11 research outputs found

    Joint data detection and channel estimation for OFDM systems

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    We develop new blind and semi-blind data detectors and channel estimators for orthogonal frequency-division multiplexing (OFDM) systems. Our data detectors require minimizing a complex, integer quadratic form in the data vector. The semi-blind detector uses both channel correlation and noise variance. The quadratic for the blind detector suffers from rank deficiency; for this, we give a low-complexity solution. Avoiding a computationally prohibitive exhaustive search, we solve our data detectors using sphere decoding (SD) and V-BLAST and provide simple adaptations of the SD algorithm. We consider how the blind detector performs under mismatch, generalize the basic data detectors to nonunitary constellations, and extend them to systems with pilots and virtual carriers. Simulations show that our data detectors perform well

    Bound-intersection detection for multiple-symbol differential unitary space-time modulation

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    This paper considers multiple-symbol differential detection (MSD) of differential unitary space-time modulation (DUSTM) over multiple-antenna systems. We derive a novel exact maximum-likelihood (ML) detector, called the bound-intersection detector (BID), using the extended Euclidean algorithm for single-symbol detection of diagonal constellations. While the ML search complexity is exponential in the number of transmit antennas and the data rate, our algorithm, particularly in high signal-to-noise ratio, achieves significant computational savings over the naive ML algorithm and the previous detector based on lattice reduction. We also develop four BID variants for MSD. The first two are ML and use branch-and-bound, the third one is suboptimal, which first uses BID to generate a candidate subset and then exhaustively searches over the reduced space, and the last one generalizes decision-feedback differential detection. Simulation results show that the BID and its MSD variants perform nearly ML, but do so with significantly reduced complexity

    Heuristic Tree Search for Detection and Decoding of Uncoded and Linear Block Coded Communication Systems

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    A heuristic tree search algorithm is developed for the maximum likelihood detection and decoding problem in a general communication system. We propose several "cheap" heuristic functions using constrained linear detectors and the minimum mean square errors (MMSE) detector. Even though the MMSE heuristic function does not guarantee the optimal solution, it has a negligible performance loss and provides a good complexity-performance tradeoff. For linear block coded systems, heuristic tree search is modified for soft decision decoding. High rate codes are decoded via the minimum state trellis, and low rate codes via the minimum complexity tree. Preprocessing is also discussed to further speed up the algorithms

    Maximum likelihood detection for differential unitary space-time modulation with carrier frequency offset

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    Can conventional differential unitary space time modulation (DUSTM) be applied when there is an unknown carrier frequency offset (CFO)? This paper answers this question affirmatively and derives the necessary maximum likelihood (ML) detection rule. The asymptotic performance of the proposed ML rule is analyzed, leading to a code design criterion for DUSTM by using the modified diversity product. The resulting proposed decision rule is a new differential modulation scheme in both the temporal and spatial domains. Two sub-optimal multiple-symbol decision rules with improved performance are also proposed. For the efficient implementation of these, we derive a modified bound intersection detector (BID), a generalization of the previously derived optimal BID for the conventional DUSTM. The simulation results show that the proposed differential modulation scheme is more robust against CFO drifting than the existing double temporal differential modulation

    Polynomial Moment Relaxation for MIMO Detection

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    We develop a polynomial-time detector for maximum likelihood (ML) detection over multiple-input multiple-output (MIMO) channels. Our proposed polynomial moment relaxation (PMR) detection gives a unified framework for MIMO detection with relaxation including semi-definite relaxation as a special case. We give three approaches to replace a finite alphabet constraint with a polynomial constraint. Since both the objective function and the constraints are polynomials, we use a moment relaxation approach by applying the dual theories of moments and positive polynomials solvable by semi-definite programming. With different relaxation orders, our PMR achieve a flexible trade-off between complexity and performance

    Performance analysis of trellis codes transmitted over fading channels

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    Trellis coded modulation (TCM) schemes, due to their bandwidth efficiency and coding gain, have been proposed for multipath fading (MF) channels. The object of this research is to analyze the performance of TCM schemes in MF channels. While many excellent studies have already been reported, they share some of the following restrictions: (1) an assumption of ideal channel measurements and ideal interleaving, (2) use of Chernoff bounds, which are loose in this case, (3) analysis of only the Rayleigh channel, ignoring the Rician channel, and (4) reliance on computer simulation to get the actual performance. Extending analytical results without these restrictions is addressed in this work. This thesis derives a saddle point approximation (SAP) method to compute the pairwise error probability (PEP) of TCM schemes transmitted over Rician fading channels. It can be applied under several conditions, including finite or ideal interleaving, and is derived for a pilot-tone model, encompassing ideal coherent detection, pilot-tone aided detection, pilot-symbol aided detection, and differential detection. Its accuracy is demonstrated by comparison to the results of numerical integration. Under ideal interleaving, the approximation can be further simplified to an expression, which is in a product form and is much tighter than the ordinary Chernoff bound on the PEP. Also, based on the SAP, the effect of finite interleaving depth on the error performance is studied. The Canadian mobile satellite (MSAT) channel has been modelled as the sum of lognormal and Rayleigh components. Previously, the performance of TCM schemes in this channel has been obtained via computer simulation. In this thesis, new analytical expressions are derived for the PEP of TCM schemes transmitted over this channel employing ideal interleaving, and the results are substantiated by means of computer simulation. In addition, first order statistics of absolute and differential phases of a shadowed Rician process are derived. This thesis presents new performance bounds of TCM schemes over nonindependent (i.e., finite interleaving) Rician fading channels. In addition, for Rayleigh fading channels with an exponential auto-covariance function, bounds resembling those for memoryless channels are derived. The bounds, being more accurate than Chernoff bounds, permit accurate estimation of system performance. The performance of concatenated coding systems and automatic-repeal-request (ARQ) systems operating on fading channels is addressed. New error expressions,which sow asymptotic error behaviour, are derived for systems which use a modified Viterbi decoding algorithm. They allow useful evaluation of the coding gain and throughput. Finally, the performance of convolutional codes in fading channels is analyzed. An upper bound on the bit error probability, the optimum power split ratio between the data and pilot signals, and the channel cut-off rate are derived.Graduat

    Generation of Bivariate Rayleigh and Nakagami-m Fading Envelopes

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    The letter presents an algorithm for generating bivariate Nakagami-m distributed fading envelopes with any desired power cross correlation. For this algorithm, the fading index m should be a positive integer ( m = 1 for Rayleigh fading). Its applications include dual-branch selection combining diversity, dualbranch switch diversity systems, and wireless channel modeling

    On the Trivariate Rician Distribution

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    An exact expression for the Joint density of three correlated Rician variables is not available in the open literature. In this letter, we derive new infinite series representations for the trivariate Rician probability density function (pdf) and the Joint cumulative distribution function (cdf). Our results are limited to the case where the inverse covariance matrix is tridiagonal. This case seems the most general one that is tractable with Miller's approach and cannot be extended to more than three Rician variables. The outage probability of triple branch selective combining (SC) receiver over correlated Rician channels is presented as an application of the density function

    Analysis of Self-Interference Cancellation under Phase Noise, CFO and IQ Imbalance in GFDM Full-Duplex Transceivers

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    This paper investigates a full-duplex base station using a generalized frequency division multiplexing (GFDM) transceiver with the radio frequency (RF) impairments phase noise, carrier frequency offset (CFO) and in-phase (I) and quadrature (Q) imbalance. To fully focus on the RF impairment issue, we study the simple configuration of single uplink user and single downlink user. They both are half duplex wireless. In the uplink, we study analog and digital self-interference (SI) cancellation and propose a complementary SI suppression method. Desired signal and residual SI powers and signal-to-interference ratio (SIR) are derived in closed form. Similarly, in the downlink, we derive desired signal power, co-channel interference signal power caused by the uplink user and SIR. The RF impairments degrade the efficiency of SI cancellation and affect GFDM more negatively than full-duplex orthogonal frequency division multiplexing (OFDM). Hence, we propose full-duplex GFDM receiver filters for maximizing the SIR for both uplink and downlink transmissions. Finally, the uplink and downlink rates and the uplink-downlink rate region are derived. Significantly, the optimal-filter based GFDM outperforms full-duplex OFDM by 25 dB higher SIR and an uplink rate increase of 500%.acceptedVersionPeer reviewe
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