| dc.description.abstract | The rapid growth of the Internet has increased the demand for broadband services. Users expect high quality, reliability and high-speed communication systems that allow easy access to this resource. Solutions, such as the x-digital subscriber line (x-DSL), which aims at high-bit-rate transmissions over twisted pairs as well as an extension of the existing cable television networks, known as hybrid fiber coaxial (HFC), appears very promising. An alternative technique, the wireless approach to the last mile access is attractive to network operators and service providers because of its reduced deployment time and cost compared to the construction of a wired infrastructure.
LMDS, which typically operates at millimeter-wave frequencies above 20 G Hz, is a two-way digital cellular system that offers a wireless access method to broadband interactive services for point-to-multipoint distribution. In this fixed broadband wireless access network, each cell is divided into multiple sectors, with each served by a sector antenna collocated within the hub. Users supported in these systems employ highly directional antennas and signal polarization to communicate with the hub station. The major advantage of using directional terminal antennas is that a large portion of the interference is attenuated by the antenna front-to-back ratio.
The system performance is limited by the signal strength over individual radio links and the amount of co-channel interference. Besides the severe attenuation of precipitation in millimetre wave band should be considered in link budget calculation, the effect of antenna and depolarisation also should be integrated into the co-channel interference calculation, since dual-polarized LMDS system is proposed to increase spectrum efficiency and high gain antenna is used to reduce interference.
Using cellular engineering methodology, an interleaved cellular pattern, that exploits the high-directivity of the subscriber antenna, is proposed. A cluster-interleaved cellular pattern is proposed by interleaving the cell clusters. The proposed cellular system can be easily developed and without making any additional equipment investment. The coverage performance was investigated by considering high signal propagation impairment for the Taiwan area.
A new cellular architecture, termed extended interleaved twisted cell (EITC),reduces the co-channel interference experienced by users located in strong interference regions. The proposed structure delivers the advantages of the interleaved cell, which manipulates the spectral efficiency of fixed broadband wireless networks. This work presents a new cell structure that combines extended cluster planning to eliminate co-channel interference by exploiting the terminal directional antenna for system deployment. The main benefit of this novel design lies in the directivity of the terminal directional antennas. This allows flexible hub deployment. The extended interleaved twisted cell is simple to implement and requires no extra equipment cost.
A dual-polarized multimode CDMA based LMDS with hexagonal cell architecture is investigated. Various cellular architectures for improving the system performance are discussed. A novel cellular pattern that exploits the interleaving scheme is proposed to reduce the impact of inter-cell interference to enhance the power of the multimode CDMA scheme in this fixed wireless network. By managing the channel polarization used in the service area, no extra equipment investment is required and better system performance is obtained.
Rain attenuation and foliage depolarization play important roles in system deployment. Developing better cellular architecture is an economical approach to enhance spectrum efficiency for LMDS. Results show that the proposed novel cellular system achieves greater improvement for system coverage performance. | en_US |