5,727 research outputs found
A new approach to joint full-rate STBC and long-code WCDMA for four transmit antenna MIMO systems
In this work, we propose a novel combination of an extended orthogonal space-time block code (EO- STBC) or a quasi-orthogonal space-time block code (QO-STBC) and a long-code wideband code division multiple access (WCDMA) scheme to exploit spatial diversity in future wireless communication systems. For a mobile communication system, a key parameter is the system capacity. Multiple antennas at the transmitter and receiver in a system have been recognized as a major technology breakthrough to increase the capacity of a wireless communication network. To mitigate this limited capacity problem, two full transmit rate STBCs are integrated into the long-code WCDMA system with four transmit antenna. The bit error rate (BER) performance for the proposed technique is compared with other conventional methods for quasi-static wireless channels. Simulation results show that the proposed full rate STBC scheme when combined with the receive antenna selection technique method yields improved BER performance schemes
Super-orthogonal space-time turbo coded OFDM systems.
Thesis (Ph.D.)-University of KwaZulu-Natal, Durban, 2012.The ever increasing demand for fast and efficient broadband wireless communication
services requires future broadband communication systems to provide a high data rate,
robust performance and low complexity within the limited available electromagnetic
spectrum. One of the identified, most-promising techniques to support high
performance and high data rate communication for future wireless broadband services
is the deployment of multi-input multi-output (MIMO) antenna systems with
orthogonal frequency division multiplexing (OFDM). The combination of MIMO and
OFDM techniques guarantees a much more reliable and robust transmission over a
hostile wireless channel through coding over the space, time and frequency domains.
In this thesis, two full-rate space-time coded OFDM systems are proposed. The first
one, designed for two transmit antennas, is called extended super-orthogonal space-time
trellis coded OFDM (ESOSTTC-OFDM), and is based on constellation rotation. The
second one, called super-quasi-orthogonal space-time trellis coded OFDM (SQOSTTCOFDM),
combines a quasi-orthogonal space-time block code with a trellis code to
provide a full-rate code for four transmit antennas. The designed space-time coded
MIMO-OFDM systems achieve a high diversity order with high coding gain by
exploiting the diversity advantage of frequency-selective fading channels.
Concatenated codes have been shown to be an effective technique of achieving reliable
communication close to the Shannon limit, provided that there is sufficient available
diversity. In a bid to improve the performance of the super orthogonal space-time
trellis code (SOSTTC) in frequency selective fading channels, five distinct
concatenated codes are proposed for MIMO-OFDM over frequency-selective fading
channels in the second part of this thesis. Four of the coding schemes are based on the
concatenation of convolutional coding, interleaving, and space-time coding, along
multiple-transmitter diversity systems, while the fifth coding scheme is based on the
concatenation of two space-time codes and interleaving. The proposed concatenated
Super-Orthogonal Space-Time Turbo-Coded OFDM System I. B. Oluwafemi 2012 vii
coding schemes in MIMO-OFDM systems achieve high diversity gain by exploiting
available diversity resources of frequency-selective fading channels and achieve a high
coding gain through concatenations by employing the turbo principle. Using computer
software simulations, the performance of the concatenated SOSTTC-OFDM schemes is
compared with those of concatenated space-time trellis codes and those of conventional
SOSTTC-OFDM schemes in frequency-selective fading channels. Simulation results
show that the concatenated SOSTTC-OFDM system outperformed the concatenated
space-time trellis codes and the conventional SOSTTC-OFDM system under the
various channel scenarios in terms of both diversity order and coding gain
Code diversity in multiple antenna wireless communication
The standard approach to the design of individual space-time codes is based
on optimizing diversity and coding gains. This geometric approach leads to
remarkable examples, such as perfect space-time block codes, for which the
complexity of Maximum Likelihood (ML) decoding is considerable. Code diversity
is an alternative and complementary approach where a small number of feedback
bits are used to select from a family of space-time codes. Different codes lead
to different induced channels at the receiver, where Channel State Information
(CSI) is used to instruct the transmitter how to choose the code. This method
of feedback provides gains associated with beamforming while minimizing the
number of feedback bits. It complements the standard approach to code design by
taking advantage of different (possibly equivalent) realizations of a
particular code design. Feedback can be combined with sub-optimal low
complexity decoding of the component codes to match ML decoding performance of
any individual code in the family. It can also be combined with ML decoding of
the component codes to improve performance beyond ML decoding performance of
any individual code. One method of implementing code diversity is the use of
feedback to adapt the phase of a transmitted signal as shown for 4 by 4
Quasi-Orthogonal Space-Time Block Code (QOSTBC) and multi-user detection using
the Alamouti code. Code diversity implemented by selecting from equivalent
variants is used to improve ML decoding performance of the Golden code. This
paper introduces a family of full rate circulant codes which can be linearly
decoded by fourier decomposition of circulant matrices within the code
diversity framework. A 3 by 3 circulant code is shown to outperform the
Alamouti code at the same transmission rate.Comment: 9 page
High-rate codes that are linear in space and time
Multiple-antenna systems that operate at high rates require simple yet effective space-time transmission schemes to handle the large traffic volume in real time. At rates of tens of bits per second per hertz, Vertical Bell Labs Layered Space-Time (V-BLAST), where every antenna transmits its own independent substream of data, has been shown to have good performance and simple encoding and decoding. Yet V-BLAST suffers from its inability to work with fewer receive antennas than transmit antennas-this deficiency is especially important for modern cellular systems, where a base station typically has more antennas than the mobile handsets. Furthermore, because V-BLAST transmits independent data streams on its antennas there is no built-in spatial coding to guard against deep fades from any given transmit antenna. On the other hand, there are many previously proposed space-time codes that have good fading resistance and simple decoding, but these codes generally have poor performance at high data rates or with many antennas. We propose a high-rate coding scheme that can handle any configuration of transmit and receive antennas and that subsumes both V-BLAST and many proposed space-time block codes as special cases. The scheme transmits substreams of data in linear combinations over space and time. The codes are designed to optimize the mutual information between the transmitted and received signals. Because of their linear structure, the codes retain the decoding simplicity of V-BLAST, and because of their information-theoretic optimality, they possess many coding advantages. We give examples of the codes and show that their performance is generally superior to earlier proposed methods over a wide range of rates and signal-to-noise ratios (SNRs)
Design of fully diverse multiple-antenna codes based on Sp(2)
Fully diverse constellations, i.e., sets of unitary matrices whose pairwise differences are nonsingular, are useful in multiple-antenna communications, especially in multiple-antenna differential modulation, since they have good pairwise error properties. Recently, group theoretic ideas, especially fixed-point-free (fpf) groups, have been used to design fully diverse constellations of unitary matrices. Here we construct four-transmit-antenna constellations appropriate for differential modulation based on the symplectic group Sp(2). They can be regarded as extensions of Alamouti's celebrated two-transmit-antenna orthogonal design which can be constructed from the group Sp(1). We further show that the structure of Sp(2) codes lends itself to efficient maximum-likelihood (ML) decoding via the sphere decoding algorithm. Finally, the performance of Sp(2) codes is compared with that of other existing codes including Alamouti's orthogonal design, a 4/spl times/4 complex orthogonal design, Cayley differential unitary space-time codes and group-based codes
Novel Feedback Calculation Technique for Improved Transmit Scheme
Extended balanced space-time block coding (EBSTBC) is able to achieve large coding gain and guarantee full diversity for any number of transmit antennas. Performance of the EBSTBC has been improved with improved transmit scheme (ITS) which is combination of the EBSTBC with transmit antenna selection. Performance of the ITS with a limited number of feedback bits approaches to performance of ideal beamforming which requires ideal channel state information at the transmitter. However, the calculation of feedback information at the receiver employs exhaustive searching scheme which is very complex and energy inefficient process. In this work, a low complexity and energy efficient feedback information scheme for the ITS receiver is proposed. Theoretical and simulation results show that the calculation complexity of feedback information is decreased more than 87% and the proposed scheme yields the same bit error rate performance with the ITS. Moreover, the proposed scheme requires very low addition memory with respect to alternative schemes
Generalized Silver Codes
For an transmit, receive antenna system (
system), a {\it{full-rate}} space time block code (STBC) transmits complex symbols per channel use. The well known Golden code is an
example of a full-rate, full-diversity STBC for 2 transmit antennas. Its
ML-decoding complexity is of the order of for square -QAM. The
Silver code for 2 transmit antennas has all the desirable properties of the
Golden code except its coding gain, but offers lower ML-decoding complexity of
the order of . Importantly, the slight loss in coding gain is negligible
compared to the advantage it offers in terms of lowering the ML-decoding
complexity. For higher number of transmit antennas, the best known codes are
the Perfect codes, which are full-rate, full-diversity, information lossless
codes (for ) but have a high ML-decoding complexity of the order
of (for , the punctured Perfect codes are
considered). In this paper, a scheme to obtain full-rate STBCs for
transmit antennas and any with reduced ML-decoding complexity of the
order of , is presented. The codes constructed are
also information lossless for , like the Perfect codes and allow
higher mutual information than the comparable punctured Perfect codes for . These codes are referred to as the {\it generalized Silver codes},
since they enjoy the same desirable properties as the comparable Perfect codes
(except possibly the coding gain) with lower ML-decoding complexity, analogous
to the Silver-Golden codes for 2 transmit antennas. Simulation results of the
symbol error rates for 4 and 8 transmit antennas show that the generalized
Silver codes match the punctured Perfect codes in error performance while
offering lower ML-decoding complexity.Comment: Accepted for publication in the IEEE Transactions on Information
Theory. This revised version has 30 pages, 7 figures and Section III has been
completely revise
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