21 |
Space-Time Coding and Space-Time Channel Modelling for Wireless CommunicationsLamahewa, Tharaka Anuradha, tharaka.lamahewa@anu.edu.au January 2007 (has links)
In this thesis we investigate the effects of the physical
constraints such as antenna aperture size, antenna geometry and
non-isotropic scattering distribution parameters (angle of
arrival/departure and angular spread) on the performance of coherent
and non-coherent space-time coded wireless communication systems.
First, we derive analytical expressions for the exact pairwise error
probability (PEP) and PEP upper-bound of coherent and non-coherent
space-time coded systems operating over spatially correlated fading
channels using a moment-generating function-based approach. These
analytical expressions account for antenna spacing, antenna
geometries and scattering distribution models. Using these new PEP
expressions, the degree of the effect of antenna spacing, antenna
geometry and angular spread is quantified on the diversity advantage
(robustness) given by a space-time code. It is shown that the number
of antennas that can be employed in a fixed antenna aperture without
diminishing the diversity advantage of a space-time code is
determined by the size of the antenna aperture, antenna geometry and
the richness of the scattering environment.
¶
In realistic channel environments the performance of space-time
coded multiple-input multiple output (MIMO) systems is significantly
reduced due to non-ideal antenna placement and non-isotropic
scattering. In this thesis, by exploiting the spatial dimension of a
MIMO channel we introduce the novel use of linear spatial precoding
(or power-loading) based on fixed and known parameters of MIMO
channels to ameliorate the effects of non-ideal antenna placement on
the performance of coherent and non-coherent space-time codes. The
spatial precoder virtually arranges the antennas into an optimal
configuration so that the spatial correlation between all antenna
elements is minimum. With this design, the precoder is fixed for
fixed antenna placement and the transmitter does not require any
feedback of channel state information (partial or full) from the
receiver. We also derive precoding schemes to exploit non-isotropic
scattering distribution parameters of the scattering channel to
improve the performance of space-time codes applied on MIMO systems
in non-isotropic scattering environments. However, these schemes
require the receiver to estimate the non-isotropic parameters and
feed them back to the transmitter.
¶
The idea of precoding based on fixed parameters of MIMO channels is
extended to maximize the capacity of spatially constrained dense
antenna arrays. It is shown that the theoretical maximum capacity
available from a fixed region of space can be achieved by power
loading based on previously unutilized channel state information
contained in the antenna locations. We analyzed the correlation
between different modal orders generated at the transmitter region
due to spatially constrained antenna arrays in non-isotropic
scattering environments, and showed that adjacent modes contribute
to higher correlation at the transmitter region. Based on this
result, a power loading scheme is proposed which reduces the effects
of correlation between adjacent modes at the transmitter region by
nulling power onto adjacent transmit modes.
¶
Furthermore, in this thesis a general space-time channel model for
down-link transmission in a mobile multiple antenna communication
system is developed. The model incorporates deterministic
quantities such as physical antenna positions and the motion of the
mobile unit (velocity and the direction), and random quantities to
capture random scattering environment modeled using a bi-angular
power distribution and, in the simplest case, the covariance between
transmit and receive angles which captures statistical
interdependency. The Kronecker model is shown to be a special case
when the power distribution is separable and is shown to
overestimate MIMO system performance whenever there is more than one
scattering cluster. Expressions for space-time cross correlations
and space-frequency cross spectra are given for a number of
scattering distributions using Gaussian and Morgenstern's family of
multivariate distributions. These new expressions extend the
classical Jake's and Clarke's correlation models to general
non-isotropic scattering environments.
|
22 |
Downlink W-CDMA performance analysis and receiver implmentation on SC140 Motorola DSPGhosh, Kaushik 30 September 2004 (has links)
High data rate applications are the trend in today's wireless technology. W-CDMA standard was designed to support such high data rates of up to 3.84 Mcps. The main purpose of this research was to analyze the feasibility of a fixed-point implementation of the W-CDMA downlink receiver algorithm on a general-purpose digital signal processor (StarCore SC140 by Motorola). The very large instruction word architecture of SC140 core is utilized to generate optimal implementation, to meet the real time timing requirements of the algorithm. The other main aim of this work was to study and evaluate the performance of the W-CDMA downlink structure with incorporated space-time transmit diversity. The effect of the channel estimation algorithm used was extensively studied too.
|
23 |
Optimization in multi-relay wireless networksNguyen, Huu Ngoc Duy 08 June 2009
The concept of cooperation in communications has drawn a lot of research attention in recent years due to its potential to improve the efficiency of wireless networks. This new form of communications allows some users to act as relays
and assist the transmission of other users' information signals. The aim of this thesis is to apply optimization techniques in the design of multi-relay wireless networks employing cooperative communications. In general, the thesis is organized into two parts: ``Distributed space-time coding' (DSTC) and ``Distributed beamforming', which cover two main approaches in cooperative communications over multi-relay networks.
<br><br>
In Part I of the thesis, various aspects of distributed implementation of space-time coding in a wireless relay network are treated. First, the thesis proposes a new fully-diverse distributed code which allows noncoherent reception at the destination. Second, the problem of coordinating the power allocation (PA) between source and relays to achieve the optimal performance of DSTC is studied and a novel PA scheme is developed. It is shown that the proposed PA scheme can obtain the maximum diversity order of DSTC and significantly outperform other suboptimal PA schemes. Third, the thesis presents the optimal PA scheme to minimize the mean-square error (MSE) in channel estimation during training phase of DSTC. The effect of imperfect channel estimation to the performance of DSTC is also thoroughly studied.
<br><br>
In Part II of the thesis, optimal distributed beamforming designs are developed for a wireless multiuser multi-relay network. Two design criteria for the optimal distributed beamforming at the relays are considered: (i) minimizing the total relay power subject to a guaranteed Quality of Service (QoS) measured in terms of signal-to-noise-ratio (SNR) at the destinations, and (ii) jointly maximizing the SNR margin at the destinations subject to power constraints at the relays. Based on convex optimization techniques,
it is shown that these problems can be formulated and solved via second-order conic programming (SOCP). In addition, this part also proposes simple and fast iterative algorithms to directly solve these optimization problems.
|
24 |
Widely-linear MMSE Receivers for Linear Dispersion Space-time Block-codesAmirhossein, Shokouh Aghaei 26 February 2009 (has links)
Space-time coding techniques are widely used in multiple-input multiple-output communication systems to mitigate the effect of multipath fading in wireless channels. An important subset of space-time codes are linear dispersion (LD) codes, which are
used for quasi-static Rayleigh flat fading channels when the channel state information (CSI) is only available at the receiver side. In this thesis, we propose a new receiver structure for LD codes. We
suggest to use widely-linear minimum-mean-squared-error (WL-MMSE) estimates of the transmitted symbols in lieu of the sufficient
statistics for maximum likelihood (ML) detection of these symbols. This structure offers both optimal and suboptimal operation modes. The structures of the proposed receivers in both modes are derived for general LD codes. As special cases, we study two important subsets of LD codes, namely orthogonal and quasi-orthogonal codes, and examine the performance of the proposed receivers for these codes.
|
25 |
Widely-linear MMSE Receivers for Linear Dispersion Space-time Block-codesAmirhossein, Shokouh Aghaei 26 February 2009 (has links)
Space-time coding techniques are widely used in multiple-input multiple-output communication systems to mitigate the effect of multipath fading in wireless channels. An important subset of space-time codes are linear dispersion (LD) codes, which are
used for quasi-static Rayleigh flat fading channels when the channel state information (CSI) is only available at the receiver side. In this thesis, we propose a new receiver structure for LD codes. We
suggest to use widely-linear minimum-mean-squared-error (WL-MMSE) estimates of the transmitted symbols in lieu of the sufficient
statistics for maximum likelihood (ML) detection of these symbols. This structure offers both optimal and suboptimal operation modes. The structures of the proposed receivers in both modes are derived for general LD codes. As special cases, we study two important subsets of LD codes, namely orthogonal and quasi-orthogonal codes, and examine the performance of the proposed receivers for these codes.
|
26 |
Cooperative Diversity for Fading Channels in the Presence of Impulsive NoiseAldharrab, Suhail Ibrahim 12 1900 (has links)
Although there already exists a rich literature on cooperative diversity, current results are mainly restricted to the conventional assumption of additive white Gaussian noise (AWGN). AWGN model realistically represents the thermal noise at the receiver, but ignores the impulsive nature of atmospheric noise, electromagnetic interference, or man-made noise which might be dominant in many practical applications. In this thesis, we investigate the performance of cooperative communication over Rayleigh fading channels in the presence of impulsive noise modeled by Middleton Class A noise.
We consider a multi-relay network with amplify-and-forward relaying and orthogonal cooperation protocol. As for the coding across the relays, we employ either space-time coding or repetition coding. For each scheme, we assume various scenarios based on relays’ location and quantify the diversity advantages through the derivation of the pairwise error probability. Based on the minimization of a union bound on the error rate performance, we further propose optimal power allocation schemes and demonstrate significant performance gains over their counterparts with equal power allocation. We finally present an extensive Monte Carlo simulation to confirm our analytical results and corroborate on our results.
|
27 |
Cooperative Diversity for Fading Channels in the Presence of Impulsive NoiseAldharrab, Suhail Ibrahim 12 1900 (has links)
Although there already exists a rich literature on cooperative diversity, current results are mainly restricted to the conventional assumption of additive white Gaussian noise (AWGN). AWGN model realistically represents the thermal noise at the receiver, but ignores the impulsive nature of atmospheric noise, electromagnetic interference, or man-made noise which might be dominant in many practical applications. In this thesis, we investigate the performance of cooperative communication over Rayleigh fading channels in the presence of impulsive noise modeled by Middleton Class A noise.
We consider a multi-relay network with amplify-and-forward relaying and orthogonal cooperation protocol. As for the coding across the relays, we employ either space-time coding or repetition coding. For each scheme, we assume various scenarios based on relays’ location and quantify the diversity advantages through the derivation of the pairwise error probability. Based on the minimization of a union bound on the error rate performance, we further propose optimal power allocation schemes and demonstrate significant performance gains over their counterparts with equal power allocation. We finally present an extensive Monte Carlo simulation to confirm our analytical results and corroborate on our results.
|
28 |
Optimization in multi-relay wireless networksNguyen, Huu Ngoc Duy 08 June 2009 (has links)
The concept of cooperation in communications has drawn a lot of research attention in recent years due to its potential to improve the efficiency of wireless networks. This new form of communications allows some users to act as relays
and assist the transmission of other users' information signals. The aim of this thesis is to apply optimization techniques in the design of multi-relay wireless networks employing cooperative communications. In general, the thesis is organized into two parts: ``Distributed space-time coding' (DSTC) and ``Distributed beamforming', which cover two main approaches in cooperative communications over multi-relay networks.
<br><br>
In Part I of the thesis, various aspects of distributed implementation of space-time coding in a wireless relay network are treated. First, the thesis proposes a new fully-diverse distributed code which allows noncoherent reception at the destination. Second, the problem of coordinating the power allocation (PA) between source and relays to achieve the optimal performance of DSTC is studied and a novel PA scheme is developed. It is shown that the proposed PA scheme can obtain the maximum diversity order of DSTC and significantly outperform other suboptimal PA schemes. Third, the thesis presents the optimal PA scheme to minimize the mean-square error (MSE) in channel estimation during training phase of DSTC. The effect of imperfect channel estimation to the performance of DSTC is also thoroughly studied.
<br><br>
In Part II of the thesis, optimal distributed beamforming designs are developed for a wireless multiuser multi-relay network. Two design criteria for the optimal distributed beamforming at the relays are considered: (i) minimizing the total relay power subject to a guaranteed Quality of Service (QoS) measured in terms of signal-to-noise-ratio (SNR) at the destinations, and (ii) jointly maximizing the SNR margin at the destinations subject to power constraints at the relays. Based on convex optimization techniques,
it is shown that these problems can be formulated and solved via second-order conic programming (SOCP). In addition, this part also proposes simple and fast iterative algorithms to directly solve these optimization problems.
|
29 |
The Methods to Enhance 3G/ Beyond 3G/ Wireless LAN Transmission Rate and EfficiencyLiu, Wen-Chung 08 July 2002 (has links)
To achieve two main objectives, viz., to increase the system capacity and having higher data rates, of 3G system for individual users, it comes up to be the unprecedented demand on both communication bandwidth and powerful DSP processing techniques. In this thesis, a new space-time encoding scheme, referred to as the Virtual Constellation Mapping (VCM) scheme associated with the turbo encoder, is devised to enhance transmission data rate and spectral efficiency. It also alleviates the requirement of powerful signal processing technique. In fact, the proposed scheme is very simple and could be used to achieve full utilizing encoding efficiency. It means that the new scheme is easy in practical implementation. To verify the advantages of this new scheme, we apply it to both the 3GPP FDD of WCDMA system and OFDM based Wireless LAN system. First, by comparing the proposed scheme with the conventional standards 3GPP scheme, the information data rate is increased from 384 kbps information data rate to 450.4 kbps, that is 17 % improvement. It should be noted by using the new approach, other system components of 3GPP, e.g., modulation scheme, control bits and the data rate of the QPSK modulators outputs, are all the same. Moreover, this VCM scheme can be applied to the multicarrier modulation or the Wireless LAN with the OFDM modulation. Computer simulation results showed that with the same transmission data rate, our scheme is more robustness compare with the conventional space-time trellis coded OFDM scheme, in high Doppler fading channel. In addition, the proposed scheme required less decoding complexity as the standards, when it is implemented in the 3GPP system and the OFDM system with space-time trellis coding scheme.
|
30 |
Performance Evaluation of Space-Time Coding on an Airborne Test PlatformTemple, Kip 10 1900 (has links)
ITC/USA 2014 Conference Proceedings / The Fiftieth Annual International Telemetering Conference and Technical Exhibition / October 20-23, 2014 / Town and Country Resort & Convention Center, San Diego, CA / Typical airborne test platforms use multiple telemetry transmit antennas in a top and bottom configuration in order to mitigate signal shadowing during maneuvers on high dynamic platforms. While mitigating one problem, this also creates a co-channel interference problem as the same signal, time delayed with differing amplitude, is sent to both antennas. Space-Time Coding (STC) was developed with the intention of mitigating this co-channel interference problem, also known as the "two antenna problem". Lab testing and preliminary flight testing of developmental and pre-production hardware has been completed and documented. This is the first test dedicated to assessing the performance of a production STC system in a real-world test environment. This paper will briefly describe lab testing that preceded the flight testing, describes the airborne and ground station configurations used during the flight test, and provides detailed results of the performance of the space time coded telemetry link as compared against a reference telemetry link.
|
Page generated in 0.0837 seconds