METHOD FOR SPECTRUM COLLABORATION IN DYNAMIC FREQUENCY-HOPPING WIRELESS REGIONAL AREA NETWORK

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wireless communication system based on cognitive radio, especially to a method of spectrum collaboration in a dynamic frequency-hopping wireless regional area network.

2. Description of the Related Art

At present in a communication protocols such as IEEE802.22, etc., no specification or description is addressed on how to effectively solve a problem of spectrum collision between two or more overlapping WRAN systems with a method of spectrum collaboration.

In a WRAN system using a cognitive radio technique, how to make full use of limited free idle frequency band to implement area access communication is in hot research in current radio communication field.

As a rule, when each consumer premise equipment (CPE) performs in-band spectrum sensing, it is necessary for this access network to spend a long quiet period in sensing authorized legal users' spectrum occupation within corresponding frequency band.

A frequency-hopping operation scheme based on dynamic frequency hopping is proposed in the above protocol for a WRAN system. With this structure, periodical frequency hopping between different idle channels is effectively adopted to drastically reduce the quiet period for in-band spectrum sensing.

Figure 1 illustrates a process that WRANl 104 and WRAN2 105 implement agile frequency hops between CHA 101 channel, CHB 102 channel and CHC 103 channel. As shown in this figure, within a first period of CHA 101, WRANl 104 operates in an available band. In a second operation period, WRANl 104 hops to an idle channel CHB 102 to implement communication. And in a third operation

period, WRANl 104 hops to an idle channel CHC 103. Similarly, for WRAN2 105, it sequentially hops from CHC 103 to CHA 101 and then to CHB 102 respectively within the three operation periods. Therefore, not only WRANl 104 and WRAN2 105 can be guaranteed to operate in idle channels, but also the CPEs can implement normal spectrum sensing during channels' quiet periods.

Figure 2 illustrates a process that WRAN201 operates during three periods such as an initial spectrum sensing stage 202 and two operation stages 203 and 204. Firstly, CPEs for WRAN implement initial spectrum sensing 202 to detect an idle frequency band CHA in which this system can normally operate and an enabling time 205. Then, during a second period, WRAN hops to CHA to transmit data as well as to perform spectrum sensing 203 on CH([0,A-n],[A+n,N]) to obtain an enabling time 206 for CHB. Next, during a third period, WRAN hops to CHB and at the same time to implement spectrum sensing 204 on CH([0,B-n],[B+n,N]). N is a total number of channels to be sensed, and n indicates a guard band.

However, how to solve the spectrum collision between multiple WRANs based on dynamic frequency hopping is in hot research at present. A widely applied solution is that a control center of WRANl that has detected the idle channel CHA announces that it has occupied this idle channel by signaling to other WRANs and at the same time, the control center monitors announcement broadcast information from other WRANs. If there is no broadcast information on the occupation of CHA, or the occupation announcement from other systems is later than that of WRANl, then WRANl hops to CHA in the next period. Thus, it is supposed that the following scenario in Figure 3 exists when this collision-free-based solution is adopted to solve the spectrum collision in a WRAN system: during a first period, WRANl 301 has obtained a CHA enabling time 303 through spectrum sensing, and WRAN2 302 has obtained a CHD enabling time, then WRANl 301 and WRANl 302 hop to CHA and CHD respectively during a second period, during which the following two cases happen: (1) both WRANl 301 and WRAN2 302 detect that only CHB is idle but obtain different enabling time, i.e., a CHB enabling time 305 and a CHB enabling time 306;

(2) WRANl 301 detects that only CHB is idle. Meanwhile, WRAN2 system detects that CHB and CHC are idle. However the CHC enabling time exceeds the maximum time delay that WRAN2 system can bear.

Obviously, the conventional collision-free solution based on contention mechanism is not able to solve the above two cases of spectrum collision.

SUMMARY OF THE INVENTION

The object of this invention is to provide a method for spectrum collaboration to solve the spectrum collision between multiple overlapped WRAN systems so as to guarantee that WRAN systems could operate more efficiently within free frequency bands.

To solve the technical problem above, a method for spectrum collaboration in a dynamic frequency- hopping wireless regional area network comprising steps of:

Consumer Premise Equipment CPE in all WRANs performing spectrum sensing and feeding relevant idle channel information back to respective control base stations; a WRAN with high priority determining spectrum resource allocation for a WRAN system in a spectrum collision state.

With the method according to present invention to solve the spectrum collision between overlapping WRANs based on dynamic frequency hop, QoS can be effectively guaranteed for WRANs. At the same time, significant problems such as the realized wireless access, greater time delay due to the lack of free idle channel resource for adjacent WRANs, can be effectively avoided. Therefore, it efficiently helps the operator to effectively consolidate the spectrum resource to improve both communication quality and reliability within the coverage of the whole WRAN.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 illustrates a dynamic frequency hopping process in multiple WRANs;

Figure 2 illustrates a dynamic frequency hopping operation in a WRAN;

Figure 3 illustrates spectrum collision between two overlapping WRANs;

Figure 4 shows a structure of overlapping WRAN systems according to present invention;

Figure 5 shows a flow of sub-channel division in the spectrum collaboration method according to present invention;

Figure 6 shows a flow operated by a system according to present invention;

Figure 7 shows a control signaling between two overlapping WRAN base stations according to present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In Figure 4, there exist two overlapping wireless regional area networks WRAN-A401 and WRAN-B402. In this case, WRAN- A401 implements spectrum sensing and obtains CHB as its target frequency band for frequency hopping during a next period. Meanwhile, WRAN-B402 also implements spectrum sensing and obtains CHB as its target frequency band for frequency hopping during a next period. Now, spectrum collision occurs between WRAN- A401 and WRAN-B402.

Thus, the idea of the present invention is to implement band sharing of the idle channel CHB by two wireless regional area networks via signaling interaction between the control centers of the overlapping WRANs. Here, WRAN-A401 occupies CHB-parl 403 and WRAN-B402 occupies CHB-part2 404.

With curves in time vs. frequency coordinates system, Figure 5 illustrates the division and sharing of frequency resources between WRAN- A501 and WRAN-B502. In this figure, channel CHB is divided into N sub-channels 0,1,...,N-I, with sub-channels [k+n,N-l] allocated to WRAN-A501, and sub-channels [0,k-n] to WRAN-B502. To avoid interference caused by the two overlapping wireless area access systems to adjacent channels, 2n sub-channels are preserved as guard band 503. Therefore, the effective bandwidth allocated to WRAN-A 501 is:

£ JF(WRAN - A) = J 1 -— j . BW _ CHB And the effective bandwidth allocated to WRAN-B 502 is:

BW[WRAN - B) = (l - a} 1 - — J • BW _ CHB

The guard band 503 has the bandwidth as follows: BW(GB) = — * BW CHB

Here the guard band parameter n is related to the overlapping area S between adjacent WRAN systems and the transmission power P for WRAN base station. The bandwidth allocation parameter ^a is determined by the base station of the WRAN system with highest priority according to the bandwidth request information from the WRAN base station with lower priority. Details on specification of priority and the interactive control signaling will be given in present invention.

Figure 6 illustrates a flow operated by a system according to present invention.

601 CPE in WRAN performs spectrum sensing and sends the spectrum sensing results to corresponding base station, and then 602 CPE waits.

603 WRAN checks whether idle channel collides. If idle channel collides and 604 WRAN has detected any other idle channel, 605 WRAN determines whether the enabling time of any other idle channel exceeds the maximum time delay. 606 WRAN prepares to hop to the selected channel if the enabling time of any other idle channel does not exceed the maximum time delay. In the meantime, the idle channel does not collide in the step 603, 610 WRAN prepares to hop to the selected channel.

In case 604 any other detected idle channels do not exist or in case 605 enabling time of any other idle channel exceeds the maximum time delay, 607 WRAN determines whether to collide with the idle channel cooperation.

In 607 if it occurs to collide with the idle channel cooperation, 608 WRAN prepares to hop to the some frequency bands of the idle channel such that WRAN can share the bandwidth of the idle channel. However, it does not occur to collide with the idle channel cooperation, in 609 WRAN prepares to hop to the selected channel.

Figure 7 illustrates a control signaling between WRAN systems according to the present invention. With reference to Figures 6 and 7, the WRAN system according to present invention operates as follows:

1. CPEs in WRAN-A and WRAN-B perfbrm spectrum sensing and send the spectrum sensing results to corresponding base stations, where the idle frequency bands are determined for next frequency hopping period.

2. base station 701 in WRAN-A and base station 702 in WRAN-B respectively broadcast message of Announcement_use_CHB703 to the WRANs around. Meanwhile they monitor the broadcast information from the WRANs. Here, with no loss of generality, it is supposed the situation that WRAN-A detects the idle channel CHB before base station 702 in WRAN-B broadcasts the announcement signal. Therefore, WRAN-A system bears higher priority.

3. If base station 701 in WRAN-A does not receive message of Announcement_use_CHB703 information from the WRANs around during the waiting period, it dynamically hops to CHB in the next period to transmit and receive data. If base station 701 in WRAN-A receives the message of Announcement_use_CHB704 and Announcement use CHC information from WRAN-B base station 702 to the WRANs around during the waiting period, it still dynamically hops to CHB in the next period to transmit and receive data. If base station 701 in WRAN-A only receives Announcement_use_CHB704 information from WRAN-B base station 702 to the WRANs around during the waiting period but the time stamp of the announcement information is later than that of WRAN-A, WRAN-A system is therefore specified to bear higher priority.

4. WRAN-B base station 702 sends a Req_co-use_CHB705 message as well as a Req_Bandwidth_WRAN-B 706 message to WRAN-A base station 701.

5. When receiving the Req_co-use_CHB705 message from WRAN-B base station 702, WRAN-A base station 702 determines whether to share CHB or not according to the Req_Bandwidth_WRAN-B 706 and its own service QoS requirements.

6. WRAN-A base station 701 sends a Rep_co-use-CHB707 response message to determine whether to share the bandwidth of CHB.

7. If WRAN-A permits WRAN-B to share channel B with it, WRAN-A base station 701 schedules and allocates relevant idle frequency bands to WRAN-A and WRAN-B, and sends a bandwidth allocation control message "Bandwidth allocation CHB708" to WRAN-B base station 702.