AU731241B2 - Adaptive antenna polarization - Google Patents

Description

P/00/011 28/5/91 Regulation 3.2

AUSTRALIA

Patents Act 1990

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT Invention Title: "ADAPTIVE ANTENNA POLARIZATION" The following statement is a full description of this invention, including the best method of performing it known to us:- Technical Field This invention relates to a method and an arrangement for compensating for variations or differences in the polarities of antennae of a communication link. One application of the arrangement is in the field of mobile telephony, in which a mobile phone communicates with a fixed base station.

Background Art The base station antenna is fixed physically but the antenna of the mobile phone can be moved in any direction. Generally mobile phone antennae are straight monopoles, and a plane of polarization which contains the monopole. Thus if the antenna is vertical its radiation pattern is vertically polarized, and if the antenna is tilted from the vertical, the polarization of its radiated energy is also tilted.

On the other hand, because the base station antenna is fixed, its radiation pattern normally remains fixed, in the vertical plane.

If a mobile phone's antenna is tilted with respect to the base station's antenna the efficiency of the radio link is decreased and may cause loss of communication or network congestion due to unnecessary handovers.

In the GSM system, the mobile phone monitors the downlink signal strength transmitted by the base station and instructs the base station to adjust its power output as required to reduce downlink communication errors due to signal fading, reflections 20 or shadowing.

The antenna polarization of a handheld mobile phone is constantly changing (with respect to the polarization of the base station antenna) resulting in frequent downlink signal degradation.

There may be a substantial difference in the required transmitted power from a base station towards the handheld mobile phone when the polarization of the mobile antenna varies between the vertical and horizontal antenna positions. If the mobile antenna is close to the horizontal position, the base station may have to increase the downlink power by up to 10 dB (10 times to that required when the mobile antenna is in the vertical position.

Conversely, the base station may monitor the uplink signal strength and instruct the mobile to increase transmission power.

Known techniques to overcome the problems of signal degradation include 3 antenna diversity and frequency hopping. These techniques are useful for overcoming signal corruption due to e.g. reflected or refracted signals. However, these techniques are not specifically aimed at the problem of skewed polarization.

Disclosure of the Invention.

This specification discloses an antenna arrangement having at least first and second cross-polarized elements. Preferably, phase shifter means are connected to change the relative phase between the first and second cross-polarized elements.

When the arrangement is used in a transmitter antenna, the signal to be transmitted can applied to both the first and second cross-polarized element through a power splitter.

The relative phase change may be achieved by interposing a controllable phase shifter between the power splitter and either the first of second cross-polarized element.

Alternatively, controllable phase shifters may be interposed between both the first and the second cross-polarized elements and the power splitter.

The controllable phase shifter may be a 900 random phase switcher that can switch between 0' and 900 phase shift on the downlink signal. This may be controlled in a pseudo-random manner to achieve a statistically stronger signal.

In a TDMA system such as the GSM mobile phone system, phase switching of 20 each timeslot may be implemented using the pseudo-random method mentioned earlier, or may be controlled based on downlink signal strength information sent by the handheld mobile to the BTS.

Brief Description of the Drawings.

Figure 1 is a schematic representation of a transmit antenna arrangement embodying the invention.

Best Mode of Carrying out the Invention.

In Figure 1, a transmitter (not shown) is connected to a power splitter 2 having two output branches 3 4. Branch 3 is connected to a first antenna element 5 having a first orientation defining the polarization of its transmitted radiation. Branch 4 is connected through controllable phase shifter 6 to second antenna element 7, which is oriented in a plane which intersects the plane of antenna element 5. The elements and 7 may be at right angles or they may be oriented to optimize transmission over a predetermined range.

However in our preferred embodiment we utilize intersecting 90' cross-polar dipoles as the antenna elements at 450 to the vertical. In this configuration a 900 polarization shift is achieved between the in phase operation of the first and second elements, and when the second element is shifted 900 with respect to the first element.

The invention may also be applied to the base station reception path with the splitter 2 replaced by a combiner. The base station monitors the power it receives from the mobile and instructs the mobile to adjust its power output appropriately. The pseudo-random polarization switching in the base station receiver path produces a statistically stronger received signal so that the power to be transmitted by the mobile can be reduced.

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Claims (15)

1. A transmitter antenna arrangement including at least one first pair of cross- polarized antennae, the arrangement including first controllable/variable/switchable phase-shifting means to impose a relative phase shift between the signals fed to each antenna of each first pair.

2. A transmitter arrangement as claimed in claim 1, including first control means to control the phase-shifting means.

3. An arrangement as claimed in claim 2 wherein the first control means is programmable to impose a pseudo-random time pattern to the phase shift from the first phase-shifting means.

4. An arrangement as claimed in any one of claims 1 to 4 wherein the phase- shifting means imposes a phase shift of 0' or 90' in response to the first control O: means. o •o S

5. An arrangement as claimed in any one of claims 1 to 4 including for each first 15 pair of cross polarized antennae, splitter means to split a signal into a pair of signals each of which is fed to one of the pair of antennae and wherein one of the pair of signals is fed to its corresponding antenna via the phase-shifting means.

6. A receiver antenna arrangement including at least one second pair of cross- polarized antennae, the arrangement including second S: 20 controllable/variable/switchable phase-shifting means to impose a relative phase shift between the signals received from each antenna of each second pair.

S7. An arrangement as claimed in claim 6 including second control means to control the second phase-shifting means.

8. An arrangement as claimed in claim 7 wherein the second control means is programmable to impose a pseudo-random time pattern to the phase shift from the second phase shifting means.

9. An arrangement as claimed in any one of claims 6 to 8 wherein the second phase-shifting means imposes a phase shift of 00 or 900 in response to the second control means.

10. An arrangement as claimed in any one of claims 6 to 9 including, for each second pair of cross-polarized antennae, combiner means to combine the received signal from each antennae of the respective second pair, and wherein one of the 6 received signals is fed to the combiner via the phase-shifting means.

11. An antenna arrangement substantially as herein described with reference to the accompanying drawings.

12. A method of compensating for the variation in the polarization of a remote antenna, the method including: providing one or more pairs of cross-polarized antennae; imposing a relative phase shift between each antennae of each pair on a pseudo-random time basis.

13. A method as claimed in claim 11, wherein the relative phase shift is switched between 0' and 90

14. A method of compensating for the variation in the polarization of a remote antenna substantially as here described with reference to Figure 1 of the accompanying drawings. DATED THIS FOURTEENTH DAY OF JULY 1997

15 ALCATEL AUSTRALIA LIMITED 0 000 005 363) *'o o° *o