GB2491837A

GB2491837A - Whitespace channel allocations in dependence on geographical location and an estimated coverage area of a communications station

Info

Publication number: GB2491837A
Application number: GB1109854.8A
Authority: GB
Inventors: William Webb; Neil Macmullen
Original assignee: Neul Ltd
Current assignee: Huawei Technologies Research and Development UK Ltd
Priority date: 2011-06-13
Filing date: 2011-06-13
Publication date: 2012-12-19
Also published as: GB201109854D0; WO2012171902A1

Abstract

An allocation system for allocating spectrum to a whitespace communications station, e.g. base station 21, comprises a database storing information indicating reserved channel allocations in a geographical area. The allocation system further comprises a channel selection unit that analyses the database so as to select a channel for use by the communications station 21 in dependence on a location of the communications station 21 within the geographical area and an estimated coverage area 22 of the communications station 21. The channel selection unit performs the analysis for a non-circular or irregular estimated coverage area 22. The estimated coverage area may be determined based upon environment, surrounding terrain, antenna elevation and/or radiation pattern, and/or transmitter power. The channel selection unit may select the channel additionally in dependence of an estimation of interference with other entities.

Description

Allocating whitespace spectrum The present invention relates to systems, methods and computer programs for allocating whitespace spectrum and whitespace communications stations.

The radio frequency spectrum is managed under two different regimes, licensed and unlicensed. In the licensed regime, a national regulator assigns a, typically exclusive, right to operate a radio system. The assignment is typically limited in terms of the permitted spectrum band, the permitted geographic area and the permitted time of usage. The regulator chooses each assignment to prevent harmful interference to other users.

The unlicensed regime does not have exclusive assignments. Any number of users may operate any device that meets certain technical and operating restrictions in an unlicensed frequency band. The regulator sets these restrictions to minimize potential interference. However, the unlicensed operation of devices leads to interference from other unlicensed devices and can cause the devices to fail.

In some countries, regulators have mixed the two regimes to form the so-called "whitespace spectrum". In some cases, whitespace spectrum is being made available within existing television broadcasting bands. In the UK, for example, whitespaces are being made available in the TV frequency bands between around 470MHz and 790MHz. The bands available for use vary from country to country.

This part of the spectrum has advantages of excellent propagation and expected availability without requiring payments.

Many wireless uses for the whitespace spectrum have been proposed, such as machine-to-machine (M2M) communication, broadband for rural areas, multimedia delivery, monitoring of vehicles, tracking goods, traffic management, remote health monitoring, environmental monitoring, defence and security.

Use of the whitespace would involve communication devices (hereinafter referred to as "terminals") consulting a whitespace database. It is proposed that a central whitespace database provided by regulators would provide a list of available spectrum for a given time and location.

Use of the whitespace would be expected to involve: -operating in an uncertain environment where the frequency availability is not guaranteed and may change from location to location and time to time; -operating in an unlicensed environment where the interference caused by other unlicensed terminals cannot be predicted and must be avoided; -minimising interference to licensed users, particularly TV receivers, by adopting technical approaches that result in the smallest possible increase in bit error rate (BER) for TV receivers for a given level of interference; and -acting as a "good neighbour" to other users of the white space by not monopolising resources or causing unnecessary interference or blocking.

Thus there is a need to manage the whitespace efficiently to meet the above challenges. Current proposals for the use of whitespace by devibes require terminals to access a whitespace database to determine which parts of the whitespace are available for the terminal to use. The terminals provide the database with their location and the database returns spectrum availability within that location.

The terminals can communicate to outside networks (e.g. the internet) and the whitespace database through a base station.

Under some proposals, for example in the UK, a base station would contact the database for a list of available channels. The base station would provide its model identification, location, height and maximum coverage radius. The database will return the channels and the validity time, setting the time period before another database enquiry is needed.

A circular theoretical coverage area can be determined based on the maximum coverage radius. The maximum coverage radius can be determined as the maximum range of the base station assuming that there are no entities surrounding the base station which can interfere with its signal. Beyond the maximum coverage radius, the signal from the base station would be too weak to cause significant interference to other entities. Thus it is advantageous to use the maximum coverage radius to determine the theoretical coverage area as it provides a simple and reliable assumption of interference potential of the base station to other entities, especially in view of the requirements to minimise interference on licensed operators.

Furthermore, by providing a simple circular theoretical coverage area, rather than a more complicated model, less data is required for specifying the coverage area to the database. This, in turn, provides a faster, simpler and cheaper system as less data needs to be sent to the database, simple protocols can be adopted in communicating with the base station, the processing required to determine the coverage area is lower and less storage space is required to store coverage area data. The coverage area data may also be sent to terminals, thus it would be an advantage to send less data, especially to smaller mobile terminals which may have lower processing and storage capabilities.

However this proposal would lead to inefficient use of the whitespace as the theoretical coverage area, which is determined from the maximum coverage radius, would be larger than in practice and so assumes greater interference potential than will occur in practice.

This invention can help to provide systems, methods and computer programs for allocating whitespace spectrum and whitespace communications stations which, at least partially, can help overcome the abovementioned problems and challenges.

The present invention can also help to provide a network for low-cost communications utilising low-frequency spectrum and techniques that enable communications over a high range.

According to an aspect of the invention, there is provided an allocation system for allocating spectrum to a whitespace communications station, the system comprising: a database configured to store information indicating reserved channel allocations in a geographical area; and a channel selection unit configured to analyse the database so as to select a channel for use by the communications station in dependence on a location of the communications station within the geographical area and an estimated coverage area of the communications station about its location, wherein the channel selection unit is configured to perform the said analysis for a non-circular estimated coverage area.

By performing the analysis for a non-circular estimated coverage area, a more accurate representation of the actual coverage area of the communications station (which can be a base station) can be provided. An estimated non-circular coverage area avoids the unnecessary removal from the list of available frequencies of a whitespace spectrum channel only used in a geographical area that does not fall within the range of the communications station but does fall within a simple circular estimated coverage area. Thus, a more efficient use of the whitespace spectrum is possible as more whitespace channels will be available for allocation in given areas as fewer channels will be unnecessarily excluded.

Furthermore, a more accurately estimated coverage area provided by a non-circular estimated coverage area, can lead to an increase in the signal quality and reliability of communication with, for example, terminals. For example, in the case of an inaccurately determined coverage area, a terminal may be located within the determined coverage area but may still be out of communication range with the communications station. By more accurately estimating the coverage area of that communications station and surrounding communications stations, the same terminal may fall out of the estimated coverage area of that communications station and into the estimated coverage area of another communications station that is within communication range of that terminal.

The channel selection unit can be further configured to perform the said analysis for an irregular estimated coverage area. An irregular estimated coverage area allows for greater accuracy in modelling the actual coverage area. The estimated coverage area can be shaped to fit around entities (which may be irregularly shaped) that cause blocking or interference. This provides a more a more efficient use of the whitespace spectrum and more reliable communication, as mentioned above.

The estimated coverage area can be determined based on one or more of the following: environment; location; surrounding terrain; antenna elevation above ground 1ev antenna radiation pattern an transmitter power. An accurate determination of the estimated coverage area provides more efficient use of the whitespace spectrum. The range of a communications station may be limited by, for example, its surroundings. For example, greater attenuation of the signal from the communications station can occur in certain environmental conditions, such as thunder storms. This would lead to a reduction in the communication range of the communications station in the area of the thunder storm. By considering the presence of the storm, the actual coverage area can be estimated more accurately.

Another example is that of hills or buildings close to the communications station that may cause the signals from the communications station to be attenuated or blocked.

By considering the terrain surrounding the communications station, a more accurate estimation of the coverage area can be provided. The radiation pattern of the communication station's antenna may also be considered when determining the estimated coverage area. The radiation pattern may not be isotropic and the antenna may have different gain factors in different directions. By considering the radiation pattern of the antenna, a more accurate determination of the coverage area can be estimated. The transmitter power can also be considered when determining the estimated coverage area. For example, the power of the transmitter may be changeable, rather than fixed. In one example, the power may be increased to compensate for the increased attenuation during a thunderstorm. In another example, the power may be decreased to decrease the actual coverage area to minimise interference with licensed operators. By considering the transmitter power, a more accurate determination of the coverage area can be estimated. By using the abovementioned factors when determining the estimated coverage area, a more accurate model of the coverage area can be determined. Using a combination of the factors can lead to a more accurate model of the coverage area. As mentioned above, an accurate estimation of the coverage area can lead to more efficient use of the whitespace spectrum and higher quality, more reliable communication.

The communications station can comprise more than one antenna, wherein each antenna has its own estimated coverage area. By providing more than one antenna, the capacity of the communications station can be increased. For example, the communications station may comprise two directional antennas, each antenna having a radiation pattern that is directed in opposing directions. Thus each antenna may have its own coverage area with its own channel allocated to it, thus doubling the bandwidth of the base station.

The channel selection unit can be further configured to analyse the database so as to select a channel that is not reserved for a location within the estimated coverage area. By selecting a channel that is not used by other entities within the estimated coverage area, the likelihood of interference is decreased and thus more reliable and efficient communication can take place. The reservation of a channel for a particular location can be for a particular period of time. In one example of a frequency hopping system, a first communications station, that has an overlapping estimated coverage area with a second communications station, can be allocated the same channel as the second communications station for a different periods of time (such that both communications systems do not communicate with same channel at the same time). Such a frequency hopping system can help provide more reliable communication, for example in the case that there is limited availability of whitespace spectrum.

The channel selection unit can be further configured to select the channel additionally in dependence of a first interference calculation, wherein the first interference calculation estimates the interference caused by the communications station to other entities and the interference caused by other entities to the communications station. The reliability, signal quality and performance of the communications station and the terminal can be increased by communicating in a part of the whitespace spectrum that will be less susceptible to interference. The first interference calculation can be used to determine the interference that may be caused by other entities (such as other RF devices, etc...) and the interference caused to other entities (such as adjacent communications stations). By calculating the potential interference, a channel of the whitespace spectrum can be determined for a communications station that would be less susceptible to interference. This would provide more efficient and reliable use of the whitespace spectrum as channels of the whitespace spectrum can be allocated such that interference is minimised on other entities (such as licensed operators and other base stations) and the interference caused by other entities is minimised on the communications station.

The first interference calculation can be based on an estimate of at least one of the following: the probability of interference caused by other communications stations; the probability of causing interference to other communication stations; and the probability of causing interference to licensed transceivers, wherein the licensed transceivers communicate using licensed spectrum. By utilising one or more of these probabilities, the accuracy of the first interference calculation can be increased, leading to the advantages mentioned above.

The system can further comprise a sub-channel selection unit configured to select a sub-channel for communication between the communications station and a terminal, wherein the sub-channel is preferentially a part of the channel selected by the channel selection unit. A sub-channel selection unit arranged to select the sub-channel can provide efficient utilisation of the whitespace spectrum and better communication performance. For example, in the case of a terminal close to the edge of the estimated coverage area of its communications station and near the estimated coverage area of another communications station or a licensed operator, the sub-channel selection unit can determine a communication sub-channel to allocate to that terminal so as to minimise interference with the other communications station as the sub-channel selection unit can analyse the database to determine which whitespace channel is allocated to the other communications station.

Alternatively or additionally, the communications station may comprise a sub- channel selection unit. In the case of a communications station selecting the sub-channel to communicate with the terminal, the communications station may not know which whitespace channels are allocated to the other communications stations, thus, the communications station may not be able to determine which sub-channel will provide the least interference. However, the communications station could communicate with the database in the allocation system, which can send reserved channel allocations data to the communications station so that the station is aware of the channels allocated to the surrounding communications stations. The communications station can select a sub-channel independently of the allocation system (after being allocated a channel). One advantage of this is that the location data of the terminals would not need to be sent to the allocation system, thus saving on bandwidth. Also, as the determination of the sub-channels would be carried out by the communications station, the allocation system would not need to carry out the processing and send the results to the communications station, thus saving on the processing overheads and communication bandwidth for the allocation system.

The sub-channel selection unit can be further configured to select the sub-channel additionally in dependence of a second interference calculation, wherein the second interference calculation estimates the interference caused by the terminal to other entities and the interference caused by other entities to the terminal. The reliability, signal quality and communication performance of the terminal can be increased by communicating in a sub-channel of the whitespace spectrum that will be less susceptible to interference. The second interference calculation can be used to determine the interference that may be caused by other entities (such as other RF devices, etc...) and the interference caused to other entities (such as other terminals). By calculating the potential interference, a sub-channel of the allocated whitespace spectrum channel can be determined for a terminal that would be less susceptible to interference. This would also provide more efficient use of the whitespace spectrum as the sub-channels can be allocated such that interference is minimised on other entities (such as other terminals within the same coverage area) and the interference caused by other entities is minimised on the terminal.

The second interference calculation can be based on an estimate of at least one of the following: the probability of interference caused by other communications stations; the probability of causing interference to other communications stations; the probability of causing interference to licensed transceivers, wherein the licensed transceivers communicate using licensed spectrum; the probability of interference caused by other terminals; and the probability of causing interference to other terminals. By utilising one or more of these probabilities, the accuracy of the second interference calculation can be increased, leading to the advantages mentioned above.

According to another aspect of the invention, there is provided a whitespace communications station, the communications station being capable of communicating on a channel allocated to it by an allocation system, and being configured to report to the allocation system information characterising an estimated coverage area of the communications station whereby the allocation system can allocate a channel to the communications station, the information characterising a non-circular estimated coverage area.

According to another aspect of the invention, there is provided a whitespace communications system comprising the allocation system and the communications station described above.

According to another aspect of the invention, there is provided a method for allocating whitespace spectrum, the method comprising the steps of: storing information indicating reserved channel allocations in a geographical area; and analysing the stored information so as to select a channel to allocate to a communications station in dependence on a location of a communications station within the geographical area and an estimated coverage area of the communications station about its location, wherein the analysing step is performed for a non-circular estimated coverage area. There is also provided a computer program for allocating whitespace spectrum, the computer program comprising code means that, when executed by a computer, will cause the computer to carry out the steps recited by this method.

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which: Figure 1 depicts the theoretical coverage area of a prior art system; Figure 2 depicts the coverage area of a base station used in a system according to the present invention; Figure 3 depicts a network of base stations used in a system according to the present invention; Figure 4 depicts a process for allocating a whitespace spectrum channel to a base station; and Figure 5 depicts a process for allocating a sub-channel of the whitespace spectrum channel to a terminal.

Figure 6 depicts a block diagram of a computer system and base stations.

Figure 1 depicts a prior art whitespace communication system 10. The prior art system 10 comprises a base station 11 and terminals TI, T2, T3 and T4. The use of whitespace may require certain factors to be considered, such as minimising interference to licensed users. Thus, it is convenient to take the maximum range of a base station to determine the coverage radius, which in turn is used to determine the theoretical coverage area of the base station. As shown in Figure 1, this leads to a circular theoretical coverage area 12. By using the maximum coverage radius to determine the theoretical coverage area 12, the potential for interference with other users is reduced.

However, in practice, the communication range of the base station II will not reach certain areas within the theoretical coverage area 12. As shown in Figure 1, entities that cause interference, such as buildings 13 and hills 14, can create areas and 16 where the signal to/from the base station is blocked and no effective communication is possible. Thus, terminals T2 and T3 would not be able to communicate with base station II. Other entities that can cause interference can include: trees, cranes, gasometers, football stadiums, wind farms and other such obstructions.

Certain atmospheric and environmental conditions can also cause a change in the range of the base station II. For example, thunderstorms can lead to increased attenuation of the signal from the base station II. This can lead to the reduction in the effective communication area of the base station, as depicted by dotted line 17. This may lead to terminals (e.g. terminal T4) close to the edge of the coverage area 12 unable to communicate with the base station 11.

The assumption, when allocating frequencies, of a circular theoretical coverage area leads to the inefficient use of the whitespace spectrum. The circular theoretical coverage area assumes a greater potential for interference than will occur in practice and thus certain geographic areas will fall within areas where effective communication is not possible.

Figure 2 depicts a communication system 20 with a whitespace communication station, such as a base station 21 and terminals TI, T2, T3 and T4.

The coverage area 22 of the base station 21 is non-circular. The perimeter of the coverage area 22 can be determined by the maximum distance (hereinafter referred to as the maximum effective distance) from the base station 21 in each direction that allows for effective communication. In the example shown in Figure 2, that distance is different in different directions due to entities that cause interference or blocking of the signal from the base station (such as buildings 23 or hills 24). The maximum effective distances from the base station are different in different directions. Thus the range of the base station 21 is different in different directions. In the case where there are no entities to cause interference or blocking, the maximum effective distance would be the same in all directions (assuming the base station is an isotropic radiator), leading to a circular coverage area.

Rather than estimating a circular coverage area like in the prior art, a more effective communication system can be provided by accurately estimating or modelling the coverage area 22 of the base station 21. For example, if the non-circular estimated coverage area of base station 21 was representative of the actual non-circular coverage area 22, terminals TI and T4 would faIl within the estimated coverage area of base station 21 and terminals T2 and T3 would not fall within the estimated coverage area of base station 21. However, it would be possible for terminals T2 and T3 to fall within the coverage areas of other base stations.

Providing alternative base stations for terminals T2 and T3 would not be possible with the prior art communication system 10, shown in Figure 1. Providing base stations with overlapping coverage areas may not be suitable for a whitespace system as this could lead to an unacceptable amount of interference between: the base stations; terminals within the overlapping coverage areas; and a terminal and a base station, wherein the terminal is not assigned to that particular base station.

Thus, in the prior art system, any communication between the base station and terminals T2 and T3 would be problematic.

The estimated coverage area can be irregular. The irregularity of the estimated coverage area can increase as the number of entities that cause interference or blocking increases (if the entities are located randomly).

The estimated coverage area of a base station can be determined by a number of means, such as computer modelling or actual measurement of signals.

Certain information can be used to determine the estimated coverage area of a base station 21. This information can include details of: the location of the base station, the terrain surrounding the base station; the environment; the antenna radiation pattern of the base station; and the transmitter power. This information can be used to characterise the estimated coverage area.

The estimated coverage area of the base station can be acquired by an allocation system (for example, the allocation system discussed further below).

There are a number of means which can be used to acquire the estimated coverage area of the base station, such as a user inputting an estimated coverage area, the base station sending its estimated coverage area or the allocation system can determine the coverage area based on certain information. In an example, the base station can send certain information (e.g. the information discussed above) to the allocation system, which can then use the information to estimate the coverage area of the base station. In another example, the allocation system may already contain geographical, topographical or other information to estimate the coverage area of a base station. The base station can send its location to the allocation system, and using the geographical and topographical information for that particular location, the allocation system can determine the estimated coverage area of the base station.

In another example, the base station can estimate its coverage area and then send the estimated coverage area information to the allocation system. The base station can estimate its coverage area by a number of methods. For example, actual signal measurements can be taken in surrounding area to determine the coverage area. This coverage area data can then be stored by the base station. In another example, location information and received signal strength by the terminals can be used to determine the coverage area.

The location of the base station can be used to estimate its coverage area.

For example, if a base station was located in a city centre, the attenuation and diffraction caused by surrounding buildings would affect the range of the base station, and thus its coverage area. The location of the base station may be variable. For example, in the case of a mobile base station, the location of base station may be constantly changing and will lead to a changeable coverage area.

Different locations may provide different environmental conditions and surrounding terrain, which will also affect the range of the base station. For example, a base station located in an area near landforms such as a hill will have its range limited as the landform will block the signal from the base station. Different environmental conditions may also act to attenuate or propagate the signal from the base station. For example, certain atmospheric conditions can cause the signals to travel much further than normal. This could lead to an enlargement of the coverage area in certain directions.

The estimated coverage area of a base station can also be determined by its features, such as its operating power and antenna radiation pattern. The power of the base station can be proportional to the size of the coverage area, in directions where there are no interfering entities. For example, referring to the example in Figure 2, if the power of base station 21 was increased, the coverage area 22 could be extended in the directions towards Ti and T4. However, entities such as building 23 or hill 24 would still act to block or interfere with the more powerful signal and the coverage area would not significantly extend in directions towards those entities.

A base station may operate with an antenna that has an anisotropic radiation pattern. The range of the base station in different directions will be dependent on the radiation pattern of its antenna. Thus, the coverage area for the base station will depend on the antenna. An antenna with a particular radiation pattern may be chosen according to the coverage needs of the base station.

A base station may comprise more than one antenna, with each antenna having its own coverage area. For example, a base station may comprise two directional antennas directed in opposite directions. This could provide a base station with two separate coverage areas. Channels can be allocated to the two antennas, such that interference is minimised, for example by allocating channels that are not adjacent and relatively far apart. Alternatively, two similar antennas may utilise different channels to, for example, help provide a low-speed and a high-speed data link for the same base station. A single antenna using different channels could also be used to provide variable speed data links.

A base station can communicate with terminals within its coverage area within a channel of the whitespace spectrum. The channel is a frequency band that can be used for communication. The channel can be split into further smaller frequency bands (sub-channels) that can also be used for communication. Multiple communications links can be established over a single channel or sub-channel by using multiplexing techniques such as CDMA.

The channel of whitespace spectrum used by the base station for a particular period of time is allocated to it by an allocation system. The allocation system comprises a database that stores information relating to reserved channels allocation in a geographical area. The reserved channels can indicate the spectrum usage by un-licensed whitespace devices and licensed devices in particular geographical areas over specified periods of time. The allocation system comprises a channel selection unit that, along with the database, can determine at least one whitespace spectrum channel to allocate to the base station based on its estimated coverage area. The allocation system may contain the details of a plurality of base stations and allocate at least one channel of whitespace spectrum to each base station.

Preferably, the allocation system operates to determine the allocation of whitespace spectrum to a number of base stations within a network. The network may be formed over one or more geographical areas. The network may be part of a local, regional, national or continental network of base stations. The allocation system may contain the following information: -The location and spectrum usage of licensed operators; -The spectrum usage (or channels reserved) for base stations.

-For each geographic location, the available whitespace channels and the time period that the spectrum is available for; -The power levels at which the whitespace channels can be used for a given area; -The location and estimated coverage area of one or more base stations; -Geographical and topographical information, -Characteristics of the licensed use such as its susceptibility to interference both according to interference received within its frequency band and signals on neighbouring bands that it is unable to completely filter; and -Characteristics of the unlicensed use such as its out-of-band emissions which can cause interference into neighbouring bands used by other users.

The allocation system can determine which part of the available whitespace spectrum to allocate to at least one of the base stations in the network based on the estimated coverage area of the base station and the interference that the allocated whitespace spectrum channel would cause on the other entities. Such other entities could be licensed operators or other base stations and terminals in the whitespace network.

The allocation system can estimate the interference that a channel of whitespace spectrum can to cause to other entities surrounding the coverage area of the base station and estimate which whitespace spectrum channel would cause the lowest interference. The whitespace spectrum channel that is estimated to cause the lowest interference is preferably allocated to the base station. Preferably, the base station uses, wholly or partly, its allocated whitespace spectrum channel to communicate with terminals located within its coverage area.

The interference calculation can be based on an estimate of the probability of causing interference at adjacent coverage areas of other base stations. This calculation can be based on the whitespace spectrum channel the other base stations use for communication within their coverage areas. For example, referring to Figure 3, the whitespace spectrum channels used by base stations 31, 41 and 51 will be considered when allocating a whitespace spectrum channel to base station 21. When considering the allocation of a whitespace spectrum channel to base station 21, the co-channel interference and adjacent-channel interference will be considered. If base station 21 is allocated the same channel as one of base stations 31, 41 or 51, the probability of co-channel interference will increase, especially in the boundary regions between the base stations using the same channel. The probability of interference due to adjacent-channel interference can be lowered if base station 21 was allocated channels that were not adjacent to channels allocated to base stations 31, 41 or 51. Thus, when considering the interference base station 21 would cause on other base stations 31, 41 and 51, base station 21 could be allocated a channel that is not the same as or adjacent to the channels allocated to adjacent base stations.

A single base station can be allocated multiple whitespace spectrum channels This could help increase the capacity of the base station. The multiple channels allocated to a single base station can be chosen so as to minimise interference between the channels. For example, by allocated two channels that are relatively far apart, the adjacent-channel interference can be minim ised.

The interference caused to other entities, such as licensed operators can also be considered. For example, referring to Figure 3, transmitter 61 may be a licensed TV operator. The TV operator could be using a first band to broadcast TV signals within coverage area 62. The channel allocation for base station 21 would be chosen to avoid unacceptable adjacent-channel interference to TV users in coverage area 62. Thus, when additionally considering licensed operators, base station 21 would be allocated an available channel that has the largest frequency difference to the first band.

Multiple channels can also be used within the same base station. If multiple channels are deployed, their timing and frequency hopping sequences can be coordinated. The frequency hopping can be used to minimise the interference to licensed operators, such as TV reception. Since there would be no constant communications link over a single channel, there will not be a permanent cause of interference to any given TV receiver. Additionally, the frequency hopping sequences can be coordinated between base stations so that interference is minimised between them. For example, the allocation system can continually monitor the channels made available to each base station and monitor the frame errors from each base station. The system can simulate various hopping assignments across each base station and determine those which result in the smallest number of frame collisions. The system can then inform each base station of the hopping sequence it is to adopt.

Additionally, the likelihood of interference caused by the other entities to base station 21 and the terminals within its coverage area 22 would also be considered when allocating a whitespace spectrum channel to that base station.

A base station can transmit a carrier signal and a synchronisation burst to provide information to terminals. The carrier signal and burst may be within an allocated whitespace channel. The synchronisation burst can be a synchronisation word that consists of symbols followed by a synchronisation word using concatenated Baker codes selected from a number of possible sequences. The sequences can be selected so that neighbouring base stations use different codes, thus reducing the probability of interference between the base stations. The burst can enable terminals to lock to the carrier and the basic timing of the burst. This provides terminals with a range of information such as the base station identity and channel/sub-channel availability.

The allocation system can allocate whitespace channels to the base stations for a finite period of time. This allows dynamic allocation of the whitespace spectrum that can be optimised when changes occur in the network. For example, the licensed operators may change their operating band or location. This change would be acknowledged by the allocation system and would re-allocate channels to the base stations to account for the change. The allocation system can also manage the frequency channel hopping between the base stations to minimise the impact of interference -both received and caused.

When allocated a channel of whitespace spectrum, the base station can then determine and allocate that channel or sub-channels of that channel to communicate with terminals within its coverage area. Alternatively, the allocation system could determine and allocate the channel or sub-channels of the allocated whitespace channel for the base station to communicate with the terminals.

When determining which sub-channels to allocate to terminals, the base station or allocation system can calculate which sub-channel would provide the least interference with other entities. The other entities could include other terminals within the same coverage area, other base stations and licensed operators.

The terminals may provide the base station (and in turn the base station may provide the allocation system) with the terminal location. The terminal may comprise means, such as GPS, which enables it to locate itself. The location of the terminal relative to the base station, other terminals, other base stations and licensed operators can be used to determine the amount of interference a whitespace channel would cause. Based on the calculated interference, the base station or the database can allocate an appropriate sub-channel for communication between the terminal and the base station. Preferably, the allocated sub-channel would be calculated as the sub-channel that would cause the lowest interference to other entities.

The terminal can report the received signal strength from the base station to the base station. This can help the base station determine the location of the terminal and whether handover to another base station would provide more effective communication.

The database can instruct a base station to implement power control for the terminals linked to the base station. For example, it may be necessary to reduce the is power of individual or all terminals because access to certain whitespace channels can only be achieved if the terminal transmit power is reduced (as the terminals may interfere with neigh bou ring entities).

Figure 4 diagrammatically shows a process by which the allocation system can allocate a channel of the whitespace spectrum to a first base station for a first specified period of time.

At step 1011 the estimated coverage area of the first base station is determined. This can be done by retrieving stored information which relates to the coverage area of the first base station. The coverage area information may be stored in the allocation system or requested from the first base station. As mentioned above the coverage area may have been estimated by actual measurements or by computer modelling. The coverage area information may then be adjusted or re-calculated for certain factors, such as environmental conditions, transceiver power, etc. At step 102, the allocation system determines which whitespace channels are available for the estimated coverage area of the first base station for the first specified time period.

At step 103, the allocation system determines the spectrum usage of licensed operators located near the estimated coverage area of the first base station. This is then used to determine which whitespace channels would be unsuitable for the first base station to use as it may cause interference to the licensed operators. The suitable channels are then considered in the step 105.

At step 104, other base stations with coverage areas adjacent to the estimated coverage area of the first base station are determined. The whitespace spectrum allocated to the other base stations for the first specified time period is then determined.

At step 105, the allocation system calculates which of the suitable channels would cause the least interference at the base stations with the adjacent coverage areas.

At step 106, the channel calculated at step 105 is then allocated to the first base station for the use by the first base station.

The process can be carried out again for the first base station at the end of the specified time period. The process can also be carried out for all base stations Figure 5 diagrammatically shows a subsequent process to that in Figure 4 which can, optionally, be carried out by the allocation system or by the base station to allocate a sub-channel of the allocated whitespace channel to a first terminal for a second specified period of time.

At step 107, the location of the terminal is determined. This can be achieved by a number of means. For example, the terminal may have a fixed location, and its location is determined during installation. The location information can then be stored locally at the terminal and/or sent to the base station and/or stored in the allocation, system. In another example, the terminal may comprise a locating means, such as a global positioning system (GFS). The terminal can then send its location information to the base station. The base station can forward this information to the allocation system. Alternatively, the base station can locate the terminal by, for example, measuring signal strength. The base station can then send the terminal location information to the database.

At step 108, the sub-channels that are available and not in use during the second specified period of time are then determined. The channel allocated to the first base station may be divided up into a plurality of sub-channels for communicating with a plurality of terminals. The available sub-channels are then considered at step 110.

At step 109, the location and the sub-channels used by other terminals within the same estimated coverage area are then determined.

At step 110, the allocation system or the base station then determines which of the available sub-channels would cause the least interference to terminals located close to the first terminal. Other factors may also be considered, such as terminal transmitter (or transceiver) power. The data rate of the terminals may also be considered when allocating the sub-channels.

At step 111, the sub-channel calculated at step 110 is allocated for use by the first terminal.

This process can be carried out again for the terminal at the end of the second specified time period. The second specified time period must be within the first specified time period. The process can also be carried out for all terminals within the coverage area of the first base station and the coverage area of all base stations in the network of base stations.

The allocation system can allocate sub-channels to the terminals for a finite period of time. This allows for a dynamic allocation of the white space spectrum that can be optimised when changes occur in the network. For example, the location of a terminal may change. This change would be acknowledged by the allocation system and would re-allocate a sub-channel to the terminal to account for the change. The allocation system can manage the sub-channel hopping between the terminals to minimise the impact of interference -both received and caused.

Figure 6 is a block diagram that depicts a computer system 201 upon which an embodiment of the invention may be implemented. Computer system 201 includes a bus 202 or any other communication mechanism for communicating information, and a processor 203 coupled with bus 201 for processing information.

Computer system 201 also includes a memory 204, such as a random access memory (RAM) or other dynamic storage device, coupled to bus 202 for storing information and instructions to be executed by processor 203. Memory 204 also may be used for storing temporary variables or other intermediate information during execution of instructions to be executed by processor 203. Memory 204 may further include a read only memory (ROM) or other static storage device for storing static information and instructions for processor 203. A storage device 205, such as a magnetic disk or optical disk, is provided and coupled to bus 202 for storing information and instructions.

The invention can be related to the use of computer system 201 for implementing the techniques described herein. According to one embodiment of the invention, those techniques are performed by computer system 201 in response to processor 203 executing one or more sequences of one or more instructions contained in memory 204. Such instructions may be read into memory 204 from another computer-readable medium, such as storage device 205. Execution of the sequences of instructions contained in memory 204 causes processor 203 to perform the process steps described herein. In alternative embodiments, hard-wired circuitry may be used in place of or in combination with software instructions to implement the invention. Thus, embodiments of the invention are not limited to any specific combination of hardware circuitry and software.

Computer system 201 also includes a communication interface 206 coupled to bus 202. Communication interface 206 provides a two-way data communication coupling to a communications link 207 that can be connected to one or more base stations BS. Communication link 207 sends and receives electrical, electromagnetic or optical signals that carry digital data representing various types of information. The communication link 207 may be establish connection through a wired or wireless network (e.g. via the internet, LAN, Wireless WAN, etc).

Computer system 201 can send messages and receive data, including program code, through the communication link 207 and communication interface 206. The received code may be executed by processor 203 as it is received, and/or stored in storage device 205, or other non-volatile storage for later execution.

Base station BS1 may comprise a communications interface 209 which is coupled to a bus 210. Communication interface 206 provides a two-way data communication coupling to communications link 207 that can be connected to computer system 201 and/or other base stations BS. Base station BS1 may comprise a processor 211, memory 212 and storage device 213 which function in a similar manner to the equivalent components described above.

Base station B81 may comprise a transceiver 214 which enables wireless communication with terminals. The transceiver 214 may be coupled to one or more ante nn as (n Qt s.h ow p n Fig re 6.) to e.n able wirele ss co mmunicatio The transceiver 214 is coupled to bus 210 which can send and receive information to the other components in the base station BS1. The invention can be related to the use of base station BS1 for implementing the techniques described herein. According to one embodiment of the invention, those techniques are performed by base station BS1 in response to processor 211 executing one or more sequences of one or more instructions contained in memory 212. Such instructions may be read into memory 204 from another computer-readable medium, such as storage device 213 or from the computer system 201 via communications link 207 and communications interface 209. Execution of the sequences of instructions contained in memory 212 causes processor 211 to perform the process steps described herein.

In one example, storage device 205 can store information such as reserved channel allocations, information relating to base stations and its surroundings, information related to licensed operators, information related to terminals, etc. Processor 203 can carry out processing to enable the analysis for selecting channels to be allocated to base stations. Processor 203 can carry out processing that can provide an estimated coverage area for base stations BS. Alternatively, processor 211 can be used to carry out the processing for providing the estimated coverage area of the base station B51. There may be instances where it would be advantageous for certain base stations in a network to carry out the processing for providing their estimated coverage area and processing for providing the estimated coverage area for other base stations to be carried out by the computer system 201.

The applicant hereby discloses in isolation each individual feature described herein and any combination of two or more such features, to the extent that such features or combinations are capable of being carried out based on the present specification as a whole in the light of the common general knowledge of a person skilled in the art, irrespective of whether such features or combinations of features solve any problems disclosed herein, and without limitation to the scope of the claims. The applicant indicates that aspects of the present invention may consist of any such individual feature or combination of features. In view of the foregoing description it will be evident to a person skilled in the art that various modifications may be made within the scope of the invention.

Claims

CLAIMS1. An allocation system for allocating spectrum to a whitespace communications station, the system comprising: a database configured to store information indicating reserved channel allocations in a geographical area; and a channel selection unit configured to analyse the database so as to select a channel for use by the communications station in dependence on a location of the communications station within the geographical area and an estimated coverage area of the communications station about its location, wherein the channel selection unit is configured to perform the said analysis for a non-circular estimated coverage area.
2. The system according to claim 1, wherein the channel selection unit is further configured to perform the said analysis for an irregular estimated coverage area.
3. The system according to claim 1 or 2, wherein the estimated coverage area is determined based on one or more of the following: environment; location; surrounding terrain; antenna elevation above ground level; antenna radiation pattern; and transmitter power.
4. The system according to any one of the preceding claims, wherein the channel selection unit is further configured to analyse the database so as to select a channel that is not reserved for a location within the estimated coverage area.
5. The system according to any one of the preceding claims, wherein the channel selection unit is further configured to select the channel additionally in dependence of a first interference calculation, wherein the first interference calculation estimates the interference caused by the communications station to other entities and the interference caused by other entities to the communications station.
6. The system according to claim 5, wherein the first interference calculation is based on an estimate of at least one of the following: the probability of interference caused by other communications stations; the probability of causing interference to other communication stations; and the probability of causing interference to licensed transceivers, wherein the licensed transceivers communicate using licensed spectrum.
7. The system according to any one of the preceding claims, wherein the system further comprises a sub-channel selection unit configured to select a sub-channel for communication between the communications station and a terminal, wherein the sub-channel is preferentially a part of the channel selected by the channel selection unit.
8. The system according to claim 7, wherein the sub-channel selection unit is further configured to select the sub-channel additionally in dependence of a second interference calculation, wherein the second interference calculation estimates the interference caused by the terminal to other entities and the interference caused by other entities to the terminal.
9. The system according to claim 8, wherein the second interference calculation is based on an estimate of at least one of the following: the probability of interference caused by other communications stations; the probability of causing interference to other communications stations; the probability of causing interference to licensed transceivers, wherein the licensed transceivers communicate using licensed spectrum; the probability of interference caused by other terminals; and the probability of causing interference to other terminals.
10.A whitespace communications station, the communications station being capable of communicating on a channel allocated to it by an allocation system, and being configured to report to the allocation system information characterising an estimated coverage area of the communications station whereby the allocation system can allocate a channel to the communications station, the information characterising a non-circular estimated coverage area.
11.The communications station according to claim 10, wherein the information characterises an irregular estimated coverage area.
12. The communications station according to claim 10 or 11, wherein the information is related to one or more of the following: environment; location; surrounding terrain; received signal strength; antenna radiation pattern; and transmitter power.
13.The communications station according to any one of claims 10 to 12, wherein the communication station is allocated a channel that is not reserved for other entities in a location within the estimated coverage area.
14.The communications station according to any one of claims 10 to 13, wherein the communications station is configured to communicate with a terminal on a sub-channel allocated by the allocation system, wherein the sub-channel is preferentially a part of the allocated channel.
15. The communications station according to any one of claims 10 to 13, wherein the communications station is configured to determine a sub-channel for communication between the communications station and a terminal, wherein the sub-channel is preferentially a part of the allocated channel.
16.The communications station according to claim 14 or 15, wherein the determination of the sub-channel is based on an interference calculation, wherein the interference calculation estimates the interference caused by the terminal to other entities and the interference caused by other entities to the terminal.
17. The communications station according to claim 16, wherein the interference calculation is based on an estimate of at least one of the following: the probability of interference caused by other communications stations; the probability of causing interference to other communications stations; the probability of causing interference to licensed transceivers, wherein the licensed transceivers communicate using licensed spectrum; the probability of interference caused by other terminals; and the probability of causing interference to other terminals.
18.A whitespace communications system comprising the allocation system according to any one of claim I to 9 and the communications station according to any one of claims 10 to 17.
19.A method for allocating whitespace spectrum, the method comprising the steps of: storing information indicating reserved channel allocations in a geographical area; and analysing the stored information so as to select a channel to allocate to a communications station in dependence on a location of a communications station within the geographical area and an estimated coverage area of the communications station about its location, wherein the analysing step is performed for a non-circular estimated coverage area.
20.The method according to claim 19, wherein the analysing step is performed for an irregular estimated coverage area.
21.The method according to claim 19 or 20, wherein the estimated coverage area is determined based on one or more of the following: location; environment; surrounding terrain; received signal strength; antenna radiation pattern; and transmitter power.
22.The method according to any one of claims 19 to 21, wherein analysing step further analyses the stored information so as to select a channel that is not reserved for a location within the estimated coverage area.
23. The method according to any one of claims 20 to 22, further comprising the step of: carrying out a first interference calculation, wherein: the first interference calculation estimates the interference caused by the communications station to other entities and the interference caused by other entities to the communications station; and the allocation of the channel is additionally in dependence of the first interference calculation.
24.The method according to claim 23, wherein the first interference calculation is based on an estimate of at least one of the following: the probability of interference caused by other communications stations; the probability of causing interference to other communications stations; and the probability of causing interference to licensed transceivers, wherein the licensed transceivers communicate using licensed spectrum.
25.The method according to any one of claims 20 to 24, further comprising the step of: determining a sub-channel of the allocated channel for communication between the communications station and a terminal.
26. The method according to claim 25, wherein the a sub-channel is determined based on a second interference calculation, wherein the second interference calculation estimates the interference caused by the terminal to other entities and the interference caused by other entities to the terminal.
27.The method according to claim 26, wherein the second interference calculation is based on an estimate of at least one of the following: the probability of interference caused by other communications stations; the probability of causing interference to other communications stations; the probability of causing interference to licensed transceivers, wherein the licensed transceivers communicate using licensed spectrum; and the probability of interference caused by other terminals; and the probability of causing interference to other terminals.
28.A computer program for allocating whitespace spectrum, the computer program comprising code means that, when executed by a computer, will cause the computer to carry out the steps in any one of claims 19-27.
29.A system substantially as herein described with reference to the accompanying drawings.
30.A method substantially as herein described with reference to the accompanying drawings.