JP4093581B2 - Wireless receiver - Google Patents

Description

The present invention relates to a wireless receiver used in a mobile communication system such as a cellular phone or a wireless LAN system.

It is known to change the demodulation method from the error detection result in order to improve the throughput of the wireless communication system. As one of the methods, there is known a method for determining whether to perform fading distortion estimation and compensation or adaptive equalization using pilot symbols from a CRC result (
For example, see Patent Document 1).
JP 2002-111756 A (page 11, FIG. 1)

In the above-described prior art, the system throughput can be improved by changing the demodulation method based on the error detection result, but there is a problem that it is not possible to take measures corresponding to the cause of the error.

The present invention has been made to solve the above-described problem, and it is estimated whether the cause of the error is due to fading or due to an interference signal. An object of the present invention is to provide a radio receiving apparatus capable of improving reception performance in general.

In order to solve the above-mentioned problem, according to an embodiment of the present invention , among received signals composed of a pilot signal and a data signal, the data signal is divided into blocks each having a preset time length, and the reliability of the data signal in each block is increased. A reliability calculation means for calculating, and a means for performing reception processing based on the calculated reliability for each block, and a null symbol is added to a block for which the reliability calculation means has calculated a reliability lower than a predetermined level. It is characterized by inserting and performing error correction decoding.

According to the present invention, since it is possible to take a measure corresponding to the cause of the error, the reception performance can be improved.

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

FIG. 1 shows a schematic configuration example of a transmitter and a receiver according to the first embodiment. Between the transmitter and the receiver, a pilot signal for estimating a transmission path and a data signal for transmitting information are time-division multiplexed and transmitted.

The transmitter includes an error detection coding processing unit 101 that adds error detection data to a data signal, an error correction coding processing unit 102 that adds an error correction code, a modulation processing unit 103 that modulates an error correction coded signal, The RF processing unit 104 converts a signal obtained by multiplexing the pilot signal and the data signal into a high frequency signal.

On the other hand, the receiver demodulates the digital signal of the baseband frequency from the RF processing unit 105 that processes the received high-frequency signal, the reliability estimation processing unit 109 that estimates the reliability of the received signal described later, and the RF processing unit 105. A QPSK demodulation processing unit 106, an error correction decoding processing unit 107 that performs error correction of the demodulated data signal, and an error detection processing unit 108 that performs error detection processing after the error correction decoding processing is performed.

A signal transmission procedure in the transmitter will be described. A data signal to be transmitted is encoded by the error detection encoding processing unit 101. The code used here is a code capable of detecting an error, such as CRC coding. In the case of CRC coding, a parity bit of the CRC code is added to the end of the data. Next, the error correction coding processing unit 102 performs coding using a code that can correct a certain amount of error on the receiving side, such as convolutional coding or turbo code. The signal subjected to error correction coding is converted into a baseband signal by the modulation processing unit 103. Data signal modulation methods include, for example, TDM (time division multiplexing), CDM (code division multiplexing), OFDM
A modulation scheme such as (orthogonal frequency division multiplexing) is used. In this example, TDM is used. As a modulation method for each carrier, a modulation method such as BPSK, QPSK, or QAM is used.
In this example, the QPSK modulation method is used.

In the transmitter, a pilot signal is inserted at the head of the data. Here, the pilot signal is a signal (unique word) that is known between the transmitter and the receiver. A series of signals in which pilot signals and data signals are time-multiplexed is called one slot. The multiplexed signal is converted into an analog signal having a carrier frequency by the RF processing unit 104 and transmitted from the antenna.

Next, a data reception processing procedure in the receiver will be described. The data received by the antenna is
The RF processing unit 105 converts the digital signal into a baseband frequency digital signal.

The converted digital signal of the baseband frequency is demodulated by the QPSK demodulation processing unit 106. The demodulated data signal is subjected to error correction decoding processing by the error correction decoding processing unit 107 and then subjected to error detection processing by the error detection processing unit 108, and the resulting data signal is output.

The reliability estimation processing unit 109 estimates the reliability of each block of the data signal that is temporally divided into N blocks (N is a positive integer) by a method described later. The estimated reliability of each block is used as a parameter for changing demodulation and decoding operations in the processing performed by the QPSK demodulation processing unit 106 and the error correction decoding processing unit 107.

FIG. 2 schematically shows an example of the slot configuration and an example of reliability for each block. One slot includes a pilot signal 201 and a data signal 202. Here, a pilot signal and a data signal are arranged at the head of the slot, but the pilot signal may be located before and after the slot or in the center. In the receiver, a reliability estimation process is performed on the data signal 202. The reliability is estimated using the noise component, signal power, and error signal power of the received signal. Here, the reliability of each block is estimated using the following equation (equation 1).

Here, M is the number of blocks to be divided from one slot, N is the number of slots for which power is averaged,
Nn (m) is the noise power in slot n and block m, En (m) is the error power from the ideal signal in slot n and block m, Sn (m) is the signal power in slot n and block m, Rk (m) Is the reliability in slot number k and block m. The larger the value of R (m), the higher the reliability of the signal of that block, indicating that the signal is less error-prone. The ideal signal is a signal obtained by making a hard decision on received data and modulating the decision result again. Since the acquisition method of the ideal signal is publicly known, detailed description is omitted.

The reliability estimation processing unit 109 calculates the reliability R (m) of the block m, estimates the cause of the error from those states, and the receiver performs a decoding process to counter the estimated cause.

FIG. 3 shows an example of the reliability distribution when the received data receives an interference signal. In this example, one slot is divided into nine blocks and the reliability R (m) is calculated, but the reliability of the third block (indicated by reference numeral 401) is the surrounding reliability. Compared to extremely low.
Thus, when only a certain block has extremely low reliability, the reliability estimation processing unit 109
It is estimated that an error has occurred due to steady interference. For example, 1/10 of the average of the reliability R
Is considered as a threshold value, and it is considered that interference occurs in a block m that is continuously below the threshold value for several slots. In such a case, the reliability estimation processing unit 109 performs error correction decoding processing unit 1
On the other hand, for data with low reliability, control is performed so that a null signal is inserted instead of the received signal. By inserting a null signal, the log likelihood ratio becomes 0 when error correction processing is performed, and error correction decoding can be performed without being affected by the interference signal.

By the way, when demodulating the data signal, it is demodulated using the transmission path estimated using the pilot signal, but since the time distance from the time when the pilot signal is received is small in the block close in time to the pilot signal, The result of transmission path estimation is close to the actual transmission path. However, since the transmission path may have changed in blocks far in time, the result of transmission path estimation may be different from the actual transmission path. As a method of avoiding this, there is a decision feedback type transmission path estimation method using a data demodulation result. However, when an interference signal is generated, it is very difficult to demodulate data located behind the interference signal in time if a decision feedback type transmission path estimation is used. Therefore, as shown in FIG. 3, when the reliability is extremely low in one block, the first block is used by using the transmission path signal estimated from the pilot signal without using the decision feedback transmission path estimation. To the last block. Thus, the influence of the interference signal can be reduced by changing the transmission path estimation method using the reliability as a parameter.

FIG. 5 schematically shows an example of the distribution of reliability of the received data signal when it is affected by fading. When both the transmitter and the receiver are stationary, or when the time position of the reception block is close to the pilot, the transmission path is estimated using the pilot, and the phase is corrected using the result. The received signal constellation returns to the position of the transmitted signal as shown in FIG. However, when the transmitter or the receiver is moving at high speed, the fading fluctuation becomes fast, so that the phase of the received signal also changes at high speed. For this reason, it is conceivable that the last block that is separated in time from the first pilot has changed from the state of the transmission path estimated by the pilot signal. As shown in FIG. 7, the phase of the received signal constellation changes from the transmitted signal point. In such a case, as shown in FIG. 5, it is conceivable that the reliability decreases as the block moves backward in time.

As shown in FIG. 5, when the distribution is such that the reliability decreases with increasing distance from the pilot signal, the reliability estimation processing unit 109 generates a fast fading fluctuation. I guess that. For example, the reliability R (m) and the reliability R (m + 1) are compared, and the relationship that the reliability R (m + 1) is smaller holds continuously for several slots in all the blocks 1 to M−1. In this case, it is assumed that fast fading fluctuation has occurred.

When the reliability estimation processing unit 109 estimates that fast fading fluctuation has occurred in the received data, it performs a process of rotating the phase of the received signal and performing demodulation again. For example, as shown in FIG. 8A, first, the received signal of the block with low reliability is turned in the direction of the solid line (counterclockwise), and QPSK demodulated again, and error correction decoding and error detection processing are performed on the entire slot. I do. At this time, if no error is detected, the decoded received data is output. If an error is detected, as shown in FIG. 8B, the received signal of the block with low reliability is rotated in the direction of the broken line (clockwise), and then QPSK demodulated again, and error correction decoding is performed on the entire slot. Error detection processing is performed. If no error is detected, the decoded received data is output.
If an error is detected, a message indicating that reception has failed is output. When such demodulation and decoding processes are performed, good results cannot be obtained unless errors due to fading fluctuations are large, that is, errors due to fading fluctuations are larger than errors due to interference or errors due to noise. For this reason, this process is not performed except when it is estimated from the reliability estimation that an error due to fading fluctuation has occurred.

  The demodulation and decoding processing based on the reliability estimation described above will be described in detail with reference to FIG.

Of the digital signal S1001 converted into the baseband frequency by the RF processing unit 105 in FIG. 9B, the pilot signal is used for transmission path estimation in the transmission path estimation processing block 1001. Noise estimation processing is performed in the noise estimation processing block 1002 based on the variance (S1002) of the pilot signal calculated here, and the estimated noise power S1003 is used for reliability estimation in the reliability estimation processing block 1003.

The other input signal S1005 is input to the QPSK demodulation processing block 1006, where the data signal is demodulated. The QPSK demodulation processing block 1006 contains information on the estimated transmission path estimated by the transmission path estimation processing block 1001. S1004 is input and demodulation is performed using this information as well. Demodulated signal S1007 is input to signal power estimation processing block 1004 and error component estimation processing block 1005, where signal power S1008 and error signal power S1009 are estimated, respectively. These estimated powers are used for reliability estimation in the reliability estimation processing block 1003. The QPSK demodulated signal S1007 is subjected to error correction decoding processing in the error correction decoding processing block 1007 and then input to the error detection processing block 1008. After the presence or absence of an error is confirmed here, the final received data signal S1013 is obtained. Is output.

In the reliability estimation processing block 1003, the reliability of each block is estimated by the above-described equation 1 using the noise power S1003 between N slots, the signal power S1008, and the error component power S1009, and the reliability distribution state for each block is estimated. Estimate the cause of the error. When it is estimated that the error is due to an interference signal, the reliability estimation processing block 1003 controls the transmission path estimation processing block 1001 so as not to perform decision feedback type transmission path estimation.
16 or a control signal S for performing error correction decoding by inserting a null signal in place of the received signal to a block with extremely low reliability for error correction decoding processing 1007
1011 is output. If the error is estimated to be due to fading,
A control signal S1010 for performing phase rotation processing on the received signal phase rotation processing block 1009 is output. At this time, in the received signal phase rotation processing block 1009, the phase is rotated with respect to the received signal S1006, and the signal S1015 whose phase is rotated is again QP
SK demodulation processing 1006, error correction decoding processing 1007, and error detection processing 1008 are performed. If no error is detected, data is output (S1013). If an error is detected, the received signal phase rotation processing block 1009 outputs a signal S1015 obtained by rotating the phase of the received signal in the direction opposite to the previous rotation. QPSK demodulation processing 1006 and error correction decoding processing 10 again
07, error detection processing 1008 is performed. If no errors are detected, output the data,
If an error is detected, the fact that error correction has failed is output.

In this way, the reliability is estimated for each block from noise power, signal power, etc., the cause of the error is estimated from the reliability distribution, the transmission path estimation method according to the estimated cause of the error, The reception performance can be improved by adaptively selecting the demodulation method and the error correction decoding method.

FIG. 10 shows a configuration example of a transmitter and a receiver according to the second embodiment. FIG. 10 differs from FIG. 1 in that a signal subjected to error correction coding is subjected to block division processing by a block division unit 1103 in the transmitter, and error detection coding processing 1104 is performed on each block.
The signal of each block is subjected to block combination processing 1105 and returned to the signal of one slot again. The combined signal is converted into a baseband signal by the modulation processing unit 1106, and the same processing as in FIG. 1 is performed.

On the other hand, in the receiver, the demodulated data signal is divided into blocks in a block division process 1110. Each block signal is subjected to error detection. The error information at this time is transferred to the reliability estimation process 1115 and used for calculation of reliability. The block signal in which the error is detected is combined with the signal in the slot unit again in the block combination processing 1112, and the error correction decoding processing unit 1113 performs the error correction decoding processing, and then the error detection processing unit 1114 performs the error detection processing. And the resulting data signal is output.

FIG. 11 schematically shows an example of the slot configuration according to the second embodiment and an example of reliability for each block. One slot is a pilot signal 1201, M data signal blocks 1202,
It consists of error detection parity bits 1203 for M data blocks. Pilot signal 1201 and data signal 1202 are time-multiplexed and transmitted. Here, a pilot signal and a data signal are arranged at the head of the slot, but the pilot signal may be located before and after the slot or in the center.

The receiver performs reliability estimation processing on the data signal 1202 for each block. As shown in FIG. 11, the estimation of reliability is performed using error detection results for each block. Here, the reliability of each block is estimated using the following equation (equation 2).

In Equation 2, M is the number of blocks to be divided from one slot, N is the number of slots taking an error rate, BL
ERn (m) is a block error rate in slot n and block m obtained by error detection, and Rk (m) is a reliability in slot number k and block m. The larger R (m), the higher the reliability of the signal of that block, indicating that the signal is less prone to error. In the reliability estimation process 1115, the reliability R (m) of the block m is calculated, the cause of the error is estimated from those states, and the receiver performs a decoding process to counter the estimated cause.

Demodulation and decoding processing based on reliability estimation performed by the receiver in FIG. 10B will be described in more detail with reference to FIG.

Of the input signal S1301, which is a digital signal converted to a baseband frequency by the RF processing unit 1108 in FIG. 10B, a pilot signal is used for transmission path estimation in the transmission path estimation processing block 1301. The input signal S1302 is demodulated by the QPSK demodulation processing block 1302 of the data signal component. At this time, the QPSK demodulation processing 1302 performs demodulation using the estimated transmission path S1304 estimated by the transmission path estimation processing 1301, and checks the presence or absence of an error for each block in the error detection processing block 1303 for each block. The error information S1314 for each block is used to calculate reliability in the reliability estimation processing block 1304. The error detection is performed for each block, and the data signal S1304 from which the error detection parity bit for each block has been removed is subjected to error correction decoding for each slot in an error correction decoding processing block 1305, and an error in the data slot is detected in the error detection processing block 1306 After confirming the presence or absence, the final received signal S1307 is output.

In the reliability estimation processing block 1304, error detection information S13 for each block between N slots.
14 is used to estimate the reliability of each block, and the cause of the error is estimated. When it is estimated that the error is due to an interference signal, a signal S1311 for controlling the transmission path estimation processing block 1301 not to perform decision feedback transmission path estimation is output, or an error correction decoding processing block 1305 is output. On the other hand, a control signal S1312 is output so that error correction decoding is performed by inserting a null signal in place of the received signal for a block with extremely low reliability. When it is estimated that the error is due to fading, a control signal S1313 is output to cause the received signal phase rotation processing block 1307 to perform phase rotation processing. The received signal phase rotation processing block 1307 at this time is the same as the processing in FIG.

As described above, in this embodiment, an error rate for each block can be easily obtained by adding an error detection code for each block at the transmitter and performing error detection processing for each block at the receiver. From this result, the reliability for each block is estimated, and the cause of the error can be estimated from the reliability distribution, so that the transmission path estimation method, demodulation method, and The reception performance can be improved by adaptively selecting the error correction decoding method.

FIG. 13 shows a configuration example of a transmitter and a receiver according to the third embodiment. The configuration of the transmitter is the same as that in FIG. 10, but the receiver has a plurality of units from the antenna to the block coupling unit.

In this embodiment, in the receiver, data received by A (A is a positive integer) number of antennas is converted into a digital signal of a baseband frequency by the RF processing unit 1808 for each antenna. The converted baseband frequency digital signal is demodulated by a QPSK demodulation processing unit 1809. The demodulated data signal is divided into blocks by a block division processing unit 1810. Each block signal is subjected to error detection. The error information at this time is passed to the reliability estimation processing unit 1816 and used for calculation of reliability. The block signal in which the error is detected is combined with the signal in the slot unit again by the block combination processing unit 1812.

The signal in slot units is added by the adder 1813 and the signals received and processed by the respective antennas are added. At this time, the addition process may be a weighted addition process.

The signal to which the data for each antenna is added is subjected to error correction decoding processing by an error correction decoding processing unit 1814, and then subjected to error detection processing by an error detection processing unit 1815, and the resulting data signal is output. .

The reliability estimation processing unit 1816 estimates the reliability using the error detection result obtained from each antenna. Here, the reliability of each block is estimated using the following equation (equation 3).

Here, A is the number of antennas, M is the number of blocks divided from one slot, N is the number of slots taking an error rate, BLERn, a (m) is the block in antenna a, slot n and block m obtained by error detection. Error rate, Rk (m) is slot number k, block m
The reliability in The larger R (m), the higher the reliability of the signal of that block, indicating that the signal is less prone to error. The reliability estimation processing unit 1816 calculates the reliability R (m) of the block m, and this value is the QPSK demodulation processing unit 1809 and the error correction decoding processing unit 1.
Used as a parameter to change the demodulation and decoding operations in the processing performed at 814.

By measuring the error rate for each block using a plurality of antennas as described above, it is possible to obtain an accurate reliability for each block in a short time. The cause of the error can be estimated in a short time from the reliability distribution for each block.

FIG. 14 shows a configuration example of a transceiver according to the fourth embodiment. Also between the transmitter / receiver A and the transmitter / receiver B, pilot signals and data for estimating the transmission path are time-division multiplexed and transmitted.

The data signal transmission / reception procedure in the transceivers A and B is the same as the procedure described with reference to FIG. 10, but in this embodiment, the modulation scheme and the transmission method are based on the reliability information received by the transceiver A from the transceiver B. The difference is that an error detection coding method is selected.

Data received by the transceiver B is converted into a digital signal having a baseband frequency by the RF processing unit 1910. The converted baseband frequency digital signal is sent to the demodulation processing unit 19.
11 is demodulated. The demodulation method at this time is selected based on the modulation method from the transceiver A that exists as information in the previous received data. The demodulated data signal is divided into blocks by a block division processing unit 1912. The data divided for each block is subjected to error correction decoding processing and error detection processing, respectively. In the error correction decoding process, the decoding method is selected based on the encoding method selected by the transceiver A that exists as information in the previous received data. Also, the error presence / absence information obtained by the error detection processing unit 1913 is sent to the reliability estimation processing unit 1916, which is used for reliability estimation for each block. The data subjected to error detection processing is subjected to block combination processing and returned to data in one slot unit.
Is output. At this time, the modulation method and encoding method signal of the next slot multiplexed on the data signal are used for error correction decoding processing and demodulation processing in the next slot. The reliability estimation processing unit 1916 estimates the reliability for each block from the error rate for each block using the above-described equation 2, estimates the cause of the error from the distribution, and adaptively optimizes the transmission path. Select an estimation method and an error correction decoding method. Further, the estimated reliability information is obtained from the transceiver B.
Is multiplexed with the data signal transmitted to the transceiver A and transmitted.

A control method using reliability in the transceiver A will be described. When the transmitter / receiver A receives data, the demodulation system 1908 performs demodulation processing and divides the data signal into reliability information measured by the transmitter / receiver B. The reliability information of the transceiver B is the control block 19 using the reliability.
09 is used to select an error correction coding method and a modulation method for each block. For example, when it is estimated that an error occurring in the transceiver B is due to a stationary interference signal, an error correction method strong against the interference signal is used for a block whose reliability is extremely lowered. The error rate in the transceiver B is reduced. Further, when it is estimated that the error occurring in the transceiver B is due to a fast fading fluctuation, the transceiver can be instructed to use the π / 4 shift differential QPSK modulation method in the modulation method. Reduce the error rate at B. The contents instructed here are multiplexed with the data signal and transmitted to the transceiver B.

FIG. 15 shows an example of a data communication procedure between the transceivers A and B. The transceiver A performs processing such as error correction coding and error detection code addition for each block, and transmits the coding method and modulation method used in the next slot and data to the transceiver B. The transceiver B performs demodulation and decoding processing for each block using the encoding scheme and modulation scheme received in the previous slot, and extracts received data, the encoding scheme and modulation scheme for the next slot. In addition, reliability information for each block is estimated. Thereafter, the transceiver B multiplexes the estimated reliability information in the transceiver B and the data to be transmitted to the transceiver A, and transmits the data. Based on the reliability information received from the transceiver A, the transceiver A selects an error encoding scheme and modulation scheme, and transmits the encoding scheme and modulation scheme used in the next slot and data to the transceiver B. To do. By repeating this, the reliability information measured by the transmitter / receiver B can be shared by the transmitter / receiver A. Therefore, the modulation scheme and the coding scheme can be selected adaptively based on this information. .

Thus, by feeding back the reliability of each slot measured by the transceiver B to the transceiver A, the cause of the error occurrence based on the reliability information can be estimated in the transceiver A. Therefore, it is possible to adaptively select an optimal modulation scheme and encoding scheme. For this reason, it is possible to further improve the reception performance in the transceiver B.

The block diagram which shows the transmitter and receiver structure which concern on 1st Embodiment. The figure which shows the slot structure which concerns on 1st Embodiment. The figure which shows the example of distribution of reliability in the case of receiving the interference signal. The figure which shows the mode of insertion of the null signal with respect to the block which has received the interference signal. The figure which shows distribution of reliability in the case of being influenced by fading. The figure which shows the example of the constellation of the received signal of a stationary state. The figure which shows the example of the constellation of the received signal of a movement state. The example of the phase rotation of the received signal which concerns on 1st Embodiment. The figure for demonstrating the procedure of the reception process which concerns on 1st Embodiment. The figure which shows the transmitting apparatus and receiver structure which concern on 2nd Embodiment. The figure which shows the slot structure which concerns on 2nd Embodiment, and a block reliability distribution example. The figure for demonstrating the procedure of the reception process which concerns on 2nd Embodiment. The figure which shows the transmitter and receiving mechanism example which concern on 3rd Embodiment. The figure which shows the transmitting apparatus and receiver structure which concern on 4th Embodiment. The figure for demonstrating the data communication procedure between the transmitter / receiver which concerns on 4th Embodiment.

Explanation of symbols

105 RF processing unit 106 QPSK demodulation processing unit 107 error correction decoding processing unit 108 error detection processing unit 109 reliability estimation processing unit

Claims (3)

A reliability calculation means for dividing the data signal into blocks of a predetermined time length among the reception signals composed of the pilot signal and the data signal, and calculating the reliability of the data signal in each block;
Means for performing reception processing based on the calculated reliability for each block ;
The block for which the reliability calculation means has calculated a reliability lower than a predetermined level includes a null thin
A radio receiving apparatus for performing error correction decoding by inserting a bolt . A reliability calculation means for dividing the data signal into blocks of a predetermined time length among the reception signals composed of the pilot signal and the data signal, and calculating the reliability of the data signal in each block;
Means for performing reception processing based on the calculated reliability for each block;
The received signal includes block division means for dividing the data signal into N (N is an integer equal to or greater than 1) blocks of a signal slot made up of a pilot signal and a data signal, and an error detection code for each divided transmission block. A signal transmitted from a wireless transmission device comprising an error detection coding means to be added and a data transmission means for time-division multiplexing and transmitting each transmission block to which the error detection code is added, and the reliability is determined for each reception Calculated using the error rate obtained by error detection decoding of the block ,
Based on the reliability information of each block calculated by the reliability calculation means,
Judgment is made using channel information alone or using the head pilot and data signal.
A radio receiving apparatus that selects whether to perform feedback type transmission path estimation .   A reliability calculation means for dividing the data signal into blocks of a predetermined time length among the reception signals composed of the pilot signal and the data signal, and calculating the reliability of the data signal in each block;
  Means for performing reception processing based on the calculated reliability for each block;
  The received signal is a data signal in a signal slot consisting of a pilot signal and a data signal.
Block dividing means for dividing the signal into N (N is an integer of 1 or more) blocks, and each divided transmission
Error detection coding means for adding an error detection code to a communication block and an error detection code
Transmission device comprising data transmission means for time-division-multiplexing and transmitting each transmitted block
And the reliability is obtained by error detection decoding of each received block.
Calculated using the error rate,
  Based on the reliability information of each block calculated by the reliability calculation means, the received signal
A radio receiving apparatus that selects whether or not to perform decoding by rotating the phase of the radio receiver.

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