186 research outputs found
Performance of Joint Channel and Physical Network Coding Based on Alamouti STBC
This work considers the protograph-coded physical network coding (PNC) based
on Alamouti space-time block coding (STBC) over Nakagami-fading two-way relay
channels, in which both the two sources and relay possess two antennas. We
first propose a novel precoding scheme at the two sources so as to implement
the iterative decoder efficiently at the relay. We further address a simplified
updating rule of the log-likelihood-ratio (LLR) in such a decoder. Based on the
simplified LLR-updating rule and Gaussian approximation, we analyze the
theoretical bit-error-rate (BER) of the system, which is shown to be consistent
with the decoding thresholds and simulated results. Moreover, the theoretical
analysis has lower computational complexity than the protograph extrinsic
information transfer (PEXIT) algorithm. Consequently, the analysis not only
provides a simple way to evaluate the error performance but also facilitates
the design of the joint channel-and-PNC (JCNC) in wireless communication
scenarios.Comment: 6 pages, 4 figures, accpete
Energy efficiency and interference management in long term evolution-advanced networks.
Doctoral Degree. University of KwaZulu-Natal, Durban.Cellular networks are continuously undergoing fast extraordinary evolution to overcome
technological challenges. The fourth generation (4G) or Long Term Evolution-Advanced
(LTE-Advanced) networks offer improvements in performance through increase in network density,
while allowing self-organisation and self-healing. The LTE-Advanced architecture is heterogeneous,
consisting of different radio access technologies (RATs), such as macrocell, smallcells, cooperative
relay nodes (RNs), having various capabilities, and coexisting in the same geographical coverage
area. These network improvements come with different challenges that affect usersâ quality of
service (QoS) and network performance. These challenges include; interference management, high
energy consumption and poor coverage of marginal users. Hence, developing mitigation schemes for
these identified challenges is the focus of this thesis.
The exponential growth of mobile broadband data usage and poor networksâ performance along
the cell edges, result in a large increase of the energy consumption for both base stations (BSs) and
users. This due to improper RN placement or deployment that creates severe inter-cell and intracell
interferences in the networks. It is therefore, necessary to investigate appropriate RN placement
techniques which offer efficient coverage extension while reducing energy consumption and mitigating
interference in LTE-Advanced femtocell networks. This work proposes energy efficient and optimal
RN placement (EEORNP) algorithm based on greedy algorithm to assure improved and effective
coverage extension. The performance of the proposed algorithm is investigated in terms of coverage
percentage and number of RN needed to cover marginalised users and found to outperform other RN
placement schemes.
Transceiver design has gained importance as one of the effective tools of interference
management. Centralised transceiver design techniques have been used to improve network
performance for LTE-Advanced networks in terms of mean square error (MSE), bit error rate (BER)
and sum-rate. The centralised transceiver design techniques are not effective and computationally
feasible for distributed cooperative heterogeneous networks, the systems considered in this thesis.
This work proposes decentralised transceivers design based on the least-square (LS) and minimum MSE (MMSE) pilot-aided channel estimations for interference management in uplink
LTE-Advanced femtocell networks. The decentralised transceiver algorithms are designed for the
femtocells, the macrocell user equipments (MUEs), RNs and the cell edge macrocell UEs (CUEs) in
the half-duplex cooperative relaying systems. The BER performances of the proposed algorithms
with the effect of channel estimation are investigated.
Finally, the EE optimisation is investigated in half-duplex multi-user multiple-input
multiple-output (MU-MIMO) relay systems. The EE optimisation is divided into sub-optimal EE
problems due to the distributed architecture of the MU-MIMO relay systems. The decentralised
approach is employed to design the transceivers such as MUEs, CUEs, RN and femtocells for the
different sub-optimal EE problems. The EE objective functions are formulated as convex
optimisation problems subject to the QoS and transmit powers constraints in case of perfect channel
state information (CSI). The non-convexity of the formulated EE optimisation problems is
surmounted by introducing the EE parameter substractive function into each proposed algorithms.
These EE parameters are updated using the Dinkelbachâs algorithm. The EE optimisation of the
proposed algorithms is achieved after finding the optimal transceivers where the unknown
interference terms in the transmit signals are designed with the zero-forcing (ZF) assumption and
estimation errors are added to improve the EE performances. With the aid of simulation results, the
performance of the proposed decentralised schemes are derived in terms of average EE evaluation
and found to be better than existing algorithms
Distributed Quasi-Orthogonal Space-Time coding in wireless cooperative relay networks
Cooperative diversity provides a new paradigm in robust wireless re- lay networks that leverages Space-Time (ST) processing techniques to combat the effects of fading. Distributing the encoding over multiple relays that potentially observe uncorrelated channels to a destination terminal has demonstrated promising results in extending range, data- rates and transmit power utilization. Specifically, Space Time Block Codes (STBCs) based on orthogonal designs have proven extremely popular at exploiting spatial diversity through simple distributed pro- cessing without channel knowledge at the relaying terminals. This thesis aims at extending further the extensive design and analysis in relay networks based on orthogonal designs in the context of Quasi- Orthogonal Space Time Block Codes (QOSTBCs).
The characterization of Quasi-Orthogonal MIMO channels for cooper- ative networks is performed under Ergodic and Non-Ergodic channel conditions. Specific to cooperative diversity, the sub-channels are as- sumed to observe different shadowing conditions as opposed to the traditional co-located communication system. Under Ergodic chan- nel assumptions novel closed-form solutions for cooperative channel capacity under the constraint of distributed-QOSTBC processing are presented. This analysis is extended to yield closed-form approx- imate expressions and their utility is verified through simulations. The effective use of partial feedback to orthogonalize the QOSTBC is examined and significant gains under specific channel conditions are demonstrated.
Distributed systems cooperating over the network introduce chal- lenges in synchronization. Without extensive network management
it is difficult to synchronize all the nodes participating in the relaying between source and destination terminals. Based on QOSTBC tech- niques simple encoding strategies are introduced that provide compa- rable throughput to schemes under synchronous conditions with neg- ligible overhead in processing throughout the protocol. Both mutli- carrier and single-carrier schemes are developed to enable the flexi- bility to limit Peak-to-Average-Power-Ratio (PAPR) and reduce the Radio Frequency (RF) requirements of the relaying terminals.
The insights gained in asynchronous design in flat-fading cooperative channels are then extended to broadband networks over frequency- selective channels where the novel application of QOSTBCs are used in distributed-Space-Time-Frequency (STF) coding. Specifically, cod- ing schemes are presented that extract both spatial and mutli-path diversity offered by the cooperative Multiple-Input Multiple-Output (MIMO) channel. To provide maximum flexibility the proposed schemes are adapted to facilitate both Decode-and-Forward (DF) and Amplify- and-Forward (AF) relaying. In-depth Pairwise-Error-Probability (PEP) analysis provides distinct design specifications which tailor the distributed- STF code to maximize the diversity and coding gain offered under the
DF and AF protocols.
Numerical simulation are used extensively to confirm the validity of the proposed cooperative schemes. The analytical and numerical re- sults demonstrate the effective use of QOSTBC over orthogonal tech- niques in a wide range of channel conditions
Hardware-Conscious Wireless Communication System Design
The work at hand is a selection of topics in efficient wireless communication system design, with topics logically divided into two groups.One group can be described as hardware designs conscious of their possibilities and limitations. In other words, it is about hardware that chooses its configuration and properties depending on the performance that needs to be delivered and the influence of external factors, with the goal of keeping the energy consumption as low as possible. Design parameters that trade off power with complexity are identified for analog, mixed signal and digital circuits, and implications of these tradeoffs are analyzed in detail. An analog front end and an LDPC channel decoder that adapt their parameters to the environment (e.g. fluctuating power level due to fading) are proposed, and it is analyzed how much power/energy these environment-adaptive structures save compared to non-adaptive designs made for the worst-case scenario. Additionally, the impact of ADC bit resolution on the energy efficiency of a massive MIMO system is examined in detail, with the goal of finding bit resolutions that maximize the energy efficiency under various system setups.In another group of themes, one can recognize systems where the system architect was conscious of fundamental limitations stemming from hardware.Put in another way, in these designs there is no attempt of tweaking or tuning the hardware. On the contrary, system design is performed so as to work around an existing and unchangeable hardware limitation. As a workaround for the problematic centralized topology, a massive MIMO base station based on the daisy chain topology is proposed and a method for signal processing tailored to the daisy chain setup is designed. In another example, a large group of cooperating relays is split into several smaller groups, each cooperatively performing relaying independently of the others. As cooperation consumes resources (such as bandwidth), splitting the system into smaller, independent cooperative parts helps save resources and is again an example of a workaround for an inherent limitation.From the analyses performed in this thesis, promising observations about hardware consciousness can be made. Adapting the structure of a hardware block to the environment can bring massive savings in energy, and simple workarounds prove to perform almost as good as the inherently limited designs, but with the limitation being successfully bypassed. As a general observation, it can be concluded that hardware consciousness pays off
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