GB2494007A

GB2494007A - Cognitive wireless communication system

Info

Publication number: GB2494007A
Application number: GB1204041.6A
Authority: GB
Inventors: Philippe Delahaye; Pierre Marchand
Original assignee: NEC Corp
Current assignee: NEC Corp
Priority date: 2011-08-23
Filing date: 2012-03-07
Publication date: 2013-02-27
Also published as: WO2013027637A3; JP2014529916A; JP5835468B2; GB201114597D0; WO2013027637A2; GB201204041D0; GB2493939A

Abstract

A cognitive radio system comprising a master node and a plurality of mobile terminals operable to communicate with each other within a licensed operating band of a primary user device. The master node receiving from at least one of the mobile nodes (5) primary user transmission information indicative of a signal strength of a primary user transmission received at the at least one mobile node (5); obtaining position information for each of the at least one mobile node (5); estimating an area (17) of possible transmission overlap between the master node (3) and the primary user (4) using the received primary user transmission information and the obtained position information; comparing the location of each mobile node (5) with the estimated area (17) of possible transmission overlap; and controlling the operation of the mobile nodes (5) in dependence upon a result of the comparison in order to avoid interference to the primary user (4) by the master node (3) and the mobile nodes (5). Some or all of the mobile terminals (5) act as sensor nodes to sense and measure the signal strength of primary user (4) transmissions. The determined signal strength may be reported within a Medium Access Control (MAC) layer frame or as part of a Random Access Procedure.

Description

Communication System The present invention relates to a communications system and to parts and methods thereof. The invention has particular, although not exclusive relevance to cognitive radio systems and devices thereof.

In wireless communications, traditionally, licensing gave systems exclusive access to distinct blocks of the electromagnetic spectrum. This is a good way to eliminate the danger of harmful interference but it can leave the majority of the allocated block of spectrum underused when and where the license holder is not active.

In order to use spectrum holes (parts of the spectrum where the licensees are not active for a given time), the idea of opportunistic access to spectrum was suggested. This idea involves two different kinds of spectrum users: legitimate users (or primary licensed users), and secondary users (or cognitive users) which are allowed to use a part of the spectrum only if the primary users are not using it or only if the generated interference (to the primary users) is acceptable.

A Cognitive Radio Device has been defined as a terminal which is aware of its electro-magnetic environment and able to adapt its transmission accordingly. A Cognitive Radio Device may sense a specific frequency band in order to estimate its occupancy and take a decision whether it transmits or not. However, the primary signals to be detected are subject to different environment changes (shadowing, fading, path loss) and therefore sometimes primary licensed users are very difficult to detect by a single cognitive radio device. In such a situation, the primary transmitter is considered to be "hidden" (i.e., hidden primary transmitter) from the sensing device, and therefore the use of a single sensing device is unlikely to provide a reliable decision.

If the primary user transmits using low power and narrow bandwidth (as may be the case with so called "PMSE" devices, such as wireless microphones), sensing in a geographical area far away from the primary transmitter becomes unreliable.

To try to address these issues, others have proposed a cooperative approach where a number of geographically distributed sensor nodes are used to sense for the primary transmitter over a wider area and report back to a master node that decides whether or not secondary users can operate within the licensed band. WO 2007/031956 A2 discloses an example of this kind of cooperative system.

However, a problem with using such a cooperative approach is that sensor nodes must be specifically instructed when and in which frequency bands to sense and when to report back to the master node. Another problem is that the master node relies on upper layers of the communications stack to control the operation of the sensor nodes and this leads to relatively long delays between the sensor node signalling the presence of the primary and the master node taking action to stop secondary users transmissions; which in turn can contribute to undesired interference for the primary licensed users during the time it takes to receive and process such signalling at the master node.

Yet another problem with using such a cooperative approach is that the master node, being situated farther away from the primary user than the sensor nodes, has only limited information on the characteristics of the transmission of the primary user, which might lead to inefficient use of resources in the area in which the master node operates.

The invention aims to provide an alternative cooperative system for detecting and reporting transmission characteristics of primary users and hence to control transmission opportunities for secondary users.

The present invention provides a master node for use with a plurality of mobile nodes, the master node comprising: receiving means for receiving from at least one of the mobile nodes primary user transmission information indicative of a signal strength of a primary user transmission received at the at least one mobile node; obtaining means for obtaining position information for each of the at least one mobile node; estimating means for estimating an area of possible transmission overlap between the master node and the primary user using the received primary user transmission information and the obtained position information; comparing means for comparing the location of each mobile node with the estimated area of possible transmission overlap; and control means for controlling the operation of the mobile nodes in dependence upon a result of the comparison in order to avoid interference to the primary user by the master node and the mobile nodes.

In one embodiment, the receiving means receives the information in a Medium Access Control, MAC, control element.

In one embodiment, the obtaining means obtains the position information for each of the at least one mobile node from the mobile node. Alternatively the obtaining means obtains the position information for each of the at least one mobile node from a positioning system or from communications with other master nodes.

In one embodiment, the control means controls the operation of the mobile nodes using at least one of: preventing use of the band of the primary user transmission, performing a handover to a different band than the band of the primary user transmission, limiting a transmission power of the mobile node in the band of the primary user transmission, and allowing the mobile node to continue transmission in the band of the primary user transmission.

In one embodiment, the control means controls a transmission power and/or a transmission direction of the master node in the band of the primary user transmission in order to avoid interference to the primary user.

In one embodiment, the control means is operable to send the primary user transmission information within a MAC control element to at least one of the plurality of mobile nodes for causing the at least one mobile node to stop its transmission within the band of the primary user transmission.

The present invention also provides a sensor node for use with a master node, the sensor node and master node being arranged to communicate with each other within a licensed operating band of a primary user device, the sensor node comprising: sensing means for sensing a transmission of the primary user device; measuring means for determining a measure of a signal strength of the sensed primary user transmission; and reporting means for reporting the determined signal strength measure to the master node; wherein the reporting means is operable to report the determined signal strength measure within a Medium Access Control, MAC, layer frame for processing by a MAC entity within the master node.

In one embodiment, the reporting means reports the determined signal strength measure within a MAC control element. The reporting means may also report an indication of the position information for the sensor node.

In one embodiment, the sensor node stops its transmission in the band of the primary user transmission. This may be done after receiving an acknowledgement from the master node.

The present invention also provides a master node for use with a plurality of mobile nodes, the master node comprising: receiving means for receiving from at least one of the mobile nodes primary user transmission information indicative of a signal strength of a primary user transmission received at the at least one mobile node; and control means for controlling the operation of the mobile nodes in dependence upon the received primary user transmission information to avoid interference to the primary user by the master node and the mobile nodes; wherein the receiving means operates at a Medium Access Control, MAC, layer of the master node and is arranged to extract the primary user transmission information from a MAC layer frame.

In one embodiment, the receiving means receives the primary user transmission information within a MAC control element.

The master node may further comprise sending means for sending an acknowledgement to the at least one mobile node for causing the mobile node to stop its transmission within the band of the primary user transmission.

The master node may further comprise sending means for sending the primary user transmission information within a MAC control element to at least one of the plurality of mobile nodes for causing the at least one mobile node to stop its transmission within the band of the primary user transmission.

The present invention also provides a sensor node for use with a master node, the sensor node and master node being operable to communicate with each other within a licensed operating band of a primary user device, the sensor node comprising: communications control means for receiving uplink resource allocation data indicating uplink resources that the sensor node can use for transmitting data to the master node; sensing means for sensing a transmission of the primary user device; reporting means for reporting a determined signal strength measure to the master node using uplink resources allocated by the master node; wherein if the sensing means senses the primary user transmission at a time when the sensor node has not been allocated uplink resources, the communications control means is arranged to request uplink resource allocation from the master node.

In one embodiment, the reporting means reports primary user transmission information, indicative of the sensed primary user transmission, in a message sent by the sensor node as part of a Random Access Procedure. The message may be an uplink request message of the Random Access Procedure and may comprise a reserved preamble that notifies the master node of detection of the primary user transmission within the licensed operating band In one embodiment, the reporting means reports the primary user transmission information within a MAC control element. The reporting means may report said determined signal strength measure, after uplink resources have been granted to the sensor node, in a further message sent by the sensor node as part of the Random Access Procedure.

The present invention also provides a master node for use with a plurality of mobile nodes, the master node comprising: receiving means for receiving from at least one of the mobile nodes primary user transmission information indicative of a signal strength of a primary user transmission received at the at least one mobile node; and control means for controlling the operation of the mobile nodes in dependence upon the received primary user transmission information to avoid interference to the primary user by the master node and the mobile nodes; wherein the receiving means is operable to receive the primary user transmission information within a message sent by the at least one mobile node as part of a Random Access Procedure.

In one embodiment, the master node receives a notification of a sensed primary user transmission, in an uplink request message sent by the mobile node as part of a Random Access Procedure. The uplink request message may comprise a reserved preamble that notifies the master node of detection of the primary user transmission within the licensed operating band.

In one embodiment, the control means is operable, in response to receiving the uplink request message comprising the reserved preamble, to control operation of the master node and the plurality of mobile nodes to avoid interference to the primary user by the master node and the mobile nodes.

In one embodiment, the receiving means receives the primary user transmission information within a MAC control element. The primary user transmission information may be received, after uplink resources have been granted to the mobile node, in a further message sent by the mobile node as part of the Random Access Procedure.

The present invention also provides a sensor node for use with a master node, the sensor node and master node being operable to communicate with each other within a Hcensed operating band of a primary user device, the sensor node comprising: means for storing a reserved preamble; means for sensing a transmission of the primary user device; and means for notifying the master node of the sensed primary user transmission, wherein the means for notifying is arranged to notify the master node by sending the stored reserved preamble in an initial message of a Random Access procedure.

The reserved preamble may be pre-programmed in the sensor node but is preferably received as a part of system information broadcast by the master node.

In one embodiment, the sensor node further comprises means for determining a signal strength measurement of the primary user transmission and means for sending the signal strength measurement to the master node. The sensor node can send the determined signal strength to the master node using uplink resources allocated to the sensor node by the master node.

In one embodiment, the sensor node further comprises means for randomly generating a preamble for use in a Random Access procedure. In this case, the sensor node may compare the randomly generated preamble with the stored reserved preamble, and when the randomly generated preamble matches the stored reserved preamble, the sensor node randomly generates another preamble for use in the Random Access procedure.

The present invention also provides a master node for use with a plurality of mobile nodes, the master node and mobile nodes being operable to communicate with each other within a licensed operating band of a primary user device, the master node comprising: means for receiving from at least one mobile node, an initial message of a Random Access procedure; means for processing the received initial message to determine whether or not the mobile node that transmitted the initial message has sensed a primary user transmission; and means for controlling operation of the mobile nodes to avoid interference to the primary user if the determining means determines that the mobile node that transmitted the initial message has sensed a primary user transmission.

In one embodiment, the master node further comprises means for storing a reserved preamble used to indicate the sensing of a primary user transmission and wherein the processing means is arranged to determine if the preamble in the received initial message matches the stored reserved preamble and to determine that the mobile node that transmitted the initial message has sensed a primary user transmission if the received preamble matches the reserved preamble.

In one embodiment, the master node further comprises means for sending the stored reserved preamble to the plurality of mobile nodes. This may be broadcast as a part of system information.

In one embodiment, the control means is arranged, in response to the determining means determining that the mobile node that transmitted the initial message has sensed a primary user transmission, to cease transmissions to other mobile terminals in the licensed operating band.

In one embodiment, the master node further comprises means for sending an uplink resource allocation message to the mobile node that has sensed the primary user transmission. This allocation may be used by the sensor node to send signal measurements back to the master node.

In one embodiment, the master node is operable to receive, from the mobile node, a signal strength measurement of the sensed primary user transmission and wherein the controlling means is arranged to re-determine control actions for each mobile node in light of the received signal strength measurement.

The present invention also provides a communications system comprising a plurality of mobile nodes and the master node according to any one of the above embodiments.

The present invention also provides a method performed by a master node that communicates with a plurality of mobile nodes within a licensed operating band of a primary user device, the method comprising: receiving from at least one of the mobile nodes primary user transmission information indicative of a signal strength of a primary user transmission received at the at least one mobile node; obtaining position information for each of the at least one mobile node; estimating an area of possible transmission overlap between the master node and the primary user using the received primary user transmission information and the obtained position information; comparing the location of each mobile node with the estimated area of possible transmission overlap; and controlling the operation of the mobile nodes in dependence upon a result of the comparison in order to avoid interference to the primary user by the master node and the mobile nodes.

In one embodiment, the information is received in a Medium Access Control, MAC, control element.

The present invention also provides a method performed by a master node that communicates with a plurality of mobile nodes within a licensed operating band of a primary user device, the method comprising: receiving from at least one of the mobile nodes primary user transmission information indicative of a signal strength of a primary user transmission received at the at least one mobile node; and controlling the operation of the mobile nodes in dependence upon the received primary user transmission information to avoid interference to the primary user by the master node and the mobile nodes; wherein the receiving step is carried out at a Medium Access Control, MAC, layer of the master node and comprises extracting the primary user transmission information from a MAC layer frame.

The present invention also provides a method performed by a mobile node that communicates with a master node within a licensed operating band of a primary user device, the method comprising: sensing a transmission of the primary user device; determining a measure of a signal strength of the sensed primary user transmission; and reporting the determined signal strength measure to the master node; wherein the reporting step comprises reporting the determined signal strength measure within a Medium Access Control, MAC, layer frame for processing by a MAC entity within the master node, The present invention also provides a method performed by a mobile node that communicates with a master node within a licensed operating band of a primary user device, the method comprising: receiving uplink resource allocation data indicating uplink resources that the sensor node can use for transmissions data to the master node; sensing a transmission of the primary user device; reporting a determined signal strength measure to the master node using uplink resources allocated by the master node; wherein if at the sensing step the sensor node has not been allocated uplink resources, the reporting step further comprises requesting uplink resource allocation from the master node.

In one embodiment, the method further comprises reporting the sensed primary user transmission, in a message sent by the sensor node as part of a Random Access Procedure. The message may be an uplink request message of the Random Access Procedure and may comprise a reserved preamble that notfles the master node of detection of the primary user transmission within the licensed operating band.

In one embodiment, the reporting step is part of a Random Access Procedure.

In one embodiment, the determined signal strength measure is reported within a MAC control element. The determined signal strength measure may be reported, after uplink resources have been granted to the sensor node, in a further message sent by the sensor node as part of the Random Access Procedure.

The present invention also provides a method performed by a master node that communicates with a plurality of mobile nodes within a licensed operating band of a primary user device, the method comprising: receiving from at least one of the mobile nodes primary user transmission information indicative of a signal strength of a primary user transmission received at the at least one mobile node; and controlling the operation of the mobile nodes in dependence upon the received primary user transmission information to avoid interference to the primary user by the master node and the mobile nodes; wherein the receiving step comprises receiving the primary user transmission information within a message sent by the at least one node as part of a Random Access Procedure.

In one embodiment, the method further comprises receiving a notification of a sensed primary user transmission, in an uplink request message sent by the sensor node as part of a Random Access Procedure. The uplink request message may comprise a reserved preamble that notifies the master node of detection of the primary user transmission within the licensed operating band.

In one embodiment, the controlling the operation comprises, in response to receiving the uplink request message, controlling operation of the plurality of mobile nodes to avoid interference to the primary user by the master node and the mobile nodes.

In one embodiment, said primary user transmission information is received within a MAC control element.

The present invention also provides a method performed by a master node that communicates with a plurality of mobile nodes within a licensed operating band of a primary user device, the method comprising: receiving from at least one mobile node, an initial message of a Random Access procedure; processing the received initial message to determine whether of not the mobile node that transmitted the initial message has sensed a primary user transmission; and controlling operation of the mobile nodes to avoid interference to the primary user if it has been determined that the mobile node that transmitted the initial message has sensed a primary user transmission.

In one embodiment the method further comprises storing, at the master node, a reserved preamble used to indicate the sensing of a primary user transmission and determining if the preamble in the received initial message matches the stored reserved preamble and determining that the mobile node that transmitted the initial message has sensed a primary user transmission if the received preamble matches the reserved preamble.

In one embodiment the method further comprises sending the stored reserved preamble to the plurality of mobile nodes as a part of system information.

In one embodiment, the controlling the operation further comprises controlling the master node, in response to determining that the mobile node that transmitted the initial message has sensed a primary user transmission, to cease transmissions to other mobile terminals in the licensed operating band.

In one embodiment, the uplink resource allocation may be provided to the mobile node that sent the initial message.

In one embodiment, the method may also comprise receiving, from the mobile node, a signal strength measurement of the sensed primary user transmission and re-determining control actions for each mobile node in light of the received signal strength measurement.

The present invention also provides a method performed by a sensor node that communicates with a master node within a licensed operating band of a primary user device, the method comprising: storing a reserved preamble; sensing a transmission of the primary user device; and notifying the master node of the sensed primary user transmission, wherein the means for notifying is arranged to notify the master node by sending the stored reserved preamble in an initial message of a Random Access procedure.

In one embodiment, the method further comprises receiving an uplink resource allocation from the master node.

In one embodiment, the method further comprises determining a signal strength measurement of the primary user transmission and sending the signal strength measurement to the master node. The determined signal strength may be sent to the master node using the uplink resource allocation received from the master node.

In one embodiment, the method further comprises randomly generating a preamble for use in a Random Access procedure. The randomly generated preamble may be compared with the stored reserved preamble, and when the randomly generated preamble matches the stored reserved preamble, another preamble may be generated for use in the Random Access procedure.

The invention provides, for all methods disclosed, corresponding computer programs or computer program products for execution on corresponding equipment, the equipment itself (user equipment, master node, mobile nodes or components thereof) and methods of updating the equipment.

Exemplary embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings in which: Figure 1 illustrates coverage areas of a master node and a primary transmitter and an overlapping region in which interference may occur; Figure 2 is a block diagram illustrating the main components of a sensor mobile terminal shown in Figure 1; Figure 3 is a black diagram illustrating the main components of the master node shown in Figure 1; Figure 4 is a flow chart illustrating the cooperative sensing technique used in the first embodiment; Figure 5 is a flow chart illustrating the steps that the master node can use to determine actions for mobile terminals to take in order to reduce interference; Figure 6A is an overview of the protocol stack used by the mobile terminal and the master node implementing the invention; Figure 6B is an overview of the lower layers of the protocol stack used by the mobile terminal and the master node implementing the invention; Figure 7A is an overview illustrating a protocol data unit implementing the invention; Figure 7B is an overview illustrating the service data unit of the protocol data unit of Figure 7A; Figure 7C is an overview of a control element used with the protocol data unit of Figure 7A; Figure 8 is a signalling diagram illustrating the communication taking place between the sensor mobile terminal and the master node according to an embodiment of the invention.

Overview Figure 1 schematically illustrates a cognitive wireless communication network 1 that has a master node 3 and a plurality of mobile terminals 5 (marked as 5a-5e) within an area 13 controlled by the master node 3. The master node 3 and the mobile terminals 5 are secondary users of a frequency band (B) that is licensed to one or more primary users. The primary users will typically include a wideband primary transmitter 4 that transmits over the whole or any part of its licensed frequency band (B) and primary user equipment 7 (marked as 7a-7c) that transmit or receive signals over different channels within the licensed band (B). As an example, the licensed band (B) may correspond to a television channel (DVB-T operating on 6MHz or 8MHz channels) and the wideband primary transmitter 4 will transmit over a number of channels whilst the primary user equipment 7 receive the transmitted signal in the whole or any part of the licensed band. Some primary user equipment 7, such as PMSE (Programme Making Special Event) devices) may also transmit within sub-bands (e.g. 200 KHz or 400KHz sub-bands) of the larger 6MHz or 8MHz television channel.

Transmissions of the mobile terminals 5 are controlled by the master node 3. The secondary users are able to communicate within all or a part of the frequency band (B) whilst the primary users are not transmitting in all or that part of the band (B); or as long as the interference caused by the transmissions of the secondary users is acceptable to the primary users. Typically the master node 3 will be fixed in location and the mobile terminals 5 can move. In the preferred embodiment, the master node 3 is a cellular telephone base station that operates in accordance with the Long Term Evolution (LTE) standards and the mobile terminals 5 are LTE user equipment, such as cellular telephones and the like.

Some or all of the mobile terminals 5 are arranged to act as sensor nodes (hereinafter referred to as sensor mobile terminals 5) that are able to sense for primary user transmissions within the licensed frequency band (B). Once a sensor mobile terminal senses a primary user transmission, it informs the master node 3 which then decides if it is allowable for any of the secondary users to transmit in any part of the licensed band (B).

As will be described in more detail below, various data and control information is transmitted between the master node 3 and the mobile terminals 5 in multiple frequency bands, including the frequency band (B) licensed to the primary user.

Further, as the mobile terminals 5 are able to move around wfthhi the area 13 controlled by the master node 3, the master node 3 keeps track of the location of the mobile terminals 5 either continuously, periodically or from time to time to ensure that communication between the master node 3 and the mobile terminals 5 can be maintained. When the mobile terminals 5 are leaving the area 13 controlled by the master node 3, transmission of data and control information is handed over to another master node (not shown) that is able to maintain transmission of data and control information with the mobile terminals 5. Handover might also be initiated for mobile terminals 5 that are still within the area 13 controlled by the master node 3 for various reasons that are well known to the person skilled in the art.

Whilst the master node 3 is typically installed at a fixed location, and hence it is able to make measurements at a single location, the sensor mobile terminals 5 can provide measurements for their current location as they move around in the area 13 controlled by the master node 3. Sensor mobile terminals 5 may be closer to the primary transmitter 4, 7 than the master node 3 and thus may make a more accurate detection and measurement of the primary user transmission. Once a sensor mobile terminal 5 has made a detection, it reports the detection and signal measurements in a signalling message that it sends to the master node 3. The master node 3 then uses the measurements from the different sensor mobile terminals 5 and information about the locations of those sensor mobile terminals 5 to establish areas of possible interference between the primary user and the secondary user of the licensed band (B). Such areas of possible interference include the area of overlap 17 between the coverage area (cell) 13 controlled by the master node 3 and the coverage area 14 of the primary transmitter 4. A sub-area 19 of possible interference might also be present where the transmission area isa of mobile terminal 5a overlaps with the coverage area 14 of the primary transmitter 4. The size of the area 17 is predominantly determined by the transmission characteristics of the master node 3 and the primary transmitter 4; and the size of sub-area 19 is mainly dependent on the location and transmission characteristics of mobile terminal 5a and primary transmitter 4.

Initially, the primary transmitter 4 is not transmitting in the licensed frequency band (B) -so there is no area of overlap 17 and the master node 3 can control all of the mobile terminals 5 operating within its cell 13 to operate within the licensed frequency band (B). However, when the primary transmitter 4 starts transmitting in the frequency band (B), the sensor mobile terminals Sb and Sc will detect this transmission and will sense the strength of the primary user signal. They will then transmit a report to the master node 3 informing the master node that they have detected the primary user transmission and the strength of that transmission. In response, the master node 3 instructs sensor mobile terminals 5b and 5c to stop transmitting on the frequency band (B) and allocates a new frequency band for subsequent transmissions with sensor mobile terminals 5b and 5c. The master node 3 also uses the reported signal strengths and the locations of the sensor mobile terminals 5b and 5c, to work out the approximate location of the primary transmitter 4 and from this to work out the coverage area 14 and hence the overlap area 17. From this information, the master node 3 can determine how much it needs to reduce its own transmission power in the licensed frequency band (B) in order to avoid its transmissions interfering with primary users located within the coverage area 14. Figure 1 shows the reduced size of the cell 13' that can be provided by the master node 3 in the frequency band (B) whilst avoiding interference with the primary user 4.

Changing the size of the cell 13 will have consequences for other mobile terminals being served by the master node 3. For example, mobile terminal 5e will be outside the cell 13 and so can't continue using the licensed frequency band (B). If the master node 3 operates another cell on a different operating frequency, then the mobile terminal 5e can be handed over to that other cell. Otherwise mobile terminal 5e will have to be handed over to a neighbouring master node 3.

Similarly, although some mobile terminals 5 are located outside the coverage area 14 of the primary user, their transmissions may extend into the coverage area 14.

This is shown for mobile terminal 5a, where its transmission range (illustrated by the area 15a) overlaps with the coverage area 14 of the primary user in the sub-area 19. Therefore, it is possible that transmissions made by mobile terminal 5a will adversely affect primary user 7a within the sub-area 19. The master node 3 can use the location information of the different sensor mobile terminals to determine which mobile terminals 5 fall into this category and then either instruct them to reduce their transmission power or hand them over to another cell operating on a different frequency.

Other mobile terminals 5 that are still located inside the reduced cell 13' and which are located far enough away from the coverage area 14 of the primary user 4 (for example mobile terminal 5d) may continue to use the licensed frequency band (B), although in this preferred embodiment, the master node 3 will track the location of such mobile terminal 5d and as it moves towards the coverage area 14, the master node 3 may instruct the mobile terminal 5d to reduce its transmission power or handover the mobile terminal 5d to another cell operating on a different frequency.

As those skilled in the art will appreciate, the master node 3 should identify the mobile terminals 5 that will be affected by the apparition of the primary transmitter 4 and perform the required control action in respect of each of them before it reduces its own transmission power in the licensed band (B).

For some of the mobile terminals 5, the required control action will be to stop transmitting in the licensed frequency band (B), for others the required control action will be to reduce their transmission power in the licensed frequency band (B), for others the required control action will be to hand them over to another cell operating on a different frequency.

In this embodiment, sensor mobile terminals 5 detecting the apparition of the primary transmitter on frequency band (B) measure the transmission power of the primary, and send an indication to the master node 3. Then they stop communications within the operating frequency band (B) after making sure that the indication has been correctly received by the master node 3. Receipt of the indication might be confirmed by the master node 3 by sending an acknowledgement message (ACK) commonly used in the Hybrid Automatic Retransmission Request (HARQ) mechanism of the air interface in LTE networks.

Sensor Mobile Terminal Figure 2 is a block diagram illustrating the main components of a sensor mobile terminal 5, shown in Figure 1. As shown, the mobile terminal 5 includes transceiver circuitry 223 which is operable to transmit signals to and to receive signals from other nodes (e.g. the master node 3) via one or more antennas 225.

A controller 227 controls the operation of the transceiver circuitry 223 in accordance with software stored in memory 237. The mobile terminal 5 also includes a user interface 229 that is controlled by the controller 227 and which allows a user to interact with the communication device. The software stored in memory 237 includes, among other things, an operating system 239, a communication module 241, a positioning module 243, a sensor module 245, a measuring module 246, a reporting module 247 and a transmission frequency control module 249.

The operating system 239 controls the operation of the mobile terminal 5. The communication module 241 controls communications between the mobile terminal and external devices via the transceiver circuitry 223 and the antenna 225. The positioning module 243 operates to determine location information for the sensor mobile terminal 5. It may be a GPS or similar satellite or terrestrial location determining module. The positioning module 243 sends regular position updates to the master node 3 either on demand or at predetermined time intervals. The sensor module 245 operates to sense for transmissions made by primary users.

The sensor module 245 will normally be able to sense for primary user transmissions within the entire licensed band (B) (and perhaps in other frequency bands as well). Whenever the sensor module 245 detects a primary user transmission, the measuring module 246 measures the power of the primary user's transmission, i.e. the intensity of electromagnetic signals in the operating frequency band (B). The results from the measuring module 246 are then transmitted back to the master node 3 by the reporting module 247. Finally, the transmission frequency control module 249 operates to receive the information transmitted from the master node 3 identifying if there are any bands within the licensed band (B) in which they can transmit opportunistic signals without interfering with a primary user; and to control the transmission frequency used by the transceiver circuitry 223 for such opportunistic transmissions accordingly.

Master Node Figure 3 is a block diagram illustrating the main components of the master node 3, shown in Figure 1. As shown, the master node 3 includes transceiver circuitry 323 which is operable to transmit signals to and to receive signals from other nodes via one or more antennas 325. A controller 327 controls the operation of the transceiver circuitry 323 in accordance with software stored in memory 337. The controller 327 is also able to communicate with other communications devices via a network interface 329. The software stored in memory 337 includes, among other things, an operating system 339, a communication module 341, a positioning module 342, a mapping module 343, a band assignment module 345, a results analysis and decision module 347 and a secondary user control module 349.

The operating system 339 is operable to control operation of the master node 3.

The communication module 341 provides the functionality to allow the master node 3 to communicate with the mobile terminals 5 via the transceiver circuitry 323 and the antenna 325 and to communicate with other network devices and nodes via the network interface 329 (which may be a copper or optical fiber interface).

The positioning module 342 allows the master node 3 to determine the location of the different mobile terminals 5, including the sensor mobile terminals 5 -either from measurements received from the mobile terminals 5 or by triangulation from signals transmitted to or received from the mobile terminals 5 by a plurality of network nodes (such as the master node 3). The band assignment module 345 operates to assign available frequency bands to mobile terminals 5 within the cell 13 controlled by the master node 3. The results analysis and decision module 347 operates to receive the sensed results back from the different sensor mobile terminals 5 and to analyse the results and to make a decision as to whether or not each mobile terminal 5 or the master node 3 itself is likely to cause interference to a primary user currently operating in any part of the licensed frequency band (B).

The secondary user control module 349 operates to inform the secondary users when to start and stop using their respective assigned frequency band, or if they need to hand over to another frequency band, or to change their transmission power to avoid interfering with the primary users.

In the above description, the master node 4 and the mobile terminals 5 have been described, for ease of understanding, as having a number of discrete modules (such as the communication modules, the positioning modules, the sensor module, the reporting module etc). Whilst these modules may be provided in this way for certain applications, for example where an existing system has been modified to implement the invention, in other applications, for example in systems designed with the inventive features in mind from the outset, these modules may be built into the overall operating system or code and so these modules may not be discernible as discrete entities.

Master node control A more detailed description of some of the novel aspects of the operation of the master node 3 and of the sensor mobile terminals 5 will now be given.

Figure 4 is flow chart illustrating the overall operation of the master node 3. As shown, in step s41, the communication module 241 of the master node 3 receives from one or more sensor mobile terminal 5 information indicative of a signal strength of a primary user transmission received at those sensor mobile terminals 5.

In step s43, the positioning module 342 obtains position information for the mobile terminals 5.

In step s45, the mapping module 343 estimates an area 17 of possible transmission overlap between the master node 3 and the primary user 4 using the received primary user transmission information and the obtained position information for the mobile terminals 5 that detected the primary user 4.

In step s47, the results analysis and decision module 347 of the master node 3 compares the location of each mobile node 5 currently being served by the master node 3 with the estimated area 17 of possible transmission overlap.

Finally, in step s49, the secondary user control module 349 of the master node 3 controls the operation of the mobile nodes 5 in dependence upon a result of the comparison, in order to avoid interference to the primary user 4 by the master node 3 and the mobile nodes 5.

Figure 5 illustrates the steps carried out by the results analysis and decision module 347 in step s47, for each of the served mobile terminals 5 within the area 13 controlled by the master node 3.

In step s50, the results analysis and decision module 347 checks whether a current mobile terminal 5 under consideration is currently operating in the licensed frequency band (B). If the mobile terminal 5 is not currently operating in this band (B), then in step sSl, the decision module 347 decides whether or not this terminal is a suitable candidate to start using frequency band B (without causing interference). If the result of this analysis is positive, then the results analysis and decision module 347 will allow the current terminal 5 to start transmitting in the licensed frequency band (B), in the step s52. If the result of the analysis in step sSl is negative, then the module 347 concludes, in step s57, that no change in the operation of the current mobile terminal 5 is necessary. After step s52 or step s57, the results analysis and decision module 347 ends consideration of the current mobile terminal 5 and starts considering the next mobile terminal 5.

If in step s50, the results analysis and decision module 347 determines that the current terminal 5 is operating in frequency band (B), then it proceeds to steps s53 where it checks whether or not the mobile terminal 5 is located within the estimated area of interference 17. If the mobile terminal 5 is not located within area 17, then the results analysis and decision module 347 will check, in step s54, whether or not the mobile terminal's transmission area 15a overlaps with coverage area 14 of the primary transmitter 4. If there is no overlap, then the results analysis and decision module 347 will conclude, in step s57, that no change in the operation of the current mobile terminal 5 is necessary and the results analysis and decision module 347 will start considering the next mobile terminal 5.

However, fin step s54, the results analysis and decision module 347 determines that there is an overlap, the processing proceeds to step s56, where a decision is made to limit the transmission power of the mobile terminal 5 in order to avoid interference. The amount by which the mobile terminal limits its transmission power depends on how close it is to the area of primary transmission. The results analysis and decision module 347 then proceeds to step s58.

At step s53, for mobile terminals 5 located within the area 17 of interference, the results analysis and decision module 347 will move to step s55, wherein a decision is made to disallow transmission in the licensed frequency band (B) for the current mobile terminal 5, and then the processing proceeds to step s58.

In step s58, the results analysis and decision module 347 determines whether handover is necessary (or indeed possible) for a mobile terminal 5 that is allowed to transmit at a limited power only, and for a mobile terminal 5 that is not allowed to transmit at all on the licensed frequency band (B). If handover is not deemed necessary (or not possible), the results analysis and decision module 347 ends its processing of the current mobile terminal 5, otherwise a handover decision is made first, in step s59.

The above steps are performed for at least those mobile terminals 5 that may cause interference to the primary users, although in this embodiment the steps are performed for all mobile terminals served by the master node 3. The decision made for each mobile terminal 5 is then communicated to them as discussed above with reference to the master node 3 and the secondary user control module 349 of Figure 3.

MAC Signalling Communication between peers of a communication system, such as the mobile terminals 5 and master node 3, is carried out according to standardised procedures. The Open System Interconnection (051) reference model describes the flow of data from one computer to another computer in a network, using a 7-layered protocol stack. As illustrated in Figure 6A, these logical layers are the Physical Layer (Layer 1), the Data Link Layer (Layer 2), the Network Layer (Layer 3), the Transport Layer (Layer 4), the Session Layer (Layer 5), the Presentation Layer (Layer 6), and the Application Layer (Layer 7), from the lowest to the highest layer, respectively.

Each logical layer has specific functions and handles a unique data format. When data flows from an upper layer to a lower layer, it is converted to the lower layer data format and a lower layer header is added to it. This process is called encapsulation. Conversely, when data flows from a lower layer to an upper layer, it is converted to the upper layer data format and the lower layer header is discarded.

The Physical Layer (Layer 1) specifies physical and electrical characteristics of the network, and handles the transmission of information over the network medium (i.e. cable or radio link).

The Data Link Layer (Layer 2) is the lowest layer in the OSI model that is concerned with addressing, i.e. labelling information with a particular destination location. The Data Link Layer is responsible for the final encapsulation of higher-level messages into frames that are sent over the network at the Physical Layer.

The Network Layer (Layer 3) performs routing and addressing and it is responsible for sending a data packet to its destination within an acceptable time period.

The Transport Layer (Layer 4) is responsible for end-to-end transport between end users. This layer performs buffering, ordering, flow control, and error checking to make sure that data is received in the correct sequence and without error.

Session Layer (Layer 5), Presentation Layer (Layer 6), and Application Layer (Layer 7) are often referred to as upper layers. These layers handle user connection and data formatting. In most network technologies, the differences between these three layers are blurred and their functions are often handled by one protocol.

With reference to Figure 6B, the Data Link Layer (Layer 2) will now be described in more detail. Data Link Layer protocols enhance the service to upper layers by increased reliability, security, and integrity. In addition, the Data Link Layer is responsible for medium access and scheduling. In LTE systems, due to its complex functions, the Data Link Layer (Layer 2) is divided into further layers, such as the Medium Access Control (MAC) Layer, the Packet Data Convergence Protocol (PDCP) Layer, and the Radio Link Control (RLC) Layer. The MAC Layer is the lowest part, close to the Physical Layer (Layer 1), and is responsible for controlling access to the physical medium. The PDCP Layer is responsible mainly for IP header compression and ciphering, and also supports lossless mobility in case of handovers and provides integrity protection to higher layer control protocols. The RLC layer comprises mainly Automatic Retransmission Request (ARQ) functionality and supports data segmentation and concatenation.

In LTE systems, the Radio Resource Control (RRC) protocol is the main controlling function in the master node 3, being responsible for establishing the radio bearers and configuring all the lower layers using RRC signalling between the master node 3 and the mobile terminals 5. The RRC Layer (Layer 3) performs a number of services and functions, such as broadcasting system information; paging; establishment, maintenance and release of an RRC connection between the mobile terminals 5 and the master node 3; security functions including key management; establishment, configuration, maintenance and release of radio bearers; mobility functions, quality of service management, mobile terminal measurement reporting and control of the reporting.

As shown above with reference to Figures GA and 6B, when a message is sent between two peers, it propagates through the protocol stack towards the lower layers, for transmission via the lowest layer, and on the receiving side, the message propagates all the way up to the peer layer in the receiving terminal. The route of messages is illustrated by the arrows in Figure 6A. For example, in LTE systems, a Layer 3 message is created on the RRC Layer and then it is processed by the PDCF layer, the RLC layer, the MAC layer, and the Physical Layer that handles the actual transmission between the mobile terminal 5 and the master node 3 (or vice versa), and after transmission to the receiving device, the message is processed again, first by the MAC layer, then the RLC layer, the PDCF layer, before it is finally delivered to the RRC layer where it is actioned. Although the logical structure of the layered protocol stack guarantees that each function is performed on the layer where it is most applicable, in interference situations, the layered architecture can introduce unnecessary delays in handling information on the apparition of a primary transmitter 4. Therefore, as will be described in more detail below, in order to inform the master node of the primary user transmission as quickly as possible, the sensor nodes are configured to transmit their control data indicating that they have sensed a primary user transmission at the MAC layer, rather than a higher layer that might typically be used.

As discussed above, when a sensor mobile terminal 5 detects the transmission of the primary transmitter 4, the sensor mobile terminal 5 measures the received power of the primary user signal and informs the master node 3 of the detected transmission and the strength of the primary user signal as received by the sensor node. In this embodiment, the measured power of transmission is reported to the master node 3 in a MAC layer signalling message that will be processed and actioned by the MAC layer of the master node 3.

Figure 7A illustrates the MAC protocol data unit 71 (PDU) used in this embodiment. A MAC PDU 71 is also commonly known as a frame, and is the unit of information that can be delivered between peers on the Data Link Layer (Layer 2). The main parts of a MAC PDU 71 are the header 72, which comprises frame control fields 73, a sequence number field 74, and address fields 75 (some of these elements might be referred to as sub-headers). The header elements define the transmission related characteristics of the MAC PDU 71, such as sender/addressee, control parameters, order of frame in a sequence of units, quality of service, whether the contents are being retransmitted etc.. The MAC service data unit 76 (SDU) contains the data intended for upper layers (e.g. RLC, PDCF, and RRC layers) to process. At the end of the MAC PDU 71 is an error detection code 79, which is usually a cyclic redundancy check (CRC) field.

In a similar fashion, the MAC layer SDU 76 might comprises a PDU 171 of a higher layer. However, if a higher layer PDU 171 does not fit within the MAC SDU 76, it will be split across several consecutive MAC SDUs 76; the technique is known as segmentation. Once all of the segments of a split higher layer PDLJ 171 have been received by the higher layer, it will be processed at the higher layer, or it will be passed on to a higher layer still. Thus the contents of the higher layer PDU 171 are processed relatively slowly compared to the header 72 of the MAC PDLJ 71.

As shown in Figure 7B, the higher layer PDU 171 also contains frame control fields 173, a sequence number field 173, address fields 175, and an SDU 176 for another layer, and also an error detection code 179.

The term used to describe the part of MAC PDU 71 after the header 72 is the payload' 78. Not all of the payload 78 is always intended for a higher layer. The frame control fields 73 might indicate the presence of one or more MAC control elements 77 in the payload 78 that are intended for the MAC layer itself, thus such control element 77 will not be sent to the higher layer. Not all MAC PDUs 71 contain a control element 77 and different MAC PDU5 71 may contain different control elements 77 as they generally don't relate to the MAC SDU 76 carrying higher layer data.

A control element 77 is always inserted as the first part of the MAC SDU 76, thus before any part of the higher layer PDU 171 is inserted. This priority guarantees that a control element 77 is processed before any higher layer data is delivered, thus any information contained therein will be processed by the master node 3 much faster than regular higher layer signalling messages, such as Radio Resource Control (RRC) messages. In this embodiment, the sensor mobile terminals 5 include the received power value in a control element 77 of the MAC signalling message (MAC PDU 71) sent from the sensor mobile terminal 5 to the master node 3. Such a control element 77 may be added to any MAC frame 71 and thus can be sent without delay.

After defining the area 17 of possible interference, the master node 3 sends, to each mobile terminal 5 causing interference, a MAC signalling message which includes the received power value in a suitable control element 77 of the MAC PDU 71. This way, the master node 3 can notify all mobile terminals 5 which need to stop transmission in the licensed band (B).

In order to implement the notification at the MAC layer, a new specific control element 77 is required in the uplink (notification from the sensor mobile terminals 5 to the master node 3), and another one in the downlink (notification from the master node 3 to mobile terminals 5). One possible format for these two new MAC control elements is shown in Figure 7C.

The MAC control element 77 has a fixed size and comprises a single octet as follows. The first two bits, bi and b2, are reserved bits, set to "0", or in this case, marked "R". The remaining bits, b3 to b8, contain a binary value corresponding to the primary received power, which is the signal level or power of the detected primary user transmission as measured at the sensor mobile terminal 5.

The presence of the control element 77 within the payload 78 is indicated by data within the frame control fields 73. In [TE systems, this frame control field data is defined by the "Logical Channel ID" (LCID) field. As we have introduced a new MAC control element 77, a new LCID has to be defined to identify the two new types of control elements 77. One possible set of LCID values that can be used for the uplink and downlink are shown in the tables below: Values of LCID for uplink Index [CID values 00000 CCCH 00001-01010 Identity of the logical channel 11000 Reserved 11001 Primary Received Power 11010 Power Headroom Report 11011 C-RNTI 11100 Truncated BSR 11101 ShortBSR 11110 L0ngBSR 11111 Padding Values of LCID for downlink Index LCID values 00000 CCCH 00001-01010 Identity of the logical channel 01011-11010 Reserved 11011 Primary Received Power 11100 UE Contention Resolution Identity 11101 Timing Advance Command 11110 DRXCommand 11111 Padding Whenever the appropriate LCID values are used in a MAC PDU 71 transmitted between the sensor mobile terminal 5 and the master node 3, the recipient will know that a MAC control element 77 is present and it will be processed at the data link layer (MAC layer). For example, the value of the primary transmission power from the control element 77 will be extracted from the MAC control element 77 by the MAC layer and used as an input for the result analysis and decision module 347 of the master node 3.

Uplink grant In an LTE system, the mobile terminals 5, including sensor mobile terminals 5 have to have been allocated uplink resources for the node to be able to transmit uplink data (including the above MAC signalling messages). Therefore, the S allocation of these uplink resources can affect the ability of the mobile terminal 5 to send the measurement report. There are three possible situations that should be considered: i) a mobile terminal 5 has been allocated sufficient uplink resources to meet its current data transmission needs, ii) a mobile terminal 5 has been allocated some uplink resources, but these do not meet its current data transmission needs, iii) a mobile terminal 5 has not been allocated any uplink resources, either because it does not have any data to send on the uplink, or for other reasons, such as a temporary overload situation in the LTE system.

Sensor mobile terminals 5 that have some uplink resource allocation (situation i or U) will be able to inform the master node 3 immediately that they detect the apparftion of the primary user 4 using the allocated resources. However, sensor mobile terminals 5 that are not actively transmitting data to the master node 3, may not have any uplink resources granted (i.e. the third situation above), and thus they might not be able to send information immediately on the received power of a detected primary user transmission. In the absence of dedicated uplink resources, such sensor mobile terminals 5 may be configured to send this information on a common channel or a signalling channel. If such channels cannot be used, the sensor mobile terminals 5 may initiate setting up a new data connection towards the master node 3 for sending the information on the received power of the primary user transmission. In LTE systems, this is called a random access procedure, whereby a new connection may be set up between the master node 3 and the mobile terminal 5, and it is illustrated in Figure 8.

As the Physical Layer (Layer 1) is shared among all the mobile terminals 5 within the cell 13, the procedure for starting communication in the uplink direction is implemented according to the following.

In step s81, the sensor mobile terminal 5 requests uplink resources, which are controlled by the master node 3. In LTE systems, this comprises the Random Access Preamble message, which is generated on the MAC layer and sent by the mobile terminal 5 to the master node 3 on the random access channel.

In step s83, the master node 3 informs the sensor mobile terminal 5 about the successful allocation of uplink resources, so that the sensor mobile terminal 5 can begin its transmission on the allocated channel. In LTE systems, this comprises the Random Access Response message, which is generated on the MAC layer by the master node 3 and contains the Cell Radio Network Temporary Identifier (C-RNTI) that uniquely identifies the mobile terminal 5. Using the Random Access Response message, the master node 3 informs the mobile terminal 5 about the correct timing-advance value to be used for subsequent transmissions and grants the first resources for an uplink transmission.

The sensor mobile terminal 5 is now able to inform the master node 3 about the apparition of the primary transmitter 4, in step s85, the mobile terminal 5 sends the uplink data using the allocated resources in which it includes the measured signal power of the detected primary user transmission in a MAC control element 77 and in the manner discussed above. In LTE systems, this comprises the RRC Connection Request message, which is generated by the RRC layer, and carries the mobile terminal 5 identity (to identify the sender of the message) and the establishment cause (to identify reason for uplink resource request). According to the present embodiment, the measurement results are inserted as a MAC control element 77 in this message and are actioned by the master node 3 on the MAC layer (Layer 2) before or instead of passing the message up to the RRC layer (Layer 3).

The master node 3 acknowledges receipt of the measurement results n step s87 and is then able to control the operation of the mobile terminals 5 within its cell 13 in the manner described above.

As the overall load in the communications system increases, the likelihood of interference with the primary user 4 also increases, but at the same time, a number of mobile terminals 5 might not have uplink resources allocated to them, making it difficult for them to inform the master node 3 about the apparition of the primary user 4 on the licensed frequency band (B), These mobile terminals 5 may use the random access procedures described in the above embodiment.

Advantages The embodiments described above offer a number of advantages including: The duration of reporting and processing the measurements is reduced, as the MAC control elements 77 provide an almost instantaneous and simple means to inform the master node 3 about the apparition of the primary user 4.

At the same time, sensing accuracy is improved, as the master node 3 receives measurement reports from a number of sensor mobile terminals 5 that are positioned at locations closer to the primary user 4 than the master node 3.

The calculation of an area 17 of possible interference contributes to better utilization of the resources available in the licensed frequency band (B), as only those mobile terminals 5 that will be affected by the apparition of the primary user 4 need to be moved to a different frequency band in order to avoid interference.

Irrespective of the uplink resources granted to the sensor mobile terminals 5, they will always be able to send the measurement results using the same format, i.e. MAC control elements 77, thereby reducing design complexity of the mobile terminals 5 and the master node 3.

Modifications and Alternatives Detailed embodiments have been described above. As those skilled in the art will appreciate, a number of modifications and alternatives can be made to the above embodiments whilst still benefiting from the inventions embodied therein. By way of illustration only a number of these alternatives and modifications will now be described.

In the above embodiments, all of the sensor mobile terminals used to sense for primary user transmissions were secondary users -i.e. they transmitted in the licensed band (B) as well as sensing in the licensed band (B). In other embodiments, one or more of the sensor mobile terminals may not be secondary users. Instead, they may simply sense within the licensed band (B) and report their sensing results accordingly.

The term primary transmitter might also refer to a base station of a wireless communications network, and also to any user stations served by such a base station within its coverage area. The received power of the primary user transmission might not represent an accurate measurement, for example, the sensor mobile terminals might estimate or derive a comparative level of the transmit power, e.g. by applying various quantization techniques.

In an embodiment where the invention is implemented in an LTE system, the master node will typically be formed by an LTE base station. Multiple base stations are provided in an LTE system and they may each operate as masters controlling sensor mobile terminals (typically user devices such as cellular telephones) within its cell(s). The base stations may operate autonomously in a de-centralised manner taking decisions about their respective localities without communicating with a higher network entity. The base stations may also co-operate with each other exchanging information over their "X2" inter-face and taking decisions based on information received from neighbouring base stations.

Although various aspects of the invention have been illustrated using a specific implementation of the MAC protocol according to an LTE system, other systems and various low-layer protocols might be used as well. The use of control elements have been demonstrated, but any other part of a MAC protocol (or other low-layer protocol) message may be used, such as a header, a sub-header, a control element, or payload.

Although various acknowledgement messages have been suggested to confirm receipt of the measurement results at the master node, in one embodiment, the sensor mobile terminals will stop using the primary licensed band immediately, i.e. before receiving such an acknowledgement message. In another embodiment, sensor mobile terminals that are operable to use multiple frequency bands might be configured to notify the master node in a band other than the primary licensed band. These modifications will further reduce the interference caused by the secondary users.

In the embodiment illustrated in Figure 8, the sensor mobile terminal is configured to send the control element with the primary user signal measurement in the third message (after uplink resources have been granted). In an alternative embodiment, the sensor mobile terminal may include the control element in the first message of the uplink request procedure; while in another embodiment, the sensor mobile terminal might employ a signalling message that is part of another procedure to send the control element.

In the embodiment illustrated in Figure 8, the control element is sent by the sensor mobile terminal in the third message of the random access procedure to notify the master node of detected primary user transmissions within the licensed frequency band (B) and the control element is also used to provide signal measurements of the primary user transmissions to the master node.

In an alternative embodiment, the notification of the detected primary user transmissions is sent by the sensor mobile terminal in the first message of the random access procedure (i.e. the initial message of the random access procedure used to request uplink resources) and the signal measurements of the primary user transmissions may be provided in a subsequent message of the random access procedure, such as the third message (i.e. once the sensor mobile terminal has been allocated and granted uplink resources by the master node).

This may be particularly advantageous because it can enable a "no grant" terminal (either a mobile terminal that is in a connected mode, whereby the mobile terminal is connected with the master node without having been allocated any uplink resources or a mobile terminal that is in an idle mode, having no current ongoing services with the master node) to notify the master node of the apparition of a primary user despite not having been granted any uplink resources for commuriicaflon wfth the master node.

In this embodiment, the master node may select a subset of the mobile terminals to behave as sensor mobile terminals, the sensor mobile terminals being capable of notifying the master node of detected primary user transmissions within the licensed frequency band (B). As a limited number of mobile terminals are selected to act as sensor mobile terminals, this reduces the likelihood of any potential overload of the random access channel by multiple mobile terminals trying to access the random access channel at the same time.

A more detailed description of how this alternative embodiment may be implemented in an LTE communications system will now be given.

In the currently proposed LTE standards, mobile terminals that have not been allocated uplink resources use a Random Access Channel (RACH) to request resources from the base station (master node). The mobile terminals can access the RACH using a contention based technique or a non-contention based technique.

In the contention based technique, each mobile terminal selects a random access transmission opportunity and also randomly selects (or generates) a preamble for inclusion in an uplink request message to be sent to the master node. In response to receiving the uplink request message, the master node will reply with a message that allocates uplink resources to the mobile terminal. However, if two or more mobile terminals happen to randomly choose the same preamble and transmit on the same RACH at the same time, then a collision may occur and, due to the collision, the master node may not receive the transmitted messages. The master node is therefore unaware of the uplink request messages. If the resource allocation message is not received by the mobile terminal within a specified time period, the mobile terminal will assume that the master node has not received the uplink request message and will therefore re-transmit the message at a higher transmission power in the next available random access opportunity.

In the non-contention based technique, the master node assigns a unique preamble to each mobile terminal. The random access transmission opportunity can either be selected by each mobile terminal or assigned by the master node.

As each assigned preamble is unique to each mobile terminal, the mobile terminals do not contend for use of the RACH -they can share use at the same time. The contention for the RACH may also be eliminated by enabling the master node to assign different random access transmission opportunities to the different mobile terminals.

Contention based embodiment In an embodiment where the mobile devices use contention based techniques for accessing the RACH, the master node assigns a single reserved preamble that all of the sensor nodes should use to notify the master node of the detection of the primary user transmission. The reserved preamble may be included in system information broadcast by the master node to the mobile terminals.

More particularly, a new specific field "Primary_detection_specific_incumbent" can be defined within the system information in order to define the specific preamble (the reserved preamble) to use in the case of primary user transmission notification. This can be defined in the RACH-ConfigCommon" information element of the RadioResourceConfigCommon" element present with the SystemlnformationBlocks (SIBS) of the system information.

The RACH-ConfigCommon information element comprising the Primary_detection_specific_incumbent element may take the following format:

-- r --

-

---r I I 1(1 ft 2, I 2,I / , , /, I I, I Prinlary_detectionppeific_incurnbent b -I e - -I--p -1J I r -j2 -, 1, / -* / I I I T F, 1

--II I -1, I I /

---i----

-I C

II I -I1, I; , L -I I I" --II I ----ft 1/ - II-II,I-I L - I / I -, ---

--I

1 1 T / ft -, I, ---*i1 I -"--I

I-

--1 (1.), Definitions of most of the parameters in the system information block can be found in TS 36.321 vlO.4.O, the content of which is hereby incorporated by reference.

The new parameter that has been added is the Primary_detection_specific_incumbent_preamble parameter.

RACH-ConfigCommon field descriptions

mac-ContentionResolution Timer Timer for contention resolution in TS 36.321. Value in subframes. Value sf8 corresponds to 8 subframes, sf16 corresponds to 16 subframes and soon.

maxHARQ-Msg3Tx Maximum number of Msg3 HARQ (Hybrid Automatic Repeat Request) transmissions in TS 36.321, used for contention based random access. Value is an integer.

messageSizeGroupA Threshold for preamble selection in TS 36.321. Value in bits. Value b56 corresponds to 66 bits, b144 corresponds to 144 bits and so on.

messagePowerOffsetGmupB * Threshold for preamble selection in TS 36.321. Value in dB. Value minusinfinity corresponds to -infinity.

* Value dBO corresponds toO dB, dBS corresponds to 5dB and so on.

numberOfR.4-Preambles Number of non-dedicated random access preambles in TS 36.321. Value is an integer. Value n4 corresponds to 4, n8 corresponds to 8 and so on.

powerRamp!ngStep Power ramping factor in TS 36.321. Value in dB. Value dBO corresponds toO dB, dB2 corresponds to 2 dB andsoon.

preambleln!tialRece!vcdTargetPower Initial preamble power in TS 36.321. Value in dBm. Value dBm-120 corresponds to -120 dBm, dBm-118 corresponds to -118 dBm and so on.

preamblesGroupAConfig Provides the configuration for preamble grouping in TS 36.321. If the field is not signalled, the size of the random access preambles groupA is equal to numberO Tr2N!S preambleTransMax Maximum number of preamble transmission in TS 36.321. Value is an integer. Value n3 corresponds to 3, Primasyfietectionspecificjncumbentj,reamb!e * Dedicated preamble which can be used by UE to notify the Incumbent detection in opportunistic operational TV channel re-Response WindowSize Duration of the RA response window in TS 36.321. Value in subframes. Value sf2 corresponds to 2 subframes, sf3 corresponds to 3 subframes and so on.

sizeOfRA-PreamblesGroupA Size of the random access preambles group A in TS 36.321. Value is an integer. Value n4 corresponds to 4, n8 corresponds to 8 and so on.

The RACH-Config-Dedicated information element is used by the master node to specify dedicated random access parameters for each mobile terminal and may comprise the following format:

RACH-ConfigDedicated field descriptions

ra-PRACH-Maskindex ExphciflyfflgnailedPRACHMaskindexfo RA Resource selection in TS 36.32 f6 ra-Preamb!&ndex ExpIicitisig! n r1Acc!!Pr!rn InTS 116 ra-Preambleindex defines the reserved preamble that the mobile terminalshall use. This table is already defined in the TS36.321 because LTE mobile devices use dedicated preambles during the hand-over procedure. In particular, during [TE hand-over, the mobile device receives the RRCConnectionReconfiguration message from the source eNB (base station) with the parameters needed for the handover (i.e. new C-RNTI, target eNB security algorithm identifiers, and optionally dedicated RACH preamble, target eNB SIB5, etc.) and is commanded by the source eNB to perform the handover and accesses the target cell via RACH following a contention-free procedure using a dedicated RACH preamble. This dedicated preamble is defined by the above RACH-Config-Dedicated table. So, in this embodiment, the master node will re-use these RACH configuration parameters to broadcast the reserved preamble to be used to notify the master node of the apparition of the primary user..

ra-PRACH-Masklndex is a index which allows the master node to restrict when the mobile terminal can transmit a random preamble.

In this embodiment, the master node and the selected sensor mobile terminals store the specific reserved preamble in memory. Therefore, when a primary user transmission is detected by a mobile terminal, the mobile terminal sends an uplink request message, comprising the reserved preamble, to the master node. If the mobile terminal does not receive an acknowledgement indicating receipt of the uplink message from the master node within a specified time period, the mobile terminal will re-transmit the uplink request message at a higher transmission power.

When the master node receives and decodes the uplink request message, it compares the received preamble with the reserved preamble stored in memory. If the received preamble matches the stored preamble reserved for notifying detection of a primary user transmission, then the master node immediately ceases the granting of uplink resources to other mobile terminals within the licensed frequency band (B) pending receipt of the primary user signal level measurements from the notifying sensor mobile terminal, thus helping to prevent interference to the primary user transmissions in the licensed frequency band (B).

In order that the sensing mobile terminal can report the measured primary user signal level to the master node, the master node responds to the initial RACH message by sending a resource allocation message to the sensor mobile terminal.

The resources allocated by the master node will typically be in a frequency band outside the licensed frequency band (B), but they may be within the licensed frequency band (B) if desired.

After having been allocated the uplink resources, the sensor mobile terminal sends a message comprising the primary user signal measurements to the master node, initiates a timer and begins monitoring a physical downlink control channel (PDCCH) for a response from the master node within a pre-determined time period set by the timer.

In response to receiving the primary user signal measurements, the master node sends a contention resolution message back to the sensor mobile terminal, which contention resolution message provides an acknowledgement to the sensor mobile terminal that the primary user signal measurements have been received. If the master node does not receive the primary user signal measurements within a defined time period, then the master node may resume allocating uplink resources within the licensed frequency band (B) to the mobile terminals.

If the sensor mobile terminal does not receive the contention resolution message within a pre-determined time period, it assumes that the master node has not received the sent primary user measurements and then starts the notification process again by sending the master node the reserved preamble in another RACH attempt. If, however, the contention resolution message is received within the pre-determined time period, then the sensor mobile terminal stops transmitting in the licensed frequency band (B) (if it has not already done so).

In response to receiving the primary user signal measurements, as well as sending the contention resolution message to the sensor mobile terminal, the master node begins to selectively control, based on the received primary user measurements, each mobile terminal operating within the licensed frequency band (B), as described above with reference to Figure 4, and more particularly as follows.

In the case where the master node determines, based on the received signal measurements of the primary user transmission, that a mobile terminal transmitting within the licensed frequency band (B) is likely to cause interference to the primary user (for example, because the mobile terminal is within the transmission range of the primary user), then the master node controls that mobile terminal to cease transmission in the licensed frequency band (B). In this case, the master node may arrange for a hand-off of the mobile terminal to another frequency band. For example, where the licensed band represents a television channel, the master node may arrange for the selected mobile terminal to hand-off to another television channel. In this manner, the selected mobile terminal may experience continued services with the master node whilst allowing the primary user priority use of the licensed frequency band (B).

In the case where the master node determines, based on the received signal measurements of the primary user transmission, that a mobile terminal transmitting within the licensed frequency band (B) is likely to cause interference to a primary user but would not cause any interference to the primary user if the mobile terminal were to limit it's transmission power, then the master node controls the mobUe terminal to Iimft it's transmission power in the Ucerised frequency band (B).

In the case where the master node determines that a mobile terminal would not be likely to cause interference to a primary user (for example, because the mobile terminal is outside of a determined transmission range of the primary user), then the mobile terminal is allowed to continue operation in the licensed frequency band (B).

Of course, there will be instances where the mobile terminal wishes to establish a communications session with the master node using the contention-based RACH technique when the mobile terminal has not detected a primary user transmission.

In this case, the mobile terminal should not use the reserved preamble. As discussed above, the mobile terminal will use a randomly generated preamble to initiate the RACH procedure. In order to avoid erroneously informing the master node of a primary user transmission, the mobile terminal must therefore check that the randomly generated preamble is not the same as the reserved preamble. If it is determined that the randomly generated preamble matches the reserved preamble, then the mobile terminal proceeds to generate another preamble.

Non-contention based embodiment In an embodiment where the mobile devices use non-contention based techniques to inform the master node of the apparition of the primary user, the master node will assign two unique reserved preambles to each of the mobile terminals. One is reserved for notifying primary user apparition and the other is used for normal non-contention based RACH procedures. This embodiment operates similarly to the contention based embodiment except that each mobile terminal is allocated a different reserved preamble. Operation in this mode may only be practical where there are a small number of sensor terminals as there will normally be a limited number of preambles that can be reserved.

A further modification of the above embodiments includes using a different pad of the MAC PDU than a control element to send the primary user transmission information, such as in a suitable field of the header or sub-headers. Some of these fields may be sent to a higher level for processing without departing from the scope of the claims.

In the above embodiments, the transmission power of some mobile terminals was limited in order to avoid interference. Instead of or in addition to limiting the transmit power, directional antennas may be used by the mobile terminals (and the master node) and the transmission direction of the transmitted signals may be changed to avoid interference with the primary user. In this way, the master node and the mobile terminals can continue using the licensed band by directing their signals away from the primary transmitter (while outside its coverage area).

In the above embodiments, a number of nodes have been described. As those skilled in the art will appreciate, such nodes may comprise any kind of communications node or device, including access points and user devices such as, for example, mobile telephones, personal digital assistants, laptop computers, web browsers, etc. In the above embodiments, a number of software modules were described. As those skilled in the art will appreciate, the software modules may be provided in compiled or un-compiled form and may be supplied to the cognitive node as a signal over a computer network, or on a recording medium. Further, the functionality performed by pad or all of this software may be performed using one or more dedicated hardware circuits. However, the use of software modules is preferred as it facilitates the updating of the node in order to update its functionality. Similarly, although the above embodiments employed transceiver circuitry, at least some of the functionality of the transceiver circuitry can be performed by software.

Various other modifications will be apparent to those skilled in the art and will not be described in further detail here.

Claims

<claim-text>Claims 1. A master node for use with a plurality of mobile nodes, the master node comprising: receiving means for receiving from at least one of the mobile nodes primary user transmission information indicative of a signal strength of a primary user transmission received at the at least one mobile node; obtaining means for obtaining position information for each of the at least one mobile node; estimating means for estimating an area of possible transmission overlap between the master node and the primary user using the received primary user transmission information and the obtained position information; comparing means for comparing the location of each mobile node with the estimated area of possible transmission overlap; and control means for controlling the operation of the mobile nodes in dependence upon a result of the comparison in order to avoid interference to the primary user by the master node and the mobile nodes.</claim-text> <claim-text>2. A master node according to claim 1, wherein the receiving means is operable to receive the information in a Medium Access Control, MAC, control element.</claim-text> <claim-text>3. A master node according to claim 1, wherein the obtaining means is operable to obtain the position information for each of the at least one mobile node from the mobile node.</claim-text> <claim-text>4. A master node according to any one of claims 1 to 3, wherein the obtaining means is operable to obtain the position information for each of the at least one mobile node from a positioning system or from communications with other master nodes.</claim-text> <claim-text>5. A master node according to any preceding claim, wherein the control means is operable to control the operation of the mobile nodes using at least one of: preventing use of the band of the primary user transmission, performing a handover to a different band than the band of the primary user transmission, limiting a transmission power of the mobile node in the band of the primary user transmission, and allowing the mobile node to continue transmission in the band of the primary user transmission.</claim-text> <claim-text>6. A master node according to any preceding claim, wherein the control means is operable to control a transmission power and/or a transmission direction of the master node in the band of the primary user transmission in order to avoid interference to the primary user.</claim-text> <claim-text>7. A master node according to any preceding claim, wherein the control means is operable to send the primary user transmission information within a MAC control element to at least one of the plurality of mobile nodes for causing the at least one mobile node to stop its transmission within the band of the primary user transmission.</claim-text> <claim-text>8. A sensor node for use with a master node, the sensor node and master node being operable to communicate with each other within a licensed operating band of a primary user device, the sensor node comprising: sensing means for sensing a transmission of the primary user device; measuring means for determining a measure of a signal strength of the sensed primary user transmission; and reporting means for reporting the determined signal strength measure to the master node; wherein the reporting means is operable to report the determined signal strength measure within a Medium Access Control, MAC, layer frame for processing by a MAC entity within the master node.</claim-text> <claim-text>9. A sensor node according to claim 8, wherein the reporting means is operable to report the determined signal strength measure within a MAC control element.</claim-text> <claim-text>10. A sensor node according to claims 8 or 9, wherein the reporting means is operable to report an indication of the position information for the sensor node.</claim-text> <claim-text>11. A sensor node according to any one of claims 8 to 10, wherein the sensor node is operable to stop its transmission in the band of the primary user transmission.</claim-text> <claim-text>12. A sensor node according to claim 11, wherein the sensor node is operable to stop its transmission in the band of the primary user transmission after receiving an acknowledgement from the master node.</claim-text> <claim-text>13. A master node for use with a plurality of mobile nodes, the master node comprising: receiving means for receiving from at least one of the mobile nodes primary user transmission information indicative of a signal strength of a primary user transmission received at the at least one mobile node; and control means for controlling the operation of the mobile nodes in dependence upon the received primary user transmission information to avoid interference to the primary user by the master node and the mobile nodes; wherein the receiving means operates at a Medium Access Control, MAC, layer of the master node and is arranged to extract the primary user transmission information from a MAC layer frame.</claim-text> <claim-text>14. A master node according to claim 13, wherein the receiving means is operable to receive the primary user transmission information within a MAC control element.</claim-text> <claim-text>15. A master node according to claims 13 or 14, further comprising sending means for sending an acknowledgement to the at least one mobile node for causing the mobile node to stop its transmission within the band of the primary user transmission.</claim-text> <claim-text>16. A master node according to claims 13 or 14, further comprising sending means for sending the primary user transmission information within a MAC control element to at least one of the plurality of mobile nodes for causing the at least one mobile node to stop its transmission within the band of the primary user transmission.</claim-text> <claim-text>17. A sensor node for use with a master node, the sensor node and master node being operable to communicate with each other within a licensed operating band of a primary user device, the sensor node comprising: communications control means for receiving upl ink resource allocation data indicating uplink resources that the sensor node can use for transmitting data to the master node; sensing means for sensing a transmission of the primary user device; reporting means for reporting a determined signal strength measure to the master node using uplink resources allocated by the master node; wherein if the sensing means senses the primary user transmission at a time when the sensor node has not been allocated uplink resources, the communications control means is arranged to request uplink resource allocation from the master node.</claim-text> <claim-text>18. A sensor node according to claim 17, wherein the reporting means is operable to report primary user transmission information, indicative of the sensed primary user transmission, in a message sent by the sensor node as part of a Random Access Procedure.</claim-text> <claim-text>19. A sensor node according to claim 18, wherein the message is an uplink request message of the Random Access Procedure and comprises a reserved preamble that notifies the master node of detection of the primary user transmission within the licensed operating band.</claim-text> <claim-text>20. A sensor node according to claim 18, wherein the reporting means is operable to report said primary user transmission information within a MAC control element.</claim-text> <claim-text>21. A sensor node according to any of claims 18 to 20, wherein the reporting means is operable to report said determined signal strength measure, after uplink resources have been granted to the sensor node, in a further message sent by the sensor node as part of the Random Access Procedure.</claim-text> <claim-text>22. A master node for use with a plurality of mobile nodes, the master node comprising: receiving means for receiving from at least one of the mobile nodes primary user transmission information indicative of a signal strength of a primary user transmission received at the at least one mobile node; and control means for controlling the operation of the mobile nodes in dependence upon the received primary user transmission information to avoid interference to the primary user by the master node and the mobile nodes; wherein the receiving means is operable to receive said primary user transmission information within a message sent by the at least one mobile node as part of a Random Access Procedure.</claim-text> <claim-text>23. A master node according to claim 22, wherein the receiving means is operable to receive a notification of a sensed primary user transmission, in an uplink request message sent by the mobile node as part of a Random Access Procedure.</claim-text> <claim-text>24. A master node according to claim 23, wherein the uplink request message comprises a reserved preamble that notifies the master node of detection of the primary user transmission within the licensed operating band.</claim-text> <claim-text>25. A master node according to claim 24, wherein the control means is operable, in response to receiving the uplink request message comprising the reserved preamble, to control operation of the master node and the plurality of mobile nodes to avoid interference to the primary user by the master node and the mobile nodes.</claim-text> <claim-text>26. A master node according to claim 22, wherein the receiving means is operable to receive said primary user transmission information within a MAC control element.</claim-text> <claim-text>27. A master node according to any of claims 22 to 26, wherein the receiving means is operable to receive said primary user transmission information, after uplink resources have been granted to the mobile node, in a further message sent by the mobile node as pad of the Random Access Procedure.</claim-text> <claim-text>28. A sensor node for use with a master node, the sensor node and master node being operable to communicate with each other within a licensed operating band of a primary user device, the sensor node comprising: means for storing a reserved preamble; means for sensing a transmission of the primary user device; and means for notifying the master node of the sensed primary user transmission, wherein the means for notifying is arranged to notify the master node by sending the stored reserved preamble in an initial message of a Random Access procedure.</claim-text> <claim-text>29. A sensor node according to claim 28, wherein the sensor node further comprises means for receiving the reserved preamble as a part of system information broadcast by the master node.</claim-text> <claim-text>30. A sensor node according to claim 28 or 29, wherein the sensor node further comprises means for receiving an uplink resource allocation from the master node.</claim-text> <claim-text>31. A sensor node according to any of claims 28 to 30, wherein the sensor node further comprises means for determining a signal strength measurement of the primary user transmission and means for sending the signal strength measurement to the master node.</claim-text> <claim-text>32. A sensor node according to claim 31 when dependent upon claim 30, wherein the sensor node is arranged to send the determined signal strength to the master node using the uplink resource allocation received from the master node.</claim-text> <claim-text>33. A sensor node according to any of claims 28 to 32, wherein the sensor node further comprises means for randomly generating a preamble for use in a Random Access procedure.</claim-text> <claim-text>34. A sensor node according to claim 33, wherein the sensor node is operable to compare the randomly generated preamble with the stored reserved preamble, and when the randomly generated preamble matches the stored reserved preamble, the sensor node is operable to randomly generate another preamble for use in the Random Access procedure.</claim-text> <claim-text>35. A master node for use with a plurality of mobile nodes, the master node and mobile nodes being operable to communicate with each other within a licensed operating band of a primary user device, the master node comprising: means for receiving from at least one mobile node, an initial message of a Random Access procedure; means for processing the received initial message to determine whether or not the mobile node that transmitted the initial message has sensed a primary user transmission; and means for controlling operation of the mobile nodes to avoid interference to the primary user if the determining means determines that the mobile node that transmitted the initial message has sensed a primary user transmission.</claim-text> <claim-text>36. A master node according to claim 35, wherein the master node further comprises means for storing a reserved preamble used to indicate the sensing of a primary user transmission and wherein the processing means is arranged to determine if the preamble in the received initial message matches the stored reserved preamble and to determine that the mobile node that transmitted the initial message has sensed a primary user transmission if the received preamble matches the reserved preamble.</claim-text> <claim-text>37. A master node according to claim 36, wherein the master node further comprises means for sending the stored reserved preamble to the plurality of mobile nodes as a part of system information.</claim-text> <claim-text>38. A master node according to any of claims 35 to 37, wherein the control means is arranged, in response to the determining means determining that the mobile node that transmitted the initial message has sensed a primary user transmission, to cease transmissions to other mobile terminals in the licensed operating band.</claim-text> <claim-text>39. A master node according to any of claims 35 to 38, wherein the master node further comprises means for sending an uplink resource allocation message to the mobile node that has sensed the primary user transmission.</claim-text> <claim-text>40. A master node according to any of claims 35 to 39, wherein the master node is operable to receive, from the mobile node, a signal strength measurement of the sensed primary user transmission and wherein the controlling means is arranged to re-determine control actions for each mobile node in light of the received signal strength measurement.</claim-text> <claim-text>41. A communications system comprising a plurality of mobile nodes and the master node according to any one of claims ito 7, 13 to 16, 22 to 27, and 35 to 40.</claim-text> <claim-text>42. A method performed by a master node that communicates with a plurality of mobile nodes within a licensed operating band of a primary user device, the method comprising: receiving from at least one of the mobile nodes primary user transmission information indicative of a signal strength of a primary user transmission received at the at least one mobile node; obtaining position information for each of the at least one mobile node; estimating an area of possible transmission overlap between the master node and the primary user using the received primary user transmission information and the obtained position information; comparing the location of each mobile node with the estimated area of possible transmission overlap; and controlling the operation of the mobile nodes in dependence upon a result of the comparison in order to avoid interference to the primary user by the master node and the mobile nodes.</claim-text> <claim-text>43. A method according to claim 42, wherein the information is received in a Medium Access Control, MAC, control element.</claim-text> <claim-text>44. A method according to claims 42 or 43, wherein the obtaining step comprises obtaining the position information for each of the at least one mobile node from the respective mobile nodes.</claim-text> <claim-text>45. A method according to any one of claims 42 or 43, wherein the obtaining step comprises obtaining the position information for each of the at least one mobile node from a position system or from communications with other master nodes.</claim-text> <claim-text>46. A method according to any one of claims 42 to 45, wherein the controlling the operation of the mobile nodes comprises at least one of: preventing use of the band of the primary user transmission, performing a handover to a different band than the band of the primary user transmission, limiting a transmission power of the mobile nodes in the band of the primary user transmission, and allowing the mobile nodes to continue transmission in the band of the primary user transmission.</claim-text> <claim-text>47. A method according to any one of claims 42 to 46, wherein the controlling step comprises controlling a transmission power and/or a transmission direction of the master node in the band of the primary user transmission in order to avoid interference to the primary user.</claim-text> <claim-text>48. A method according to any one of claims 42 to 47, wherein controlling step comprises sending the primary user transmission information within a MAC control element to at least one of the plurality of mobile nodes for causing the at least one mobile node to stop its transmission within the band of the primary user transmission.</claim-text> <claim-text>49. A method performed by a master node that communicates with a plurality of mobile nodes within a licensed operating band of a primary user device, the method comprising: receiving from at least one of the mobile nodes primary user transmission information indicative of a signal strength of a primary user transmission received at the at least one mobile node; and controlling the operation of the mobile nodes in dependence upon the received primary user transmission information to avoid interference to the primary user by the master node and the mobile nodes; wherein the receiving step is carried out at a Medium Access Control, MAC, layer of the master node and comprises extracting the primary user transmission information from a MAC layer frame.</claim-text> <claim-text>50. A method according to claim 49, wherein the receiving step comprises receiving the primary user transmission information within a MAC control element.</claim-text> <claim-text>51. A method according to claims 49 or 50, further comprising sending an acknowledgement to the at least one mobile node causing the mobile node stopping its transmission within the band of primary user transmission.</claim-text> <claim-text>52. A method according to claims 49 or 50, further comprising sending the primary user transmission information within a MAC control element to at least one of the plurality of mobile nodes for causing the at least one mobile node to stop its transmission within the band of the primary user transmission.</claim-text> <claim-text>53. A method performed by a mobile node that communicates with a master node within a licensed operating band of a primary user device, the method comprising: sensing a transmission of the primary user device; determining a measure of a signal strength of the sensed primary user transmission; and reporting the determined signal strength measure to the master node; wherein the reporting step comprises reporting the determined signal strength measure within a Medium Access Control, MAC, layer frame for processing by a MAC entity within the master node.</claim-text> <claim-text>54. A method according to claim 53, wherein the reporting step comprises reporting the determined signal strength measure within a MAC control element.</claim-text> <claim-text>55. A method according to claims 53 or 54, wherein the reporting step comprises reporting an indication of the band of primary user transmission.</claim-text> <claim-text>56. A method according to any one of claims 53 to 55, wherein the reporting step comprises reporting an indication of the position information for the sensor node.</claim-text> <claim-text>57. A method according to any one of claims 54 to 56, further comprising the mobile node stopping its transmission in the band of the primary user transmission.</claim-text> <claim-text>58. A method according to claim 57, wherein the step of stopping transmission in the band of the primary user transmission is preceded by a step of receiving an acknowledgement from the master node.</claim-text> <claim-text>59. A method performed by a mobile node that communicates with a master node within a licensed operating band of a primary user device, the method comprising: receiving uplink resource allocation data indicating uplink resources that the sensor node can use for transmissions data to the master node; sensing a transmission of the primary user device; reporting a determined signal strength measure to the master node using uplink resources allocated by the master node; wherein if at the sensing step the sensor node has not been allocated uplink resources, the reporting step further comprises requesting uplink resource allocation from the master node.</claim-text> <claim-text>60. A method according to claim 59, further comprising reporting the sensed primary user transmission, in a message sent by the sensor node as part of a Random Access Procedure.</claim-text> <claim-text>61. A method according to claim 60, wherein the message is an uplink request message of the Random Access Procedure and comprises a reserved preamble that notifies the master node of detection of the primary user transmission within the licensed operating band.</claim-text> <claim-text>62. A method according to claim 59, wherein the reporting step is part of a Random Access Procedure.</claim-text> <claim-text>63. A method according to claims 59 or 60, wherein the determined signal strength measure is reported within a MAC control element.</claim-text> <claim-text>64. A method according to claims 59 to 63, wherein the determined signal strength measure is reported, after uplink resources have been granted to the sensor node, in a further message sent by the sensor node as part of the Random Access Procedure.</claim-text> <claim-text>65. A method performed by a master node that communicates with a plurality of mobile nodes within a licensed operating band of a primary user device, the method comprising: receiving from at least one of the mobile nodes primary user transmission information indicative of a signal strength of a primary user transmission received at the at least one mobile node; and controlling the operation of the mobile nodes in dependence upon the received primary user transmission information to avoid interference to the primary user by the master node and the mobile nodes; wherein the receiving step comprises receiving said primary user transmission information within a message sent by the at least one mobile node as part of a Random Access Procedure.</claim-text> <claim-text>66. A method according to claim 65, further comprising receiving a notification of a sensed primary user transmission, in an uplink request message sent by the sensor node as part of a Random Access Procedure.</claim-text> <claim-text>67. A method according to claim 66, wherein the uplink request message comprises a reserved preamble that notifies the master node of detection of the primary user transmission within the licensed operating band.</claim-text> <claim-text>68. A method according to claim 67, wherein the controlling the operation comprises, in response to receiving the uplink request message, controlling operation of the plurality of mobile nodes to avoid interference to the primary user by the master node and the mobile nodes.</claim-text> <claim-text>69. A method according to any of claims 65 to 68, wherein said primary user transmission information is received within a MAC control element.</claim-text> <claim-text>70. A method according to any of claims 65 to 68, wherein the controlling the operation comprises sending the primary user transmission information within a MAC control element to at least one of the plurality of mobile nodes for causing the at least one mobile node to stop its transmission within the band of the primary user transmission.</claim-text> <claim-text>71. A method performed by a master node that communicates with a plurality of mobile nodes within a licensed operating band of a primary user device, the method comprising: receiving from at least one mobile node, an initial message of a Random Access procedure; processing the received initial message to determine whether of not the mobile node that transmitted the initial message has sensed a primary user transmission; and controlling operation of the mobile nodes to avoid interference to the primary user if it has been determined that the mobile node that transmitted the initial message has sensed a primary user transmission.</claim-text> <claim-text>72. A method according to claim 71, further comprising storing, at the master node, a reserved preamble used to indicate the sensing of a primary user transmission and determining if the preamble in the received initial message matches the stored reserved preamble and determining that the mobile node that transmitted the initial message has sensed a primary user transmission if the received preamble matches the reserved preamble.</claim-text> <claim-text>73. A method according to claim 71 or 72, further comprising sending the stored reserved preamble to the plurality of mobile nodes as a part of system information.</claim-text> <claim-text>74. A method according to any of claims 71 to 73, wherein the controlling the operation further comprises controlling the master node, in response to determining that the mobile node that transmitted the initial message has sensed a primary user transmission, to cease transmissions to other mobile terminals in the licensed operating band.</claim-text> <claim-text>75. A method according to any of claims 71 to 74, further comprising providing uplink resource allocation to the mobile node that sent the initial message.</claim-text> <claim-text>76. A method according to claim 74, further comprising receiving, from the mobile node, a signal strength measurement of the sensed primary user transmission and re-determining control actions for each mobile node in light of the received signal strength measurement.</claim-text> <claim-text>77. A method performed by a sensor node that communicates with a master node within a licensed operating band of a primary user device, the method comprising: storing a reserved preamble; sensing a transmission of the primary user device; and notifying the master node of the sensed primary user transmission, wherein the means for notifying is arranged to notify the master node by sending the stored reserved preamble in an initial message of a Random Access procedure.</claim-text> <claim-text>78. A method according to claim 77, further comprising receiving the reserved preamble as a part of system information broadcast by the master node.</claim-text> <claim-text>79. A method according to claim 77 or 78, further comprising receiving an uplink resource allocation from the master node.</claim-text> <claim-text>80. A method according to any of claims 77 to 79, further comprising determining a signal strength measurement of the primary user transmission and sending the signal strength measurement to the master node.</claim-text> <claim-text>81. A method according to claim 80 when dependent upon claim 79, further comprising sending the determined signal strength to the master node using the uplink resource allocation received from the master node.</claim-text> <claim-text>82. A method according to any of claims 78 to 81, further comprising randomly generating a preamble for use in a Random Access procedure.</claim-text> <claim-text>83. A method according to claim 82, further comprising comparing the randomly generated preamble with the stored reserved preamble, and when the randomly generated preamble matches the stored reserved preamble, randomly generating another preamble for use in the Random Access procedure.</claim-text> <claim-text>84. A computer implementable instructions product comprising computer implementable instructions for causing a programmable communications node to become configured as the master node according to any one of claims 1 to 7,13to16,22to27,and35to4O.</claim-text> <claim-text>85. A computer implementable instructions product comprising computer implementable instructions for causing a programmable communications node to become configured as the sensor node according to any one of claims 8 to 12,17to21,and28to34.</claim-text>