The IEEE 802.11 wireless local area network (WLAN) standard supports multiple transmission modes. However, the higher mandatory data rate mode does not necessarily yield higher throughput. This research started from the relationship between the link throughput and the channel's carrier-to-noise (C/N) ratio. Two algorithms are proposed, a throughput optimization and transmitter power saving (TOTPS) algorithm and an extended throughput optimization and transmitter power saving (ETOTPS) algorithm, based on the knowledge of the C/N ratio at the receiver. In particular, we take the approach of adjusting link parameters like transmitter power and transmission mode to achieve the maximum throughput at different C/N values. Since the TOTPS algorithm tends to reduce the transmitter power without degrading the link throughput, transmitter power can be saved. This not only prolongs battery life, which is critical in ad hoc wireless networks, but also reduces the potential interference to neighboring wireless network systems. The ETOTPS algorithm, on the other hand, aims for higher throughput by trading in more transmitter power. This is particularly desired for high-speed data transfer in an emergency situation. Both algorithms are developed to be applied to IEEE 802.11b, IEEE 802.11a and IEEE 802.11g links. / Ph. D.

Yes / This paper presents an approach to implement an automatically tuning antenna for optimising power transfer suitable for software defined radio (SDR). Automatic tuning is accomplished using a closed loop impedance tuning network comprising of an impedance sensor and control unit. The sensor provides the control unit with data on the transmit or receive power, and the algorithm is used to impedance of a T-network of LC components to optimize the antenna impedance to maximise power transmission or reception. The effectiveness of the proposed tuning algorithm in relation to impedance matching and convergence on the optimum matching network goal is shown to be superior compared with the conventional tuning algorithm. / This work is partially supported by innovation programme under grant agreement H2020-MSCA-ITN-2016 SECRET-722424 and the financial support from the UK Engineering and Physical Sciences Research Council (EPSRC) under grant EP/E022936/1

Thesis (MScEng)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: A well-known problem with FM-CW radar systems is the leakage of transmitter power into the receiver which leads to the making of close-in targets, and can severely limit the system dynamic range performance. This thesis considers two solutions to this radar system problem for a low frequency radar operating in the VHF band. The first method to suppress coupling is using separate transmit and receive antennas designed in such a way as to reduce coupling between them. The second is to design a negative feedback loop as part of the radar receiver where the feedback loop adaptively reduces the amount of transmitter leakage through to the receiver. This project details the realisation of these two solutions. A number of antenna designs are modelled in software and simulated to determine their characteristics of which the transmit-to-receive coupling is the key parameter. As no low coupling configuration could be found a simple configuration is chosen and practical measurements are taken. These antennas are then used in the radar system that is to be built. An FM-CW radar system is designed and simulated using software with a negative feedback loop being designed and implemented into the radar simulation. A practical radar system is then made inclusive of the feedback loop. Measurements are then taken to determine the efficacy of the feedback loop. / AFRIKAANSE OPSOMMING: ʼn Bekende probleem met FM-CW radar stelsels is die lekkasie van versender krag tot in die ontvanger wat lei tot die maak van nabye teikens en kan die stelsel se dinamiese sendbereik steng beperk. Hierdie tesis oorweeg twee oplossings tot hierdie probleem vir ʼn lae frekwensie radar wat in die VHF band werk. Die eerste metode wat na gekyk word om die koppeling te onderdruk is om die twee antennas van die radar stelsel so te ontwerp sodat die hoeveelheid koppeling tussen hulle verminder is. Die tweede is om ʼn negatiewe terugvoerlus as deel van die ontvanger te ontwerp. Hierdie terugvoerlus sal die versender lekkasie sein aanpassend in die ontvanger verminder. In hierdie projek word die realisering van bogenoemde oplossings uiteengeset. ʼn Paar verskillende antenna ontwerpe word gemodelleer in sagteware en word gesimuleer om hul karakteristieke te bepaal. Die belangrikste van hierdie faktore is die versender na ontvanger koppeling. Sienend dat geen ontwerp met ʼn lae genoeg koppeling gevind kon word nie, is ʼn eenvoudige ontwerp gekies en praktiese metings daarvan geneem. Hierdie antennas word dan gebruik in die radar stelsel wat gebou sal word. ʼn FM-CW radar stelsel word ontwerp en gesimuleer in sagteware. Die negatiewe terugvoerlus word ook ontwerp en geïmplementeer in die radar simulasie. ʼn Praktiese radar stelsel word dan gemaak insluitend die terugvoerlus. Metings word dan geneem om die effektiwiteit daarvan te bepaal.