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The Use of Loopback Band Scanning for Intermodulation Estimation in GSM Picocellular Cell Planning. Disclosure Number: IPCOM000004622D
Original Publication Date: 2001-Mar-01
Included in the Prior Art Database: 2001-Mar-01
Document File: 2 page(s) / 25K

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Chris Brice: AUTHOR [+2]


The Use of Loopback Band Scanning for Intermodulation Estimation in GSM Picocellular Cell Planning.

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The Use of Loopback Band Scanning for Intermodulation Estimation in GSM Picocellular Cell Planning.

Chris Brice, Neil Turner

In a picocellular in-building system, it is beneficial to be able to perform automated cell planning at regular intervals, to overcome new interfering systems, propagation differences over time, or to add or remove transceivers. Usually cell planning requires a specialist team on-site to perform measurements and then to implement any changes in frequency plan or transmitter power.

If an automated system of frequency planning can be implemented, it can be performed more rapidly, at more regular intervals, and at much lower cost to the operator. This paper describes a simple method to aid that process that can be implemented using loopback hardware.

The transceiver hardware can be used to demodulate other downlink signals by tuning the receiver to the transmit band using the loopback hardware. This can be used to measure the magnitude of other base stations in the vicinity, switching out receive-band filters as necessary. If each channel in the transmit band is measured (either channel by channel, or wideband analysis) then a picture can be built up of the rf environment, which can be used for cell planning.

In the cell planning process, the operator will have a finite number of channels available to use. The choice of which channel to use in which location (ie which transceiver) depends upon other local interferers, and the effect that they will have on the system operation.

Consider the following scenario. Two external interferers (base stations from a competitor's network) produce strong signals at frequencies fl and f2. These signals will be incident at the antenna of the mobiles being used. The front end of the mobile receiver will produce intermodulation products as a result of the two incident signals. Generally the most important products will be the third-order ones, generated at 2.fl f2 and 2.f2 f1. In the cell planning process, the operator will attempt to avoid using frequencies that are already in use, and the loopback technique will allow these to be measured by each installed transceiver. Downlink power level reporting by the mobile will only report the adjacent cells of the operator's own network, and will not include any data on other operator's transmitters. It can be assumed that the operator has sufficient knowledge of its own network for planning purposes.

It is important that the cell planners consider not only the channels used, but also any intermodulation products that may be generated by them. Returning to the scenario above, intermodulation products will be generated at 2.fl f2 and 2.f2 fl. The effect would be as follows: if one of these channels were to be used in the cell plan, these intermodulation products would fall and produce a signal in the receiver IF that would be of a certain magnitude; the downlink signal from the desired transceiver would have to be higher than the unwanted product by an amoun...