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We consider a cognitive radio network in which a set of base stations make opportunistic spectrum access to support wireless subscribers within their covering cells. The spectrum of interest is divided into independent channels licensed to the primary users. Channel assignment and power control must be carried out in the cognitive network so that no excessive interference is caused to the primary...
We consider multiple-input multiple-output (MIMO) radar systems with widely spaced transmit and receive antennas. We treat the problem of detecting point targets when one or more target parameters of interest are unknown. We provide a composite hypothesis testing framework for jointly estimating such parameters along with detecting the target while only a finite number of signal samples are available...
We develop accurate and robust one-dimensional EXIT chart methods to design raptor codes with binary and higher-order modulations on AWGN channels over any desired range of SNRs. We formulate the check-node degree distribution optimization as a linear program that optimizes a suitable objective function of the desired operating points. The throughput curves predicted by the analysis are easily compared...
Statistics that are obtained from the demodulator are used in a direct-sequence spread-spectrum receiver to provide an estimate of the signal-to-noise ratio. We evaluate the applicability to spread-spectrum multiple-access systems of an SNR estimator that was proposed previously for SNR estimation in systems for which the only disturbance is thermal noise. The proposed estimate does not require the...
The performance of a serially concatenated convolutional code (SCCC) for frequency hopped M-ary phase shift keying communication systems over an additive white Gaussian channel noise (AWGN) in the presence of a partial-band noise jammer is discussed in the paper. The scaling of the log-likelihood ratio (LLR) which improves the SNR dynamic range and the jamming strategy are also discussed in the paper...
Unequal error protection (UEP) and rateless coding are both methods used to combat channel uncertainty. With a rateless code, the code rate automatically adapts to the channel quality through the use of incremental redundancy. However, a rateless code lacks the ability to differentiate priorities and all bits suffer the same long delay in poor channel conditions. In contrast, UEP ensures reliable...
Military applications often require traffic to be multicast to a group of receivers. It has previously been shown that linear network coding is useful in conjunction with physical-layer multicasting for reliable multicast delivery over fading channels. Superposition coding is an effective way to deliver information to a single receiver over a fading channel. However, we have shown in previous work...
Cognitive Radio (CR) networks present a difficult set of challenges due to the fluctuating nature of the available spectrum and wide ranging number of applications, each having different Quality of Service (QoS) requirements. This paper studies the key enabling technologies of Cognitive Radio and makes contributions in two key areas: sensing and learning. We shall first present the software testbed...
Frequency-hopping (FH) spread-spectrum anti-jam systems are susceptible to degraded performance by follower jammers, which intercept the transmitted signal, attempt to determine in which of a number of bins the hop is located, and then jam in that bin only. Three factors are addressed that provide some protection against follower jammers. One is the differential time delay between the direct intended...
This paper investigates the invariant detection problem of quadrature phase-shift keying (QPSK) direct sequence spread spectrum (DS-SS) signals in additive white Gaussian noise (AWGN). Using the complex Gaussian mixture signal model and invariance principle, we consider the constant-false-alarm-rate (CFAR) invariant detectors and other sub-optimal invariant tests, including the uniformly-most-powerful-invariant...
As cellular technologies evolve, evaluation of modulation schemes with frequency selective fading is an important consideration. We present methods to evaluate a high data rate DS-SS BPSK reverse link, over a wideband channel, with filters and a modified delayed signature dual finger RAKE. For several years the standard Gaussian approximation has been used to estimate error rate of DS-SS BPSK. We...
Electronic warfare (EW) is commonly divided into three subfields: electronic warfare support (ES), electronic attack (EA), and electronic protection (EP). Among them, ES systems take charge of collecting and analyzing the received signal from enemy's emitters and then provide the processed information to friendly EA and EP systems. The information is of critical importance because it is the first...
This paper considers a synchronous DS-CDMA system where channel state information at the base station is acquired via uplink training and channel feedback is used to provide the terminals with the optimal uplink signatures. We examine the tradeoffs involved in the proportioning of a resource block between training, data, and feedback symbols, with linear (matched filter and minimum mean-square error)...
The performance of an oversampled multiband wideband digital receiver is presented in this paper. Unlike previous works that assume a single channel receiver and a conventional analog-to-digital converter (ADC), where the quantization error is modeled as an additive uniform random noise, this paper includes the effects of an oversampled sigma-delta (??-??) ADC with noise shaping and an automatic gain...
This work proposes a method for localizing a single near-field source using a moving array. Using a phase correction factor calculated from two sequences of selected data snapshots, we extend the array aperture and compute the initial estimates of the source's bearing and range from the extended data sets. With the initial estimates of bearing and range we construct a phase difference factor to modify...
In this paper we formulate OFDM signals based on explicit pulse shaping filtering. A rectangular pulse in time domain for shaping filtering is most often used, but it has SNR loss compared to a shaping filter with a brick-wall frequency domain filter since in practice both require guard time or guard band. Our formulation of OFDM signal based purely on shaping filter may provide a common platform,...
The majority of prior work in signal-to-noise ratio estimation makes fairly strong assumptions concerning a priori knowledge of the channel state and signal. For instance, many of these estimators assume knowledge of the modulation scheme of the signal, or even complete knowledge of the transmitted set of modulated data symbols (typically through the use of training sequences). Even more universally,...
We investigate the risk associated with multihop wireless communications due to eavesdropping. When the same message traverses cross a multihop wireless network, potential security leaks may occur because of intelligent and collaborative eavesdroppers even if all individual links from source to destination have signal leakage below a security threshold. We termed this phenomenon ??cumulative security...
Most communication styles in tactical networks are one-to-many communications, which is multicast transmission. Recently, tactical networks has been evolving to Ad-Hoc-like distributed networks with OFDM-based Wideband Networking Waveform (WNW). In this paper, novel rate-adaptive multicast transmission method over OFDM-based wireless networks is proposed. Transmission rate for wireless multicast over...
We study a distributed algorithm for adjusting beamforming vectors in a peer-to-peer wireless network with multiple-input multiple-output (MIMO) channels. Each transmitter precoding matrix has rank one, and a linear minimum mean squared error (MMSE) filter is applied at each receiver. Our objective is to maximize the total utility summed over all users, where each user's utility is a function of the...
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