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M. Brandl:
"Datenübertragungssysteme mit Chirpmodulation";
Supervisor, Reviewer: F. Seifert, A. Goiser; Institut für Industrielle Elektronik und Materialwissenschaften, 2001.

With the increasing use of the industrial scientific and medical (ISM) bands at 2.45 and 5.8 GHz, spread spectrum data transmission systems are applied now to domestic and industrial wireless local area networks (WLAN). The new IEEE 802.11 standard defines the modulation schemes, conditions of interoperability and co-channel operation. This dissertation presents cheap and very robust solutions for WLAN spread spectrum systems (SSS) designed and built by implementation of chirp transmission and impulse compression. The chirp signals are generated by application of a broadband electrical impulse to a dispersive surface acoustic wave (SAW) delay line. In the receiver, designed matched SAW filters are used for impulse compression. In chapter 1 and 2 the fundamentals of SAW devices and the theory of chirp signals is discussed. In chapter 3 a survey on the IEEE standard 802.11 for WLAN in ISM bands is shown. For indoor data communications two low cost chirp spread spectrum systems based on SAW devices have been developed. In chapter 4 the fundamentals of operation and the calculation of the bit error rate for these systems with binary orthogonal keying (BOK) and with chirp pulse position modulation (CPPM) are given. In chapter 5, a technique of fast adaptive interference cancellation without loss of simplicity is developed: The SAW dispersive delay line is divided into a number of subsections and is used for chirp impulse compression with external summation. Since the SAW dispersive delay line shows a fixed relation between time domain and frequency domain, given by the geometry of the transducer. Each subsection corresponds to a frequency band within the bandwidth of the chirp. By gating off one section by an adaptive circuit, interferences in the corresponding subband will be suppressed. The remaining compressed impulses of each section are in phase and their sums are clearly detectable. A CPPM prototype with tapped matched filters for adaptive signal processing was built and tested for different electromagnetically polluted indoor environments. This system gates out interferences and shows a good performance even in presence of strong jamming. Due to the wide bandwidth, an excellent immunity against Rayleigh fading was observed. In chapter 6 the specifications of the CPPM data transmission system are listed and simulation results are compared with measurements.