Harlan B. Russell

Energy-efficient transmission and routing protocols for wireless multiple-hop networks and spread-spectrum radios

We describe link and network layer protocols that can conserve energy in store-and-forward packet radio networks. At the link layer, an adaptive-transmission protocol allows the radios to adjust the power in the transmitted signal and the information rate to respond to variations in interference and propagation loss. The network layer protocols are designed to account for the energy requirements of the alternative routes for each source-destination pair. Routing is accomplished using least-resistance routing (LRR) with a metric that includes a measure of the energy consumption.

Routing in frequency-hop packet radio networks with partial-band jamming

Research in adaptive, decentralized routing for frequency-hop packet radio networks with mobile partial-band jamming. A routing technique called least-resistance routing (LRR) is developed, and various versions of this routing method are examined. LRR uses a quantitative assessment of the interference environment experienced by a radios receiver to determine a resistance value for that radio. Two components for the interference environment are considered: transmissions from other radios and partial-band jamming. The resistances for each of the radios in a particular path are combined to form the path resistance, and packets are forwarded on the path with the smallest resistance. Comparisons are made between different versions of LRR and between LRR and previously developed adaptive routing techniques. It is found that LRR is an effective way for dealing with mobile jamming in a frequency-hop packet radio network. Significant increases in throughput and end-to-end probability of success are obtained with LRR. >

Properties of a transmission assignment algorithm for multiple-hop packet radio networks

We study an algorithm, originally defined by Lyui (1991), for assigning collision-free broadcast transmissions for packet radio networks. The method has a number of advantages - it is distributed, fair, permits each terminal to calculate a different frame size, requires only a limited exchange of information, and does not require a contention-based channel-access protocol. These properties make the assignment algorithm particularly useful for dynamic ad hoc networks because the transmission assignments can be easily and quickly adapted to local changes in the topology. An improved description of Lyuis algorithm is given and new simulation results are presented to demonstrate the properties of the transmission assignments for a variety of large networks.

Distributed and adaptive TDMA algorithms for multiple-hop mobile networks

Time-division multiple-access (TDMA) protocols can support contention-free link-level broadcast transmissions in mobile, multiple-hop wireless networks. However, it is typically difficult to adapt TDMA assignments to dynamic topologies. The paper defines and discusses two algorithms for adjusting TDMA slot assignments to the dynamic changes of a mobile network. Our new protocols offer three significant advantages: (1) the information required by the protocols is gathered exclusively from a terminals local neighborhood; (2) global coordination is not required; (3) changes to the state information at a terminal do not need to be distributed to all terminals in the network. The operation of the algorithms is evaluated with an extensive simulation study using a large number of randomly generated networks in which the diameters, degrees, and number of nodes are varied. Results show that the efficiency of the algorithms, determined as the average number of transmission slots assigned per terminal, is better under static conditions than two cases chosen for reference; the efficiency does not degrade significantly under dynamic conditions for which the algorithms continually adjust to added and deleted links. For the networks considered, the algorithms typically converge in times on the order of several hundred slots and a convergence bound approximately four times larger is established. Convergence time is shown to increase in almost a linear fashion with terminal radius and it is relatively insensitive to the number of terminals.

An adaptive-transmission protocol for frequency-hop wireless communication networks

An energy-efficient adaptive-transmission protocol for mobile frequency-hop spread-spectrum wireless communication networks is described and evaluated. The purpose of the protocol is to permit each of the mobile terminals to adjust its transmitter power and code rate to match the characteristics of the time-varying communication links in the network. The proposed adaptive-transmission protocol bases its choice of transmission parameters on a very simple form of side information that is easy to obtain in a FH communication receiver. The performance of the adaptive-transmission protocol is evaluated for networks in which each communication link may have a time-varying propagation loss and intermittent partial-band interference. Our results demonstrate that the adaptive-transmission protocol can improve the utility of a link and reduce energy consumption by adjusting the transmission parameters in response to changes in the side information.

Adaptive transmission protocols for frequency-hop radio networks

The focus of this paper is on the performance of an adaptive transmission protocol for frequency-hop (FH) radio networks in which the radios can adjust the power in the transmitted signal and the rate of a Reed-Solomon code to respond to variations in partial-band interference and propagation loss. The adaptation is based on side information from the FH receiver and on information derived from the decoder. The results presented in this paper are obtained from a simulation of a wireless FH radio network in which the characteristics of the links are time-varying. These results demonstrate that the adaptive transmission protocol can improve the quality of a link by adapting to variations in both path-loss and interference to take advantage of favorable channel conditions.

Energy-efficient routing in frequency-hop networks with adaptive transmission

We describe and evaluate an energy-efficient protocol for routing traffic in frequency-hop (FH) store-and-forward packet radio networks that employ an adaptive transmission protocol. The adaptive transmission protocol allows the radios to adjust the power in the transmitted signal and the rate of a Reed-Solomon code to respond to variations in partial-band interference and propagation loss. Routing is accomplished using least-resistance routing (LRR) with a new metric that provides a quantitative assessment of the ability of a radio to receive and forward packets and includes a measure of the energy that is expected to be required for successful transmission. The new energy metric and LRR are integrated with the adaptive transmission protocol, and the performance of the new protocol suite is evaluated for a distributed FH network. The performance results presented in this paper are obtained from a simulation of wireless FH radio networks in which the characteristics of the links vary with time. The results demonstrate that in FH networks that employ an adaptive transmission protocol, the new method for routing can adapt quickly to changes in interference conditions. We find that LRR with the energy metric works with the adaptive transmission protocol to improve the information throughput and energy efficiency of the network.

Routing for multimedia traffic in wireless frequency-hop communication networks

A new method is described for routing multimedia traffic in a frequency-hop (FH) store-and-forward packet radio network. The method is illustrated for traffic of two types, each type having its own throughput, delay, and error-rate requirements. A typical application is the routing of voice and data packets in a distributed multiple-hop network. In such an application, voice packets cannot tolerate much delay, but they are allowed to contain a small number of frame erasures while data packets must be delivered error-free even if a moderate delay is required to do so. The fully distributed routing protocol presented in the paper takes into account the type of service required for each type of traffic, and it adapts to the interference as seen by the FH radio receivers in the network. Our approach to multimedia routing is based on least-resistance routing with different link and path resistance metrics for different message types. Each of the resistance metrics for a link reflects the ability of the link to provide the service required by the one of the message types. This includes, but is not limited to, a measure of the likelihood of successful reception by the FH radio receiver for that link. The route selection for a particular type of packet depends on the resistances of the links along the routes from that packets source to its destination. In general, different routes may be selected for different types of packets. The primary conclusion of this paper is that the quality of service increases for each of the two types of multimedia traffic if the routing protocol accounts for the type of message that is being relayed.

An adaptive transmission-scheduling protocol for mobile ad hoc networks

Transmission-scheduling protocols can support contention-free link-level broadcast transmissions and delay sensitive traffic in mobile, multiple-hop packet radio networks. Use of transmission-scheduling protocols, however, can be very inefficient in mobile environments due to the difficulty in adapting transmission schedules. The paper defines a new adaptive and distributed protocol that permits a terminal to adapt transmission assignments to changes in topology using information it collects from its local neighborhood only. Because global coordination among all the terminals is not required and changes to transmission assignments are distributed to nearby terminals only, the protocol can adapt quickly to changes in the network connectivity. The two key parameters that affect the ability of the protocol to adapt to changes in connectivity are the rate of connectivity changes and the number of terminals near the connectivity changes. Using simulation, we determine the ranges for these parameters for which our adaptive protocol can maintain collision-free schedules with an acceptable level of overhead. The stability of the protocol is also characterized by showing that the protocol can quickly return to a collision-free transmission schedule after a period of very rapid changes in connectivity. Our channel-access protocol does not require a contention-based random-access phase to adapt the transmission schedules, and thus its ability to adapt quickly does not deteriorate with an increase in the traffic load.

A distributed load-based transmission scheduling protocol for wireless ad hoc networks

This paper presents a load-based transmission scheduling (LoBaTS) protocol for wireless ad hoc networks. Since terminals in these networks may be required to forward unequal amounts of traffic, a transmission scheduling protocol which assigns equal transmission capacity to all terminals may result in traffic bottlenecks as traffic load increases. The LoBaTS protocol allows terminals to alter their existing transmission schedules so that those terminals which are required to forward more traffic can reserve additional transmission slots, thereby alleviating traffic bottlenecks. The LoBaTS protocol is designed to avoid creation of new traffic bottlenecks, maintain collision-free broadcast transmissions, and execute with minimal disruption to the network. In addition, it requires only local information to operate, making it suitable for implementation in a distributed-control environment. Simulations utilizing a variety of test networks and traffic conditions show that the LoBaTS protocol greatly improves end-to-end packet delay, throughput, and completion rate when compared to a transmission schedule which does not account for traffic load.