A generalized energy consumption analysis in multihop wireless networks

We study the performance metrics associated with TCP-regulated traffic in multi-hop wireless networks that use a common physical channel (e.g., IEEE 802.11). In contrast to earlier analyses, we focus simultaneously on two key operating metrics - the energy efficiency and the session throughput. Using analysis and simulations, we show how these metrics are strongly influenced by the radio transmission range of individual nodes. Due to tradeoffs between the individual packet transmission energy and the likelihood of retransmissions, the total energy consumption is a convex function of the number of hops (and hence, of the transmission range). On the other hand, the TCP session throughput decreases supra-linearly with a decrease in the transmission range. In certain scenarios, the overall network capacity can then be a concave function of the transmission range. Based on our analysis of the performance of an individual TCP session, we finally study how parameters such as the node density and the radio transmission range affect the overall network capacity under different operating conditions. Our analysis shows that capacity metrics at the TCP layer behave quite differently than corresponding idealized link-layer metrics.

Network coding data distribution technology between streams of emergency system based-wireless multi-hop network

Due to the increasing number of wireless devices, the issue of energy efficiency that requires high data rate with reliability has spawned tremendous research interests in recent years. In wireless networks, major problem that needs to be addressed is that multihop transmission, though requiring lower transmit power, incurs more circuit energy consumption than that of single-hop transmission and leads to more bit errors. Thus we are motivated to study the energy efficiency of multihop wireless networks with unreliable links, where such a problem is even more serious. Specifically, with a flat Rayleigh fading channel, our network model jointly considers the transmit energy and circuit energy, and characterizes the unreliability caused by the wireless nature with the assumption of probabilistic links. Based on that, we formulate our problems of energy consumption normalized by the source-destination (S-D) path loss, and derive the optimal set of signal-to-noise ratios in each hop to minimize the normalized energy consumption. In addition, our theoretical results exhibit a clear relation between the normalized energy consumption and the delay constraint, and meanwhile disclose the crucial impact that the circuit energy has on the monotonicity of the normalized energy consumption. More specifically, we find that the normalized total energy consumption with the delay constraint decreases as the number of hops increases when the number of hops is small, and increases as the number of hops increases when it is large. Extensive simulations confirm the theoretical results. Our findings shed light on the design, implementation, and operation of real-world energy-efficient multihop wireless networks.

In this study we investigate the interaction between TCP and MAC layer in a wireless multi-hop network. This type of network has traditionally found applications in the military (automated battlefield), law enforcement (search and rescue) and disaster recovery (flood, earthquake), where there is no fixed wired infrastructure. Wireless "ad-hoc" multi-hop networks have previously been proposed for nomadic computing applications. Key requirements in all the above applications are reliable data transfer and congestion control, features that are generally supported by TCP. Unfortunately, TCP performs on wireless in a much less predictable way than on wired protocols. Using simulation, we provide new insight into two critical problems of TCP over wireless multi-hop. The first is the conflict between data packets and ACKs, which causes TCP performance to degrade for window sizes greater than 1 packet. The second is the interaction between MAC and TCP layer backoff timers which causes severe unfairness and capture conditions. In the paper, we identify these problems in several representative simulation runs on various topologies and traffic patterns and indicate possible remedies to improve TCP efficiency over a wireless multi-hop network.

This paper addresses the Quality of Service (QoS) degradation problem of wireless relay node failures in multihop Worldwide interoperable Microwave Access (WiMAX) and Long Term Evolution (LTE) networks. In general, node protection in a communication network increases the reliability of the traffic flow from source to destination. For wireless networks, implementing the traditional 1+1 protection scheme increases the capital cost, as resources cannot be fully utilized. On the other hand, the design and implementation of the 1:N protection scheme in wireless networks for greater value of N (> 2) is very difficult, due to wireless network coverage and the physical layer design. To overcome the above drawbacks, a technique based on network coding is proposed for node protection in multihop wireless networks. In multihop wireless networks, few research efforts are concentrated on node protection schemes using network coding. Moreover, to best of our knowledge, no reports have been published on measuring the QoS performance for node protection in 4G wireless networks using network coding. In this paper, we first describe the node protection scheme using XOR network coding for multihop 4G wireless networks. Then, we measure the QoS performance, such as packet delivery ratio (PDR), latency and jitter, for different scenarios. The scenarios include a failure of a single relay node and failures of two relay nodes with and without our protection scheme and user's mobility. The simulation results show that the QoS performance with protection against a single relay node failure and failures of two relay nodes are very close to that of no failure scenario, while the network reliability increases due to the protection mechanism. Also, we report a decoding problem in multihop wireless networks using XOR network coding.

While TCP is highly successful in the wire-line Internet, its performance fast degrades as the number of hops increases in multihop wireless networks It is due to not only the half-duplex nature of the wireless medium, but also the two-way feature of TCP In order to improve TCP performance in multihop wireless networks, we pay attention to its cumulative ACK policy Systematically exploiting the redundant nature of the ACK policy, we replace some ACKs with data packets We call this scheme block acknowledgement In consequence, the throughput is significantly increased at the slight weakening of ACK reliability We evaluate the performance of TCP with and without the block acknowledgement through simulations and analysis.

We investigate the impact of symbol rate control, modulation level control, and the number of hops on the area spectral efficiency of interference-limited multihop radio networks. By controlling symbol rate and modulation level, data rate can be adapted according to received power. In addition, varying the number of hops can control received power. First., we evaluate the achievable end-to-end throughput of multihop transmission assuming symbol rate and modulation level control. Numerical results reveal that by controlling symbol rate or using multihop transmission, the end-to-end communication range can be extended at the cost of end-to-end throughput, and this may result in lower area spectral efficiency. Next, an expression for the area spectral efficiency of multihop radio networks is derived as a function of the number of hops and the end-to-end throughput. Numerical results also reveal that the resulting area spectral efficiency depends on the specific circumstances, which, however, can be increased only by using multihop transmission.

Consider a wireless multihop network where nodes are randomly distributed in a given area following a homogeneous Poisson process. The hop count statistics, viz. the probabilities related to the number of hops between two nodes, are important for performance analysis of the multihop networks. In this paper, we provide analytical results on the probability that two nodes separated by a known euclidean distance are k hops apart in networks subject to both shadowing and small-scale fading. Some interesting results are derived which have generic significance. For example, it is shown that the locations of nodes three or more hops away provide little information in determining the relationship of a node with other nodes in the network. This observation is useful for the design of distributed routing, localization, and network security algorithms. As an illustration of the application of our results, we derive the effective energy consumption per successfully transmitted packet in end-to-end packet transmissions. We show that there exists an optimum transmission range which minimizes the effective energy consumption. The results provide useful guidelines on the design of a randomly deployed network in a more realistic radio environment.

In many networks there is a necessity to transmit data packets flows, the intensity of which exceeds the throughput of one channel SpaceWire, GigaSpaceWire, SpaceFibre. This flow can be a packet flow from a single source to a single destination, for example, from a camera to a monitor. Also, a packet flow can include packets from different sources to different destinations that goes via two neighboring routers. An example is transmission of packets between two routers located on the boundaries of neighboring regions. The packets, belonging to one flow can have almost same length (transmission of uncompressed video), or quite different length (transmission of compressed video, transmission of packets with different content between two regions). The adaptive routing can be used for transmission of such packet flows. This mechanism includes in SpaceWire standard. A set of alternative output ports (a group of ports) can be determined in routing table for the logical (or regional address). Any output port from this group (if connection for this port is established and port is not occupied by other packet) may be used for transmission of packet with this address. Thus, the summary throughput of all ports belongs to the group can be used for transmission of data packets with this address. However, the possibility of parallel transmission of packets from this flow to different output ports belongs to the group is required for effective utilization of this summary throughput. If the length of packets may be different or if the quantity of input ports for considered flows is not equal to the quantity of output ports in the group, the router should include special mechanisms to ensure efficient parallel transmission of packets to all ports belongs to the group. Adaptive routing for intensive data flows transmission can be implemented not only in SpaceWire/GigaSpaceWire networks, but also in SpaceFibre networks. We consider the specific of its implementation taking into account the features of data link layer (virtual channels with a fairly large buffers, retry mechanism) In this paper we discuss possible implementations of these mechanisms for SpaceWire, GigaSpaceWire and SpaceFibre, estimate achievable bandwidth utilization of port's group, the overhead of the implementation of these mechanisms for packets flows with different characteristics. A side effect of adaptive routing is a possible mismatch of the order in which packets are sent to the network form the source and the order of their receipt by destination. We evaluate the packet's window size that required in the destination node for recovery order of packets and the associated delays. The ports of router belonging to the same group may be connected to one or several different routers (according to the standard). In the first case all packets from the flow will be transmitted via one chain of routers (via one path via network). In the second case, they will be transmitted through the network in different ways. The reordering of packets is possible in both cases. However, in the first case, the mechanisms, that prevent the packets reordering, can be implement in routers. But its implementation can lead to decrease of throughput utilization, to additional hardware costs and to increase of packet's transmission time. In the paper we estimate these overheads for data packets flows with different parameters.

A Generic Algorithm to Improve the Performance of Wireless Sensor Network Protocol

We present concatenated random parity forwarding technique that enables the network coding gain to increase with each additional hop in wireless multi-hop networks of multiple sources, multiple relays, and single destination. The increased network coding gain allows the nodes closer to the destination to reduce their transmit power. This feature is particularly useful in many-to-one type multi-hop wireless networks, where nodes located closer to the destination are expected to relay more data, and hence consume more energy. The proposed approach can compensate for this increased energy consumption by the enhanced network coding gain for the nodes closer to the destination. The parity bits are generated independently and randomly at the relays from some finite field, and forwarded to the next node. This makes the protocol overhead minimal in coordinating the relay nodes and enables a decentralized network operation. Also, it allows relay nodes to be easily added with little overhead as the network scale increases. The presented model incorporates random distribution of nodes in the network. We analyze the probability of decoding error and the network coding gain as a function of the the number of hops and network configurations.

Wireless multi-hop local area networks use in general scheduling schemes that assume the network capacity to be known. Indeed in most of the throughput-optimal algorithms the sources are assumed to send at a rate within the capacity region. However, measurements made on real deployments show that the network capacity is usually difficult to characterize and also time-varying. It is therefore important to understand how the network behaves when the sources attempt to transmit at a rate above capacity. Toward this goal, we show 3-phase regime in the effect of the input rate λ on the end-to-end throughput μ of a multi-hop network. First, when λ is smaller than a threshold λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> , μ is an increasing function of λ. Second, when λ is larger than another threshold λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> > λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> , μ is independent of λ. Third, when λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> <; λ <; λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , μ decreases with λ. To understand this phenomenon, we capture the relation between the end-to-end throughput and the queue stability with a mathematical model that allows us to explain and derive the exact values of the transition points λi. We then validate experimentally our simulation results with measurements on a testbed composed of five wireless routers.

Algorithms for minimum-energy routing in wireless networks typically select minimum cost multihop paths. In scenarios where the transmission power is fixed, each link has the same cost and the minimum hop path is selected. In situations where the transmission power can be varied with the distance of the link, the link cost is higher for longer hops; the energy aware routing algorithms select a path with a large number of small distance hops. In this chapter, we argue that such a formulation based solely on the energy spent in a single transmission is not able to find minimum energy paths for end to end reliable packet transmissions. The proper metric should include the total energy (including that expended for any retransmissions necessary) spent in reliably delivering the packet to its final destination. We first examine how link error rates affect this retransmission aware metric, and how it leads to an efficient choice between a path with a large number of short distance hops and another with a smaller number of large distance hops. Such studies motivate the definition of a link cost that is a function of both the energy required for a single transmission attempt across the link and the link error rate. This cost function captures the cumulative energy expended in reliable data transfer, for both reliable and unreliable link layers. Through detailed simulations, we show that such schemes can lead to up to 30-70% energy savings over best known current schemes, under realistic environments. We next describe how these techniques can be applied to work with on demand routing protocols. In particular, we focus on one specific on demand routing protocol, namely Ad hoc On Demand routing protocol (AODV), and show how it should be adapted to compute energy efficient reliable paths. We perform a detailed study of the AODV protocol and our energy efficient vari ants, under various noise and node mobility conditions. Our results show that even in low noise environments there are specific scenarios where an unmodified on demand protocol will achieve significantly lower throughput in comparison to our modified variants. Our results show that our proposed variants of on demand routing protocols can achieve between 10% to orders of magnitude improvement in energy efficiency of reliable data paths.

Adaptive per hop differentiation for end-to-end delay assurance in multihop wireless networks

Network Coding (NC) has been a solution scheme for data exchange in communications that amalgamate data packets, especially in multi-hop wireless networks. Existing studies demonstrated the use of NC in wireless networks by evaluating its key advantages. The store-code-forward approach of network coding at relay nodes brings out the most relevant benefits in the performance metrics, such as power, throughput, and goodput in communication. COPE is a fundamental protocol, which exploits link diversity and the broadcast nature of a wireless medium using the XOR criteria for data packet amalgamation. COPE is unsuccessful in the exploration of maximum compatibility packets through which opportunistic routing can be maximized. Hence, to identify maximum compatibility packets at relay nodes, the paper presents the uses of Artificial Bee Colony (ABC) optimization algorithm integrated with shortest path planning technique for optimal routing. The authors have successfully demonstrated the validation of Routing-aware Heuristic-based Opportunistic Network Coding (RHONC) mechanism in the multi-hop wireless network. The paper evaluates the proposed mechanism, and enhances throughput gain, goodput gain, and reduced energy consumption against COPE.