WO2001052580A2

WO2001052580A2 - Method and system for selecting an optimal antenna location

Info

Publication number: WO2001052580A2
Application number: PCT/SE2001/000056
Authority: WO
Inventors: Olof Erik Grimlund; Kjell Arne Ljungdahl; Jan Arie Van Houvelingen
Original assignee: Telefonaktiebolaget L M Ericsson (Publ)
Priority date: 2000-01-14
Filing date: 2001-01-12
Publication date: 2001-07-19
Also published as: UY26531A1; AR026827A1; AU2001228962A1; WO2001052580A3

Abstract

In a telecommunication system employing at least one fixed radio terminal and at least one base station, an acceptable location for an antenna is determined. A location is selected for the antenna, and a signal is exchanged between the base station and the antenna at the selected location. A signal strength of the signal is measured, and an interference level of the signal is estimated. A determination is made whether the selected location is acceptable based on the measured signal strength and the estimated interference level.

Description

METHOD AND SYSTEM FOR SELECTING AN OPTIMAL

ANTENNA LOCATION

BACKGROUND This invention relates generally to a method and system for selecting an antenna location. More particularly, this invention relates to a method and system for selecting a location for an antenna for a fixed radio terminal in a telecommunication system.

Fixed radio terminals are used in various systems, such as Radio in the Local Loop (RLL), cellular systems employing fixed cellular terminals, e.g., GSM/TDMA/WCDMA systems, satellite systems, and Wireless LAN systems. One of the major driving forces behind these systems is low line cost.

To achieve low line cost, it is important that the fixed terminals are installed quickly and in a manner such that later reinstallation will not be needed. It is also important that the terminals are installed with as low a path loss as possible to provide a good link budget and thereby minimize the number of base station sites required.

Typically, the optimal spot for mounting an antenna is found by making signal strength measurements of the received signal at various locations and selecting the location with the strongest received signal strength. These signal strength measurements are often made by the terminal. A problem with this approach is that the terminals are typically not calibrated and may thus lead to inexact measurements. Assume, for example, that the terminals have a tolerance of ± 4 dB in measured received signal strength as required, e.g., by the GSM specification. A margin of 4 dB has to be added to compensate for terminals reporting signal strengths higher or lower than the actual received signal strength. Then, if the actual received signal strength measured by a terminal to be installed is 4 dB too low, the indication from the terminal is 8 dB too low. Thus, the signal strength indicated by the terminal might be too low, though the location is acceptable. It might, therefore, be hard for the installer to find an acceptable location for installing the antenna.

Moreover, the measured signal strength alone does not always provide a reliable estimate of the link quality. Interference also should be taken into account. Interference can be estimated by measuring the bit error rate (BER). A problem with BER measurements is that they generally require a long period of time to perform, thus adding significantly to the installation time. For example, a 10^~3 BER target with a 6 dB margin for seasonal change means that a BER below 10^"5 should be measured. It may take up to 10 hours to collect enough measurements to ensure that the BER is below 10^"5.

There is thus a need for a technique for selecting an antenna location that is easy, quick and accurate.

SUMMARY It is therefore an object of this invention to provide a technique for selecting an antenna location that is easy, quick and accurate.

According to exemplary embodiments, this and other objects are met by a method and system for determining an optimal location for an antenna connected to a terminal.

An initial location for the antenna is selected, and a signal is exchanged between, e.g., a base station and the antenna at the selected location. A signal strength of the signal is measured, and an interference level of the signal is estimated. A determination is made whether the selected location is acceptable based on the measured signal strength and the estimated interference level.

According to exemplary embodiments, the terminal may be mounted indoors or outdoors. The antenna may be mounted indoors, e.g., if the antenna is close to the base station, or outdoors.

According to one embodiment, the signal strength may be measured at the terminal. According to another embodiment, the signal strength may be measured at the base station and reported to the terminal. According to exemplary embodiments, the estimation of the interference level may be performed by measuring an error rate of the signal at the terminal or the base station. In order to speed up measurements, the signal may be attenuated by decreasing the output power from the base station or from the terminal. BRIEF DESCRIPTION OF THE DRAWINGS

The features, objects, and advantages of this invention will become apparent by reading this description in conjunction with the accompanying drawings, in which like reference numerals refer to like elements and in which: FIGS. 1 A and IB illustrate exemplary fixed radio communication systems according to the present invention; and

FIG. 2 illustrates a method according to exemplary embodiments.

DETAILED DESCRIPTION For illustrative purposes, the following description is directed to a cellular radio communication system, but it will be understood that this invention is not so limited and applies to other types of communication systems.

According to exemplary embodiments, signal strength and signal interference are considered in determining where to install an antenna for a fixed terminal. The signal strength and the signal interference may by derived from several measurements averaged together or from a maximum measured value.

According to a first aspect of the invention, a fixed radio telecommunications terminal mounted indoors can be used together with an antenna unit mounted outdoors. FIG. 1 A illustrates a communication system with a fixed radio terminal, e.g., a fixed cellular terminal (FCT) 100, mounted indoors and an antenna unit 200 mounted outdoors. The FCT 100 receives signals from and transmits signals over an air interface 25 to, e.g., a base station 50, via the antenna unit 200. The FCT 100 may be connected to a telephone 500. The FCT 100 includes radio parts, digital parts and other parts, e.g., a power supply. Also, the FCT 100 may include a data adaptor 105 for fax and data to facilitate communication with a personal computer 400 via a modem 300. The FCT 100 is connected to the antenna unit 200 via, e.g., a coaxial cable. It should be appreciated that the antenna unit 200 may, instead, be mounted indoors, e.g., if the terminal is placed close to the base station. FIG. IB illustrates an exemplary communication system according to another aspect of the invention. In the system shown in FIG. IB, the radio parts are located outdoors. Other devices, e.g., a data adaptor (FDA) 160 and a power supply (PS) 170, 180 may be located indoors to facilitate installation and replacement. According to an exemplary embodiment, received signal strength may be measured at the fixed terminal or at the antenna. To increase the signal strength measurement accuracy, external calibrated measurement equipment can be used, e.g., equipment connected to the external antenna. Alternatively, the terminal can be calibrated, e.g., in the factory, or hardware/software can be added in the terminal so that the terminal measures with higher accuracy.

According to another embodiment, the signal strength may be measured by measuring the received signal strength in a signal transmitted from the radio terminal to the base station. The transmitted signal from the terminal has a relatively high accuracy, e.g., ±1 dB, thus affording an accurate measurement. The measurement equipment in the base station can be calibrated with a low relative increase in cost. The measured signal strength can be reported by the base station to the terminal, e.g., as a short message service (SMS) message.

According to an exemplary embodiment, a BER measurement may be made at the terminal. Alternatively, the BER measurement may be made at the base station, and the result of the measurement may be sent to the terminal, e.g., as an SMS message. As yet another alternative, the terminal may transmit a known bit pattern to the base station, the base station may receive and re-transmit the pattern back to the terminal, and the terminal may then measure the BER in the received re-transmitted pattern. The BER measurement can be made faster by attenuating the received signal. Assume for example, that the target BER for an acceptable amount of interference is 10^"5 (including margin). If the received signal is attenuated by 6 dB, the BER target of 10^"5 translates into a target of about 10^"3. Only a few minutes are required to make sure the BER is below 10³. Thus, by attenuating the received signal, the BER measurement time is reduced from several hours to only a few minutes. According to an exemplaiy embodiment, attenuation may be achieved by reducing the output power at the base station, if the BER measurement is made at the terminal, or by reducing the power of the terminal, if the BER measurement is made at the base station or if the BER measurement is made at the terminal using a re-transmitted pattern received from the base station. In the GSM system, for example, attenuation may be achieved using the downlink power control mechanism in which the radio terminal reports a measured signal strength to the base station which uses the reported measured signal strength to control the downlink output power. If the radio terminal purposely reports too high a measured signal strength during the measurement period, the base station responds by reducing the downlink output power, thus attenuating the signal received by the terminal.

Based on the measured signal strength and the BER, the terminal determines whether the selected location for the antenna is acceptable. This determination may be made, e.g., by a microprocessor in the terminal. For example, if the measured signal strength is within a predetermined range, and the BER is less than a predetermined target, the location is determined to be acceptable. The range for the measured signal strength depends, e.g., on the technology, environment, and the distance from the base station. For a GSM terminal, an example of an acceptable measured signal strength range may be -80 dBm to -90 dBm. FIG. 2 illustrates a method for selecting a location for mounting an antenna according to an exemplary embodiment. The method begins at step 200 at which an initial location of an antenna is selected based, e.g., on the direction of the base station. At step 210, a signal is exchanged between the base station and the antenna at the selected location. At step 220, a signal strength of the signal is measured. The signal strength may be measured, at the terminal or may be measured at the base station and reported to the terminal. At step 230, an interference level of the signal is estimated based, e.g., on BER measurements made at the terminal or made at the base station and reported to the terminal. At step 240, a determination is made whether the selected location is acceptable, based on the measured signal strength and the estimated interference level. If the location is not acceptable, the process starts again, and another location is selected. If the location is acceptable, the antenna and terminal are mounted at step 250.

According to exemplary embodiments, a location for mounting an antenna for a fixed radio terminal is selected based on measured signal strength and estimated interference level. According to exemplary embodiments, the selection of the location is made easily, quickly and accurately, leading to a low average line cost.

It will be appreciated by those of ordinary skill in the art that this invention can be embodied in other specific forms without departing from its essential character. The embodiments described above should therefore be considered in all respects to be illustrative and not restrictive. For example, although described above with reference to a GSM system employing a fixed cellular terminal, the invention is also applicable in other types of communication systems.

Claims

WHAT IS CLAIMED IS:

1. In a telecommumcation system employing at least one fixed radio terminal and at least one base station, a method for determining an acceptable location for an antenna, the method comprising the steps of: selecting a location for the antenna; exchanging a signal between the base station and the antenna at the selected location; measuring a signal strength of the signal; estimating an interference level of the signal; and determining whether the selected location is acceptable based on the measured signal strength and the estimated interference level.

2. The method of claim 1 , wherein the signal strength is measured at the terminal.

3. The method of claim 1, wherein the signal strength is measured at the base station and reported to the terminal.

4. The method of claim 1, wherein the step of estimating an interference level comprises measuring an error rate of the signal.

5. The method of claim 4, further comprising attenuating the transmitted signal before measuring the error rate.

The method of claim 4, wherein the error rate is measured at the terminal.

7. The method of claim 5, wherein the error rate is measured at the terminal.

8. The method of claim 7, wherein the step of attenuating comprises decreasing the output power of the base station.

9. The method of claim 7, wherein the step of attenuating comprises: reporting to the base station a signal strength that is higher than the measured signal strength; and attenuating the signal transmitted by the base station based on the reported signal strength.

10. The method of claim 4, wherein the error rate is measured at the base station and reported to the terminal.

11. The method of claim 5, wherein the step of attenuating comprises decreasing the output power of the terminal, and the error rate is measured at the base station and reported to the terminal.

12. The method of claim 4, wherein the terminal sends a known bit pattern to the base station, the base station re-transmits the bit pattern to the terminal without changes, and the error rate is measured at the terminal.

13. The method of claim 5, wherein the terminal sends a known bit pattern to the base station, the base station retransmits the pattern without changes, and the error rate is measured at the terminal.

14. The method of claim 13, wherein the step of attenuating comprises decreasing the output power of the terminal.

15. The method of claim 13, wherein the step of attenuating comprises decreasing the output power of the base station.

16. A system for determining an acceptable location for an antenna in a communication system comprising at least one fixed radio terminal and at least one base station, the system comprising: means for measuring a signal strength of a signal exchanged between the base station and the antenna at a selected location; means for estimating an interference level of the signal; and means for determining whether the selected location is acceptable based on the measured signal strength and the estimated interference level.

17. The system of claim 16, wherein the means for measuring the signal strength is included in the terminal.

18. The system of claim 16, wherein the means for measuring the signal strength is included in the base station, and the base station includes means for reporting the measured signal strength to the terminal.

19. The system of claim 16, wherein the estimating means estimates an interference level by measuring an error rate of the signal.

20. The system of claim 19, further comprising means for attenuating the signal before measuring the error rate.

21. The system of claim 19, wherein the error rate is measured at the terminal.

22. The system of claim 20, wherein the error rate is measured at the terminal.

23. The system of claim 22, wherein the means for attenuating decreases the output power of the base station.

24. The system of claim 22, wherein the means for attenuating comprises: means for reporting to the base station a signal strength that is higher than the measured signal strength; and means for attenuating the signal transmitted by the base station based on the reported signal strength.

25. The system of claim 19, wherein the error rate is measured at the base station and reported to the terminal.

26. The system of claim 20, wherein the means for attenuating decreases the output power at the terminal, and the error rate is measured at the base station and reported to the terminal.

27. The system of claim 19, wherein the terminal sends a known bit pattern to the base station, the base station retransmits the bit pattern to the terminal without changes, and the error rate is measured at the terminal.

28. The system of claim 20, wherein the terminal sends a known bit pattern to the base station, the base station retransmits the bit pattern to the terminal without changes, and the error rate is measured at the terminal.

29. The system of claim 28, wherein the means for attenuating decreases the output power of the terminal.

30. The system of claim 28, wherein the means for attenuating decreases the output power of the base station.