There has been increasing interest in incorporating sensing systems into objects or the environment for monitoring purposes. In this work we compare approaches to performing fully-distributed anomaly detection as a means of detecting security threats for objects equipped with sensing and communication abilities. With the desirability of increased visibility into the cargo in the transport chain and the goal of improving security, we consider the approach of equipping cargo with sensing and communication capabilities as a means of ensuring the security of the cargo as a key application. We have gathered real sensor test data from a rail trial and used the collected data to test the feasibility of the anomaly detection approach. The results demonstrate the effectiveness of our approach.

Dynamic spectrum access networks are expected to operate in a manner that is transparent to the incumbent licensed spectrum users. Conventional non-adaptive wideband spectrum sensing approaches could potentially be inefficient since they employ the same scanning resolution to track signals, even though different signals require spectrum scans with different sensing parameters. In this paper, we present an adaptive spectrum sensing framework that varies its parameters according to the characteristics of the spectrum of interest. Furthermore, we propose a dynamic scheduling algorithm for spectrum sensing that can be implemented in both a conservative and non-conservative manner. This algorithm allocates different time resolutions to several portions of spectrum using a backoff mechanism. The proposed algorithm has been employed to perform the 'listenbefore- talk' function of a cognitive radio, and performance results have been obtained with respect to the improvement in the sensing efficiency over a non-adaptive approach, secondary spectrum utilization, and interference rate.

The software defined radios movement is revolutionizing radio design by separating function from specific implementation. Like traditional software systems, software defined radio systems use a common operational definition that may be realized across numerous platforms. This paper describes initial efforts at realizing the promise of software defined radios by synthesizing radios to multiple implementation fabrics from a common Rosetta specification. We outline the approach by describing specifications used at each abstraction level, the operations implemented to synthesize radios, and various analysis techniques used to provide assurance in the resulting radio.

In this paper, we present a novel algorithm for reducing sidelobe interference power levels in OFDM-based cognitive radios. Existing techniques for sidelobe suppression can be computationally intensive when determining the complex-valued amplitude levels for the cancellation subcarriers. Exploiting the fact that different sequences have different sidelobe power levels, the proposed algorithm employs a constellation expansion-based iterative approach in order to suppress the sidelobe power levels. An important advantage of the proposed technique is that, no side information needs to be transmitted. Simulation results show that the proposed algorithm can be employed in a wide range of operating conditions at the cost of a slight increase in the bit error rate and the peak-to-average power ratio characteristics.

In this paper, we present a novel peak-to-average power ratio (PAPR) reduction algorithm for OFDM systems employing a symbol balancing approach with several non-data bearing (NDB) subcarriers. The proposed algorithm assigns the NDB subcarriers values that, when combined with interleaving, reduces the long correlation patterns of the input frame that can potentially lead to high PAPR. Furthermore, the proposed algorithm can use either a fixed number of NDB subcarriers or a variable number of NDB subcarriers according to the amount of inter-subcarrier correlation, thus attempting to increase the data throughput of the system. Simulation results for a 256-subcarrier OFDM system employing QPSK symbols and 16 interleavers can achieve a PAPR reduction of 4 dB for a complementary cumulative distribution of 0.01%.

In this paper, we present a quantitative comparison of two agile modulation techniques employed by cognitive radio transceivers operating in a dynamic spectrum access (DSA) network. One of the modulation technique is non-contiguous orthogonal frequency division multiplexing (NC-OFDM), which is designed to avoid interference with the transmissions of incumbent users by deactivating subcarriers within their vicinity. The other modulation technique under study is a variant of multicarrier code division multiple access (MC-CDMA). Although several studies comparing conventional OFDM and MC-CDMA has been conducted in literature to justify robust error performance of MC-CDMA, a quantitative performance evaluation of these schemes has not been performed when employed in a DSA network. Due to deactivated subcarriers in DSA networks, in this paper we showed their performance can be significantly different from the conventional setup. Analytical expressions for the error probability of an NC-OFDM transceiver have been derived and compared with computer simulation results. The results show that the error robustness of NC-OFDM is relatively constant regardless of the number of deactivated subcarriers, unlike MC-CDMA transmissions, whose error performance degrades with an increase in deactivated subcarriers. 1

In this paper, we propose a novel channel sounding technique, called the multicarrier direct sequence swept time delay cross-correlation (MC-DS-STDCC), which is designed to minimize the interference with incumbent licensed transmissions within the context of a dynamic spectrum access (DSA) network. Conventional channel sounders employ the same transmit power level when operating over a specific frequency band. However, the maximum-tolerable transmit power levels permitted across the spectrum within a DSA network can potentially be non-uniform. Our proposed channel sounder is designed to tailor the transmit power level across the frequency band of operation, limiting it to the constraints imposed by both licensed and unlicensed devices, as well as by regulatory agencies. Employing a combination of multicarrier spread spectrum modulation and a conventional channel sounding approach, our proposed technique achieves a mean squared error of the estimated channel impulse response of 10-3at an SNR of -13 dB and -17 dB respectively for 15- and 31-chip spreading sequences.

In this paper we present the design process of an orthogonal frequency division multiplexing (OFDM) implementation for the Kansas University Agile Radio (KUAR). The KUAR is a portable, experimental, FPGA-based software-defined radio unit employed as a test bed to facilitate advanced research into frequency agile and cognitive radios. The baseband processing in this implementation is accomplished entirely on a Xilinx Virtex-II Pro FPGA that is built into the KUAR Our OFDM PHY implementation demonstrates the capabilities of the KUAR and serves as an important first step towards conducting actual experiments on multicarrier schemes for dynamic spectrum access communications, such as non-contiguous (NC)-OFDM.

In this paper, we present a statistical analysis of the peak-to-average power ratio (PAPR) for non-contiguous orthogonal frequency division multiplexing (NC-OFDM) signals. When studying contiguous OFDM signals, most PAPR analysis techniques assume the symbols to be identically and independently distributed (i.i.d.). However, in an NC-OFDM transmission, where a large number of subcarriers could be deactivated, this assumption is no longer valid. The proposed PAPR analysis is derived specifically for the NC-OFDM transmission scenario. Results show that NC-OFDM signal exhibit higher PAPR values relative to contiguous OFDM transmission at the same information rate.

Abstract This paper presents a genetic‐algorithm driven, cognitive radio decision engine that determines the optimal radio transmission parameters for single and multicarrier systems. Determining the appropriate radio parameters, given a dynamic wireless channel environment is the primary feature of cognitive radios for wireless communication systems. Genetic algorithms (GAs) are designed to select the optimal transmission parameters by scoring a subset of parameters and evolving them until the optimal value is reached for a given goal. Although there have been implementations of GA‐based single carrier cognitive radio engines, the performance of these algorithms has not been thoroughly analyzed nor have the fitness functions employed by the algorithms been explored in detail. Multicarrier systems are common in today's communication environment, thus cognitive techniques that account for only single‐carrier systems neglect the practical issues of multiple carriers. A set of accurate single carrier and multicarrier fitness functions for our GA implementation that completely control the evolution of the algorithm have been derived. The performance analysis results illustrate the trade‐offs between the convergence time of the GA and the size of the GA search space. Copyright © 2007 John Wiley & Sons, Ltd.

In this paper, we present a novel low complexity algorithm for reducing the peak-to-average power ratio (PAPR) occurring in OFDM-based cognitive radios. Although several PAPR reduction algorithms exist in the literature, they are often only effective for specific scenarios. Our proposed algorithm exploits the agility of cognitive radio technology to rapidly choose and employ the appropriate PAPR reduction approach from a set of approaches to achieve a large decrease in PAPR, given the current operating conditions. The results show that for a wide range of operating conditions, the proposed algorithm achieves a large decrease in PAPR, unlikely the PAPR results when only a single reduction approach is employed across the same wide range.

An active networking architecture provides the infrastructure for applications to inject user programs into the nodes of the network. This enables customization of the network nodes so that application-specific services can be downloaded into the network in the form of new protocols. We look at the different kinds of services that applications require from the network. We study these services to identify common characteristics so that services can be grouped into classes of protocols. We argue that this study permits us to develop a methodology that helps in rapidly designing and deploying new protocols.

The rapidly deployable radio network (RDRN) is an architecture and experimental system to develop and evaluate hardware and software components suitable for implementing mobile, rapidly deployable, and adaptive wireless communications systems. The driving application for the RDRN is the need to quickly establish a communications infrastructure following a natural disaster, during a law enforcement activity, or rapid deployment of military force. The RDRN project incorporates digitally controlled antenna beams, programmable radios, adaptive protocols at the link layer, and mobile node management. This paper describes the architecture for the RDRN and a prototype system built to evaluate key system components.

Most algorithms proposed for controlling traffic prior to entering ATM networks are based on static mechanisms. Such static control mechanisms do not account for the dynamics of the user traffic or the network state. Some dynamic control algorithms have been proposed, but most of these algorithms are extremely complex and may make it difficult to provide real time control. In this paper, we present an adaptive rate control algorithm that has been implemented in hardware. The algorithm controls the traffic submitted by a source based on the indirectly observed average rate and burst size for the source. The algorithm is highly efficient and thereby provides real time control at high speed. Our implementation, in concert with flow control in the local area network, provides the basis for ATM-based high performance distributed systems.

This paper describes performance measurements taken in the MAGIC gigabit testbed relating to the performance of TCP in wide area ATM networks. The behavior of TCP with and without cell level pacing is studied. In particular, we focus on results that indicate that the TCP rate control mechanism alone is inadequate for congestion avoidance and control in wide-area gigabit networks. We also present results showing that TCP augmented by cell-level pacing addresses these problems and allows the full bandwidth capacity to be utilized. These results demonstrate the viability of high performance distributed systems based on wide area ATM networks given the proper ATM traffic management infrastructure.

Receive Path Termination in a SONET network is required to perform the path level functionality. The Synchronous Payload Envelope (SPE) of a SONET frame must first be located using the payload pointers in the SONET Line overhead. Once the SPE is located, the path termination device must keep track of it and provide information to higher level protocols about its location and status. While the most crucial functionality must be handled in hardware, the entire overhead information is stored for processing by a line card processor. The incoming SONET stream is processed in words of 32 bits each. The quadruple OC-3c mode (OC-12) occupies almost an entire Xilinx XC 3195 Field Programmable Gate Array (FPGA). The SONET OC-12c mode processing takes fewer gates but requires the large chip to perform a Bit Interleaved Parity (BIP) check on the SPE. The interface to both designs is physically identical and they can form a part of a line card that is capable of two distinct modes of operation.>

The Synchronous Optical Network (SONET) and Synchronous Digital Hierarchy (SDH) form a high speed data transmission standard used to transport various types of payloads. Asynchronous Transport Mode (ATM) cells are an increasingly important payload type. This paper describes two pipelined implementations of these mapping functions. The first implementation maps a stream of ATM cells into a SONET OC-12 synchronous payload envelope (SPE). The second circuit maps distinct ATM cell streams into four SONET OC-3c SPE's, which in turn can form a SONET OC-12 signal. Both of these implementations operate at 622 Mb/s. They have been implemented on a single, Xilinx XC3195 Field Programmable Gate Array (FPGA) and have an identical physical interface. This design is part of a system line card that can transmit and receive in the above mentioned modes.>

This paper describes a gigabit LAN/WAN gateway being developed for the MAGIC gigabit testbed. The gateway interfaces a gigabit LAN developed by Digital's Systems Research Center and the MAGIC SONET/ATM wide area network. The gateway provides 622 Mb/s throughput between the LAN and WAN environments, and supports either a single STS-12c or four STS-3c tributaries. Traffic measurement capability and support for multiple bandwidth management schemes are provided by this architecture.>

Image analysis, at the higher levels, works with extracted regions and line segments and their properties, not with the original raster data. Thus, a spatial information system must be able to store points, lines, and areas as well as their properties and interrelationships. In a previous paper (Shapiro and Haralick [17]), we proposed for this purpose an entity-oriented relational database system. In this paper, we describe our first experimental spatial information system which employs these concepts to store and retrieve watershed data for a portion of the state of Virginia. We describe the logical and physical design of the system and discuss the architectural implications.