1,314 research outputs found
A Systematic Framework for the Construction of Optimal Complete Complementary Codes
The complete complementary code (CCC) is a sequence family with ideal
correlation sums which was proposed by Suehiro and Hatori. Numerous literatures
show its applications to direct-spread code-division multiple access (DS-CDMA)
systems for inter-channel interference (ICI)-free communication with improved
spectral efficiency. In this paper, we propose a systematic framework for the
construction of CCCs based on -shift cross-orthogonal sequence families
(-CO-SFs). We show theoretical bounds on the size of -CO-SFs and CCCs,
and give a set of four algorithms for their generation and extension. The
algorithms are optimal in the sense that the size of resulted sequence families
achieves theoretical bounds and, with the algorithms, we can construct an
optimal CCC consisting of sequences whose lengths are not only almost arbitrary
but even variable between sequence families. We also discuss the family size,
alphabet size, and lengths of constructible CCCs based on the proposed
algorithms
Interference-Mitigating Waveform Design for Next-Generation Wireless Systems
A brief historical perspective of the evolution of waveform designs employed in consecutive generations of wireless communications systems is provided, highlighting the range of often conflicting demands on the various waveform characteristics. As the culmination of recent advances in the field the underlying benefits of various Multiple Input Multiple Output (MIMO) schemes are highlighted and exemplified. As an integral part of the appropriate waveform design, cognizance is given to the particular choice of the duplexing scheme used for supporting full-duplex communications and it is demonstrated that Time Division Duplexing (TDD) is substantially outperformed by Frequency Division Duplexing (FDD), unless the TDD scheme is combined with further sophisticated scheduling, MIMOs and/or adaptive modulation/coding. It is also argued that the specific choice of the Direct-Sequence (DS) spreading codes invoked in DS-CDMA predetermines the properties of the system. It is demonstrated that a specifically designed family of spreading codes exhibits a so-called interference-free window (IFW) and hence the resultant system is capable of outperforming its standardised counterpart employing classic Orthogonal Variable Spreading Factor (OVSF) codes under realistic dispersive channel conditions, provided that the interfering multi-user and multipath components arrive within this IFW. This condition may be ensured with the aid of quasisynchronous adaptive timing advance control. However, a limitation of the system is that the number of spreading codes exhibiting a certain IFW is limited, although this problem may be mitigated with the aid of novel code design principles, employing a combination of several spreading sequences in the time-frequency and spatial-domain. The paper is concluded by quantifying the achievable user load of a UTRA-like TDD Code Division Multiple Access (CDMA) system employing Loosely Synchronized (LS) spreading codes exhibiting an IFW in comparison to that of its counterpart using OVSF codes. Both system's performance is enhanced using beamforming MIMOs
Cyclic Prefix-Free MC-CDMA Arrayed MIMO Communication Systems
The objective of this thesis is to investigate MC-CDMA MIMO systems where
the antenna array geometry is taken into consideration. In most MC-CDMA
systems, cyclic pre xes, which reduce the spectral eÂą ciency, are used. In order
to improve the spectral efficiency, this research study is focused on cyclic pre x-
free MC-CDMA MIMO architectures.
Initially, space-time wireless channel models are developed by considering the
spatio-temporal mechanisms of the radio channel, such as multipath propaga-
tion. The spatio-temporal channel models are based on the concept of the array
manifold vector, which enables the parametric modelling of the channel.
The array manifold vector is extended to the multi-carrier space-time array
(MC-STAR) manifold matrix which enables the use of spatio-temporal signal
processing techniques. Based on the modelling, a new cyclic pre x-free MC-
CDMA arrayed MIMO communication system is proposed and its performance
is compared with a representative existing system. Furthermore, a MUSIC-type
algorithm is then developed for the estimation of the channel parameters of the
received signal.
This proposed cyclic pre x-free MC-CDMA arrayed MIMO system is then
extended to consider the effects of spatial diffusion in the wireless channel. Spatial
diffusion is an important channel impairment which is often ignored and the
failure to consider such effects leads to less than satisfactory performance. A
subspace-based approach is proposed for the estimation of the channel parameters
and spatial spread and reception of the desired signal.
Finally, the problem of joint optimization of the transmit and receive beam-
forming weights in the downlink of a cyclic pre x-free MC-CDMA arrayed MIMO
communication system is investigated. A subcarrier-cooperative approach is used
for the transmit beamforming so that there is greater flexibility in the allocation
of channel symbols. The resulting optimization problem, with a per-antenna
transmit power constraint, is solved by the Lagrange multiplier method and an
iterative algorithm is proposed
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Intelligent genetic algorithms for next-generation broadband multi-carrier CDMA wireless networks
This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.This dissertation proposes a novel intelligent system architecture for next-generation broadband multi-carrier CDMA wireless networks. In our system, two novel and similar intelligent genetic algorithms, namely Minimum Distance guided GAs (MDGAs) are invented for both peak-to-average power ratio (PAPR) reduction at the transmitter side and multi-user detection (MUD) at the receiver side. Meanwhile, we derive a theoretical BER performance analysis for the proposed MC-CDMA system in A WGN channel. Our analytical results show that the theoretical BER performance of synchronized MC-CDMA system is the same as that of the synchronized DS-CDMA system which is also used as a theoretical guidance of our novel MUD receiver design. In contrast to traditional GAs, our MDGAs start with a balanced ratio of exploration and exploitation which is maintained throughout the process. In our algorithms, a new replacement strategy is designed which increases significantly the convergence rate
and reduces dramatically computational complexity as compared to the conventional GAs. The simulation results demonstrate that, if compared to those schemes using exhaustive search and traditional GAs, (1) our MDGA-based P APR reduction scheme achieves 99.52% and 50+% reductions in computational complexity, respectively; (2)
our MDGA-based MUD scheme achieves 99.54% and 50+% reductions in computational complexity, respectively. The use of one core MDGA solution for both issues can ease the hardware design and dramatically reduce the implementation cost in practice
A multi-levelled OFDM-CDMA modem using complete complementary codes
In this paper, we introduce a novel multiple access
scheme based on a combination of a multi-levelled modem and
multi-carrier techniques with the use of complete complementary
codes. This modulation technique combines a multi-dimensional
code division multiple access (CDMA) modem with recent designs
of perfectly complete complementary orthogonal codes.
The rotational properties of the spreading codes are further
exploited to improve the modulation technique, throughput,
spectral efficiency, and capacity. Additionally, the system is
extended by making use of multiple carrier frequencies as in
OFDM, with the additional benefits of being able to spread
data in frequency and/or in time. The modem offers multiple
access interference MAI-free and multipath interference MI-free
operation in both asynchronous and synchronous communication,
due to perfect autocorrelation and zero cross-correlation properties
of the spreading codes. The unique multi-levelled multiple
access modulation technique together with the integration of
complete complementary codes, produces a spectrally efficient
output signal with high data throughput rates, better noise
tolerances in harsh channel conditions and an increased user
capacity.The Department of Trade and
Industry (DTI), South Africahttp://www.saiee.org.za//content.php?pageID=200#ai201
Parameters of Communication Systems Based on OFDM-CDMA
CĂl disertaÄnĂ prĂĄce leĆŸĂ v oblasti modelovĂĄnĂ a vyhodnocenĂ bezdrĂĄtovĂœch komunikaÄnĂch systĂ©mĆŻ s dvojrozmÄrnĂœm rozprostĂrĂĄnĂm signĂĄlu a jejich klĂÄovĂœch parametrĆŻ v zĂĄvislosti na vybranĂœch vlastnostech modernĂho bezdrĂĄtovĂ©ho komunikaÄnĂho ĆetÄzce. VĂœzkumnĂ© metody pouĆŸitĂ© v tĂ©to prĂĄci spoÄĂvajĂ pĆedevĆĄĂm ve vĂœvoji softwarovĂ©ho simulĂĄtoru pro prostĆedĂ Matlab, s jehoĆŸ pomocĂ, a s vyuĆŸitĂm statistickĂ©ho pĆĂstupu, jsou navrĆŸenĂ© algoritmy ovÄĆeny. DĂĄle je pouĆŸit simulĂĄtor fyzickĂ© vrstvy dle 3rd Generation Partnership Project Long Term Evolution (3GPP LTE), vyvinutĂœ na TechnickĂ© univerzitÄ ve VĂdni. Tento pĆedstavuje ideĂĄlnĂ platformu pro implementaci metody dvojrozmÄrnĂ©ho (2D) rozprostĂrĂĄnĂ a jejĂ vyhodnocenĂ s pĆihlĂ©dnutĂm k souÄasnĂœm bezdrĂĄtovĂœm komunikaÄnĂm systĂ©mĆŻm. ZjiĆĄtÄnĂ prezentovanĂĄ v tĂ©to prĂĄci pĆedstavujĂ pĆedevĆĄĂm ovÄĆenĂ ĂșÄinnosti systĂ©mu nazvanĂ©ho jako Variable Spreading Factor - Orthogonal Code Frequency Division Multiplex (VSF-OFCDM), kterĂœ vyuĆŸĂvĂĄ principu 2D rozprostĂrĂĄnĂ signĂĄlu a zjiĆĄtÄnĂ, ĆŸe VSF-OFCDM systĂ©m pĆekonĂĄvĂĄ systĂ©my vyuĆŸĂvajĂcĂ Orthogonal Division Frequency Multiplex (OFDM), nebo Code Division Multiple Access (CDMA). DĂĄle byla navrĆŸena metoda 2D rozprostĂrĂĄnĂ signĂĄlu v systĂ©mu LTE, kde se tĂ©ĆŸ potvrdila jejĂ ĂșÄinnost. DĂky ĂșÄinnÄjĆĄĂmu potlaÄenĂ vlivu rychlĂ© variace pĆenosovĂ©ho kanĂĄlu v zĂĄvislosti na frekvenci a Äase, dosahuje systĂ©m VSF-OFCDM znatelnÄ vyĆĄĆĄĂ datovĂ© prostupnosti.The focus of this research is in the area of modeling and evaluating of the wireless systems with two dimensional signal spreading, itâs key parameters and dependencies on other features in modern wireless communication chain. The research method adopted in this dissertation includes a development of Matlab based simulators which exploits a statistical approach to show a contribution of proposed algorithms. Furthermore, a model of physical layer of the 3rd Generation Partnership Project Long Term Evolution (3GPP LTE), developed by the Vienna University of Technology, was utilized as a simulation environment suitable for implementation of a two dimensional (2D) signal spreading method and its evaluation as well as comparison of achieved results with the state-of-the-art systems. The findings from this research provide evidence that the Variable Spreading Factor - Orthogonal Code Frequency Division Multiplex (hereafter VSF-OFCDM) employing a 2D spreading is a promising wireless access scheme superior to Orthogonal Division Frequency Multiplex (OFDM) or Code Division Multiple Access (CDMA) and is capable to significantly increase the data rates in wireless transmission due to the capability of such system to effectively cope with fast time and frequency fluctuations in the wireless transmission channel.
A NOVEL CONSTRUCTION OF VECTOR COMBINATORIAL (VC) CODE FAMILIES AND DETECTION SCHEME FOR SAC OCDMA SYSTEMS
There has been growing interests in using optical code division multiple access
(OCDMA) systems for the next generation high-speed optical fiber networks. The
advantage of spectral amplitude coding (SAC-OCDMA) over conventional OCDMA
systems is that, when using appropriate detection technique, the multiple access
interference (MAI) can totally be canceled. The motivation of this research is to
develop new code families to enhance the overall performance of optical OCDMA
systems. Four aspects are tackled in this research. Firstly, a comprehensive discussion
takes place on all important aspects of existing codes from advantages and
disadvantages point of view. Two algorithms are proposed to construct several code
families namely Vector Combinatorial (VC). Secondly, a new detection technique
based on exclusive-OR (XOR) logic is developed and compared to the reported
detection techniques. Thirdly, a software simulation for SAC OCDMA system with
the VC families using a commercial optical system, Virtual Photonic Instrument,
âVPITM TransmissionMaker 7.1â is conducted. Finally, an extensive investigation to
study and characterize the VC-OCDMA in local area network (LAN) is conducted.
For the performance analysis, the effects of phase-induced intensity noise (PIIN), shot
noise, and thermal noise are considered simultaneously. The performances of the
system compared to reported systems were characterized by referring to the signal to
noise ratio (SNR), the bit error rate (BER) and the effective power (Psr). Numerical
results show that, an acceptable BER of 10â9 was achieved by the VC codes with 120
active users while a much better performance can be achieved when the effective
received power Psr > -26 dBm. In particular, the BER can be significantly improved
when the VC optimal channel spacing width is carefully selected; best performance
occurs at a spacing bandwidth between 0.8 and 1 nm. The simulation results indicate
that VC code has a superior performance compared to other reported codes for the
same transmission quality. It is also found that for a transmitted power at 0 dBm, the
BER specified by eye diagrams patterns are 10-14 and 10-5 for VC and Modified
Quadratic Congruence (MQC) codes respectively
Space time transceiver design over multipath fading channels
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