A Proposed Architecture for a High-Data Rate Mobile Lmds Network
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This thesis proposes a system architecture for a high-data rate mobile Local Multipoint Distribution Service (LMDS) Network. Its goal is to provide a workable "strawman" design that can serve as a basis for further research. The architecture is designed to offer broadband services to train commuters via LMDS. The thesis provides a broad overview of system aspects, such as Doppler shift, modulation selection, and error correction coding. These parameters and others are important in providing a robust design.
This thesis discusses a set of criteria that seek the best approach in terms of economical feasibility, throughput capabilities, design complexity, data routing, and robustness in serving multiple mobile units simultaneously. These criteria are examined through link budget analysis, layout designs, and throughput efficiency.
System throughput specifications are calculated for services, such as web browsing, email, ftp, and voice services to 100 train commuters. The information rate was 134.4 Mbps. The information rate plus overhead, which includes routing, bit and framing synchronization, and error correction coding, was approximately 201.51 Mbps. Using Carson's rule, the total required bandwidth for downstream transmissions was approximately 263 MHz. This throughput requirement was a criterion in selecting the appropriate system architecture.
Three approaches were evaluated: LMDS Infostations, Tower Sites, and Infostations/Tower Sites. Infostations are low-powered wireless cells designed to offer individual pockets of high bandwidth connectivity for broadband services. Tower Sites use switched antenna beams to offer continuous services to train commuters. The hybrid solution, Infostations/Tower Sites, offers continuous services with increased power requirements and increased base stations separation when compared to the Infostation approach.
Link budgets were examined for the Infostations and Tower Site approach. The initial required power for the Infostation was 1 mW. A 42.4 dB Eb/No link margin was computed using the Friis equation. The initial required power for the Tower Site approach was 500 mW. A 10.2 dB Eb/No link margin was computed with this approach. Tradeoffs with the non-fixed parameters were made to vary the link margins.
An economically feasible number of required units were also determined. Approximately 3,000 low-powered Infostations would be needed to offer continuous service. Only 93 Tower Sites would be required and 4*93 Tower Site/Infostation units would be needed to supply continuous, seamless services over a 230-miles coverage area.
The LMDS Tower Site was chosen to be the most suitable approach because of its robustness in meeting the pre-defined criteria.
- Masters Theses