No description available.

Thesis (MEng)--University of South Australia, 1996

This thesis describes the design of a baseband digital predistortion architecture for radio frequency (RF) amplifier linearization. Existing amplifier linearization techniques are first examined. The nonlinearity of an amplifier can be characterized as amplitude-to-amplitude distortion and amplitude-to-phase distortion. The distortion can be corrected by providing a predistorted driver signal (both in amplitude and phase) to the amplifier. This counteracts the nonlinearity of the amplifier so that the overall system is more linear. A pipelined predistortion architecture is designed to allow fast processing speed, and is capable of providing linearization for a bandwidth of 25 Mhz. The simulation results show significant improvement in amplifier's performance using predistortion technique. The system bandwidth versus cost is examined by using commercially available components. / Graduation date: 1996

The uplink of code division multiple access (CDMA) cellular radio systems is often interference limited. The interference originates from many users whose transmission powers are not observable for the system. This thesis introduces uplink load and applies means of explicitly considering the users’ radio environment when approximating and controlling the load. A desirable property of all cellular radio systems is uplink feasibility, i.e., existence of finite user transmission powers to support the allocated services. Uplink load can be considered as a measure of how far from infeasibility the system is. The performed characterization of uplink load lead to two concrete definitions related to the amount of received and transmitted power, respectively. An important part of the total load is the intercell load which is caused by users connected to neighboring base stations. If not carefully handled, the intercell load can jeopardize uplink feasibility. Conversely, knowledge of a lower intercell load can be used to increase the resource assignments. A common denominator in all the work in this thesis is that the intercell load is explicitly considered. When approximating uplink load, a centralized approach is adopted to study information gathered in several base stations. This yields good approximations of the average load. However, centralized approximations can not detect momentarily peaks in the load. A number of resource allocation algorithms making control decisions in the local base stations are proposed based on experience from characterizing uplink load. As the algorithms study the intercell load, yet without measuring the interference power, they are robust in the sense that they will never assign resources yielding an infeasible system. A straightforward way of controlling the uplink load is to use measurements of the received interference power. This approach, just as the proposed load approximations, can gain from knowing the background noise power. The same framework used for designing robust resource allocation algorithms, is also used for estimating the background noise power.

The rapidly developing wireless market has spawned a multitude of different standards for cellular, PCS, and wireless data. To allow users the ability to access services conforming to disparate standards, multimode handsets capable of software reconfiguration are needed. These "software radios" are distinguished from their traditional counterparts by their strong reliance on digital channel filtering and demodulation which may be reprogrammed to receive different standards. In these radios, higher dynamic range is required from the analog portion, most notably, the analog-to-digital converter (ADC). This research examines through analysis and simulation the performance requirements of analog-to-digital converters for use in radios which are conformant to the AMPS, IS-54, GSM, and IS-95 cellular standards. Simulations reveal the degradation in performance under conditions of off-channel interference, fading, and converter nonlinearities. Included in this analysis is the design of automatic gain control (AGC) for narrowband and IS-95 spread spectrum systems to optimize quantization noise and distortion due to A/D overload. Lastly, methods for improving the dynamic range of the analog-to-digital interface such as nonuniform quantization, companding, and dither are presented. The development of a novel A/D using a direct-sequence pseudo-noise (DSPN) technique in conjunction with an asymmetrical quantizer is presented and compared with standard dither techniques. Advantages of this technique compared to ordinary ADC's include an almost one bit improvement in resolution, quantization noise whitening, elimination of A/D offsets, and the ability to simultaneously digitize multiple analog signals with a single quantizer. The technique requires no synchronization and is easily implemented. / Master of Science