JP6827339B2 - Wireless communication device - Google Patents

Description

The present invention relates to TDD-type wireless communication, and more particularly to a technique for shortening a no-signal period between TDD frames.

A device configuration of a conventional TDD (Time Division Duplex) wireless transmission / reception system will be described with reference to FIG.
The wireless transmission / reception system of the figure includes a mobile station 101 having a transmission / reception control unit 103, a transmission / reception high frequency unit 104, and an antenna 105, and a base station 102 having a transmission / reception control unit 108, a transmission / reception high frequency unit 107, and an antenna 106.

The transmission / reception control unit 103 outputs an IF (intermediate frequency) signal of a UL (Up Link) subframe to the transmission / reception high frequency unit 104. The transmission / reception high frequency unit 104 to which the UL subframe is input up-converts the input signal into an RF (radio frequency) signal, amplifies it, and outputs it to the antenna 105. The signal transmitted from the antenna 105 is received by the antenna 106 and input to the transmission / reception high frequency unit 107. The transmission / reception high frequency unit 107 down-converts the input signal and outputs it to the transmission / reception control unit 108. The transmission / reception control unit 108 demodulates / decodes the input signal, and outputs the IF signal of the DL (Down Link) subframe to the transmission / reception high frequency unit 107 when the reception of the UL subframe is completed.
Subsequent processing sends and receives DL subframes in the reverse order of UL subframe propagation.

The internal configurations of the transmission / reception control units 103 and 108 will be described with reference to FIG.
The IF signals input from the transmission / reception control units 103 and 108 are input to the AD conversion unit 201, converted into digital signals, and output to the demodulation / decoding unit 202 and the preamble cross-correlation unit 203. The demodulation / decoding unit 202 demodulates the input signal and performs error correction / decoding. The preamble cross-correlation unit 203 performs a cross-correlation calculation between the received signal and a known preamble pattern in order to detect the timing at which the preamble at the beginning of the subframe is received. Since the cross-correlation peak has a sharp correlation waveform, for example, the timing at which the cross-correlation result exceeds the threshold value is estimated as the preamble position, and the estimated timing is notified to the timing adjustment unit 204.

The timing adjustment unit 204 can know the reception completion timing of the subframe being received from the start timing of the subframe obtained by the preamble cross-correlation unit 203 and the UL period set in advance. The timing adjustment unit 204 calculates the transmission start timing at which DL transmission can be started based on the reception completion timing of this subframe, and notifies the DL information temporary storage memory 205 of the timing. Here, since the process of calculating the transmission signal (processing from the modulation unit 206 to the DA conversion unit 208) requires a predetermined time, the timing adjustment unit 204 notifies the transmission start timing in advance of the calculation time of the transmission signal. To do.

The DL information temporary storage memory 205 temporarily stores the UL information in the memory, starts reading at the transmission start timing input from the timing adjustment unit 204, and outputs the UL information signal to the modulation unit 206. The modulation unit 206 modulates the input signal and outputs the signal to the IFFT unit 207. The IFFT 207 converts the input signal into a time domain signal and outputs it to the DA conversion unit 208. The DA conversion unit 208 converts the input signal into analog and outputs it to the transmission / reception high frequency units 104 and 107.

JP-A-2007-110317

FIG. 3 shows a system configuration in which the path length between the transmission / reception high frequency unit 107 and the transmission / reception control unit 108 is extended by using an optical fiber in the IF signal transmission unit of the base station 102 of FIG. Since the operations of the processing units having the same reference numerals as those in FIG. 1 are the same, the description thereof will be omitted.
At the base station 102, the signal down-converted by the transmission / reception high frequency unit 107 is output to the electric / optical converter 301. The electric / optical conversion device 301 converts the input IF signal into an optical signal and outputs it to the electric / optical conversion device 303 via the optical fiber 302. The path length of the optical fiber 302 may be several hundred kilometers or more, and in that case, a propagation delay of several hundred μs occurs. The electric / optical conversion device 303 converts the input optical signal into an electric signal and outputs it to the transmission / reception control unit 108.

The total delay time T from the transmission / reception control unit 103 of the mobile station 101 to the transmission / reception control unit 108 of the base station 102 will be examined.
Here, the delay time from the transmission / reception control unit 103 to the transmission / reception high frequency unit 104 is t1, the delay time from the transmission / reception high frequency unit 104 to the antenna 105 is t2, the delay time from the antenna 105 to the antenna 106 is t3, and the transmission / reception high frequency from the antenna 106. The delay time to the unit 107 is t4, the delay time from the transmission / reception high frequency unit 107 to the electric / optical conversion device 301 is t5, the delay time from the electric / optical conversion device 301 to the electric / optical conversion device 303 is t6, and the electric / optical conversion device 303. The delay time from the conversion device 303 to the transmission / reception control unit 108 is t7.
The delay times t1, t2, t4, t5 and t7 are sufficiently smaller than the delay times t3 and t6 and can be treated as 0. Therefore, the delay time T is dominated by the total value of the delay time t3 due to spatial propagation and the delay time t6 due to the optical fiber.

FIG. 4 shows a TDD timing chart in the case where the delay time t3 due to spatial propagation and the delay time t6 due to the optical fiber are present as described above. Since the DL subframe also propagates in the same propagation path, it causes the same delay as the UL subframe.
As a result, in the mobile station 101, from the completion of transmission of the UL subframe to the start of reception of the DL subframe, the delay time t3 due to spatial propagation and the delay time t6 due to the optical fiber are twice the total value T (round trip). There is a 2T no-signal period. This non-signal period becomes a guard time, and as a result, the overall throughput decreases.

The present invention has been made in view of the above-mentioned conventional circumstances, and an object of the present invention is to shorten the no-signal period in TDD-type communication.

In the present invention, in order to achieve the above object, the wireless communication device is configured as follows.
That is, in a TDD wireless communication device in which a reception frame received from the other party's device and a transmission frame transmitted from the own device are transmitted and received at different timings, the first processing unit connected to the antenna and the transmission It has a timing adjusting unit for adjusting the timing of starting frame transmission, and includes a second processing unit connected to the first processing unit via an optical fiber, and the timing adjusting unit is the first processing unit. The round-trip time of the signal reciprocating between the and the second processing unit is measured, and the second processing unit precedes the reciprocating time by the timing at which the reception of the reception frame is completed in the second processing unit. It is characterized in that it adjusts so that the transmission of the transmission frame is started from.

With such a configuration, the timing of starting the transmission of the transmission frame from the second processing unit is advanced in anticipation of the delay (round trip) due to the optical fiber between the first processing unit and the second processing unit. Since the transmission of the transmission frame can be started immediately after the reception of the reception frame is completed in the first processing unit, the no-signal period in the TDD method communication can be shortened.

Here, the first processing unit has a circuit structure that returns the signal transmitted from the second processing unit to the second processing unit, and the timing adjusting unit receives the signal transmitted from the second processing unit. The time until the signal is folded back by the first processing unit and received by the second processing unit may be measured as the round-trip time.

The present invention can also be applied to a wireless communication device including a plurality of transmission / reception systems having the antenna, the first processing unit, and the optical fiber, and performing MIMO communication using the plurality of transmission / reception systems.
In such a wireless communication device, a channel prediction unit that predicts the channel characteristics for the next reception frame based on pilot symbols arranged at predetermined intervals in the reception frame, and a channel characteristic predicted by the channel prediction unit. A weight calculation unit for calculating a precoding weight to be transmitted to a device on the other side for MIMO communication is provided, and the channel prediction unit determines the number of pilot symbols used for predicting channel characteristics according to the round trip time. It is preferable to change it.

Here, when switching the transmission / reception system used for MIMO communication, the transmission / reception system before switching may be used for demodulation and decoding of the received frame, and the transmission / reception system after switching may be used for calculating the precoding weight. ..

In addition, when switching the transmission / reception system used for MIMO communication, each transmission / reception system added or deleted by switching is weighted so that the transmission / reception system used for demodulation / decoding of the received frame and calculation of the precoding weight is gradually switched. At the same time, the weighting for calculating the precoding weight may be delayed from the weighting for demodulation and decoding of the received frame.

According to the wireless communication device according to the present invention, it is possible to shorten the no-signal period in TDD type communication.

It is a figure which shows the configuration example of the general TDD system wireless communication system. It is a figure which shows the configuration example of the transmission / reception control part in the wireless communication system of FIG. It is a figure which shows the configuration example of the TDD type wireless communication system which has a delay by an optical fiber. It is a figure which shows the timing chart of the TDD frame in the wireless communication system of FIG. It is a figure which shows the timing chart of the TDD frame by the wireless communication system which concerns on this invention. It is a figure which shows the 1st configuration example of the transmission / reception high frequency part of the base station in 1st Example. It is a figure which shows the 2nd configuration example of the transmission / reception high frequency part of the base station in 1st Example. It is a figure which shows the configuration example of the transmission / reception control part of the base station in 1st Example. It is a figure which shows the configuration example of the wireless communication system of TDD-4x4 MIMO. It is a figure which shows the configuration example of the transmission / reception control part of the base station in 2nd Example. It is a figure which shows the timing chart which generates the information of DL frame by using the channel prediction. It is a figure which shows the timing chart of the advance transmission function and channel prediction in the 2nd Example. It is a figure which shows the structural example of the channel prediction part of the base station in 2nd Example. It is a figure which shows the configuration example of the wireless communication system of TDD-4x4 MIMO which has 8 transmission / reception branches in a base station. It is a figure which shows the timing chart of the branch switching of the base station in the wireless communication system of FIG. It is a figure which shows the timing chart of the branch switching of the 1st method in 3rd Example. It is a figure which shows the timing chart of the branch switching of the 2nd method in 3rd Example. It is a figure which shows the configuration example which added the branch switching function to the base station in 3rd Example. It is a figure which shows another configuration example which added the branch switching function to the base station in 3rd Example. It is a figure which shows the configuration example of the system synthesis switching part in the transmission / reception control part of a base station in 3rd Example.

Prior to explaining the embodiment of the present invention, the advance transmission function, which is one of the features of the present invention, will be described with reference to FIG. FIG. 5 shows a timing chart of a TDD frame by the wireless communication system according to the present invention.
The optical fiber 302 enables full-duplex communication in which the UL subframe and the DL subframe can coexist at the same time. Utilizing this, in the wireless communication system according to the present invention, the transmission start of the DL subframe is advanced by 2 × t6 (round trip of the delay time by the optical fiber) than usual. As a result, the no-signal period between the UL subframe and the DL subframe in the mobile station 101 can be shortened to 2 × t3 (round trip of the delay time due to space), and the throughput can be improved.

As a first embodiment of the present invention, a wireless communication system that solves the above-mentioned problem of throughput reduction will be described with reference to FIGS. 6 to 8. In the first embodiment, a wireless communication system for shortening the guard time described in FIG. 4 from the period 2T and improving the throughput is provided. That is, by outputting the transmission signal from the transmission / reception control unit 108 earlier than usual, the guard time is shortened and the throughput is improved.

In the wireless communication system having the configuration as shown in FIG. 3, the internal configurations of the transmission / reception high frequency unit 107 and the transmission / reception control unit 108 on the base station side for transmitting in advance by twice the delay time t6 by the optical fiber 302 will be described. To do.

In order to transmit in advance by twice the delay time (t6) of the optical fiber 302, it is necessary to measure and hold only the delay time (t6) of the optical fiber 302. Therefore, in the base station 102, the time until the signal transmitted from the transmission / reception control unit 108 is folded back by the transmission / reception high frequency unit 107 and received by the transmission / reception control unit 108 is measured and held.
Here, two configurations of FIGS. 6 and 7 will be described as a mechanism for folding back the signal at the transmission / reception high frequency section 107.

FIG. 6 shows a first configuration example in which a dedicated folding circuit is added in the transmission / reception high frequency section 107 in order to fold the signal for measuring the propagation time.
First, the operation during normal transmission will be described. In this case, the folding switch 604 and the RF switch 606 are connected to the PA605 side.
The IF signal input from the transmission / reception control unit 108 is input to the mixer 601. In the mixer 601 using the local signal input from the synthesizer 602, the IF signal is up-converted to a frequency to be transmitted to space and output to the filter 603. The filter 603 removes signals in a band outside the transmission frequency band so that unnecessary waves are not transmitted. The RF signal that has passed through the filter 603 is input to the PA605 through the folding switch 604. The PA605 amplifies the input RF signal and outputs it to the antenna 106 through the RF switch 606.

Next, the operation at the time of normal reception will be described. In this case, the RF switch 606 and the folding switch 609 are connected to the LNA607 side.
The signal received by the antenna 106 is input to the LNA 607 through the RF switch 606. The LNA 607 amplifies the input RF signal and outputs it to the filter 610 through the return switch 609. The filter 610 removes signals in a band outside the reception band for the purpose of improving reception characteristics, and outputs the signals to the mixer 611. The mixer 611 down-converts the RF signal from the filter 610 using the local signal input from the synthesizer 602, and outputs it as an IF signal to the transmission / reception control unit 108.

Next, the operation at the time of propagating time measurement will be described. In this case, the return switches 604 and 609 are connected to the ATT608 side.
The IF signal input from the transmission / reception control unit 108 is input to the mixer 601. The mixer 601 upconverts the IF signal to a frequency transmitted to space and outputs it to the filter 603. The filter 603 removes signals in a band outside the transmission frequency band. The RF signal that has passed through the filter 603 is input to the ATT 608 through the return switch 604. The ATT 608 attenuates the signal to match the received signal level and outputs it to the filter 610 via the wrap switch 609. The filter 610 removes signals in a band outside the reception band and outputs the signals to the mixer 611. The mixer 611 down-converts the RF signal from the filter 610 and outputs it as an IF signal to the transmission / reception control unit 108.
Through the above path, it is possible to return the signal input to the transmission / reception high frequency unit 107 and output it to the transmission / reception control unit 108.

FIG. 7 shows a second configuration example in which the wrapping using the switch 606 is used to wrap the signal for the propagation time measurement.
The method of the second configuration example utilizes the fact that the isolation of the RF switch 606 in the transmission / reception high frequency section 107 is low. That is, as shown in FIG. 7, when the RF switch 606 is connected to the PA605 side, a part of the transmission signal output from the PA605 leaks to the LNA607 side, and this is used to input to the transmission / reception high frequency section 107. A part of the signal is folded back and output to the transmission / reception control unit 108.

The first configuration example shown in FIG. 6 is not suitable for real-time delay time measurement because it has a disadvantage that transmission / reception cannot be performed when measuring the delay by the optical fiber 302, but the second configuration example shown in FIG. 7 is not suitable. Then, it is possible to measure the delay time in real time during normal TDD operation.
The mechanism for returning the IF signal input from the transmission / reception control unit 108 to the transmission / reception high frequency unit 107 in the base station 102 has been described above.

Next, the reciprocating delay time is measured by using the signal folded back by the transmission / reception high frequency unit 107, and the internal configuration of the transmission / reception control unit 108 for transmitting twice the delay time of the optical fiber 302 in advance. Will be described with reference to FIG. FIG. 8 shows a configuration example of a transmission / reception control unit to which a preceding transmission function is added. Since the operations of the processing units with the same reference numerals as those in FIG. 2 are the same, the description thereof will be omitted. In the following figures as well, since the processing units having the same reference numerals as those in the preceding figures have the same operations, the description thereof will be omitted.
In order to realize the advance transmission function of this example, the transmission / reception control unit 108 has a UL cross-correlation mask unit 801 and a DL cross-correlation mask unit 802, a timing controller 803 corresponding to the advance transmission function, a counter 804, and a delay unit 805. The unit 810 is provided.

The preamble cross-correlation unit 203 inputs the preamble start timing (the start timing of the subframe) to the UL cross-correlation mask unit 801 and the DL cross-correlation mask unit 802.
When the known preamble pattern is common to the UL subframe and the DL subframe, the preamble start timing is set when the UL subframe is received and when the signal obtained by folding back the DL subframe is received by the transmission / reception high frequency section 107. can get.

Since the counter 804 wants to complete the count by using the preamble start timing when the signal obtained by folding back the DL subframe is received, it is necessary to mask the preamble start timing of the UL subframe.
On the other hand, in the advance transmission function compatible timing controller 803, since the transmission timing of the DL subframe is determined using the preamble start timing of the UL subframe, the preamble start timing when the signal obtained by folding back the DL subframe is received is masked. There is a need to.
Therefore, the preamble head timing, which does not require the subsequent processing, is masked by the UL cross-correlation mask unit 801 and the DL cross-correlation mask unit 802.

The UL cross-correlation mask unit 801 masks the preamble start timing when the UL subframe is received. Therefore, a process of replacing a period other than a period having a sufficient margin time (for example, 400us delay when the optical fiber cable length = about 60 km) for measuring the delay time in the optical fiber from the start of transmission of the DL subframe to 0. Is performed and output to the counter 804.

The DL cross-correlation mask unit 802 masks the preamble start timing when the DL subframe is received. Therefore, contrary to the UL cross-correlation mask unit 801, a process of replacing the period having a sufficient margin time for measuring the delay time in the optical fiber from the start of transmission of the DL subframe to 0 is performed, and the advance transmission function is performed. Output to the corresponding timing controller 803.

If the preamble pattern of the UL subframe and the DL subframe is an uncorrelated pattern, the UL cross-correlation mask unit 801 and the DL cross-correlation mask unit 802 become unnecessary. In this case, two types of preamble cross-correlation parts are required, one for the UL subframe and the other for the DL subframe.

The DL information temporary storage memory 205 outputs a timing signal to the delay unit 805 at the same time as the start of reading.
In the delay unit 805, the same delay as the total of the processing time of the modulation unit 206 and the processing time of the IFFT 207 is added to the timing signal and output to the counter 804.

The counter 804 measures twice the value (round trip time) of the delay time in the optical fiber. Specifically, the counter 804 resets the count value by the timing signal input from the delay unit 805, and starts measurement (counting) from the timing when the DL subframe starts transmission. Then, the measurement (counting) is stopped at the preamble start timing from the UL cross-correlation mask unit 801 and the count value is output to the timing controller 803 corresponding to the advance transmission function. As a result, it is possible to measure the time until the signal of the DL subframe is folded back by the transmission / reception high frequency unit 107 and received by the transmission / reception control unit 108, that is, twice the delay time in the optical fiber.

After measuring twice the delay time in the optical fiber, the timing controller 803 compatible with the advance transmission function determines the count value (twice the delay time in the optical fiber) input from the counter 804 and the preamble reception timing of the DL subframe. The read start signal is output to the DL information temporary storage memory 205 so that the DL subframe is transmitted at the same time when the UL subframe is received by the transmission / reception high frequency unit 108.
With the above configuration, the no-signal period between the UL subframe and the DL subframe can be shortened, and the throughput can be improved.

Next, a second embodiment according to the present invention will be described. In the first embodiment, the transmission signal advance output for shortening the guard time due to the delay time in the optical fiber or the like has been described. In the second embodiment, a configuration extended to MIMO (Multiple-Input and Multiple-Output) transmission having a unique mode transmission function will be described in the first embodiment.

FIG. 9 shows a configuration in which the configuration of FIG. 3 is extended to 4x4 MIMO. In the wireless communication system shown in the figure, the mobile station 101 is provided with four antennas 105, and the base station 102 is provided with four antennas 106, a transmission / reception high frequency unit 107, an electric / optical conversion device 301, an optical fiber 302, and electric / optical. A conversion device 303 is provided. There is no change in the device configuration except that there are four transmission / reception systems each.
In 4x4 MIMO, the transmission stream signals of the four systems transmitted from each antenna 105 are combined in space and received by each antenna 106.

In the following, a configuration in which a unique mode transmission function is added to the above MIMO apparatus configuration will be described.
In eigenmode transmission, a matrix in which each transmission stream is orthogonal in space is multiplied by a MIMO transmitter according to the characteristics of the MIMO propagation path (hereinafter, multiplication of a spatial orthogonalization matrix is referred to as "precoding". ) Therefore, transmission can be performed with the optimum transmission beam for the MIMO propagation path.
In order to perform the unique mode transmission, it is necessary to notify the transmitting side of the propagation path information or the precoding weight, and bidirectional communication is required. In this embodiment, the TDD system is adopted as the bidirectional communication system, and the advance transmission function described in the first embodiment is applied.

The internal configuration of the transmission / reception control unit 108 for realizing the unique mode transmission will be described with reference to FIG. The configuration of FIG. 10 is a method of notifying the mobile station 101 of the precoding weight.
In the transmission / reception control unit 108 of this example, each transmission / reception system is expanded to four in order to perform unique mode transmission, and the FFT unit (frequency analysis unit) 1001, the inter-system delay difference adjustment unit 1002, the spatial filter unit 1003, and the channel. The estimation unit 1004, the channel prediction unit 1005, the singular value decomposition unit 1006, the frame delay unit 1007, and the decoding unit 1008 have been added.

The FFT unit 1001 converts the input digital signal into a signal in the frequency domain and outputs it to the inter-system delay difference adjusting unit 1002.
When there is a delay difference between the receiving systems, the inter-system delay difference adjusting unit 1002 adjusts the delay difference so that it becomes 0 by adjusting the delay times of all the systems to the system with the longest delay, and delays. The time-adjusted signal is output to the spatial filter unit 1003 and the channel estimation unit 1004.

The channel estimation unit 1004 extracts a pilot symbol from the input signal, estimates the characteristics of the MIMO propagation path of the entire band by interpolating the extracted pilot symbol, and outputs the channel estimation result. Here, in order to estimate the characteristics of the MIMO propagation path, the pilot symbol is configured to insert known signals in advance in the time and frequency domain of the transmission signal so that they are orthogonal to each other between the transmission antenna systems. ing.
The signal from the channel estimation unit 1004 is output to the spatial filter 1003 and the channel prediction unit 1005. This channel estimation result is used for demodulating the received signal and calculating the precoding weight.

In demodulation of the received signal, MIMO demodulation processing such as spatial filter processing is performed by the spatial filter 1003 based on the channel estimation result of the currently received frame.
On the other hand, in the calculation of the precoding weight, since the precoding weight is fed back to the base station, the frame to which the weight is applied is the next frame. If the frame length is sufficiently short for the propagation path variation, even if the precoding weight calculated from the propagation path characteristics of the current frame is used for the propagation path characteristics of the next frame, no significant characteristic deterioration occurs (channel). Highly coherent in time). However, in an operation in which the mobile station 101 is moving at high speed, the propagation path characteristics fluctuate drastically and the propagation path characteristics differ between frames, and as a result, the orthogonality of the transmission stream in the natural mode transmission collapses. , Deterioration of transmission performance will occur. Therefore, the channel prediction unit 1005 predicts the channel characteristics of the next frame from the propagation path characteristics of the current frame to reduce the deterioration of the characteristics.
As described above, the channel prediction unit 1005 has a function of estimating the propagation path characteristics of the next frame, and the details thereof will be described later. The predicted propagation path characteristics predicted by the channel prediction unit 1005 are output to the singular value decomposition unit 1006.

The singular value decomposition unit 1006 calculates a precoding weight suitable for the predicted propagation path characteristics by performing singular value decomposition on the input predicted propagation path characteristics. The precoding weight calculated by the singular value decomposition unit 1006 is output to the DL information temporary storage memory 205 and the frame delay unit 1007.

The frame delay unit 1007 delays the input signal by 1 TDD frame and outputs it to the spatial filter 1003. When processing the current frame with the spatial filter 1003, the precoding weight applied to the current frame is required, so that the frame delay unit 1007 needs to delay one frame.

The spatial filter 1003 uses the input received signal after frequency conversion, the channel estimation result, and the precoding weight to perform spatial separation processing of the received signal and output it to the decoding unit 1008.
The decoding unit 1008 performs error correction decoding processing from the input signal.
The process for generating a signal for notifying the mobile station 101 of the precoding weight in the DL subframe is the same as the description performed using FIG.

The operation of the channel prediction unit 1005 will be described in detail below with reference to FIG.
In the TDD system natural mode transmission, as described above, the frame used for calculating the precoding weight and the frame to which the calculated precoding weight is applied differ by one frame. Therefore, if the propagation path fluctuates greatly, reception is performed. The characteristics deteriorate. Therefore, the channel prediction unit 1005 predicts the propagation path characteristics one frame ahead.

The channel prediction unit 1005 predicts the characteristics of the pilot symbols of the next UL subframe by using a plurality of pilot symbols included in the UL subframe. As this prediction method, various methods such as primary extrapolation and ARMA (Auto Regressive Moving Average) can be applied, but in the present invention, these prediction methods are not restricted. The precoding weight is calculated using this prediction result.

As shown in the first embodiment, when the delay of the propagation path of the optical fiber or the like is large, it is necessary to apply the advance output function of the transmission signal. However, the signal transmitted in advance needs to be modulated with respect to the precoding weight information calculated from the channel prediction result, but there are cases where the reception of the pilot symbol required for channel prediction is not in time for the advance transmission time. is there. A timing chart in such a case is shown in FIG.
When the advance transmission function is used in an environment with a long delay time due to an optical fiber or the like, as shown in FIG. 12, it is necessary to transmit the DL subframe before receiving the fourth pilot symbol, so that the channel is predicted. Cannot receive all pilot symbols to do.

Therefore, in the second embodiment, the number of pilot symbols used for channel prediction is adaptively changed according to the delay amount of the optical fiber. For example, as shown in FIG. 12, when the DL subframe must be transmitted before receiving the fourth pilot symbol from the beginning, the prediction is made using the third pilot symbol from the beginning. Do. This makes it possible to generate DL subframe data symbols using the channel prediction results.

A configuration for changing the number of pilot symbols used for channel prediction using the information on the delay time of propagation by the optical fiber shown in the first embodiment will be described with reference to FIG.
The channel estimation result input from the channel estimation unit 1004 is stored in the memory 1301. The memory 1301 stores all the channel estimation results of the panlot symbol in the 1UL subframe period.

In the channel prediction unit 1302 for 1 pilot symbol, when the channel estimation result of the first pilot symbol from the beginning is input to the memory 1031, channel prediction (through output) is performed using only that, and the selector 1306 is reached. Output.
The channel prediction unit 1303 for two pilot symbols reads the channel estimation results of the two pilot symbols from the memory 1031 and performs channel prediction when the channel estimation results of the second pilot symbol from the beginning are input to the memory 1031. , Output to selector 1306.
Similar to the channel prediction unit 1303 for the 2 pilot symbols, the channel estimation result of the 3rd or 4th pilot symbol is stored in the memory 1031 of the channel prediction unit 1304 for the 3 pilot symbols and the channel prediction unit 1305 for the 4 pilot symbols. At the time of input to, these channel estimation results are read from the memory 1031 to perform channel prediction, and output to the selector 1306.

By the above processing, the channel prediction result for each number of pilot symbols used is input to the selector 1306.
The channel prediction symbol number selection circuit 1307 determines the number of channel prediction symbols to be used based on the counter value (delay time amount in the optical fiber) from the counter 804, and outputs the channel prediction selection signal to the selector 1306.
The selector 1306 selects the channel prediction result based on the channel prediction selection signal and outputs it to the singular value decomposition unit 1006.

According to the second embodiment described above, even in a wireless communication system in which propagation delay occurs due to an optical fiber or the like and specific mode transmission MIMO that requires channel prediction is performed under the conditions, the propagation delay is observed. By performing channel prediction adapted to the propagation delay time, it is possible to reduce the deterioration of transmission performance and the guard time caused by the propagation delay.

Next, a third embodiment according to the present invention will be described. In the third embodiment, in the wireless communication system that performs MIMO transmission described in the second embodiment, a configuration in which a plurality of receiving antennas are distributed and arranged will be described.
FIG. 14 shows the configuration of a TDD-4x4 MIMO wireless communication system having eight transmission / reception branches at the base station 102. In the system shown in the figure, the antennas 106 of each branch of the base station 102 are distributed so that even if the mobile station 101 moves significantly, one of the branches can always receive with a high CNR (carrier-to-noise ratio). It is a configuration intended to be.

Since the signal transmitted from the antenna 105 of the mobile station 101 has a difference in the propagation distance to each antenna 106 of the base station 102, the CNR of the signal received by each antenna 106 is different, but all the base stations 102 It is received by the antenna 106 of. In order to reduce the calculation scale for reception, the transmission / reception control unit 108 of the base station 102 determines the priority based on the reception CNR and the like, selects four systems having high priority, and performs demodulation / decoding processing. Here, the transmission / reception branch of each system is expressed as BrN (N is the system number).

In the system of FIG. 14, since the optimum transmission / reception branch changes with the movement of the mobile station 101, the transmission / reception control unit 108 needs to switch the transmission / reception branch (handover). The timing at that time will be described along with the timing chart (in order from top to bottom) shown in FIG.
The mobile station 101 transmits a UL subframe (1) without precoding for the first transmission.
The base station 102 calculates the precoding weight from the propagation path characteristics when the UL subframe (1) is received, and notifies the mobile station 101 of the precoding weight by the DL subframe (2). The branches used to calculate the precoding weight at this time are Br1, Br2, Br3, and Br4, which are the same as the optimum branch.

The mobile station 101 multiplies the precoding weight received in the DL subframe (2) by the transmission signal to transmit the UL subframe (3).
In the base station 102, Br1, Br2, Br3, Br4, which is the same as the optimum branch of the received timing, is used for demodulation of the UL subframe (3), and the precoding weight is calculated in the same manner as Br1, Br2, Br3, The DL subframe (4) is transmitted to the mobile station 101 using Br4.
The mobile station 101 receives the DL subframe (4) in the same manner as the reception of the DL subframe (2), and transmits the UL subframe (5).

In the base station 102 that has received the UL subframe (5), the optimum branch of the received timing has changed to Br2, Br3, Br4, Br5. Therefore, in the conventional method, demodulation / decoding and precoding weight calculation are performed. Both use the same Br2, Br3, Br4, Br5 as the optimal branch. At that time, the precoding applied to the UL subframe (5) is calculated from Br1, Br2, Br3, and Br4. Therefore, when the selected branches Br2, Br3, Br4, and Br5 are used for demodulation / decoding, the branch used for precoding is different, so that the reception characteristics are significantly deteriorated.

Therefore, in the third embodiment, the channel estimation result used for the demodulation and error correction / decoding processing and the channel estimation (or channel prediction) result used for the precoding calculation processing of the next frame are respectively performed at the timing when the base station 102 performs the handover. Use different signals for. Hereinafter, the timing chart of the first method shown in FIG. 16 will be described in detail. It should be noted that the process up to the transmission of the UL subframe (5) is the same as in FIG.

In the base station 102, when receiving and processing the UL subframe (5) (at the time of handover), as the branch used for demodulation and error correction / decoding processing, the same Br1, Br2, as the branch used at the time of calculating the precoding weight By using Br3 and Br4, it is possible to demodulate / decode normally. On the other hand, Br2, Br3, Br4, Br5 are used to calculate the precoding weight to be notified to the mobile station 101 in the DL subframe (6).

The reception of the DL subframe (6) and the transmission of the UL subframe (7) on the mobile station 101 are performed in the same manner as the reception of the DL subframe (2) and the UL subframe (3).
When the UL subframe (7) is received by the base station 102, Br2, Br3, Br4, and Br5 are used for both demodulation / decoding and calculation of the precoding weight.

As described above, in the handover to switch the transmission / reception branch, the branch before switching is used for demodulation / decoding, and the branch after switching is used for calculating the precoding weight. It is possible to switch branches without degrading.

As another solution in the third embodiment, Br1 excluded from the optimum branch and Br5 newly added to the optimum branch may be weighted by α (t) and β (t) and synthesized. Here, t indicates a TDD frame number. Hereinafter, the timing chart of the second method shown in FIG. 17 will be described in detail.

For the first frame (t = 0) of branch switching, α (0) = 1, β (0) = 0, and the values of α (t) and β (t) are gradually changed for each frame, and finally α. It is changed so that (t) = 0 and β (t) = 1.
When demodulating the received frame of frame number t, the propagation path characteristic when the target frame is received is α (t) Br1 + β (t) Br5, whereas it is used to calculate the precoding weight applied to the target frame. The resulting propagation path characteristics are α (t-1) Br1 + β (t-1) Br5. Therefore, it is necessary to increase the number of frames to be switched so that the difference between α (t) Br1 + β (t) Br5 and α (t-1) Br1 + β (t-1) Br5 can be ignored.

As described above, each branch added or deleted by switching is weighted and pre-used so that the branch used for demodulation / decoding and calculation of precoding weight is gradually switched during the handover to switch the transmission / reception branch. By delaying the weighting for calculating the coding weight from the weighting for demodulation / decoding, it is possible to switch branches without deteriorating the transmission characteristics at the time of handover.

Next, branch switching in a system having transmission / reception branches exceeding the number of branches that can be processed by the singular value decomposition unit 1006 will be described with reference to FIG.
The transmission / reception control unit 106 of FIG. 18 has a system selection determination circuit 1801, a frame delay unit 1802, and a system selection unit 1803, 1804, 1085 added to the configuration of FIG.

The system selection determination circuit 1801 selects the optimum system from the reception CNR of each reception system, and outputs a system selection signal indicating the selected system to the frame delay unit 1802 and the system selection unit 1805.
The frame delay unit 1802 delays the input system selection signal by 1 TDD frame and outputs it to the system selection unit 1803 and the system selection unit 1804.

Each system selection unit 1803, 1804, 1805 selects and outputs four systems from, for example, eight systems according to the input system selection signal. That is, the system selection unit 1803 selects 4 systems from the 8 system signals input from the inter-system delay difference adjusting unit 1002 based on the system selection signal at the time of the previous UL subframe reception, and outputs the system to the spatial filter 1003. To do. Further, the system selection unit 1804 selects four systems from the eight system signals input from the channel prediction unit 1005 based on the system selection signal at the time of the previous UL subframe reception, and outputs the four systems to the spatial filter 1003. Further, the system selection unit 1805 selects 4 systems from the 8 system signals input from the channel prediction unit 1005 based on the system selection signal at the time of receiving the UL subframe this time, and outputs them to the singular value decomposition unit 1006. ..

With such a circuit, the switching of the branch used for the demodulation process and the calculation of the precoding weight can be delayed by one frame. By this process, the transmission / reception branch used to calculate the precoding weight applied to the received frame and the transmission / reception branch when demodulating / decoding the received frame always match, and no frame whose characteristics deteriorate occurs.

In general, in the singular value decomposition unit 1006, the amount of calculation increases exponentially as the number of received branches increases. Therefore, branch switching in a system in which the number of branches that can be processed by the singular value decomposition unit 1006 is limited and the number of transmission / reception branches exceeds the number of branches that can be processed by the singular value decomposition unit 1006 will be described with reference to FIG.
The transmission / reception control unit 106 of FIG. 19 has a system selection determination circuit 1801 and a system synthesis switching unit 1901 added to the configuration of FIG.

When a signal is input from the AD conversion unit 201 of eight systems, the system synthesis switching unit 1901 selects and outputs four systems of signals based on the system selection signal input from the system selection circuit 1801. Therefore, the number of processing units in the subsequent stage can be reduced to four systems.
In FIG. 19, the number of transmission / reception branches is 8 and the number of processing-compatible branches of the singular value decomposition unit 1006 is 4, but the number of processing-compatible branches of the singular value decomposition unit 1006 is N. (However, M ≧ N) may be set.

FIG. 20 shows the details of the system synthesis switching unit 1901.
The sorting unit 2001 sorts the eight digital signals in order of signal quality based on the system selection signal input from the system selection determination circuit 1801, and outputs the signals of the upper three systems to the FFT unit 1001. Then, the signals of the 4th and 5th positions are output to the weighted synthesis unit 1002.
The weighted synthesis unit 1002 weights and synthesizes the two input digital signals according to the quality between the systems, and outputs the digital signals to the FFT unit 1001. However, the weighting coefficient is changed for each frame, and the change width is made sufficiently small to reduce the difference in propagation path characteristics between frames.
By such processing, it is possible to suppress deterioration of characteristics due to branch switching.

As described above with reference to each embodiment, the base station 102, which is a wireless communication device according to an example of the present invention, is generally described as follows in order to shorten the no-signal period in TDD system communication. It is configured in.
That is, the base station 102 includes a transmission / reception high frequency unit 107 connected to the antenna 106 and a transmission / reception control unit 108 connected to the transmission / reception high frequency unit 107 via an optical fiber 302. The transmission / reception control unit 108 has a timing adjustment unit 810 that adjusts the timing at which transmission of the DL subframe is started. The timing adjustment unit 810 measures the round-trip time of the signal reciprocating between the transmission / reception high-frequency unit 107 and the transmission / reception control unit 108, and precedes the timing at which the reception of the UL subframe is completed by the transmission / reception control unit 108. The transmission / reception control unit 108 adjusts so that the transmission of the DL subframe is started at the same timing.

With such a configuration, the timing of starting the transmission of the DL subframe from the transmission / reception control unit 108 is preceded in anticipation of the delay (reciprocating portion) due to the optical fiber 302 between the transmission / reception high frequency unit 107 and the transmission / reception control unit 108. Can be done. As a result, transmission of the DL subframe can be started immediately after the transmission / reception high frequency unit 107 finishes receiving the UL subframe. Therefore, it is possible to automatically adjust the no-signal period to the minimum in the TDD system wireless communication system in which the transmission delay due to the optical fiber exists, and it is possible to shorten the guard time and improve the throughput.

Here, the transmission / reception high frequency unit 107 has a circuit structure that returns the signal transmitted from the transmission / reception control unit 108 to the transmission / reception control unit 108, and the timing adjustment unit 810 has a timing adjustment unit 810 in which the signal transmitted from the transmission / reception control unit 108 is the transmission / reception high frequency unit 107. The time until the signal is returned by the transmission / reception control unit 108 and received by the transmission / reception control unit 108 may be measured as the round-trip time.

Further, the base station 102 may be a wireless communication device including a plurality of transmission / reception systems composed of an antenna 106, a transmission / reception high frequency unit 107, an optical fiber 302, and the like, and performing MIMO communication using these plurality of transmission / reception systems.
In this case, the base station 102 is based on the channel prediction unit 1005 that predicts the channel characteristics for the next UL subframe based on the pilot symbols arranged at predetermined intervals in the UL subframe, and the predicted channel characteristics. The channel prediction unit 1005 includes a singular value decomposition unit 1006 for calculating the precoding weight to be transmitted to the mobile station 101 (the device on the other side) for MIMO communication, and the channel prediction unit 1005 determines the number of pilot symbols used for predicting the channel characteristics. It is preferable to change according to the round trip time.

As a result, even when the unique mode transmission is realized in the TDD-MIMO wireless communication system in which the delay time differs for each transmission / reception branch, the no-signal period can be automatically adjusted for each branch to the minimum, and the channel prediction can be performed. By adaptively changing the number of pilot symbols used in the above according to the delay time, it is possible to use the channel prediction function in combination to improve the transmission characteristics.

When switching the transmission / reception system used for MIMO communication, the transmission / reception system before switching may be used for demodulation and decoding of the UL subframe, and the transmission / reception system after switching may be used for calculating the precoding weight.
Alternatively, when switching the transmission / reception system used for MIMO communication, each transmission / reception system added or deleted by switching is weighted so that the transmission / reception system used for demodulation / decoding of the UL subframe and calculation of the precoding weight is gradually switched. At the same time, the weighting for the calculation of the precoding weight may be delayed from the weighting for the demodulation and decoding of the UL subframe.
With such a configuration, the transmission / reception branch can be stably switched even in a wireless communication system in which the number of transmission / reception branches that can perform MIMO processing is exceeded.

Here, the configurations of the system, the device, and the like according to the present invention are not necessarily limited to those shown above, and various configurations may be used.
Further, the present invention can be provided, for example, as a method or method for executing the process according to the present invention, a program for realizing such a method or method, a storage medium for storing the program, or the like.

The present invention can be used in various wireless communication devices that perform TDD-type wireless communication.

101: Mobile station, 102: Base station, 103, 108: Transmission / reception control unit, 104, 107: Transmission / reception high frequency unit, 105, 106: Antenna, 201: AD converter, 202: Demodulation / decoding unit, 203: Preamble mutual correlation Unit, 204: Timing adjustment unit, 205: DL information temporary storage memory, 206: Modulation unit, 207: Fourier unit, 208: DA conversion unit, 301, 303: Electric / optical converter, 302: Optical fiber, 601: Mixer , 602: Synthesizer, 603: Filter, 604: Folding switch, 605: PA, 606: RF switch, 607: LNA, 608: ATT, 609: Folding switch, 610: Filter, 611: Mixer, 801: UL mutual Correlation mask part, 802: DL mutual correlation mask part, 803: Advance transmission function compatible timing controller, 804: Counter, 805: Delay part, 810: Timing adjustment part, 1001: FFT part, 1002: Intersystem delay difference adjustment part, 1003: Spatial filter, 1004: Channel estimation unit, 1005: Channel prediction unit, 1006: Singularity decomposition unit, 1007: Frame delay unit, 1008: Decoding unit, 1301: Memory, 1302: 1 Pilot symbol channel prediction unit, 1303 : 2 Pilot symbol channel prediction unit, 1304: 3 Pilot symbol channel prediction unit, 1305: 4 Pilot symbol channel prediction unit, 1306: Selector, 1307: Channel prediction symbol number selection unit, 1801: System selection determination circuit, 1802 : Frame delay section, 1803-1805: System selection section, 1901: System synthesis switching section, 2001: Sorting section, 2002: Weighted synthesis section

Claims (4)

In a TDD-type wireless communication device in which a reception frame received from the other device and a transmission frame transmitted from the own device are transmitted and received at different timings.
In order to perform MIMO communication, a plurality of transmission / reception systems each having an antenna, a first processing unit connected to the antenna, and an optical fiber connected to the first processing unit,
A timing adjustment unit for adjusting the timing of starting the transmission of the transmission frame, and a second processing unit which is connected through the optical fiber to the first processing unit of said plurality of transceiver systems,
The timing adjusting unit measures the round-trip time of the signal reciprocating between the first processing unit and the second processing unit, and the reciprocating time is equal to the timing at which the reception of the receiving frame is completed by the second processing unit. adjusted so that transmission of the transmission frame from the second processing unit at the timing obtained by preceding the start of,
The second processing unit has a channel prediction unit that predicts the channel characteristics for the next reception frame based on pilot symbols arranged at predetermined intervals in the reception frame, and a channel characteristic predicted by the channel prediction unit. Based on this, it also has a weight calculation unit that calculates the precoding weight to be transmitted to the device on the other side for MIMO communication.
The channel prediction unit is a wireless communication device characterized in that the number of pilot symbols used for predicting channel characteristics is changed according to the round trip time . In the wireless communication device according to claim 1,
The first processing unit has a circuit structure that returns a signal transmitted from the second processing unit to the second processing unit.
The timing adjusting unit is characterized in that the time until the signal transmitted from the second processing unit is folded back by the first processing unit and received by the second processing unit is measured as the round-trip time. Communication device. In the wireless communication device according to claim 1 or 2 .
When switching the transmission / reception system used for MIMO communication, the transmission / reception system before switching is used for demodulation and decoding of the received frame, and the transmission / reception system after switching is used for calculating the precoding weight. apparatus. In the wireless communication device according to claim 1 or 2 .
When switching the transmission / reception system used for MIMO communication, each transmission / reception system added or deleted by switching is weighted so that the transmission / reception system used for demodulation / decoding of received frames and calculation of precoding weight is gradually switched. A wireless communication device characterized in that the weighting for calculating the precoding weight is delayed from the weighting for demodulation and decoding of received frames.

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