No. 2 (2003)
Published:
2003-06-30
ARTICLES FROM THIS ISSUE
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Applications of Hadamard matrices
Abstract
We present a number of applications of Hadamard matrices to signal processing, optical multiplexing, error correction coding, and design and analysis of statistics.
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Design of filterbank transceivers for dispersive channels with arbitrary-length impulse response
Abstract
This paper addresses the joint design of transmitter and receiver for multichannel data transmission over dispersive channels. The transmitter is assumed to consist of FIR filters and the channel impulse response is allowed to have an arbitrary length. The design criterion is the maximization of the information rate between transmitter input and receiver output under the constraint of a fixed transmit power. A link to minimum mean squared error designs for a similar setting is established. The proposed algorithm allows a straightforward transmitter design and generally yields a near-optimum solution for the transmit filters. Under certain conditions, the exact solution for the globally optimal transmitter is obtained.
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Blind frequency offset estimation for overlap PCC-OFDM systems in presence of phase noise
Abstract
This paper presents a technique for frequency offset estimation for polynomial cancellation coded orthogonal frequency division multiplexing with symbols overlapped in the time domain (overlap PCC-OFDM) in the presence of phase noise. The frequency offset estimator is designed based on the subcarrier pair imbalance (SPI) caused by frequency offset. The estimation is performed in the frequency domain at the output of the receiver discrete Fourier transform (DFT). No training symbols or pilot tones are required. Simulations show that this estimator is an approximately linear function of frequency offset. Phase noise does not significantly affect the variance performance of the estimator.
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LPAR: an adaptive routing strategy for MANETs
Abstract
This paper presents a new global positioning system (GPS)-based routing protocol, called location-based point-to-point adaptive routing (LPAR) for mobile ad hoc networks. This protocol utilises a 3-state route discovery strategy in a point-to-point manner to reduce routing overhead while maximising throughput in medium to large mobile ad hoc networks. In LPAR, data transmission is adaptable to changing network conditions. This is achieved by using a primary and a secondary data forwarding strategy to transfer data from the source to the destination when the condition of the route is changed during data transmission. A simulation study is performed to compare the performance of LPAR with a number of different exisiting routing algorithms. Our results indicate that LPAR produces less overhead than other simulated routing strategies, while maintains high levels of throughput.
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Performance analysis of reactive shortest path and multi-path routing mechanism with load balance
Abstract
Research on multi-path routing protocols to provide improved throughput and route resilience as compared with single-path routing has been explored in details in the context of wired networks. However, multi-path routing mechanism has not been explored thoroughly in the domain of ad hoc networks. In this paper, we analyze and compare reactive single-path and multi-path routing with load balance mechanisms in ad hoc networks, in terms of overhead, traffic distribution and connection throughput. The results reveals that in comparison with general single-path routing protocol, multi-path routing mechanism creates more overheads but provides better performance in congestion and capacity, provided that the route length is within a certain upper bound which is derivable. The analytical results are further confirmed by simulation.
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Linear quadratic power control for CDMA systems
Abstract
In this paper, we present a robust decentralized method for jointly performing channel estimation and closed loop power control for the reverse link of CDMA networks. Our method, based on linear quadratic Gaussian (LQG) control systems theory and Kalman filtering, does not require any training symbols for channel or signal to interference ratio (SIR) estimation. The main interest of this new scheme is that it improves the performance of current SIR based power control techniques while avoiding the problem of power escalation, which is often observed in current systems.
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Queuing models for cellular networks with generalised Erlang service distributions
Abstract
Providing seamless handover is one of the major problems in mobile communication environments. Careful dimensioning of the network and the underlying teletraffic analysis plays a major role in determining the various grade of services (GoSs) that can be provided at various network loads for handover users. It has been shown that the channel holding time of a cell, one of the important parameters in any teletraffic analysis, can be accurately modelled by Erlang distributions. This paper focuses on solving queuing systems with generalised Erlang service distributions and exponential arrival distributions. We present the quasi-birth-death (QBD) process, which characterises the queuing models with generalised Erlang service and exponential interarrival distributions. We then use the properties of Erlang distributions and characteristics of channel allocation process of cellular networks to simplify the queues used to model cellular networks. The use of these simplifications provide a significant reduction in computation time required to solve these QBDs.
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Adaptive handover control in IP-based mobility networks
Abstract
In this paper, we propose framework for an adaptive handover control architecture (AHCA), which aims at enhancing overall IP handover performance while maximising utilisation of resources in wireless access networks. The IP handover procedures in the AHCA adapt dynamically to network conditions, as well as to a wide range of user profiles and application quality of service (QoS) requirements. To confirm our expectations that the AHCA will bring performance benefits in heterogeneous mobile IP networking environment, we have investigated basic performance characteristics of different handover mechanisms. The preliminary simulation results demonstrate that the AHCA will bring significant performance improvements as compared with non adaptive IP handovers.
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A concept of Differentiated Services architecture supporting military oriented Quality of Service
Abstract
This paper presents a concept of IP Differentiated Services (DiffServ) architecture in conjunction with bandwidth brokerage and policy based network management, all aimed at efficient and flexible provision of the military oriented Quality of Service (M-QoS) features in the Australian Defence (strategic) wide area network and its satellite trunk interconnections with the tactical domain. Typical DiffServ functions are analysed in the paper with regard to their roles in offering M-QoS. Some preliminary simulation results of applying these mechanisms to achieve traffic policing and differentiation for (UDP) video traffic streams, are also presented. Finally, the paper proposes the use of bandwidth brokerage in each DiffServ domain to facilitate automatic Service Level Specification (SLS) arrangements with end-user applications, and policy based network management to support the flexible implementation of bandwidth brokerage.
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Bandwidth broker extension for optimal resource management
Abstract
Bandwidth broker (BB), resource manager of differentiated services domain cannot provide per domain behavior (PDB) attribute information to customers and neighboring domains at the time of service level agreement (SLA) negotiation. Extending BB`s functionality to calculate PDB attributes can help it to negotiate SLAs dynamically and efficiently. Using current measurements or historic data about PDB attributes, bandwidth broker can perform off-line analysis to evaluate the range of quality of service (QoS) parameters that its domain can offer. Using these values BB can perform optimal capacity planning of the links and provide better QoS guarantees.
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Manipulation of compressed data using MPEG-7 low level audio descriptors
Abstract
This paper analyses the consistency of a set of MPEG-7 low level audio descriptors when the input audio stream has previously been compressed with a lossy compression algorithm. The analysis results show that lossy compression has a detrimental effect on the integrity of practical search and retrieval schemes that utilize the low level audio descriptors. Methods are then proposed to reduce the detrimental effects of compression in searching schemes. These proposed methods include improved searches, switched adaptive scalar and vector prediction, and other prediction schemes based on machine learning principles. Of the proposed schemes the results indicate that searching which incorporates previous and future frames combined with machine learning based prediction best nullifies the effects of compression. However, future scope is identified to further improve the reliability of the MPEG-7 audio descriptors in practical search environments.
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Fully spatial and SNR scalable, SPIHT-based image coding for transmission over heterogenous networks
Abstract
This paper presents a fully scalable image coding scheme based on the set partitioning in hierarchical trees (SPIHT) algorithm. The proposed algorithm, called fully scalable SPIHT (FS-SPIHT), adds the spatial scalability feature to the SPIHT algorithm. It provides this new functionality without sacrificing other important features of the original SPIHT bitstream such as: compression efficiency, full embeddedness and rate scalability. The flexible output bitstream of the FS-SPIHT encoder which consists of a set of embedded parts related to different resolutions and quality levels can be easily adapted (reordered) to given bandwidth and resolution requirements by a simple parser without decoding the bitstream. FS-SPIHT is a very good candidate for image communication over heterogenous networks which requires high degree of scalability from image coding systems.
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On a method to improve correlation properties of orthogonal polyphase spreading sequences
Abstract
In this paper, we propose a simple but efficient method for improving correlation properties of polyphase spreading sequences for asynchronous direct sequence code division multiple access (DS CDMA) applications. The proposed method can be used to reduce the mean square value of aperiodic crosscorrelation or the mean square value of aperiodic autocorrelation, the maximum value of aperiodic crosscorrelation functions, merit factor or other properties of the sequence set. The important feature of the method is that while it modifies correlation properties of the sequence set, it preserves sequence orthogonality for perfect synchronization, if this is the property of the original sequence set.
