Extraction of primary and co-channel signals

Details Extraction of primary and co-channel signals Extraction of primary and co-channel signals

1999-10-06

2001-11-27

Trost, William (Department: 2683)

Telecommunications

Transmitter and receiver at separate stations

Distortion, noise, or other interference prevention,...

C455S067150, C455S067700, C455S296000, C455S304000, C455S297000, C455S456500, C375S340000, C375S342000, C375S355000

Reexamination Certificate

active

06324382

ABSTRACT:

TECHNICAL FIELD
This invention relates to extraction of primary and co-channel signals, for example a primary signal and an interfering co-channel signal in a GSM mobile telephone system.
BACKGROUND ART
An important factor in implementing and managing mobile telephone systems is the determination of quality of reception by mobile units of the signals broadcast by base transceiver stations (BTSs). This determination can be valuable in identifying the cause of, for example, high levels of interruptions to calls (dropped calls) in specific geographic areas. To this end, a “drive system” is used, comprising a small test system housed in a vehicle such as a car or van. The test system typically incorporates a “test mobile” handset, independent signal receiving and measurement equipment, a geographic location system (such as a global positioning system—GPS—receiver), and a mobile computer to coordinate the operation of these devices and record the results obtained.
One significant function typically desired in a drive system is the detection, measurement and identification of co-channel signals, i.e. signals occupying the same frequency band or channel as, and interfering with, the mobile telephone system signal intended to occupy that channel.
The conventional method of co-channel detection uses a directional antenna coupled to a receiver. While the vehicle is stationary the antenna is progressively rotated stepwise through a complete circle. At each directional setting the received signal strength is recorded and if need be demodulated to identify a possible interferer. All this information then has to be combined to form a complete picture of the reception characteristics at that location. This is a very complex and time-consuming process requiring a skilled technician for what is essentially a data collection process. Another drawback of this approach is that the separate measurements are temporally uncorrelated and so cannot represent the instantaneous received signal quality. To get around this, a multiple receiver/antenna setup can be used, but this is complex and costly.
It is an object of this invention to provide a method and apparatus for extraction of primary and co-channel signals which reduce the time required for the measurement to be made and which can be used with an omni-directional antenna.
DISCLOSURE OF INVENTION
According to one aspect of this invention there is provided a method of extracting a primary signal from a composite signal containing said primary signal and a co-channel signal, comprising the steps of:
receiving said composite signal;
estimating at least one metric which characterises propagation conditions encountered by said primary signal, by sampling said composite signal and grouping samples according to their instantaneous rate of change of rotation in the complex plane; and
deriving an estimate of said primary signal from said composite signal in accordance with said metric.
The invention enables a single omni-directional antenna and receiver to be used, permitting a very simple equipment setup. In one embodiment a measurement process, implemented for example by digital signal processing (DSP) software, takes a “snapshot” of the received signal and extracts from it the main signal and its associated channel distortion. These components are then analysed and detected. The whole measurement operation can be completed in seconds. Thus all the results refer to the same time instant, and provide a true picture of the instantaneous received signal quality. Furthermore, the measurement can be performed in a moving vehicle. Owing to the simplicity of equipment configuration and operation, the data collection can be carried out by a less skilled technician than is required for previous systems.


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