Frederick J. Block

A protocol for adaptive transmission in direct-sequence spread-spectrum packet radio networks

Wireless communication channels may change greatly from one transmission to the next, due to variations in propagation loss and interference. The use of fixed transmission parameters for such channels results in wasted energy when channel conditions are good. Adaptation of the power, code rate, and symbol rate reduces energy consumption and interference caused to other systems. Such adaptation requires information about the characteristics of the channel, which is more difficult to obtain in a packet radio network (PRN) or other mobile ad hoc network than in a typical cellular communication system. We develop methods for providing partial information about the channel state from three statistics that are derived by different subsystems in the receiving terminals of a direct-sequence spread-spectrum PRN. We present and evaluate a protocol that uses this information to adapt the transmission parameters in response to changes in interference and propagation conditions in the network. The performance of the new adaptive-transmission protocol is compared with a system with fixed transmission parameters and with an adaptive protocol that is furnished with perfect knowledge of the channel state at the completion of each transmission.

An energy-efficient routing protocol for wireless sensor networks with battery level uncertainty

A wireless microsensor network consists of a large number of low-cost nodes communicating with a base station. The nodes have limited energy and short transmission ranges. By employing estimates of the remaining battery energy in routing, the use of radios nearing energy exhaustion can be discouraged. Knowledge of the rate at which a node is consuming its energy provides additional useful information. This paper investigates novel routing metrics that incorporate both kinds of information to improve network performance. Also, in practice, there may be some error in a nodes estimate of its battery level. The metrics are designed to explicitly account for uncertainty in remaining energy. Numerical results using several statistical models for this uncertainty show that the proposed metrics outperform a variety of alternatives.

Energy-efficient self-organizing communication protocols for wireless sensor networks

A challenge in the design of wireless microsensor networks is the preservation of battery life in the microsensor nodes. Energy is expended not only in transmitting packets, but also in listening to the channel. This paper presents energy-preserving channel-access and routing protocols for self-organized communication in a wireless microsensor network containing a large number of low-cost nodes and a base station. The routing protocols are designed to use the remaining energy of the radios in making routing decisions. Performance is compared to a protocol that does not utilize energy information.

Design considerations for next-generation airborne tactical networks

Airborne tactical networks (ATNs) have provided protected air-to-air communications for military aircraft for several decades. To support emerging and future warfighter needs, the next generation of systems will require significant improvements to provide higher capacity, longer range, greater flexibility, and increased interoperability. Governed by domain characteristics such as long transmission ranges, low-to-medium data rates, latency constraints, and link protection needs, the air tactical domain poses several unique requirements on link and network design. Developing next-generation ATNs requires an understanding of the airborne tactical domain, including the design constraints and challenges at various layers of the network stack. In this article, we provide an overview of the unique domain characteristics of ATNs and highlight the key design challenges and research areas associated with the physical, link, and network layers.

Information for routing in energy-constrained ad hoc networks

Abstract In wireless ad hoc networks consisting of battery-limited nodes, communication protocols must be energy-aware to prevent early network failure due to radios exhausting their energy supplies. Incorporating current estimates of battery levels into routing metrics has been shown to reduce the demand on radios with little remaining energy and allow them to participate in the network longer. In addition to knowledge of current battery levels, estimates of how quickly radios are consuming energy may also be helpful in extending network lifetime. We present a family of routing metrics that incorporate a radio’s rate of energy consumption. Simulation results show that the proposed family of metrics performs well under a variety of traffic models and network topologies.

Parallel acquisition of multicarrier direct-sequence spread-spectrum signals

The frequency diversity of multicarrier direct-sequence signaling can potentially offer robust performance in frequency-selective channels. This paper focuses on the acquisition of multicarrier signals. The maximum-likelihood decision rule for parallel acquisition in frequency-selective fading is derived. Methods for acquisition with a limited number of correlators are also discussed. The performance is compared to that of single-carrier systems, where the effects of acquisition on error rates are determined. Results show that the multicarrier system can give slightly better performance.

Parallel acquisition of multicarrier direct-sequence spread-spectrum signals in fading and partial-band interference

The frequency diversity of multicarrier direct-sequence signaling can potentially offer robust performance in frequency-selective channels. The paper focuses on the acquisition of multicarrier signals in channels containing fading and partial-band interference. The maximum-likelihood decision rule for parallel acquisition in frequency-selective fading and partial-band interference is derived. Several simpler, near-optimal decision rules are also discussed. The performance of these decision rules is compared to that of equal-gain combining for multicarrier acquisition. Results show that the decision rules designed specifically for partial-band interference give significantly better performance. Methods of acquisition with a limited number of correlators are also discussed. Finally, the potential benefits of estimating the signal strength on each subcarrier prior to acquisition are examined.

An adaptive-transmission protocol for direct-sequence spread-spectrum packet radio networks

Wireless communication channels may change greatly from one transmission to the next due to variations in propagation loss and interference. The use of fixed transmission parameters for such channels results in wasted energy when channel conditions are good. Adaptation of the power, code rate, and symbol rate reduces energy consumption and interference caused to other systems. Such adaptation requires information about the characteristics of the channel, which is more difficult to obtain in a packet radio network or other mobile ad hoc network than in a typical cellular communication system. We present techniques to provide partial information about the channel state, and we describe and evaluate a protocol that uses this information to adapt the transmission parameters in a direct-sequence spread-spectrum packet radio network. The channel-state information consists of three statistics that are derived in different subsystems of the receiver. From these statistics, the receiver extracts information about the channel conditions which is provided to the transmitter in an acknowledgment packet or control packet. The performance of the adaptive-transmission protocol is compared to a system with fixed transmission parameters and to an adaptive protocol that is furnished with perfect knowledge of the channel state at the completion of each transmission.

Routing to preserve energy in ad hoc networks subject to jamming

Typical applications for ad hoc radio networks require that some or all radios in the network rely on batteries as energy sources. As a result, communication protocols for such networks should be designed to preserve limited energy supplies. Because the choice of a route to a traffic sink influences how often radios must transmit and receive, poor route selection can quickly deplete the batteries of certain nodes. Previous work has shown that a networks lifetime can be extended by assigning higher routing costs to nodes with little remaining energy and nodes that must use high transmitter power levels to reach neighbor radios. Route selection can be complicated by time-varying link conditions. Radios may be subject to interference from other nearby communication systems, hostile jammers, and other, non-communication sources of noise. Because a radio may need to increase its transmitter power or lower its data rate to compensate for the interference, a route that first appears to have only a small cost may later require much greater energy expenditure when transmitting packets. Frequent route selection can help radios avoid using links with interference but can also reduce throughput and increase energy consumption due to the increased number of routing control messages that must be sent. We investigate the effects of time-varying interference on the lifetime of ad hoc networks. It is shown that there is a tradeoff between packet delay and node lifetime. We show that it is possible to design the system to perform well under a wide variety of channel conditions.

Parallel acquisition of multicarrier direct-sequence spread-spectrum signals in partial-band interference

The frequency diversity of multicarrier direct-sequence signaling can potentially offer robust performance in frequency-selective channels. This paper focuses on the acquisition of multicarrier signals in channels containing fading and partial-band interference. The maximum-likelihood decision rule for parallel acquisition in frequency selective fading and partial-band interference is derived. Several simpler, near-optimal decision rules are also discussed. The performance of these decision rules is compared to that of equal-gain combining for multicarrier acquisition. Results show that the decision rules designed specifically for partial-band interference give significantly better performance.