JP2011135263A - Mobile station and reception timing adjustment method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a mobile station for reducing interference between symbols specific to an OFDMA system, and also to provide a reception timing adjustment method. <P>SOLUTION: The mobile station measures the reception quality of radio signals to be transmitted from the respective base stations adopting an orthogonal frequency division multiple access system, estimates the propagation delay time of each radio signal to be transmitted from each one of the base stations, selects as a connection destination one of the base stations where the reception quality is equal to or more than prescribed quality, detects another base station among the base stations, which is to be the interference source of the selected base station, and adjusts a reception timing for receiving the radio signal from the selected base station, on the basis of the propagation delay time in the selected base station and the propagation delay time in another base station when another base station to be the interference source is detected. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a mobile station and a reception timing adjustment method, and more particularly, to a technique for suppressing radio wave interference caused by neighboring cells.

  In a conventional mobile communication system, a mobile station selects a base station as a connection destination based on reception quality of radio signals transmitted from neighboring base stations.

  For example, XGP (eXtended Global Platform) adopting OFDMA (Orthogonal Frequency Division Multiple Access) and TDMA / TDD (Time Division Multiple Access / Time Division Duplex) ), The mobile station selects a base station to be connected based on RSSI (Received Signal Strength Indication) of radio signals transmitted from neighboring base stations (see Non-Patent Document 1).

  By the way, in a mobile communication system that employs OFDMA, such as XGP, FFT is performed on an OFDM signal for one symbol consisting of a redundant signal called a FFT (Fast Fourier Transform) and a data signal for demodulation of the OFDM signal. By applying the above, one symbol data is obtained. However, if FFT is performed at a timing that crosses the boundary between two adjacent OFDM signals, so-called inter symbol interference (ISI) occurs, and correct demodulation cannot be performed.

  Therefore, the mobile station adjusts the transmission timing of the radio signal to the base station based on the propagation delay time of the radio signal transmitted from the connected base station (see, for example, Patent Document 1). Thereby, the time difference between the reception timing of the radio signal transmitted from the mobile station close to the base station and the reception timing of the radio signal transmitted from the mobile station far from the base station is less than the CP length (allowable delay time), Generation of intersymbol interference is suppressed.

JP 2002-77087 A

“ARIB STD-95 Version 1.2“ OFDMA / TDMA TDD Broadband Wireless Access System (Next Generation PHS) ””, March 18, 2009, Radio Industry

  In the conventional mobile communication system, the transmission timing is adjusted when a radio signal is transmitted from the mobile station to the base station. However, in the transmission of a radio signal from the base station to the mobile station, if the transmission timing is adjusted, it is necessary to adjust the transmission timing for all terminals that transmit the radio signal at the same transmission timing connected to the base station. . Therefore, the transmission timing is not adjusted in the transmission of the radio signal from the base station to the mobile station. In the mobile communication system, since the connection destination of the mobile station is determined based on the reception quality of the radio signal from the base station, the base station close to the mobile station is not necessarily selected as the connection destination. For example, if the reception quality of a radio signal transmitted from a base station that is far but has good line of sight is higher than the reception quality of a radio signal transmitted from a base station that has a close but poor line of sight, the mobile station Select the station as the connection destination.

  For this reason, in a mobile communication system employing the OFDMA scheme, the far base station that transmits a radio signal to a mobile station connected to a far base station may be an intersymbol interference source for neighboring cells. Hereinafter, this reason will be described with reference to FIGS.

  FIG. 7 is a diagram showing a conventional mobile communication system 50 that employs the OFDMA scheme. As shown in FIG. 7, mobile stations 52-1, 52-2, and 52-3 are connected to base stations 54-1, 54-2, and 54-3, respectively. The cells 56-1 to 56-3 of 54-3 are assumed to overlap each other. In addition, it is assumed that radio signal transmission / reception timings are synchronized between the base stations 54-1 to 54-3.

  Here, the mobile station 52-2 is a radio transmitted from the base station 54-1 close to the mobile station 52-2 due to the influence of the building 58 located between the mobile station 52-2 and the base station 54-1. Since the reception quality of the radio signal transmitted from the base station 54-2 far from the mobile station 52-2 is higher than the reception quality of the signal, the mobile station 52-2 selects the base station 54-2 as the connection destination. is doing.

  At this time, the radio signal transmitted from the base station 54-2 reaches not only the mobile station 52-2 but also the mobile station 52-1. Therefore, depending on the positional relationship among the base station 54-2, the mobile station 52-1 and the mobile station 52-2, as shown in FIG. 8, the mobile station 52-1 of the radio signal transmitted from the base station 54-2. May be delayed by more than the CP length than the reception timing at the mobile station 52-1 of the radio signal transmitted from the base station 54-1. In this case, the mobile station 52-1 has two adjacent symbols. Since the FFT is performed at a timing that crosses the boundary of the OFDM signal, noise power is generated due to the intersymbol interference unique to the OFDMA scheme.

  As described above, in a mobile communication system employing the OFDMA method, a remote base station that transmits a radio signal to a mobile station connected to a remote base station is connected to a base station closer to the remote base station. May be an intersymbol interference source for communications of mobile stations.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a mobile station and a reception timing adjustment method that can reduce intersymbol interference unique to the OFDMA scheme.

  In order to solve the above-described problems, a mobile station according to a first aspect of the invention includes a measurement unit that measures reception quality of radio signals transmitted from each of a plurality of base stations that employ an orthogonal frequency division multiple access scheme, The estimation means for estimating a propagation delay time of a radio signal transmitted from each of a plurality of base stations, and a base station having a reception quality equal to or higher than a predetermined quality among the plurality of base stations is selected as a connection destination A selection means, a detection means for detecting another base station that can be an interference source of the selected base station, and another base station that can be the interference source among the plurality of base stations; Adjusting means for adjusting a reception timing for receiving a radio signal from the selected base station based on a propagation delay time in the selected base station and a propagation delay time in the other base station; Characterized in that it contains.

  In the mobile station according to the second invention, the estimating means estimates a propagation delay time of the radio signal based on a reception timing of the radio signal transmitted from each of the plurality of base stations. And

  In the mobile station according to a third aspect of the invention, the estimating means acquires the distance between the mobile station and each of the plurality of base stations, and is transmitted from each of the plurality of base stations based on the distance. The propagation delay time of a wireless signal is estimated.

  In order to solve the above-described problems, a reception timing adjustment method according to a fourth aspect of the present invention includes a step of measuring reception quality of radio signals transmitted from each of a plurality of base stations adopting an orthogonal frequency division multiple access scheme, Estimating a propagation delay time of a radio signal transmitted from each of the plurality of base stations, and selecting one of the plurality of base stations as a connection destination that has a reception quality equal to or higher than a predetermined quality The step of detecting another base station that can be an interference source of the selected base station from among the plurality of base stations, and the selection when another base station that can be the interference source is detected. The reception timing for receiving the radio signal from the selected base station is adjusted based on the propagation delay time in the selected base station and the propagation delay time in the other base station. A step that, characterized in that it comprises a.

It is a figure which shows the structure of the mobile communication system which concerns on embodiment of this invention. It is a figure which shows the radio channel structure in the mobile communication system which concerns on this embodiment. It is a functional block diagram of the mobile station which concerns on this embodiment. It is a figure which shows the table at the time of the mobile station which concerns on this embodiment memorize | stores information. It is a figure which shows an example of the relationship between the received signal from the base station 14-1, the received signal from the base station 14-2, and the FFT timing in the mobile station 12-1 shown in FIG. It is a flowchart which shows the reception timing adjustment process of the mobile station which concerns on this embodiment. It is a figure which shows the structure of the conventional mobile communication system which employ | adopts an OFDMA system. It is a figure which shows an example of the relationship between the received signal from the base station 54-1, the received signal from the base station 54-2, and the FFT timing in the mobile station 52-1 shown in FIG.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a diagram showing a configuration of a mobile communication system 10 according to an embodiment of the present invention. As shown in FIG. 1, a mobile communication system 10 includes a mobile station 12 (only one is shown here), a plurality of base stations 14 (here, base stations 14-1 to 14- located around the mobile station 12). 3 is shown). Here, it is assumed that the cells 16-1 to 16-3 of the base stations 14-1 to 14-3 overlap each other.

  The base station 14 performs radio communication with the mobile station 12 located in the cell 16 of the own station by the OFDMA method and the TDMA / TDD method. Examples of the mobile station 12 include a mobile phone, a communication card, and a portable information terminal with a built-in communication function.

  FIG. 2 is a diagram showing a radio channel configuration in the mobile communication system 10 (vertical axis: frequency, horizontal axis: time). As shown in FIG. 2, in the mobile communication system 10, a TDMA frame having a predetermined period (here, 5 ms) is divided into an uplink subframe (2.5 ms) and a downlink subframe (2.5 ms), and each subframe is further divided. Are equally divided into a plurality of time slots (here, Slot 1 to Slot 4). Between the base stations 14-1 to 14-3, the radio signal transmission / reception timing is synchronized (frame) so that the boundary of the TDMA frame (radio signal transmission / reception cycle) falls within a predetermined time (for example, within ± 10 μs). Is synchronized). In addition, a plurality of OFDMA subchannels (here, Sch1 to Sch18) in a predetermined frequency band are defined.

  The minimum unit of the radio channel that the base station 14 allocates to the mobile station 12 is called a PRU (Physical Resource Unit), and each PRU is one of time slots (Slot 1 to Slot 4) and one of subchannels (Sch 1 to Sch 18). , Belonging to. In both the uplink subframe and the downlink subframe, each PRU is determined to be identified by consecutive PRU numbers (1, 2, 3,...) Starting from 1, and PRUs having the same PRU number are It is supposed to be used in pairs. That is, the PRU is assigned symmetrically in the vertical direction.

 Among these, a PRU belonging to a specific subchannel (here, Sch1) is defined as a CCH (Common Channel) shared by one or more mobile stations 12. Also, non-overlapping CCH transmission / reception timings (hereinafter simply referred to as “CCH timings”) that are repeated at a predetermined cycle are assigned to each base station 14. Specifically, any one of 80 time slot pairs (4 pairs of upper and lower time slots × 20 frames) included in 20 consecutive frames is allocated to each base station 14 as CCH timing. Each base station 14 transmits / receives various control signals to / from one or more mobile stations 12 located in the cell 16 of the own station at the CCH timing assigned to the own station.

 On the other hand, PRUs belonging to subchannels other than the specific subchannel (here, Sch2 to Sch18) are used as ICH (Individual Channel) individually assigned to each mobile station 12. In principle, one ICH is assigned to each mobile station 12 as an individual control channel and is mainly used for transmission of control information. One or more communication channels are assigned to each mobile station 12 and mainly communication data. EXCH (Extra Channel) and the like used for transmission.

  The mobile station 12 receives a radio signal transmitted from each of the surrounding base stations 14 (including the connected base station 14). Radio signals transmitted from the base station 14 include BCCH (Broadcasting Control Channel) transmitted via the CCH, PCH (Paging Channel), control signals transmitted via the ICH, There are communication signals.

  Then, the mobile station 12 estimates the reception timing of the radio signal based on the propagation delay time of the received radio signal. Then, the reception timing is adjusted so that the radio signal transmitted from the base station 14 selected as the connection destination does not overlap with the reception timing of the radio signal transmitted from other neighboring base stations 14. For this reason, the mobile communication system 10 can reduce intersymbol interference peculiar to the ODMA scheme while maintaining the communication of the mobile station 12.

  Below, the structure with which the mobile station 12 is provided in order to implement | achieve the said process is demonstrated concretely.

  FIG. 3 is a functional block diagram of the mobile station 12. As shown in FIG. 3, the mobile station 12 includes an antenna 20, a reception RF unit 22, a reception baseband unit 24, a reception quality measurement unit 26, a propagation delay time estimation unit 28, a reception timing adjustment unit 30, a control unit 32, a transmission A baseband unit 34, a transmission RF unit 36, and a storage unit 38 are included.

  The antenna 20 receives a radio signal transmitted from each of the surrounding base stations 14 (including the connected base station 14), and outputs the received radio signal (received signal) to the reception RF unit 22. Further, the antenna 20 transmits the radio signal supplied from the transmission RF unit 36 to the base station 14 being connected or the base station 14 being a connection destination.

  The reception RF unit 22 includes a low noise amplifier, a frequency converter, a band pass filter, and an A / D converter. The reception RF unit 22 amplifies the radio signal input from the antenna 20 with a low noise amplifier, down-converts it to an intermediate frequency signal, further converts it into a digital signal, and then outputs it to the reception baseband signal unit 24 .

  The reception baseband unit 24 includes a serial-parallel converter, an FFT (Fast Fourier Transform) unit, a parallel-serial converter, and a demodulation unit (not shown). The reception baseband unit 24 performs serial-parallel conversion, CP removal, primary demodulation (fast Fourier transform), parallel-serial conversion, secondary demodulation (symbol demapping), and the like on the digital signal input from the reception RF unit 22. The received data obtained is output to an upper layer (not shown).

  The reception quality measurement unit 26 measures the reception quality of the radio signal transmitted from each of the neighboring base stations 14 based on the complex symbol sequence obtained by the primary demodulation (fast Fourier transform) in the reception baseband unit 24. To do. The radio signal transmitted from the base station 14 is transmitted via BCCH (broadcast control channel), PCH (simultaneous call channel), and ICH (individual channel) transmitted via CCH (common channel). There are control signals, communication signals, and the like, and the line quality detected by the reception quality measuring unit 26 includes RSSI (Reception Signal Strength), SINR (Signal to Interference and Noise Ratio), FER (Frame Error Rate).

  The propagation delay time estimation unit 28 estimates the propagation delay time of the radio signal transmitted from each of the neighboring base stations 14. The radio signal transmitted from the base station 14 includes a training symbol (known signal) for frame synchronization. Therefore, the propagation delay time estimation unit 28 detects a correlation value between the complex symbol sequence obtained by the primary demodulation (fast Fourier transform) in the reception baseband unit 24 and the training symbol, and a correlation value equal to or greater than a predetermined value is detected. The detected timing is acquired as the reception timing of the radio signal transmitted from the base station 14. Then, the propagation delay time estimation unit 28 estimates the propagation delay time of the radio signal based on the acquired reception timing of the radio signal.

  The propagation delay time estimation unit 28 acquires the distance between the mobile station 12 and each of the surrounding base stations 14, and based on the distance, the propagation delay of the radio signal transmitted from each of the surrounding base stations 14 is obtained. The time may be estimated. The distance between the mobile station 12 and the base station 14 is calculated from, for example, the position of the mobile station 12 and the position of the base station 14 acquired based on GPS information or the like.

  Based on the reception quality measured by the reception quality measurement unit 26 and the propagation delay time estimated by the propagation delay time estimation unit 28, the reception timing adjustment unit 30 connects any of the surrounding base stations 14 to the connection destination. And the reception timing is adjusted so that the radio signal transmitted from the selected base station 14 does not overlap the reception timing of the radio signal transmitted from another base station 14.

  Specifically, first, the reception timing adjustment unit 30 receives the reception quality and the propagation delay time measured by the reception quality measurement unit 26 in the surrounding base station 14 in advance at a predetermined cycle (for example, 20 frame cycle). The propagation delay time estimated by the estimation unit 28 is acquired. The acquired information is stored in the storage unit 38. In addition, it is desirable to add the information such as the identification information of each neighboring base station 14 to the acquired information and store it in the storage unit 38 as a list (see FIG. 4).

  The reception timing adjustment unit 30 selects the base station 14 to be connected when starting communication, for example, when the mobile station 12 makes a call. When the base station 14 is selected, one of the base stations 14 stored in the storage unit 38 and having a reception quality of the surrounding base stations 14 equal to or higher than a predetermined quality is selected as a connection destination. Here, the reception timing adjustment unit 30 further selects a propagation delay time stored in the storage unit 38 that is less than the CP length (allowable delay time) among the propagation delay times of the neighboring base stations 14. May be further included. Next, the reception timing adjustment unit 30 grasps the reception timing of the selected base station 14 from the propagation delay time stored in the storage unit 38 and becomes an interference source when receiving a radio signal at the grasped reception timing. Other possible base stations 14 are detected. Detection of another base station 14 that can be an interference source uses the reception quality and / or propagation delay time of neighboring base stations 14 stored in the storage unit 38. Then, the reception timing adjusting unit 30 adjusts the reception timing so as not to overlap with the reception timing of the radio signal transmitted from another base station 14 that can be an interference source.

  FIG. 5 shows an example of reception timing adjustment in the reception timing adjustment unit 30. The mobile station 12 can receive radio signals transmitted from the base stations 14-1 and 14-2, and stores information related to each base station in the storage unit 38 as a list as shown in FIG. . When the reception timing adjustment unit 30 starts communication, it is assumed that the base station 14-1 is selected as a connection destination, and further, the base station 14-2 is detected as a base station that is an interference source. In this case, as shown in FIG. 5, the reception timing of the radio signal from the base station 14-2 overlaps with the reception timing (A) of the radio signal from the base station 14-1 due to the influence of the propagation delay time. Therefore, the reception timing adjustment unit 30 adjusts the reception timing at which the radio signal from the base station 14-1 can be received as the reception timing (B) from the estimated propagation delay time from the base station 14-1. Thereby, since the radio signal from the base station 14-2 does not overlap the reception timing of the radio signal from the base station 14-1, even if FFT is performed at the reception timing, intersymbol interference can be avoided. It becomes possible.

  When the mobile station 12 starts communication, the control unit 32 instructs the reception timing adjustment unit 30 to select the base station 14 to be connected and adjust the reception timing. And each part of the mobile station 12 is controlled so that it communicates with the base station 14 selected in the reception timing adjustment part 30, and the adjusted reception timing.

  The transmission baseband unit 34 includes a series-parallel converter, an IFFT (Inverse Fast Fourier Transform) unit, a parallel-serial converter, and a modulation unit (not shown). The transmission baseband unit 34 performs primary modulation (symbol mapping), serial-parallel conversion, transmission data addressed to the connected base station 14 or the connected base station 14 input from an upper layer (not shown), Secondary modulation (inverse fast Fourier transform), addition of CP, parallel serial conversion, and the like are performed, and the obtained digital signal is output to the transmission RF unit 36.

  The transmission RF unit 36 includes a power amplifier, a frequency converter, a band pass filter, and a D / A converter. The transmission RF unit 36 converts the digital signal input from the transmission baseband unit 34 into an analog signal, then up-converts it to a radio signal, amplifies it to a transmission output level with a power amplifier, and then supplies it to the antenna 20 .

  The storage unit 38 stores identification information, reception quality, and propagation delay time in the surrounding base stations 14 acquired by the reception timing adjustment unit 30 at a predetermined cycle (for example, 20 frame cycle). As a method for storing these pieces of information, it is desirable to store them as a list as shown in FIG.

  Next, an example of operations related to connection destination selection of the mobile station 12 and reception timing adjustment will be described.

  FIG. 6 is a flowchart showing the reception timing adjustment process of the mobile station 12. Here, as shown in FIG. 1, it is assumed that the mobile station 12 can receive radio signals transmitted from the base stations 14-1 and 14-2.

  As shown in FIG. 6, the mobile station 12 receives SINR (reception quality) of radio signals transmitted from the base stations 14-1 and 14-2 located around the mobile station 12 in a predetermined cycle (for example, 20 frame cycle). 1) is measured (S100). Further, the mobile station 12 estimates the propagation delay time of the radio signal transmitted from each of the base stations 14-1 and 14-2 (S102).

  Next, the mobile station 12 determines whether or not a request to start communication with the base station 14 has been made by a user operation or the like (S104). When a request to start communication is made (S104: Y), the process proceeds to S106. On the other hand, if the request for starting communication has not been made (S104: N), the process proceeds to S100.

  When a request to start communication is made (S104: Y), the mobile station 12 determines that the measured SINR of the base stations 14-1 and 14-2 is a predetermined value (to maintain communication). A base station 14 (here, base station 14-1) that is equal to or greater than the SINR threshold) is selected (S106). Next, based on the reception timing based on the reception delay time of the selected base station 14 and the reception timing based on the reception delay time of the surrounding base station 14 (in this case, the base station 14-2), The base station 14 is detected (S108). If another base station (in this case, the base station 14-2) that can be an interference source is detected (S108: Y), the process proceeds to S110. If not detected (S108: N), the process proceeds to S112. .

  When another base station that can be an interference source is detected (S108: Y), the mobile station adjusts the reception timing of the radio signal transmitted from the connected base station 14 (S110). This timing adjustment is performed based on the propagation delay time of the radio signal from the connected base station 14 so that the reception timing adjustment is less than the CP length (allowable delay time). Then, the mobile station 12 starts communication with the connected base station 14 (S112) and ends this process.

  According to the mobile communication system 10 described above, the mobile station 12 selects a base station 14 that can be expected to have a communication quality higher than a predetermined quality as a connection destination, and further adjusts the reception timing so that interference does not occur. For this reason, the intersymbol interference peculiar to the OFDMA system can be reduced.

  The present invention is not limited to the above embodiment.

  For example, the present invention is not limited to a scene where the mobile station 12 performs a new connection, but can also be applied to a scene where the mobile station 12 performs a handover.

  10, 50 mobile communication system, 12, 52 mobile station, 14, 54 base station, 16, 56 cells, 20 antenna, 22 reception RF unit, 24 reception baseband unit, 26 reception quality measurement unit, 28 propagation delay time estimation unit , 30 Reception timing adjustment, 32 control unit, 34 transmission baseband unit, 36 transmission RF unit, 38 storage unit, 58 building.

Claims (4)

Measuring means for measuring the reception quality of radio signals transmitted from each of a plurality of base stations adopting the orthogonal frequency division multiple access method;
Estimating means for estimating a propagation delay time of a radio signal transmitted from each of the plurality of base stations;
A selection means for selecting, as a connection destination, any of the plurality of base stations whose reception quality is a predetermined quality or higher;
Detecting means for detecting another base station that can be an interference source of the selected base station among the plurality of base stations;
When another base station that can be the interference source is detected, a radio from the selected base station is determined based on the propagation delay time in the selected base station and the propagation delay time in the other base station. Adjusting means for adjusting a reception timing for receiving a signal;
A mobile station characterized by comprising: The mobile station according to claim 1, wherein
The estimating means estimates a propagation delay time of the radio signal based on a reception timing of the radio signal transmitted from each of the plurality of base stations;
A mobile station characterized by that. The mobile station according to claim 1, wherein
The estimation means acquires the distance between the mobile station and each of the plurality of base stations, and estimates a propagation delay time of a radio signal transmitted from each of the plurality of base stations based on the distance,
A mobile station characterized by that. Measuring reception quality of radio signals transmitted from each of a plurality of base stations adopting an orthogonal frequency division multiple access scheme;
Estimating a propagation delay time of a radio signal transmitted from each of the plurality of base stations;
Selecting any one of the plurality of base stations as a connection destination that has a reception quality equal to or higher than a predetermined quality;
Detecting, among the plurality of base stations, other base stations that can be interference sources of the selected base station;
When another base station that can be the interference source is detected, a radio from the selected base station is determined based on the propagation delay time in the selected base station and the propagation delay time in the other base station. Adjusting the reception timing of receiving a signal;
A reception timing adjustment method for a mobile station, comprising:

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