WO2007000740A1

WO2007000740A1 - System and method for opportunistic spectrum-sharing by spectrum agile radios (sara)

Info

Publication number: WO2007000740A1
Application number: PCT/IB2006/052137
Authority: WO
Inventors: Stefan Mangold; Chun-Ting Chou
Original assignee: Koninklijke Philips Electronics, N.V.
Priority date: 2005-06-28
Filing date: 2006-06-27
Publication date: 2007-01-04
Also published as: JP2008547346A; KR20080021699A; CN101213763A

Abstract

An apparatus (301. i), system (300) and method are provided for opportunistically sharing spectrum between and among Spectrum Agile Radio (SARA) devices (301.i), primary (3O2.i) and secondary devices (303.i). A primary device (3O2.i) is a licensed radio system operating in licensed bands. A secondary device (303. i) is any system/device operated in an unlicensed band. Each SARA device (301.i) maintains a Spectrum Opportunity Map (SOM) (200), which is populated by the SARAs (301.i) using the spectrum and by sharing SOMs (200) among SARAs (301.i). A SARA device (301/i) probes the medium for evidence of spectrum usage and may receive explicit information concerning spectrum usage from a primary (3O2.i) which it then records in its SOM (200) and may share its SOM (200) with other SARA devices (301.i).

Description

SYSTEM AND METHOD FOR OPPORTUNISTIC SPECTRUM -SHARING BY SPECTRUM AGILE RADIOS (SARA)

The present invention relates to a system and method for opportunistic spectrum sharing by spectrum agile radios (SARAs) with a primary, a secondary and other SARA devices.

The increasing popularity of radio communication networks in recent years, and of wearable, hand-held computing and communicating devices, as well as consumer electronics, indicates that there will be an ever increasing demand for radio communication networks providing high capacity communication. Considering this increase in demand, it is clear that the existing radio spectrum will not satisfy the expected demand in the future, due to the limited nature of radio resources. Today, consumer electronics radio communication systems operate mainly in unlicensed bands. Radio resources in the unlicensed bands are generally considered as being efficiently used, because of the high penetration of unlicensed radio devices. However, most of the radio spectrum is allocated to traditional licensed radio services, and often not used at all. With the traditional regulation of radio spectrum we have today, resources are often not efficiently utilized. This problem is addressed by Spectrum Agile Radio (SARA).

The objective of SARA is to make efficient use of spectrum without interfering with existing users of that spectrum. A primary is a licensed radio system, operating in licensed bands. A secondary is an unlicensed radio system, operating in ISM or U-NII bands. The possible types of coexisting systems include a primary, another SARA, and a secondary, and, depending on the types of users a SARA device is required to have different functionalities and interact accordingly. For example, for coexistence with a pri mary, a SARA device has to immediately move away from the occupied spectrum if the interference level it is generating is intolerable to the primary.

Thus, a way of using the unused spectrum is needed, that is efficient, effective, and meets requirements to vacate spectrum gracefully when its use causes intolerable conditions for a primary. The system and method of the present invention provide an effective and efficient method for radio spectrum usage by SARA devices based on opportunistically detecting and occupying radio spectrum not being used by others.

To improve the efficiency of the usage of radio spectrum, SARA devices modified according to the present invention make use of the licensed radio spectrum in an opportunistic way. SARA devices seek opportunities, i.e. unused radio resources, prior to communicating. SARA devices communicate using the identified opportunities without interfering with the operation of licensed radio systems. The way of identifying spectrum opportunities is regulated by SARA policies. With the help of SARA policies, radio regulators can control the behavior of SARA devices, if they have design methods available that allow defining the framework for creating the SARA policies. For the framework, SARA policies have to b e designed to determine how and when to make use of radio resources. SARA policies may evolve over time.

The existing IEEE 802.11 wireless LAN is able to support limited spectrum agility. In case that the current channel is noisy, the wireless LAN can switch to other channels in unlicensed radio spectrum with the help of what is referred to as dynamic frequency selection. The main difference between an IEEE 802.11 wireless LAN and a SARA network is that SARA devices operate in parts of the frequency spectrum that are usually exclusively used by other radio systems. These other radio systems are usually licensed through radio regulations, and have exclusive access to the assigned spectrum. Only if a SARA device identifies parts of the radio spectrum as not being used by the licensed radio systems (that means, only if a so- called spectrum opportunity is detected), it will use the respective radio resources. A SARA network must not create harmful interference on these licensed radio systems.

FIG. 1 illustrates two SARA devices communicating in a part of the spectrum already occupied by a primary;

FIG. 2 illustrates a spectrum opportunity map (SOM) according to the present invention; FIG. 3 illustrates a system of SARA devices sharing spectrum with primary and secondary devices; and

FIG. 4 illustrates a SARA device modified according to the present invention. It is to be understood by persons of ordinary skill in the art that the following descriptions are provided for purposes of illustration and not for limitation. An artisan understands that there are many variations that lie within the spirit of the invention and the scope of the appended claims. For the purposes of clarity and simplicity, unnecessary detail of known functions and operations may be omitted from the current description so as not to obscure the present invention.

The system and method of the present invention provides a way for a Spectrum Agile Radio to keep track of spectrum usage and to opportunistically use spectrum so that more of the spectrum, both licensed and unlicensed, is used. A communicating SARA device is termed a "SARA station" and a backoff entity that resides in such a SARA station is termed a "SARA backoff entity". A set of communicating SARA stations is termed a "SARA network."

SARA is an extension of the conventional wireless Local Area Network (LAN) technology. The objective of SARA is to make efficient use of spectrum without interfering with the existing systems. Depending on the types of coexisting systems, such as a primary, another SARA network or SARA device, or a secondary, the SARA is required to have different functionalities and interact accordingly. For the coexistence with a primary, SARA has to move away from the occupied spectrum immediately if the interfer ence level it is generating is intolerable to the primary. This introduces the problems of: (1) how SARA devices detect the existence of a primary;

(2) how SARA devices estimate the interference level perceived by the primary, due to occupancy of the spectrum; and

(3) if the interference is too high, how fast SARA devices should vacate after detecting the presence of primary. For coexistence with other radio systems, SARA may or may not need to vacate, depending on the extent to which these systems can cooperate:

• If cooperation does not exist, the decision will rely only on individual systems (disjoint decision): if a SARA device can estimate the interference level it is receiving from other radio systems and the interference it is generating to , it can make decisions (i.e., use that spectrum band or choose another) based on these information

(individually optimal decision). If it decides to use that spectrum, it may result in unacceptable interference to the coexisting systems such that they may either move away from this spectrum band since they perceive a new interference source, or for example, increase transmission power to force the new user to move away (classical resource competing problem).

• If some cooperation exists between different radio systems, we may have more degrees of freedom to handle the coexisting problem. For example, they can exchange the spectrum usage information, such as the interferences they may generate to each other. Based on that, a socially optimal decision can be made.

Referring now to FIG. 2, a spectrum opportunity map or SOM is illustrated for preferred embodiments. The purpose of the SOM and extensions thereof, is to provide a predefined memory structure for a persistent store of spectrum usage. The SOM or variation thereof, is maintained by each SARA device for each spectrum band and is kept up -to-date by the SARA device and exchanged with other SARA devices. It is a representation of a SARA's knowledge about local spectrum usage. Typically, a SOM comprises a band 201 and corresponding band availability 202 with l=available and 0=not available, band interference level 203, band distribution parameters 204, band regulation requirements 205, and band priority 206. Band priority is decided by the SARA. A SARA device may be required to estimate the interference it is generating to other radio systems. Even though a SARA device can estimate the interference level it is generating to the coexisting systems, it is difficult to estimate the total interference that another radio system perceives, because of some hidden interference sources. An example of three communicating devices is shown in FIG. 1. Here, P 102 is assumed to be able to coexist with A 101 before B 103 tries to use the same spectrum band. Unless P 102 informs B 103 about the existence and activity of A 101, B 103 may decide to use the same spectrum band because the detected interference by B 103 is low (assuming A 101 is hidden from B). Therefore, P 102 may suffer from the resulting interference generated by A 101 and B 103. IfP 102 is a primary, the result is unacceptable, in most of the cases.

In all preferred embodiments an Adaptive Hopping Sequence is used. That is, the SARA devices perform spectrum opportunity selection/reselection in a manner than can be analogized to the process of conventional frequency hopping. Instead of "hopping" for the purpose of spectrum spreading, it is hopping among unoccupied or lightly -loaded spectrum bands. Thus, instead of using a random hopping sequence with a very high hopping rate, a hopping sequence is generated based on the information of spectrum opportunities, collected in a spectrum opportunity map (SOM) illustrated in FIG. 2, by the SARA devices. Moreover, a hopping by a SARA device is triggered by any change in the spectrum usage condition reflected in the SARA device's SOM. A. In a first preferred embodiment, SARA devices time -share the spectrum with a primary by obtaining information before making a decision whether or not to use a spectrum band. The information a SARA collects includes: a. Is a given spectrum available? b. If the answer to (a) is YES, what is the current interference level? c. Given (a, b), how long will this be?

In a preferred embodiment, there are three possible ways to get this information .

1. A primary provides information: Each primary may provide some information indicating the availability of spectrum band. For example, a beacon can be used to signal an upcoming idle interval which SARA devices can use/occupy. This provides SARA the exact information about the usage pattern of the primary. Also, if the primary's behavior is predictable (e.g., periodically on/off), the SARA devices can also take advantage of the predictability and react accordingly. In this case, a. and c. are given and b. is bipolar: busy/idle.

2. The SARA devices collect information : Given that a primary does not provide any information, it is the SARA device's responsibility to collect any information needed. In order to collect a., SARA devices need to probe/detect the spectrum.

If the result of a. is NO (channel is unavailable), the SARA devices check the availability of the spectrum for the purpose of future usage. However, in order to reduce the detection overhead, the detection must be performed in an intelligent manner. In a preferred embodiment, an exponential random increase for the interval between consecutive probing/detecting events is used by a SARA device.

• The tradeoff in this case is between detection overhead and detection latency, where detection latency is defined as the time interval between the time a spectrum band is available and the time the SARA device detects it. • If the result of a. is YES (channel is idle), the SARA devices may decide whether or not to use that spectrum band based on the informati on of c. It should be noted that complete information of c. is difficult to collect unless the primary provides information. If the SARA devices decide not to use the spectrum, the SARA devices follow the procedure as in the case of detecting a busy channel.

For improved resource management, in a preferred embodiment each primary is associated with a so-called vacancy latency. Evacuation latency is defined as the maximum time during which transmission by a SARA station is allowed to interfere with transm ission of a primary. Without such a tolerance, time-sharing with a primary is less feasible. It must be noted that the concept of vacancy latency is also associated with a radio system that is used, for example, for radar systems.

In the case where spectrum appears to be available, i.e., a. and c. indicate availability: I. In a preferred embodiment SARA devices probe the wireless medium with respect to the vacancy latency. For example, a SARA device probes the wireless medium with an interval no greater than the primary's vacancy latency. Moreover, the interval is chosen to avoid any synchronization/correlation with other SARA's probing the medium. Each of the SARA devices randomly chooses an interval in [0, vacancy latency]. Once SARA devices detect primary activity, the SARA devices must leave immediately.

II. Even though the probing results indicate spectrum availability, the SARA devices still vacate the spectrum if the results of b. and c. provide a strong indication of upcoming primary activity, e.g., periodicity of primary usage. This is beneficial to both the SARA devices and the primary: SARA devices can find another available spectrum before being forced to leave and there will be no interference with the primary by the SARA devices. However, the information acquired in b. concerning the current interference level must be more detailed and not just an indication of busy/idle, for example, by using more memory in a SOM. IE. The length of time the spectrum will be available is estimated, using statistical techniques and observed prior usage of the spectrum by the primary.

3. Each of the SARA devices provides information to other SARA devices concerning spectrum usage that it has obtained from the primary. B. In a second preferred embodiment, SARA devices time-share the spectrum among themselves.

For a SARA device, the differences between sharing with a primary and with another SARA device are: 1. sharing spectrum resources with a primary has stricter requirements and the primary has priority;

2. temporal coexistence with another SARA device is allowed under the regulations while that with a primary may not be allowed;

3. active cooperation between SARA devices is possible, e.g., exchange of SOMS;

4. joint decisions/action: unlike sharing with a primary, SARA devices can coordinate/cooperate to some extent in order to accomplish - a. protect the communication of a SARA device itself from being interfered with by another SARA device, b. protect/improve another SARA device's communication, and c. jointly protect a primary's communication.

C. In a third preferred embodiment, SARA devices time-share with secondaries where a secondary can be any system/device operated in an unlicensed band. In addition, such secondaries may have also be spectrum agile, e.g., IEEE 802. I lk devices and sys tems. For a SARA device, the differences between sharing with secondaries as compared to primaries and other SARA devices are:

1. Interfering with each other is allowed under some regulation requirements;

2. cooperation is impossible; and

3. only disjoint action i s possible and each system may- a. protect its own transmission from others' interference, e.g., by increasing its transmission power, and b. protect others' transmission, e.g., by reducing its transmission power or leaving the shared spectrum band.

Referring now to FIGs. 3 and 4, in all preferred embodiments, a SARA device 301. i scans 'n' frequency bands 407 of the radio spectrum and maintains a Spectrum Opportunity Map 200 of spectrum occupancy information. Based on this Spectrum Opportunity Map 200, that the SARA device maintains locally using a SOM Processing Module 406 a as a result of information gathered by scanning the n bands as well as received from other radio devices 301-3.i , the SARA device 301.i can decide to share the spectrum in the parts of the spectrum that are not used by a primary 3O2.i or other secondaries 303.i. This sharing decision, in a preferred embodiment, is accomplished by a Band Info Processing Module 403 included in the SARA device by the Band Info Processing Module 403 analyzing the Spectrum Opportunity Map 200 for sharing opportunities. In a first preferred embodiment, the system, apparatus, and method of the present invention work as follows so that a SARA device can time -share the spectrum with a primary. First, the SARA device 301. i assumes the frequency spectrum is divided into n bands 407. Then, the SARA device 301.i monitors each of the n bands simultaneously by receiving transmissions in these n bands by an included receiver 402 and transmitting in each of the received n bands 407 for up to a specified length of time equal to an agreed upon vacancy latency. Then, using an included SOM Info Processing Module 406, the SARA device 301.i updates a Spectrum Opportunity Map 200 with measurements and received information of the occupancies of these n bands 407. If the SARA device 301.i discovers that some parts of the n bands 407 are not used. The SARA device 30 Li probes all the n bands 407 at all times when the SARA device 301.i has no data to transmit. The SARA device 301. i updates its local SOM 200 and makes decisions to occupy or not particular bands based on the probing results and database 200 updates received from primaries and other SARA devices. If the SARA device 301.i discovers that one of the bands it is occupying has some new occupancy, the SARA device 301.i detects whether it is a primary 3O2.i or secondary 303.i occupancy. If it is a primary 3O2.i occupancy, the SARA device 301.i immediately vacates the band and updates is SOM appropriately. The SARA device 301.i may then share its new SOM with other SARA devices.

The primary 3O2.i occupancies are detected based on the fact that the signature of the waveforms of the primaries is already known, e.g., stored in an included memory 408, and is detectable by a SARA device 301.i. As an example, if the detected occupancy is in the TV band, the SARA device knows the signature of the synchronization pulse of both analog and digital TVs.

If it is a secondary 303.i occupancy, the SARA device 301.i updates its SOM and may or may not decide to vacate the band occupied by the secondary. The SARA device 301.i may decide to vacate the channel if it can find enough opportunities based on information in its SOM in the other bands of the spectrum. However, if the SARA device 301.i finds that there is not enough spectrum availability then the SARA device 301.i may decide to coexist with the other secondary 303.i. The SARA device 301.i may then share its new SOM with other SARA devices.

While the preferred embodiments of the present invention have been illustrated and described, it will be understood by those skilled in the art that the management frame, device architecture and methods as described herein are illustrative and various changes and modifications may be made and equivalents may be substituted for elements thereof without departing from the true scope of the present invention. In addition, many modifications may be made to adapt the teachings of the present invention to a particular situation without departing from its central scope. Therefore, it is intended that the present invention not be limited to the particular embodiments disclosed as the best mode contemplated for carrying out the present invention, but that the present invention include all embodiments falling with the scope of the appended claims.

Claims

We claim:

1. A method for opportunistically sharing the radio spectrum by a spectrum agile radio (SARA) (301.i), comprising the steps of: when at least one other device occupies a part of the radio spectrum, acquiring a predefined set of spectrum occupancy information for the at least one other device; storing the acquired spectrum occupancy information for the at least one other device in a Spectrum Opportunity Map (SOM) (200); and time-sharing the spectrum with the at least one other device (301.i 3O2.i 303. i) in a pre-determined way based on the stored information (200).

2. The method of claim 1 , wherein: the radio spectrum is divided into a plurality of bands (201) (407); the spectrum occupancy information (SOM) (200) (201-206) is related to each of the plurality of bands (201) (407); and the time-sharing step further comprises the step of performing an adaptive hopping sequence among the plurality of bands (407) by performing the steps of - determining unoccupied and lightly-loaded bands of the plurality (201) based on the stored information of the SOM (200) (201 -206), estimating the length of time each determined band (201) (407) will be available; and randomly hopping to the bands (201) (407) having an estimated length of time available that exceeds a pre-determined tolerance; and occupying the bands randomly hopped to based on a pre-determined occupancy criteria.

3. The method of claim 2, wherein the estimating step further comprises the step of using statistical techniques and an observed prior usage of the spectrum by the primary (302.1).

4. The method of claim 2, wherein the at least one other device is selected from the group consisting of a primary (3O2.i), at least one other SARA device (301. i), and at least one secondary (303.i).

5. The method of claim 4, when the at least one other device is a primary (3O2.i), the acquiring step further comprises one of the steps of: receiving from the primary (3O2.i) at least a part of the pre -determined set of spectrum occupancy information (SOM) (201 -206); and the SARA device (301.i) probing the spectrum at random intervals to collect any occupancy information of the pre -determined set that is not provided by the primary (3O2.i).

6. The method of claim 5, wherein said predetermined interval increases exponentially.

7. The method of claim 5, wherein: the receiving step further comprises the step of receiving exact information about the usage pattern (204)of the primary (3O2.i) from the primary (302.i); and the time-sharing step further comprises the step of when the usage pattern (204) of the primary (301.i) is one of known and predictable, defining future usage of the spectrum by the SARA device (301.i) in terms of the usage pattern (204) of the primary (3O2.i).

8. The method of claim 7, when the at least one other device is at least one other SARA device (301.i), the acquiring step further comprises the step of actively cooperating with the at least one other SARA device (301.i).

9. The method of claim 8, wherein the cooperating step further comprises the steps of: exchanging SOMs (200) with the at least one other SARA device (301.i); taking joint action with the at least one other SARA device (301.i) by performing the steps of- protecting communications of the SARA device (301.i) itself from being interfered with by another SARA device (301.i); protecting communication of the at least one other SARA (301.i) device from being interfered with; jointly protecting communication of a primary (3 O2.i) by the SARA device (301.i) and the at least one other SARA device (301.1).

10. The method of claim 9, when the at least one other device is a secondary (303.i), the acquiring step further comprises taking independent action by the at least one SARA device (301.i) by performing the steps of: protecting an own transmission from interference by other devices (301.i 3O2.i 303.i); and protecting the transmissions of other devices (301.i 3O2.i 303.i).

11. The method of claim 10, wherein the step of protecting an own transmission comprises the step of increasing an own transmission power by the SARA device (301.i).

12. The method of claim 10, wherein the step of protecting the transmissions of other devices (301.i 3O2.i 303.i) comprises the step selected from the group consisting of reducing an own transmission power and leaving a shared spectrum band.

13. The method of claim 11, wherein the step of protecting an own transmission comprises the step of increasing an own transmission power by the SARA device (301.i).

14. The method of claim 10, wherein the probing step further comprises the step of probing the wireless medium for an interval randomly chosen from [0,vacancy latency] where vacancy latency is a predetermined maximum time during which transmiss ion by a SARA device (301.i) is allowed to interfere with transmission of a primary (3O2.i);

15. The method of claim 1, wherein the SOM (200) comprises information for each of 'n' predetermined bands (201) of the radio spectrum including: an occupancy indicator (202), an interference level (203) of the SARA with a device occupying the band; at least one distribution parameter (204) describing the future usage of the spectrum by the device occupying the band; and at least one regulation requirement (205) describing a constraint on sharing the band by radio devices.

16. An apparatus (301.i) for opportunistically sharing the radio spectrum by a spectrum agile radio (SARA), comprising: an antenna (401); a receiver (402) connected to the antenna (401) to prob e the medium for radio spectrum occupancy and receive spectrum occupancy information from other devices (301.i 302.0; a transmitter (404) connected to the antenna (401) to transmit radio spectrum occupancy information to other agile radios (301. i); a band information processing module (403) connected to the receiver (402) and the transmitter (404) to respectively determine occupied parts of the radio frequency spectrum from the sensed radio spectrum occupancy, combine the data of the determined occupied parts with data of the received occupancy information to obtain the bands of the radio frequency spectrum that are being used, to store the band occupancy information in a spectrum opportunity map (SOM) and time-share the spectrum opportunistically with other radio devices using the method of claim 14 which is based on the stored information, wherein, the receiver (402) only senses the medium when the SARA (301.i) device is not transmitting and the band information processing module (403) immediately vacates an occupied band whenever a new occupancy by a primary (3O2.i) is detected.

17. An radio system (300) comprising a plurality of spectrum agile radio (SARA) devices (301.i) that are configured to jointly perform the method of claim 14 and thereby share the radio spectrum opportunistically among the plurality and among any of at least one primary (3O2.i) and at least one secondary (303.i).