JP2007300212A - Wireless communication system, wireless base station, and control method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent spatial multiplexing communication from becoming unstable owing to delay of signal propagation. <P>SOLUTION: The wireless communication system includes a plurality of mobile stations, and a wireless base station 10 for performing wireless communication with the plurality of the mobile stations by spatial multiplexing. In the system, each mobile station includes transmission means for receiving a down-signal transmitted in succession from the wireless base station 10, and transmitting, after a predetermined time, up-signal to the wireless base station 10. The wireless base station 10 includes a reception timing measurer 24 for successively measuring reception timing of each of up-signals sent from each mobile station by the transmission means; and a transmission timing corrector 30 for successively correcting transmission timing of the own-signal transmitted to the plurality of the mobile stations, so as to maintain a relative time difference of the measured reception timings. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to wireless communication technology, and more particularly to spatial multiplexing technology for mobile communication.

One method for effectively using a limited frequency in mobile communication is communication using a spatial multiplexing method. In order to stably perform communication in the spatial multiplexing system, conventionally, transmission timing of a downlink signal transmitted from a base station to a mobile station has been controlled before starting communication by spatial multiplexing (Patent Literature). 1, see Patent Document 2).
JP 2002-101448 A Japanese Patent No. 3728292

  According to the prior art, immediately after the start of communication by spatial multiplexing, a state where stable communication by spatial multiplexing can be performed was maintained. However, if the communication environment changes due to movement of the mobile station or addition of an obstacle between the mobile station and the base station, there may be a delay in signal propagation between the mobile station and the base station. When this signal propagation delay occurs, the reception timing of the uplink signal from the mobile station that performs spatial multiplexing deviates from that at the start of multiplexing, and there is a problem that communication by spatial multiplexing becomes unstable.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a radio communication system, a radio base station, and a radio base station that prevent spatial multiplexing from becoming unstable due to a signal propagation delay. It is to provide a control method.

  In order to solve the above problems, a radio communication system according to the present invention is a radio communication system including a plurality of mobile stations and a radio base station that performs radio communication by spatial multiplexing with the plurality of mobile stations, Each of the plurality of mobile stations includes transmission means for transmitting an uplink signal to the radio base station at a predetermined time after receiving a downlink signal sequentially transmitted from the radio base station, The measurement unit that sequentially measures the reception timing of each uplink signal transmitted from each mobile station by the transmission unit, and the measurement so as to maintain a relative time difference between the reception timings measured by the measurement unit. Transmission timing correction means for sequentially correcting the transmission timing of the downlink signals transmitted to the plurality of mobile stations based on the reception timing sequentially measured by the means; And wherein the Mukoto.

  Further, the radio base station according to the present invention includes a plurality of mobile stations each including transmission means for transmitting an uplink signal to the radio base station at a predetermined time after receiving a downlink signal sequentially transmitted from the radio base station. A wireless base station that performs wireless communication by spatial multiplexing, a measuring unit that sequentially measures the reception timing of each uplink signal transmitted from each mobile station by the transmitting unit, and each reception that is measured by the measuring unit Transmission timing correction means for sequentially correcting transmission timings of downlink signals to be transmitted to the plurality of mobile stations based on reception timings sequentially measured by the measurement means so as to maintain a relative timing difference. It is characterized by including.

  The radio base station control method according to the present invention includes a plurality of transmission units each of which includes a transmission unit that transmits an uplink signal to the radio base station at a predetermined time after receiving a downlink signal sequentially transmitted from the radio base station. A control method of a radio base station that performs radio communication by spatial multiplexing with a mobile station, wherein a measurement step of sequentially measuring each reception timing of an uplink signal transmitted from each mobile station by the transmission means, and the measurement step Transmission that sequentially corrects the transmission timing of downlink signals to be transmitted to the plurality of mobile stations based on the reception timing sequentially measured by the measurement step so as to maintain the relative time difference between the measured reception timings. And a timing correction step.

  In the present invention, the radio base station performs radio communication by spatial multiplexing with a plurality of mobile stations. Each mobile station transmits the uplink signal to the radio base station at a predetermined time after receiving the downlink signal transmitted from the radio base station. The radio base station sequentially measures the reception timing of the uplink signal transmitted from each mobile station. Then, the radio base station sequentially corrects the transmission timing of the downlink signal transmitted to each mobile station based on the sequentially measured reception timing so that the relative time difference of each measured reception timing is maintained. .

  According to the present invention, even if a signal propagation delay occurs between the radio base station and at least some of the mobile stations, transmission is performed to each mobile station based on the reception timing of the uplink signal transmitted from each mobile station. The downstream signal transmission timing is corrected so that the relative difference between these reception timings is maintained. In this way, it is possible to prevent the communication by spatial multiplexing from becoming unstable due to signal propagation delay.

  In one aspect of the present invention, the radio base station further includes storage means for storing reception timings respectively measured by the measurement means at a predetermined timing, and the transmission timing correction means is determined by the storage means. A calculation unit that calculates, for each mobile station, a change amount of the reception timing sequentially measured by the measurement unit with respect to the stored reception timing, and based on the change amount calculated for each mobile station by the calculation unit, Assume that transmission timings of downlink signals transmitted to a plurality of mobile stations are sequentially corrected. In this way, the radio base station calculates the amount of change in the reception timing of each mobile station sequentially measured based on the reception timing of the uplink signal of each mobile station measured at a predetermined timing, and based on the calculated amount of change Thus, the transmission timing of the downlink signal to each mobile station is corrected. As a result, it is possible to prevent the communication by spatial multiplexing from becoming unstable due to the delay of signal propagation.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described in detail with reference to the drawings.

  FIG. 1 is a system configuration diagram of a wireless communication system 1 according to an embodiment of the present invention. As shown in FIG. 1, the radio communication system 1 includes a radio base station 10 and a plurality of mobile stations 100A, 100B, 100C, and 100D. Hereinafter, the content common to each mobile station is referred to as a mobile station 100.

  The radio base station 10 performs radio communication with the mobile station 100 in the communication area 50. The radio base station 10 includes an adaptive array device, and can perform radio communication with a plurality of mobile stations 100 using a spatial multiplexing scheme. In the present embodiment, description will be given below assuming that the mobile stations 100A and 100B are communicating with the radio base station 10 by spatial multiplexing.

  The mobile station 100 is an information terminal that performs mobile communication such as a PHS and a mobile phone. The signal transmission / reception timing in the mobile station 100 as a premise of the present invention will be described below. FIG. 2 is a sequence diagram showing signal transmission / reception timing of the mobile station 100. As shown in FIG. 2, the mobile station 100 receives the downlink burst from the radio base station 10 (S101), and after a certain time (2.5 ms in the figure), the mobile station 100 An upstream burst is transmitted (S102). Here, the mobile station 100 measures a certain time starting from the time when reception of the downlink burst is started. Then, the mobile station 100 transmits an uplink burst at a timing when a certain time has elapsed.

  FIG. 3 is a diagram illustrating a signal transmission / reception cycle between the radio base station 10 and the mobile stations 100A and 100B. In the present embodiment, as described above, a case where the radio base station 10, the two mobile stations 100A, and the mobile station 100B are performing communication by spatial multiplexing will be described.

  FIG. 3 shows the timing at which the radio base station 10 transmits downlink signals to the mobile stations 100A and 100B and receives uplink signals from the mobile stations 100A and 100B. In the figure, Tx represents a downlink signal transmitted from the radio base station 10 to the mobile station 100, and Rx represents an uplink signal received from the mobile station 100 by the radio base station 10. Then, Tx is transmitted from the radio base station 10 and a period until the next Tx is transmitted is defined as a transmission / reception cycle. In FIG. 3, three transmission / reception cycles are included, and it is assumed that time advances from the left to the right, and the first, second, and third cycles are set in time series.

  The first cycle is a transmission / reception cycle when the mobile stations 100A and 100B start communication by spatial multiplexing. When the radio base station 10 selects a mobile station that performs spatial multiplexing, a set of mobile stations suitable for spatial multiplexing is selected including the signal reception timing. Therefore, the difference in the reception timing of the uplink signal Rx with the mobile stations 100A and 100B in the first cycle is a target timing difference to be maintained. In the example shown in FIG. 3, the timing difference is zero.

  In the second cycle, it is assumed that there is a delay in signal propagation between the radio base stations 10 and 100A due to some cause. In this case, as shown in the figure, the timing for receiving the uplink signal from the mobile station 100A is delayed from the timing for receiving the uplink signal from the mobile station 100B. Then, the radio base station 10 calculates how much deviation has occurred in the relative difference in the reception timing for receiving the uplink signal from each mobile station that performs spatial multiplexing. Then, the radio base station 10 corrects the transmission timing of the downlink signal Rx to be transmitted to the mobile station 100 in the third cycle according to the calculated deviation.

  In the third cycle, the transmission timing of the downlink signal transmitted to the mobile station 100A is advanced by the amount of the previously calculated deviation. As a result, in the third cycle, as a result, the difference in the reception timing of the uplink signals from the mobile station 100A and the mobile station 100B returns to the state at the start of multiplexing (first cycle).

  In order to realize the above processing, a configuration provided in the radio base station 10 according to the present invention will be described below.

  FIG. 4 is a functional block diagram of the radio base station 10. As illustrated in FIG. 4, the radio base station 10 includes, as a functional configuration, a radio unit 20, a demodulation unit 22, a reception timing measurement unit 24, a reception timing change amount calculation unit 28, a reception timing storage unit 26, a transmission timing. A correction unit 30 and a modulation unit 32 are included. Each unit is a function realized by using hardware configuring the radio base station 10. Details of each part will be described below.

  The radio unit 20 is connected to a plurality of radio antennas 21 and has a function of transmitting / receiving signals to / from the mobile station 100 while controlling the radio antennas 21. The radio unit 20 adjusts the amplitude and phase of transmission / reception signals for each radio antenna 21 of the plurality of radio antennas 21. In this way, the radio base station 10 can form directivity of transmission / reception waves and perform communication with the mobile station 100 by spatial multiplexing.

  The demodulator 22 has a function of demodulating the signal. The demodulator 22 separates and extracts the signal of each mobile station from the reception signals received by the plurality of radio antennas 21 using the weight calculated for each mobile station. Then, the demodulator 22 performs demodulation processing on each of the separated and extracted signals and outputs demodulated data of each mobile station.

  The reception timing measurement unit 24 has a function of sequentially measuring the reception timing of each uplink signal transmitted from each mobile station 100. For example, when wireless communication is performed between the radio base station 10 and the mobile station 100 according to the PHS standard, the reception timing measurement unit 24 measures the reception timing as follows.

  In this embodiment, it is assumed that a plurality of channels are time-division multiplexed in one TDMA / TDD frame in accordance with the PHS standard. The reception timing measurement unit 24 acquires a signal separated and extracted for each mobile station 100 for each time slot in each TDMA / TDD frame. Then, for each mobile station 100 communicating in the time slot, the reception timing of the mobile station 100 is measured based on the time when a UW (unique word) signal is received with reference to the start point of the time slot. Further, the time when the UW is received is determined as follows.

  The position where the UW signal is included in the uplink signal transmitted in one time slot is determined in advance. The radio base station 10 stores a reception waveform of the UW signal in advance. Then, the radio base station 10 uses the signal waveform stored in advance and the received signal separated and extracted for each mobile station 100 by the demodulator 22 to the position assumed to correspond to the UW signal and the signal waveform of several symbols before and after the position. A correlation value indicating the degree of coincidence with is calculated. Based on this correlation value, the timing at which the UW signal is actually received is determined. Then, the actual reception timing of the signal of each mobile station 100 is obtained from the determined reception timing of the UW signal with reference to the start point of the time slot. In this way, the reception timing measurement unit 24 measures the reception timing of each mobile station 100.

  The reception timing storage unit 26 has a function of storing the reception timing measured for each mobile station by the reception timing measurement unit 24 at a predetermined timing. The reception timing storage unit 26 is a function realized by a memory that includes the radio base station 10 as hardware. In the present embodiment, the predetermined timing is the time when the mobile station starts communication by spatial multiplexing, and the reception timing of each mobile station at that time is stored.

  The reception timing change amount calculation unit 28 has a function of calculating, for each mobile station, a change amount of the reception timing sequentially measured by the reception timing measurement unit 24 with respect to the reception timing stored in the reception timing storage unit 26. This is a function realized by a processor included as hardware configuring the radio base station 10 operating according to a program read from the memory.

  The processing in the reception timing change amount calculation unit 28 will be described below using a specific example. In the reception timing measurement unit 24, the reception timing measured for the mobile station 100 </ b> A and the mobile station 100 </ b> B in the period t of a certain transmission / reception cycle (t is an integer equal to or greater than 0 and t = 0 represents the time of start of multiplexing) Let Ta (t) and Tb (t). At this time, the reception timings stored in the reception timing storage unit 26 are Ta (0) and Tb (0). Then, in the period t of a certain transmission / reception cycle, the amount of change ΔTa in the reception timing of the mobile station 100A is calculated as ΔTa = Ta (t) −Ta (0). Also, the amount of change ΔTb in the reception timing of the mobile station 100B is calculated as ΔTb = Tb (t) −Tb (0).

  The transmission timing correction unit 30 performs a plurality of movements based on the reception timing sequentially measured by the reception timing measurement unit 24 so as to maintain a relative time difference between the reception timings measured by the reception timing measurement unit 24. It has a function of sequentially correcting the transmission timing of the downlink signal transmitted to the station. The following two methods will be described as an example of a method for correcting the transmission timing so as to maintain the relative time difference of the reception timing.

  First, as a first method, one of a plurality of mobile stations performing spatial multiplexing is selected as a reference, and based on the amount of change calculated by the reception timing change amount calculation unit 28, the other mobile stations This is a method of correcting the transmission timing. Here, when the change amount of the reception timing of the mobile station 100A is ΔTa and the change amount of the reception timing of the mobile station 100B is ΔTb, the transmission timing is corrected as follows. In this example, when the mobile station 100B is selected as a reference, the transmission timing of the other mobile station 100A is advanced by ΔTa−ΔTb. If ΔTa−ΔTb takes a negative value, the transmission timing is delayed.

  As a modification of this method, when there are three or more mobile stations performing spatial multiplexing, a mobile station having a median value among the amount of change in reception timing (for example, ΔTa, ΔTb, ΔTc...). May be selected as a reference, and transmission timings of other mobile stations may be corrected. Further, the mobile station to be selected is not limited to one having a median value, but may be one having a minimum value, a maximum value, or other criteria.

  Next, the second method will be described. As a second method, for each mobile station that performs spatial multiplexing, the transmission timing is corrected based on the calculated amount of change in reception timing. In this method, for example, when the reception timing interval at the start of multiplexing of the mobile stations 100A and 100B is I, the transmission timing for the mobile station 100A is advanced by ΔTa−t · I, and the transmission is performed for the mobile station 100B. The timing may be corrected by increasing the timing by ΔTb−t · I.

  Then, the transmission timing correction unit 30 notifies the modulation unit 32 of the calculated transmission timing correction value.

  The modulation unit 32 has a function of performing signal modulation processing. In the present embodiment, the modulation unit 32 performs the modulation process by assigning the position of the transmission timing based on the correction value of the transmission timing notified by the transmission timing correction unit 30. Then, the modulated signal is decomposed by spatial multiplexing, each signal is transferred to the radio unit 20, and transmitted to the mobile stations 100A and 100B via the plurality of radio antennas 21.

  Hereinafter, the details of the operation of radio base station 10 according to the embodiment of the present invention will be described.

  FIG. 5 is a flowchart related to the transmission timing control process performed in the radio base station 10. As shown in FIG. 5, the radio base station 10 measures the reception timing of the uplink signal of each mobile station at the time of starting communication by spatial multiplexing, and stores the value (referred to as A) in association with each mobile station. (S201). Then, the radio base station 10 sequentially measures the uplink signal reception timing (B) for each mobile station (S202). The radio base station 10 calculates the difference C between A and B for each mobile station (S203). Then, based on the calculated C value of each mobile station, the downlink signal transmission timing is corrected so as to maintain a relative difference in reception timing at the start of multiplexing of each mobile station (S204). Specific processing regarding this correction is as described in the description of the transmission timing correction unit 30. The radio base station 10 transmits a downlink signal to each mobile station at the corrected transmission timing (S205). The above correction is repeated while communication by spatial multiplexing is continued with the mobile station. That is, when the communication by spatial multiplexing is not terminated (S206: N), the process returns to the process S202 and is repeated, and when the communication by spatial multiplexing is terminated (S206: Y), the process is terminated.

  According to the radio communication system according to the embodiment of the present invention described above, the reception timing of the uplink signal transmitted from each mobile station even if a signal propagation delay occurs between the radio base station and the mobile station. Based on the above, the transmission timing of the downlink signal transmitted to each mobile station is corrected so that the relative difference between these reception timings is maintained. In this way, it is possible to prevent the communication by spatial multiplexing from becoming unstable due to signal propagation delay.

  The present invention is not limited to the above embodiment.

  For example, the reception timing storage unit 26 may store a relative difference between reception timings for a plurality of mobile stations performing spatial multiplexing. In this case, one mobile station serving as a reference is selected from a plurality of mobile stations performing spatial multiplexing, and the time difference between the reception timings of other mobile stations based on the reception timing of the selected mobile station is determined. You may make it memorize | store. Then, based on the reception timing of each mobile station sequentially measured by the radio base station, the transmission timing to each mobile station may be corrected so as to maintain the relative difference between the stored reception timings. .

1 is a system configuration diagram of a radio communication system according to an embodiment of the present invention. It is the sequence diagram which showed the transmission / reception timing of the signal of a mobile station. It is a figure which shows the transmission / reception cycle of the signal with a radio base station and a mobile station. It is a functional block diagram of a radio base station. It is a flowchart regarding the control process of the transmission timing performed in a radio base station.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Radio communication system, 10 Radio base station, 20 Radio part, 21 Radio antenna, 22 Demodulation part, 24 Reception timing measurement part, 26 Reception timing memory | storage part, 28 Reception timing change amount calculation part, 30 Transmission timing correction part, 32 Modulation Part, 50 communication area, 100A, 100B, 100C, 100D mobile station.

Claims (4)

A wireless communication system including a plurality of mobile stations and a wireless base station that performs wireless communication with the plurality of mobile stations by spatial multiplexing,
Each of the plurality of mobile stations is
Transmitting means for transmitting an uplink signal to the radio base station at a predetermined time after receiving a downlink signal sequentially transmitted from the radio base station,
The radio base station is
Measurement means for sequentially measuring the reception timing of each uplink signal transmitted from each mobile station by the transmission means;
Based on the reception timing sequentially measured by the measurement means, the transmission timing of the downlink signal to be transmitted to the plurality of mobile stations is maintained so as to maintain the relative time difference between the reception timings measured by the measurement means. A wireless communication system, comprising: transmission timing correction means for sequentially correcting the transmission timing. The wireless communication system according to claim 1,
The radio base station is
A storage means for storing the reception timings respectively measured by the measurement means at a predetermined timing;
The transmission timing correction means includes
Calculating means for calculating, for each mobile station, the amount of change in reception timing sequentially measured by the measurement means relative to the reception timing stored by the storage means;
Based on the amount of change calculated for each mobile station by the calculating means, sequentially correct the transmission timing of the downlink signal transmitted to the plurality of mobile stations,
A wireless communication system. A radio base station that performs radio communication by spatial multiplexing with a plurality of mobile stations each including transmission means for transmitting an uplink signal to the radio base station within a predetermined time after receiving a downlink signal sequentially transmitted from the radio base station There,
Measurement means for sequentially measuring the reception timing of each uplink signal transmitted from each mobile station by the transmission means;
Based on the reception timing sequentially measured by the measurement means, the transmission timing of the downlink signal to be transmitted to the plurality of mobile stations is maintained so as to maintain the relative time difference between the reception timings measured by the measurement means. Transmission timing correction means for sequentially correcting;
A radio base station comprising: A radio base station that performs radio communication by spatial multiplexing with a plurality of mobile stations each including transmission means for transmitting an uplink signal to the radio base station within a predetermined time after receiving a downlink signal sequentially transmitted from the radio base station A control method,
A measurement step of sequentially measuring the reception timing of each uplink signal transmitted from each mobile station by the transmission means;
Based on the reception timing sequentially measured by the measurement step, the transmission timing of the downlink signal transmitted to the plurality of mobile stations is maintained so as to maintain the relative time difference between the reception timings measured by the measurement step. A transmission timing correction step for sequentially correcting;
A control method for a radio base station, comprising:

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