are characterized by scale-free power-law connectivity distribution and a few densely populated nodes, known as hubs. We envision that wireless communication or sensor networks are directly deployed over such real-world networks to facilitate communication among participating entities. Here nodes move in such a way that they exhibit scale-free connectivity distribution at any instance, which cannot be modeled by most of the prior mobility models such as random waypoint (RWP) mobility model. This paper proposes clustered mobility model (CMM), which facilitates in forming hubs in a network satisfying the scale-free property. We call this a scale-free wireless network (SFWN). In CMM, it is possible to control the degree of node concentration or non-homogeneity to easily assess the strengths and weaknesses of the scale-free phenomena. To the best of the authors' knowledge, there has been no such mobility model reported in the literature and we believe the proposed CMM can be usefully used to investigate the properties of the SFWNs that are likely to occur in a real deployment of wireless multihop and sensor networks. Another important feature of CMM is that it does not possess any unintended spatial and temporal characteristics found in other mobility models such as RWP. Finally, to highlight the difference between a SFWN and a conventional wireless network, extensive simulation study has been conducted to measure network capacities at the physical, link and network layers.Index Terms-Connectivity distribution, mobility model, network capacity, random waypoint mobility, scale-free wireless networks.