JP5448962B2 - Wireless communication system, transmission control method, and receiving station - Google Patents

Description

  The present invention relates to a radio communication system and a transmission control method that efficiently perform cooperative coherent transmission between a plurality of radio stations.

  In future high-speed wireless communication, a large transmission power is required for the terminal as the transmission speed increases. However, since there is a limit to the transmission power of radio stations, there is an expectation for cooperative coherent transmission as a solution. In coordinated coherent transmission, a plurality of radio stations generate the same signal on the transmission side, and the phase is adjusted so that the signal can be received on the reception side with the same carrier phase. As a result, signals from a plurality of radio stations are strengthened at the phase level and can be received with high power (see, for example, Non-Patent Document 1).

  Non-Patent Document 2 describes a technique in which a transmission-side radio station performs cooperative coherent transmission using information fed back from a reception side. In the control in this case, first, a plurality of radio stations performing a cooperative operation transmit orthogonal pilot signals on the downlink, and the receiving terminal station individually measures the pilot signals transmitted from each radio station. Then, the terminal station generates feedback information such as a relative phase to be adjusted based on the channel measurement result, and notifies the radio station of the pilot signal transmission source on the uplink. When each radio station acquires feedback information, each radio station determines a transmission weight based on the information and transmits the same data signal simultaneously on the downlink. By such control, the terminal station can receive signals from a plurality of radio stations coherently.

P. Larsson and R. Hu, "Large-scale cooperative relaying network with optimal coherent combining under aggregate relay power constraints", Proc. Of FTC, 2003. R1-093778, “Comparison of CSI Feedback Schemes (section 2.2.2)”, Alcatel-Lucent, Alcatel-Lucent Shanghai Bell, 3GPP RAN1 # 58bis, Nov.2009.

  However, when signals are coherently transmitted from a plurality of radio stations in a real environment, the timing at which the signals from the plurality of radio stations arrive at the receiving station is not always the same. When the signal reaching the receiving station is different for each wireless station, the state is equivalent to a propagation environment in which a multipath with a large delay occurs. As a result, the frequency selective fading in the frequency domain becomes large in the receiving station, which causes a problem that the coherency of the signal cannot be maintained in a wide band. For example, as shown in FIG. 16, when there is a shift in the arrival timing of each signal transmitted from the first and second radio stations to the terminal station, in order to maintain coherency at each frequency The feedback control for adjusting the relative phase of the radio station in units of a small band (band W0) as shown in the figure is necessary, and the amount of feedback signal increases.

  The present invention has been made in view of the above, and an object of the present invention is to obtain a radio communication system and a transmission control method capable of signal transmission with a small amount of feedback signal and maintaining coherency.

  In order to solve the above-described problems and achieve the object, the present invention includes a wireless communication system that includes a plurality of transmitting stations and a receiving station, and transmits the same data signal from each of the plurality of transmitting stations to the receiving station. The receiving station calculates a difference in signal arrival timing from each transmitting station based on different pilot signals transmitted simultaneously from the plurality of transmitting stations, and the plurality of transmitting stations Is transmitted, the data signal is cyclically delayed by a delay amount that reduces the deviation of the signal arrival timing calculated by the receiving station.

  According to the present invention, the receiving station calculates the deviation of the signal arrival timing from each transmitting station based on the pilot signal from each transmitting station, and each transmitting station calculates at the receiving station when transmitting the data signal. Since the data signal is cyclically delayed so that the arrival timing shift is reduced, it is possible to realize signal transmission that maintains coherency with a small amount of feedback signal.

FIG. 1 is a diagram illustrating a configuration example of a wireless communication system according to the first embodiment. FIG. 2 is a diagram illustrating an example of cyclic delay processing. FIG. 3A is a diagram illustrating a configuration example of a radio station when cyclic delay is performed in the time domain. FIG. 3-2 is a diagram illustrating a configuration example of a radio station when performing cyclic delay in the frequency domain. FIG. 4 is a diagram illustrating a modification of the first embodiment. FIG. 5 is a diagram illustrating received signals in the terminal station when the cyclic delay is not performed and when the cyclic delay is performed. FIG. 6 is a diagram illustrating an example of a system configuration assumed in the second embodiment. FIG. 7-1 is a diagram illustrating a configuration example of a transmission operation in the radio station according to the second embodiment. FIG. 7-2 is a diagram illustrating a configuration example of a transmission operation in the radio station according to the second embodiment. FIG. 8 is a diagram illustrating a feedback operation from the terminal station to the radio station and a signal format of the delay amount to be fed back. FIG. 9 is a diagram illustrating an example of a delay control operation according to the third embodiment. FIG. 10 is a diagram showing a total cyclic delay amount in the radio station when the delay amount signal format shown in FIG. 8 and a plurality of cyclic delay controls shown in FIG. 9 are applied. FIG. 11 is a diagram illustrating an example of a control signal format notified from the terminal station to the radio station in the radio communication system according to the fourth embodiment. FIG. 12 is a diagram for explaining a control operation in the radio communication system according to the fourth embodiment. FIG. 13 is a diagram for explaining a control operation in the wireless communication system according to the fifth embodiment. FIG. 14 is a diagram for explaining a modification of the control operation in the wireless communication system according to the fifth embodiment. FIG. 15 is a diagram illustrating a control operation in the wireless communication system according to the sixth embodiment. FIG. 16 is a diagram for explaining the problem.

  Hereinafter, embodiments of a wireless communication system and a transmission control method according to the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments. For convenience, in each embodiment, a coherent communication transmitting station is referred to as a “wireless station” and a receiving station is referred to as a “terminal station”. However, all the embodiments have any combination of wireless communication devices. Is applicable. Further, an example in which there are two wireless stations that perform transmission will be described, but the present invention can also be applied to a case where there are three or more wireless stations.

Embodiment 1 FIG.
In the present embodiment, in an environment where the timings of signals simultaneously transmitted from a plurality of radio stations reaching the receiving station are different, each radio station applies different cyclic delays to the same transmission signal and is transmitted from each radio station. In addition, a method for controlling to reduce the amount of deviation of the timing at which the same signal reaches the terminal station is disclosed.

  FIG. 1 is a diagram showing a configuration example of a radio communication system according to the present embodiment, and this system includes radio stations 1A and 1B that are coherent transmission transmitting stations and a terminal station 2 that is a receiving station. Yes. In FIG. 1, configuration examples of functional blocks related to the signal transmission operation of each radio station and functional blocks related to the signal reception operation of the terminal station that is the receiving station are also described.

  As shown in FIG. 1, the radio stations 1A and 1B have the same configuration, and a cyclic delay is performed on the signal generator 11 that generates a transmission signal and the output signal from the signal generator 11 as necessary. And a GI adding unit 13 for adding a guard interval (hereinafter referred to as GI) to the output signal from the cyclic delay processing unit 12. The signal after adding the GI is transmitted from the antenna to the terminal station 2.

  In addition, the terminal station 2 includes a GI removal unit 21 that removes GI from a signal received by the antenna, and a reception processing unit 22 that performs reception processing on the signal from which the GI has been removed.

  The transmission control operation of this embodiment will be described with reference to FIG. In this embodiment, a transmission control operation in the case where the wireless communication system in FIG. 1 is a system to which the OFDM scheme is applied will be described.

  In the transmission control according to the present embodiment, first, a plurality of radio stations 1A and 1B transmit pilot signals of different sequences to the terminal station 2. The terminal station 2 measures the reception timing of each pilot signal transmitted from the radio stations 1A and 1B. In measuring the reception timing, the correlation between the reception signal and the pilot signal sequence (known sequence) is taken, and the timing at which the correlation value becomes the largest is determined as the signal reception timing. In addition, many other methods for measuring the reception timing are conventionally known, and the terminal station 2 may use any method to measure the reception timing.

  Next, the terminal station 2 determines the delay of the signals from the radio stations 1A and 1B with respect to a certain reference time (the difference between the reference time and the arrival timing of each signal), and uses the determination result as delay information to the radio stations 1A and 1B. Notice. The wireless stations 1A and 1B that have received the notification of the delay information cyclically delay the signal by the amount of the notified delay information in the subsequent signal transmission.

  Here, the cyclic delay processing will be described. FIG. 2 is a diagram illustrating an example of cyclic delay processing. As shown in the figure, in the cyclic delay process, the information symbol is delayed by the delay time τ, and the signal part (signal part P) deviated from the original start time and end time (start time and end time when there is no delay) is Move to signal part Q. Thus, in the cyclic delay, an equivalent delay can be added to the signal while maintaining the start time and the end time.

  The case where the OFDM symbol is cyclically delayed will be described in more detail. The OFDM symbol in the time domain is X (n) (0 ≦ n ≦ N−1 (N: number of FFT points)), the OFDM symbol after performing cyclic delay is Y (n), and the number of cyclic delay samples is T. Then, Y (n) is represented by the following formula.

Y (n) = X (n-T mod N)
“T mod N” represents a remainder (≧ 0) obtained by dividing T by N.

  The cyclic delay of the OFDM symbol in the time domain is equivalent to giving a phase rotation for each subcarrier in the frequency domain. Therefore, if the Fourier transform of X (n) and Y (n) is set to X (f) and Y (f), respectively, the relationship of the following equation is established.

Y (f) = X (f) exp (−j2πfτ / N)
Note that f represents a subcarrier number. From this relationship, the cyclic delay signal is also generated by multiplying the signal X (f) before IFFT (Inverse Fast Fourier Transform) by a phase rotation exp (−j2πfτ / N) different for each subcarrier. it can.

  3A is a diagram illustrating a configuration example of a radio station when cyclic delay is performed in the time domain, and FIG. 3B is a diagram illustrating a configuration example of the radio station when cyclic delay is performed in the frequency domain. is there.

  As illustrated in FIG. 3A, when performing cyclic delay in the time domain, the signal generation unit performs IFFT on the transmission signal to convert it to a time domain signal, and outputs the signal. The cyclic delay processing unit Perform cyclic delay processing in the time domain.

  On the other hand, when performing cyclic delay in the frequency domain, as illustrated in FIG. 3B, the signal generation unit outputs a transmission signal in the frequency domain, and the cyclic delay processing unit performs phase shift on the output signal from the signal generation unit. A cyclic delay process is performed by multiplying the rotation exp (−j2πfτ / N).

  Regardless of which of these configurations is employed, the signal waveform transmitted to the terminal station is the same, and in either case, a cyclic delay can be realized. Although detailed explanation is omitted, GI (guard interval) is added after performing cyclic delay.

  In FIG. 1, the terminal station notifies the delay information to both of the two radio stations (radio stations 1A and 1B), but notifies the delay information to only one radio station as shown in FIG. It may be a configuration. FIG. 4 is a diagram illustrating a modification of the first embodiment. In this case, the terminal station notifies only one of the two radio stations of the relative delay (cyclic delay amount) of the reception timing of the signal from each radio station. For example, using the pilot signal that arrives first as a reference, the difference between this arrival timing and the arrival timing of the other pilot signal (the pilot signal that arrived later) is calculated, and the result of the calculation is used as the relative delay information. Transmit to signal source radio station. The wireless station that has received the relative delay information transmits a signal after performing cyclic delay processing according to the received information. Thereby, the reception timing of the signal from each radio station in the terminal station becomes substantially the same. For convenience of explanation, in FIG. 4, it is described that the radio station on which the cyclic delay amount is not fed back does not include the cyclic delay processing unit, but actually, only the cyclic delay processing is not performed. (A cyclic delay processing unit is provided, but cyclic delay processing is not performed).

  As described above, when the cyclic delay processing described in the present embodiment is performed, the terminal station 2 can receive the signal waveforms from the radio station 1A and the radio station 1B at substantially the same timing. FIG. 5 is a diagram showing received signals at the terminal station 2 when the cyclic delay is not implemented (in the case of conventional control not applying the present invention) and when the cyclic delay is implemented (when the present invention is applied). It is. Each of the radio station 1A and the radio station 1B transmits a signal with a GI added. When receiving a signal from each radio station, the terminal station 2 extracts the number of samples for the OFDM symbol from the received signal and performs FFT (Fast Fourier Transform) to obtain the received signal for each subcarrier. obtain. At this time, as shown in the upper part of FIG. 5, since the timing of arrival of signals from the radio stations 1A and 1B is different in the conventional control, the state is the same as when multipath fading with a large delay occurs. On the other hand, as shown in the lower part of FIG. 5, when the present invention is applied, the signals from the radio station 1A and the radio station 1B overlap at the terminal station 2 at the same time by cyclically delaying the transmission signal. Therefore, the state is the same as when multipath fading with a small delay occurs. As a result, as shown in FIG. 1, the frequency characteristics of the channel can be stabilized over a wide band W1, and coherency can be maintained over a wide band.

  When each radio station (radio station 1A, 1B) determines the cyclic delay amount according to the delay information notified from the terminal station 2, each pilot station transmits a different pilot signal as in the conventional coherent transmission control. The terminal station 2 uses the pilot signals received from the radio stations 1A and 1B to measure the relative phase of the transmission signals from the radio stations 1A and 1B, and notifies the radio stations 1A and 1B of the measurement results. At this time, since coherency is maintained in a wide band, the terminal station 2 may adjust the relative phase in a band unit wider than in the case where the conventional control is applied. As described above, according to the control method of the present embodiment, the band unit for reporting the relative phase can be widened as compared with the conventional method. As a result, it is possible to reduce the amount of information to be fed back and the control amount of the feedback operation.

As described above, in the radio communication system according to the present embodiment, the plurality of radio stations on the data signal transmission side and the terminal station on the reception side perform the transmission control operation in the following procedure.
(1) Each radio station transmits a pilot signal individually.
(2) The terminal station detects the signal reception timing (signal arrival timing) from each radio station using the pilot signal from each radio station.
(3) The terminal station notifies delay information (including relative delay information) or cyclic delay information to each radio station or a radio station other than the reference radio station.
(4) The wireless station that has received the delay information determines a cyclic delay amount based on the delay information, and thereafter performs a cyclic delay on the transmission signal.

  As a result, it is possible to realize a radio communication system capable of signal transmission while maintaining coherency with a small amount of feedback signal.

  In the description so far, the delay information or the cyclic delay information is notified, but it can be considered that the signal timing difference is notified. Further, since the cyclic delay of time τ is equivalent to multiplying the phase rotation exp (−j2πfτ / N) that differs for each subcarrier, the phase rotation amount 2πτ / N in the frequency domain is calculated from the terminal station instead of the delay amount τ. You may notify each radio station.

  Unlike the simple delay, the cyclic delay does not require the transmission side (each radio station) to change the transmission start time and the transmission end time of the transmission symbol, and can be realized only by simple signal processing in the time domain or frequency domain. Therefore, each radio station does not need to change the time synchronization timing. When each radio station also supports other terminal stations in its own cell (when simultaneously transmitting data signals to a plurality of terminal stations), it transmits to other terminal stations 2 in the cell. It is necessary to match the transmission timing of the signal to be transmitted and the OFDM symbol. Therefore, although it is difficult to add different delays for each terminal station in normal delay processing, the cyclic delay does not change the transmission start time and end time of transmission symbols, so signals to different terminal stations are sent at the same timing. Can be transmitted as an OFDM symbol. Therefore, this embodiment is further effective when the wireless station supports a plurality of terminal stations.

Embodiment 2. FIG.
Next, the second embodiment will be described. In the present embodiment, a control operation in the case where a radio station accommodates a plurality of terminal stations will be described.

  FIG. 6 is a diagram illustrating an example of a system configuration assumed in the present embodiment. In the system shown in FIG. 6, the wireless station A supports terminal stations # 1 and # 2 in its own cell, and the terminal stations # 1 and # 2 are targets of coherent transmission with other wireless stations. It shall be. Specifically, wireless station A and wireless station B perform coherent transmission to terminal station # 1, and wireless station A and wireless station C perform coherent transmission to terminal station # 2. In the case of such a system configuration, the terminal stations # 1 and # 2 independently notify the delay information to the wireless station A, and the wireless station A implements each transmission signal to the terminal stations # 1 and # 2. The amount of cyclic delay to be determined is determined individually. The cyclic delay procedure (delay amount determination procedure and transmission control procedure after determination) for terminal stations # 1 and # 2 is the same as that of the first embodiment.

  7A and 7B are diagrams illustrating a configuration example of a transmission operation in the radio station according to the second embodiment, and support two terminal stations (terminal stations # 1 and # 2) (two terminals). The data signal is transmitted to the station at the same time). FIG. 7A shows a configuration when cyclic delay is performed in the time domain, and FIG. 7-2 shows a configuration when cyclic delay is performed in the frequency domain.

  As shown in FIG. 7A, in the case of implementing cyclic delay in the time domain, the radio station individually determines the cyclic delay amount for each terminal station, and then the signal generator transmits the data signal to each terminal station. And the IFFT unit performs IFFT on each data signal. Then, the cyclic delay processing unit performs cyclic delay with each determined delay amount for each data signal after being converted into a time domain signal by the IFFT unit, and each signal after the cyclic delay is performed. Is transmitted to each terminal station after the GI is added by the GI adding unit.

  Also, as shown in FIG. 7-2, in the case where the radio station performs cyclic delay in the frequency domain, after determining the cyclic delay amount for each terminal station individually, the signal generation unit transmits data to each terminal station. A signal is generated, and cyclic delay is performed with each determined delay amount for each data signal generated by the signal generation unit which is a frequency domain signal. Then, the IFFT unit performs IFFT on each signal after the cyclic delay is performed, and each signal after the IFFT is transmitted to each terminal station after GI is added by the GI adding unit.

  As a result, the signal reception timing from the radio station A in each terminal station can be aligned with the signal reception timing from another radio station (radio station B or C).

  In the description so far, the delay information or the cyclic delay information is notified, but it can also be considered that the signal timing difference is notified. Further, since the cyclic delay of time τ is equivalent to multiplying the phase rotation exp (−j2πfτ / N) that differs for each subcarrier, the phase rotation amount 2πτ / N in the frequency domain is calculated from the terminal station instead of the delay amount τ. You may notify each radio station.

  Thus, in the present embodiment, the radio station transmits a pilot signal to each terminal station accommodated therein, and as a result, the cyclic delay amount for each terminal station is set according to the delay information notified from each terminal station. In the subsequent transmission processing, the cyclic delay for the transmission signal is performed with the determined delay amount. Thereby, even when a plurality of terminal stations are accommodated, the same effect as in the first embodiment can be obtained.

Embodiment 3 FIG.
Next, Embodiment 3 will be described. In the present embodiment, a delay information feedback method from a terminal station to a radio station, which is applicable to the first and second embodiments, is disclosed.

  FIG. 8 is a diagram illustrating a feedback operation from the terminal station to the radio station and a signal format of the delay amount to be fed back.

As shown in the figure, in the present embodiment, the terminal station feeds back the delay amount only to the wireless station A out of the two wireless stations (radio stations A and B) of the signal transmission source, and the wireless station A By performing a cyclic delay and transmitting a signal, control is performed so as to reach the terminal station at almost the same timing as the signal transmitted from the wireless station B. In the delay amount feedback operation, the relationship between the delay information bits to be fed back and the delay amount is given as follows.
Delay information bit Delay amount
00 0.000 symbol
01 0.025 symbols
10 0.050 symbols
11 0.100 symbols

  That is, a delay amount that is not a uniform delay interval is used for the delay information bits. As described above, the present embodiment is characterized in that the delay amount is notified using a table in which delay amounts that are not uniform delay intervals are mapped to information bits. The operation in which the terminal station determines the delay amount to be fed back and the operation in which the radio station performs the cyclic delay according to the fed back delay amount are as described in the first or second embodiment.

  In this embodiment, delay control (adjustment of delay amount) is performed not only once between the radio station A and the terminal station, but also multiple times. FIG. 9 is a diagram illustrating an example of the delay control operation of the present embodiment. In the operation shown in FIG. 9, the wireless station A performs the first pilot signal transmission, and the terminal station first determines and notifies the first delay amount based on the pilot signal from the wireless station A (wireless station A Notification). The wireless station A sets so as to perform a cyclic delay on the transmission signal in accordance with the notified delay amount (delay information). Then, the wireless station A transmits the pilot signal again while performing a cyclic delay according to the set contents, and the terminal station determines and notifies the second delay amount to be corrected based on the pilot signal. The wireless station A changes the setting of the delay amount when the cyclic delay is performed according to the notified second delay amount. The radio station A further transmits the pilot signal again while performing a cyclic delay according to the changed setting contents, and the terminal station determines and notifies the third delay amount to be corrected based on the pilot signal. Do. As described above, in the present embodiment, the delay amount is notified and the delay amount is determined (adjusted) a plurality of times between the radio station and the terminal station that perform cyclic delay.

  FIG. 10 is a diagram showing a total cyclic delay amount in the radio station A when the delay amount signal format shown in FIG. 8 and a plurality of cyclic delay controls shown in FIG. 9 are applied. In FIG. 10, the terminal station cannot accurately notify the delay amount τ originally desired to be notified by one delay amount notification. This is because the number of control bits is limited and a quantization error occurs. Therefore, the closest delay amount (here, (11)) is selected in the first notification. The terminal station selects a delay amount that should be further corrected for the pilot signal for which the wireless station A has performed the cyclic delay even in the second and third notifications, and notifies the wireless station A ((10) in the example of FIG. 10). , (01) is notified).

  By performing such a series of controls, the reception timing can be adjusted with a small time resolution. This is an effect obtained by mapping the delay amount of non-uniform intervals as shown in FIG. 8 to information bits.

  Note that each time the wireless station A transmits a pilot signal once, the terminal station does not feed back the delay amount only once, but the delay amount is fed back a plurality of times for each pilot signal transmission. Also good. That is, when the number of information bits indicating the delay amount is limited and the maximum delay amount that can be notified by one feedback is smaller than the measurement result, the terminal station notifies the measurement result in a plurality of times. Configure. In this case, after transmitting the pilot signal, the wireless station performs a cyclic delay of the transmission signal with a delay amount corresponding to the total value of the delay amounts notified over a plurality of times. This can reduce the number of times that the radio station transmits the pilot signal, and eliminates the need for the radio station to set the delay amount of the cyclic delay a plurality of times.

  Here, a comparison is made between a case in which delay amounts with non-uniform intervals are mapped to information bits (feedback control in this embodiment) and a case in which delay amounts with uniform intervals are mapped to information bits (conventional feedback control).

For example, consider the case where the mapping of delay amount to information bits is made uniform as follows.
Delay information bit Delay amount
00 0.000 symbol
01 0.033 symbols
10 0.066 symbols
11 0.100 symbols

  In this case, the obtained time resolution is 0.033 symbols. On the other hand, when the mapping shown in FIG. 8 is used, a highly accurate time resolution of 0.025 symbols can be obtained.

As another example, consider the case where the delay amount is mapped to information bits at uniform intervals as follows.
Delay information bit Delay amount
00 0.000 symbol
01 0.025 symbols
10 0.050 symbols
11 0.075 symbols

  In this case, a time resolution of 0.025 symbols can be obtained as in the case of using the mapping shown in FIG. 8, but the maximum delay correction amount in one feedback is 0.075 symbols, and a large delay is corrected. For this purpose, many delay control iterations are required.

  For convenience, the operation in the case where feedback is repeatedly performed until the delay amount reaches an ideal value (zero) has been described. However, the delay amount may not be adjusted to an ideal value. Therefore, the repetition of the processing may be terminated when, for example, the delay amount becomes equal to or less than a predetermined value, or when the number of repetitions reaches a predetermined number.

  As described above, in this embodiment, when the cyclic delay amount determined by the terminal station is fed back to the radio station, a table in which delay amounts having non-uniform delay intervals are mapped to information bits is used. Thus, even when the amount of information (number of information bits) that can be notified by one feedback process is small, the delay can be controlled with a small number of delay control repetitions and high time resolution. In addition, since the delay amount notification from the terminal station to the radio station and the cyclic delay control are repeated a plurality of times, the delay amount can be adjusted with high time resolution.

  Since the cyclic delay of time τ is equivalent to multiplying the phase rotation exp (−j2πfτ / N) that differs for each subcarrier, the phase rotation amount 2πτ / N in the frequency domain is calculated from the terminal station instead of the delay amount τ. You may notify each radio station. In this case, the non-uniform delay amount τ shown in the present embodiment can be replaced with the non-uniform phase rotation amount 2πτ / N. Thus, the present embodiment also includes a configuration for notifying the amount of phase rotation having non-uniform phase rotation in the table as information bits.

Embodiment 4 FIG.
Next, the fourth embodiment will be described. In the present embodiment, a form different from Embodiments 1 to 3 is disclosed regarding a feedback method from the terminal station 2 to the radio station in coherent transmission control.

  In the first embodiment, a case has been described in which only the cyclic delay control of each radio station (radio station 1A, 1B) is performed in the feedback operation (notification of delay amount information of the cyclic delay), but in this embodiment, the cyclic delay is performed. A case will be described in which the control of the transmission phase of the signal from each wireless station is also performed simultaneously with the control. Similar to the first to third embodiments, an example in which there are two wireless stations (wireless stations 1A and 1B) that transmit the same signal in cooperation with each other will be described.

  FIG. 11 is a diagram illustrating an example of a control signal (feedback information) format notified from the terminal station to the radio station in the radio communication system according to the present embodiment. As shown in the figure, the control signal used in the present embodiment is the delay amount of the cyclic delay processing, the coherent bandwidth, and the inter-station relative phase (inter-station relative phase in the nth band, n = 1, 2,...). Is included. FIG. 12 is a diagram for explaining the control operation of the present embodiment. More specifically, FIG. 12 illustrates a coherent bandwidth assumed in the control signal format and a band (1 to 3) delimited by the coherent bandwidth. It is the figure which showed the frequency equivalent to the (th band).

  In the radio communication system according to the present embodiment, the cyclic delay control and the transmission phase control of the radio stations 1A and 1B are simultaneously performed in the following procedure.

(A) Each radio station (radio station 1A, 1B) individually transmits a pilot signal.
(B) The terminal station detects the signal reception timing (signal arrival timing) from each radio station using the pilot signal from each radio station.
(C) The terminal station estimates the reception phase in each frequency band from each radio station obtained after performing delay control by cyclic delay in each radio station, and determines the bandwidth where the reception phase is stable as the coherent bandwidth .
(D) The terminal station uses the coherent bandwidth as one processing target unit, and in each processing target unit, the relative phase of each radio station (radio station 1A, 1B) with respect to a predetermined reference phase, or the radio station 1A and 1B The relative phase between them is calculated.
(E) The terminal station transmits, to each radio station or a radio station other than the reference radio station, delay information (including relative delay information or cyclic delay information), a coherent bandwidth, and a unit of the coherent bandwidth. The inter-station phase information (including the inter-station relative phase) is notified as a control signal (for example, in the format of FIG. 11).
(F) Receiving the control signal from the terminal station, each wireless station B adjusts the phase of the signal according to the inter-station phase information notified in units of coherent bands, and further transmits the signal after performing a cyclic delay according to the delay information. .

  The procedures (A) and (B) are the same as the procedures (1) and (2) shown in the first embodiment. Further, operations related to cyclic delay control (determination of delay amount in terminal station and notification to radio station, cyclic delay operation in radio station) are as described in the first embodiment.

  By the above control procedure, each radio station (radio station 1A, 1B) can perform coherent transmission by simultaneously performing cyclic adjustment and phase adjustment for each band (coherent bandwidth). As a result, the control time can be shortened compared to the first embodiment in which these controls are performed individually. Further, the number of times each radio station 1A, 1B transmits a pilot signal necessary for control can be reduced.

  The procedure (C) will be described in more detail. An example in which the two radio stations 1A and 1B perform coherent transmission to the terminal station 2 will be described.

  The terminal station 2 is assumed to receive signals of complex amplitudes a (f) and b (f) at the frequency f from the radio stations 1A and 1B, respectively. At this time, the reception amplitude at the terminal station 2 after the wireless station 1A performs the cyclic delay of time τ is given by “a (f) exp (−j2πfτ / N)”. Accordingly, the terminal station 2 can estimate the reception amplitude of the signal when the wireless station 1A performs a cyclic delay. Further, the terminal station 2 compares the complex amplitude “a (f) exp (−j2πfτ / N)” of the signal from the radio station 1A with the complex amplitude “b (f)” of the signal from the radio station 1B. As shown in FIG. 12, the bandwidth of the frequency f at which the relative phase can be regarded as substantially constant is determined as the coherent band.

  In step (D), the complex amplitude “a (f) exp (−j2πfτ / N)” of the signal from the radio station 1A and the complex amplitude “b (f) of the signal from the radio station 1B are obtained for each coherent bandwidth. In step (E), the relative phase of each coherent band is notified to the radio station 1A. In the procedure (F), the radio station 1A adjusts the phase according to the inter-station phase information notified from the terminal station 2, and further performs a cyclic delay according to the delay information to transmit a signal. The operation of adjusting the phase according to the inter-station phase information corresponds to the operation of adjusting the phase so as to be the same phase as the signal from the radio station 1B and transmitting the signal. Signals can be received with the same phase.

  As described above, in the radio communication system according to the present embodiment, the terminal station that has received the different pilot signals transmitted from the respective radio stations calculates the cyclic delay amount, and further, based on the determined cyclic delay amount, To calculate the relative phase between signals for each coherent bandwidth when a signal is transmitted after cyclic delay with the delay amount, and feed back the calculated cyclic delay amount and relative phase information to the radio station It was. In addition, the radio station that has received the feedback information transmits a signal by performing phase adjustment and cyclic delay according to the received information. As a result, each wireless station can perform coherent transmission by simultaneously performing cyclic delay and phase adjustment. As a result, the control time can be shortened, and control signals transmitted and received between the radio station and the terminal station can be reduced.

  In the above description, the information on the relative phase is fed back and each radio station performs phase adjustment. This is because the terminal station notifies weight information including the phase, and each radio station adjusts the phase according to the weight information. You can also see that you are doing. Therefore, the relative phase information may be replaced with weight information.

  Further, the coherent bandwidth depends on the propagation environment, the cyclic delay accuracy, and the like, and can be configured to be adaptively changed.

Embodiment 5 FIG.
Next, the fifth embodiment will be described. In the present embodiment, a mode different from that of the fourth embodiment is disclosed regarding the feedback method from the terminal station 2 to the radio station in the coherent transmission control.

  In many wireless communication environments, the phase of the channel tends to change with time due to fading, but the delay time does not change abruptly. For example, at a frequency of 2 GHz, when a terminal station on the signal receiving side moves by one wavelength in the signal arrival direction, the phase changes by 2π, but the delay time only changes by 0.5 ns.

  The cyclic delay control described in the first to fourth embodiments is performed for a large delay that affects the coherent band. However, in practical wireless communication systems (for example, 3GPP-LTE, LTE-Advanced), etc. A delay time of 0.5 ns has little effect on the coherent bandwidth. On the other hand, if the phase of the signal is rotated by π, coherency with other radio stations is completely lost. Therefore, phase control at the radio stations needs to be performed at short time intervals.

  Therefore, in the radio communication system according to the present embodiment, the terminal station notifies the radio station of the delay amount, the coherent bandwidth, and the relative phase information at different time periods. FIG. 13 is a diagram for explaining the control operation in the radio communication system of the present embodiment, and shows an example of the transmission time of feedback information notified from the terminal station to the radio station. As shown in FIG. 13, in the radio communication system according to the present embodiment, the period for reporting the relative phase information is made shorter than the period for reporting the delay amount and the coherent band. By adjusting the phase using the relative phase information notified in this short cycle, the radio station appropriately adjusts the signal transmitted from the other terminal station that performs coherent transmission and the signal transmitted by itself to be in phase with the terminal. Can be controlled.

  Note that when the control of the present embodiment is applied to the above-described fourth embodiment, the control procedure is as follows. Each radio station transmits a pilot signal at a constant period, and each terminal station basically calculates the relative phase of each received signal every time it receives a pilot signal. However, every time a pilot signal is received a predetermined number of times (for example, 5 times), a shift amount (delay amount) of signal reception timing from each radio station is calculated based on the received pilot signal, and further, based on this calculation result Then, the relative phase of each received signal is calculated. That is, every time the number of pilot signal receptions reaches an integral multiple of the predetermined number, the amount of delay used in cyclic delay processing is reviewed (reset). The predetermined number may be an integer of 2 or more.

  As described above, in the radio communication system according to the present embodiment, the terminal station notifies phase information that is likely to change with time in a short cycle, while the delay amount and coherent band information are notified in a long cycle. As a result, it is possible to prevent sending more control information than necessary as feedback information, and to prevent control operations (control of delay amount that is difficult to change over time) from being performed more frequently than necessary. can do. As a result, efficient coherent transmission control can be realized. As described in the fourth embodiment, the phase information may be viewed as weight information.

  Further, even when the delay amount and the coherent band are notified in the same cycle, it is possible to notify at different times as shown in FIG. In this case, the amount of control information can be dispersed over time. In order for a terminal station to transmit a large amount of control information at once, a large amount of transmission power is required temporarily. On the other hand, the peak of transmission power can be reduced by transmitting control information dispersed in time as shown in FIG. Further, in FIG. 14, by determining a rule such as notifying the coherent bandwidth in the next time frame in which the delay amount is notified, two parameters are set while making the notification period of the delay amount and the coherent bandwidth the same. Can be effectively notified.

Embodiment 6 FIG.
Next, the sixth embodiment will be described. In the wireless communication system according to the present embodiment, in the procedure (F) shown in the fourth embodiment, each wireless station performs phase adjustment and further performs cyclic delay according to delay information to transmit a signal. A control signal (details will be described later) is transmitted simultaneously.

  In the wireless communication system of the present embodiment, when a terminal station receives a signal transmitted by each wireless station (wireless stations 1A and 1B) after performing phase adjustment and cyclic delay, channel estimation is performed first to obtain an estimated channel. Based on this, the data signal is demodulated. At this time, when a reference signal of a known sequence is included in the signal subjected to phase adjustment and cyclic delay, the terminal station can perform channel estimation using the reference signal.

  However, when the radio stations A and B support many terminal stations, the radio stations 1A and 1B transmit only a common reference signal to each terminal station, and transmit reference signals for individual terminal stations. Sometimes not. The common reference signal is a signal common to all terminal stations, and the wireless stations 1A and 1B transmit the common reference signal without performing cyclic delay and phase adjustment.

  In this case, the terminal station needs to perform channel estimation for demodulating the signal for the terminal station, using a common reference signal that is not subjected to cyclic delay and phase adjustment. In order to perform this channel estimation smoothly, in the radio communication system of the present embodiment, each radio station (radio station 1A, 1B) performs a cyclic operation performed on a transmission signal for terminal station 2, as shown in FIG. Information regarding delay and phase adjustment is transmitted as control information in the downlink. By receiving this control information, the terminal station 2 can grasp the information regarding the cyclic delay and the phase adjustment performed by the wireless stations 1A and 1B on the transmission signal directed to itself (terminal station 2). Further, the terminal station 2 considers the influence of the cyclic delay and the phase adjustment on the channel estimation result obtained using the common reference signal, so that the radio station 1A or 1B is directed to itself after the cyclic delay and the phase adjustment. The channel phase of the transmitted data signal can be estimated individually. Furthermore, by synthesizing the channel of the signal from each radio station, the synthesized channel can be grasped and the data signal can be demodulated.

  For the same reason as in the fifth embodiment, it is more preferable that the radio stations 1A and 1B change the cyclic delay amount in a long cycle and perform phase adjustment in a short cycle. In this case, the radio stations 1A and 1B transmit the control information related to the cyclic delay amount in a long cycle and efficiently transmit the control information to the terminal station by transmitting the control information related to the adjustment phase in a short cycle. Is possible.

  Thus, this embodiment is characterized in that each wireless station notifies the terminal station of control information related to the cyclic delay amount and phase adjustment. As a result, the terminal station can perform channel estimation of the coherently transmitted data signal using the common reference signal.

Embodiment 7 FIG.
Next, Embodiment 7 will be described. In the first to sixth embodiments, the control operation in the case where each of a plurality of wireless stations that perform coherent transmission has one antenna has been described. In this embodiment, among the wireless stations that perform coherent transmission, A control operation in a case where one or more of the plurality of antennas has a plurality of antennas will be described.

  When a plurality of radio stations performing coherent transmission include a radio station having a plurality of antennas, the same cyclic delay is applied to the plurality of antennas in the radio station having a plurality of antennas. This is because signals transmitted from a plurality of antennas of one radio station have substantially the same delay. Therefore, even when the radio station has a plurality of antennas, the terminal station only has to notify the radio station having a plurality of antennas of only one delay information.

  When a radio station having a plurality of antennas transmits a pilot signal for measuring a delay (shift in arrival timing) of a signal from each radio station by a terminal station, the pilot signal is transmitted from only one of the plurality of antennas. May be transmitted.

  As described above, in the radio communication system according to the present embodiment, when a radio station having a plurality of antennas is included in a plurality of radio stations performing coherent transmission, the terminal station Signals transmitted from each antenna with a delay amount according to the notified one delay information are determined by notifying one common delay information in each antenna provided in the radio station. It was decided to delay the tour. As a result, the amount of control information to be notified can be reduced as compared with the case of notifying delay information for each antenna to a radio station having a plurality of antennas.

  Note that the control operations described in the first to seventh embodiments can be applied in appropriate combination according to the system configuration and the like. In addition, the configuration in which the cyclic delay is performed in the time domain and the configuration in the frequency domain described in the first embodiment and the like can be applied to each radio station. That is, a configuration in which some of a plurality of radio stations that perform coherent transmission perform cyclic delay in the time domain and the rest perform cyclic delay in the frequency domain may be employed. In terms of terms, in the mobile communication system, “terminal” may be referred to as “user”, but of course, “terminal” may be replaced with “user”. In addition, the “pilot signal” may be called “reference signal”, “reference signal”, “sounding signal”, or “known signal”, but may be read as any of these terms. The “phase information” described in the first to seventh embodiments may be “phase amplitude information”, “complex amplitude information”, or “weight information”.

  As described above, the wireless communication system according to the present invention is useful for realizing high-quality data transmission by transmitting the same signal from a plurality of transmitting stations. It is suitable for a wireless communication system that performs transmission control according to the feedback information.

1A, 1B Radio station 2 Terminal station 11 Signal generator 12 Cyclic delay processor 13 GI adder 21 GI remover 22 Reception processor

Claims (23)

A wireless communication system comprising a plurality of transmitting stations and receiving stations, and transmitting the same data signal from each of the plurality of transmitting stations to the receiving station,
The receiving station calculates a difference in signal arrival timing from each transmitting station based on different pilot signals transmitted simultaneously from the plurality of transmitting stations,
The plurality of transmitting stations, when transmitting a data signal, cyclically delays the data signal by a delay amount so as to reduce a shift in signal arrival timing calculated by the receiving station ,
When the receiving station notifies the transmission station of the calculation result of the signal arrival timing deviation, a table in which different deviation amounts are associated with each value indicated by a predetermined number of bits is used. A wireless communication system , wherein each bit value is associated with each shift amount so that a difference between adjacent values becomes non-uniform when the shift amounts are arranged in descending or ascending order . The receiving station calculates a difference between a predetermined reference timing and the arrival timing of a pilot signal from each transmitting station, and notifies each transmitting result as a delay amount to a corresponding transmitting station. The wireless communication system according to 1. The receiving station, with respect to the one of the pilot signals from each transmit station issues calculate the deviation between the arrival time of the incoming timing and other pilot signals of the reference and the pilot signal, the pilot signal and the reference the wireless communication system according to claim 1, characterized in that notify the calculation result to the source base station. After calculating the signal arrival timing shift, the receiving station further determines the delay amount of the cyclic delay performed by each transmitting station based on the calculation result, and notifies the corresponding transmitting station of each determination result. The wireless communication system according to claim 1. The wireless communication system according to any one of claims 1 to 4, wherein the transmitting station performs cyclic delay in a time domain. The wireless communication system according to any one of claims 1 to 4, wherein the transmitting station performs cyclic delay in a frequency domain. When the transmitting station transmits a signal to a plurality of receiving stations,
Information indicating the relationship between the arrival timing of the signal transmitted by itself and the signal transmitted from the other transmitting station, which is transmitted from each receiving station to each of the plurality of receiving stations and notified from each receiving station. The wireless communication system according to any one of claims 1 to 6, wherein a data signal transmitted to each receiving station is cyclically delayed with a different delay amount for each receiving station based on. The transmitting station transmits a pilot signal common to each receiving station as the pilot signal, and determines a cyclic delay amount to be given to a data signal to be transmitted to each receiving station based on the information indicating the relation of the arrival timing. Then, notify each receiving station of the determined cyclic delay amount,
The wireless communication system according to claim 7, wherein each receiving station performs channel estimation for demodulating a data signal based on a cyclic delay amount notified from the transmitting station and the common pilot signal. When the difference between the calculation result of the deviation of the signal arrival timing and the maximum deviation amount included in the table is larger than a specified value,
The receiving station is
The wireless communication system according to claim 1, wherein the calculation result notification operation using the table is repeatedly executed until the difference becomes equal to or less than the specified value. The receiving station is
After calculating the signal arrival timing deviation from each transmitting station, based on the measurement result, the relative phase of the signal from each transmitting station is calculated, and the arrival timing deviation calculation result and the relative phase The wireless communication system according to any one of claims 1 to 9, wherein a calculation result is notified to a corresponding transmitting station. Each transmitting station periodically transmits a pilot signal,
The receiving station is
When the number of pilot signal receptions is an integer multiple of N (N is an integer of 2 or more),
The signal arrival timing deviation from each transmission station is calculated, and the relative phase of the signal from each transmission station is calculated based on the measurement result, and the arrival timing deviation calculation result and the relative phase Execute feedback processing to notify the calculation result to the corresponding transmitting station,
Also,
If the number of pilot signal receptions is not an integer multiple of N,
Based on the received pilot signals, calculates the relative phase of the signal from each transmitting station, according to claim 1-9, characterized in that performing the feedback process of notifying the calculation result of the relative phase to the corresponding transmitting station The wireless communication system according to any one of the above. When there is a transmitting station having a plurality of antennas among the plurality of transmitting stations,
The receiving station to the transmitting station having a plurality of antennas, more of claims 1 to 1 1, characterized in that an instruction to cyclic delay by the same delay amount signal transmitted from each antenna The wireless communication system according to claim 1. When the transmitting station includes a plurality of antennas,
A pilot signal is transmitted from any one of the antennas to the receiving station, and a relationship between arrival timing of a signal transmitted from the transmitting station and a signal transmitted from another transmitting station notified from the receiving station is shown. information, on the basis of the radio communication system according to any one of claims 1 to 1 1, characterized in that the cyclic delay in the same delay amount data signal to be transmitted to the receiving station from each antenna. In a wireless communication system including a plurality of transmitting stations and a receiving station, a transmission control method for transmitting the same data signal from each of the plurality of transmitting stations to the receiving station,
A pilot signal transmission step in which the plurality of transmitting stations simultaneously transmit different pilot signals to the receiving station; and
A calculation step in which the receiving station calculates a deviation in signal arrival timing from each transmitting station based on a pilot signal transmitted from each transmitting station;
A plurality of transmitting stations, a data signal transmitting step of cyclically delaying a data signal by a delay amount so as to reduce a deviation in signal arrival timing calculated by the receiving station, and simultaneously transmitting to the receiving station;
Only including,
In the calculating step, the calculation result of the signal arrival timing deviation is further notified to each transmitting station using a table in which different deviation amounts correspond to the respective values indicated by the predetermined number of bits,
In the table, each bit value is associated with each shift amount so that the difference between adjacent values when the shift amounts are arranged in descending or ascending order is non-uniform.
The transmission control method characterized by the above-mentioned. The calculation step includes calculating a difference between a predetermined reference timing and an arrival timing of a pilot signal from each transmission station, and notifying the corresponding transmission station of each calculation result as a delay amount. 5. The transmission control method according to 4 . In the calculation step, with respect to the one of the pilot signals from each transmit station issues calculate the deviation between the arrival time of the incoming timing and other pilot signals of the reference and the pilot signal, the pilot signal and the reference transmission control method according to claim 1 4, characterized by notifying the calculation result to the source base station. In the calculation step, after calculating the deviation of the signal arrival timing, the delay amount of the cyclic delay performed by each transmitting station is determined based on the calculation result, and the determination result is notified to the corresponding transmitting station. transmission control method according to claim 1 4, characterized in that. The data signal transmitted in step, the transmission control method according to any one of claims 1 4 to 1 7 which comprises carrying out the cyclic delay in the time domain. The data signal in the transmission step, the transmission control method according to any one of claims 1 4 to 1 7 which comprises carrying out the cyclic delay in the frequency domain. When the difference between the calculation result of the deviation of the signal arrival timing and the maximum deviation amount included in the table is larger than a specified value,
The transmission according to any one of claims 14 to 19, wherein in the calculation step, the calculation result notification operation using the table is repeatedly executed until the difference becomes equal to or less than the specified value. Control method. In the calculation step, after calculating the deviation of the signal arrival timing from each transmitting station, further, based on the measurement result, calculating the relative phase of the signal from each transmitting station, the calculation result of the arrival timing deviation, and transmission control method according to claim 1 4-2 0 and notifies the calculation result of the relative phase to the corresponding transmitting station. In a wireless communication system including a plurality of transmitting stations and a receiving station, a transmission control method for transmitting the same data signal from each of the plurality of transmitting stations to the receiving station,
A pilot signal transmission step in which the plurality of transmitting stations periodically transmit different pilot signals simultaneously to the receiving station;
When the number of executions of the pilot signal transmission step is N (N is an integer equal to or greater than 2), the receiving station receives a signal from each transmitting station based on a pilot signal transmitted from each transmitting station. The arrival timing shift is calculated, and the relative phase of the signal from each transmitting station is calculated based on the measurement result, and the arrival timing shift calculation result and the relative phase calculation result corresponding to the transmission result are calculated. Feedback processing to notify the station, and if the number of receptions of the pilot signal is not an integer multiple of N, the relative phase of the signal from each transmitting station is calculated based on the received pilot signal, A feedback step for executing a feedback process for notifying the corresponding transmitting station of the calculation result of the relative phase;
Each time the plurality of transmitting stations execute the pilot signal transmission step N times, the data signal is cyclically delayed to the receiving station by a delay amount that is notified from the receiving station so as to reduce a deviation in arrival timing. A data signal transmission step for transmitting simultaneously;
Including a transmission control method.   A plurality of transmitting stations and a receiving station, wherein the plurality of transmitting stations are the receiving stations of the wireless communication system that respectively transmit the same data signal so as to reduce a deviation amount of arrival timing to the receiving station. There,
  Based on the different pilot signals transmitted simultaneously from the plurality of transmitting stations, the deviation of the signal arrival timing from each transmitting station is calculated, the calculation result is notified to each of the plurality of transmitting stations, and the signal arrival timing is calculated. Execute the process of cyclically delaying the data signal with a delay amount that reduces the deviation,
  When notifying the transmission station of the calculation result of the signal arrival timing deviation, a table in which different deviation amounts are associated with the respective values indicated by the predetermined number of bits is used. Each bit value is associated with each shift amount so that the difference between adjacent values when arranged in descending or ascending order is non-uniform.
  A receiving station characterized by that.

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