2,078 research outputs found
Error Rates of the Maximum-Likelihood Detector for Arbitrary Constellations: Convex/Concave Behavior and Applications
Motivated by a recent surge of interest in convex optimization techniques,
convexity/concavity properties of error rates of the maximum likelihood
detector operating in the AWGN channel are studied and extended to
frequency-flat slow-fading channels. Generic conditions are identified under
which the symbol error rate (SER) is convex/concave for arbitrary
multi-dimensional constellations. In particular, the SER is convex in SNR for
any one- and two-dimensional constellation, and also in higher dimensions at
high SNR. Pairwise error probability and bit error rate are shown to be convex
at high SNR, for arbitrary constellations and bit mapping. Universal bounds for
the SER 1st and 2nd derivatives are obtained, which hold for arbitrary
constellations and are tight for some of them. Applications of the results are
discussed, which include optimum power allocation in spatial multiplexing
systems, optimum power/time sharing to decrease or increase (jamming problem)
error rate, an implication for fading channels ("fading is never good in low
dimensions") and optimization of a unitary-precoded OFDM system. For example,
the error rate bounds of a unitary-precoded OFDM system with QPSK modulation,
which reveal the best and worst precoding, are extended to arbitrary
constellations, which may also include coding. The reported results also apply
to the interference channel under Gaussian approximation, to the bit error rate
when it can be expressed or approximated as a non-negative linear combination
of individual symbol error rates, and to coded systems.Comment: accepted by IEEE IT Transaction
MGF Approach to the Analysis of Generalized Two-Ray Fading Models
We analyze a class of Generalized Two-Ray (GTR) fading channels that consist
of two line of sight (LOS) components with random phase plus a diffuse
component. We derive a closed form expression for the moment generating
function (MGF) of the signal-to-noise ratio (SNR) for this model, which greatly
simplifies its analysis. This expression arises from the observation that the
GTR fading model can be expressed in terms of a conditional underlying Rician
distribution. We illustrate the approach to derive simple expressions for
statistics and performance metrics of interest such as the amount of fading,
the level crossing rate, the symbol error rate, and the ergodic capacity in GTR
fading channels. We also show that the effect of considering a more general
distribution for the phase difference between the LOS components has an impact
on the average SNR.Comment: 14 pages, 8 Figures and 2 Tables. This work has been accepted for
publication at IEEE Transactions on Wireless Communications. Copyright (c)
2014 IEEE. Personal use of this material is permitted. However, permission to
use this material for any other purposes must be obtained from the IEEE by
sending a request to [email protected]
Digital communications over fading channels
In this report, the probabilities of bit error for the most commonly used digital modulation techniques are analyzed. Analytic solutions are developed for the probability of bit error when the signal is affected by the most commonly encountered impairment to system performance for a wireless channel, the transmission of the signal over a fading channel. In this report, the effect of a slow, flat Ricean fading channel on communications systems performance is examined. Since channel fading significantly degrades the performance of a communication system, the performance of digital communication systems that also use forward error correction channel coding is analyzed for hard decision decoding and, where appropriate, for soft decision decoding. Diversity, another technique to mitigate the effect of fading channels on digital communication systems performance, is also discussed. Also included is a discussion of the effect of narrowband noise interference, both continuous and pulsed, on digital communication systems. We then discuss the analysis of the probability of bit error for the combination of error correction coding and diversity. Following this, we briefly discuss spread spectrum systems. Next, we examine the link budget analysis and various models for channel loss. Finally, we examine in detail the second generation digital wireless standard Global System for Mobile (GSM).Approved for public release; distribution is unlimited
Performance Analysis of Coherent and Noncoherent Modulation under I/Q Imbalance
In-phase/quadrature-phase Imbalance (IQI) is considered a major
performance-limiting impairment in direct-conversion transceivers. Its effects
become even more pronounced at higher carrier frequencies such as the
millimeter-wave frequency bands being considered for 5G systems. In this paper,
we quantify the effects of IQI on the performance of different modulation
schemes under multipath fading channels. This is realized by developing a
general framework for the symbol error rate (SER) analysis of coherent phase
shift keying, noncoherent differential phase shift keying and noncoherent
frequency shift keying under IQI effects. In this context, the moment
generating function of the signal-to-interference-plus-noise-ratio is first
derived for both single-carrier and multi-carrier systems suffering from
transmitter (TX) IQI only, receiver (RX) IQI only and joint TX/RX IQI.
Capitalizing on this, we derive analytic expressions for the SER of the
different modulation schemes. These expressions are corroborated by comparisons
with corresponding results from computer simulations and they provide insights
into the dependence of IQI on the system parameters. We demonstrate that the
effects of IQI differ considerably depending on the considered system as some
cases of single-carrier transmission appear robust to IQI, whereas
multi-carrier systems experiencing IQI at the RX require compensation in order
to achieve a reliable communication link
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