SATNAC 2009 Conference Papers

Access Networks

Title:                Testbed Validation for the Evaluation of a Delay Aware Routing Metric for Ad Hoc Networks


Authors:            Melvin Ferreira (North-West University), Albert Helberg (North-West University)


Abstract:           There is a growing need for real-time multimedia applications to be supported in ad hoc networking environments.  Most current ad hoc routing protocols only support best-effort routing. By adopting Quality of Service (QoS) aware routing metrics, one can extend the set of multimedia services that run in an ad hoc network. Firstly, in this paper we present a 4 node wireless prototype testbed that was constructed to analyse ad hoc routing protocol behaviour. The testbed architecture is described and its ability to allow for repeatable and reproducible experimentation is verified.  Secondly, we practically implement enhancements to the AODV (Ad Hoc On-demand Distance Vector) routing protocol.  The routing metric is changed from hop count to measured end-to-end delay. This allows AODV to take the requirements of delay-sensitive applications such as voice and video services into account when selecting a route. Evaluation in the prototype testbed shows that the delay metric exhibits beneficial QoS properties.


Title:                Effect of RLC Transmission Modes for Differentiated Traffic Types in HSDPA via GEO Satellite


Authors:            Aiyetoro Gbolahan (University of KwaZulu-Natal), Fambirai Takawira (University of KwaZulu-Natal)


Abstract:           This paper investigates the effect of the Radio Link Control (RLC) operation modes for different types of UMTS traffic over a Satellite High Speed Downlink Packet Access (S-HSDPA) air interface. Satellite Systems are expected to complement the terrestrial access network and work with the same core network. The geostationary bent-pipe satellite has been considered for this work. The transmission of different traffic types was observed for both Acknowledge Mode (AM) and Unacknowledged Mode (UM) by investigating the effect of the cross-layer interactions between the application layer and RLC sub-layer of the data link layer. Our aim is to recommend which transmission mode is best for each traffic types and to compare the results with the Terrestrial HSDPA air interface scenario.


Title:                Predicting Low Earth Orbit Satellite Communications Quality and Visibility over Time


Authors:            John Gilmore (University of Stellenbosch), Riaan Wolhuter (University of Stellenbosch)


Abstract:           Low-Earth-orbit satellite communication link margins vary greatly as the satellite moves in its orbit around the Earth. A major design consideration that needs to be addressed for any satellite system is the choice of  forward-error correction code (FEC). The type of FEC and the optimal packet length are chosen so as to optimise the system for all expected link margins. This optimisation takes into account the fact that the link margin varies over time. FECs are used to minimise the amount of power used in the transmitter. This paper presents a link quality prediction scheme, that would enable both the satellite and ground station to adjust the coding rates used in real-time. The error performance of the code as a function of predicted link quality will be optimised by this scheme.  An adaptive coding and modulation scheme would make the satellite communication system more efficient by increasing the volumetric data throughput.


Title:                Performance Evaluation of Low-Complexity Decision-Feedback Detector for SM-MIMOOFDM Systems


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


Abstract:           Spatially multiplexed multiple–input multipleoutput orthogonal frequency division multiplexing (SM-MIMOOFDM) technology is envisaged to raise transmission capacity over the wireless channels up to 10bps/Hz, allowing for ubiquitous access to multimedia services in the 4G cellular networks. Future transceivers will incorporate MIMO antenna arrays of larger dimensions than those specified in the presently existing standards (with maximum 4 antennas). Thus, a crucial part of the cost-effective system design will deal with the lowcomplexity detector architecture, providing for optimal or suboptimal performance. In this paper, we propose such a detection technique and examine its error rate performance in the conditions of the dynamic channel model.


Title:                Channel Capacity Performance of Transmit Antenna Selective MIMO System in Weibull Fading


Authors:            Mzabalazo Lupupa (University of Cape Town), Mqhele Dlodlo (University of Cape Town)


Abstract:           Multiple-input multiple-output (MIMO) systems play a great role in improving communication in wireless systems. But an increase in the number of antennas used in a communication system results in increased system complexity. To address this drawback associated with MIMO systems we propose the use of a transmit antenna selective MIMO system. In this the best performing transmit antenna is selected from all the available antennas for communication. The signalto- noise ratio (SNR) performance of the proposed system is studied as the number of antennas used in the system is increased. In studying the SNR performance, maximal-ratio-combining (MRC) is used as the optimal combining technique at the receiver end. Average channel performance is also investigated as we vary the number of antennas used. The Weibull fading channel is considered in studying the performance of the transmit antenna selective MIMO system. We further illustrate the effect of the Weibull fading parameter on the average channel capacity performance.


Title:                Performance Evaluation of IMS Multimedia over WiMAX


Authors:            Francis Masuabi (University of Cape Town), Denys Vera (University of Cape Town), Neco Ventura (University of Cape Town)


Abstract:           Telecommunication has evolved steadily to meet the ever increasing demand of users. Hence, the Internet Protocol Multimedia Subsystem (IMS) will make it possible to provide ubiquitous computing to the end-user. WiMAX is based on the IEEE 802.16 standard engineered to provide wireless broadband access, but the main focus of this study, is the use of fixed WiMAX as a backhaul for VoIP and IPTV. A performance aluation of VoIP and IPTV quality of service was done over the WiMAX network. We examine the performance of these services over various codecs, analyzing the key performance metrics such as delay, latency, jitter and packet loss. With respect to VoIP sessions, the quality of the service was measured using the ITU-T E Model. Our results concluded that the G.711 (PCMA and PCMU) is the better VoIP codec as it used no compression scheme in addition to its bit rate being relatively higher than that of GSM.


Title:                DRMACSN: New MAC protocol for Wireless Sensor Networks


Authors:            Thippeswamy Muddenahalli (University of KwaZulu-Natal), Fambirai Takawira (University of KwaZulu-Natal)


Abstract:           In this paper, we propose a new distributed, load balanced, and route aware medium access control protocol for Code Division Multiple Access (CDMA) based Wireless sensor networks (DRMACS). Wireless Sensor networks (WSN), a new class of devices, have the potential to revolutionize the capturing, processing, and communication of critical data for use by first responders. Sensor networks consist of small, low-power, and low-cost devices with limited computational and wireless communication capabilities. They represent the next step in wireless communication’s miniaturization, and their power and size make it feasible to embed them into wearable vital sign monitors, location-tracking tags in buildings, and first responder uniform gear. The sensor nodes can only transmit a finite number of bits before they run out of energy. Thus, reducing the energy consumption per bit for end-to-end data transmission is an important design consideration for such networks. We show how our design would improve the MAC protocol with sleep and wakeup schemes that could achieve greater energy savings, reliability and increased system capacity. In this paper, we present findings for the delay, and the throughput of a new improved proposed MAC protocol.


Title:                Evaluation of LDPC Forward Error Correction Schemes for Telemetry Satellite Systems


Authors:            Francois Olivier (University of Stellenbosch), Riaan Wolhuter (University of Stellenbosch)


Abstract:           This paper evaluates the proposed implementation of short length low density parity check (LDPC) codes within the telemetry space protocol. Due to the varying orbital patterns of low earth orbit (LEO) satellites, limited communication time windows need to be optimised to maximise data throughput. Most popular connection oriented protocols focus on correcting congestion related link errors, but with a unique set of link related bit errors introduced on the satellite channel, conventional protocols degrades the performance of LEO satellite communication. The telemetry (TM) protocol specified by the European Cooperation for Space Standardisation will be evaluated with a mission specific implementation for error control coding. Using iterative decoding schemes, short length LDPC show large coding gains with low complexity hardware requirements. A coding scheme implementing an approximation algorithm is shown as a low complexity solution with good error performance.


Title:                Range Based Power Control for Multi-Radio Multi-Channel Wireless Mesh Networks


Authors:            Thomas Olwal (Tshwane University of Technology), Barend van Wyk (Tshwane University of Technology), Karim  Djouani (F’SATIE), Yskandar Hamam (F’SATIE), Patrick Siarry (F’SATIE), Ntsibane Ntlatlapa (Council for Industrial and Scientific Research)


Abstract:           Multi-Radio Multi-Channel (MRMC) systems are key to power control problems in WMNs. In this paper, we present a range based dynamic power control for MRMC WMNs.  First, WMN is represented as a set of disjoint Unified Channel Graphs (UCGs). Second, each radio assigned to a unique UCG adjusts the transmission power locally using predicted connectivity ranges with other nodes. A new power selection MRMC unification protocol (PMMUP) is proposed that coordinates local power optimizations at the radios of a node. The efficacy of the proposed method is investigated through simulations. 


Title:                Design and Implementation of Wireless Sensor Network for Wildlife Monitoring


Authors:            Nolan Pillay (Eskom),  Thippeswamy Muddenahalli (University of KwaZulu-Natal)


Abstract:           Wireless Sensor Networks (WSN) is a popular and interesting field of research in the study of wildlife. In this paper, the design of a WSN that will be used to remotely monitor wildlife is proposed. The sensor nodes designed were small, low powered units to allow them to be mounted onto animals. Each sensor node was designed to monitor the body temperature of the animal it was mounted to and the light intensity of the animal’s external environment. This sensed data was then relayed to a base station node for further processing. A user application program running on the base station computer was developed to receive the data from the base station node and store it in a structured text file format for further analysis. Both the hardware and software designs of the WSN and the data sample collected from the sensor nodes relating to temperature and light are   presented.


Title:                Linear Detector Performance in Ill-Conditioned MIMO OFDM Channels


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


Abstract:           This work investigates the performance of linear detector based receivers in MIMO OFDM systems. Two linear detectors are compared that is: Zero Forcing (ZF) and the Minimum Mean Square Error (MMSE). The introduction of interference cancellation will be shown to greatly improve linear detector Bit Error Rates (BER). The performance of one successive interference detector, called the V-Blast, is further evaluated in ill-conditioned channel conditions. This work investigates performance of MIMO OFDM detectors in a spatially correlated channel so as to enhance Quality of Service (QoS). The Weichselberger channel model with ill-conditioned characteristics will be used in the performance evaluation of the MIMO OFDM detectors. Tikhonov regularization is  used to improve the performance of successive interference based detectors.


Title:                Per Cell Propagation Model Calibration Approach for Mobile Positioning


Authors:            Dominic Samoita (Tshwane University of Technology), Francois Rocaries (Tshwane University of Technology) , Yskandar Hamam  (Tshwane University of Technology)


Abstract:           This paper presents results of research on per cell propagation calibration-based mobile positioning for GSM. A novel mobile positioning system for GSM networks is proposed and assessed by field measurements and simulations. It utilizes timing advance, Received Signal Strength (RSS) and a per celltuned propagation prediction model. Clutter features are modelled to closely represent the real environment to enhance the accuracy of the signal strength prediction. The obtained results indicate     that estimation of the mobile position at a sufficient accuracy for most of the location-based services does not have to involve significant changes in the terminals and in the network infrastructure. The performed field measurements and simulation of the designed mobile positioning system reveal that mobile users can be located with an accuracy of 40 meters. Furthermore, the method is computationally light-weight and can be integrated onto any RSS-based algorithm.


Title:                A Comparison of Scheduling Algorithms in HSDPA


Authors:            Stefan Scriba (Telkom SA), Fambirai Takawira (University of KwaZulu-Natal)


Abstract:           This paper compares the behaviour of EDF and Opportunistic-EDF (O-EDF) with that of Round Robin, PFT, and MaxC/I. Video, voice and web traffic are transmitted through an HSDPA air interface. The resultant queueing delay and fairness are measured and compared for each scheduler.


Title:                Estimation of a Probability of Inteference in a Cellular Communication Network Using the Monte-Carlo Technique


Authors:            Nyah Temaneh (University of Swaziland)


Abstract            A Monte-Carlo technique based methodology for the estimation of a probability of interference in a cellular communication network is presented. This probability is considered for the case of mobile to base (Up Link or Reverse channel) and base to mobile (Down Link or Forward channel) interferences. The effect of random user location in their respective cells is taken into account, and the impact of lognormal shadowing is also studied. The simulation results obtained, when compared with known results are found to be in agreement.


Title:                Baseband Carrier Recovery and Phase Tracking as a Doppler Compensation Technique for A Zero-IF SDR


Authors:            Ewald van der Westhuizen (University of Stellenbosch), Gert-Jan van Rooyen (University of Stellenbosch)


Abstract:           Compensating for the Doppler effect is a significant problem in low earth orbit (LEO) satellite communications. The effect of Doppler shift is that the baseband carrier signal is shifted in the frequency spectrum. This paper presents the design and analysis of a two-stage baseband carrier recovery algorithm for software-defined radio (SDR). The first-stage frequency-locked loop calculates a coarse estimate of the baseband carrier frequency.  After a predetermined settling time, the coarse estimation stage switches to the second stage, in which fine tracking is performed by digital phase-locked loop. Two methods for the first-stage coarse carrier frequency estimation are compared. The first uses a feed-forward method, while the second method uses a feedback mechanism. The algorithms are implemented as part of an SDR modem running on a Freescale DSP56311 digital signal processor. Care is also taken in ensuring efficient implementation, e.g. by avoiding operations such as division, and by avoiding computationally intensive calculations.


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