The primary task in any cognitive radio (CR) network is to dynamically explore the radio spectrum and reliably determine portion(s) of the frequency band that may be used for the communication ...link(s). Accordingly, each CR node in the network has to be equipped with a spectrum analyzer. In this paper, we propose filter banks as a tool for spectrum sensing in CR systems. Various choices of filter banks are suggested and their performance are evaluated theoretically and through numerical examples. Moreover, the proposed spectrum analyzer is contrasted with the Thomson's multitaper (MT) method - a method that in the recent literature has been recognized as the best choice for spectrum sensing in CR systems. A novel derivation of the MT method that facilitates our comparisons as well as reveals an important aspect of the MT method that has been less emphasized in the recent literature is also presented.
Designing matched transmit and receive filters whose combination satisfies the Nyquist condition is a classical problem in digital communication systems. In this correspondence, we propose a novel ...method for designing such filters. The proposed method is based on a cost function whose minimization leads to designs that can strike a balance between the stopband attenuation, the residual intersymbol interference (ISI), robust sensitivity to timing jitter, and/or reduced peak-to-average power ratio (PAR). An iterative algorithm for optimizing the proposed cost function is suggested and its excellent performance is shown by presenting a variety of design examples. Compared to the published works, the proposed method offers the following unique advantages. By introducing a symmetry in the filter coefficients, filters with reduced computational complexity can be designed. We also introduce a design parameter that allows one to strike a balance between the PAR and other features of the desired filter.
In this paper, we develop novel Bayesian detection methods that are applicable to both synchronous code-division multiple-access and multiple-input multiple-output communication systems. Markov chain ...Monte Carlo (MCMC) simulation techniques are used to obtain Bayesian estimates (soft information) of the transmitted symbols. Unlike previous reports that widely use statistical inference to estimate a posteriori probability (APP) values, we present alternative statistical methods that are developed by viewing the underlying problem as a multidimensional Monte Carlo integration. We show that this approach leads to results that are similar to those that would be obtained through a proper Rao-Blackwellization technique and thus conclude that our proposed methods are superior to those reported in the literature. We also note that when the channel signal-to-noise ratio is high, MCMC simulator experiences some very slow modes of convergence. Thus accurate estimation of APP values requires simulations of very long Markov chains, which may be infeasible in practice. We propose two solutions to this problem using the theory of importance sampling. Extensive computer simulations show that both solutions improve the system performance greatly. We also compare the proposed MCMC detection algorithms with the sphere decoding and minimum mean square error turbo detectors and show that the MCMC detectors have superior performance.
The cosine modulated filter bank (CMFB) is introduced as a multicarrier modulation (MCM) technique for wideband data transmission over wireless channels. Under the name discrete wavelet multitone ...modulation, CMFB has been considered for data transmission over digital subscriber lines. We propose a new receiver structure that is different from those proposed previously. The new structure simplifies the task of channel equalization, by reducing the number of equalizer parameters significantly. We also propose a novel blind equalization algorithm that fits very nicely in the proposed structure. Moreover, we discuss the bandwidth efficiency of the proposed CMFB-MCM system and show that it is superior to the conventional (single carrier) quadrature amplitude modulation (QAM) and orthogonal frequency-division multiplexing (OFDM). The CMFB is found to be a signal processing block that stacks a number of vestigial sideband modulated signals in a number of overlapping subchannels in the most efficient way. The proposed CMFB-MCM is also compared to OFDM with respect to bit-error rate performance. Under the conditions that the channel impulse response duration remains less than the length of cyclic prefix, OFDM is found marginally superior to CMFB-MCM. However, OFDM degrades very fast when the channel impulse response duration exceeds the length of the cyclic prefix. CMFB-MCM, on the other hand, is found less sensitive to variations in channel impulse response duration.
Analysis of the Optimum Precoder in SC-FDMA Yuen, C. H. G.; Farhang-Boroujeny, B.
IEEE transactions on wireless communications,
11/2012, Volume:
11, Issue:
11
Journal Article
Peer reviewed
The third generation partnership project (3GPP) long term evolution (LTE) radio standard has adopted a special form of orthogonal frequency division multiplexing (OFDM) method for the uplink of ...multiple access networks. This method which is called single carrier frequency division multiple access (SC-FDMA) applies a precoding to each user data set in each OFDM symbol to control its peak-to-average power ratio (PAPR). Some recent works have proposed minimization of the variance of the instantaneous power of the output signal of the transmitter as a means of reducing PAPR to near its minimum value. However, the studies so far have been based on intuitions and observation of some numerical results. The goal of this paper is to develop a mathematical procedure to further establish the significance of this method. We formulate the problem in the form of a method of Lagrange multipliers and analyze its second-order conditions to confirm analytically that the optimal window is indeed a strict local minimizer. We also analyze and compensate the noise enhancement penalty of the optimal window. Our analysis also leads us to find new window functions that further reduce the PAPR and improve the BER performance.
We propose an adaptive, low-complexity, blind carrier tracking algorithm that takes advantage of the in-band ripple of the orthogonal frequency-division multiplexing (OFDM) power spectral density ...(PSD). With the aid of a comb filter, the proposed algorithm tracks the location of the ripple peaks and provides an estimate of the carrier offset. Analytical results are presented that predict the expected performance and show the consistency and robustness of the proposed algorithm in environments characterized by time-varying carrier offsets and frequency-selective fading channels. Computer simulations that corroborate the theoretical analysis are also presented.
A carrier offset in OFDM system simulation is generally considered to be slowly time-varying, so that, over short simulation periods, it may be considered to be a constant quantity. However, ...depending on system mobility, carrier frequency, and communication duration, time-varying carrier offsets caused by Doppler effects can be significant in a real physical environment. Few researchers have addressed this in their works. Of those who have addressed this, many present simplified, vague, or inaccurate time-varying carrier offset models. In this paper, we present a more realistic time-varying carrier offset model and present expressions for carrier offset correction that maximize the signal-to-interference ratio (SIR). We also provide guidelines for when the application of the time-varying carrier offset model is crucial for correct OFDM system evaluation.
This paper presents a new class of adaptive filtering algorithms to solve the stereophonic acoustic echo cancelation (AEC) problem in teleconferencing systems. While stereophonic AEC may be seen as a ...simple generalization of the well-known single-channel AEC, it is a fundamentally far more complex and challenging problem to solve. The main reason being the strong cross correlation that exists between the two input audio channels. In the past, nonlinearities have been introduced to reduce this correlation. However, nonlinearities bring with it additional harmonics that are undesirable. We propose an elegant linear technique to decorrelate the two-channel input signals and thus avoid the undesirable nonlinear distortions. We derive two low complexity adaptive algorithms based on the two-channel gradient lattice algorithm. The models assume the input sequences to the adaptive filters to be autoregressive (AR) processes whose orders are much lower than the lengths of the adaptive filters. This results in an algorithm, whose complexity is only slightly higher than the normalized least-mean-square (NLMS) algorithm; the simplest adaptive filtering method. Simulation results show that the proposed algorithms perform favorably when compared with the state-of-the-art algorithms.
Multiuser/multiple-input-multiple-output detectors that use Markov chain Monte Carlo (MCMC) simulation techniques to obtain likelihood of information bits have been developed recently. In this paper, ...we explore the implementation details of one such detector and present an efficient hardware architecture of it. The first step in development of this architecture is to derive a log-domain version of the Gibbs sampler, an efficient method of obtaining samples of MCMC simulator. This formulation is numerically stable and can operate with low precision. The log- domain formulation also lends itself to a hardware architecture that involves only addition, subtraction, and compare operations. Moreover, pipelining is introduced in the proposed architecture straightforwardly. We also explore the word-length requirement of the developed architecture through computer simulations.
Construction was completed during summer 2013 on the Telescope Array RAdar (TARA) bi-static radar observatory for Ultra-High Energy Cosmic Rays (UHECR). TARA is co-located with the Telescope Array, ...the largest “conventional” cosmic ray detector in the Northern Hemisphere, in radio-quiet Western Utah. TARA employs an 8MW Effective Radiated Power (ERP) VHF transmitter and smart receiver system based on a 250MS/s data acquisition system in an effort to detect the scatter of sounding radiation by UHECR-induced atmospheric ionization. TARA seeks to demonstrate bi-static radar as a useful new remote sensing technique for UHECRs. In this report, we describe the design and performance of the TARA transmitter and receiver systems.
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