678 research outputs found
Towards Fully Optimized BICM Transceivers
Bit-interleaved coded modulation (BICM) transceivers often use equally spaced
constellations and a random interleaver. In this paper, we propose a new BICM
design, which considers hierarchical (nonequally spaced) constellations, a
bit-level multiplexer, and multiple interleavers. It is shown that this new
scheme increases the degrees of freedom that can be exploited in order to
improve its performance. Analytical bounds on the bit error rate (BER) of the
system in terms of the constellation parameters and the multiplexing rules are
developed for the additive white Gaussian Noise (AWGN) and Nakagami- fading
channels. These bounds are then used to design the BICM transceiver. Numerical
results show that, compared to conventional BICM designs, and for a target BER
of , gains up to 3 dB in the AWGN channel are obtained. For fading
channels, the gains depend on the fading parameter, and reach 2 dB for a target
BER of and .Comment: Submitted to the IEEE Transactions on Communication
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Optical fibre communication over a noisy partially coherent channel
As global IP traffic grows unceasingly, optical networks demand for technology upgrades in order to keep the feared “capacity crunch” away. The most celebrated technologies of coherent detection and wavelength-division multiplexing (WDM), widely deployed in long-haul links, are gaining ground in access networks, which is particularly challenging due to the shared-cost requirements, leading to denser channel spacings and the use of cheaper devices that tend to be noisier. In order to make the most of this technology combination, it is crucial to have a model of the channel that accurately describes all the present sources of noise. Traditionally, the most used model has been the additive white Gaussian noise (AWGN) channel, which, although only accounting for a linear contribution of complex noise and being insensitive to rotational phenomena, has shown its validity in numerous studies, as well as in commercial equipment. In this thesis, however, it is observed that the adoption of coherent detection and WDM, with lower-grade semiconductor lasers showing a moderate linewidth, yields scenarios where a phase-sensitive model becomes a must. The partially coherent AWGN (PCAWGN) channel is a popular choice that fulfils this need, but its high complexity due to non-trivial functions involved, deprives it from being suitable in high-speed digital circuits. The main goal of this thesis is to describe a reduced-complexity approximation in polar coordinates, accurate enough to find its applicability in modern systems. Furthermore, this works explores some possible end-to-end applications, like channel capacity estimation or symbol detection, assessing its performance by means of extensive simulations. Lastly, the emerging field of complex modulation of directly modulated lasers is revisited, with a special interest in how the proposed approximation can help to improve the performance of previously reported techniques, as well as proposing a new way to design spiral-shaped constellations aimed to maximise the channel capacity
Performance bound for generalized M-QAM constellations in time-discrete multipath rayleigh fading channels with channel estimation errors
In this paper we derive a lower bound on the bit error rate (BER) for the individual bit streams that can be mapped simultaneously in an hierarchical way onto generalized multilevel quadrature amplitude modulations (M-QAM). The expressions are valid for time-discrete multipath Rayleigh fading environments with imperfect channel estimation and can be regarded as an extension of the well-known matched filter bound (MFB).info:eu-repo/semantics/acceptedVersio
Exhaustive Gaussian Approach for performance evaluation of direct-detection OFDM systems employing square and cross QAM
An exhaustive Gaussian approach (EGA) is
proposed to evaluate, through numerical simulation, the bit error ratio (BER) of direct-detection orthogonal frequency division multiplexing systems employing square and cross quadrature amplitude modulation. Excellent agreement
between the BER estimates from the direct error counting (DEC) and the EGA is shown for different levels of optical
signal-to-noise ratio and signal distortion. It is shown that the EGA requires about three orders of magnitude less in
computation time than the DEC method for BER levels around 10-6, with the difference getting higher for lower
BER levels.info:eu-repo/semantics/publishedVersio
Analytical Matched Filter Bound for M-QAM Hierarchical Constellations with Diversity Reception in Multipath Rayleigh Fading Channels
In this paper, we derive matched filter bound (MFB)
expressions for the performance of hierarchical quadrature
amplitude modulations (M-HQAM) over time-discrete multipath
Rayleigh fading environments with diversity. The expressions
are valid for multipath environments where different paths and
antennas can be correlated. Since hierarchical constellations are
usually employed to achieve unequal bit error protection, the
MFB expressions are given in terms of the individual bit error
rate (BER) for the different bit streams. Although typically the
MFB is obtained assuming slow time varying channels, fast
varying channels are also considered in this paper
A low-complexity 2D signal space diversity solution for future broadcasting systems
-DVB-T2 was the first industrial standard deploying rotated and cyclic Q
delayed (RCQD)modulation to improve performance over fading channels. This
enablesimportantgains compared toconventional quadrature amplitude
modulations(QAM) under severe channel conditions.However, the corresponding
demodulation complexitystill prevents its use forwider applications. This paper
proposes several rotation angles for different QAM constellations anda
corresponding low-complexity detection method. Results show that the proposed
solution simplifies both the transmitter and the receiver with often
betterperformancethan the proposed angles in DVB-T2. Compared with the lowest
complexity demappers currently used in DVB-T2, the proposed solution achieves
an additional reduction bymore than 60%. Index Terms- DVB-T2, Rotated and
Cyclic Q Delayed (RCQD) Modulations, Signal Space Diversity (SSD), Fading
Channel, Quadrature Amplitude Modulations (QAM), Max-Log,
ComputationalComplexity
Performance analysis of MIMO-OFDM systems using complex Gaussian quadratic forms
En este trabajo se proponen aportaciones originales para el análisis de prestaciones en sistemas multiantena con múltiples portadoras, mediante el desarrollo de nuevas técnicas matemáticas para el cálculo de probabilidades de error. Así, ha sido posible analizar el efecto de no idealidades (estimación de canal imperfecta, offset de continua, desbalanceo I/Q…) en las prestaciones de sistemas de comunicaciones móviles e inalámbricas
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