Patent Application
20080096564
For a more complete understanding of the present disclosure and its advantages, reference is now made to the following description when taken in conjunction with the accompanying drawings, in which like reference numerals represent like parts:
A preferred embodiment of the present invention will be described herein below with reference to the accompanying drawings. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail.
Hereinafter, a technique will be described in which signals of neighboring Base Stations (BSs) are scanned to determine a handover time in a broadband wireless communication system. In the following descriptions, the wireless communication system is an Orthogonal Frequency Division Multiplexing (OFDM) system. However, this is by way of example only. The present invention may also be easily applied to other types of wireless communication systems.
Referring to
The CINR measuring unit 301 measures a CINR using a preamble signal of a serving Base Station (BS) or a neighboring BS. The measured CINR is provided to the handover controller 305 and the scanning request time determining unit 309.
The message processor 303 analyzes a message received from the BSs. For example, when a scanning response message is received from the BS, the message processor 303 checks information on a scanning start time and information on a scanning performing time, each of which information is included in the received message.
The handover controller 305 determines whether to perform a handover by using CINR information provided from the CINR measuring unit 301, and performs the handover. Although not shown, the handover controller 305 includes a scanning unit. The scanning unit obtains synchronization with the neighboring BS that uses a different frequency band and compares an average CINR of the neighboring BS with an average CINR of the serving BS. In addition, although not shown, the handover controller 305 further includes a handover unit. If the average CINR of the neighboring BS is greater than that of the serving BS, the handover unit performs a handover.
The message generator 307 generates a control message to be transmitted to the BSs, and outputs the control message to the wireless communication unit 311. For example, the message generator 307 generates a scanning request message for checking the CINR of the neighboring BS that uses the different frequency band.
The scanning request time determining unit 309 receives the CINR of the serving BS from the CINR measuring unit 301, and regulates a scanning time period in an adaptive manner according to the CINR of the serving BS. In other words, if the scanning process needs to be performed again because a handover requirement is not satisfied after scanning neighboring BSs, the scanning request time determining unit 309 determines a scanning time period for the request of re-scanning. For example, the scanning request time determining unit 309 may determine the scanning time period as shown in Table 1 below in which the CINR of the serving BS is divided into several levels, and the scanning time period is determined according to each level.
In Table 1, T1, T2, and T3 denote scanning request standby time periods determined according to the CINR, where first reference signal>second reference signal>third reference signal and T1>T2>T3.
The wireless communication unit 311 includes a radio frequency (RF) receiver 313, an analog-to-digital converter (ADC) 315, an OFDM demodulator 317, a resource de-mapper 319, a demodulator/decoder 321, a coder/modulator 323, a resource mapper 325, an OFDM modulator 327, a digital-to-analog converter (DAC) 329, and an RF transmitter 331.
The RF receiver 313 converts an RF signal received through an antenna into a baseband signal. The ADC 315 converts an analog signal provided from the RF receiver 313 into a digital signal. The OFDM demodulator 317 converts a time-domain signal provided from the ADC 315 into a frequency-domain signal through a Fast Fourier Transform (FFT) operation. The resource de-mapper 319 extracts data which is mapped to the frequency domain, when the data is provided from the OFDM demodulator 317 and corresponds to an allocated resource. The demodulator/decoder 321 demodulates and decodes the data provided from the resource de-mapper 319 by using a predetermined method.
The coder/modulator 323 converts the data using a predetermined method. The resource mapper 325 maps the data provided from the coder/modulator 323 to a sub-carrier resource. The OFDM modulator 327 converts the frequency-domain signal, which has been mapped to a frequency resource by the resource mapper 325, into a time-domain signal through an Inverse Fast Fourier Transform (IFFT) operation. The DAC 329 converts a digital signal provided from the OFDM modulator 327 into an analog signal. The RF transmitter 331 converts a baseband signal provided from the DAC 329 into an RF signal, and then transmits the RF signal through the antenna.
In the aforementioned structure, the handover controller 305 may perform functions of the scanning request time determining unit 309. Although the two elements 305 and 309 are distinctively depicted in the figure, this is for description purposes only. Thus, in practice, the functions of the scanning request time determining unit 309 may be wholly or partially performed by the handover controller 305.
Referring to
Upon obtaining the information on the neighboring BSs, in step 403, the neighboring BSs to which a handover is possible are checked to detect a neighboring BS that uses a frequency band different from that of the serving BS.
In step 405, a CINR of the serving BS is continuously monitored.
In step 407, it is checked whether the CINR of the serving BS decreases below a scanning reference value.
If the CINR of the serving BS decrease below the reference value, in step 409, a scanning process is performed. That is, a signaling operation of the scanning process is performed for the serving BS, and thereafter the MS is disconnected from the serving BS. Then, the MS obtains synchronization with the neighboring BS, and measures a CINR of the neighboring BS.
After performing the scanning process, in step 411, the CINR of the neighboring BS is compared with the CINR of the serving BS. Herein, the CINR is obtained by averaging a plurality of CINRs for a predetermined time period.
If the CINR of the neighboring BS is greater than the CINR of the serving BS, that is, if a handover requirement is satisfied, in step 413, a handover is performed to the neighboring BS.
Otherwise, if the handover requirement is not satisfied, the procedure goes to step 415 to determine a scanning time period according to the CINR of the serving BS.
After determining the scanning time period, in step 417, it is checked whether the determined scanning time period is over.
If the scanning time period is over, the procedure returns to step 407 to check whether the CINR of the serving BS is below the scanning reference value.
Referring to
If the CINR decreases below the second reference value, the MS modifies the scanning time period to T2 and then performs the scanning process. When the time period T2 is set to the scanning time period, it is possible to perform a handover at a relatively proper time in comparison with the conventional method. That is, the number of times of performing the scanning process is less than the conventional method, and a handover time is similar to the conventional method.
The MS measures the CINR using a signal received from the BS, and the CINR is used as a reference for determining a handover. The CINR is only an example for representing a strength of a received signal. Thus, besides the CINR, either an SNR or an SINR, or combination of the two may be used to represent the strength of the received signal.
According to the present invention, a scanning time period is adaptively regulated according to a CINR of a serving base station (BS) in a broadband wireless communication system. Therefore, a handover can be performed at an exact time while reducing the number of times of communication disconnection in the process of scanning.
Although the present disclosure has been described with an exemplary embodiment, various changes and modifications may be suggested to one skilled in the art. It is intended that the present disclosure encompass such changes and modifications as fall within the scope of the appended claims. Therefore, the scope of the invention is defined not by the detailed description of the invention but by the appended claims, and all differences within the scope will be construed as being included in the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-0102362 | Oct 2006 | KR | national |
