Multiplex communications – Communication over free space – Repeater
Reexamination Certificate
1998-09-08
2001-09-04
Hsu, Alpus H. (Department: 2661)
Multiplex communications
Communication over free space
Repeater
C370S320000, C455S522000
Reexamination Certificate
active
06285664
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the field of wireless communications and in particular, to a method and apparatus for estimating pilot coverages under different radio frequency conditions.
BACKGROUND OF THE INVENTION
Wireless mobile communications provide the greatest convenience for users to access voice and data services essentially anywhere and anytime. Code Division Multiple Access (“CDMA”) communication systems are one of the most promising digital wireless communication systems that can provide the desired mix of voice and data services. CDMA modulation techniques permit a large number of system users to communicate with one another.
The geographic coverage provided by the communications system is divided into coverage areas referred to as cells, where each cell corresponds to a base station. The cell may be further divided into multiple sectors. Communication channels allocated to a given cell and/or sector are determined according to various known methods. Each base station transmits a pilot signal that serves as a beacon for mobile radios that are in the base station's cell. The base stations use the same pilot signal but with different tuning offsets such that they may be distinguished. The geographic coverage provided by the base stations are also referred to as pilot coverages.
Given a system configuration, one optimization goal of the system engineer is to provide a good radio frequency (“RF”) environment. Two factors in such an optimization are (1) minimizing multiple pilot regions (which are areas where pilot signals from different base stations have roughly the same signal strength), and (2) minimizing the impact of interference from other base stations. Each of these factors—pilot signal overlap and intercell interference—are directly impacted by the transmit power levels of base stations in a wireless system. Thus, a goal of the optimization process is to find base station transmit power levels which generally produce minimal pilot signal overlap and intercell interference. Such optimum transmit power levels are also a function of traffic load on the base stations.
Typically, once the base stations are positioned, a terminal for measuring received pilot signal strengths, such as a mobile station or pilot scanner, is used in the field to collect and generate a set of baseline data of pilot signal strength from various base stations (referred to as “baseline pilot survey data”). The baseline pilot survey data and the initial power settings of the base stations are then analyzed to identify RF problem areas, such as pilot signal overlap and intercell interference. The initial base station power settings are then adjusted in a conventional manner to correct the identified RF problems areas. The terminal is then used again to gather a new set of pilot survey data based on the adjusted power settings. These steps are repeated until the pilot signal overlap and intercell interference are minimized. The procedure is repeated for different traffic channel load conditions, where traffic channel load refers to the number of mobiles being served at a given time. Optimizing the system for different RF conditions or environments using currently available methods is, therefore, time consuming and expensive.
SUMMARY OF THE INVENTION
The present invention is an apparatus and method for minimizing pilot signal overlap and intercell interference by estimating changes in pilot coverages due to different traffic loading and base station power conditions. Specifically, the present invention determines from the baseline pilot survey data, the appropriate base station power settings for different traffic loads on the forward link, by minimizing pilot signal overlap and intercell interference. Importantly, the pilot coverage estimation only requires measurement of two parameters: (1) the transmitted pilot E
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, which is the ratio of the average transmit energy per chip for the pilot to the total transmit power spectral density, and (2) the mobile radio received pilot E
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, which is the ratio of the combined pilot energy per chip to the total received power spectral density at the mobile.
In an exemplary embodiment of the present invention, the system determines changes in the mobile received pilot E
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by varying a pair of adjustment factors that relate to the base station transmit power and the traffic channel load conditions on the forward link. Base station initial traffic loading data and baseline pilot survey data are initially stored in terms of E
C
/I
O
. For each combination of the variable adjustment factors, the system calculates the changes from the baseline pilot survey data. The adjustment factors are varied until an optimum base station power setting (i.e., minimum pilot signal overlap, etc.) is obtained for each traffic channel load condition in the forward link. This results in a group of optimized base station power settings. The base station transmit power setting is then determined by selecting one setting that for example, corresponds to an actual loading condition of the base station, from the group of optimized transmit power settings.
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patent: 5577025 (1996-11-01), Skinner et al.
patent: 5771461 (1998-06-01), Love et al.
patent: 5852778 (1998-12-01), Labedz
patent: 5889768 (1999-03-01), Storm et al.
patent: 5920549 (1999-07-01), Bruckert et al.
patent: 6160799 (2000-12-01), Krause et al.
patent: WO 98 07207 (1998-02-01), None
Bernstein Neil E.
Wu Xiao Cheng
Gibbons Del Deo Dolan Griffinger & Vecchione
Hsu Alpus H.
Lucent Technologies - Inc.
Nguyen Brian
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