Abou Chakra, Sara (2004) La Boucle Locale Radio et la Démodulation directe de signaux larges bandes à 26GHz. PhD thesis Communications et Electronique, ENST - COMELEC Communication et Electronique, ENST.

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Abstract

The Wireless Local Loop (WLL) is a system using radio signals as a substitute for copper, to complete the "last mile" between the subscriber and the Public Switched Telephone Network (PSTN). The WLL must offer the following services: the phone voice, data in and digital services. In France, the frequency bands allocated to the WLL are around 26 and 3.5 GHz. The 26 GHz WLL characteristics are defined by the standard IEEE 802.16c.
Within the framework of this thesis, a loop made up of two transceivers functioning in the 26 GHz band was studied. The system was initially made up of components commercially available. It was simulated with ADS software of Agilent Technologies, and then implemented at the RFM laboratory.
The receivers employed in this platform were heterodyne receivers. Their structure was thus complex and the transmission deteriorated by the amplitude and phase I and Q imbalance. In order to reduce its complexity while keeping the same performances of the system, we chose to propose a new homodyne receiver by introducing the "five-port" reflectometer.
The five-port reflectometer is a linear passive circuit having two inputs and three outputs. It consists of an interferometric circuit with five accesses and three power detectors. A five-port demodulator in coaxial technology was thus introduced into the 26 GHz transmission system. The demodulation being validated with this circuit, a five-port demodulator in MHIC technology was carried out.
In order to regenerate the I and Q signals from the output voltages of the five-port demodulator, a particular digital algorithm processes these three signals. This digital signal processing carries out frame and symbol synchronisation simultaneously as well as carrier synchronization on each data frame. It also includes an adaptive self-calibration procedure which makes it possible to regenerate I and Q signals while compensating all the transmission chain defaults. The same digital signal processing performs also compensation of the I and Q imbalance for a classical squared demodulator.
The complete transmission system was validated by carrying out the demodulation of signals modulated in QPSK and 16QAM with bit rates reaching 40 Mbit/s. The obtained phase constellation diagrams were well normalised and the bit error rates were very close of those defined by the WLL standard.

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