This report focuses on the application of adaptive arrays to the Advanced Mobile Phone Service (AMPS) and Code Division Multiple Access (CDMA) cellular systems. Adaptive arrays have been proposed as early as in the 1960s to improve the signal quality, but most of its applications were restricted to defense purposes. Recently, there has been a surge in interest of applying adaptive arrays for cellular systems. This work introduces new blind adaptive array algorithms for AMPS and CDMA signals. The theoretical capacity limit using an adaptive array at the base station for an AMPS cellular system is derived in this work. One of the significant contributions in this research is a macrocell channel model which provides angle-of-arrival (AOA) statistics of the multipath components. Practical issues involved in the implementation of an adaptive array are addressed and the author's implementation of an 8-element adaptive array operating at 2.05 GHz is explained. This research also analyzes the capacity that can be offered by an adaptive array in a system where CDMA users co-exist with existing AMPS users. A novel cellular CDMA system which exploits adaptive arrays is introduced and the capacity offered by this system is compared with existing and other systems exploiting spatial dimension.

Novel adaptive array algorithms and their impact on cellular system capacity

A method for co-channel interference suppression and signal separation was proposed in a previous work. It uses the amplitude variation of the composite signal to estimate the parasitic phase modulation impinged on the strong desired signal by the weak interference signal. This estimate is then used to cancel out the distortion of the composite signal, revealing the desired signal. In the cancellation process, amplitude estimates for both signals were obtained from measurements. Errors in estimating these magnitudes limit the quality of cancellation and signal separation performance. An adaptive method is proposed which improves these estimates and, hence, results in a better cancellation of interference. A criterion for performance measure was chosen to be the variance of the envelope of the weak signal estimate and is shown to be directly related to the cancellation quality. A random search algorithm was used to vary the signal magnitude estimates to achieve better estimates. Numerical simulation experiments were performed to prove the concept, including Gaussian noise. >

Adaptive co-channel interference cancellation and signal separation method

Im nachrichtentechnischen Sinne dienen Modulation und Demodulation zur Aufarbeitung von Nachrichten in eine Signalform, die die Ubertragung der Nachrichten uber eine grostmogliche Entfernung unter Wahrung des erforderlichen Storabstands gewahrleistet, wobei die spezifischen Eigenschaften des Ubertragungsmediums zu berucksichtigen sind.

Modulation und Demodulation

The reduction of FM interference caused by the reception of adjacent or co-channel signals is examined. Techniques to allow the demodulation of a weak FM signal, when in the presence of a stronger one, are described. The description is extended to include methods where the residual interference is reduced independent of which signal is being demodulated, i.e. the normal FM capture effect is enhanced. FM interference reduction from co-channel sources cannot be perfect and is subject to distortions arising from the format of the signal modulations. Such distortions may be tolerable in certain cases. The magnitude and frequency of these distortions can be assessed through the performance of a wideband phase-shifting process which ideally has to provide an exact and absolute quadrature shift.

Study of adjacent and co-channel FM interference reduction

5 List of abbreviations 7 List of major symbols 8 1. Introduetion 11 1.1. Background 11 1.2. Terminology 14 1.3. Organizations and responsibilities 15 1.4. Scope of the thesis and survey of the contents 19 1.5. References 21 2. Radio-inteiference problems and mutual coordination 23 2.1. Introduetion 23 2.2. Review of practical interference problems 23 2.2.1. General remarks 23 2.2.2. Interference between terrestrial stations 24 2.2.3. lnterference between satellite-earth links 26 2.2.4. Interference between terrestrial stations and earth stations 28 2.2.5. System studies 30 2.3. Interference from digital radio-relay stations into satellite TV receivers 32 2.4. Coordination areas 34 2.5. Relerences 40 3. Transhorizon propagation mechanisms -a review 43 3.1. General introduetion 43 3.2. Introduetion to transhorizon-propagation research 43 3.2.1. Time variability 43 3.2.2. General concepts and terminology 44 3.2.3. Presentation of results 50 3.3. Review of transhorizon-propagation mechanisms 50 3.3.1. General remarks 50 3.3.2. Permanent clear-air mechanisms 52 3.3.3. Occasional clear-air mechanisms 55 3.3.4. Permanent scatter mechanisms 58 3.3.5. Occasional scatter mechanisms 58 3.4. Relative importance of the mechanisms 61 3.5. References 61 4. Clear-air transhorizon propagation 65 4.1. Introduetion 65 4.2. Review of clear-air interference-predietion models 65 4.2.1. General remarks 65 4.2.2. CCIR interference-prediction model 66 4.2.3. Other clear-air interference--prt:>diction models 68 4.3. Transhorizon-propagation experiments 70 4.3.1. Measurement programme and equipment 70 4.3.2. Experimental results obtained at EUT 72 4.3.3. Discussion of the experimental results 73

Reduction of transhorizon radio interference in satellite earth stations

As a result of investigation of interference into FM systems, a new algorithm for the process of demodulation is proposed. When compared to the method using the conventional limiter-discriminator, it offers better immunity against the baseband interference noise. Desired signal processing is performed by the functional devices added to the conventional limiter-discriminator in such a way that this new demodulator can be optimized in the sense of the minimum baseband interference noise. The statistics of the wanted and interfering signals must be known. Several examples involving interference problems in FDM-FM radio-relay systems carrying multichannel telephone signals are elaborated to illustrate the performances of the proposed demodulator. FDM-FM, PSK, or FSK systems are considered the cause of the interference. The noise power ratio (NPR) at the output of the conventional limiter-discriminator and the improvement factor offered by the new demodulator, obtained on digital computer, are presented versus baseband frequency in the form of diagrams. Different IF filters in FDM-FM receiver and transmit filters in the interfering systems are taken into account. The improvement offered by the proposed demodulator is of such a degree that some of the important restrictions in planning different radio systems could be relaxed.

A New Demodulation Method Improving FM System Interference Immunity

A new proposed robust FM demodulator (RFMD) is a simplified version of the recently reported demodulator (FMD) [1] which improves FM system interference immunity. The RFMD is applied to combat the adjacent channel interference and its improvement factor is only negligibly smaller than that of the FMD.

A New Robust FM Demodulator Reducing Adjacent Radio-Channel Interference Noise

A general method for the accurate analysis of the response of a frequency demodulator using feedback (FMFB) to an arbitrary frequency modulated (FM) signal is developed. This approach is employed to determine the FMFB outputs for two specific modulating signals, Gaussian noise, and a single sine wave. The proposed method is then applied to three different FMFB configurations differing in their low-pass filter structure. As a result, generalized curves enabling easy evaluation of the intermodulation (IM) distortion and the harmonic distortion are obtained. When designing the FMFB on the basis of these results, the influence of the relevant system parameters, such as IF filter bandwidth, feedback factor, position of the channel in the baseband, structure of the low-pass filter, etc., on the nonlinear properties of the FMFB can be controlled, simply and in a straightforward manner. The accuracy of the method has been verified in those rare cases for which solutions are already known.

Z. Stojanovic

Papers

A New Demodulation Method Improving FM System Interference Immunity

A New Robust FM Demodulator Reducing Adjacent Radio-Channel Interference Noise

Nonlinear Distortion Analysis in the Frequency Demodulator Using Feedback