Performance of a transmit delay scheme in digital simulcast environment

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Tezin Türü: Yüksek Lisans

Tezin Yürütüldüğü Kurum: Orta Doğu Teknik Üniversitesi, Mühendislik Fakültesi, Elektrik ve Elektronik Mühendisliği Bölümü, Türkiye

Tezin Onay Tarihi: 2004

Öğrenci: AYFER ÖZGÜR

Danışman: YALÇIN TANIK

Özet:

Simulcasting is a spectrally efficient wide area coverage technique that can be advantageous in private mobile radio applications such as emergency services. In a simulcast network, multiple base stations broadcast the same information on a single nominal carrier frequency, causing severe multipath interference at a receiver in the overlap region of several neighboring base stations. In this thesis, we introduce a transmit delay scheme for simulcast networks and investigate the performance of the scheme in LOS and Rayleigh fading environments. In this scheme a relative transmit delay is introduced between neighboring base stations to extend the differential delay between different paths in the overlap regions, from the order of the carrier period to the order of the symbol period, thus transform RF carrier interference into ISI. The receiver employs MLSE to obtain diversity gain from ISI. The performance of the system is evaluated using analytical bounds and simulations carried out for an MLSE based p/4 DQPSK receiver and the results show that the proposed scheme operates succesfully, turning destructive interference disadvantage into a multipath diversity advantage, provided that a sufficient delay is used between the base stations. The أsufficientؤ delay value is determined by considering the coverage properties of the scheme and is in fact أoptimumؤ, since more than sufficient transmit delays result in useless increased receiver complexity. We provide our results using parameters for the TETRA system, however, the results of the work can readily be used for other systems.