37 research outputs found
Transmit Power Allocation for Successive Interference Cancellation in Multicode MIMO Systems
Paper approved by X. Wang, the Editor for Multiuser Detection and
Equalization of the IEEE Communications Society. Manuscript received June
10, 2005; revised November 2, 2006 and July 23, 2007. This paper was
presented in part at the IEEE International Conference on Communications,
Seoul, Korea, May 2005.Multiple-input multiple-output (MIMO) system
with multicode transmission can provide high speed data services
by transmitting independent parallel substreams from multiple
antennas and through multicode channelization. In this paper,
we first introduce an iterative two-stage successive interference
cancellation (SIC) detection scheme for a multicode MIMO
system. The proposed technique cancels the interference signals
successively in the space domain followed by the code domain.
Next, we develop various transmit power allocation schemes over
different data substreams for the proposed detection process to
improve error rate performance. The joint transmit power allocation
is derived to make the post-detection signal-to-interferenceplus-
noise ratio (SINR) become the same for all substreams
in both the space and code domains. As a computationally
efficient scheme, we propose a two-stage power allocation scheme,
which allocates the total transmit power to the substreams in
the code domain at the first stage, and allocates this code
domain power to the substreams in the space domain at the
second stage. Furthermore, variable and constant power ratio
(PR) schemes are derived to reduce the feedback overhead. In
particular, the constant PR scheme utilizes the transmit power
ratio determined by the long-term statistical properties of the
fading channel amplitudes, and achieves significantly reduced
feedback rate. Numerical results show that the proposed transmit
power allocation schemes for the two-stage SIC significantly
outperform the equal power allocation scheme
Efficient Radio Resource Allocation Schemes and Code Optimizations for High Speed Downlink Packet Access Transmission
An important enhancement on the Wideband Code Division Multiple Access
(WCDMA) air interface of the 3G mobile communications, High Speed Downlink
Packet Access (HSDPA) standard has been launched to realize higher spectral
utilization efficiency. It introduces the features of multicode CDMA transmission
and Adaptive Modulation and Coding (AMC) technique, which makes radio resource
allocation feasible and essential. This thesis studies channel-aware resource
allocation schemes, coupled with fast power adjustment and spreading code optimization
techniques, for the HSDPA standard operating over frequency selective
channel.
A two-group resource allocation scheme is developed in order to achieve a
promising balance between performance enhancement and time efficiency. It only
requires calculating two parameters to specify the allocations of discrete bit rates
and transmitted symbol energies in all channels. The thesis develops the calculation
methods of the two parameters for interference-free and interference-present
channels, respectively. For the interference-present channels, the performance of
two-group allocation can be further enhanced by applying a clustering-based channel
removal scheme.
In order to make the two-group approach more time-efficient, reduction in
matrix inversions in optimum energy calculation is then discussed. When the
Minimum Mean Square Error (MMSE) equalizer is applied, optimum energy allocation
can be calculated by iterating a set of eigenvalues and eigenvectors. By
using the MMSE Successive Interference Cancellation (SIC) receiver, the optimum
energies are calculated recursively combined with an optimum channel ordering
scheme for enhancement in both system performance and time efficiency.
This thesis then studies the signature optimization methods with multipath
channel and examines their system performances when combined with different
resource allocation methods. Two multipath-aware signature optimization methods
are developed by applying iterative optimization techniques, for the system
using MMSE equalizer and MMSE precoder respectively. A PAM system using
complex signature sequences is also examined for improving resource utilization
efficiency, where two receiving schemes are proposed to fully take advantage of
PAM features. In addition by applying a short chip sampling window, a Singular
Value Decomposition (SVD) based interference-free signature design method is
presented
Coded Parity Packet Transmission Method for Two Group Resource Allocation
Gap value control is investigated when the number of source and parity packets
is adjusted in a concatenated coding scheme whilst keeping the overall coding
rate fixed. Packet-based outer codes which are generated from bit-wise XOR
combinations of the source packets are used to adjust the number of both source
packets. Having the source packets, the number of parity packets, which are the
bit-wise XOR combinations of the source packets can be adjusted such that the
gap value, which measures the gap between the theoretical and the required
signal-to-noise ratio (SNR), is controlled without changing the actual coding
rate. Consequently, the required SNR reduces, yielding a lower required energy
to realize the transmission data rate. Integrating this coding technique with
a two-group resource allocation scheme renders efficient utilization of the total
energy to further improve the data rates. With a relatively small-sized set of
discrete data rates, the system throughput achieved by the proposed two-group
loading scheme is observed to be approximately equal to that of the existing
loading scheme, which is operated with a much larger set of discrete data rates.
The gain obtained by the proposed scheme over the existing equal rate and
equal energy loading scheme is approximately 5 dB. Furthermore, a successive
interference cancellation scheme is also integrated with this coding technique,
which can be used to decode and provide consecutive symbols for inter-symbol
interference (ISI) and multiple access interference (MAI) mitigation. With this
integrated scheme, the computational complexity is signi cantly reduced by
eliminating matrix inversions. In the same manner, the proposed coding scheme
is also incorporated into a novel fixed energy loading, which distributes packets
over parallel channels, to control the gap value of the data rates although the
SNR of each code channel varies from each other
Coded Parity Packet Transmission Method for Two Group Resource Allocation
Gap value control is investigated when the number of source and parity packets
is adjusted in a concatenated coding scheme whilst keeping the overall coding
rate fixed. Packet-based outer codes which are generated from bit-wise XOR
combinations of the source packets are used to adjust the number of both source
packets. Having the source packets, the number of parity packets, which are the
bit-wise XOR combinations of the source packets can be adjusted such that the
gap value, which measures the gap between the theoretical and the required
signal-to-noise ratio (SNR), is controlled without changing the actual coding
rate. Consequently, the required SNR reduces, yielding a lower required energy
to realize the transmission data rate. Integrating this coding technique with
a two-group resource allocation scheme renders efficient utilization of the total
energy to further improve the data rates. With a relatively small-sized set of
discrete data rates, the system throughput achieved by the proposed two-group
loading scheme is observed to be approximately equal to that of the existing
loading scheme, which is operated with a much larger set of discrete data rates.
The gain obtained by the proposed scheme over the existing equal rate and
equal energy loading scheme is approximately 5 dB. Furthermore, a successive
interference cancellation scheme is also integrated with this coding technique,
which can be used to decode and provide consecutive symbols for inter-symbol
interference (ISI) and multiple access interference (MAI) mitigation. With this
integrated scheme, the computational complexity is signi cantly reduced by
eliminating matrix inversions. In the same manner, the proposed coding scheme
is also incorporated into a novel fixed energy loading, which distributes packets
over parallel channels, to control the gap value of the data rates although the
SNR of each code channel varies from each other
Multicarrier CDMA systems with MIMO technology
The rapid demand for broadband wireless access with fast multimedia services initiated a vast research on the development of new wireless systems that will provide high spectral efficiencies and data rates. A potential candidate for future generation wireless systems is multi-carrier code division multiple access (MC-CDMA). To achieve higher user capacities and increase the system data rate, various multiple-input multiple-output (MIMO) technologies such as spatial multiplexing and spatial diversity techniques have been proposed recently and combined with MC-CDMA.This research proposes a chip level coded ordered successive spatial and multiuser interference cancellation (OSSMIC) receiver for downlink MIMO MC-CDMA systems. As the conventional chip level OSIC receiver [1] is unable to overcome multiple access interference (MAI) and performs poorly in multiuser scenarios, the proposed receiver cancels both spatial and multiuser interference by requiring only the knowledge of the desired user's spreading sequence. Simulation results show that the proposed receiver not only performs better than the existing linear detectors [2] but also outperforms both the chip and symbol level OSIC receivers. In this work we also compare the error rate performance between our proposed system and MIMO orthogonal frequency division multiple access (MIMO OFDMA) system and we justify the comparisons with a pairwise error probability (PEP) analysis. MIMO MC-CDMA demonstrates a better performance over MIMO OFDMA under low system loads whereas in high system loads, MIMO OFDMA outperforms MIMO MC-CDMA. However if all users' spreading sequences are used at the desired user receiver, MIMO MC-CDMA performs better than MIMO OFDMA at all system loads.In the second part of this work, user grouping algorithms are proposed to provide power minimisation in grouped MC-CDMA and space-time block code (STBC) MC-CDMA systems. When the allocation is performed without a fair data rate requirement, the optimal solution to the minimisation problem is provided. However when some fairness is considered, the optimal solution requires high computational complexity and hence we solve this problem by proposing two suboptimal algorithms. Simulation results illustrate a significantly reduced power consumption in comparison with other techniques.EThOS - Electronic Theses Online ServiceEPSRCGBUnited Kingdo
Convergence of packet communications over the evolved mobile networks; signal processing and protocol performance
In this thesis, the convergence of packet communications over the evolved mobile networks is studied. The Long Term Evolution (LTE) process is dominating the Third Generation Partnership Project (3GPP) in order to bring technologies to the markets in the spirit of continuous innovation. The global markets of mobile information services are growing towards the Mobile Information Society.
The thesis begins with the principles and theories of the multiple-access transmission schemes, transmitter receiver techniques and signal processing algorithms. Next, packet communications and Internet protocols are referred from the IETF standards with the characteristics of mobile communications in the focus. The mobile network architecture and protocols bind together the evolved packet system of Internet communications to the radio access network technologies. Specifics of the traffic models are shortly visited for their statistical meaning in the radio performance analysis. Radio resource management algorithms and protocols, also procedures, are covered addressing their relevance for the system performance. Throughout these Chapters, the commonalities and differentiators of the WCDMA, WCDMA/HSPA and LTE are covered. The main outcome of the thesis is the performance analysis of the LTE technology beginning from the early discoveries to the analysis of various system features and finally converging to an extensive system analysis campaign. The system performance is analysed with the characteristics of voice over the Internet and best effort traffic of the Internet. These traffic classes represent the majority of the mobile traffic in the converged packet networks, and yet they are simple enough for a fair and generic analysis of technologies. The thesis consists of publications and inventions created by the author that proposed several improvements to the 3G technologies towards the LTE. In the system analysis, the LTE showed by the factor of at least 2.5 to 3 times higher system measures compared to the WCDMA/HSPA reference. The WCDMA/HSPA networks are currently available with over 400 million subscribers and showing increasing growth, in the meanwhile the first LTE roll-outs are scheduled to begin in 2010. Sophisticated 3G LTE mobile devices are expected to appear fluently for all consumer segments in the following years
On the performance and capacity of space-time block coded multicarrier CDMA communication systems
Ph.DDOCTOR OF PHILOSOPH
Time diversity solutions to cope with lost packets
A dissertation submitted to Departamento de Engenharia Electrotécnica of Faculdade de Ciências e Tecnologia of Universidade Nova de Lisboa in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Engenharia Electrotécnica e de ComputadoresModern broadband wireless systems require high throughputs and can also have very high
Quality-of-Service (QoS) requirements, namely small error rates and short delays. A high spectral efficiency is needed to meet these requirements. Lost packets, either due to errors or collisions, are usually discarded and need to be retransmitted, leading to performance degradation.
An alternative to simple retransmission that can improve both power and spectral
efficiency is to combine the signals associated to different transmission attempts.
This thesis analyses two time diversity approaches to cope with lost packets that are
relatively similar at physical layer but handle different packet loss causes. The first is a lowcomplexity Diversity-Combining (DC) Automatic Repeat reQuest (ARQ) scheme employed in a Time Division Multiple Access (TDMA) architecture, adapted for channels dedicated to a single user. The second is a Network-assisted Diversity Multiple Access (NDMA) scheme, which is a multi-packet detection approach able to separate multiple mobile terminals transmitting simultaneously in one slot using temporal diversity. This thesis combines these techniques with Single Carrier with Frequency Division Equalizer (SC-FDE) systems, which are widely recognized as the best candidates for the uplink of future broadband wireless systems.
It proposes a new NDMA scheme capable of handling more Mobile Terminals (MTs)
than the user separation capacity of the receiver. This thesis also proposes a set of analytical tools that can be used to analyse and optimize the use of these two systems. These tools are then employed to compare both approaches in terms of error rate, throughput and delay performances, and taking the implementation complexity into consideration.
Finally, it is shown that both approaches represent viable solutions for future broadband wireless communications complementing each other.Fundação para a Ciência e Tecnologia - PhD grant(SFRH/BD/41515/2007); CTS multi-annual funding project PEst-OE/EEI/UI0066/2011, IT
pluri-annual funding project PEst-OE/EEI/LA0008/2011, U-BOAT project PTDC/EEATEL/
67066/2006, MPSat project PTDC/EEA-TEL/099074/2008 and OPPORTUNISTICCR
project PTDC/EEA-TEL/115981/200