JP5281845B2 - Wireless communication system, wireless communication terminal, and base station selection method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radio communication system selecting a more optimal radio base station during handing off between frequencies. <P>SOLUTION: Each radio base station uses a specific sub carrier to transmit a beacon pilot at predetermined timing. In a radio communication terminal, when a beacon extracting part 6 extracts the beacon pilot from each received signal from a plurality of radio base stations including the currently connected radio base station in communication, a propagation loss estimating/correcting part 9 estimates propagation loss between respective radio base stations on the basis of the beacon pilot, and uses difference between the currently communicating frequency and a frequency operated by a radio base station of a handing off destination to correct the propagation loss. An optimal base station determining part 10 determines a radio base station at the handing off destination on the basis of the corrected propagation loss. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a radio communication system, a radio communication terminal, and a base station selection method for selecting a base station using a beacon signal.

In the UMB (Ultra Mobile Broadband) system, which is being standardized by 3GPP2 (Third Generation Partnership Project 2), F-based handoff (inter-frequency handoff) between radio base stations operated at different frequencies is supported. -A physical channel called BPICH (Forward link Beacon Pilot Channel) is provided. A signal transmitted using this physical channel will be referred to as a beacon pilot. When a plurality of frequency bands exist, the radio base station transmits this beacon / pilot to all bands including its own band. As a result, a terminal connected to one of the bands can estimate the channel quality with a radio base station operating in another band and determine an optimum handoff destination. An outline of the operation of beacon / pilot transmission is shown in FIG. Here, two frequency bands are assumed, which are called channel bands X and Y, respectively, and radio base stations operating in the bands are called AP0 and AP1, respectively. In the figure, the operation of AP0 is shown. The hatched portion is a subcarrier used other than the beacon pilot, and the black dot in the figure is a beacon pilot. In an OFDM symbol that performs beacon / pilot transmission, beacon / pilot transmission is performed using only one subcarrier in this way. Therefore, since all transmission power can be concentrated only on a specific subcarrier, it has a feature that a wider coverage than a normal physical channel can be realized. AP0 transmits a beacon / pilot in channel band Y in the same way as it transmits a beacon / pilot in channel band X. As a result, the terminal (AT0) connected to the channel band Y can also estimate the propagation loss with AP0. That is, if the transmission power of the beacon pilot is known, AT0 propagates between AP0 and AT0 using the RSSI (Receive Signal Strength Indictor) value of the beacon pilot transmitted from AP0. The loss can be estimated. This propagation loss is assumed to be PL0. Since AT0 is originally connected to AP1, it is also possible to estimate the propagation loss (PL1) with AP1 using a pilot signal transmitted by AP1. By comparing the two propagation losses obtained in this way, PL0 and PL1, selecting the radio base station with the smaller value, and handing off, the optimum radio base station can be selected even when straddling frequencies. It is possible to select. This is the advantage of using a beacon pilot, but if it is not used, the terminal will need to monitor both the channel band X and Y signals periodically, so that it tunes the RF frequency. Will have to.
JP 7-501918A Special table 2003-509982 gazette

  The operation of the beacon / pilot is considered to function ideally to some extent when the frequency difference between the channel bands X and Y is relatively small, but is considered to cause a problem when the frequency difference is large. In general, it is known that the higher the frequency, the larger the propagation loss. Therefore, when there is a large difference in the frequency band between the channel bands X and Y, the propagation loss estimated by the beacon pilot and the actual This is because the propagation loss in the operating band is greatly different. In the example of FIG. 1, assuming that the channel band X is 2 GHz and the channel band Y is 800 MHz, when the AT0 connected to the AP1 estimates the propagation loss with the AP0, the frequency band of the channel band Y, that is, At 800 MHz. Even if it is determined that AP0 is more advantageous based on the propagation loss obtained here and the handoff is performed to AP0 operating in the channel band X, that is, the 2 GHz band, the assumed propagation loss because the frequency is different. And may be very different. Therefore, an optimal radio base station may not be selected at the time of handoff.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a radio communication system and a radio communication terminal capable of selecting a more optimal radio base station at the time of inter-frequency handoff. And providing a base station selection method.

In order to achieve the above object, the present invention provides a wireless communication system including a plurality of wireless base stations and a wireless communication terminal that performs wireless communication with the wireless base station. Allotted and each radio base station transmits a beacon signal in the allocated operating frequency band, and the radio communication terminal extracts a beacon signal transmitted from each radio base station Based on the extraction unit, the beacon signal extracted by the beacon extraction unit, the propagation loss estimation unit for estimating the propagation loss in the operating frequency band of each radio base station , and the radio base station currently connected to the communication using the difference of the operating frequency band and said operating frequency band allocated to each radio base station, wherein is the estimated for each of the radio base station Den A propagation loss compensation unit for correcting the loss, using each of the corrected propagation loss in the propagation loss correction unit, characterized in that it comprises a base station determination unit which determines the handoff destination base station.

  The wireless communication system of the present invention includes a propagation loss comparison and correction unit, and the propagation loss comparison and correction unit corrects the propagation loss corrected by the propagation loss correction unit and an operating frequency band of an actual handoff destination radio base station. It is preferable to accumulate the difference from the propagation loss at, and further correct the propagation loss corrected by the propagation loss correction unit using the difference.

Further, the present invention is a wireless communication terminal that performs wireless communication with a plurality of wireless base stations, a beacon extracting unit that extracts a beacon signal transmitted from each wireless base station, and a beacon extracted by the beacon extracting unit A propagation loss estimator for estimating a propagation loss in an operating frequency band of each radio base station based on a signal; an operating frequency band assigned to a radio base station currently connected to communication; and an assigned radio frequency to each radio base station using the difference between the operational frequency band has a propagation loss correction section that corrects the estimated propagation loss for said each of radio base stations, with each of the corrected propagation loss in the propagation loss compensation unit, And a base station determination unit that determines a handoff destination radio base station.

The present invention is also a base station selection method for a wireless communication terminal that performs wireless communication with a plurality of wireless base stations, the step of extracting a beacon signal transmitted from each wireless base station, and the extracted beacon signal Based on the operation frequency band of each radio base station is estimated, the operation frequency band assigned to the currently connected radio base station and the operation frequency band assigned to each radio base station Using the difference, correcting the propagation loss for each of the radio base stations, and determining the handoff destination radio base station using each of the corrected propagation losses. To do.

  Since the present invention corrects the propagation loss due to the frequency difference in the terminal, a more optimal radio base station can be selected at the time of inter-frequency handoff.

  Embodiments of the present invention will be described with reference to the drawings. The wireless communication system of the present invention is a UMB (Ultra Mobile Broadband) system that is being standardized by 3GPP2 (Third Generation Partnership Project 2). In the wireless communication system of the present invention, different operating frequency bands are assigned to each wireless base station, and each wireless base station uses a specific subcarrier (beacon frequency) and beacon pilot (beacon signal) at a predetermined timing. ).

  FIG. 2 is a block diagram showing an example of the configuration of a wireless communication terminal used in the wireless communication system of the present invention. The radio communication terminal shown in FIG. 2 amplifies and frequency-converts a received signal, converts it to a baseband signal, a demodulator 3 that demodulates by FFT (Fast Fourier Transform), etc., and other than beacon / pilot A decoding unit 4 for decoding a signal, a beacon detection unit 6 for extracting a beacon / pilot transmitted from each radio base station of a plurality of radio base stations including a radio base station currently in communication connection, An RSSI calculation unit 7 that measures an RSSI (Receive Signal Strength Indictor) value, a system information storage unit 8 that holds information on beacon transmission power and operating frequency of each radio base station, and each radio base station A propagation loss estimator 9a for estimating a propagation loss between a beacon, a frequency band to which a beacon frequency is assigned, and an operating frequency band assigned to each radio base station And the propagation loss correction unit 9b for correcting the estimated propagation loss for each radio base station, and the handoff destination radio base station based on the propagation loss corrected by the propagation loss correction unit 9b. An optimum base station determining unit 10 for determining is provided. In FIG. 2, the propagation loss estimation unit 9a and the propagation loss correction unit 9b constitute the propagation loss estimation / correction unit 9.

  The received signal input from the antenna 1 is normally amplified and frequency converted by the receiving unit 2, converted into a baseband signal, and then demodulated by FFT or IQ planar mapping in the demodulating unit 3. Here, the encoded received data other than the beacon / pilot is extracted after being subjected to processing such as error correction in the decoding unit 4, and is sent to the data link layer and further higher layers.

  The beacon / pilot is sent to the beacon detection unit 6 after the demodulation process by the demodulation unit 3. As described above, the beacon pilot is characterized in that the power density is higher than that of a normal data subcarrier because power is concentrated on only a specific subcarrier. Therefore, the beacon detector 6 can detect a subcarrier on which a beacon / pilot is transmitted by a peak search or the like. Further, since the hopping pattern of the beacon pilot is determined by the ID (unique identification value) of the radio base station, the radio that is transmitted by reading the sequence of the subcarrier numbers in which the beacon pilot exists is read. The ID of the base station can be obtained.

  After obtaining the ID of the radio base station, the RSSI calculator 7 measures the RSSI value from the amplitude of the beacon / pilot. Next, the propagation loss estimation unit 9b estimates the propagation loss between each radio base station based on the known beacon / pilot transmission power and the RSSI value of the beacon / pilot measured by the RSSI calculation unit 7. . Since the wireless communication terminal holds information regarding the beacon transmission power of each wireless base station and the operating frequency of each wireless base station in the system information storage unit 8, the wireless base station that transmitted the beacon / pilot using these information It is possible to estimate the propagation loss in the frequency band operated by the station.

ＣＯＳＴ ２３１ 拡張Ｈａｔａモデル

ここで、上記の２式のａには共通して次の式が用いられる。

Next, the propagation loss correction unit 9b estimates the propagation loss using the difference between the frequency band currently used for communication and the frequency band operated in the radio base station that is a candidate for the handoff destination. Propagation loss is corrected. In other words, the propagation loss estimator 9b is operated by the operating frequency band assigned to the currently communicating base station and the radio base station that transmitted the beacon / pilot (the radio base station that is a handoff destination candidate). The propagation loss estimated by the propagation loss estimation unit 9a is corrected using the difference from the frequency band.
Well-known propagation models include the COST 231 Hata model and the extended Hata model. In these propagation models, the propagation loss is calculated by the following equation.
COST 231 Hata model

COST 231 Extended Hata model

Here, the following equation is commonly used for the above two equations a.

Based on the above formula, the relationship between the propagation loss L [dB] and the base station-terminal distance R [m] in the 800 MHz band and the 2 GHz band is expressed by the following formula.
f = 800 MHz: L = 35 × log 10 (R) +19.6
f = 2 GHz: L = 35 × log 10 (R) +32.2
Here, base station antenna height = 32 m and terminal antenna height = 1.5 m. From the above equation, it can be seen that when this propagation model is assumed, there is a difference of about 12.6 dB between the 800 MHz band and the 2 GHz band. The propagation loss correction unit 9b corrects the estimated propagation loss using this difference. The optimum base station determination unit 10 determines the radio base station that has obtained the smallest value among the corrected propagation losses obtained above as the handoff destination target.

  Actually, it is often considered that there is a case where the propagation model does not follow the propagation model. Therefore, the propagation loss value corrected by the propagation loss estimation / correction unit 9 and the actual propagation loss value measured after the handoff are calculated. The difference may be accumulated, and the propagation loss may be further corrected using this difference. The configuration of the wireless communication terminal in this case is shown in FIG. 3 further includes a reference signal RSSI calculation unit 11 that measures an RSSI value of a pilot signal, a propagation loss estimation unit 12 that estimates a propagation loss between radio base stations, and a beacon pilot. Then, the propagation loss comparison correction unit 13 that compares the propagation loss obtained by the correction with the propagation loss in the operating frequency band of the actual handoff destination radio base station to obtain the difference, and the propagation loss comparison correction unit 13 A propagation loss difference storage unit 14 for storing the obtained difference is provided.

  The reference signal RSSI calculation unit 11 measures the RSSI value of the pilot signal transmitted from the radio base station connected after handoff instead of the beacon / pilot, and the propagation loss estimation unit 12 communicates with the radio base station. Estimate the propagation loss. In other words, this corresponds to the result of actually measuring the propagation loss with the connected radio base station. The propagation loss comparison / correction unit 13 compares the propagation loss estimated by the beacon / pilot and obtained by the correction (the propagation loss estimated / corrected by the propagation loss estimation / correction unit 9) with the actually measured propagation loss. The difference is stored in the propagation loss difference storage unit 14. By saving in the propagation loss difference storage unit 14, it is possible to use it for obtaining a long-term average value of the difference. Further, the propagation loss comparison and correction unit 13 further corrects the propagation loss obtained by the correction using the average value of the differences. After the correction in the propagation loss comparison and correction unit 13, the processing in the beacon detection unit 6 described above, the processing in the RSSI calculation unit 7, the processing in the system information storage unit 8, and the propagation loss estimation / correction unit 9 The process is executed, and the optimum base station determination unit 10 further determines a radio base station that is a candidate for a handoff destination.

  In addition, the propagation equation used above depends greatly on the propagation environment such as line-of-sight (LOS) communication and non-line-of-sight (NLOS) communication. Therefore, in order to increase this accuracy, the profile of the delayed wave is measured. Thus, it is possible to provide a process for performing estimation using another propagation model.

It is a figure explaining the operation | movement outline | summary of beacon pilot transmission. It is a block diagram which shows an example of a structure of a radio | wireless communication terminal. It is a block diagram which shows an example of a structure of a radio | wireless communication terminal.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Antenna 2 Receiving part 3 Demodulation part 4 Decoding part 6 Beacon detection part 7 RSSI calculation part 8 System information storage part 9 Propagation loss estimation / correction part 10 Optimal base station determination part 11 Reference signal RSSI calculation part 12 Propagation loss estimation part 13 Propagation Loss comparison correction unit 14 Propagation loss difference storage unit

Claims (4)

In a wireless communication system comprising a plurality of wireless base stations and a wireless communication terminal that performs wireless communication with the wireless base station,
A different operating frequency band is assigned to each radio base station,
Each of the wireless base stations transmits a beacon signal in the assigned operating frequency band ,
The wireless communication terminal is
A beacon extraction unit that extracts the beacon signal transmitted from each of the wireless base stations;
Based on the beacon signal extracted by the beacon extraction unit, a propagation loss estimation unit for estimating the propagation loss in the operating frequency band of each radio base station,
The estimated propagation loss for each radio base station is corrected using the difference between the operating frequency band assigned to the radio base station currently connected to the communication and the operating frequency band assigned to each radio base station. A propagation loss correction unit,
Using each of the propagation loss corrected by the propagation loss correction unit, a base station determination unit that determines a handoff destination radio base station,
A wireless communication system comprising: Propagation loss comparison and correction unit
The propagation loss comparison correction unit is
The propagation loss corrected by the propagation loss correction unit;
Accumulate the difference from the propagation loss in the operating frequency band of the actual base station of the handoff,
The radio communication system according to claim 1, wherein the propagation loss corrected by the propagation loss correction unit is further corrected using the difference. A wireless communication terminal that performs wireless communication with a plurality of wireless base stations,
A beacon extractor for extracting a beacon signal transmitted from each wireless base station;
Based on the beacon signal extracted by the beacon extraction unit, a propagation loss estimation unit for estimating the propagation loss in the operating frequency band of each radio base station,
The estimated propagation loss for each radio base station is corrected using the difference between the operating frequency band assigned to the radio base station currently connected to the communication and the operating frequency band assigned to each radio base station. A propagation loss correction unit,
Using each of the propagation loss corrected by the propagation loss correction unit, a base station determination unit that determines a handoff destination radio base station,
A wireless communication terminal comprising: A base station selection method for a wireless communication terminal that performs wireless communication with a plurality of wireless base stations,
Extracting a beacon signal transmitted from each radio base station;
Based on the extracted beacon signal, the propagation loss in the operation frequency band of each radio base station is estimated, and the operation frequency band assigned to the radio base station currently connected to the communication and the radio base station Correcting the propagation loss for each of the radio base stations using a difference with an operating frequency band; and
Determining a handoff destination radio base station using each of the corrected propagation losses;
A base station selection method for a wireless communication terminal, comprising:

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