Robert J. O'Dea

Relative location estimation in wireless sensor networks

Self-configuration in wireless sensor networks is a general class of estimation problems that we study via the Cramer-Rao bound (CRB). Specifically, we consider sensor location estimation when sensors measure received signal strength (RSS) or time-of-arrival (TOA) between themselves and neighboring sensors. A small fraction of sensors in the network have a known location, whereas the remaining locations must be estimated. We derive CRBs and maximum-likelihood estimators (MLEs) under Gaussian and log-normal models for the TOA and RSS measurements, respectively. An extensive TOA and RSS measurement campaign in an indoor office area illustrates MLE performance. Finally, relative location estimation algorithms are implemented in a wireless sensor network testbed and deployed in indoor and outdoor environments. The measurements and testbed experiments demonstrate 1-m RMS location errors using TOA, and 1- to 2-m RMS location errors using RSS.

Relative location in wireless networks

In ad-hoc networks, location estimation must be designed for mobility and zero-configuration. A peer-to-peer relative location system uses pair-wise range estimates made between devices and their neighbors. Devices are not required to be in range of fixed base stations, instead, a few known-location devices in the network allow the remaining devices to calculate their location using a maximum-likelihood (ML) method derived in this paper. This paper presents simulations using both a standard channel model and actual indoor channel measurements for verification. Both simulation and measurements show that a peer-to-peer relative location system can provide accurate location estimation using received signal strength (RSS) as a ranging method.

Peak power and bandwidth efficient linear modulation

In portable wireless communication systems, power consumption is of major concern. Traditional modulation and coding schemes have been designed from the standpoint of minimizing average power. However, for linear power amplifiers needed for spectrally efficient modulation formats, amplifier efficiency and hence power consumption are determined by the peak power of the transmitted signal. This paper looks into modulation formats which minimize peak power and retain high spectral efficiency. Peak power is broken into a sum (in terms of decibels) of average power and a peak-to-average power ratio, and a variety of modulation formats are evaluated in terms of peak power efficiency in both a Gaussian noise and Rayleigh fading channel. A generalized phase shift keying (PSK) modulation format is developed and shown to offer superior peak power efficiency relative to that of commonly used linear modulation formats. Two schemes are presented for reducing the peak-to-average power ratio of various modulation formats. First, data translation codes are used to avoid data sequences which cause large peaks in the transmitted signal. This approach was found to be most productive in quadrature amplitude modulation (QAM) formats. Finally, an adaptive peak suppression algorithm is presented which further reduces the peak-to-average power ratios of the PSK and generalized PSK formats. The peak suppression algorithm is also applicable to /spl pi//4-QPSK and was found to improve peak power efficiency of that format by about 1.25 dB over a Rayleigh fading channel.

The importance of the multipoint-to-multipoint indoor radio channel in ad hoc networks

In the study of the multipoint-to-multipoint (M2M) radio channel, the physical backbone of wireless ad hoc networks, has direct application in the simulation and design of multi-hop routing protocols. The ad hoc network radio channel differs from the point-to-point or point-to-multipoint channels previously investigated, since each device may communicate with any other device. First, this paper presents a M2M measurement campaign conducted in an open-plan office area at 925 MHz. The measurements are analyzed to demonstrate spatial correlation between neighboring hops in the network. Then, the measurements are used to numerically characterize the effectiveness of a minimum-energy routing scheme. These measurements show that using existing models in the simulation of ad hoc networks can result in inaccurate results. Observations are made about the performance of a minimum-energy routing protocol in a real M2M radio channel. Finally, a channel model is suggested to more accurately represent the M2M radio channel.

A new chip-level differential detection system for DS-CDMA

In this paper we mathematically prove that if the original spreading Pseudo-Noise (PN) code is an m-sequence or a Gold-sequence, then the chip-by-chip differential decoding (CBCDD) sequence of the original PN code is a cyclic shift version of the original PN sequence. By utilizing this property, we design a new chip-level differential detection system for DS-CDMA, which does not require any chip-level differential encoding in the transmitter. We demonstrate simplicity of implementation and robust operation in the presence of carrier frequency shift.

Early Opportunities for Commercialization of TV Whitespace in the U.S

We propose the use of IP-based broadband wireless protocols to address many of the applications needs in the Television White Space (TVWS) frequencies that will be available for secondary usage in the U.S. beginning in 2009. The work includes a discussion of TVWS physical and regulatory characteristic and a view of the TVWS usage models that may be applied in various market spaces, including the home, the enterprise, public safety and wireless mobile service providers. We show that a protocol based on IEEE 802.16e or a similar broadband wireless protocol could be adapted to meet many of the needs in this space.

Multiple symbol noncoherent detection of GMSK

This paper studies the problem of noncoherent detection of Gaussian minimum shift keying (GMSK). Particular attention is focussed on the popular case of BT=0.25, but the concepts presented apply to other cases as well in addition to the general case of continuous phase frequency shift keying (CPFSK). The optimum noncoherent detector is shown to consist of a bank of matched filters followed by a sequence estimator. The metric which must be optimized by the sequence estimator is explicitly given. A simple approximation is introduced which allows the number of matched filters to be reduced from 16 to 3 for GMSK (BT=0.25). A suboptimal metric is introduced which is interpreted as an N-symbol differential detection metric. Based on this metric, a receiver structure is then presented which uses the Viterbi algorithm with a 2/sup N/ state trellis to perform the sequence estimation. Simulation results indicate that it is possible to obtain performance within 1 dB of optimum coherent detection on either a Gaussian noise or a slowly Rayleigh fading channel with the N=4 symbol differential detector.

Multiple symbol differential detection for trellis-coded MPSK over Rayleigh fading channels

This paper presents a multiple-symbol differential detection scheme for coded and interleaved transmission of MPSK data. The performance of this scheme is then evaluated for transmission of digitized voice over a Rayleigh fading channel. It is found that in terms of bit error rate, the improvement given by using multiple-symbol differential detection is minimal, but when evaluated in terms of frame-error rate, the multiple-symbol scheme gives about 1.25-dB improvement. Another 0.75-dB improvement can be obtained by also using a serial list Viterbi algorithm.

A new code-timing estimation algorithm for DS-CDMA

A DS-CDMA receiver requires accurate timing information to synchronize the receiver PN code correlator with the received signal. When utilized for position location applications, the DS-CDMA receiver must further provide accurate timing information to the location algorithm. Typically, DS-CDMA timing estimation algorithms require the transmission of a training sequence to establish timing lock. In addition, the carrier frequency drift encountered in many wireless communication applications adversely effects the performance of these algorithms. This paper introduces a new DS-CDMA code-timing estimation algorithm that operates without a training sequence and provides robustness to carrier frequency drift.

Optimum root placement in a multiple-hop wireless network

A multi-hop wireless network using a rooted spanning tree as routing backbone has to deal with reliability and congestion problem when the network size increases. In this paper, we consider the problem of adding a new root with its own rooted spanning tree to the network to alleviate such problems. Based on minimum-depth and minimum-load metrics, we present efficient algorithm that achieves optimum selection of root(s).