SATNAC 2007 Conference Papers

Access Networks

Title:                   Performance Evaluation of An Integrated Vertical Handover Model for Next Generation Mobile Networks Using Virtual MAC Addresses

Authors:              Hossen Altwelib (The Higher Institute of Industry, Libya),
Majdi Ashibani (The Higher Institute of Industry), Fathi Ben Shatwan (The Higher Institute of Industry)

Abstract:             The integration of existing cellular systems with wireless access technologies, such as wireless LANs, have attracted considerable attention during the past few years. There are a number of challenges need to be addressed including authentication, security, QoS support, and mobility management. Efficient mobility management, and especially handover management, is considered one of the major factors toward a seamless connectivity across networks of different technologies. This paper proposes a link layer (layer 2) handover ,the proposed link layer handover presents a possible UMTS-WLAN interworking architecture and proposes a new method facilitates seamless vertical handover (VHO) between UMTS and WLAN networks. Our proposal is based on provisioning a virtual media access control (VMAC) addressing the mobile user on the UMTS network at the time of vertical handover to the WLAN. In this paper, we also describe the design and implementation of the Gateway Hotspot Support node (GHSN) in detail and present experimental performance results that have been obtained from the simulation model to validate our proposal architectural. In this paper, we have come up with novel integrated model that has augmented the UMTS and WLAN individual models.


Title:                   Wireless Broadband: Comparartive Analysis of HSDPA vs. WiMAX

Authors:              Otieno Amimo-Rayolla (French South African Technical Institute in Electronics),
Anish Kurien (Tshwane University of Technology), Damien Chatelain (French South African Technical Institute in Electronics), Marcel Odhiambo (University of South Africa)

Abstract:             The ever growing demand for data and multimedia content has seen a surge in evolutionary wireless networking. This growth, largely driven by the success of data and media streaming over the all-encompassing communication medium, the internet, and ubiquitous availability of digital multimedia technology, has seen a sudden influx of partly complementary, partly substitutive network technologies such as HSPA, WLAN, WI-FI, Flash-OFDM, DVB-H and Bluetooth, bringing with them an upsurge in throughput (in Mbs). This paper gives an overview of the comparative analysis of two major technologies HSDPA and WiMAX, as a precursor to the complete experimental and simulation study of real-time streaming services (video) and optimization of existing networks. This paper will focus on technical comparisons with simulation examples, giving suggestions as to why the disparities in performance exist.


Title:                   The Factors Influencing Signal Propagations in the Underground Cable for Broadband Power-Line Communications (PLC) Systems

Authors:              Justinia Anatory (University of Dar es Salam),
Nelson Theethayi (Uppsala University) 

Abstract:             Recently power-line network has been proposed for broadband power-line communications. The network construction in most of the countries is the mixture of overhead and underground networks. The underground cable power transmission system is widely used in urban low voltage power distribution systems. In order to access the performance of such distribution systems as a low voltage broadband power line communication (BPLC) channel, this paper investigates the effects of load impedance, line length and branches on such systems, with special emphasis to the power line networks found in Tanzania. From the frequency response of the transfer function (ratio of the received and transmitted signals), it is seen that position of notches and peaks in the magnitude are largely affected (observed in the time domain responses too) by the above said network configuration and parameters. The observations presented in the paper could be helpful in suitable design of the PLC systems for a better data transfer and system performance.


Title:                   Service-Class-Based Joint Call Admission Control and Adaptive Bandwidth Management Scheme for Heterogeneous Wireless Networks

Authors:              Olabisi Falowo (University of Cape Town),
H. Anthony Chan (University of Cape Town) 

Abstract:             Joint call admission control (JCAC) can significantly improve connection-level quality of service (QoS) in heterogeneous wireless networks. This paper proposes serviceclass based JCAC and adaptive bandwidth management scheme to enhance connection-level QoS in heterogeneous cellular networks, where each cellular network is optimized to support specific classes of service. We develop an analytical model for the JCAC scheme using a multi-dimensional Markov chain. Two connection-level QoS metrics, new call blocking probability and handoff call dropping probability, are derived and evaluated for the heterogeneous cellular network. Numerical results show that the proposed JCAC scheme reduces handoff call dropping probability and new call blocking probability in heterogeneous cellular networks.


Title:                   Optimisation of the Pilot-to-Data Power Ratio in the MQAM-Modulated OFDM Systems with MMSE Channel Estimation

Authors:              Eugene Golovins (University of Cape Town),
Neco Ventura (University of Cape Town) 

Abstract:             Modern high-rate wireless OFDM systems use dedicated pilot subcarriers to obtain regular estimates of the channel frequency response and perform equalisation followed by coherent detection on other (data) subcarriers. Boosting power of the pilot subcarriers relative to the data subcarriers can increase channel estimation accuracy. However due to the overall transmit signal power constraint, dictated by energy conservation and restricted service zone radius, it will inevitably lead to degradation of performance of the equaliser detector couple being a result of the receiver noise level growth on the data subcarriers. In this article we derive an analytical expression for the optimal pilot-to-data power ratio (PDR) providing maximum signal-to-noise power ratio (SNR) at the output of the equaliser and hence improving BER performance. We also examine effects of the optimal and suboptimal minimum mean squared error (MMSE) channel estimator design and their impact on PDR selection.


Title:                   Fountain Codes and their possible application in standards like GSM

Authors:              Trienko Grobler (University of Pretoria),
Corne Olivier (University of Pretoria), Jacobus Vlok Olivier (University of Pretoria)

Abstract:             In this paper we review the concept of a fountain code and explore its possible application in standards like GSM. Our main focus is on the decoding of Tornado codes (predecessor of fountain codes) in typical mobile wireless channels encountered in GSM and WiMax standards. Channel conditions considered include AWGN and flat fading. The application of fountain codes in GSM is appealing due to the graph structure of these codes and the coding configuration in current GSM standards.


Title:                   Low Complexity Adaptive Frequency-Domain Equalizer for Quasi-Orthogonal Space-Time Block Code over Frequency-Selective Channels

Authors:              Lethukuthula Gumede (University of Kwazulu-Natal),
Hong-Jun Xu (University of Kwazulu-Natal), Fambirai Takawira (University of Kwazulu-Natal)

Abstract:             This paper investigate the performance of an adaptive frequency-domain equalizer for quasi-orthogonal space-time block coded (QSTBC) over frequency selective fading channels.  The QSTBC takes the advantage of the intrinsic orthogonal space-time block code (OSTBC) within it to reduce the complexity of the recursive least square (RLS) to that of least mean square (LMS) without compromising performance.  The receiver with perfect channel state information is compare to the adaptive receiver under investigation.  Also the effects of some of the parameters of the receiver are presented in the simulations.  The simulation results for the OSTBC adaptive receiver are used as benchmark to compare with receiver under investigation.


Title:                   Overview of the Meraka wireless grid test bed for evaluation of ad-hoc routing protocols

Authors:              David Johnson (Meraka Institute, CSIR),
Albert Lysko (Meraka Institute, CSIR)

Abstract:              Predicting the performance of ad-hoc networking protocols has typically been performed by making use of software

                                based simulation tools. Experimental study and validation of such predictions is vital to obtaining more realistic results, but may not be possible under the constrained environment of network simulators. This paper presents experimental comparisons of routing protocols using a 7 by 7 grid of closely spaced WiFi nodes. It firstly demonstrates the usefulness of the grid in its ability to emulate a real world multi-hop ad-hoc network. It specifically compares hop count, routing traffic overhead, throughput, delay and packet loss for three protocols which are listed by the IETF MANET working group. These are AODV, OLSR and DYMO


Title:                   ** Cellular Network Fault Prediction Using Mobile Intelligent Agent Technology

Authors:              Paul Kogeda (University of the Western Cape),
Johnson Agbinya (University of Technology Sydney) 

Abstract:             Proactive cellular network fault automation models using mobile intelligent agent are presented in this paper. Cellular networks are uncertain and dynamic in their behaviours and therefore we use different artifi-cial intelligent techniques to develop platform independ-ent, autonomous, reasoning, scalable and robust agent that can report on any unforeseen anomaly within the cellular network service provider. The specific design and implementation is done using Java Agent DEvelop-ment Framework (JADE). We set up a simple wire-less network consisting of four devices for our experi-ments, which lasted seven days. The partial results ob-tained from the experiments conducted are presented and discussed in this paper.


Title:                   Turbo Space-Time Multiuser Detection for DS-CDMA Systems in Rayleigh Fading Channels

Authors:              Derrick B. Mashwama (University of Cape Town),
Emmanuel O. Bejide (University of Cape Town) 

Abstract:             In this paper, we investigate the performance of the partitioned and the iterative approach to concatenation of the Parallel Interference Cancellation (PIC) technique with turbo detection in the Space-Time Block Coded (STBC) system. The paper studies the comparative performance of both concatenation approaches. It was observed that at low Signal to Noise Ratio (SNR) the Iterative Approach (IA) performs better than the Partitioned Approach (PA). However, as the fidelity of the received signal increases the PA starts to have a better performance than the IA. Both PA and IA system performances are shown to be dependent on the diversity level, system loading, channel conditions and detector parameters. A case is made for the design of a switching algorithm that monitors the ‘crossover’ point and switches to the better performing concatenation approach for a given system setup.


Title:                   Low-Density Parity-Check Code Design for GSM

Authors:              Andre Martin Mc Donald (University of Pretoria),
Jan Corne Olivier (University of Pretoria) 

Abstract:             We present a technique for designing low-density parity-check (LDPC) code matrices for the MCS-1 to MCS-4 coding schemes of GSM. We demonstrate that these codes have significant performance gains over randomly constructed LDPC codes in the GSM setup. The new codes also show significant gains in performance over the conventional MCS-1 to MCS-4 GSM coding schemes when compared in terms of the bit-error rate.


Title:                   A Performance Comparison of Wireless Multi-Hop Network Topologies Based on Average Node Degree

Authors:              Pragasen Mudali (University of Zululand),
Thulani Nyandeni (University of Zululand), Matthew Adigun (University of Zululand)

Abstract:             The average node degree of a wireless multihop network is an important factor in the overall network performance. This paper evaluates five practical network topologies that leverage the regular layout of buildings. The performance comparisons are based on the network’s average node degrees with the purpose of discovering the optimum average node degree. Simulation results show that the optimal node degree amongst the network topologies surveyed is four. This information is useful for the planning of an ever-increasing number of wireless multi-hop network deployments throughout the world.


Title:                   Rainfall Rate Distribution For LOS Radio Systems in Botswana

Authors:              Chrispin Mulangu (University of Kwazulu-Natal),
Pius Owolawi (University of Kwazulu-Natal), Thomas Afullo (University of Kwazulu-Natal)

Abstract:             The estimated cumulative distributions (CDFs) of rainfall rate for 4 locations in Botswana are reported in this paper based on 10-year rainfall data. The daily rainfall sampled over 24 hours is converted to the ITU-R recommended integration time of one minute. The method used is based on cumulative distribution identity of known one-minute rain-rate sites with their corresponding daily integration time compared with sites having unknown one-minute integration time. Consequently, values of coefficients a and b so determined are used to convert daily rain rates into oneminute rain rates for corresponding similar CDF sites of the target regions of Botswana. The resulting cumulative rainfall rate and relations between them are compared with the relevant ITU-R Recommendation P.837-1 and P.837-4. Based on this, an additional two rain zones are proposed alongside the seven ITU-R rain zones for Southern Africa.


Title:                   Extending WiFi Access For Rural Reach

Authors:              Kribashnee Naidoo (University of Kwa-Zulu Natal),
Rathilall Sewsunker (University of Kwa-Zulu Natal) 

Abstract:             WiFi can be used for last-mile IP connectivity to rural users. In initial roll-out, hotspots can be positioned at community centres such as schools, clinics, hospitals or call-centres. The study will consider a typical South African rural region, with telecommunications services traffic estimates. The study focuses on IEEE 802.11G deployment option based on the requirements of the South African case. The research investigates the maximum number of VoIP calls with reasonable QoS that can be sustained on a WiFi network.


Title:                   Dynamic Power Control On-demand Routing Protocol

Authors:              Elisha Oketch Ochola (Tshwane University of Technology / F'SATIE),
Damien Chatelain (F'SATIE), Anish Kurien (Tshwane University of Technology), James Oyedapo (Tshwane University of Technology)

Abstract:             Power control for mobile Ad hoc networks has received an increasing research interest in recent years. Routing is one of the major sources of power consumption in mobile nodes. In particular, consumption is significantly high when Ad hoc routing is employed as nodes are assigned additional operations to support the routing of packets from other nodes. In this paper, we optimise transmission power in slow mobile Ad hoc networks to reduce power consumption. This is adaptively and deterministically achieved by arriving at the optimum transmission power between every two nodes within the transmission range of each other (neighbors), without use of heuristic safety factors. We simulate an Ad hoc On-demand Distance Vector routing (AODV); and provide an optimum transmission power aware routing algorithm for mobile Ad hoc network. The on-demand algorithm sends out request for routes to the destination only if the source has data packet(s) to transmit and does not maintain routes that are not in active communication. Simulation results show that our scheme improves energy efficiency for AODV routing protocol leading to a considerable reduction in total power consumption to route a packet from source to destination node.


Title:                   Repeat-Puncture Superorthogonal Convolutional Turbo Codes in AWGN and Flat Rayleigh Fading Channels

Authors:              Narushan Pillay (University of Kwazulu-Natal),
Hongjun Xu (University of Kwazulu-Natal), Fambirai Takawira (University of Kwazulu-Natal)

Abstract:             Repeat-Puncture Turbo Codes (RPTC), an extension of the conventional turbo coding algorithm, has shown a significant increase in performance at moderate to high signal-to-noise (SNR) ratios.  Superorthogonal Convolutional Turbo Codes (SCTC) makes use of superorthogonal signals to improve the performance of conventional Turbo Codes (TC). By combining Superorthogonal Convolutional Turbo Codes and Repeat-Puncture Turbo Codes a coding scheme that exhibits a more superior performance results.  In this paper, we study a new low-rate coding scheme Repeat-Puncture Superorthogonal Convolutional Turbo Codes (RPSCTC) that makes use of superorthogonal signaling, together with repetition and puncturing to improve the performance of Turbo Codes for reliable and effective communications. Simulation results in additive white Gaussian noise (AWGN) and flat Rayleigh fading (FRF) channels are presented together with analytical bounds of bit-error probabilities derived from transfer function bounding techniques.


Title:                   Field testing of the Alvarion BreezeMAX as a last mile access technology

Authors:              Ingrid Siebörger (Rhodes University),
Alfredo Terzoli (Rhodes University) 

Abstract:             With an alarmingly low teledensity of approximately 12 % in South Africa, and not much hope of further wired infrastructure at the local loop level – as the costs incurred are high compared to potential revenue – wireless connectivity could be a great asset and service in South Africa. This paper looks at how WiMAX technologies, and specifically the Alvarion BreezeMAX, could be used in providing much needed telecommunications infrastructure to both rural and urban areas in South Africa, providing broadband data throughput rates together with excellent network reliability and low latency.


Title:                   Performance Evaluation of WiMAX for Rural Backhaul

Authors:              Verosha Singh (University of KwaZulu-Natal)
Rathilall Sewsunker (University of KwaZulu-Natal) 

Abstract:             Technologies such as WiFi and WiMAX, can be powerful driving forces for increasing rural connectivity. This paper proposes the use of WiMAX as backhaul to WiFi hotspots in order to provide sustainable and easy to deploy rural telecommunication services. The hotspots will take the form of telecentres. The IP-based network will provide voice, data and Internet services. This work evaluates the performance of WiMAX as a backhaul technology based on a typical South African rural region as a case study. Telecommunication traffic estimates for the region are determined. The future demands on the proposed network are also considered. Quality of service measurements based on these user requirements include IP packet loss and delay, as well as perceived voice quality during peak traffic periods.


Title:                   A Measurement-Aided Model-Based Admission Control Scheme for IEEE 802.11e EDCA Wireless LANs

Authors:              Conroy Andre Smith (University of Cape Town),
Neco Ventura (University of Cape Town) 

Abstract:             The IEEE 802.11e standard was introduced to overcome the lack of Quality of Service (QoS) support for the legacy IEEE 802.11 Wireless LANs. However, channel overloading still remains a major problem, as the QoS of traffic flows are degraded with a heavy load on the wireless channels. This paper proposes a measurement-aided model-based admission control scheme for IEEE 802.11e Enhanced Distributed Channel Access (EDCA) Wireless Local Area Networks (WLANs). It presents an overview of an Admission Control Unit (ACU) that is capable of providing quantitative QoS guarantees to all existing flows. The ACU in the Access Point (AP) makes use of measured collision statistics to estimate the achievable throughput that stations can achieve at saturated network conditions. The achievable throughput estimations are based on a 2-state markov chain model of the IEEE 802.11 contention based channel access scheme. Simulation results indicate that the analytical model is fairly accurate.


Title:                   ** PowerLine Communications an Integrative Solution to the Digital Divide and Broadband Delivery in the Rural Community of South Africa

Authors:              Loyd Tinarwo (University of Fort Hare),
Martin Mandioma (University of Fort Hare), Hippolyte Muyingi (University of Fort Hare)

Abstract:             Ensuring Broadband delivery and addressing Digital Divide needs integration of solutions that positively influence and affect the “Broadband for All” theme in South Africa. The authors argue that though relatively new, Broadband PowerLine Communications (PLC) is capable of solving the Digital Divide problem, characterizing the non-broadband communities of South Africa. Besides defining what is, Digital Divide and citing the advantages of the broadband PLC technology, the study present a comparative analysis of the PLC Network and the Ethernet Network under FTP load experiments in an Open Source Software Environment. The research investigates the competitiveness and comparability of PLC Network as technology that can bring substantial effect to the South African non-broadband communities if implemented at an extensive scale.


Title:                   A Performance Comparison of Candidate 4G Air-Interfaces in a Simulated Cellular Environment

Authors:              Ryan van den Bergh (University of the Witwatersrand),
Hu Hanrahan (University of the Witwatersrand) 

Abstract:             Development of the Fourth Generation of mobile communication systems, or 4G, has already begun in various organizations and research institutions worldwide. There is currently no single conclusive definition for 4G systems, and the process of 4G standardization will only begin after the World Radiocommunication Conference in 2007. The purpose of this paper is to evaluate the performance of two candidate 4G air-interface architectures, namely OFDMA and MC-CDMA, so that a recommendation can be made as to which architecture should form the core component of a new 4G access network system. To determine the appropriate choice of air-interface for 4G systems, a series of simulations was run using a realistic model of a cellular wireless environment. The results from those simulations were analysed and it was determined that, due to the absence of multiple access interference as found in MC-CDMA, OFDMA systems better met the defined requirements for a 4G air-interface.


Title:                   Towards Gigabit DSL (GDSL): Design of a CC/MC-CDMA modem

Authors:              Jacques van Wyk (University of Pretoria),
Louis Linde (University of Pretoria) 

Abstract:             With the introduction of VDSL2 and the implementation of Fibre-to-the-Curb (FTTC), the theoretical limit of DSL technology is pushed even further than currently known ADSL technology. Current research is investigating the possibility of symmetric DSL at 1 Gbps (GDSL). This paper addresses the design and implementation of a complete complementary multi-carrier code-division multiple access (CC/MC-CDMA) transmitter / receiver pair.This fully functional modem combines the virtues of both orthogonal frequency division multiplexing (OFDM) and conventional code division multiple access (CDMA) to support many users simultaneously with higher spectral efficiencies than conventional CDMA systems and better noise tolerance than existing DSL solutions. By expanding the proposed system further, symmetric Gigabit DSL (GDSL) can be supported.

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