WO2007094604A1 - Method for sensing spectrum and arranging quiet period in cognitive radio system, customer premise equipment, base station and superframe structure using the same - Google Patents

Method for sensing spectrum and arranging quiet period in cognitive radio system, customer premise equipment, base station and superframe structure using the same Download PDF

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Publication number
WO2007094604A1
WO2007094604A1 PCT/KR2007/000776 KR2007000776W WO2007094604A1 WO 2007094604 A1 WO2007094604 A1 WO 2007094604A1 KR 2007000776 W KR2007000776 W KR 2007000776W WO 2007094604 A1 WO2007094604 A1 WO 2007094604A1
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WO
WIPO (PCT)
Prior art keywords
qps
frequency channels
cognitive radio
cpe
frequency
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PCT/KR2007/000776
Other languages
French (fr)
Inventor
Bub-Joo Kang
Gwangzeen Ko
Sung-Hyun Hwang
Myung-Sun Song
Chang-Joo Kim
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Electronics And Telecommunications Research Institute
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Publication date
Priority to KR20060014230 priority Critical
Priority to KR10-2006-0014230 priority
Priority to KR20070014976A priority patent/KR101397111B1/en
Priority to KR10-2007-0014976 priority
Application filed by Electronics And Telecommunications Research Institute filed Critical Electronics And Telecommunications Research Institute
Priority claimed from US12/279,248 external-priority patent/US8675594B2/en
Publication of WO2007094604A1 publication Critical patent/WO2007094604A1/en

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Classifications

    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04BTRANSMISSION
    • H04B1/00Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/69Spread spectrum techniques
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04WWIRELESS COMMUNICATION NETWORKS
    • H04W16/00Network planning, e.g. coverage or traffic planning tools; Network deployment, e.g. resource partitioning or cells structures
    • H04W16/14Spectrum sharing arrangements between different networks
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04WWIRELESS COMMUNICATION NETWORKS
    • H04W72/00Local resource management, e.g. wireless traffic scheduling or selection or allocation of wireless resources
    • H04W72/04Wireless resource allocation
    • H04W72/08Wireless resource allocation where an allocation plan is defined based on quality criteria
    • H04W72/082Wireless resource allocation where an allocation plan is defined based on quality criteria using the level of interference

Abstract

Provided are methods of spectrum sensing and assigning quiet periods in a cogn itive radio system in order to increase the reliability of detection regarding whether an in cumbent user appears in his/her frequency channel, customer premises equipment (CP E), a base station, and the structure of a super frame for performing the methods. The spectrum sensing method includes communicating with a base station (BS) and perfor ming spectrum sensing for frequency channels having quiet periods (QPs) during the Q Ps of the frequency channels used in the cognitive radio system, wherein the QPs of th e frequency channels do not overlap each other.

Description

METHOD FOR SENSING SPECTRUM AND ARRANGING QUIET PERIOD IN

COGNITIVE RADIO SYSTEM, CUSTOMER PREMISE EQUIPMENT7 BASE STATION

AND SUPERFRAME STRUCTURE USING THE SAME

TECHNICAL FIELD

The present invention relates to spectrum sensing technology used in cognitive r adio technology, and more particularly, to methods of spectrum sensing and assigning quiet periods in a cognitive radio system in order to more accurately detect whether an i ncumbent user appears in his/her frequency channel that is being currently used by cog nitive radio equipment, customer premises equipment (CPE), a base station, and the str ucture of a super frame, which are used to perform the methods.

BACKGROUND ART In cognitive radio systems, cognitive radio equipment uses an incumbent user's f requency band (or frequency channel) when the incumbent user does not occupy the fr equency band. Examples of cognitive radio equipment are base stations and custome r premises equipments (CPEs), which are included in cognitive radio systems, lncumb ent users may be referred to as primary users. Cognitive radio systems may be referr ed to as secondary user systems.

In cognitive radio systems, spectrum sensing technology examines the spectrum of a frequency band in order to allow cognitive radio equipment to use an incumbent u ser's frequency channel and check if the incumbent user appears in the frequency chan nel when the cognitive radio equipment uses the frequency channel. Cognitive radio systems basically must guarantee the vested rights of incumbent users to use their own frequency channels as much as they can. To this end, another spectrum sensing technology for more accurately detecting whether an incumbent user' s frequency channel is preoccupied by cognitive radio equipment, i.e., whether an incu mbent user appears in the frequency channel, is needed. BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present invention will beco me more apparent by describing in detail exemplary embodiments thereof with referenc e to the attached drawings in which:

FIG. 1 is a state transition diagram of frequency channels according to an embod iment of the present invention; i FIG. 2 illustrates an exemplary wireless regional area network (WRAN) system a ccording to an embodiment of the present invention;

FIG. 3 illustrates super frame formats according to an embodiment of the presen t invention; FIGS. 4A, 4B, and 4C illustrate assignments of frequency channels of an active s et, a candidate set, a remaining set, and an occupied set according to an embodiment of the present invention;

FIGS. 5A and 5B illustrate super frame formats according to another embodimen t of the present invention; FIG. 6 illustrates super frame formats according to another embodiment of the pr esent invention;

FIG. 7 is a block diagram of an apparatus for assigning quiet periods (QPs) in a c ognitive radio system according to an embodiment of the present invention;

FIG. 8 is a block diagram of a WRAN system according to an embodiment of the present invention;

FIG. 9 is a flowchart illustrating a method of assigning QPs in a cognitive radio sy stem according to an embodiment of the present invention;

FIG. 10 is a flowchart illustrating a spectrum sensing method of a WRAN base st ation (BS) according to an embodiment of the present invention; and FIG. 11 is a flowchart illustrating a spectrum sensing method of customer premis es equipment (CPE) according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Technical Goal of the Invention

The present invention provides methods of spectrum sensing and assigning quie t periods in a cognitive radio system in order to increase the reliability of detection regar ding whether an incumbent user appears in his/her frequency channel, customer premi ses equipment (CPE), a base station, and the structure of a super frame for performing the methods.

Disclosure of the Invention

According to an aspect of the present invention, there is provided a spectrum se nsing method performed by customer premises equipment (CPE) in a cognitive radio sy stem comprising: communicating with a base station (BS); and performing spectrum se nsing for frequency channels having quiet periods (QPs) during the QPs of the frequenc y channels used in the cognitive radio system, wherein the QPs of the frequency chann els do not overlap each other. Each super frame of the cognitive radio system may include a plurality of frames, locations of the frames including QPs differ from each other between different frequen cy channels.

Each super frame of the cognitive radio system may include a single QP per freq uency channel. The method may further include: receiving information on the assignment of the

QPs of the frequency channels from the BS, wherein the spectrum sensing is performe d based on the information on the assignment of the QPs.

The method may further comprise: notifying the BS about a spectrum sensing re suit. The QPs of frequency channels which are channel-bonded do not overlap each other.

Each super frame of the cognitive radio system may include the plurality of frame s, the locations of the frames including QPs differ from each other between different fre quency channels, the locations of the frames including QPs are adjacent to each other between the frequency channels which are channel-bonded.

The locations of the frames including QPs may be adjacent to each other in the o rder of the frequency channels between the frequency channels which are channel-bon ded.

According to another aspect of the present invention, there is provided a spectru m sensing method performed by a BS in a cognitive radio system comprising: communi eating with at least one CPE; and performing spectrum sensing for frequency channels having QPs during the QPs of the frequency channels used in the cognitive radio syste m, wherein the QPs of the frequency channels do not overlap each other.

Each super frame of the cognitive radio system may include a plurality of frames, locations of the frames including QPs differ from each other between different frequen cy channels.

Each super frame of the cognitive radio system may include a single QP per freq uency channel. The method may further comprise: transmitting information on the assignment of the QPs of the frequency channels to the at least one CPE.

The method may further comprise: receiving a spectrum sensing result from the at least one CPE. QPs of frequency channels which are channel-bonded may do not overlap each other.

Each super frame of the cognitive radio system may include a plurality of frames, the locations of the frames including QPs differ from each other between different freq uency channels, the locations of the frames including QPs are adjacent to each other b etween the frequency channels which are channel-bonded.

The locations of the frames including QPs may be adjacent to each other in the o rder of the frequency channels between the frequency channels which are channel-bon ded.

According to another aspect of the present invention, there is provided a method of assigning QPs to perform spectrum sensing in a cognitive radio system comprising: d etermining at least one frequency channel to which the QPs are assigned; and establis hing time locations of the QPs of the at least one frequency channel, wherein the establ ishing of the time locations comprises: if two or more frequency channels are determine d, establishing time locations of QPs of the frequency channels so that the QPs do not overlap each other between different frequency channels.

The establishing of the time locations may comprise: establishing time locations of the QPs based on a channel conversion time of a device belonging to the cognitive r adio system.

Each super frame of the cognitive radio system may include a plurality of frames, wherein the establishing of the time locations further comprises: forming the super fra mes so that the time locations of the frames including QPs differ from each other betwe en different frequency channels.

The establishing of the time locations may further comprise: assigning the QPs o f frequency channels which are channel-bonded to the super frames so that the time Io cations of the frames including the QPs are adjacent to each other in the order of the fr equency channels.

According to another aspect of the present invention, there is provided CPE in a cognitive radio system comprising: a transmitter/receiver communicating with a BS; and a sensor performing spectrum sensing for frequency channels having QPs during the QPs of the frequency channels used in the cognitive radio system, wherein the QPs of t he frequency channels do not overlap each other.

Each super frame of the cognitive radio system may include a plurality of frames, locations of the frames including QPs differ from each other between different frequen cy channels.

The transmitter/receiver may receive information on the assignment of the QPs o f the frequency channels from the BS, the sensor performs spectrum sensing based on the information on the assignment of the QPs.

The transmitter/receiver may notify a spectrum sensing result of the BS. According to another aspect of the present invention, there is provided a BS in a cognitive radio system comprising: a transmitter/receiver communicating with at least o ne CPE; and a sensor performing spectrum sensing for frequency channels having QPs during the QPs of the frequency channels used in the cognitive radio system, wherein t he QPs of the frequency channels do not overlap each other. Each super frame of the cognitive radio system may include a plurality of frames, locations of the frames including QPs differ from each other between different frequen cy channels.

The transmitter/receiver may transmit information on the assignment of the QPs of the frequency channels to the at least one CPE. The transmitter/receiver may receive a spectrum sensing result from the at least one CPE.

According to another aspect of the present invention, there is provided an appar atus for assigning QPs to perform spectrum sensing in a cognitive radio system compris ing: a determiner determining at least one frequency channel to which the QPs are assi gned; and an establisher establishing time locations of the QPs of the at least one frequ ency channel, wherein the establisher, if the determiner determines two or more freque ncy channels, establishes the time locations of QPs of the frequency channels so that t he QPs do not overlap each other between different frequency channels.

The establisher may establish the time locations of the QPs based on a channel conversion time of a device belonging to the cognitive radio system.

Each super frame of the cognitive radio system includes a plurality of frames, wh erein the establisher forms the super frame so that the time locations of the frames incl uding QPs differ from each other between different frequency channels. According to another aspect of the present invention, there is provided a structur e of a super frame for spectrum sensing performed by a BS or CPE in a cognitive radio system, wherein the super frame includes at least one QP in each of frequency channel s used in the cognitive radio system, and the QPs of the frequency channels do not ove rlap each other.

The super frame may include a plurality of frames, and locations of the frames in eluding QPs differ from each other between different frequency channels.

The super frame may include a single QP per frequency channel.

The QPs may be established based on a channel conversion time required by a sensor to perform spectrum sensing.

QPs of frequency channels which are channel-bonded may do not overlap each other.

The super frame may include a plurality of frames, locations of the frames includi ng QPs differ from each other between different frequency channels, and the locations of the frames including QPs are adjacent to each other between the frequency channel s which are channel-bonded.

Effect of the Invention

The present invention can increase the reliability of detection regarding whether an incumbent user appears in his/her frequency channel in a cognitive radio system.

BEST MODES FOR CARRYING OUT THE INVENTION

The present invention will now be described more fully with reference to the acco mpanying drawings. The present invention relates to spectrum sensing technology for more accurate! y detecting whether an incumbent user's frequency channel is used by cognitive radio e quipment, i.e., whether an incumbent user appears in the frequency channel.

More particularly, the present invention relates to distributed spectrum sensing te chnology for checking, by cognitive radio equipment, if an incumbent user appears in a n incumbent user's frequency channel among frequency channels belonging to an activ e set. The active set is a set of frequency channels currently being used in a cognitive radio system and is a combination of active sets 1 and 2, which will be described later. The definition of the active sets 1 and 2 is as follows. Active set 1 Ai = {f|f is a frequency channel currently being used by cognitive radi o equipment to transmit and receive information}

Active set 2 A2 = {f|f is a frequency channel currently being used by a cognitive r adio system, except frequency channels belonging to the active set 1} Besides the active sets 1 and 2, the definition of a candidate set, a remaining set

, and an occupied set is as follows.

Candidate set C = {f|f is an unused frequency channel exceeding a communicati on quality threshold}

Remaining set R = {f|f is an unused frequency channel not exceeding the commu nication quality threshold}

Occupied set O = {f|f is a frequency channel being used by an incumbent user}

The purpose of performing spectrum sensing in the cognitive radio system will no w be briefly described. Spectrum sensing is performed for frequency channels belongi ng to the active set in order to detect the appearance of an incumbent user and vacate a frequency channel of the incumbent user. Spectrum sensing is performed for the ca ndidate set, the remaining set, and the occupied set in order to detect whether an unus ed frequency channel exists and to efficiently use the detected unused frequency chann el.

The present invention relates to, in particular, a method of performing spectrum s ensing for frequency channels belonging to the active set during a QP. In order to clari fy the subject matter of the present invention, the operation of the spectrum sensing for the candidate set, the remaining set, and the occupied set is not described. However, it will be fully understood by those of ordinary skill in the art that the spectrum sensing f or the candidate set, the remaining set, and the occupied set can be applied to the pres ent invention.

The QP is a period when cognitive radio equipment stops transmitting informatio n through a frequency channel assigned to the cognitive radio equipment. In the prese nt invention, different frequency channels have different locations of QPs.

FIG. 1 is a state transition diagram of frequency channels according to an embod iment of the present invention. In more detail, sets belonging to frequency channels c hange due to variations of state of frequency channels. Examples of variations of stat e of frequency channels are changes in appearance of an incumbent user, quality of fre quency channels, or the like. Referring to FIG. 1 , arrows S1 through S7 will now be de scribed. State transition of arrow S1: where a frequency channel belonging to an active s et, a candidate set, and a remaining set is occupied by an incumbent user.

State transition of arrow S2: where communication quality of a frequency channe I in an unused state after the incumbent user releases the frequency channel exceeds a communication quality threshold.

State transition of arrow S3: where communication quality of the frequency chan nel in an unused state after the incumbent user releases the frequency channel does n ot exceed the communication quality threshold.

State transition of arrow S4: where communication quality of a frequency channe I belonging to the remaining set exceeds a communication quality threshold satisfying th e requirement of the candidate set.

State transition of arrow S5: where a frequency channel belonging to the Candida te set is assigned to a secondary user.

State transition of arrow S6: where communication quality of a frequency channe I belonging to the candidate set does not exceed the communication quality threshold s atisfying the requirement of the candidate set.

State transition of arrow S7: where communication quality of a frequency channe I in an unused state after belonging to the active set, i.e., the frequency channel used a nd then released by the secondary user, exceeds the communication quality threshold satisfying the requirement of the candidate set.

In the present specification, for the descriptive convenience, the technical idea of the present invention is described using a wireless regional area network (WRAN) syst em among cognitive radio systems, i.e., secondary user systems. However, it will be f ully understood by those of ordinary skill in the art that distributed spectrum sensing tec hnology can be applied to any secondary user system as well as the WRAN system.

The WRAN system uses a V/UHF TV band using cognitive radio technology whil e an incumbent user is not using the V/UHF TV band. The WRAN system includes at I east one WRAN base station (BS) and at least one item of customer premises equipme nt (CPE). The WRAN BS corresponds to a BS belonging to the cognitive radio system . The CPE corresponds to a terminal belonging to the cognitive radio system. The te rm WRAN device refers to the WRAN BS and the CPE, and corresponds to a cognitive radio device.

In the present specification, when the WRAN system includes a plurality of cells, the operation of the WRAN device included in a single cell will be described. FIG. 2 illustrates an exemplary WRAN system according to an embodiment of th e present invention. Referring to FIG. 2, the WRAN system comprises a WRAN BS an d first through fifth CPEs CPE_1 , CPE_2, CPE_3, CPE_4, and CPE_5.

An active set, conventional spectrum sensing technology, and a spectrum sensin g method according to an embodiment of the present invention will now be described wi th reference to FIG. 2.

With respect to the active set, the first and second CPEs CPE_1 and CPE_2 co mmunicate with the WRAN BS through a first frequency channel CHJ . The third and fourth CPEs CPE_3 and CPE_4 communicate with the WRAN BS through a second fre quency channel CH_2. The fifth CPE_5 communicates with the WRAN BS through a t hird frequency channel CH_3.

In view of the first CPE CPE_1 or the second CPE CPE_2, an active set 1 is {CH _1} and active set 2 is {CH_2, CH_3}. In view of the third CPE CPE_3 or the fourth CP E CPE_4, an active set 1 is {CH_2} and active set 2 is {CH_1 , CH_3}. In view of the fif th CPE CPE_5, an active set 1 is {CH_3} and active set 2 is {CH_1 , CH_2}. In view of t he WRAN BS, active set 1 is {CH_1 , CH_2, CH_3}, and active set 2 is {}. Active set of the WRAN system is (CHJ 1 CH_2, CH_3}.

With regard to conventional spectrum sensing technology, the WRAN BS and th e first through fifth CPEs CPEJ , CPE_2, CPE_3, CPE_4, and CPE_5 perform spectru m sensing for frequency channels belonging to the active set 1 in view of their respectiv e position. For example, the fifth CPE CPE_5 performs spectrum sensing for the third frequency channel CH_3 to determine whether an incumbent user appears on the third frequency channel CH_3. If the fifth CPE CPE_5 determines that the incumbent user appears on the third frequency channel CH_3, the third CPE CPE_3 must release the t hird frequency channel CH_3 that is currently being used by the third CPE CPE_3, i.e., stop using the third frequency channel CH_3.

According to the conventional spectrum sensing technology, the spectrum sensin g for the first frequency channel CHJ is performed by the WRAN BS, the first CPE CP EJ , and the second CPE CPE_2, the spectrum sensing for the second frequency chan nel CH_2 is performed by the WRAN BS, the third CPE CPE_3, and the fourth CPE CP E_4, and the spectrum sensing for the third frequency channel CH_3 is performed by th e WRAN BS and the fifth CPE CPE_5.

With respect to the spectrum sensing method according to an embodiment of the present invention, the WRAN BS and the first through fifth CPEs CPEJ , CPE_2, CPE _3, CPE_4, and CPE_5 perform spectrum sensing for frequency channels belonging to the active sets 1 and 2. The spectrum sensing for the first frequency channel CH_1 , th e second frequency channel CH_2, and the third frequency channel CH_3 is performed by all of the WRAN BS and the first through fifth CPEs CPE_1 , CPE_2, CPE_3, CPE_ 4, and CPE_5.

Provided that the first through fifth CPEs CPE_1 , CPE_2, CPE_3, CPE_4, and C PE_5 notify the WRAN BS of the result of the spectrum sensing, the comparison betwe en the conventional spectrum sensing method and the spectrum sensing method of an embodiment of the present invention will now be described in terms of the effect. According to the conventional spectrum sensing method, the WRAN BS can use three kinds of results of the spectrum sensing performed by the WRAN BS, the first CP E CPEJl , and the second CPE CPE_2 in order to determine whether the incumbent us er appears on the first frequency channel CH_1. Meanwhile, according to the spectru m sensing method of an embodiment of the present invention, the WRAN BS can use s ix kinds of results of the spectrum sensing performed by the WRAN BS and the first thr ough fifth CPEs CPEJI 1 CPE_2, CPE_3, CPE_4, and CPE_5 in order to determine wh ether the incumbent user appears on the first frequency channel CH_1. Therefore, it will be fully understood that the WRAN BS of an embodiment of the present invention th at uses the results of the spectrum sensing more than those of the conventional WRAN BS can more accurately detect the appearance of the incumbent user. Furthermore, i t will be fully understood that if an incumbent user of the first frequency channel CH_1 i s located near the fifth CPE CPE_5, the spectrum sensing method of an embodiment of the present invention that performs the spectrum sensing for the first frequency chann el CH_1 by the first through fifth CPEs CPE_1 , CPE_2, CPE_3, CPE_4, and CPE_5 ca n more accurately detect whether the incumbent user of the first frequency channel CH _1 appears than the conventional spectrum sensing method.

The spectrum sensing for frequency channels belonging to active sets may be p erformed during a QP. Thus, the structure of a super frame including the QP will now be described. The super frame used in the WRAN system of an embodiment of the present inv ention may have different QPs according to frequency channels. The reason for this is that it is difficult to realize an adaptive wideband filter to support a super frame where each frequency channel has the same location of QP in terms of time. The interval between two adjacent two QPs in terms of time may be determined according to a channel conversion time of a sensor included in a WRAN device. Whe n a first QP corresponds to the first frequency channel CH_1 , and a second QP corresp onds to the second frequency channel CH_2, the sensor performs the spectrum sensin g for the first frequency channel CH_1 during the first QP and then converts the first fre quency channel CH_1 into the second frequency channel CH_2 before arriving at the s econd QP.

Assuming that the super frame includes a plurality of frames, the assignment req uirements of QPs will now be described in detail with reference to FIGS. 3, 4, and 5. FIG. 3 illustrates super frame formats according to an embodiment of the presen t invention. In detail, FIG. 3 illustrates super frames of respective frequency channels belonging to an active set.

Referring to FIG. 3, in a time division duplex (TDD) system, the first frequency ch annel CH_1 is assigned to the first CPE CPE_1 , and the second through Fth frequency channels CH 2 through CH_F are respectively assigned to the second through Fth CPE s CPE 2 through CPE F. In more detail, since a WRAN system currently uses the firs t through Fth frequency channels CH_1 through CH_F, current active set is {CH_1 , CH__ 2, through to CH_F}.

Each super frame includes N frames. One of the N frames includes a QP of the first through Fth QPs QP_1 , QP_2, through to QP_F having a period of time Tq. In det ail, the first through Fth QPs QP_1 , QP_2, through to QP_F are established in a frame d esignated by a medium access control (MAC) layer.

A period of time T5 denotes a sensing period of each frequency channel. A peri od of time Tf denotes a channel conversion time of a sensor included in a WRAN devic e.

In particular, the remarkable characteristic of the super frame is that the first thro ugh Fth QPs QP_1 , QP_2, through to QP_F have different time locations according to fr equency channels. In more detail, when two or more frequency channels belonging to an active set are currently being used, the first through Fth QPs QP_1 , QP_2, through to QP_F may not be assigned to the same frame. The above characteristic of the super frame is applied when the sensor included in the WRAN device performs the spectrum sensing for a single frequency channel each time. In particular, in the assignment of adjacent QPs in view of time the channel conversion time Tf of the sensor may be consi dered. In other words, the sensor can convert the first frequency channel CH_1 into th e second frequency channel CH_2 within the period of time Tf.

The length of each super frame is between 100 msec and 500 msec. The lengt h of each frame is about 10 msec. The channel conversion time Tf can vary according to the sensor in the super frame format. Considering the fact that the channel conver sion time for performing hard handoff of a mobile communication terminal is generally 2

~3 msec, the channel conversion time Tf can be 2 msec in the super frame format.

FIGS. 4A, 4B, and 4C illustrate assignments of frequency channels of an active s et, a candidate set, a remaining set, and an occupied set according to an embodiment of the present invention. Referring to FIG. 4A, a WRAN system uses a single frequenc y channel. Referring to FIGS. 4B and 4C, the WRAN system uses two channel-bonde d frequency channels and three channel-bonded frequency channels, respectively. Fr equency channels f-1 , f, and the like have bandwidths of 6, 7, or 8 MHz.

Referring to FIG. 4A, a WRAN BS operates a frequency channel f, the active set A={f}, and the occupied set O = {f-2, f+2}. Other unused frequency channels f-5, f-4, f- 3, f-1 , f+1 , f+3, f+4, and f+5 are classified as the candidate set C={f-5, f-4, f+4, f+5} and the remaining set R={f-3, f-1 , f+1 , f+3} according to the quality of the frequency chann els.

Referring to FIG. 4B, the WRAN BS operates the frequency channels f and f+1 which are channel-bonded, the active set A={f, f+1}, and the occupied set O = {f-2, f+3}. Other unused frequency channels f-5, f-4, f-3, f-1 , f+2, f+4, and f+5 are classified as th e candidate set O{f-5, f-4, f+5} and the remaining set R={f-3, f-1 , f+2, f+3} according to the quality of the frequency channels.

Referring to FIG. 4C, the WRAN BS operates the frequency channels f-1 , f, and f +1 which are channel-bonded, the active set A={f-1 , f, f+1}, and the occupied set O = {f- 3, f+3}. Other unused frequency channels f-5, f-4, f-2, f+2, f+4, and f+5 are classified as the candidate set C={f-5, f+5} and the remaining set R={f-4, f-2, f+2, f+4} according t o the quality of the frequency channels.

FIGS. 5A and 5B illustrate super frame formats according to another embodimen t of the present invention. Referring to FIG. 5A, when a WRAN device uses three freq uency channels f-1 , f, and f+1 which are channel-bonded, QPs of the frequency channe

Is f-1 , f, and f+1 are assigned to mth and m+1 st super frames. Referring to FIG. 5B, wh en the WRAN device uses two frequency channels f-1 and f which are channel-bonded, QPs of the frequency channels f-1 and f are assigned to mth and m+1 st super frames.

The definition of the periods of time Tq> Tf, and T8 are the same as described wit h reference to FIG. 3 and thus their descriptions will not be repeated here. The assignment of QPs illustrated in FIGS. 5A and 5B satisfy the requirements f or the assignment of QPs described above with reference to FIG. 2. In particular, in th e present embodiment, QPs of the frequency channels which are channel-bonded are a ssigned adjacent to each other in the order of the frequency channels. A media acces s control (MAC) layer of the WRAN BS establishes the assignment of QPs and provides all CPEs with information on the assignment of QPs. The information on the assignm ent of QPs includes information on time locations of QPs according to frequency chann els. The assigning of QPs based on a regular rule that QPs of the frequency channels which are channel-bonded are sequentially assigned as illustrated in FIGS. 5A and 5B results in a reduction of the amount of data required for transmitting the information on t he assignment of QPs.

FIG. 6 illustrates super frame formats according to another embodiment of the pr esent invention. Referring to FIG. 6, QPs of frequency channels which are channel-bo nded as illustrated in FIG. 5 and are not channel-bonded as illustrated in FIG. 3 are assi gned to mth and m+1 st super frames. The definition of the periods of time Tq> Tf, and Ts are the same as those describ ed with reference to FIG. 3 and thus their descriptions will not be repeated here.

The first CPE CPE_1 uses the first frequency channel ChM , the second frequen cy channel CH_2, and the third frequency channel CH_3 which are channel-bonded. The second CPE CPE_2 uses an Fth frequency channel CH_F. Therefore, in view of the first CPE CPEJ , an active set 1 is {CH_1 , CH_2, CH_3

}, and an active set 2 is {CH_F}. Likewise, in view of the second frequency channel C H_2, an active set 1 is {CH_F}, and an active set 2 is {CH_1 , CH_2, CH_3}.

An occupied set is {CH_5} since an incumbent user occupies the fifth frequency channel CH_5. Each CPE may have a different candidate set and remaining set since the candi date set and the remaining set vary according to quality of frequency channels as descri bed above. For descriptive convenience, in the present embodiment, the first CPE CP E_1 and the second frequency channel CH__2 have the same candidate sets {channel 7 , channel 8, through to channel F-2}. The first CPE CPEJ and the second frequency channel CH_2 have the same occupied sets {channel 4, channel 6, channel F-1}.

Frames including QPs are sequentially adjacent to each other between the frequ ency channels CH_1 , CH_2, and CH_3, which are channel-bonded, which is the same as those described with reference to FIG. 5. QPs of the frequency channels CH_1 , C H_2, CH__3, CH_F belonging to the active sets 1 are assigned in different frames and th us do not overlap in terms of time as described with reference to FIG. 2.

FIG. 7 is a block diagram of an apparatus for assigning QPs in a cognitive radio system according to an embodiment of the present invention. Referring to FIG. 7, the apparatus for assigning QPs in the cognitive radio system comprises a determiner 700 and an establisher 710. The apparatus for assigning QPs in the cognitive radio syste m of the present embodiment that satisfies the requirements for the assignment of QPs is generally included in a WRAN BS but the present invention is not limited thereto. Th at is, the apparatus for assigning QPs in the cognitive radio system of the present embo diment can be a separate apparatus of a WRAN system.

The determiner 700 determines at least one frequency channel to which QPs are assigned. The frequency channel to which QPs are assigned means a frequency cha nnel belonging to an active set.

The establisher 710 establishes time locations of QPs of the at least one frequen cy channel. In particular, if two or more frequency channels are determined, the establ isher 710 establishes time locations of QPs of each frequency channel so that the QPs do not overlap between different frequency channels. The establisher 710 may establi sh time locations of the QPs according to the channel conversion time of the cognitive r adio equipment. If each super frame of a cognitive radio system includes a plurality of frames as il lustrated in FIGS. 3, 5, and 6, the establisher 710 forms the super frames to include in order to differentiate frames including QPs between different frequency channels. Wh en the establisher 710 assigns QPs of frequency channels which are channel-bonded t o the super frames, frames including QPs may be adjacent to each other in the order of the frequency channels.

FIG. 8 is a block diagram of a WRAN system according to an embodiment of the present invention. Referring to FIG. 8, the WRAN system comprises a WRAN BS 80 0, a first CPE 810, and a second CPE 820. In the present embodiment, the WRAN B S 800 that includes the apparatus for assigning QPs in the cognitive radio system illustr ated in FIG. 7 assigns QPs in advance.

The WRAN BS 800 comprises a transmitter/receiver 802 and a sensor 804. Th e first CPE 810 comprises a transmitter/receiver 812 and a sensor 814. The second C PE 820 comprises a transmitter/receiver 822 and a sensor 824.

The WRAN system of the present embodiment is a TDD system. The first frequ ency channel CH_1 is allocated to the first CPE 810. The second frequency channels CH_2 is allocated to the second CPE 820.

First, the operation of the WRAN BS 800 will now be described. The transmitter/receiver 802 communicates with the first CPE 810 via the first fre quency channel CH_1 , communicates with the second CPE 820 via the second frequen cy channel CH_2, and does not perform transmission via the first or the second frequen cy channel CH_1 or CH_2 during a QP of the WRAN BS 800. The transmitter/receiv er 802 may transmit information on the assignment of QPs of the first and second frequ ency channels CH_1 and CH_2 belonging to an active set to the first CPE 810 and the second CPE 820. The transmitter/receiver 802 may receive each result obtained by p erforming spectrum sensing for the first CPE 810 and the second CPE 820 from the firs t CPE 810 and the second CPE 820. Therefore, the WRAN BS 800 can utilize a result obtained by performing spectrum sensing and the results obtained by performing spec trum sensing for the first CPE 810 and the second CPE 820, thereby performing more r eliable spectrum sensing (i.e. detection of the appearance of an incumbent user).

The sensor 804 performs spectrum sensing for the first frequency channel CH_1 during a QP of the first frequency channel ChM , converts the first frequency channel CH_1 into the second frequency channel CH_2 before a QP of the second frequency c hannel CH_2, and performs spectrum sensing for the second frequency channel CH_2 during a QP of the second frequency channel CH_2.

Second, the operation of the first CPE 810 will now be described. The transmitter/receiver 812 communicates with the WRAN BS 800 via the first f requency channel CH_1 but does not perform transmission during a QP of the first freq uency channel ChM . The transmitter/receiver 812 may receive information on the as signment of QPs of the first and second frequency channels ChM and CH_2 belonging to the active set from the WRAN BS 800. The transmitter/receiver 812 may notify a r esult obtained by performing spectrum sensing for the first CPE 810, i.e., a sensing res ult obtained by the sensor 814, of the WRAN BS 800. The sensor 814 performs spectrum sensing for the first frequency channel CH_1 during the QP of the first frequency channel CH_1 based on the information on the as signment of QPs received from the transmitter/receiver 812, converts the first frequency channel CH__1 into the second frequency channel CH_2, and performs spectrum sensi ng for the second frequency channel CH_2 during the QP of the second frequency cha nnel CH_2.

Third, the operation of the second CPE 820 will now be described. The transmitter/receiver 822 communicates with the WRAN BS 800 via the seco nd frequency channel CH_2 but does not perform transmission during a QP of the seco nd frequency channel CH_2. The transmitter/receiver 822 may receive information on the assignment of QPs of the first and second frequency channels CH_1 and CH_2 bel onging to the active set from the WRAN BS 800. The transmitter/receiver 822 may not ify a result obtained by performing spectrum sensing for the second CPE 820, i.e., a se nsing result obtained by the sensor 824, of the WRAN BS 800. The sensor 824 performs spectrum sensing for the first frequency channel CH_1 during the QP of the first frequency channel CH_1 based on the information on the as signment of QPs received from the transmitter/receiver 822, converts the first frequency channel CH_1 into the second frequency channel CH_2, and performs spectrum sensi ng for the second frequency channel CH_2 during the QP of the second frequency cha nnel CH_2.

FIG. 9 is a flowchart illustrating a method of assigning QPs in a cognitive radio sy stem according to an embodiment of the present invention. The method of assigning QPs in the cognitive radio system will now be described with reference to FIG. 7.

Referring to FIG. 9, the determiner 700 determines at least one frequency chann el to which QPs are assigned (S900). The frequency channel to which QPs are assign ed means a frequency channel belonging to an active set.

The establisher 710 establishes time locations of QPs of the at least one frequen cy channel (S910). A method of establishing time locations of QPs is the same as des cribed with reference to FIG. 7 and the description thereof will not be repeated here. FIG. 10 is a flowchart illustrating a spectrum sensing method of a WRAN BS ace ording to an embodiment of the present invention. The spectrum sensing method of th e WRAN BS will now be described with reference to FIG. 8, assuming that QPs are pre viously assigned. Referring to FIG. 10, the transmitter/receiver 802 transmits information on the as signment of QPs of the first and second frequency channels ChM and CH_2 to the first CPE 810 and the second CPE 820 (S1000).

The transmitter/receiver 802 communicates with the first CPE 810 via the first fre quency channel CH__1 , communicates with the second CPE 820 via the second frequen cy channel CH_2, and does not perform transmission via the first or the second frequen cy channel CH__1 or CH_2 during a QP of the WRAN BS 800 (S1010). In S1010, the sensor 804 performs spectrum sensing for the first frequency channel CH_1 during the QP of the first frequency channel CH_1 , converts the first frequency channel CH_1 into the second frequency channel CH__2 before the QP of the second frequency channel C H_2, and performs spectrum sensing for the second frequency channel CH_2 during th e QP of the second frequency channel CH_2.

The transmitter/receiver 802 receives each sensing result from the first CPE 810 and the second CPE 820 (S1020). Therefore, it will be fully understood by those of or dinary skill in the art that the spectrum sensing method can further finally detect whethe r an incumbent user appears on the frequency channels belonging to an active set base d on the received sensing result and a result obtained by performing spectrum sensing of the WRAN BS.

FIG. 11 is a flowchart illustrating a spectrum sensing method of CPE according t o an embodiment of the present invention. The spectrum sensing method of CPE will now be described with reference to FIG. 8.

Referring to FIG. 11 , the transmitter/receiver 812 may receive information on the assignment of QPs of the first and second frequency channels CH_1 and CH_2 broadc asted from the WRAN BS 800 (S1100). The transmitter/receiver 812 communicates w ith the WRAN BS 800 through the first frequency channel CH_1 but does not communic ate with the WRAN BS 800 during a QP of the first frequency channel ChM (S1110). In S1110, the sensor 814 performs spectrum sensing for the first frequency channel CH _1 during the QP of the first frequency channel ChM based on the information receive d in S1100, and performs spectrum sensing for the second frequency channel CH_2 du ring the QP of the second frequency channel CH_2. The communication of the transm itter/receiver 812 and the spectrum sensing performed by the sensor 814 occur in S1 1 1 0 according to the super frames illustrated in FIGS. 3, 5, and 6.

The transmitter/receiver 812 transmits a sensing result obtained by the sensor 8 14 in S1110 to the WRAN BS 800 (S1120). The present invention can also be embodied as computer readable code on a co mputer readable recording medium. The computer readable recording medium is any d ata storage device that can store data which can be thereafter read by a computer syst em. Examples of the computer readable recording medium include read-only memory ( ROM), random-access memory (RAM), CD-ROMs, magnetic tapes, floppy disks, optical data storage devices, and carrier waves. The computer readable recording medium c an also be distributed network coupled computer systems so that the computer readabl e code is stored and executed in a distributed fashion. Also, functional programs, cod e and code segments for accomplishing the present invention can be easily construed b y programmer skilled in the art to which the present invention pertains.

While the present invention has been particularly shown and described with refer ence to exemplary embodiments thereof, it will be understood by those of ordinary skill i n the art that various changes in form and details may be made therein without departin g from the spirit and scope of the invention as defined by the appended claims. The e xemplary embodiments should be considered in a descriptive sense only and not for pu rposes of limitation. Therefore, the scope of the present invention is defined not by the detailed description of the invention but by the appended claims, and all differences wi thin the scope of the present invention will be construed as being included in the presen t invention.

Claims

1. A spectrum sensing method performed by customer premises equipment (CP E) in a cognitive radio system comprising: communicating with a base station (BS); and performing spectrum sensing for frequency channels having quiet periods (QPs) during the QPs of the frequency channels used in the cognitive radio system, wherein the QPs of the frequency channels do not overlap each other.
2. The method of claim 1 , wherein each super frame of the cognitive radio syste m includes a plurality of frames, locations of the frames including QPs differ from each other between different fre quency channels.
3. The method of claim 1 or 2, wherein each super frame of the cognitive radio s ystem includes a single QP per frequency channel.
4. The method of claim 1 , further comprising: receiving information on the assignment of the QPs of the frequency channels fro m the BS, wherein the spectrum sensing is performed based on the information on the assi gnment of the QPs.
5. The method of claim 1 , further comprising: notifying the BS about a spectrum sensing result.
6. The method of claim 1 , wherein QPs of frequency channels which are channel -bonded do not overlap each other.
7. The method of claim 1 or 4, wherein each super frame of the cognitive radio s ystem includes the plurality of frames, the locations of the frames including QPs differ from each other between differen t frequency channels, the locations of the frames including QPs are adjacent to each other between the frequency channels which are channel-bonded.
8. The method of claim 7, wherein the locations of the frames including QPs are adjacent to each other in the order of the frequency channels between the frequency ch annels which are channel-bonded.
9. A spectrum sensing method performed by a BS in a cognitive radio system co mprising: communicating with at least one CPE; and performing spectrum sensing for frequency channels having QPs during the QPs of the frequency channels used in the cognitive radio system, wherein the QPs of the frequency channels do not overlap each other.
10. The method of claim 9, wherein each super frame of the cognitive radio syste m includes a plurality of frames, locations of the frames including QPs differ from each other between different fre quency channels.
11. The method of claim 9 or 10, wherein each super frame of the cognitive radio system includes a single QP per frequency channel.
12. The method of claim 9, further comprising: transmitting information on the as signment of the QPs of the frequency channels to the at least one CPE.
13. The method of claim 9, further comprising: receiving a spectrum sensing resu It from the at least one CPE.
14. The method of claim 9, wherein QPs of frequency channels which are chann el-bonded do not overlap each other.
15. The method of claim 9 or 12, wherein each super frame of the cognitive radio system includes a plurality of frames, the locations of the frames including QPs differ from each other between differen t frequency channels, the locations of the frames including QPs are adjacent to each other between the frequency channels which are channel-bonded.
16. The method of claim 15, wherein the locations of the frames including QPs ar e adjacent to each other in the order of the frequency channels between the frequency channels which are channel-bonded.
17. A method of assigning QPs to perform spectrum sensing in a cognitive radio system comprising: determining at least one frequency channel to which the QPs are assigned; and establishing time locations of the QPs of the at least one frequency channel, wherein the establishing of the time locations comprises: if two or more frequency channels are determined, establishing time locations of
QPs of the frequency channels so that the QPs do not overlap each other between diffe rent frequency channels.
18. The method of claim 17, wherein the establishing of the time locations compr ises: establishing time locations of the QPs based on a channel conversion time of a d evice belonging to the cognitive radio system.
19. The method of claim 17, wherein each super frame of the cognitive radio syst em includes a plurality of frames, wherein the establishing of the time locations further comprises: forming the super frames so that the time locations of the frames including QPs differ from each other between different frequency channels.
20. The method of claim 19, wherein the establishing of the time locations further comprises: assigning the QPs of frequency channels which are channel-bonded to the super frames so that the time locations of the frames including the QPs are adjacent to each other in the order of the frequency channels.
21. CPE in a cognitive radio system comprising: a transmitter/receiver communicating with a BS; and a sensor performing spectrum sensing for frequency channels having QPs during the QPs of the frequency channels used in the cognitive radio system, wherein the QPs of the frequency channels do not overlap each other.
22. The CPE of claim 21 , wherein each super frame of the cognitive radio syste m includes a plurality of frames, locations of the frames including QPs differ from each other between different fre quency channels.
23. The CPE of claim 21 , wherein the transmitter/receiver receives information o n the assignment of the QPs of the frequency channels from the BS, the sensor performs spectrum sensing based on the information on the assignm ent of the QPs.
24. The CPE of claim 21 , wherein the transmitter/receiver notifies a spectrum se nsing result of the BS.
25. A BS in a cognitive radio system comprising: a transmitter/receiver communicating with at least one CPE; and a sensor performing spectrum sensing for frequency channels having QPs during the QPs of the frequency channels used in the cognitive radio system, wherein the QPs of the frequency channels do not overlap each other.
26. The BS of claim 25, wherein each super frame of the cognitive radio system i ncludes a plurality of frames, locations of the frames including QPs differ from each other between different fre quency channels.
27. The BS of claim 25, wherein the transmitter/receiver transmits information on the assignment of the QPs of the frequency channels to the at least one CPE.
28. The BS of claim 25, wherein the transmitter/receiver receives a spectrum sen sing result from the at least one CPE.
29. An apparatus for assigning QPs to perform spectrum sensing in a cognitive r adio system comprising: a determiner determining at least one frequency channel to which the QPs are a ssigned; and an establisher establishing time locations of the QPs of the at least one frequenc y channel, wherein the establisher, if the determiner determines two or more frequency cha nnels, establishes the time locations of QPs of the frequency channels so that the QPs do not overlap each other between different frequency channels.
30. The apparatus of claim 29, wherein the establisher establishes the time locati ons of the QPs based on a channel conversion time of a device belonging to the cogniti ve radio system.
31. The apparatus of claim 29, wherein each super frame of the cognitive radio s ystem includes a plurality of frames, wherein the establisher forms the super frame so that the time locations of the fr ames including QPs differ from each other between different frequency channels.
32. A structure of a super frame for spectrum sensing performed by a BS or CPE in a cognitive radio system, wherein the super frame includes at least one QP in each of frequency channels used in the cognitive radio system, and the QPs of the frequency channels do not overlap each other.
33. The structure of claim 32, wherein the super frame includes a plurality of fra mes, and locations of the frames including QPs differ from each other between different fre quency channels.
34. The structure of claim 32 or 33, wherein the super frame includes a single Q P per frequency channel.
35. The structure of claim 32 or 33, wherein the QPs are established based on a channel conversion time required by a sensor to perform spectrum sensing.
36. The structure of claim 32, wherein QPs of frequency channels which are cha nnel-bonded do not overlap each other.
37. The structure of claim 32, wherein the super frame includes a plurality of fra mes, locations of the frames including QPs differ from each other between different fre quency channels, and the locations of the frames including QPs are adjacent to each other between the frequency channels which are channel-bonded.
38. A computer readable recording medium storing a program for executing a m ethod of any one of claims 1 through 20.
PCT/KR2007/000776 2006-02-14 2007-02-14 Method for sensing spectrum and arranging quiet period in cognitive radio system, customer premise equipment, base station and superframe structure using the same WO2007094604A1 (en)

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