Search

In this paper we develop closed form approximations for the probability density function (PDF) of the reliability metrics (L-values) in bit-interleaved coded modulation (BICM). The expressions are valid for [M.sup.2]-ary quadrature amplitude modulations ([M.sup.2]-QAM) with binary reflected Gray mapping when the metrics are calculated using the so-called max-log approximation. Based on the developed expressions, we also propose two simple Gaussian mixture approximations that are analytically tractable. We apply our developments to efficiently calculate the BICM capacity, and to develop bounds on the coded bit-error rate when a convolutional code is used. The coded performance of a hybrid automatic repeat request (HARQ) based on constellation rearrangement is also evaluated. Index Terms--BER, BICM, convolutional codes, constellation rearrangement, gray mapping, HARQ, logarithmic likelihood ratios, L-values, PDF, QAM, union bound.

In this paper we consider hybrid automatic repeat request transmission based on binary phase shift keying modulation. Our objective is to improve the performance of the retransmissions, keeping at the same time the complexity and the performance of the first transmission unaltered. We conclude that the so-called mapping rearrangement (MR) may considerably improve the performance if multi-dimensional modulation is applied. We evaluate the theoretical limits of bit-interleaved coded modulation with MR, verify the functioning of the practical coding scheme, and propose to improve the performance via iterative detection-decoding (BICM-ID) which brings considerable gains. In particular, for high coding rates, a 4 dB SNR gain over transmission without MR may be achieved. Index Terms--Mapping rearrangement, constellation rearrangement, mapping diversity, binary phase shift keying, automatic repeat request, iterative detection, bit-interleaved coded modulation, BICM, ARQ, BICM-ID, BPSK, QPSK.

In this paper, we evaluate the bit error rate (BER) of bit-interleaved coded modulation (BICM) receivers that operate with a priori information obtained from the decoder during the so-called turbo iterations. We use Bonferroni-type lower and upper bounds to tightly estimate the BER performance in the range of signal-to-noise ratio (SNR) of interest. The results are shown to be useful for the convergence analysis of the iterative demapping via the so-called extrinsic information transfer (EXIT) charts and for the evaluation of the coded performance of BICM with iterative demapping (BICM-ID). Index Terms--BICM with iterative demapping (BICM-ID), bit-interleaved coded modulation (BICM), Bonferroni bounds, iterative demapping, turbo decoding, turbo demapping.

The major computation cost of pseudo-spectral method comes from the evaluation of differentiation matrix multiplication. In the past, uniform or Chebyshev collocation points are used for sampling. The differentiation matrix multiplication was evaluated by fast Fourier transform (FFT) or fast cosine transform (FCT), in order to reduce the computation complexity from O([N.sup.2]) to O(N log (N)). However, the intrinsic properties of FFT or FCT may cause the wraparound effect and Gibbs phenomenon. Moreover, FFT or FCT is not applicable to other collocation t points such as Legendre and Hermite. In order to improve the accuracy and applicability of the pseudo-spectral method, the fast multipole method (FMM) is exploited to substitute the FFT or a FCT. By making use of the similarity of the N-body problem and the collocation problem, a new FMM-based pseudo-spectral time domain method is developed in this paper. Index Terms--Cardinal functions, fast multipole method, pseudo-spectral method.

In the popular bit-interleaved coded modulation (BICM) the output of the channel encoder and the input of the modulator are separated by a bit-level interleaver. From the decoder's point of view, the modulator, the transmission channel, and the demodulator (calculating bits' reliability metrics) become a memoryless BICM channel with binary inputs and real outputs. In unfaded channels, the BICM channel's outputs (reliability metrics) are known to be Gaussian for binary- or quaternary phase shift keying but their probability density function (PDF) is not known for higher-order modulation. We fill this gap by presenting an algorithmic method to calculate closed-form expressions for the PDF of reliability metrics in BICM with arbitrary modulation and bits-to-symbol mapping when the so-called max-log approximation is applied. Such probabilistic description of BICM channel is useful to analyze, from an information-theoretic point of view, any BICM constellation/mapping design. Index Terms--Logarithmic likelihood ratios, L-values, bit-interleaved coded modulation, probability density functions, soft-input decoding, LLR, BICM, PDF.

We analyze the methodology and present the interpretation of results obtained in the measurement of the temporal Ricean K-factor and the time-autocovariance function of the received power for fixed narrowband wireless links in urban residential environments. Our main observation is that the time-autocovariance function (and thus both the temporal K-factor and the coherence time) fundamentally depends on a combination of the characterization of the transmit-receive path and whether the street-level moving objects are in the field of view of the antennas. In most practical cases the latter refers only to the customer premises antenna, as the base station is typically placed at a much greater distance from moving scatterers. No significant basis was found for the popular conjecture that the K-factor is mainly influenced by the excess path loss. However, a strong correlation between coherence times and temporal K-factor was observed over a wide range of link conditions. We also found that the time-autocovariance function can be quite accurately modeled by the weighted sum of two exponentially decaying functions: one with a time constant on the order of 1 s and the other typically slower by one order of magnitude. The results will be helpful in establishing design criteria for radio systems such as multiple input-multiple output that need to estimate the channel response and its persistence in time and for media access control (MAC) layer transmission protocols whose efficiency is affected by the depth and duration of channel outages. Index Terms--Autocovariance, coherence time, Ricean fading channels, temporal fading.

A diffraction field-focusing equation based on a specific conical-segment linearization procedure is derived for the Fresnel zone plate (FZP) lens of arbitrary curved profile and is applied for contrasting plane, spherical, parabolic and conical zone plate lenses, convex-side illuminated by a paraxial plane wave front. Two sets of 100-GHz curvilinear and plane FZP lenses are studied numerically with regards to their dimensions, axial focusing intensity and footprint, and frequency bandwidth. For the first set, where the curvilinear and plane lenses share a common lens base aperture and have equal focal lengths, the following new finding has resulted: regardless of their different in shape profiles the FZP lenses have equal zone numbers and produce similar axial focusing. The second set also consists of plane, spherical, parabolic and conical lenses. They share a common apex, and have equal in diameter base apertures and focal lengths but different thicknesses. For such disposition and proportions, the FZP lenses possess different zone numbers and focusing parameters (gain, efficiency, footprint and bandwidth). The belief that the curvilinear FZP have superior (or inferior) electromagnetic characteristics, compared to those of the plane FZP lens with equal number of zones is not in general true. Their relative focusing qualities can vary significantly depending on the lens positioning and dimensions. Index Terms--Focusing, Fresnel zone-plate (FZP) lenses, lenses, millimeter-wave lenses.

A simple inexpensive on-wall Fresnel zone plate (FZP) lens for indoor focusing of microwave signals is studied. It consists of concentric metal rings mounted on the outside of an exterior building wall. In our theoretical and empirical work the on-wall FZP lens is illuminated normally by a plane or spherical wave, of vertical or horizontal polarization, but other, more general incidence situations can be treated by similar means. The scalar quasi-optical focusing theory of the free-space zone plate has been modified and used for design and analysis of one-, two-, and three-ring on-wall FZP lenses. It is found that the presence of the wall does not change the FZP lens focusing efficiency significantly, but it has a strong axial defocusing effect. A 2-GHz FZP lens assembly consisting of three metal rings made out of thin antimosquito mesh has a focusing efficiency of about 15 dB (measured) and 14 dB (calculated), and axial defocusing of about 0.22 m. Some variations of on-wall/on-roof FZP lenses and their feasible applications in the microwave/millimeter-wave communication links are also discussed. Index Terms--Fresnel zone plate (FZP) lenses and antennas, microwave lenses, propagation.

The prediction of wall losses is a fundamental aspect in the planning of cellular systems. The broad variety of building materials and construction codes makes accurate attenuation prediction very difficult without the support of specific construction data or measurements. In this paper, the attenuation and equivalent electric parameters [epsilon] and [sigma] of brick and doubly reinforced concrete walls are estimated for the 900-MHz band by fitting simple ray tracing models to empirical transmission data. The measurement setup is described, and extensive experimental results justifying the quasioptical modeling are presented. Index Terms--Materials parameters, measurements, modeling and simulation, RF propagation, RF system engineering.