Routing Algorithms for Energy‐Efficient Reliable Packet Delivery in 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.

A general framework for efficient geographic routing in wireless networks

Our objective is to analyze and minimize the amount of energy needed to transmit packets in a multihop wireless network, such as a sensor network or an ad hoc network. The total energy consumed to transmit a packet from a source to a destination is a function of the number of hops along the path and the energy needed to successfully transmit a packet in one hop. Given a path, the number of hops needed depends on the transmission range. The energy consumed for a successful transmission in a hop depends on not only the transmission range but also the medium access strategy. In this paper, we generalize the analysis of the energy consumption on packet transmission in multihop wireless networks. The analysis is applicable to a range of multiaccess schemes from TDM to random access schemes. The results show that typically, there is a transmission range that results in the minimum energy. However, a smaller transmission range does not always lead to less energy consumed by packet transmission. The optimum energy consumption is the result of balancing several factors, including: 1) the ratio of an overhead packet length to a data packet length, where overhead packets refer to the control packets used to reserve the media or the data packets involved in collisions; 2) the number of transmissions of the overhead packets; 3) the number of hops along a path; and 4) the transmission range.

As Wireless Sensor Network (WSN) is spread across wide geographically area, global end-to-end estimates of control parameters can't predict timely reporting of data. However, as packet progresses over multihop WSN, routing decisions may have to be adapted according to changed environment parameters/conditions. Many algorithms lack dynamic adaptability to changed environment conditions. Real Time WSN need to trade off latency, path traversed in number of hops and energy cost as per dynamically changing conditions. Earned Value Management (EVM) is project management technique to trade-off schedule, cost and quality constraint. As part of this work, it is hereby suggested to adapt routing decision at each hop based on Earned Value Management of latency, energy cost and path traversed in number of hops at that time. At initial step, End-to-end estimated values for latency, energy cost and path traversed in number of hops are allocated for each flow. Estimate to complete (ETC) values for all parameters are calculated at each hop and used to decide how much is estimated remaining value of all parameters to reach at the destination. Based on ETC values, routing decisions can be adapted. At the end of delivery, variance with planned value is calculated. This value can be used to refine end-to-end estimates. The whole process can be divided into following steps: Estimate End-to-end values for latency, energy cost, number of hops, Estimate to complete (ETC) - Calculate Estimated Values for latency, energy cost, number of hops to reach at destination., Adapt or refine the control parameters such as speed or transmission power as per ETC values for latency, energy cost, number of hops. If destination can't be reached by adapting control parameters, packets are dropped., Calculate Variance with respect to planned values and refine end-to-end estimates Using Earned Value technique helps in tracking the actual progress made till current time. It helps in taking corrective action early; hence it is more cost effective. It also helps in effective usage of limited resources of WSN by dropping packets which can't reach destination within desired latency.

As distributed information services like the World Wide Web become increasingly popular on the Internet, problems of scale are clearly evident. A promising technique that addresses many of these problems is service (or document) replication. However, when a service is replicated, clients then need the additional ability to find a ``good'''' provider of that service. In this paper we report on techniques for finding good service providers without a priori knowledge of server location or network topology. We consider the use of two principal metrics for measuring distance in the Internet: hops, and round-trip latency. We show that these two metrics yield very different results in practice. Surprisingly, we show data indicating that the number of hops between two hosts in the Internet is {\em not\/} strongly correlated to round-trip latency. Thus, the distance in hops between two hosts is not necessarily a good predictor of the expected latency of a document transfer. Instead of using known or measured distances in hops, we show that the extra cost at runtime incurred by dynamic latency measurement is well justified based on the resulting improved performance. In addition we show that selection based on dynamic latency measurement performs much better in practice that any static selection scheme. Finally, the difference between the distribution of hops and latencies is fundamental enough to suggest differences in algorithms for server replication. We show that conclusions drawn about service replication based on the distribution of hops need to be revised when the distribution of latencies is considered instead.

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.

In this study, we evaluate the statistical characteristics of packet transmission routes and the hops in wireless multi-route and multi-hop network. Although the wireless network is based on cellar system, we consider the use of forwarding nodes for relaying the packets transmitted by user nodes. The network includes use of multiple routes from a user to base stations. Few researches have been done for statistical evaluations on the network, so far. In our route building method, nodes determine the connectivity based on SNR (signal-to-noise power ratio) of received signals. Our model employs free space propagation power loss model to derive SNR. We observe that the number of routes increases with the number of forwarding nodes and their transmit power. On the other hand, the number of hops per route is saturated with increases of those parameters. We conclude that an adequate selection of the parameters enables to suppress the number of hops

The increasing demand for higher data rates pushes the boundaries of the currently used radio spectrum. The terahertz (THz) frequency band (0.1-10 THz) is widely considered by scientific community to address spectrum scarcity. In this paper we developed a theoretical model for device-to-device (D2D) communication operating in THz band. We also derived a close form formula of data rates, outage probability, and energy efficiency. Our simulation results show an improvement of data rates and energy efficiency while decreasing the outage probability of D2D communication in THz. For instance, there is 86% of increase in energy efficiency when the transmission power is 19dBm. Finally, the improvement of energy efficiency is 87% using optimal transmission power due to 50 resource blocks.

Instability of wireless networks and high mobility of vehicles make effective and reliable delivery of packets in VANETs a challenging issue. Anypath routing is proposed to tackle this issue in multi hop VANET communications. Link stability and quality parameters are used in cost metrics proposed for Anypath routing. Both of them prefer near hops in the forwarding set and as a result, the number of hops and delay in Anypath VANET communications are increased. In this paper a new cost metric for Anypath VANET routing is proposed to reduce the hop count and delay and increase the network throughput and the packet delivery ratio. The simulation results indicate superior performance of the proposed cost function over other tested methods such as SAF and LLA.

A significant amount of research on optimal scheduling has focused on the case where links can transmit with only a single bit-rate and a single transmission power. This paper develops techniques to accommodate multiple bit-rates and multiple transmission powers as well as a continuum of transmission powers. Optimizing over a large number of bit-rates and transmission powers typically increases the computed throughput at the expense of increasing the computation time. This paper examines the trade-off between computed throughput and computation time, with emphasis on the case when the relationship between bit-rate and SINR is the same as it is for 802.11a/g. One finding of this paper is a progression of Pareto optimal schemes that increases the computed capacity. A second finding is that optimizing over two transmission powers and two or three bit-rates achieves nearly the same throughput as optimizing over a continuum of transmission powers and all supported bit-rates. However, optimizing over a continuum of transmission powers and all supported bit-rates is far more computationally complex than optimizing over two transmission powers and a few bit-rates.

We have developed a cost-effective wireless multi-hop network system for accessing core networks. Cost-effectiveness can be provided to users by offering them a wireless multi-hop network in which a wireless link enables multiple hops between access points (APs) and reduces the number of APs connected to a wired network. The key issues of wireless multi-hop networks are routing and security. We proposed a hybrid routing for wireless multi-hop networks that combines on-demand and table-driven routing, a packet check scheme between APs, and an authentication scheme. To ensure both correct routing and security, the system makes use of a wireless multi-hop (WM) layer between the IP and medium access control (MAC) layers. This paper evaluates the system based on its FTP throughput, round-trip time, and route creation time. The FTP throughput was about 3.5 Mbps even when there were four hops in an 802.11b wireless LAN. We believe that our wireless multi-hop network system is useful for providing cost-effective broadband access service.

The paper addresses mobility control routing in robotic sensor wireless networks, where either mobile sensors or mobile actuators assist in wireless data intensive transmissions from sensors. Given a communication request between a source destination pair, the problem is to find a route and move each node on the route to its desired location, such that total transmission power is minimized. We study the optimal number of hops and optimal distance of adjacent nodes on the route. We propose OHCR algorithm that is based on the optimal number of hops on the route. We further propose MPoPR algorithm that minimizes transmission power over progress. After finding an initial path, strategies of move in rounds and move directly are both considered to move nodes to desirable locations. Extensive simulations are conducted to evaluate our proposed routing algorithms.

We define a transmission power adaptation-based routing technique that finds optimal paths for minimum energy reliable data transfer in multi-hop wireless networks. This optimal choice of the transmission power depends on the link distance between the two nodes and the channel characteristics. Typical energy efficient routing techniques use a transmission power such that the received signal power at the destination minimally exceeds a desired threshold signal strength level. In this paper we argue that such a choice of the transmission power does not always lead to optimal energy routes, since it does not consider differences in the receiver noise levels.

In underwater acoustic sensor networks (UANs), reliable packet delivery is critical in data collection and monitoring of the oceans. It primarily relies on the design of routing protocols to guarantee network durability and connectivity. However, utilizing routing design to achieve enhanced network longevity and reliable packet forwarding is challenging due to the complex underwater environment, unstable link connectivity, high transmission power, and high propagation latency. Thus, we propose a novel routing strategy called the longevity-oriented and reliable forwarding percolation (LRP) routing protocol. The goal of LRP is to ensure reliability by exploring multipath percolation-based routing and extend network longevity by energy control and residual energy optimization. Network reliability can be estimated using a built-in calculation model, and the source node controls energy and records the residual energy to extend the network lifetime. Utilizing an optimization of the network reliability requirement and residual energy, we develop a routing strategy to select the activated link set and node set for each hop in an energy-saving and reliable way. Moreover, a recursive approach is used to avoid the occurrence of void regions. Simulation results exhibit the effectiveness of the power control and routing strategy and demonstrate its superiority over the benchmarks in terms of network longevity and reliability.

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.