Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1996-12-18
2001-01-09
Bost, Dwayne D. (Department: 2744)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S067150
Reexamination Certificate
active
06173185
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to wireless communications and in particular to cellular telephony.
2. Description of the Related Art
Frequently wireless network designers and equipment suppliers are tasked with providing reliability estimates for coverage of cellular systems. Service providers want to know how reliable their coverage is and want to be able to offer more reliable service to their customers.
Two standard ways to express cell reliability are illustrated in FIG.
1
. They are contour (or cell edge) reliability as illustrated in FIG.
1
a,
which gives the reliability of a user who travels the contour of the cell edge; and cell area reliability as illustrated in FIG.
1
b,
which gives the reliability of a user who may be anywhere within the confines of the entire cell boundary—not just on the cell edge. Both standards are often specified by a user or service provider.
The coverage probabilities requested by a user typically range from 70% to 99%. For example, public safety users generally require 95% contour reliability which corresponds to no more than a 5% failure within the entire coverage area. Commercial users may be satisfied with 70% contour reliability which translates to a 90% reliability across the entire cell area.
Previous designers were required to perform extensive RF measurements to establish cell boundary and reliability figures of merit. Typically, field engineers would drive the cell area collecting data with a Received Signal Strength Indicator (RSSI) receiver for measuring the received signal strength from a central transmitter. The exact location of the receiver is known through Global Positioning System (GPS) receivers attached to the RSSI receiver. The previous systems and methods for estimating cell coverage and reliability used hundreds and thousands of data points and still came up with estimates that ranged within plus or minus ten percent of actual (later) measurements were reluctantly considered acceptable.
The well known Hata method for estimating path loss is inherently error-prone and is valid over only a very limited range under certain specific conditions. A different correction factor is needed each and every time the method is used. The correction factor may be determined for either a small, medium or large sized city and does not take into account features of the particular cell under study. The unreliability is magnified if used to calculate cell radius and/or reliability.
There is accordingly a need for a new method and apparatus for reliably measuring and predicting the boundary of a cell and for the coverage within the cell in order to solve or ameliorate one or more of the above-described problems.
SUMMARY OF THE INVENTION
An accurate computer implemented method and apparatus for measuring and predicting the RF coverage of single cells is presented. The method measures the distance from the base station to the cell edge and quantifies the accuracy by also specifying a range uncertainty. In addition, the method provides an estimate of the area reliability of the region which is an order of magnitude more accurate than other approaches that estimate the coverage from a proportion of signal strength measurements. Empirical formulas are given that approximate the inaccuracies of both of these estimates.
Since the method uses linear regression to estimate the minimum mean square path loss to the cell edge, the technique represents the best circular approximation to the actual cell edge contour. As such, the method is ideal for cell site planning with omni directional antennas. However, the approach can easily be modified to provide equally valid coverage measurements for sectorized cell sites. This invention applies to any wireless technology to accurately determine the range to desired contours that satisfy the required RF coverage criterion. For example, using standard CW drive test measurements, this technique can help verify that the RF design meets the proper amount of overlap in coverage needed to support the soft hand-off regions of CDMA.
The minimum cell area that must be driven to validate the RF coverage can be calculated from three major cellular design parameters: 1) the amount of lognormal fading in the cell, 2) the desired cell edge uncertainty, and 3) the cell radius.
The limiting factor in determining the quality of RF cellular coverage is the accuracy that is required to estimate the effective cell radius. Estimates of the effective radius of each cell may be included as part of the pre-build validation procedure for any wireless installation.
An object of the invention is to determine the number of signal strength measurements needed to accurately estimate the cell radius R from the base station to the cell edge for both a given cell contour and cell area reliability. A further object of the invention is to estimate the coverage reliability of a cell with a finite number of signal strength measurements. A still further object of the invention is to minimize the area from which samples are taken in estimating cell radius R.
Further features of the above-described invention will become apparent from the detailed description hereinafter.
The foregoing features together with certain other features described hereinafter enable the overall system to have properties differing not just by a matter of degree from any related art, but offering an order of magnitude more efficient use of processing time and resources.
Additional features and advantages of the invention will be set forth in part in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate preferred embodiments of the apparatus and method according to the invention and, together with the description, serve to explain the principles of the invention.
REFERENCES:
patent: 4748655 (1988-05-01), Thrower et al.
patent: 5442804 (1995-08-01), Gunmar et al.
patent: 5465390 (1995-11-01), Cohen
Peterson et al, System performance prediction for personal communication systems, 1995 IEEE 45th Vehicular Technology Conference, Chicago, IL, USA, vol. 2, pp. 749-753, Jul. 28, 1995.*
Bernardin Charles P.
Yee Meng F.
Bost Dwayne D.
Crane John D.
Gelin Jean A.
Northern Telecom Limited
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