Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
2000-05-10
2003-08-12
Trost, William (Department: 2683)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S446000, C455S421000, C455S423000, C455S424000, C455S067150, C455S067700
Reexamination Certificate
active
06606494
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to cellular telephone systems and to modeling cellular telephone systems for optimizing utilization of the available overall radio spectrum. More particularly, the present invention relates to a reliable performance prediction based upon a measurement technique for unobtrusive gathering of data about the performance of the cellular system without interruption of normal operation and for complex analysis of the gathered data.
The service area of a wireless communications system is partitioned into connected service domains known as cells, where radio telephone (cellular) users communicate, via radio links, with the base station serving the cell. The cells can be further partitioned into segments. The base station is coupled to the land line network.
Presently available commercial mobile communication systems typically include a plurality of fixed cells each of which transmits signals to and receives signals from mobile units within its communication area. In AMPS or FDMA systems, each base station is assigned a plurality of channels (each 30 KHz wide) within a frequency spectrum over which it can communicate with mobile units. A mobile unit within range of the base station communicates with the base station using these channels. Typically, the channels used by a base station are separated from one another in some manner (typically skipping 1, 7 or 21 intermediate channels) sufficiently that signals on any channel do not interfere with signals on another channel used by that base station. To accomplish this, an operator typically allots to a base station a group of channels each of which is widely separated from the next. So long as a mobile unit is within the area in which the signal from a base station is strong enough and is communicating with only that base station, there is no interference with the communication. The present invention will also operate with GSM and iDEN systems which do not rely on the same frequency divisions multiple access method.
In a common type of mobile system called Time Division Multiple Access (TDMA), which includes IS-54 and IS-136, GSM and iDEN each frequency channel is further time divided into additional channels within each frequency. Each base station sends and receives in bursts during some number of different intervals or time slots. These time intervals within frequency bands then effectively constitute the individual channels. In order to distinguish the channel divisions within a frequency and to distinguish channels of a common frequency between overlapping cells digital codes are used. For example, IS-136 utilizes Digital Verification Color Codes unique to a channel at a cell, are used. GSM uses Base Station identification codes.
In order to allow mobile units to transmit and receive telephone communications as the units travel over a wide geographic area, each cell is normally physically positioned so that its area of coverage is adjacent to and overlaps the areas of coverage of a number of other cells. When a mobile unit moves from an area covered by one base station to an area covered by another base station, communications with the mobile unit are transferred (handed off) from one base station to another in an area where the coverage from the adjoining cells overlaps. Because of this overlapping coverage, the channels allotted to the individual cells are carefully selected so that adjoining cells do not transmit or receive on the same channels. This separation is typically accomplished by assigning a group of widely separated non-interfering channels to some central cell and then assigning other groups of widely separated non-interfering channels to the cells surrounding that central cell using a pattern which does not reuse the same channels for the cells surrounding the central cell. The pattern of channel assignments continues similarly with the other cells adjoining the first group of cells. Often adjacent or overlapping cells will transmit on the same frequency and both will be received by a mobile wireless unit. However, because of the digital codes identifying each channel, the mobile wireless unit can process the appropriate signal and ignore any additional reception.
It is desirable to provide a process by which interference between cellular telephone system channels operating at the same frequency and/or adjacent frequencies may be accurately predicted over each entire cell of an entire system based upon dynamic information corresponding to in-use performance and for adaptively reallocating channels based upon the in-use interference performance to maximize capacity while minimizing overall interference within the system.
SUMMARY OF THE INVENTION
The performance, in terms of service evaluation quality, is the goal of the collection and analysis taught herein. The drive testing measures RF propagation of a cellular system. Performance quality is determined by the analysis of the measured test drive data. Drive testing is used to aid in evaluation of the system, to determine cell placement and channel distribution and to evaluate sector interference. A cellular service area is analyzed and a drive route is established. Determination of a proper and effective drive route is essential for proper system evaluation. The drive route is based on a complex analysis of the system, including its electronic and geographic features. Once a drive route is established, one or more vehicles are driven through the cellular system to collect data. The vehicles are provided with radio receivers for detecting the signal strength from the cell sites and with positioning equipment such as GPS receivers to determine the location corresponding to a received signal. The vehicle are also equipped with data collection equipment, such as computers for collection and correlation of the data.
The measurement system is typically installed in a vehicle. Data is collected as the vehicle travels a predetermined route within the service area. The measurement system can also be used to collect data within a building, although this requires a different mechanism for providing the positioning information. The typical measurement system consists of a scanning receiver, GPS, and laptop computer. The scanning receiver produces signal level measurements for a predetermined list of channels while the GPS provides positioning (latitude/longitude) information. The laptop computer logs the signal level and positioning information during the measurement event.
A scanning receiver tuned to a particular frequency, cannot distinguish between separate signals on that same frequency and therefore does not have the ability to determine if a signal originates from one or more than one cell antenna in an AMPS/FDDMA system. Because of the overlap of signals when all of the cell sites are active, the test vehicles cannot accurately determine a signal level from a given antenna location. A received signal level may be the combination of signals from more than one base station. In order to avoid this problem when drive testing an AMPS system, individual antennas on each sector are keyed-up to a constantly transmitting state on a single particular frequency distinct from all of the other sectors. This is commonly referred to as a keyed-up or beacon signal. By tuning to a particular frequency, a receiver in a test vehicle can accurately determine the base station corresponding to the received signal and can determine the signal level from that single sector.
In key up testing, a unique test channel is established on each sector that propagates into a measurement area. By establishing a unique test channel on a sector, measurements for the given channel can be positively associated to the source sector. This methodology for establishing the unique test channel requires modifications to the system. The test channel is placed in a mode such that it transmits a constant signal, which is referred to as a “key-up”. In addition, the same channel (and sometimes adjacent channels) is turned off (“blocked”) on all other sectors that
Arpee John
Gutowski Stan
Touati Mustafa
ScoreBoard, Inc.
Torres Marcos
Trost William
Zito Joseph J.
Zito tlp
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