GB2477978A

GB2477978A - An access point performs MIMO communication with beam selection based on throughput measurements for different beam direction combinations

Info

Publication number: GB2477978A
Application number: GB1002945A
Authority: GB
Inventors: Piers Glydon; Andrew Fox
Original assignee: Deltenna Ltd
Current assignee: Deltenna Ltd
Priority date: 2010-02-22
Filing date: 2010-02-22
Publication date: 2011-08-24
Also published as: GB201002945D0; WO2011101678A1

Abstract

An access point comprises at least two radio transceiver circuits for respective data communications paths, and allows the selection of respective beam directions from a plurality of available beam directions for the data communications paths. In order to establish a link between an access point and a cellular communications network using a MIMO technique, a plurality of combinations of beam directions selected from the plurality of available beam directions are determined; for each combination of beam directions, a link is established such that each of the radio transceiver circuits is connected with a respective beam direction of the combination of beam directions; an available data throughput with said combination of beam directions is measured; and the combination of beam directions with which the highest data throughput can be achieved is selected.

Description

ACCESS POINT

This invention relates to an access point, and in particular to an access point that can be used to provide improved coverage for a user of a cellular communications network.

W02008/068495 discloses a wireless access point, which allows a device to establish a wireless connection with it, and establishes a backhaul link into a cellular communications network. Unlike many conventional devices, which have omnidirectional antennas, and establish links with the cellular basestation that provides the strongest signal, the access point disclosed in W02008/068495 has a controllably directional antenna, and chooses to establish a link with the cellular basestation that is able to provide the highest data rate with the cellular network.

It is now recognized that it would be desirable to be able to use such an access point in conjunction with a cellular network that uses multiple input, multiple output (MIMO) techniques. However, the device disclosed in W02008/068495 may in practice not achieve the highest available data rate.

For example, when the cellular network assumes the use of a 2x2 MIMO system, it is appreciated that the maximum data throughput might be achieved if the wireless access point selects two beam directions, in such a way that both of these beam directions allow the establishment of a connection with a MIMO-capable basestation.

However, if the possible beam directions are tested in turn, and one of those beam directions is selected on the basis of the data rate that can be achieved, it is possible that this selected beam direction may establish a connection with a basestation that is not MIMO-capable. As a result, it is not then possible to select a second beam direction that achieves any additional data throughput, and so the best combination of beam directions may not be achieved.

According to a first aspect of the present invention, there is provided a method of establishing a link between an access point and a cellular communications network using a MIMO technique, wherein the access point comprises at least two radio transceiver circuits for respective data communications paths, and wherein the access point allows the selection of respective beam directions from a plurality of available beam directions for the data communications paths, the method comprising: determining a plurality of combinations of beam directions selected from the plurality of available beam directions; for each combination of beam directions, establishing a link such that each of the radio transceiver circuits is connected with a respective beam direction of the combination of beam directions; measuring an available data throughput with said combination of beam directions; and selecting the combination of beam directions with which the highest data throughput can be achieved.

According to a second aspect of the present invention, there is provided an access point adapted to operate in accordance with the method of the first aspect.

For a better understanding of the present invention, and to show how it may be put into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 is a block schematic diagram, illustrating a first wireless communication system in accordance with an aspect of the invention.

Figure 2 is a more detailed block schematic diagram of an access point in the system of Figure 1.

Figure 3 is a more detailed block schematic diagram of a part of the access point of Figure 2.

Figure 4 is a block schematic diagram, illustrating a second communication system in accordance with an aspect of the invention.

Figure 5 is a more detailed block schematic diagram of an access point in the system of Figure 4.

Figure 6 is a flow chart, illustrating a method in accordance with the present invention.

Figure 1 shows a wireless communications environment 10, containing a wireless access point 12. The wireless access point 12 provides wireless access for a user of a suitably equipped mobile communications device 14, which may for example be a laptop computer, or another portable device. The wireless access point 12 can for example operate in accordance with one of the family of IEEE 802.11 standards, for example the standards commonly known as WiFi or WiMax. Alternatively, the wireless access point 12 can for example be a GSM pico base station, or any other base station or access point providing local area wireless coverage. For this purpose, the wireless access point 12 includes a first antenna 16, which may for example be an omnidirectional antenna.

The user of the mobile communications device 14, and other suitably equipped devices within the coverage area of the access point 12, can then transfer data to and from the access point 12. In order for the user of the mobile communications device 14 to be able to communicate with other users, or to be able to download data, for example from websites, the access point 12 needs to have a connection over a suitable network.

In the example shown in Figure 1, the wireless access point 12 is located in a wireless communications environment 10, which is typical of many urban areas, in that the wireless access point 12 is located in the coverage areas of a number of cellular base stations, in this case a first base station (BS1) 18, a second base station (BS2) 20 and a third base station (BS3) 22. As is well known, each of these cellular base stations 18, 20, 22 has a connection into the Public Switched Telephone Network (PSTN) (not shown), or into a packet data network, allowing it to establish voice and data calls to and from users of mobile phones and other suitably equipped mobile communications devices within their respective coverage areas.

In accordance with the invention, the access point 12 is provided with a suitable antenna 24, and radio frequency communications circuitry (not shown in Figure 1), allowing it to establish a connection with some or all of the cellular base stations 18, 20, 22. By establishing a connection with one of the cellular base stations, the access point 12 is able to transfer data between the user 14 and a location accessible over the PSTN. For example, the access point can establish a connection between the user 14 and a website to allow the user 14 to download content from the website. Thus, the access point 12 uses the respective cellular network to provide backhaul for its data.

As another illustrative example, the user device may be a VoIP (Voice over IP [Internet Protocol]) phone, establishing an IP connection through the access point 12, with backhaul over the cellular network, to another VoIP phone having an internet connection.

Figure 2 is a schematic diagram, illustrating in more detail the form of the access point 12. As mentioned previously, the access point 12 has a first antenna 16, for communication with users of suitably equipped mobile communications devices, in accordance with one of the family of IEEE 802.11 standards, and the antenna 16, may for example be an omnidirectional antenna to allow communication with suitably equipped mobile communications devices in the whole area around the access point 12.

The antenna 16 is connected to local area coverage RF circuitry 26, as would conventionally be found in an access point operating in accordance with that standard.

For example, where the access point 12 operates in accordance with one of the family of IEEE 802.11 standards, the local area coverage RF circuitry 26 is able to convert received signals into the appropriate data stream, and is able to convert incoming data into signals suitable for transmission over the wireless interface in accordance with that standard.

The local area coverage RF circuitry 26 is connected to cellular coverage RF circuitry 28, as would conventionally be found in a mobile communications device suitable for operating in accordance with the relevant standard or standards. For example, where the access point 12 is intended to establish a connection with a cellular base station (for example, one of the base stations 18, 20, 22) operating in accordance with the GSM standard, then the cellular coverage RF circuitry 28 includes appropriate GSM circuitry. Similarly, where the access point 12 is also intended to establish a connection with a cellular base station (for example, one of the base stations 18, 20, 22) operating in accordance with the UMTS standard, then the cellular coverage RF circuitry 28 also includes appropriate UMTS circuitry.

In this illustrated embodiment of the invention, the cellular coverage RF circuitry 28 is connected to power control circuitry 30, as will be described in more detail below.

The power control circuitry 30 is connected to antenna direction control circuitry 32, which in turn is connected to the cellular antenna 24.

The cellular coverage RF circuitry 28, the power control circuitry 30, and the antenna direction control circuitry 32 operate under the control of a controller 34.

The access point 12 receives electrical power from a power source 36. The power source 36 may be a mains electrical power source, or an electrochemical battery, or may be a power source deriving energy from its environment, such as a solar power source, or a wind power source, or combined wind/solar power source.

The access point 12 operates under the control of a management system 38. The management system 38 is typically contained in firmware running on a processor inside the access point, and can control the operation of the access point 12. It can alternatively be provided on a remote computer. For example, the management system 38 can be connected to the access point 12 over an existing local area network (LAN), or may be wirelessly connected to the access point 12, for example allowing the remote management system 38 to configure the link via ftp, or via a website provided for that purpose. The management system 38 can then, for example, control the security of the access point, determining which user devices are permitted to establish connections thereto.

Figure 3 is a more detailed block schematic diagram of a part of the access point 12.

Specifically, Figure 3 shows in more detail the cellular coverage RF circuitry 28, the power control circuitry 30, the antenna direction control circuitry 32, and the cellular antenna 24.

As shown in Figure 3, the antenna 24 includes four antenna elements 24a, 24b, 24c, 24d, although it will be appreciated that any convenient number of antenna elements can be provided. In particular, an antenna with eight antenna elements may be particularly suitable for this implementation. Each of these antenna elements 24a, 24b, 24c, 24d is directional. That is, each of the antenna elements 24a, 24b, 24c, 24d transmits signals preferentially in one direction, in azimuth, and is most sensitive to received signals from the same direction. These preferential directions are preferably all different, and are equally spaced around the azimuth, such that the antenna 24 is essentially omnidirectional. However, it is also possible for the antenna 24 to be formed of antenna elements whose preferential directions are not equally spaced in this way, with the result that the antenna 24 will not be omnidirectional, but will be at least somewhat directional.

As mentioned above, the cellular coverage RF circuitry 28 is connected to power control circuitry 30, which is shown in more detail in Figure 3. For example, the power control circuitry 30 could include a duplexer 42, for separating and combining signals at the RF transmit and receive frequencies in the relevant cellular networks.

Thus, transmit signals from the cellular coverage RF circuitry 28 pass through the duplexer 42 to a power amplifier 44, before being passed to the antenna direction control circuitry 32. The power amplifier is provided in order to be able to amplify the signals more than would usually be the case in a cellular user equipment, thereby allowing the access point to establish a connection to a cellular base station (for example one of the base stations 18, 20, 22, shown in Figure 1) that is more distant than the base station that a cellular base station would conventionally access. The degree of amplification provided by the power amplifier 44 is determined by the controller 34 by means of a signal passed along a control line 46.

Somewhat similarly, received signals from the antenna 24 and the antenna direction control circuitry 32 pass through a low noise amplifier 48, before being passed through the duplexer 42 to the cellular coverage RF circuitry 28. The low noise amplifier 48 is provided in order to be able to amplify the signals more than would usually be the case in a cellular user equipment, thereby allowing the access point to estabtish a connection to a cellular base station (for example one of the base stations 18, 20, 22, shown in Figure 1) that is more distant than the base station that a cellular base station would conventionally access. The degree of amplification provided by the low noise amplifier 48 is determined by the controller 34 by means of a signal passed along a control line 50.

After passing through the power amplifier 44, the transmit signals are divided, and passed through respective gain control elements, in this case controllable attenuators 52a, 52b, 52c, 52d, and through respective duplexers 54a, 54b, 54c, 54d to the respective antenna elements 24a, 24b, 24c, 24d.

Somewhat similarly, received signals from the antenna elements 24a, 24b, 24c, 24d pass through the respective duplexers 54a, 54b, 54c, 54d to respective gain control elements, in this case controllable attenuators 56a, 56b, 56c, 56d, before being combined and passed to the low noise amplifier 48.

The degree of attenuation provided by each of the controllable attenuators 52a, 52b, 52c, 52d, and 56a, 56b, 56c, 56d is determined by the controller 34 by means of signals passed along a control line, or lines, 58.

Thus, by controlling the degree of attenuation in each of the signal paths to and from the antenna elements 24a, 24b, 24c, 24d, the effective beam shape of the antenna 24 can be altered. That is, if each of the controllable attenuators 52a, 52b, 52c, 52d, and 56a, 56b, 56c, 56d provides an equal degree of attenuation, or provides no attenuation at all, the antenna elements 24a, 24b, 24c, 24d transmit signals with equal amplitudes, and are equally sensitive to received signals, and so, depending on the respective preferred directions of the antenna elements 24a, 24b, 24c, 24d, the antenna 24 may be effectively omnidirectional.

By contrast, if the signals in the signal paths to and from one of the antenna elements 24a, 24b, 24c, 24d are not attenuated, or are only slightly attenuated, while the signals in the signal paths to and from the other antenna elements 24a, 24b, 24c, 24d are strongly attenuated, the effective beam shape of the antenna 24 strongly resembles the beam shape provided by the antenna element whose signals are not attenuated, or are only slightly attenuated.

That is, by suitable control of the controllable attenuators 52a, 52b, 52c, 52d, and 56a, 56b, 56c, 56d the antenna 24 can be made to be highly directional.

Usually, the controllable attenuators 52a, 52b, 52c, 52d, and 56a, 56b, 56c, 56d are controlled such that the attenuators of the pairs 52a, 56a; 52b, 56b; 52c, 56c; and 52d, 56d in the signal paths to and from the respective antenna elements 24a, 24b, 24c, 24d are controlled in the same way, such that the antenna 24 has the same beam shape and size in the uplink path as in the downlink path, but this need not necessarily be the case.

Although the invention is illustrated above with reference to an embodiment in which controllable attenuators are located in the signal paths to and from the antenna elements, it is equally possible to provide a beam switched antenna, with switches provided, for switching the respective antenna elements into and out of the signal paths. Thus, by switching only one or a small number of the antenna elements into the signal paths, the antenna 24 can be made highly directional.

Further, the antenna may alternatively include only a small number of antenna elements, such that they form a directional antenna, with means being provided (for example, a mechanical rotational device) for altering the direction of the antenna.

Controlling the antenna 24 such that it becomes somewhat directional has the further advantage that the transmission paths from the access point 12 to one of the cellular base stations, and from the cellular base station to the access point 12 become much less affected by multipath transmissions. For example, to illustrate this, if the antenna 24 of an access point 12 is made directional, with its preferred direction pointing towards the cellular base station with which it has established a connection, the access point is less likely to be affected by reflections of the signals transmitted from the cellular base station, because these reflections are likely to be arriving from a direction that is different from the preferred direction.

Figure 4 is a block schematic diagram of an alternative communications system in accordance with an aspect of the invention. In this system, there is again provided an access point 92 located in a wireless communications environment 10, and specifically located in the coverage areas of a first base station (BS1) 18, a second base station (BS2) 20 and a third base station (BS3) 22, forming part of one or more cellular telephone networks.

In accordance with the invention, the access point 92 is provided with a suitable antenna 24, and radio frequency communications circuitry allowing it to establish a connection with some or all of the cellular base stations 18, 20, 22.

Figure 5 is a more detailed block schematic diagram showing the form of the access point 92. Specifically, the access point 92 includes a local area network interface 94, which may for example be an Ethernet interface, allowing one or more computers 14 or other devices to establish a connection thereto. The connections of the computers may be wired or wireless. The local area network interface 94 is connected to cellular coverage RF circuitry 28, power control circuitry 30, antenna direction control circuitry 32, and a cellular antenna 24, all of which are as described above with reference to Figure 2 and Figure 3, and therefore will not be described in more detail. The access point 92 also includes a management system 36, as described above with reference to Figure 2 and Figure 3, which therefore will not be described in more detail. In this case, the functionality of the access point 92 can simply be provided in a personal computer, for example the computer 14, which therefore may not be a portable device.

In accordance with an aspect of the invention, the access point 92 provides backhaul for data that the user of the computer 14 wishes to communicate through the access point 92.

In a preferred embodiment, the cellular coverage RF circuitry 28 is provided on a data card, for example such as a so-called 3G data card. As is known, such a data card can conventionally be inserted into a mobile device, such as a portable computer, in order to allow a user of the portable computer to communicate over the relevant cellular network. In this case, the data card can be inserted into the access point 12, or the access point 92, in order to allow a user of a device having a wireless or wired connection into the access point to communicate over the relevant cellular network.

Figure 6 is a flow chart, illustrating a process in accordance with an aspect of the invention, which may be performed in, or under the control of, the controller 34 in the access point 12 or the access point 92.

The method starts in step 100, at a time when the access point is first powered up, for example. At this point, the process described below can be performed on the basis of preconfigured parameters, or the user can be given an opportunity to set various parameters, depending on his intended usage of the device.

In step 102, the beam control circuitry is operated such that the first transceiver circuitry TRX1 operates with one of the available beam directions. That is, the gain control elements in the paths between the first transceiver circuitry TRX1 and the antenna elements are controlled such that the first transceiver circuitry TRX1 transmits data to, and receives data from, that one beam direction.

As described above, different beam directions can be achieved by control of the amplitudes of the signals in the signal paths to and from the antenna elements. In some situations, for example where the cellular communications system uses an asymmetric MIMO scheme, it may be advantageous to use beam directions that each include signals in the signal paths to and from multiple antenna elements. However, the invention will be described in more detail with reference to an embodiment in which the available beam directions each correspond to the preferred direction of a single one of the antenna elements. For example, in the case where the antenna of the access point has four directional antenna elements, the gain control circuitry can be adjusted so that the first transceiver circuitry TRXI is connected to one of the antenna elements, so that the beam direction is determined by the directionality of that one antenna element.

In step 104, the beam control circuitry is operated such that the second transceiver circuitry TRX2 operates with a different one of the available beam directions. That is, the gain control elements in the paths between the second transceiver circuitry TRX2 and the antenna elements are controlled such that the second transceiver circuitry TRX2 transmits data to, and receives data from, that one beam direction.

The aim of the invention is to try and take advantage of the gains that can potentially be obtained by virtue of the fact that the cellular network includes one or more basestations that uses MIMO technology. Therefore, the access point operates in step 104 such that the beam direction selected in step 104 is different from the beam direction selected in step 102.

The method then proceeds to step 106, in which the available data throughput is measured. This can be done in different ways. For example, with the connection set up, a file transfer of a known size can be performed, and the time taken for the transfer measured. This gives a measure of the average available data rate during the file transfer. As an alternative, the file transfer can be performed for a predetermined duration, such as lOs or 30s, and the amount of data transferred in that time can be measured. This also gives a measure of the average data rate available during the time of the file transfer, with the certainty of how long the test will take. As an alternative, or in addition, the peak data rate available during the file transfer can be measured. The measure of the available data throughput that is used can then be either the peak data rate, or some combination of the average data rate and the peak data rate. As a further alternative, or in addition, the minimum data rate available during the file transfer can be measured. The measure of the available data throughput that is used can then be either the minimum rate, or some combination of the average data rate and the minimum data rate, or some combination of the average data rate, the peak data rate and the minimum data rate.

The user may be able to select the measure that is used, for example based on the way in which he intends to use the device, or this may be preset in the device. The data throughput that is available for data uploads may be different from the data throughput that is available for data downloads. Therefore, the file transfer can be performed as an upload or as a download, or both. The measure of the available data throughput that is used can then be either the uplink data throughput, or the downlink data throughput, or some average of the two. The user may be able to select the measure that is used, for example based on the way in which he intends to use the device, or this may be preset in the device.

In step 108, it is determined whether there are any other available beam directions that have not yet been used for the second transceiver circuitry TRX2 with the current beam direction of the first transceiver circuitry TRX1. If using symmetrical MIMO, when making this determination, beam directions are ignored if they have already been used as the beam direction for the first transceiver circuitry TRX1 at a time when the current beam direction of the first transceiver circuitry TRX1 was being used for the second transceiver circuitry TRX2.

If it is determined in step 108 that there is at least one other beam direction for the second transceiver circuitry TRX2 that has not yet been tested, the process returns to step 104, in which the beam control circuitry is operated such that the second transceiver circuitry TRX2 operates with this beam direction, or one of these beam directions.

When all possible beam directions have been tested for the second transceiver circuitry TRX2, the process passes to step 110, in which it is determined whether there are any other available beam directions that have not yet been used for the first transceiver circuitry TRX1.

If it is determined in step 110 that there is at least one other beam direction for the first transceiver circuitry TRX1 that has not yet been tested, the process returns to step 102, in which the beam control circuitry is operated such that the first transceiver circuitry TRX1 operates with this beam direction, or one of these beam directions.

The process then continues as described above, with different possible beam directions for the second transceiver circuitry TRX2 being tested.

Thus, the process as described above tests all possible combinations of beam directions for the two transceiver circuits. Moreover, the process avoids repeated combinations, since a situation where the first transceiver circuitry TRXI uses a first beam direction and the second transceiver circuitry TRX2 uses a second beam direction is exactly equivalent to a situation where the first transceiver circuitry TRX1 uses the second beam direction and the second transceiver circuitry TRX2 uses the first beam direction.

For a case as illustrated here, where at least some of the basestations of the cellular communications network are operating in accordance with a 2x2 MIMO system, the highest data throughput can be achieved by using two different beam directions, and hence it is necessary for the wireless access point to have two transceiver circuits. In other situations, where a higher order MIMO is in use, it is necessary to provide a corresponding higher number of transceiver circuits.

For the access point illustrated herein, having four directional antenna elements, providing four possible beam directions, the two beam directions that are to be used are therefore selected from these four possible beam directions.

The table below shows the operation of the method described above, in this case, where the four possible beam directions are denoted as A, B, C and D, and the method is iterated to ensure that the data throughout is measured for all possible combinations of these beam directions.

Iteration TRX1 TRX2 1 A B 2 A C 3 A D 4 B C B 0 6 C D As mentioned above, it is not necessary to test the data throughput using beam direction B for TRX1 and beam direction A for TRX2, because this is exactly equivalent to the situation using beam direction A for TRX1 and beam direction B for TRX2, etc. Where the access point has a different number of possible beam directions, then, of course, a different number of iterations are required to test all possible combinations.

When all possible combinations have been tested, the method passes to step 112, in which the measured data throughput results achieved during the various iterations of step 106 are compared. As described above, the measure of data throughput that is used may be the average data rate, or the peak data rate, or a combination of the two.

The combination of beam directions that achieved the highest measured data throughput is then selected for future use.

As described above, all possible combinations of beam directions are tested.

However, in other embodiments of the invention, only a subset of the possible combinations is tested. For example, when the antenna device has a large number of antenna elements, whose preferred directions are therefore relatively closely spaced apart from each other, it may be sufficient to test alternate beam directions only. For example, data throughput tests can be carried out using only one half of the beam directions (the odd-numbered beam directions, counting round the azimuth, say) for TRX1 and the other half of the beam directions (the even-numbered beam directions, say) for TRX2.

The process can be repeated as required, for example once per day or once per week, at a time to be determined. For example, performing the process at night minimizes the likelihood that the testing procedure will interfere with any traffic in the network.

However, performing the process at times when the network traffic is at typical levels means that the selected beam directions are those likely to give the best data throughput in use of the device.

Claims

CLAIMS1. A method of establishing a link between an access point and a cellular communications network using a MIMO technique, wherein the access point comprises at least two radio transceiver circuits for respective data communications paths, and wherein the access point allows the selection of respective beam directions from a plurality of available beam directions for the data communications paths, the method comprising: determining a plurality of combinations of beam directions selected from the plurality of available beam directions; for each combination of beam directions, establishing a link such that each of the radio transceiver circuits is connected with a respective beam direction of the combination of beam directions; measuring an available data throughput with said combination of beam directions; and selecting the combination of beam directions with which the highest data throughput can be achieved.
2. A method as claimed in claim 1, wherein the access point comprises an antenna device having a plurality of directional antenna elements, and wherein the available beam directions correspond to preferred directions of transmission/reception of the directional antenna elements.
3. A method as claimed in claim 1 or 2, wherein the plurality of combinations of beam directions comprises every possible combination of beam directions in which each of the radio transceiver circuits is connected with a different beam direction.
4. A method as claimed in claim 1 or 2, wherein the plurality of combinations of beam directions comprises a subset of the possible combinations of beam directions.
5. A method as claimed in one of claims 1 to 4, comprising measuring the available data throughput for a data download.
6. A method as claimed in one of claims 1 to 4, comprising measuring the available data throughput for a data upload.
7. A method as claimed in one of claims 1 to 4, comprising measuring the available data throughputs for a data download and for a data download, and forming a combined measure of the available data throughput from the measured available data throughputs.
8. A method as claimed in one of claims 1 to 7, comprising measuring an average available data throughput.
9. A method as claimed in one of claims 1 to 7, comprising measuring a peak available data throughput.
10. A method as claimed in one of claims 1 to 7, comprising measuring an average available data throughput and a peak available data throughput, and forming a combined measure of the available data throughput from the measured available data throughputs.
11. An access point, comprising: at least two radio transceiver circuits for respective data communications paths; an antenna, having a plurality of available beam directions such that respective beam directions from the plurality of available beam directions can be selected for each of the data communications paths, the access point being configured to: determine a plurality of combinations of beam directions selected from the plurality of available beam directions; for each combination of beam directions, establish a link such that each of the radio transceiver circuits is connected with a respective beam direction of the combination of beam directions; measure an available data throughput with said combination of beam directions; and select the combination of beam directions with which the highest data throughput can be achieved.