GB2505965A

GB2505965A - Co-ordinating wireless transmissions in a distributed antenna system

Info

Publication number: GB2505965A
Application number: GB1216652.6A
Authority: GB
Inventors: Parag Gopal Kulkarni
Original assignee: Toshiba Research Europe Ltd
Current assignee: Toshiba Europe Ltd
Priority date: 2012-09-18
Filing date: 2012-09-18
Publication date: 2014-03-19
Anticipated expiration: 2032-09-18
Also published as: GB201216652D0; US20140080498A1; CN103687022A; GB2505965B; JP2014090406A

Abstract

A controller for coordinating wireless transmissions between a plurality of radio units and one or more user devices, each radio unit having a respective geographic area of coverage, for example, in a distributed antenna system (DAS). The controller signals each each radio unit to broadcast a pilot signal over its respective geographic area of coverage, the pilot signal being designed to elicit a response signal from each user device located within the radio unit's area of coverage. The controller then receives from the radio units information specifying the user devices from which the respective radio unit has received a response signal. The controller is configured to use the information received from the radio units to determine which user devices are located within range of each radio unit. From this information, a matrix is created to assign resources to the radio units to ensure coverage and minimise interference between the radio units.

Description

I

Controller for coordinating wireless transmissions between a plurality of radio units and one or more user devices

Field

Embodiments described herein relate to a controller for coordinating wireless transmissions between a plurality of radio units and one or more user devices;

Background

Coordinated Antenna Base-station (CoAB) systems can provide improved cellular coverage and capacity in large indoor environments, e.g. in office buildings with several floors, shopping malls etc. A typical CoAB deployment comprises of a master unit (MU e.g. one per building) and several hub units (HU, one per floor). Each hub unit HU may communicate with several remote units (RU), there being multiple RUs deployed on a single floor, with each one being uniquely identifiable by the HU.

Reusing the entire frequency band at each HU (and hence at the RUs connected to the HU) offers scope for better coverage/capacity. However interference between RLJs needs to be carefully managed.

In traditional cellular systems, resource allocation aims to maximise the aggregate throughput by allocating each subcarrier exclusively to the user device (UE) with the best channel quality indicator COl for the subcarrier under consideration. However, the complexity of such allocation is proportional to the number of sub-carriers. Given the large number of subcarriers e.g. in an LTE system, the complexity of such allocation may be very high. One solution Es to allocate resources in chunks (i.e. sets of subcarriers, also referred to as Resource Blocks RB) rather than on a subcarrier-by-subcarrier basis to terminals based on the 001 conditions reported by the user device.

However, such an approach does not take into account the local network neighbourhood of the user device, and allows for the possibility that two closely located user devices may be allocated similar resource blocks, leading to a risk of interference.

Brief description of Figures

Figure 1 shows a Coordinated Antenna Base-station (CoAB) system including a controller according to an embodiment; Figure 2 shows a schematic of a method employed by the system of Figure 1; Figure 3 shows a schematic of how pilot signals sent from the radio units of Figure 1 may be offset in time from one another; Figure 4 shows a table in which data received by the controller of Figure 1 is used to determine the relative distances between each user device and radio unit according to an embodiment; Figure 5 shows an example of a resource allocation matrix for the Coordinated Antenna Base-station (CoAB) system of Figure 1; Figure 6 shows a Coordinated Antenna Base-station (CoAB) system including a controller according to an embodiment, wherein the controLler communicates with a plurality of radio units via a plurality of hub units; Figure 7 shows an example of a table compiled by a controller on receipt of information encoded in response signals sent from the user devices in Figure 6; and Figure 8 shows an example of a resource allocation matrix for the Coordinated Antenna Base-station (CoAB) system of Figure 6.

Detailed Description

A first embodiment provides a controller for coordinating wireless transmissions between a plurality of radio units and one or more user devices, each radio unit having a respective geographic area of coverage, the controller comprising: a first module for signaling each radio unit to broadcast a pilot signal over its respective geographic area of coverage, the pilot signal being designed to elicit a response signal from each user device Located within the radio unit's area of coverage, a second moduFe for receiving from each radio unit information specifying the user devices from which the respective radio unit has received a response signal, the controller being configured to use the information received from the radio units to determine which user devices are located within range of each radio unit.

In some embodiments, the information that the controller receives from a respective radio unit may specify one or more characteristics of the response signals that the radio unit has received from the user devices.

In some embodiments; for each user device, the controller is configured to determine the radio units for which the user device is in range, and to rank those radio units in terms of their distance from the user device.

In some embodiments; for each user device, the controller is configured to determine each respective radio units place in the ranking based on one or more of the characteristics of the response signal that the radio unit receives from that user device.

In some embodiments? said characteristics include the strength of the response signal that the respective radio unit receives from the user device. In some embodiments, said characteristics include the delay in time between transmitting a pilot signal from the respective radio unit and receiving the response signal at the radio unit.

In some embodiments, the response signal that the user device sends to the respective radio unit includes an indication of the strength of the pilot signal that the user device has received from the radio unit. The controller may be configured to determine the radio unit's place in the ranking based on the strength of the pilot signal indicated in the response signal.

In some embodiments, the controller is configured to use the information received from the radio units to allocate one or more resource blocks to each radio unit. In some embodiments, each resource block comprises a group of one or more subcarriers.

In some embodiments, the controller is configured to periodically request the radio units to broadcast new pilot signals and subsequently receive updated information from each radio unit. The controller may be configured to reallocate the resource blocks based on the updated information.

In some embodiments, the controller is configured to generate a resource allocation matrix comprising a list of each radio unit and the resource blocks presently aFlocated to that radio unit.

In some embodiments, the controller is configured to transmit and receive information to and from the radio units via one or more hub units.

Another embodiment provides a method of coordinating wireless transmissions between a plurality of radio units and one or more user devices, each radio unit having a respective geographic area of coverage, the method comprising: broadcasting a respective pilot signal from each radio unit, the pilot signal being designed to elicit response signals from the user devices located within the respective radio unit's area of coverage, transmitting information from each radio unit to a controller, the information specifying the user devices from which the respective radio unit has received a response signal, and determining at the controller the user devices that are located within range of each radio unit.

In some embodiments, the method comprises determining, for each user device, the radio units for which the user device is in range, and ranking those radio units in terms of their distance from the user device.

In some embodiments; each respective radio unit's place in the ranking is determined based on one or more characteristics of the response signal that the radio unit receives from the user device.

In some embodiments, the characteristics include the strength of the response signal that the respective radio unit receives from the user device.

In some embodiments, the response signal that the user device sends to the respective radio unit includes an indication of the strength of the pilot signal that the user device has received from the radio unit. The method may comprise determining the radio unit's place in the ranking based on the strength of the pilot signal indicated in the response signal.

In some embodiments, the characteristics include the delay in time between transmitting a pilot signal from the respective radio unit and receiving the response signal at the radio unit.

In some embodiments, the information received from the radio units at the controller is used to allocate one or more resource blocks to each radio unit.

In some embodiments, the controller periodically requests the radio units to broadcast new pilot signals and subsequently receives updated information from each radio unit.

The resource blocks may be reallocated based on the updated information.

In some embodiments, the method comprises generating a resource allocation matrix comprising a hst of each radio unit and the resource blocks presently allocated to each radio unit.

Embodiments described herein provide a method to aggregate and maintain information collected from radio units at a controller, maintain information pertaining to the resources allocated by the controller and to share this information with other hub units. Such information (which encompasses who is using what in the neighbourhood) can be useful during a resource allocationlre-allocation process in order to minimise interference by identifying potential interferers.

Figure 1 shows a Coordinated Antenna Base-station (CoAB) system including a controller 1 according to an embodiment. The controller 1 is used to control wireless transmissions from a pair of radio units RU1, RU2. Each radio unit has a respective area of geographic coverage 3, 5. The geographic area of coverage defines the region over which wireless signals broadcast from the radio unit remain above a threshold intensity, and so will be detectable by a user device.

As shown in Figure 1, a first user device UE1 is located within the area of coverage of the first radio unit RU1. A second user device UE2 is situated at a point within the area of coverage of both the first and second radio units. Consequently, UE1 will be able to detect signals broadcast from the first radio unit RU only, whilst UE2 will be capable of detecting signals broadcast from both the first and second radio units.

In the present embodiment, the controller determines which of the two user devices UE1 and UE2 are within range of each radio unit. The method by which the controller does so is shown schernatica]ly in Figure 2. At step 321, the controller signals to each radio unit to broadcast a pilot signal over its respective area of coverage. The radio units then broadcast their respective pi[ot signals (steps S23a, S23b). When a user device receives one of the pilot signals, it decodes the pilot signal to determine the identity of the radio unit from which the signal has been broadcast. The user device then broadcasts a response signal to the radio unit in question, wherein the response signal includes an identification of the user device. In step 325a, S25b, the radio units receive the response signals sent from the user device(s) in their respective areas of coverage and use this information to determine which user devices are presently within range. The radio units then relay this information to the controller (step S27a, S27b).

The controller compiles the information received from each radio unit to determine which user devices are presently within range of each radio unit.

In the example shown in Figure 1, UE1 lies within range of the first radio unit only and will therefore detect the pilot signal from RU1, but not from RU2. User device liE2, in contrast, will detect the piJot signals sent from both radio units. Consequently, the first radio unit RU1 will receive a response signal from UE1 whilst the second radio unit will receive a response signal from both UE1 and UE2. The controller will then be able to determine that UE1 is within range of radio unit 1, and UE21s in range of both RU1 and RU?.

In some embodiments, the controller may configure each radio unit to transmit a pilot signal at a predefined timeslot. For example, as shown in Figure 3, each radio unit may transmit its pilot signal in a timeslot 7, 9 that is unique to that radio unit.

In some embodiments, the response signal that is sent from a respective user device to a radio unit may also include information that can be used to estimate the distance between the radio unit and the user device in question. For example, the response signal may include an indication of the power level of the pilot signa[ at the point it was received by the user device. The power of the pilot signal will diminish as a function of the distance between the radio unit and the user device-Therefore, the power of the pilot signal as received by the user device will provide an indication of the distance of the user device from the radio unit. When the response signal includes this information, the radio unit (or controller) will be able to estimate the distance between the radio unit and the user device.

Alternatively, or in addition, the radio unit or controller may estimate the distance between the radio unit and the user device based on the actual strength of the response signal that the radio unit receives from the user device. In some embodiments, the radio unit may estimate the distance based on the temporal delay between transmitting a pilot signal, and receiving the response signal from the user device.

Where the radio unit estimates the distance between itself and a respective user device, it may relay that estimation to the controller. Alternatively, the radio unit may function in a passive mode and simply relay details of the response signal(s) to the controller. The controller may then itself process the data to estimate the distance between the radio unit and each user device that the radio unit has received a response signal from. Doing so can reduce the processing burden on the radio unit.

In this way, the controller is able to determine not only which user devices are within range of each radio unit, but is also able to obtain information concerning the distance between each user device and the radio units that they are in contact with.

In some embodiments, the controller may store the information it receives from the radio units in the form of a table. Figure 4 shows an example of such a table for the arrangement shown in Figure 1.

The table indicates that UE1 is within range of RU1 alone, whilst UE2 is within range of both RU1 and RU2. In addition, the table of Figure 4 also includes various data items that can be used to estimate the distance between each radio unit and user device. In the example shown in Figure 4, these data items include a measurement of the strength of the pilot signal received by the user device, the delay between broadcasting the pilot signal from a respective radio unit and receiving a response from each user device, and the strength of the response signal received at the radio unit.

Since the distance between the first user device UE1 and the radio unit RU1 is smaller than the distance between the second user device UE2 and the radio unit RU1, the strength of the response signal that RU1 receives from UE1 (0.4) is greater than that of the response signal that RU1 receives from UE2 (0.3). Similarly, the delay between broadcasting the pilot signal from RU1 and receiving a response signal from UE1 (0.5) is shorter than the delay between broadcasting the pilot signal from RU1 and receiving the response signal from UE2 (0.9).

Since UE2 is within range of both RU1 and RU2, the entry for UE2 includes data for both radio units. Here! it can be seen that the response signal received at RU2 from UE2 (06) is greater than that received at RU1 (0.3). The same result is mirrored by the relative strength of the pilot signals that UE2 receives from these two radio units.

Based on the information encoded in the response signals, the controller is able to rank the radio units in terms of their distance from each user device. In the case of user device UE1, the only radio unit within range is RU1, hence RU1 will be awarded a distance ranking of 1 by default. In the case of UE2, the controller is able to determine that UE2 lies closer to RU2 than it does to RU1. Consequently, the controller assigns a distance ranking of ito RU2, and a ranking of 2 to RU1. In this way, the controller is able to build up a picture of the network neighbourhood of each user device.

The controller may use the data received from the radio units to mitigate the effects of interference. In the example shown in Figure 1, RU1 is communicating with UE1, whilst RU2 is communicating with UE2. However! since UE2 is also within range of UE1, it is possible that transmissions between RU2 and UF. will be subject to interference from RU1. The risk of interference can be reduced, for example, by ensuring that RU1 and RU7 transmit on separate frequencies, which are located far apart on the frequency spectrum.

The controller may use the information in Figure 4 to determine the resource blocks that should be assigned to each radio unit RU1 and RU7. Figure 5 shows an example of a resource allocation matrix compiled by the controller of Figure 1. Each radio unit RU1. RU2 can be allocated one or more radio resource blocks RB1, RB2...., RBN for transmissions, where each resource block itself comprises a group of one or more subearriers. In the matrix, a value of I is used to denote that a particular resource block is allocated to a radio unit, whilst a value of 0 denotes that the radio unit in question is not presently allocated that resource block. In the example shown in Figure 5, the first radio unit RU1 is allocated resource block RB1, whilst the second radio unit RU2 is allocated resource block RB2. In this way, it is possible to reduce interference at user device UE2, as the user device can filter signals received from the two radio units based on their different frequencies.

The resource allocation matrix may be updated by the controller in response to changes in the location and I or activity of the various user devices.

Figure 6 shows an embodiment in which the controller 1 takes the form of a master unit MU that communicates with the radio units via a plurality of hub units HU1 and HU2.

The hub units function as intermediaries between the controller and one or more radio units.

In this embodiment, a first pair of radio units RU11 and RU12 are both controlled via the first hub unit HU1, whilst a second pair of radio units RU21 and RU22 are controlled via the second hub HU2. The radio units RU1, RU12, RU21. and RU2, have respective geographic areas of coverage 11, 13, 15, 17.

A first user device UE1 is located in the area of coverage of the first radio unit RU11. A second user device UE2 is located in the area of coverage of both the first radio unit RU11 and the second radio unit RU12 A third user device UE3 is located within the area of coverage of the first and second radio units RU11 and RU12 and also the third radio unit RU21. User device UE4 is located within range of the third radio unit RU,1 only, and UE5 is within range of both the third and fourth radio units RU21 and RU22 In common with embodiments described above, the controller is configured to signal to each radio unit to broadcast a pilot signal over its respective geographic area of coverage. To do so, the controller MU sends a signal to the hub units HU1 and HU2, which in turn relay the signal to their respective pairs of radio units RU11 / RU12 and RU21 / RU in order to cause the radio units to broadcast the pilot signals. As before, each radio unit will receive a response signal from the user devices located within its respective geographic area of coverage. The information encoded in the response signals is relayed back to the respective hub unit to which the radio unit in question is connected. The hub units HU1 and HLJ2 compile the data from their respective pairs of radio units RU11 / RU12 and RU21 / RU22 and relay this back to the controller MU. The signals sent from each hub unit to the controller may include an identification of the hub unit. The controller is thereby able to determine which user devices are in range of the different radio units.

Figure 7 shows an example of a table compiled by the controller on receipt of the information encoded in the response signals sent from each user device. For each user device UE1 -UE5. the controller is able to determine: 1) the radio units for which the user device is in range ii) the relative distance of the user device from each of those radio units iii) the hub unit being used to communicate with each respective radio unit For example, referring to row one of the table of Figure 7, user device UE1 is in range of radio unit RU11 alone, which is connected to hub unit HU1 In contrast, referrLng to row3 of the table, user device UE3 is seen to be within range of RU11 and RU72, both of which are communicating with the controller via hub unit HU1. User device UE3 is also within range of RU21, which is linked to the controller via HU2. Based on the strength of the pilot signaLs received by the user devices (or the strength of the response signals received by the radio units), the controller is able to determine that user device UF, is closest to radio unit RU11, followed by RU2, and then RU21.

As before, the controller may use the information shown in Figure 7 to update a resource allocation matrix for the system. By knowing which neighbouring radio units a user device is able to detect signals from, and by knowing the resources that these neighbouring radio units are using, it is possible to identify potential sources of interference (if any). This information can then aid in the resource allocation/reallocation procedure with the aim of eliminating (where possible) or minimising the impact of interference.

For example, based on the information shown in Figure 7, the controller can determine that user device UE3 is within range of 3 separate radio units, RU11, RU12, and RU2.1. In order to avoid interference at UE, the controller can first allocate a different resource block to radio units RU11 and RU12, from that which is allocated to radio unit RU21 The controller is also able to determine that the radio units RU11 and RU12 should each be allocated their own, distinct frequency bands1 otherwise there is a risk of interference occurring at user device UE2 which still lies within range of both of those stations.

Figure 8 shows a resource allocation matrix for the embodiment shown in Figure 6.

Each one of the 3 radio units RU11, RU12, and RU21 has been allocated a separate resource block, thereby reducing the chance of interference occurring at user devices UE3 and UE2. The fourth radio unit RU22 has meanwhile been allocated the same resource block as RU11. Assigning the same resource block to radio units RU11 and RU22 does not present a problem because there is no single user device presently located within both their areas of coverage; the only user device that lies within range of radio unit RU22 is UE5. Although UE,5 is also located within range of both RU21, RU21 has already been assigned a resource block different from that of RU11. Therefore, from the point of view of UE5, there is no risk in allocating the same resource block as RU11 to RU22.

Thus, embodiments described herein provide information concerning the radio neighbourhood around a user device (for example, the radio units that a user device can hear and the resources that are currently allocated to these radio units). As a result, it is possible to make a better informed decision as to what resources should be allocated to a particular user device. For example, embodiments described herein allow the controller to establish the following: i) which are the other hub units I radio units in the vicinity of a given user device? ii) which of these is the nearest/furthest from the user device? iii) what resources are currently being used in each of these hub units / radio units? iv) are there any particular resource block allocations that may be resulting in interference to the user device? v) Are there resources that are presently not in use by these hub unit/radio units and that can be allocated to the user device? This is in marked contrast to conventional DAS systems, in which a controller will typically allocate resources to a user device based on the channel quality information COl reported by the user device, While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the invention. Indeed, the novel methods, devices and systems described herein may be embodied in a variety of forms; furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the invention. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.

Claims

Claims 1. A controller for coordinating wireless transmissions between a plurality of radio units and one or more user devices, each radio unit having a respective geographic area of coverage, the controller comprising: a first module for signaling each radio unit to broadcast a pilot signal over its respective geographic area of coverage, the pilot signal being designed to elicit a response signal from each user device located within the radio unit's area of coverage, a second module for receiving from each radio unit information specifying the user devices from which the respective radio unit has received a response signal, the controller being configured to use the information received from the radio units to determine which user devices are located within range of each radio unit.
2. A controller according to claim 1, wherein for each user device, the controller is configured to determine the radio units for which the user device is in range, and to rank those radio units in terms of their distance from the user device.
3. A controUer according to claim 2, wherein for each user device, the controller is configured to determine a respective radio unit's place in the ranking based on one or more characteristics of the response signal that the radio unit receives from that user device.
4. A controller according to claim 3, wherein said characteristics include the strength of the response signal that the respective radio unit receives from the user device.
5. A controller according to claim 3 or 4, wherein the response signal that the user device sends to the respective radio unit includes an indication of the strength of the pilot signal that the user device has received from the radio unit, the controller being configured to determine the radio unit's place in the ranking based on the strength of the pilot signal indicated in the response signal.
6. A controller according to any one of claims 3 to 5, wherein said characteristics include the delay in time between transmitting a pilot signal from the respective radio unit and receiving the response signal at the radio unit.
7. A controller according to any one of the preceding claims, wherein the controller is configured to use the information received from the radio units to allocate one or more resource blocks to each radio unit.
8. A controller according to claim 7, wherein the controller is configured to periodically request the radio units to broadcast new pilot signals and subsequently receive updated information from each radio unit, the controller being configured to reallocate the resource blocks based on the updated information.
9. A controller according to claim 7 or 8, wherein the controller is configured to generate a resource allocation matrix comprising a list of each radio unit and the resource blocks presently allocated to that radio unit.
10. A controller according to any one of the preceding claims, wherein the controller is configured to transmit and receive information to and from the radio units via one or more hub units.
11. A method of coordinating wireless transmissions between a plurality of radio units and one or more user devices, each radio unit having a respective geographic area of coverage, the method comprising: broadcasting a respective pilot signal from each radio unit, the pilot signal being designed to elicit response signals from the user devices located within the respective radio unit's area of coverage, transmitting information from each radio unit to a controller, the Enformation specifying the user devices from which the respective radio unit has received a response signal; and determining at the controller the user devices that are located within range of each radio unit.
12. A method according to claim 11, further comprising determining, for each user device, the radio units for which the user device is in range, and ranking those radio units ri terms of their distance from the user device.
13. A method according to claim 12, wherein each respective radio unit's place in the ranking is determined based on one or more characteristics of the response signal that the radio unit receives from the user device.
14. A method according to claim 13, wherein said characteristics include the strength of the response signal that the respective radio unit receives from the user device.
15. A method according to claim 13 or 14, wherein the response signal that the user device sends to the respective radio unft includes an indication of the strength of the pilot signal that the user device has received from the radio unit, and the method comprises determining the radio unit's place in the ranking based on the strength of the pilot signal indicated in the response signal.
16. A method according to any one of claims 13 to 15, wherein said characteristics include the delay in time between transmitting a pilot signaL from the respective radio unit and receiving the response signal at the radio unit.
17. A method according to any one of claims 11 to 16, wherein the information received from the radio units at the controller is used to allocate one or more resource blocks to each radio unit.
18. A method according to claim 17, wherein the controller periodically requests the radio units to broadcast new pilot signaLs and subsequently receives updated information from each radio unit, wherein the resource blocks are reallocated based on the updated information.
19. A method according to claim 17 or 18, comprising generating a resource allocation matrix comprising a list of each radio unit and the resource blocks presently allocated to each radio unit.