GB2382954A

GB2382954A - A telecommunications station such as a umts base station and a method of detecting a parameter of a signal transmitted therefrom

Info

Publication number: GB2382954A
Application number: GB0128998A
Authority: GB
Inventors: Stephen Edward Cooper; Andrea Corrias
Original assignee: Lucent Technologies Inc
Current assignee: Nokia of America Corp
Priority date: 2001-12-04
Filing date: 2001-12-04
Publication date: 2003-06-11
Anticipated expiration: 2021-12-04
Also published as: GB0128998D0; GB2382954B

Abstract

A telecommunications station has a first antenna operative to transmit a first signal in a first frequency band. It also comprises second antenna operative to receive which is connected to a filter assembly operative to pass signals in a second frequency band to a signal detector. In use a fraction of the first signal at the first frequency band transmitted by the first antenna is received by the second antenna. That is coupled around the filter assembly by way of a coupler so as to bypass the filter assembly so as to be passed to the signal detector so as to enable a parameter of said first signal to be detected.

Description

A TELECOMMUNICATIONS STATION SUCH AS A UMTS BASE STATION AND A METHOD OF DETECTING A PARAMETER OF A SIGNAL TRANSMITTED THEREFROM Technical Field The present invention relates to a telecommunications station comprising a first antenna operative to transmit a first signal in a first frequency band, and a second antenna operative to receive which is connected to a filter assembly operative to pass signals in a second frequency band to a signal detector. The present invention also relateds to a method of detecting a parameter of a signal transmitted therefrom.

Background of the Invention Many wireless communication systems use receive diversity, i. e combining multiple received signals, to improve system performance. A typical configuration is to have both a transmitting and receiving antenna and a receive-only antenna. The antennas are often placed parallel to each other and have a typical isolation of 20 to 30dB. In other words, the receive-only antenna picks up the transmitted signal from the other antenna with a coupling loss of 20 to 30dB.

It is required to check that receive-only antennas are working during normal operation. The current known way of doing this involves sending a signal of a known level into the receive-only antenna from an on-board signal generator and measuring the level of the reflected power. By comparing the input and output signal the return loss (in dBs) can be calculated and therefore the integrity of the receive-only antenna can be determined i. e. whether the antenna is functioning correctly. This requires the signal generator to have known output power level. Also cabling and connectors are required to input this signal to the receive-only antenna.

Measuring the return loss provides feedback information used in some forms of linearisation techniques. Linearisation allows amplifiers to be operated in their more efficient non-linear region, whilst maintaining a linear output spectrum. One way to do this is to distort the input signal in the opposite way to the amplifier characteristic.

Another way is to remove the distortion from the amplifier output.

In the case of the transmit-and-receive antenna it is possible to measure the incident and reflected levels of a signal sent for transmission. Again by comparison of these two signals it is possible to calculate its return loss and hence determine whether that antenna is operating correctly.

Summary of the Invention The present invention provides a telecommunications station comprising a first antenna operative to transmit a first signal in a first frequency band, and a second antenna operative to receive which is connected to a filter assembly operative to pass signals in a second frequency band to a signal detector, in use a fraction of the first signal at the first frequency band transmitted by the first antenna is received by the second antenna and coupled around the filter assembly by way of a coupler so as to bypass the filter assembly so as to be passed to the signal detector so as to enable a parameter of said first signal to be detected.

Preferably the detector is operative to determine from the detected parameter value dependent on the magnitude of the received signal whether the antennas are acceptably functioning.

Preferred embodiments provide a technique to determine the integrity of a receive-only antenna in a wireless communication system. They use the known crosscoupling loss between a transmit-and-receive antenna and a receive-only antenna, and use of a coupler within a duplexer on the receive path. Electrical coupling between the two antennas provides a signal of known level that can be used for measuring attenuation on the receive path and hence determining antenna integrity.

Advantages of the present invention in its preferred embodiments include that the requirement to generate a separate signal purely for antenna integrity testing is removed. The need for a separate circuitry to process received test signals is avoided; avoiding also the need for associated cables and connectors. The wiring of the base station is simplified. The base station is cheaper, and in addition the system performance is improved because no signals such as test signals need be transmitted out of the receive antenna. The simple coupler allows normal operational signals to be used

to check antenna integrity. This allows more efficient use of cables within the base station.

Preferably the signal detector comprises a power meter operative to measure the parameter, the parameter being power.

Preferably the filter assembly includes an amplifier of received signals.

Preferably the signal generator and detector together comprise a radio unit.

Preferably the station is a base station. Preferably the station is compliant with the Universal Mobile Telecommunications System UMTS standard or another third generation or higher standard. Preferably the station is a Universal Mobile Telecommunications System UMTS base station.

Preferably the filter assembly and antennas are mast-, pole-and/or tower-mounted.

Preferably the station is operative using a plurality of first signals for transmission at different frequencies, the parameter of each first signal being detected by the detector. Preferably the subsequent first signals for transmission are altered dependent on the detected parameter of said first signal. Preferably the detected parameter is used as feedback to linearise a subsequent first signal for transmission.

Preferably the first antenna is operative to transmit and receive and the second antenna is operative to receive only.

Preferably the first and second antennas are cross polarised.

The present invention also provides corresponding methods.

The present invention also provides a method of detecting a parameter of a first signal transmitted in a first frequency band by a first antenna of a telecommunications station, the station further comprising a second antenna connected to a filter assembly operative to pass signals in a second frequency band to a signal detector, receiving by the second antenna of a fraction of the first signal at the first frequency band transmitted by the first antenna and coupling the signal around the filter assembly to bypass the filter assembly so as to pass the signal to the detector to enable a parameter of said first signal to be detected.

Brief Description of the Drawings A preferred embodiment of the present invention will now be described by way of example and with reference to the drawings, in which: Figure 1 is a diagrammatic illustration of a base station for wireless communications.

Detailed Description As shown in Figure 1, a Universal Mobile Telecommunications System UMTS base station 2 for telecommunications with mobile terminals (not shown) has a cross-polarised antenna assembly 4 including a transmit-and-receive antenna 6 (i. e. operative to transmit and receive) configured in cross-polarised relation to a receiveonly antenna 8 (i. e. operative to receive only). Transmission from the base station 2 is undertaken at a frequency (transmit frequency band) offset from the reception frequency (receive frequency band).

The base station 2 includes radio circuitry 10 including an outlet port (TxA) and an inlet port (RxA) both connected by way of transmit and receive filters in filter block 12 to the transmit-and-receive antenna 6.

The receive-only antenna is connected by a duplexer 14 to an inlet port (RxB) of the radio circuitry 10 for processing received signals. The duplexer 14 consists of a filter 16 in series with a low noise amplifier 18, the filter 16 and amplifier 18 being in parallel with a coupler 20.

It is the coupler 20 from an input port 22 of the duplexer 14 to the output 24 of the duplexer 14 which bypasses the filter 16 and low noise amplifier 18 and so couples the signal received at the transmit frequency by the receive-only antenna (at e. g.

40dB lower than the signal sent to the transmit and receive antenna 6 for transmission) to the radio circuitry 10 for processing.

The signals arriving at the radio circuitry 10 via the RxB input port thus include another signal received from the mobile (not shown); and in addition a relatively low level signal of the same frequency and shape, and proportional to, the signal transmitted from the transmit-and receive antenna 6.

At the output port 24 of the duplexer 14 there is thus provided an amplified receive frequency band signal that is passed to the radio circuitry 10.

However, there also a low level transmit frequency band signal that is passed to the

radio circuitry 10. In the radio circuitry 10 there are a number of options possible to deal with the two signals. In one embodiment, a low cost ceramic duplexer (not shown) is used to split the signals to different receivers (one for the signal from the mobiles (not shown) and one for the signal via coupler 20 from the base station 2). In an alternative embodiment (not shown) one receiver is used instead that can tune to both transmit and receive frequency bands and so demodulate the two signals. There are various options for splitting the two signals.

From the known coupling losses due to both the antenna assembly 4 and the coupler 20 of receive duplexer 14 and the known losses due to cables and connectors, it is possible to calculate the output power of the transmit path. It is possible to use this information to calculate the gain of the receive antenna, and so determine its integrity, i. e whether it is functioning correctly. In addition, where appropriate, measurements can be performed on the output signal frequency spectrum such as determining spectral integrity.

Detection circuitry in or connected to the radio circuitry 10 is used to measure the level of the coupled transmit signal from the receive-only antenna 8.

Electrical coupling between the two antennas 6,8 remains quite stable in operation, which allows the base station 2 to carry out regular comparative measurements in order to detect the integrity of the antenna assembly 4.

The preferred embodiment described with the aid of Figure 1 shows use with cross polarised antennas 6,8. An alternative embodiment (not shown) has spatially separated antennas instead.

The duplex filter 12 and duplexer 14 and any associated amplifiers can be tower mounted or otherwise. The transmit feedback mechanism using the coupler 20 is usable for multiple frequencies of signals as occur in for multiple carrier frequency operation, and in single carrier frequency cases. The transmit power data is usable for a wide range of linearisation techniques.

Although the base station shown in Figure 1 is a UMTS NodeB, this development is applicable to other base station technologies that would have use for measurements of transmitted power by the transmitting base station.

Claims

Claims:

1. A telecommunications station comprising a first antenna operative to transmit a first signal in a first frequency band, and a second antenna operative to receive which is connected to a filter assembly operative to pass signals in a second frequency band to a signal detector, in use a fraction of the first signal at the first frequency band transmitted by the first antenna is received by the second antenna and coupled around the filter assembly by way of a coupler so as to bypass the filter assembly so as to be passed to the signal detector so as to enable a parameter of said first signal to be detected.

2. A station according to claim 1, in which the detector is operative to determine from the detected parameter value dependent on the magnitude of the received signal whether the antennas are acceptably functioning.

3 A station according to claim 1 or claim 2, in which the signal detector comprises a power meter operative to measure the parameter, the parameter being power.

4. A station according to any preceding claim, in which the filter assembly includes an amplifier of received signals.

5. A station according to any preceding claim, in which the signal generator and detector together comprise a radio unit.

6. A station according to any preceding claim, being a base station.

7. A station according to claim 6, which is compliant with the Universal Mobile Telecommunications System UMTS standard or another third generation or higher standard.

8. A station according to claim 6 or claim 7, being a Universal Mobile ZD Telecommunications System UMTS base station.

9. A station according to any preceding claim, in which the filter assembly and antennas are mast-, pole-and/or tower-mounted.

10. A station according to any preceding claim, operative using a plurality of first signals for transmission at different frequencies, the parameter of each first signal being detected by the detector.

11. A station according to any preceding claim, in which the subsequent first signals for transmission are altered dependent on the detected parameter of said first signal.

12. A station according to claim 11, in which the detected parameter is used as feedback to linearise a subsequent first signal for transmission.

13. A station according to any preceding claim, in which the first antenna is operative to transmit and receive and the second antenna is operative to receive only.

14. A station according to any preceding claim, in which first and second antennas are cross polarised.

15. A method of detecting a parameter of a first signal transmitted in a first frequency band by a first antenna of a telecommunications station, the station further comprising a second antenna connected to a filter assembly operative to pass signals in a second frequency band to a signal detector, receiving by the second antenna of a fraction of the first signal at the first frequency band transmitted by the first antenna and coupling the signal around the filter assembly to bypass the filter assembly so as to pass the signal to the detector to enable a parameter of said first signal to be detected.

16. A telecommunications station as hereinbefore described with reference to the Figure.

17. A method as hereinbefore described with reference to the Figure.