20 research outputs found
Multiproduct Uniform Polar Quantizer
The aim of this paper is to reduce the complexity of the unrestricted uniform polar quantizer (UUPQ), keeping its high performances. To achieve this, in this paper we propose the multiproduct uniform polar quantizer (MUPQ), where several consecutive magnitude levels are joined in segments and within each segment the uniform product quantization is performed (i.e. all levels within one segments have the same number of phase levels). MUPQ is much simpler for realization than UUPQ, but it achieves similar performances as UUPQ. Since MUPQ has low complexity and achieves much better performances than the scalar uniform quantizer, it can be widely used instead of scalar uniform quantizers to improve performances, for any signal with the Gaussian distribution
Log-Polar Quantizer with the Embedded G.711 Codec
In this paper a new two-dimensional vector quantizer for memoryless Gaussian source, realized in polar coordinates, is proposed. The G.711 codec is embedded in our vector quantizer, and therefore our vector quantizer is compatible with the G.711 codec. It is simple for realization and it has much better performances, compared to the G.711 codec, such as much higher SQNR (signal-to-quantization noise ratio) for the same bit-rate, or bit-rate decrease for the same SQNR. The G.711 codec is widely used in many systems, especially in PSTN (public switched telephone network). Due to compatibility with the G.711 standard, our vector quantizer can be realized with simple software modification of the existing the G.711 codec, and therefore it can be very easily implemented in PSTN and other systems. So, small investments are needed for wide implementation of our model, but significant improvement of performances can be obtained
PIECEWISE-LINEAR RADIAL COMPRESSION FUNCTION FOR PYRAMID TWO-DIMENSIONAL QUANTIZER
In this paper a companding-type approach is presented to designing the pyramid two-dimensional quantizer whose cells are obtained by radial spreading of the cubic cells. For a memoryless Laplacian source, the optimal radial compression function and rate allocation between the radius and location quantizers are determined subject to the mean-squared error (MSE) criterion. The results also include formulation of a new method for linearization of compression function, based on a compression function derivative discretization. It is of special importance since the unclosed-form of optimal radial compression function causes certain difficulties in companding quantizer implementation
Cooperative Distributed Transmission and Reception
In telecommunications, a cooperative scheme refers to a method where two or more users share or combine their information in order to increase diversity gain or power gain. In contrast to conventional point-to-point communications, cooperative communications allow different users in a wireless network to share resources so that instead of maximizing the performance of its own link, each user collaborates with its neighbours to achieve an overall improvement in performance. In this dissertation, we consider different models for transmission and reception and explore cooperative techniques that increase the reliability and capacity gains in wireless networks, with consideration to practical issues such as channel estimation errors and backhaul constraints.
This dissertation considers the design and performance of cooperative communication techniques. Particularly, the first part of this dissertation focuses on the performance comparison between interference alignment and opportunistic transmission for a 3-user single-input single- output (SISO) interference channel in terms of average sum rate in the presence of channel estimation errors. In the case of interference alignment, channel estimation errors cause interference leakage which consequently results in a loss of achievable rate. In the case of opportunistic transmission, channel estimation errors result in a non-zero probability of incorrectly choosing the node with the best channel. The effect of these impairments is quantified in terms of the achievable average sum rate of these transmission techniques. Analysis and numerical examples show that SISO interference alignment can achieve better average sum rate with good channel estimates and at high SNR whereas opportunistic transmission provides better performance at low SNR and/or when the channel estimates are poor.
We next considers the problem of jointly decoding binary phase shift keyed (BPSK) messages from a single distant transmitter to a cooperative receive cluster connected by a local area network (LAN). An approximate distributed receive beamforming algorithm is proposed based on the exchange of coarsely- quantized observations among some or all of the nodes in the receive cluster. By taking into account the differences in channel quality across the receive cluster, the quantized information from other nodes in the receive cluster can be appropriately combined with locally unquantized information to form an approximation of the ideal receive beamformer decision statistic. The LAN throughput requirements of this technique are derived as a function of the number of participating nodes in the receive cluster, the forward link code rate, and the quantization parameters. Using information-theoretic analysis and simulations of an LDPC coded system in fading channels, numerical results show that the performance penalty (in terms of outage probability and block error rate) due to coarse quantization is small in the low SNR regimes enabled by cooperative distributed reception. An upper/lower bound approximation is derived based on a circle approximation in the channel magnitude domain which provides a pretty fast way to compute the outage probability performance for a system with arbitrary number of receivers at a given SNR.
In the final part of this dissertation, we discuss the distributed reception technique with higher- order modulation schemes in the forward link. The extension from BPSK to QPSK is straightforward and is studied in the second part of this dissertation. The extension to 8PSK, 4PAM and 16QAM forward links, however, is not trivial. For 8PSK, two techniques are proposed: pseudobeamforming and 3-bit belief combining where the first one is intuitive and turns out to be suboptimal,the latter is optimal in terms of outage probability performance. The idea of belief combining can be applied to the 4PAM and 16QAM and it is shown that better/finer quantizer design can further improve the block error rate performance. Information-theoretic analysis and numerical results are provided to show that significant reliability and SNR gains can be achieved by using the proposed schemes
Projektovanje višenivoskih konstelacija signala za komunikacione sisteme sa ograničenom snagom
In modern digital communication systems, a huge amount of
data is transmitted, so that research aimed at achieving more
efficient transmission is necessary, which makes the topic of this
doctoral dissertation relevant and important. The subject of
research in this doctoral dissertation is how to improve the power
efficiency of multilevel PAM (Pulse Amplitude Modulation) and
APSK (Amplitude Phase Shift Keying) constellations in
power-limited communication systems, such as optical
communications, satellite communications, wireless
communications, multiple-input multiple-output systems.
A constellation is defined by the geometric-space partition and
probabilities of constellation points. Therefore, under constellation
designing or constellation shaping the methods that optimize
modulation format by adjusting the geometric-space location
and/or probabilities of constellation points are assumed. All these
methods are categorized within three constellation shaping
schemes: geometric constellation shaping, probabilistic
constellation shaping and hybrid probabilistic-geometric
constellation shaping.
Constellation shaping has been usually performed by
optimizing some metric that characterize a channel or by
optimizing the minimum Euclidean distance. Instead of this, in this
dissertation constellation shaping is performed by applying
designing techniques from quantization theory. Namely, the
existence of similarity in the geometric-space representation ofconstellation and quantization motivates us to apply the
quantization designing methods in constellation shaping.
Special attention is paid to reducing the constellation
complexity, that is to designing the piecewise-uniform
constellations in terms of the geometric-space partition and
probability distribution of constellation points. Methods for
designing constellation inspired by piecewise-linear companding
quantization have been proposed. Also, a novel designing concept
that employs the companding technique in constellation shaping
on a totally different manner has been proposed.
Power efficiency is the ability of a modulation technique to
preserve the fidelity/quality of digital data at low values of the
signal-to-noise ratio, and is expressed as the signal-to-noise ratio
per bit required to achieve a given error probability. In the
dissertation we deal with designing power-efficient multilevel
constellations for channels dominated by the additive white
Gaussian noise, and the metric for constellation performance
evaluation is a functional dependence of symbol error probability
on signal-to-noise ratio per bit for uncoded constellation in channel
with additive white Gausssian noise. The accuracy of analyzes and
achieved results has been verified by performing simulations
Load Modulation for Backscatter Communication: Channel Capacity and Near-Capacity Schemes
In backscatter communication (BC), a passive tag transmits information by
just affecting an external electromagnetic field through load modulation.
Thereby, the feed current of the excited tag antenna is modulated by adapting
the passive termination load. This paper studies the achievable information
rates with a freely adaptable passive load. As a prerequisite, we unify
monostatic, bistatic, and ambient BC with circuit-based system modeling. We
present the crucial insight that channel capacity is described by existing
results on peak-power-limited quadrature Gaussian channels, because the
steady-state tag current phasor lies on a disk. Consequently, we derive the
channel capacity for the case of an unmodulated external field, for general
passive, purely reactive, or purely resistive tag loads. We find that
modulating both resistance and reactance is important for very high rates. We
discuss the capacity-achieving load statistics, rate asymptotics, technical
conclusions, and rate losses from value-range-constrained loads (which are
found to be small for moderate constraints).
We then demonstrate that near-capacity rates can be attained by more
practical schemes: (i) amplitude-and-phase-shift keying on the reflection
coefficient and (ii) simple load circuits of a few switched resistors and
capacitors.
Finally, we draw conclusions for the ambient BC channel capacity in important
special cases.Comment: This work has been submitted to the IEEE for possible publication.
Copyright may be transferred without notice. Included conference paper:
arXiv:2201.0024
Proceedings of the Mobile Satellite Conference
A satellite-based mobile communications system provides voice and data communications to mobile users over a vast geographic area. The technical and service characteristics of mobile satellite systems (MSSs) are presented and form an in-depth view of the current MSS status at the system and subsystem levels. Major emphasis is placed on developments, current and future, in the following critical MSS technology areas: vehicle antennas, networking, modulation and coding, speech compression, channel characterization, space segment technology and MSS experiments. Also, the mobile satellite communications needs of government agencies are addressed, as is the MSS potential to fulfill them
Proceedings of the Second International Mobile Satellite Conference (IMSC 1990)
Presented here are the proceedings of the Second International Mobile Satellite Conference (IMSC), held June 17-20, 1990 in Ottawa, Canada. Topics covered include future mobile satellite communications concepts, aeronautical applications, modulation and coding, propagation and experimental systems, mobile terminal equipment, network architecture and control, regulatory and policy considerations, vehicle antennas, and speech compression