Low-power concurrent use in the spectrum bands 1781.7 – 1785 MHz paired with 1876.7 – 1880 MHz

Technical Study (1): Published 28 July 2005

Summary

This technical study ("Technical Study") has been prepared by Ofcom, in connection with the proposed award of wireless telegraphy licences to use the spectrum bands 1781.7 – 1785 MHz paired with 1876.7 – 1880 MHz (the “Spectrum Bands”). It is issued in support of, and should be read together with, the Ofcom Consultation Document "Award of available spectrum: 1781.7-1785 MHz paired with 1876.7-1880 MHz" published on 28 July 2005 ("Consultation Document"). Terms and expressions used in this Technical Study are as defined in the Consultation Document.

The Technical Study is intended solely as a means for Ofcom to consider the viability of offering concurrent low power licences to use the Spectrum Bands and the development of technical conditions for inclusion in the licences. It is being made available for information purposes only. It is made available on the express understanding that it will only be used for the sole purpose of assisting in reviewing and responding to the Consultation Document, and not in assessing whether to participate in the proposed award of licences to use the Spectrum Bands. The Technical Study is not intended to form any part of the basis of any investment decision or other evaluation or any decision to participate in the proposed award of licences to use the Spectrum Bands and should not be considered as a recommendation by Ofcom or any of its advisers to do so. Any party considering participating in the proposed award of licences to use the Spectrum Bands must make its own independent assessment of the technical viability of using the Spectrum Bands and the potential value of a licence to use the Spectrum Bands after making such investigation as it may deem necessary in order to determine whether to participate. All information contained in this Technical Study is subject to updating, modification and amendment.

No person should construe the content of the Technical Study, or any other communication by or on behalf of Ofcom or any of its other advisers, as technical, financial, legal, tax or other advice. Accordingly, any person considering participating in the proposed award of licences to use the Spectrum Bands (either directly or by investing in another enterprise) should consult its own advisers as to these and other matters or in respect of any other assignment of any radio spectrum.

Coverage and Capacity

This analysis confirms that a low power system based on GSM pico cells operating at the 23dBm power level can provide coverage in an example multi-storey office scenario. Two pico cells per floor would meet the coverage requirements in the example 50m × 120m office building. For a population of 300 people per floor, the two pico cells would also meet the traffic demand.

A seven-floor frequency re-use provides call success probability above 97% across the 50m range of the pico cell. For six-floor re-use the call success probability drops to 94% at the edge of the cell.

Coordination between neighbouring buildings in the commercial environment
A probabilistic analysis of interference between neighbouring office buildings with indoor GSM pico cells operating on the same radio frequency indicates that a 97% probability of call success inside each office could be achieved with 550m separation between buildings if there were no obstructions between them. For a building separation of 150m the probability of call success is achieved is better than 90%. We conclude that coordination is necessary.

We conclude that it is possible to serve users up to 40m within a building using an external base station with a power limit of 23dBm. However, to penetrate to users 50 meters within a building would require a higher power (30dBm would be needed to give a reasonable separation between the base station and building).

An outdoor micro cell could cause interference to an in-building pico cell system. At 3km a 23dBm micro cell reduces the call success probability on the pico cell system below 90% while a separation of 10km would be required for 97% call success. These figures are reduced significantly if there is an obstruction in the path. Adding a building on a 730m path gives a call success rate of 97%. However, if the outdoor micro cell has a power of 30dBm it is not possible to achieve a call success of 97% even with an obstructing building in the path unless the distance between the cells is unreasonably long.

We propose a maximum antenna height for outdoor installations of 10m as a means to reduce the occurrence of unobstructed interference paths. We also propose a maximum power level of 23dBm EIRP to prevent interference over a significant area.

Residential scenario

This analysis confirms that a GSM system based on a pico cell operating at the 0dBm power level can provide coverage in an example terraced house scenario.

A probabilistic analysis of interference between co-frequency indoor GSM pico cells located within a row of terraced houses indicates that a 97% probability of call success inside each house could be achieved with a separation of two houses.

A probabilistic analysis of interference between co-frequency indoor GSM pico cells located within houses in opposite terraces indicates that coordination will be required and that it will only be possible to assign frequencies from a total of 15 at random if the usage percentages are relatively low.

Use of low power CDMA

Under a technology neutral licence it is conceivable that both narrowband (e.g. low-power GSM) and wideband (e.g. low-power cdma2000 1x) systems could be deployed. As an example of the deployment of both wideband and narrowband systems, this analysis considers the impact of a low-power cdma2000 1x system on a low-power GSM system.

A probabilistic analysis of interference from an 23dBm indoor cdma2000 1x pico cell system into a co-frequency indoor GSM pico cell system indicates that achieving a 97% probability of call success inside the office would require a 250m separation distance between the buildings for a 50m radius serving cell if there were no obstructions between them. We conclude that coordination may be necessary.

The full document is available below