2,536 research outputs found
Transmission and detection for space-time block coding and v-blast systems
This dissertation focuses on topics of data transmission and detection of space -time block codes (STBC). The STBCs can be divided into two main categories, namely, the orthogonal space-time block codes (OSTBC) and the quasi-orthogonal space-time codes (Q-OSTBC). The space-time block coded systems from transceiver design perspective for both narrow-band and frequency selective wireless environment are studied. The dissertation also processes and studies a fast iterative detection scheme for a high-rate space-time transmission system, the V-BLAST system.
In Chapter 2, a new OSTBC scheme with full-rate and full-diversity, which can be used on QPSK transceiver systems with four transmit antennas and any number of receivers is studied. The newly proposed coding scheme is a non-linear coding. Compared with full-diversity QOSTBC, an obvious advantage of our proposed new OSTBC is that the coded signals transmitted through all four transmit antennas do not experience any constellation expansion.
In Chapter 3, a new fast coherent detection algorithm is proposed to provide maximum likelihood (ML) detection for Q-OSTBC. The new detection scheme is also very useful to analysis the diversity property of Q-OSTBC and design full diversity Q-OSTBC codes. The complexity of the new proposed detection algorithm can be independent to the modulation order and is especially suitable for high data rate transmission.
In Chapter 4, the space-time coding schemes in frequency selective channels are studied. Q-OSTC transmission and detection schemes are firstly extended for frequency selective wireless environment. A new block based quasi-orthogonal space-time block encoding and decoding (Q-OSTBC) scheme for a wireless system with four transmit antennas is proposed in frequency selective fading channels. The proposed MLSE detection scheme effectively combats channel dispersion and frequency selectivity due to multipath, yet still provides full diversity gain. However, since the computational complexity of MLSE detection increases exponentially with the maximum delay of the frequency selective channel, a fast sub-optimal detection scheme using MMSE equalizer is also proposed, especially for channels with large delays.
The Chapter 5 focuses on the V-BLAST system, an important high-rate space-time data transmission scheme. A reduced complexity ML detection scheme for VBLAST systems, which uses a pre-decoder guided local exhaustive search is proposed and studied. A polygon searching algorithm and an ordered successive interference cancellation (O-SIC) sphere searching algorithm are major components of the proposed multi-step ML detectors. At reasonable high SNRs, our algorithms have low complexity comparable to that of O-SIC algorithm, while they provide significant performance improvement. Another new low complexity algorithm termed ordered group-wise interference cancellation (O-GIC) is also proposed for the detection of high dimensional V-BLAST systems. The O-GIC based detection scheme is a sub-optimal detection scheme, however, it outperforms the O-SIC
High rate space time code with linear decoding complexity for multiple transmitting antennas
The multipath nature of the wireless channel, results in a superposition of the signals of each path at the receiver. This can lead to either constructive or destructive interference. Strong destructive interference is frequently referred to as deep fade and may result in temporary failure of communication due to the severe drop in the channel\u27s signal-to-noise ratio (SNR). To avoid this situation, signal diversity might be introduced. When having more than one antenna at the transmitter and / or receiver, forming a Multiple-Input Multiple-Output (MIMO) channel, spatial diversity can be employed to overcome the fading problem. Space time block codes (STBC) have been shown to be used well with the MIMO channel. Each type of STBC is designed to optimize a different criteria such as rate and diversity, while other characteristics of the code are its error performance and decoding computational complexity. The Orthogonal STBC (OSTBC) family of codes is known to achieve full diversity as well as very simple implementation of the Maximum Likelihood (ML) decoder. However, it was proven that, with complex symbol constellation one cannot achieve a full rate code when the number of transmitting antennas is larger than two. Quasi OSTBC are codes with full rate but with the penalty of more complex decoding, and in general does not achieve full diversity.
In this work, new techniques for OSTBC transmission / decoding are explored, such that a full rate code can be transmitted and decoded with linear complexity. The Row Elimination Method (REM) for OSTBC transmission is introduced, which basically involves the transmission of only part of the original OSTBC codeword, resulting in a full rate code termed Semi-Orthogonal STBC (SSTBC). Novel decoding scheme is presented, such that the SSTBC decoding computational complexity remains linear although the transmitted codeword is not orthogonal anymore. A new OSTBC, that complies with the new scheme\u27s requirements, is presented for any number of transmit antennas. The performance of the new scheme is studied under various settings, such as system with limited feedback and multiple antennas at the receiver.
The general decoding techniques presented for STBC, assume perfect channel knowledge at the receiver. It was shown, that the performance of any STBC system is severely degraded due to partial channel state information, results from imperfect channel estimation. To minimize the performance loss, one may lengthen the training sequences used for the channel estimation which, inevitably, results in some rate loss. In addition, complex decoding schemes can be used at the receiver to jointly decode the data while enhancing the channel estimation. It is suggested in this work to apply adaptive techniques to mitigate the performance loss without the penalty of additional rate loss or complex decoding. Namely, the bootstrap algorithm is used to further refine the received signals, resulting in better effective rate and performance in the presence of channel estimation errors. Modified implementations for the bootstrap\u27s weights calculation method are also presented, to improve the convergence rate of the algorithm, as well as to maintain a very low computational burden
Full Diversity Space-Time Block Codes with Low-Complexity Partial Interference Cancellation Group Decoding
Partial interference cancellation (PIC) group decoding proposed by Guo and
Xia is an attractive low-complexity alternative to the optimal processing for
multiple-input multiple-output (MIMO) wireless communications. It can well deal
with the tradeoff among rate, diversity and complexity of space-time block
codes (STBC). In this paper, a systematic design of full-diversity STBC with
low-complexity PIC group decoding is proposed. The proposed code design is
featured as a group-orthogonal STBC by replacing every element of an Alamouti
code matrix with an elementary matrix composed of multiple diagonal layers of
coded symbols. With the PIC group decoding and a particular grouping scheme,
the proposed STBC can achieve full diversity, a rate of and a
low-complexity decoding for transmit antennas. Simulation results show that
the proposed codes can achieve the full diversity with PIC group decoding while
requiring half decoding complexity of the existing codes.Comment: 10 pages, 3 figures
A Novel Construction of Multi-group Decodable Space-Time Block Codes
Complex Orthogonal Design (COD) codes are known to have the lowest detection
complexity among Space-Time Block Codes (STBCs). However, the rate of square
COD codes decreases exponentially with the number of transmit antennas. The
Quasi-Orthogonal Design (QOD) codes emerged to provide a compromise between
rate and complexity as they offer higher rates compared to COD codes at the
expense of an increase of decoding complexity through partially relaxing the
orthogonality conditions. The QOD codes were then generalized with the so
called g-symbol and g-group decodable STBCs where the number of orthogonal
groups of symbols is no longer restricted to two as in the QOD case. However,
the adopted approach for the construction of such codes is based on sufficient
but not necessary conditions which may limit the achievable rates for any
number of orthogonal groups. In this paper, we limit ourselves to the case of
Unitary Weight (UW)-g-group decodable STBCs for 2^a transmit antennas where the
weight matrices are required to be single thread matrices with non-zero entries
in {1,-1,j,-j} and address the problem of finding the highest achievable rate
for any number of orthogonal groups. This special type of weight matrices
guarantees full symbol-wise diversity and subsumes a wide range of existing
codes in the literature. We show that in this case an exhaustive search can be
applied to find the maximum achievable rates for UW-g-group decodable STBCs
with g>1. For this purpose, we extend our previously proposed approach for
constructing UW-2-group decodable STBCs based on necessary and sufficient
conditions to the case of UW-g-group decodable STBCs in a recursive manner.Comment: 12 pages, and 5 tables, accepted for publication in IEEE transactions
on communication
Maximum Rate of Unitary-Weight, Single-Symbol Decodable STBCs
It is well known that the Space-time Block Codes (STBCs) from Complex
orthogonal designs (CODs) are single-symbol decodable/symbol-by-symbol
decodable (SSD). The weight matrices of the square CODs are all unitary and
obtainable from the unitary matrix representations of Clifford Algebras when
the number of transmit antennas is a power of 2. The rate of the square
CODs for has been shown to be complex symbols per
channel use. However, SSD codes having unitary-weight matrices need not be
CODs, an example being the Minimum-Decoding-Complexity STBCs from
Quasi-Orthogonal Designs. In this paper, an achievable upper bound on the rate
of any unitary-weight SSD code is derived to be complex
symbols per channel use for antennas, and this upper bound is larger than
that of the CODs. By way of code construction, the interrelationship between
the weight matrices of unitary-weight SSD codes is studied. Also, the coding
gain of all unitary-weight SSD codes is proved to be the same for QAM
constellations and conditions that are necessary for unitary-weight SSD codes
to achieve full transmit diversity and optimum coding gain are presented.Comment: accepted for publication in the IEEE Transactions on Information
Theory, 9 pages, 1 figure, 1 Tabl
- …