GB2393077A

GB2393077A - Aligning a directional antenna towards an access point using location information

Info

Publication number: GB2393077A
Application number: GB0221371A
Authority: GB
Inventors: Peter Lockhart; Stephen Mccann
Original assignee: Roke Manor Research Ltd
Current assignee: Roke Manor Research Ltd
Priority date: 2002-09-14
Filing date: 2002-09-14
Publication date: 2004-03-17
Also published as: CN1742500B; CN1742500A; AU2003273867A8; AU2003273867A1; GB0221371D0; WO2004025900A3; WO2004025900A2

Abstract

Within a wireless communications system there is broadcast an orientation signal containing position data identifying the position of devices within the system. A mobile terminal in receipt of the position data contained in the orientation signal is able to use this data to determine the location of a device towards which to direct its directional antenna. This allows mobile terminals to easily locate access points without the need for beam searching, and allows the directional beams to be narrow, which minimises the transmit power. Useful for operation at high radio frequencies where otherwise the transmission power would be too high. This system could be used for directing communications from a mobile terminal to a base station or between terminals in an "ad-hoc" system.

Description

MOBILE COMMUNICATION SYSTEM

This invention relates to a wireless mobile communications network. Wireless Access Networks (WANs) are well known. In many 5 types of WANs mobile terminals within the area covered by the Network communicate by radio with access points of the network, the access points being distributed over the area of radio coverage. Each access point is hard wired to other parts of the network and provides an interface between the wired and wireless parts of the network. So called "ad hoc" 10 WANs operate without any base stations or access points and in such networks radio signals may be routed directly from one mobile terminal to another.

Some of the next generation of WANs will operate at higher radio frequencies than those used by current networks. For example, the 15 planned Japanese High Speed Wireless Area Network b (HiSWANb) system will operate at a radio frequency of 25 GHz. The wavelength of such a radio system will be about 1 cm, which is small enough to necessitate that a terminal and an access point operating in the system be in line of sight (LoS) of each other to successfully communicate.

20 It is anticipated that beam steering techniques will be widely used in systems such as HiSWANb. Beam steering from access points to terminals (i. e the downlink channel) is known but it is envisaged that in systems such as HiSWANb each terminal will be provided with a phased antenna array or smart antenna or some other type of directional antenna 25 so that terminal to access point (i.e the uplink channel) communication can also be achieved using a narrow communication beam.

This will be necessary because signal frequencies will be so high that only directional antennas will be able to deliver sufficient power to

- 2 reach distant access points. Advantageously, beamforming on the uplink channel will also increase the number of users that can be supported in individual cells, or by individual access points because inter-user interference will be minimised.

5 It is anticipated that directional antennas and high frequency communication beams will be advantageously used in many other types of wireless communication systems, including ad hoc wireless networks.

A problem associated with mobile terminal to access point communication ( or terminal to terminal communication in an ad hoc 10 network) using a directional antenna, is that in order communicate with a suitable access point, it is necessary for the terminal to know where to direct its directional antenna towards.

Thus, each time the terminal seeks to initiate communication in the network or each time the terminal is handed over from one access point 15 to another in the network, the terminal must first locate an access point to lock its directional antenna or communication beam onto.

Beam searching or scanning is one way of a terminal locating a suitable access point to communicate with, but with no knowledge of an access point's location, the time taken to achieve lock may be too slow to 20 meet quality of service requirements, and in particular to retain seamless handover. The present invention seeks to alleviate the above mentioned problems. According to the present invention there is provided a wireless 25 communications system comprising a number of wireless communications devices, within which system there is broadcast an orientation signal containing position data identifying the position of one or more of the devices, wherein a mobile terminal operating in the system

and in receipt of the position data contained in the orientation signal is able to use the position data to determine the position of a device towards which to direct a directional antenna of the mobile terminal.

According to the present invention there is also provided a mobile 5 terminal for operating in a wireless communications network, the terminal comprising; a receiver means for receiving a signal broadcast within the network, the signal containing information identifying the location of one or more wireless devices in the network, a directional antenna; and processing means for determining from the signal the lO location of a wireless device towards which the mobile terminal is to direct the directional antenna.

According to the present invention there is also provided a method of operating a mobile terminal in a wireless communications network, the method comprising; receiving at the mobile terminal a signal broadcast 15 within the network, the signal containing information identifying the location of one or more wireless devices in the network; and processing the received signal to determine the location of a wireless device towards which the mobile terminal is able to direct a directional antenna.

The orientations signal is not necessarily transmitted from the 20 wireless devices within the network; it may be external.

Embodiments of the present invention will now be described with reference to the accompanying drawings in which: Figure 1 shows, schematically, a mobile communications system embodying the present invention.

25 Figure 2 shows, in block diagrammatic form, a communications subsystem of a mobile terminal.

Figure 3 shows schematically, a mobile communications system embodying the present invention.

- 4 Referring now to Figure 1 of the accompanying drawings, an exemplary communications system l embodying the present invention comprises a number of access points of which by way of example first 2 and second 3 access points at Location A and Location B respectively are 5 shown. A mobile station 4, for example, a laptop computer is located within the system 1. It is intended that the mobile station 4 transmit up-

link data to and receive down link data from which ever access point is best or optimally located in the vicinity of the mobile station 4 to communicate with the mobile station 4.

10 The mobile station 4 comprises, a smart antenna, a phased array or any other type of beam forming system coupled to a processor that is capable when provided with information about the location of an access point of focussing a transmission beam associated with the antenna upon the access point. Beam forming techniques are very well known to those 15 skilled in the art and thus will not be discussed in any detail here.

The system 1 further comprises a transmitting source in this example, masts 5, 6 and 7 distributed in the system 1 and transmitting an Omnidirectional orientation signal (OS) for reception at the mobile station 4. The signal (OS) contains or encodes information identifying 20 the geographical position of access points in the network and thus allows the position of one or more access points in the vicinity of the mobile terminal 4 to be determined at the mobile terminal 4.

The signal (OS) is a relatively low bandwidth signal and is transmitted at a low enough frequency to ensure that the mobile station 4 25 need not be in line of sight of a transmitter to receive this signal.

Preferably, the signal (OS) also includes additional resource information about the access points, for example, signal strength, bandwidth and radio channel price information. Such information is

- s - useful to enable mobile terminals to make policy decisions about mobility and handovers.

In some embodiments of the invention the access points will be at fixed locations. In other embodiments of the invention the access points 5 themselves will be mobile and the location of the moving access points will be constantly updated within the signal (OS).

The process by which the mobile station 4 initiates communication with a selected access point will be described with reference to Figure 2 of the accompanying drawings, which shows in block diagram form, a 10 communication sub-system 10 of the mobile station 4.

The communication sub-system 10 comprises an omni-directional antenna l l coupled to receiving circuits 12 arranged to receive the signal (OS) transmitted by the transmitters 5 to 7. The sub-system 10 further comprises access point position determining processor 13, coupled to the 15 receiver circuits 12 and arranged to extract from the signal (OS) the data identifying the position of access points in the system 1.

The sub-system 10 is further provided with a mobile station position determiner 14 for determining the position of the mobile station 4 in the system 1.

20 When the mobile station 4 needs to initiate a connection to an access point, the processor 13 determines from the received signal (OS), the position of neighbouring access points and the position determiner 14 determines the current position of the mobile station.

The position of the mobile station 4 may be determined using any 25 of a number of standard techniques. For example, the position determiner 14 may be coupled to the receive circuitry 12 and arranged to determine the position of the mobile station 4 from some additional coding in the signal (OS) itself (e.g. GPS Satellite determination if the

- 6 transmitters 5 to 7 are satellites, signal strength timing information etc).

Alternatively, if the mobile station 4 receives a signal (OS) from three or more transmitters of known location the position determiner 14 may use triangulation to determine the position of the mobile station 4.

5 Alternatively, the position determiner 14 may comprise an internal navigation device for determining the position of the mobile station 4 using dead reckoning techniques. Other techniques by which the mobile station may determine its position will be known to those possessed of the appropriate skills.

10 The position of the mobile terminal 4, the positions of the access points extracted from the signal (OS), and any additional signal strength information about the access points extracted from the signal (OS) are fed to a processor 15. In the absence of any additional resource information contained in the signal (OS) about the access points the processor 15 will 15 simply select the nearest access point to the mobile station 4 as the access point to form a connection with. If resource information is provided to the processor 15 then the processor 15 may calculate that the optimum connection would be with an access point other than the one nearest to the mobile terminal 4 20 Having determined the optimum access point with which to form a connection the processor 15 controls beam steering means 16 to steer or orientate a narrow high bandwidth communication beam from antenna 17 onto the optimum access point (access point 2 in the example shown in Figure 1). Thus the mobile terminal 4 is able to quickly locate the most 25 suitable access point to initiate and then to continue a connection with.

It will be appreciated that systems embodying the present invention will benefit from reduced times taken to handover from old to new access points. This is because a mobile terminal may use the signal (OS) to

- 7 identify the location of a new access point prior to a handover from the old access point occurring. Having knowledge of the new access points location and possibly additional resource information allows the terminal to 5 switch its beam from the old to the new access point without any beam searching thus minimising the handover time.

Since the invention allows mobile terminals to easily locate access points without the need for beam searching, the directional beams used by the terminals may be particularly narrow, thereby minimising transmit 10 power.

In this embodiment there are dedicated transmitters for transmitting the signal (OS) with each of the transmitters transmitting a signal containing information identifying the geographical location of a number of access points. Known terrestrial radio navigation systems 15 such as TACAN may be used to provide the signal (OS). Alternatively, the transmitters may be satellites and a satellite system such as the GPS system may be used to provide the signal (OS).

One or more of the access points themselves could be used to transmit the omni-directional orientation signal in the network. in this 20 instance, each access point would include in its transmitted signal information identifying the location of that access point and if so required, information identifying the location of neighbouring access points as well.

In some embodiments of the invention the access points may 25 themselves be satellites in earth orbit and the mobile terminals be located on vehicles moving on or above the earth's surface.

For example, a preferred embodiment of the invention comprises a geostationary television satellite and a mobile terminal for receiving

- 8 signals from the satellite that is located on a vehicle for example, a ship.

The mobile terminal is provided with a directional antenna for example, a 30 sectored antenna that must be directed towards the satellite to lock onto the satellite signal.

5 In this embodiment, the satellite itself may transmit the signal (OS) in a wide-angle beam directed onto the earth's surface. On reception of the signal (OS) at the ship, the information in the signal identifying the satellites location may be used in conjunction with information identifying the ship's location to correctly orientate the sectored antenna 10 of the terminal to lock onto the satellite signal.

Referring now to figure 3 of the accompanying drawings there is illustrated a further communications system 20 embodying the present invention. The communications system 20 is an ad hoc network comprising a plurality of mobile stations of which by way of example 15 first 21, second 22 and third 23 mobile stations are illustrated.

As is well known, an ad-hoc wireless network is a network which operates without any base stations or access points. In an ad-hoc wireless network each mobile terminal is capable of acting as a router so that communication signals can be relayed from one mobile station to another 20 in the network.

In the ad-hoc network 20 each mobile station 21 to 23 transmits a low frequency omni-directional orientation signal (OS) in which is encoded data identifying the current location of that respective terminal.

To this end, each terminal is provided with a means of identifying its 25 current location, for example a GPS system or a dead-reckoning navigational system and a transmitter for encoding and transmitting the location data in the orientation signal (OS). The mobile stations 21 to 23 may for example be located on vehicles.

- 9 - Each terminal 21 to 23 is provided with a communication sub-

system l O as already described with respect to Figure 2.

Any mobile station in receipt of one or more of the signals (OS) is able to, by means of the processor 13, determine or extract from the 5 signals (OS) the data identifying the current location of neighbouring terminals. This data together with data generated by the position determiner 14 identifying the current location of the terminal receiving the OS signal itself are fed to processor 16 for processing to select or identify a neighbouring terminal for the receiving terminal to form a 10 connection with.

Having identified a terminal to form a connection with, processor 15 controls beam steering means 16 to direct a directional antenna towards the selected terminal. If one or both terminals are moving the processor 15 uses the information contained in the signal (OS) and the 15 information generated by the position determiner 14 to control the beam steering means 16 to keep the communication beam directed at the selected terminal.

To maintain the coherence of the ad-hoc network, terminals may operate with multiple directional antennas simultaneously to allow 20 tracking of a number of communication terminals within the network.

Claims

- 10 CLAIMS

1. A wireless communications system comprising a number of wireless communications devices, within which system there is broadcast 5 an orientation signal containing position data identifying the position of one or more of the devices, wherein a mobile terminal operating in the system and in receipt of the position data contained in the orientation signal is able to use the position data to determine the position of a device towards which to direct a directional antenna of the mobile terminal.

2. A system according to claim 1 wherein the mobile terminal uses data identifying the location of the mobile terminal and the position data contained in the signal to determine a direction along which to direct the directional antenna towards the device.

3. A system according to claim 1 or 2, wherein the mobile terminal uses the data contained in the signal and the data identifying the position of the mobile terminal to identify and select a device nearest the mobile terminal as the device towards which to direct the directional antenna.

4. A system according to claim 2 or 3 wherein the signal further contains resource information about the one or more devices and wherein the mobile terminal in receipt of the information is able to use the resource information in selecting a device towards which to direct the 25 directional antenna.

5. A system according to any of claims 1 to 3, wherein the one or more devices comprise access points or base stations distributed in an

- 11 area covered by the system for providing wireless access to the system for one or more mobile terminal operating in the system.

6. A system according to any of claims 1 to 3, wherein the one or 5 more devices are mobile devices and the system is an 'ad-hoc' system.

7. A system according to any of claims 1 to 3, wherein the system is a satellite system and the one or more devices comprise at least one satellite.

8. A system according to any preceding claim, wherein the signal is broadcast omni-directionally in the area covered by the system.

9. A system according to any preceding claim, wherein any of the one 15 or more devices are moving devices and wherein information contained in the signal identifying the location of any device is periodically up dated.

10. A mobile terminal for operating in a wireless communications 20 network, the terminal comprising; a receiver means for receiving a signal broadcast in the network, the signal containing information identifying the location of one or more a directional antenna; and 25 processing means for determining from the signal the location of a wireless device towards which the mobile terminal is to direct the directional antenna.

- 12

11. A mobile terminal according to claim 10, the terminal comprising: position determining means for determining the position of the terminal in the network.

12. A mobile terminal according to claim 11, wherein the processing means is arranged to select from a plurality of devices the location of which are identified in the signal, a selected device for the terminal to direct the directional antenna towards.

13. A mobile terminal according to claim 12 wherein the selection of a device by the processing means is at least partly based upon the position of the mobile terminal as determined by the position determining means and the position of each of the plurality of devices as determined by the 15 processing means from the signal.

14. A mobile terminal according to claim 13 wherein the processing means is arranged to select the device nearest the terminal as the selected device.

15. A mobile terminal according to claim 13, wherein the processing means is arranged to select a device at least partly in dependence upon resource information about each of devices which is also contained in the signal.

16. A mobile terminal according to any of claims 10 to 15, wherein the processing means is arranged to determine the direction between the

- 13 mobile terminal and the device towards which the mobile terminal is to direct the directional antenna.

17. A mobile terminal according to claim 16, wherein the directional 5 antenna is a beam former.

18. A mobile terminal according to claim 16, wherein the directional antenna is a sectored antenna.

10

19. A method of operating a mobile terminal in a wireless communications network, the method comprising; receiving at the mobile terminal a signal broadcast within else network, the signal containing information identifying the location ol one or more wireless devices in the network; and 15 processing the received signal to determine the location ol a wireless device towards which tle mobile terminal is able to direct a directional a'tenrra 2() A method according to claim 19 the method comprising:

20 deter-mining to position ol the mobile terminal: and directing a directional antenna Afros the mobile terminal towarcis a wireless device the location of which is identified in the received signal

21 A rneth'd according to claim 9() the method comprising selecting 25 Tom a plurality of devices the Indication of which are identified in the signal. a selected device for the mobile terminal to direct the directional antenna towards.

- 14

22. A method according to claim 21 wherein the selection of a device is at least partly based upon the determined position of the mobile termin.il and the detern-iined position of each of the plurality of crevices.

S

23. A rnetliod according to claim 21 or 2 wherein the selected device is the ctevice determineci to be that nearest the termii.il.

24. A method according tc' claim 22, wherein the selected device is selected at least partly iTi dependence upon resource information aboiit 10 each of the crevices iclentitiecl in the signal.