Apparatus and method for controlling effect of interference in wireless communication system

An apparatus and a method for selecting a candidate channel to change an operating channel so as to minimize effect of interference in a wireless communication system using a Cognitive Radio (CR) function are provided. The method includes confirming an operating channel of at least one neighbor cell and candidate channel set to a third group by the neighbor cell; setting a candidate channel used as the operating channel of the neighbor cell among at least one candidate channels changeable to the operating channel, to a third group of lowest priority; setting candidate channels set to the third group of the neighbor cell among candidate channels not set to the third group, to a second group; and setting candidate channels set to neither the second group nor the third group, to a first group of highest priority.

The present application claims the benefit under 35 U.S.C. §119(a) to a Korean patent application filed in the Korean Intellectual Property Office on Feb. 12, 2008 and assigned Serial No. 10-2008-0012466, the entire disclosure of which is hereby incorporated by reference.

TECHNICAL FIELD OF THE INVENTION

The present invention relates generally to a wireless communication system using a Cognitive Radio (CR) function. More particularly, the present invention relates to an apparatus and a method for giving priority to candidate channels to change an operating channel in the wireless communication system.

BACKGROUND OF THE INVENTION

Recent advances of the wireless communication technology lead to the coexistence of systems using different communication schemes. For example, systems using the 2G Code Division Multiple Access (CDMA) scheme coexist with systems using the 3G International Mobile Telecommunication (IMT)-2000 scheme and systems using the 4G Orthogonal Frequency Division Multiplexing (OFDMA) scheme. The systems using different communication schemes provide services using different frequency bands.

Limited frequency resources for radio communications are insufficient for the coexisting systems of the different communication schemes.

To address this problem, research has been conducted on a Cognitive Radio (CR) technique, which senses unused frequency band or channel from the frequency bands allocated to a specific system and allows other system to use the sensed frequency band or channel. For instance, when a system for transmitting an incumbent signal allocates the frequency bands, the system does not use some channels of the allocated frequency band. In this case, to transmit the incumbent signal, a wireless communication system using the CR function detects the unused channels in the allocated frequency band and uses the detected channels to provide service to terminals in the service coverage.

When using the CR function as above, the wireless communication system services the terminals in the service coverage using the unused channels in the frequency band allocated to the particular system. When the incumbent signal intends to use the operating channels in use, the cells using the CR function should empty their operating channels. Accordingly, with the CR function, the wireless communication system cannot deliberately conduct the frequency planning in advance.

When using the CR function, the cells constitute a set of candidate channels to change their operation channel in use. When the incumbent signal intends to use the operating channel, the cells change the operating channel by selecting one of the candidate channels of the candidate channel set.

When the channel selected by the cell of the CR function to change the operating channel is the same as a channel of a neighbor cell, the wireless communication system is subject to the degradation of the system performance because of interference from the neighbor cell.

Hence, the wireless communication system using the CR function needs a basis for the cells to select channels to be included to the candidate channels and a basis for the cells to select a channel from the candidate channel set.

SUMMARY OF THE INVENTION

To address the above-discussed deficiencies of the prior art, it is a primary aspect of the present invention to address at least the above mentioned problems and/or disadvantages and to provide at least the advantages described below. Accordingly, an aspect of the present invention is to provide an apparatus and a method for giving priority to candidate channels to change an operating channel so as to minimize effect of interference between cells in a wireless communication system using a Cognitive Radio (CR) function.

Another aspect of the present invention is to provide an apparatus and a method for giving priority to candidate channels to maximize a distance between cells which reuse channels in a wireless communication system using a CR function.

According to one aspect of the present invention, a method for determining a priority of candidate channels at a serving node in a wireless communication system which uses a CR function includes confirming an operating channel of at least one neighbor cell and candidate channel set to a third group by the neighbor cell. The method also includes setting a candidate channel, used as the operating channel of the neighbor cell among at least one candidate channels changeable to the operating channel, to a third group of lowest priority The method further includes setting candidate channels, set to the third group of the neighbor cell among candidate channels not set to the third group, to a second group; and setting candidate channels set to neither the second group nor the third group, to a first group of highest priority.

According to another aspect of the present invention, a method for changing an operating channel at a serving node in a wireless communication system that uses a CR function includes setting at least one priority group with at least one candidate channel changeable to the operating channel by taking into account an operating channel of at least one neighbor cell. The method also includes when detecting an incumbent signal, selecting a candidate channel to change the operation channel based on priority of the candidate channels. The method further includes changing the operating channel to the selected candidate channel.

According to yet another aspect of the present invention, an apparatus for a base station to use a CR function in a wireless communication system includes a priority controller for generating at least one priority group with at least one candidate channel changeable to an operating channel of the base station by taking into account an operating channel of at least one neighbor cell. The apparatus also includes a controller for, when an incumbent signal is detected, selecting a candidate channel to change the operating channel based on priority of the candidate channels. Further, the apparatus includes a frequency controller for changing the operating channel under control of the controller.

DETAILED DESCRIPTION OF THE INVENTION

Exemplary embodiments of the present invention provide a technique for giving priority to candidate channels to change an operating channel in a wireless communication system using a Cognitive Radio (CR) function.

Hereinafter, while a base station using the CR function is assumed to use an unused channel in a broadcasting service system, the base station may utilize an unused channel of another system.

Using the CR function, the base station, upon detecting an incumbent signal, changes its operating channel by selecting one of candidate channels of a candidate channel set. To select the candidate channel that minimizes interference with neighbor cells, the base station assigns a priority to each of the candidate channels. For example, the base station determines a group of the candidate channels given the same priority to assign the priority to the candidate channel as shown inFIG. 1. In one example, the base station includes three groups distinguished by the priority. Herein, a first group included to the candidate channel set indicates the set of the channels of the highest priority, and a third group indicates the set of the channels of the lowest priority.

FIG. 1is a flowchart of a method for assigning priority to candidate channels in a wireless communication system according to an exemplary embodiment of the present invention.

When detecting an incumbent signal, the base station confirms candidate channels in step101. The candidate channel is a channel selectable for the change of the operating channel of the base station.

In step103, the base station checks the operating channels of the neighbor cells. For example, the base station checks the operating channels of the neighbor cells using Coexistence Beacon Protocol (CBP) packets provided from the neighbor cells. The base station transmits a CBP packet, including its operating channel information, to the neighbor cells.

In step105, the base station sets candidate channels used as the operating channels of the neighbor cells amongst the candidate channels confirmed in step101as the third group. When the base station sets its operating channel to the same operating channel of the neighbor cells, interference is caused with the neighbor cells. Thus, the base station sets the candidate channels used as the operating channels of the neighbor cells to the third group with the lowest priority.

In step107, the base station checks the candidate channels of the third group of the neighbor cells. For example, the base station confirms the candidate channels of the third group of the neighbor cells using the CBP packets provided from the neighbor cells. The base station transmits information regarding the candidate channels, set to the third group in step105, to the neighbor cells using the CBP packet.

In step109, the base station sets candidate channels belonging to the third group of the neighbor cells among the candidate channels, confirmed in step101, to the second group. The base station removes the candidate channels, set to the third group in step105, from the second group.

In step111, the base station sets candidate channels belonging to neither the second group nor the third group among the candidate channels, confirmed in step101, to the first group.

Next, the base station finishes this process.

As stated above, the base station confirms the operating channels and the third group information of the neighbor cells using the CBP packets. The CBP packets containing the operating channels of the neighbor cells may be the same as, or different from, the CBP packets containing the third group information of the neighbor cells. Accordingly, the base station can transmit its operating channel information and the third group information using the same CBP packets or using different CBP packets.

When the wireless communication system is configured as shown inFIG. 2, a base station200that manages a cell A gives priority to the candidate channels using CBP packets provided from neighbor cells.

FIG. 2depicts a structure for giving priority to the candidate channels in the wireless communication system according to an exemplary embodiment of the present invention.

The base station200, managing the cell A, uses a channel F0as its operating channel inFIG. 2.

Provided that candidate channels of the base station200are F1through F7, the base station200defines the operating channels F1, F3and F5of the neighbor cells as the third group. Herein, the base station200confirms the operating channels of the neighbor cells using the CBP packets.

Next, the base station200defines the candidate channels F1, F2and F3belonging to the third group of the neighbor cells as the second group. The base station200removes the candidate channel F1, which belongs to the third group among the candidate channels F1, F2and F3of the second group, from the second group. The base station200confirms the candidate channels belonging to the third group of the neighbor cells using the CBP packets.

After setting the second group and the third group, the base station200defines the candidate channel which belongs to neither the second group nor the third group amongst the candidate channels of the candidate channel set as the first group.

After the candidate channels have been given the priority as above, when the base station detects an incumbent signal that the base station intends to use its operating channel, the base station changes the operating channel by taking into account the priority of the candidate channels as shown inFIG. 3.

FIG. 3is a flowchart of a method for selecting a candidate channel to change an operating channel in the wireless communication system according to an exemplary embodiment of the present invention.

Detecting an incumbent signal, the base station confirms the candidate channels to change the operating channel in step301.

In step303, the base station assigns a priority to the candidate channels. For example, the base station determines the priority of the candidate channels by taking into account the operating channels of the neighbor cells as shown inFIG. 1.

In step305, the base station checks whether the incumbent signal is detected in the operating channel.

When detecting the incumbent signal, the base station recognizes that the detected incumbent signal intends to use its operating channel. Thus, the base station checks whether there are candidate channels belonging to the first group in step307.

When detecting the candidate channels in the first group, the base station checks the number of the candidate channels of the first group in step309.

When the number of the candidate channels in the first group is two or more in step309, the base station selects a candidate channel for changing the operating channel by taking into account signal strengths received in the candidate channels of the first group in step311. For instance, the base station selects the candidate channel of the weakest signal of the CBP packet among the candidate channels, as the candidate channel for changing the operating channel.

In step313, the base station changes the operating channel to the selected candidate channel.

Meanwhile, when there is a single candidate channel in the first group in step309, the base station changes the operating channel to the single candidate channel in step313.

When there are no candidate channels in the first group in step307, the base station checks whether there are candidate channels belonging to the second group with the second highest priority after the first group in step315.

Confirming the candidate channels in the second group, the base station checks the number of the candidate channels in the second group in step317.

When the number of the candidate channels of the second group is two or more in step317, the base station selects a candidate channel for changing the operating channel by taking into account signal strengths received in the candidate channels in step319. For instance, the base station selects the candidate channel of the weakest signal of the CBP packet among the candidate channels, as the candidate channel for changing the operating channel.

Next, the base station changes the operating channel to the selected candidate channel in step313.

Meanwhile, when there is a single candidate channel in the second group in step317, the base station changes the operating channel to the single candidate channel in step313.

When there are no candidate channels in the second group in step315, the base station checks the number of the candidate channels of the third group of the lowest priority in step321.

When the number of the candidate channels of the third group is two or more, the base station selects a candidate channel for changing the operating channel by taking into account signal strengths received in the candidate channels in step323. For instance, the base station selects the candidate channel of the weakest signal of the CBP packet among the candidate channels, as the candidate channel for changing the operating channel.

Next, the base station changes the operating channel to the selected candidate channel in step313.

When there is a single candidate channel in the third group in step321, the base station changes the operating channel to the single candidate channel in step313.

Next, the base station finishes this process.

Now, descriptions explain a structure of the base station for selecting the candidate channel to change the operating channel based on the priority given to the candidate channels.

FIG. 4is a block diagram of the base station for giving priority to the candidate channels in the wireless communication system according to an exemplary embodiment of the present invention. While the wireless communication system is assumed to adopt a Time Division Duplex (TDD) scheme, the present invention is application to other communication schemes.

The base station ofFIG. 4includes a Radio Frequency (RF) switch400, a receiver410, a controller420, a transmitter430, and a frequency controller440.

According to a TDD signal, the RF switch400connects an antenna and the receiver410in the reception period and connects the antenna and the transmitter430in the transmission period.

The receiver410includes an RF processor411, an Analog/Digital Converter (ADC)413, an Orthogonal Frequency Division Multiplexing (OFDM) demodulator415, a decoder417, and a message processor419.

The RF processor411converts an RF signal received in the designated channel to a baseband analog signal under the control of the frequency controller440. The ADC413converts the analog signal output from the RF processor411to digital sample data. The OFDM demodulator415converts the time-domain sample data output from the ADC413to frequency-domain data using Fourier transform. The OFDM demodulator415performs the fast Fourier transform using a Fast Fourier Transform (FFT) operator.

The decoder417selects data of subcarriers to be received from the frequency-domain data output from the OFDM demodulator415. Next, the decoder417demodulates and decodes the selected data according to a preset Modulation and Coding Scheme (MCS) level.

The message processor419decomposes the control message output from the decoder417and provides the result to the controller420. For example, the message processor419provides the CBP packets received in the operating channels of the neighbor base stations to the controller420.

The controller420controls the entire operation of the base station to execute the CR function. For example, upon detecting the incumbent signal in the operating channel, the controller420selects the candidate channel to change the operating channel by taking into account the priority of the candidate channels. Next, the controller420controls the frequency controller440to change the operating channel to the selected candidate channel.

The controller420confirms the operating channel information of the neighbor base stations and the candidate channel information set to the third group from the CBP packets fed from the message processor419and provides the confirmed information to the priority controller421. The controller420controls to send the operating channel information of the base station and the candidate channel information of the third group information using the CBP packets.

The priority controller421determines the priority of the candidate channels using the operating channels of the neighbor base stations and the information of the candidate channels set to the third group provided from the controller420. For example, the priority controller421defines the candidate channels used as the operating channels of the neighbor base stations among the candidate channels, as the third group of the lowest priority. Next, the priority controller421defines the candidate channels set to the third group of the neighbor base stations among the candidate channels not set to the third group, to the second group. Lastly, the priority controller421defines the candidate channels set to neither the second group nor the third group, as the first group of the highest priority.

The controller420selects the candidate channel to change the operating channel based on the priority determined at the priority controller421. When the same priority group includes two or more candidate channels, the controller421selects the candidate channel to change the operating channel by taking into account the receive signal strength of the CBP packets received in the candidate channels. For example, the controller421selects the candidate channel of the weakest signal strength of the CBP packet.

The frequency controller440controls the channel for sending the signal from the transmitter430and the channel for receiving the signal at the receiver410under the control of the controller420.

The transmitter430includes a message generator431, an encoder433, an OFDM modulator435, a Digital/Analog Converter (DAC)437, and an RF processor439.

The message generator431generates the CBP packets to be sent to the neighbor base stations under the control of the controller420. For example, the message generator431generates the CBP packet including the operating channel information of the base station under the control of the controller420. Under the control of the controller420, the message generator431also generates the CBP packet including the information of the candidate channels set to the third group at the priority controller421.

The encoder433encodes and modulates the message output from the message generator431according to the corresponding MCS level. The OFDM modulator435converts the frequency-domain data output from the encoder433to time-domain sample data (OFDM symbols) using Inverse FFT (IFFT). The OFDM modulator435conducts the IFFT using an IFFT operator.

The DAC437converts the sample data output from the OFDM modulator435to an analog signal. The RF processor439converts the analog signal output from the DAC437to an RF signal of the relevant channel under the control of the frequency controller440.

As set forth above, the wireless communication system with the CR function constitutes the candidate channel set by assigning the priority to the candidate channels so as to maximize the distance between the cells which use the channels. Therefore, when the cells using the CR function change their operating channel, the interference influence between the neighbor cells can be mitigated.