Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
2000-10-03
2004-05-11
Chin, Vivian (Department: 2682)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S423000, C455S063100
Reexamination Certificate
active
06735436
ABSTRACT:
TECHNICAL FIELD
This invention relates in general to wireless telecommunications networks and applications and, in particular, to a method and system of performing interference analysis among cells in a telecommunications network. More particularly, the invention relates to a method and system of estimating the accuracy of interference analysis based on traffic/disturbance event correlations.
BACKGROUND OF THE INVENTION
Without limiting the scope of the invention, its background is described in connection with identifying, analyzing and quantifying uplink/downlink interference in a wireless telecommunications network, as an example.
Present-day mobile telephony has spurred rapid technological advances in both wireless and wireline communications. The wireless industry, in particular, is a rapidly growing industry, with advances, improvements, and technological breakthroughs occurring on an almost daily basis. Many mobile or wireless telecommunications systems, among them the European GSM-system, have passed through several generations of advancements and development phases, and system designers are now concentrating on further improvements to such systems, including system refinements and the introduction of optional subscriber services.
Most wireless telecommunication systems are implemented as cellular telephone networks wherein a group of Base Transceiver Stations (BTS), or base stations are served by a centrally located switch. The switch is commonly referred to as a Mobile Switching Center (MSC). The base stations are spaced apart from each other by distances of between one-half and twenty kilometers. Each base station is assigned a number of two-way voice and control channels. The voice channels transmit voice signals to and from proximately located mobile stations, and transmit control information to and from these mobile stations, usually for the purpose of establishing a voice communications link.
A typical cellular telephone network also includes a group of interconnected MSCs, which operate in association with a Gateway Mobile Switching Center (GMSC) through which the cellular telephone network interconnects with a conventional Public Switched Telephone Network (PSTN). In addition, at least one Home Location Register (HLR) operates within the cellular telephone network. The HLR stores network subscriber information, including the identified location of current mobile stations within the network.
In response to an incoming call placed to a mobile station, the MSC queries the HLR to determine the current location of the mobile station. The HLR “looks up” the current location of the mobile station and contacts the currently serving MSC to pre-route the call and retrieve a temporary location directory number, which is utilized to route the call through the telecommunications network for termination of the call to the mobile station. The MSC instructs the base station serving the cell in which the mobile station is located to page the mobile station. Responding to the page, the mobile station requests assignment of a channel, and the network terminates the call through the serving MSC and over the assigned channel.
Calls by mobile subscribers can be affected by interference which can cause radio disturbance events which, in turn, limit the efficiency of the network. As such, it is important to identify those cells within the network, which are sources of and subject to radio disturbance events. Interference internal to the network often results from call activity within a specific network cell site. Cells that are sources of to disturbances are described as “offenders.” A radio disturbance event typically occurs during a cellular call, either on the downlink (from a base station to a mobile station), or on the uplink (from a mobile station to a base station). The disturbance event can be limited to several types of interference, including co-channel interference, adjacent channel interference or external interference.
Various methods exist for determining when a cell has been disturbed. Typically, a comparison of signal strength versus a measurement of speech quality can be employed to determine the Bit Error Rate (BER) of the transmission channel. When sufficient signal strength is correlated with degraded speech quality for an extended period of time (usually measured in seconds), that cell can be considered “disturbed.” Failure to identify and analyze sources of such disturbances could result in poor channel quality and the sealing of devices, which means they are unavailable for use in handling calls.
Additionally, several methods and systems currently exist for identifying disturbed cells within the wireless telecommunications networks. One of the most widely utilized methods involves downlink interference prediction tools, or prediction methods, which use model-based prediction algorithms. Such tools predict where interference may exist within a given network coverage area. The predictions are then utilized for frequency and cell planning, particularly in initial network designs. The validity of such predictions is dependent on a number of factors, including the accuracy of the propagation model utilized and the resolution of the terrain data. Such tools are helpful in identifying the cells that are causing downlink interference, but taken together are often inaccurate because of the dependence on predictions. That is, such prediction tools do not always account for “real-life” sources of interferences in the coverage area as determined through more empirical measurement methods.
Another method utilized to identify disturbed and offending cells involves drive testing by field personnel. The drive test can be performed by turning off all adjacent/co-channel transmitters for a particular disturbed cell and then keying up each transmitter individually. A drive test team, in the meantime, drives the area in a motorized vehicle to observe and measure interference within the drive area. This method is inherently labor intensive and costly since it requires continuous measurement by field personnel. In addition, the drive-test approach, while sometimes useful, does not take into account variations in mobile station types and is limited to the extent that only several possible offenders can be investigated.
The Related Application t (U.S. patent application Ser. No. 09/ 426,139) provides a cost effective method of identifying and analyzing sources of interference in the network that utilizes available qualitative data about the network. Essentially, the Related Application discloses a technique where traffic/disturbance event correlations are assembled and analyzed in order to narrow the field of possible offender cells for a specific disturbed cell. By relating disturbance events in one cell to traffic events (or call activity) in surrounding cells, a way of analyzing interference within the network is provided.
While the correlation technique of the Related Application is useful, there is no known way to quantify the accuracy of such traffic/disturbance “correlation” techniques. It is known that certain correlations are naturally occurring within the network without consideration of the interference factor. Such naturally occurring correlations can give a false sense of confidence in terms of positively being able to identify a disturbance source in the network. A way of taking into consideration the effect of false matches would therefore be advantageous. What is needed is a way of estimating the probability of false event correlations to confirm that call activity in one or more of the offending cells is the likely cause of interference in a given cell.
SUMMARY OF THE INVENTION
The present invention provides a method and system for quantifying the probability of false event correlations occurring from random matches in a telecommunications network. With the present invention, the network operator can use the probability of false event correlations to confirm that call activity in one or more of the offending cells is likely to be the cause of the interference in the g
McCauley Houston
Shah Ali R.
Chin Vivian
Ericsson Inc.
West Lewis
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