Portland State University. Department of Electrical Engineering
Term of Graduation
Date of Publication
Master of Science (M.S.) in Electrical Engineering
Cell phone systems -- Noise, Mobile communication systems -- Design, Wireless communication systems -- Design and construction
1 online resource (vi, 80 pages)
Wireless cellular mobile communications is a rapidly growing global technology which places increasing demands on a limited electromagnetic radio frequency spectrum. However, in North America only a 25 MHz block of spectrum has been allocated to each of two service providers. This must be utilized for all services offered within their assigned market.
The wireless cellular link from the mobile or portable phone to terrestrial base stations utilize this limited frequency spectrum. This is divided into 416 two-way channels, each 30 kHz in width, a subset of which is assigned to each base station. As more base stations are constructed, these channels are reused on a spatial basis causing increased intra-system interference in the service area. This interference can deteriorate voice service quality if it is not contained within industry accepted limits.
The 3 sector per cell, 7 cell per cluster cellular system design is utilized in many domestic markets. It is based on an early system model in which the random characteristics of the interfering signals are simulated using a log-normal distribution. However, interference measurements in the Portland, Oregon cellular network, which also utilizes this design, confirms that the receive signal strength from combined interferers more closely follows a Rayleigh distribution. As a direct result, the mean interference level must be from 0.3 to 2.2 dB higher than previously thought to achieve acceptable network performance. This thesis shows that interference objectives for good voice quality cannot be met by a rigorous application of this design because it does not provide adequate spatial separation between base stations which have been constructed in an environment with relatively flat topology.
Measurements are made in various cellular network configurations and terrain topologies to help identify the primary contributors to poor interference. Cell sectoring, a method of isolating a portion of the interfering sources from the desired service area, is evaluated and does reduce interference. The severe terrain obstructions associated with hilly environments contribute additional interfering radio signal path loss. These are shown to have a profound impact on interference results in the cellular system.
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Wand, David A., "Achieving Cochannel Interference Objectives Over Selected Topologies in the Portland, Oregon Cellular Network" (1997). Dissertations and Theses. Paper 6275.