Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1998-09-29
2001-01-16
Maung, Nay (Department: 2744)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S424000, C455S067150, C455S067700, C455S063300
Reexamination Certificate
active
06175734
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to radiocommunication systems, and more particularly to a method and system for measuring cell relations in a cellular communication system.
BACKGROUND OF THE INVENTION
Generally, in a cellular radiocommunication system, a coverage area is divided into smaller sub-areas known as cells, where each cell is assigned a set of radio resources for serving subscribers. In a FDMA (Frequency Division Multiple Access) cellular system, the radio resources comprise multiplexed radio frequency channels. In a TDMA system (Time Division Multiple Access), the information is transmitted during assigned time slots of a set of radio frequency channels, with different users being assigned corresponding time slots on the same or different radio frequency channels. In both the FDMA and TDMA cellular systems, however, the assignment of the radio frequency channels between the cells produces two types of interference: co-channel interference and adjacent channel interference. Co-channel interference results if two separate signals are sent on the same frequency simultaneously, thereby limiting the ability of a receiver receiving both signals to separate them for detection of the desired signal. Adjacent channel interference results if channels that are adjacent to each other in the frequency spectrum are used in the same geographical area. Transmissions on a radio frequency channel tend to leak to adjacent frequencies and cause interference.
Conventionally, co-channel interference and adjacent channel interference in cellular systems are reduced by intelligently dividing the radio frequency resources among the cells. Most cellular systems use a predefined frequency re-use pattern that is optimized based on a particular characteristic of a coverage area. Under such frequency re-use pattern, adjacent cells are assigned different radio frequency channels, with the same radio frequency channel assignment being repeated for distant cells. Because some of the radio frequency channels are re-used in distant cells, co-channel interference can not be totally eliminated.
Improved frequency planning that relies on cell relations can further reduce co-channel. The cell relations among the cells is often expressed by statistically estimating measured cell relation parameters. Known methods for estimating cell relations have focused on measuring overall interference in a certain cell. Such measurements are usually done, while ordinary communication traffic is in progress. Under such circumstances, it is often difficult to identify the source of a signal for measurement purposes, since the radio frequency channel over which measurements are made may include contributions from several sources. It is thus difficult to accurately measure how much transmissions in one cell interferes with transmissions in another cell, if such transmissions occurs simultaneously on the same frequency. As a result, conventional methods do not provide an accurate representation of cell relations among the cells.
It is, therefore, desirable to accurately measure cell relations, preferably, in both the up-link direction and downlink direction, without interfering with ongoing traffic.
SUMMARY OF THE INVENTION
Briefly, according to the present invention, the method for determining cell relations in a cellular communication system transmits signals from one or more transmitters over a plurality of radio frequency channels that are assigned to the cells. The transmitted signals over the plurality of radio frequency channels are received at each one of the cells and their received signal strengths are measured at corresponding measurement times. The received signal strength measurements and corresponding measurement times are processed to determine whether a measured received signal strength at a corresponding measurement time is based on a transmission from a single transmitter in a cell. In the exemplary embodiment of the invention, the determination of whether a measured received signal strength is from a single transmitter in a cell is based on a record of ongoing calls within the communication system. Based on received signal strength measurements that are determined to be from single transmitters, cell relation values between the cells are determined, either in terms of path gain values or C/I ratios.
According to some of the more detailed features of the present invention, the received signal strength measurements correspond to uplink received signal strength measurements, where the one or more receivers are one or more base stations. Each base station has a call allocation list that prioritizes the radio frequency channels assigned to incoming calls within its cell. According to one feature of the invention, the call allocation lists in at least two of the base stations are arranged to increase the probability of measuring received signal strength from single transmitters. More specifically, the call allocation list in one base station prioritizes the radio frequency channels allocatable to the calls in a reverse order relative to the prioritization of the radio frequency channels allocatable to calls at the other base station.
According to yet other more detailed features of the present invention, the received signal strength measurements correspond to downlink received signal strength measurements, with the one or more receivers being one or more mobile stations. Each base station incorporates a list that prioritizes the radio frequency channels over which received signal strength from a base station is measured. In the exemplary embodiment, the list of the plurality of radio frequency channels used for received signal strength measurements at the mobile stations is included as a part of a MAHO list transmitted to the mobile stations at the beginning of a call.
REFERENCES:
patent: 2 311 912 (1997-10-01), None
patent: 9827763 (1998-06-01), None
Cuffaro Angelo
Desgagn{acute over (e)} Michel
Minichiello Pat
Sammour Mohammed
Burns Doane Swecker & Mathis L.L.P.
Gary Erika A.
Maung Nay
Telefonaktiebolaget LM Ericsson
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