JP2007096382A - Wireless communication system, and transmitter and receiver thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wireless communication system, and a transmitter and a receiver thereof, wherein distortion caused in a power amplifier on a transmitter side is surely compensated without deteriorating a reception characteristic on a receiver side. <P>SOLUTION: The receiver side apparatus (receiver) receives a wireless signal sent from the transmitter side apparatus (transmitter) opposite to the receiver, a distortion detection section 115 detects a distortion amount by a power amplifier 107 of the transmitter from a received wireless signal, and informs the transmitter of the detected distortion amount. A mapping table memory in the transmitter stores a mapping table corresponding to the distortion amount in advance, and the transmitter compensates the nonlinear distortion produced from the power amplifier 107 by selecting the optimum mapping table and using the selected table. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a radio communication system used in, for example, an FWA (Fixed Wireless Access) system, and in particular, a radio communication system having a predistortion function that compensates in advance for non-linear distortion generated in a power amplifier, and a transmitter and a receiver thereof. About.

  When a power amplifier used in a transmitter of a wireless communication system is operated at a high operating point in order to obtain a high output, nonlinear distortion occurs in amplitude and phase due to the influence of input / output characteristics of the power amplifier. In order to avoid such distortion, various schemes have been proposed. For example, a predistortion scheme that measures distortion of a transmission signal by a power amplifier in advance and corrects modulation of the transmission signal based on the measured distortion. Has been proposed (see, for example, Patent Document 1). According to this method, it is possible to cope with a change in distortion characteristics due to a temperature change, aging change, etc. of the power amplifier.

JP 2004-242134 A

  However, in the method of compensating distortion characteristics on the transmission side as in the prior art, there are cases where the receiving side is overcompensated or insufficiently compensated. In particular, a QAM (Quadrature Amplitude Modulation) modulation scheme having a high modulation multi-level number may cause a significant deterioration in reception characteristics.

  The present invention has been made paying attention to the above circumstances, and the object of the present invention is to provide a wireless communication device that can reliably compensate for distortion occurring in the power amplifier on the transmission side without degrading the reception characteristics on the reception side. It is to provide a communication system and a transmission device and a reception device thereof.

In order to achieve the above object, a radio communication system of the present invention, a transmission apparatus and a reception apparatus thereof include a symbol mapping unit that maps a transmission bit string on a complex plane and outputs a transmission baseband signal representing the mapping value, Transmission comprising: a radio signal generation unit that generates a radio signal modulated by a transmission baseband signal output from a symbol mapping unit; and a power amplifier that amplifies and outputs the radio signal generated by the radio signal generation unit Receiving a radio signal arriving from the apparatus, the transmitting apparatus, demodulating the radio signal to generate a received baseband signal, and performing symbol determination on the received baseband signal, A symbol determination unit that outputs a bit string representing a determination result; the received baseband signal; and the bit string Wherein comprising a distortion amount detecting means for detecting the amount of distortion by the power amplifier, and a receiving device and a notification means for notifying the detected distortion amount to the transmission device from. The symbol mapping unit outputs a mapping value reflecting a reverse characteristic of the distortion characteristic of the power amplifier as the transmission baseband signal according to the transmission bit string and the distortion amount notified from the reception apparatus. It is characterized by.

  In the above-described configuration, the amount of distortion by the power amplifier of the transmission device is detected in the reception device, and the transmission device compensates for distortion characteristics based on the amount of distortion by the power amplifier notified from the reception device. With this configuration, it is possible to reliably compensate for distortion generated in the power amplifier without degrading reception characteristics in symbol determination of the receiving apparatus.

  In the radio communication system of the present invention, the symbol mapping unit stores a plurality of sets of mapping values reflecting the inverse characteristics of distortion characteristics of the power amplifier in association with the distortion amounts, and the transmission bit string and the reception A mapping value corresponding to the distortion amount notified from the apparatus is output. In this way, for example, it is possible to perform distortion compensation by selecting an optimum mapping table from a plurality of mapping tables reflecting the inverse characteristic of the distortion characteristic.

  Further, in the wireless communication system of the present invention, the distortion amount detection means detects the distortion amount based on a preset symbol point among a plurality of symbol points in the symbol determination unit. In this way, the amount of detection processing can be reduced compared to the case where the amount of distortion is detected based on all the symbol points.

  Therefore, according to the present invention, it is possible to provide a radio communication system capable of reliably compensating for distortion generated in the power amplifier without degrading the reception characteristic on the receiving side, and its transmitting apparatus and receiving apparatus.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a block configuration diagram showing an embodiment of a transmission / reception apparatus having both a transmission apparatus and a reception apparatus used in a wireless communication system according to the present invention.
This transmission / reception apparatus includes a channel encoding unit 100, an address encoding unit 101, a mapping table memory 102, a transmission filter unit 103, an orthogonal modulation unit 104, a DA conversion unit 105, a transmission RF (Radio Frequency) as transmission side blocks. ) Unit 106 and a power amplifier 107. Also, as a reception side block, a reception RF unit 110, an AD conversion unit 111, an orthogonal demodulation unit 112, a reception filter unit 113, an equalizer 118, a symbol determination unit 114, a distortion amount detection unit 115, a channel decode Unit 116 and an averaging processing unit 117. Furthermore, a duplexer 108 and an antenna 109 that are used together in transmission and reception are provided.

  First, the basic operation of the transmission side block will be described. FIG. 2 is a diagram illustrating an example of a configuration of a radio frame and control information output from the transmission side block. In this embodiment, a case where the modulation scheme is 16QAM (16-positions Quadrature Amplitude Modulation) and the nonlinear distortion generated in the power amplifier 107 is a distortion due to a phase will be described as an example. FIG. 3 shows an example of a 16QAM constellation. Bit sequences corresponding to each symbol point are shown in parentheses in the figure.

  In the block on the transmission side, first, a frame having a structure as shown in FIG. 2 is generated by the channel encoding unit 100 and output to the address encoding unit 101 as data in symbol units. The frame is composed of an equalization training pattern TRN, radio device control data RCB, original transmission data DATA, and a guard interval GUARD at the frame boundary.

  The mapping process is basically a process of referring to the in-phase component and the quadrature component from the mapping table memory 102 in accordance with the symbol input to the address encoding unit 101. At this time, the data stored in the mapping table memory 102 is a value obtained by measuring in advance nonlinear distortion generated in the power amplifier 107 and adding the inverse characteristic thereof. In the present embodiment, as an example, four types of distortion compensation patterns as shown in FIG. 4 are prepared in advance, and the reference destination is switched according to the amount of distortion detected by the opposite receiver described later. The total number of distortion compensation patterns can be arbitrarily set. At this time, there is a trade-off between the required memory capacity and the accuracy of tracking distortion.

  After the mapping is completed, the mapping value output from the mapping table memory 102 is subjected to waveform shaping / sampling rate conversion by the transmission filter 103, digital quadrature modulated by the quadrature modulation unit 104, and then passed through the DA conversion unit 105 as an IF band signal. Output. Thereafter, the transmission RF unit 106 converts the frequency to the RF band, and the power amplifier 107 amplifies the power. At this time, non-linear distortion occurs, but most of the distortion is canceled by the reverse characteristic distortion added in advance in the baseband processing. Thereafter, the signal is transmitted to the wireless line by the antenna 109 via the duplexer 108.

  Next, the basic operation of the receiving block will be described. It should be noted that the determination timing, the level of the received signal, the phase, and the like need to be adjusted for processing on the reception side, particularly for symbol determination. However, since these processes are not the essence of the present invention, description and explanation in FIG. 1 are omitted.

  The radio signal received by the antenna 109 is frequency-converted to the IF band in the reception RF unit 110 through the duplexer 108. The IF band signal is converted into a digital signal by the AD converter 111. Further, the digital signal is quadrature demodulated by the quadrature demodulator 112, and the reception filter 113 performs waveform shaping and removal of out-of-band components to output a baseband signal. The baseband signal output from the reception filter 113 is linearly equalized by the equalizer 118 and then input to the symbol determination unit 114.

  The result determined by the symbol determining unit 114 is output to the channel decoding unit 116 as a bit sequence in symbol units, and is a control block (corresponding to RCB in FIG. 2) and a data block (corresponding to DATA in FIG. 2). ) For each time, and outputs the result to a predetermined output destination. Among these outputs, there is a distortion amount detected by the on-coming wireless device. The distortion amount is output to the address encoding unit 101. The address encoding unit 101 selects a mapping table based on the distortion amount, and generates an address value that refers to the selected mapping table.

  Next, a mechanism for detecting overcompensation / undercompensation by the power amplifier 107 in the receiving side block, which is one of the features of the present invention, will be described. This processing is performed by the distortion detection unit 115 that detects the distortion amount and the averaging processing unit 117 that averages a plurality of distortion amounts detected in a predetermined period. The distortion detection unit 115 compares the output including the nonlinear distortion from the equalizer 118 with the coordinate value of the symbol point without distortion obtained from the determination result of the symbol determination unit 114. For example, as shown in FIG. 5, the output from the symbol determination unit 114 is represented by a dot, and the output from the equalizer 118 is a dot, which is a coordinate comparison between the two. As can be seen from FIG. 5, the output from the equalizer 118 includes noise in addition to distortion due to overcompensation / undercompensation of the power amplifier 107. The averaging processing unit 117 is for removing this noise component.

  Note that the distortion detection / averaging process does not necessarily have to be performed for all symbol points. For example, as shown in FIG. 6, it is possible to pay attention only to the outermost four points on the signal space. In the averaging process in this case, the symbol points in the first quadrant are kept as they are, and the regions in the second to fourth quadrants are rotated and moved to the first quadrant, and then averaging is performed using these four points. The distortion amount averaged in this way is output to the channel encoding unit 100, inserted at a predetermined position in the frame (the position of “detection distortion amount” in FIG. 2), and transmitted to the opposite radio device.

  The outline of the operation of each unit has been described above. A method of transmitting the detected distortion amount will be described with reference to FIG. FIG. 7 shows a state in which communication is performed between the wireless device 71 and the wireless device 72. Note that the wireless device 71 and the wireless device 72 have the same configuration as that of the transmission / reception apparatus shown in FIG.

  First, in step 1, a wireless signal is transmitted from the wireless device 71, and the wireless device 72 detects the distortion amount of the transmission wave from the received wireless signal. Next, in step 2, the wireless device 72 transmits the detected distortion amount to the wireless device 71. As shown in FIG. 2, the distortion amount information is added to the control block RCB of the transmission frame. In step 3, the wireless device 71 receives the transmission frame that has arrived from the wireless device 72, decodes the control block RCB in the received frame, and extracts the amount of distortion. In step 4, the wireless device 71 switches the mapping table used in the mapping table memory 102 based on the distortion amount extracted from the received frame.

  As described above, in this embodiment, the receiving side block detects the distortion amount by the power amplifier 107 of the transmitting side block, and feeds back the detected distortion amount to the transmitting side block. An adaptive distortion compensation can be easily performed without providing a compensation feedback system. As a result, it is possible to flexibly cope with changes in the characteristics of the power amplifier, such as changes in temperature and changes over time.

  The present invention is not limited to the above embodiment. In the above embodiment, the phase distortion generated by the power amplifier 107 has been described as an example. However, when amplitude distortion occurs or when both amplitude distortion and phase distortion occur, distortion compensation characteristics corresponding to each are similarly provided. Distortion compensation can be performed by providing a reflected mapping table.

  In the above-described embodiment, the transmission / reception apparatus having both the transmission-side block and the reception-side block has been described. However, the transmission apparatus having the transmission-side block and the reception apparatus having the reception-side block may be configured as separate apparatuses. Is possible. In addition, the configuration and operation procedure and contents of the transmission side block and the reception side block can be variously modified without departing from the scope of the present invention.

  In short, the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, you may combine suitably the component covering different embodiment.

The block block diagram which shows one Embodiment of the transmission / reception apparatus concerning this invention. The figure which shows an example of a structure of a radio | wireless frame and control information. The figure which shows an example of the constellation of 16QAM. The figure which shows the structural example of the mapping table for predistortion stored in the memory for mapping tables shown in FIG. The figure which shows the constellation of 16QAM of a received signal. The figure which shows the constellation at the time of paying attention to distortion of four points outside. The figure which shows the procedure which transmits the distortion amount detected from the received signal to the opposite radio | wireless machine.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 100 ... Channel encoding part 101 ... Address encoding part 102 ... Mapping table memory 103 ... Transmission filter part 104 ... Orthogonal modulation part 105 ... DA conversion part 106 ... Transmission RF part 107 ... Power amplifier 108 ... Duplexer 109 ... antenna 110 ... reception RF unit 111 ... AD conversion unit 112 ... orthogonal demodulation unit 113 ... reception filter unit 114 ... symbol determination unit 115 ... distortion detection unit 116 ... channel decoding unit 117 ... Averaging processing unit, 118 ... Equalizer.

Claims (5)

A symbol mapping unit that maps a transmission bit string on a complex plane and outputs a transmission baseband signal representing the mapping value, and a radio signal that generates a radio signal modulated by the transmission baseband signal output from the symbol mapping unit A transmission device comprising: a generation unit; and a power amplifier that amplifies and outputs a radio signal generated by the radio signal generation unit;
A reception baseband signal generation unit that receives a radio signal arriving from the transmission device, demodulates the radio signal to generate a reception baseband signal, performs symbol determination on the reception baseband signal, and determines a determination result. A symbol determination unit that outputs a representative bit string, a distortion amount detection unit that detects a distortion amount by the power amplifier from the received baseband signal and the bit string, and a notification unit that notifies the transmission apparatus of the detected distortion amount A receiving device comprising:
The symbol mapping unit outputs, as the transmission baseband signal, a mapping value reflecting a reverse characteristic of the distortion characteristic of the power amplifier according to the transmission bit string and the distortion amount notified from the reception apparatus. A wireless communication system.   The symbol mapping unit stores a plurality of sets of mapping values reflecting the inverse characteristic of the distortion characteristic of the power amplifier in association with the distortion amount, and corresponds to the distortion amount notified from the transmission bit string and the receiving device. 2. The wireless communication system according to claim 1, wherein the mapping value is output.   2. The wireless communication system according to claim 1, wherein the distortion amount detecting unit detects the distortion amount based on a preset symbol point among a plurality of symbol points in the symbol determination unit. A symbol mapping unit for mapping a transmission bit string on a complex plane and outputting a transmission baseband signal representing the mapping value;
A radio signal generation unit that generates a radio signal modulated by a transmission baseband signal output from the symbol mapping unit;
A power amplifier that amplifies and outputs the radio signal generated by the radio signal generation unit;
Means for receiving the amount of distortion by the power amplifier notified from the opposite receiving device,
The symbol mapping unit outputs a mapping value reflecting a reverse characteristic of a distortion characteristic of the power amplifier as the transmission baseband signal according to the transmission bit string and the distortion amount. Means for receiving a radio signal amplified by a power amplifier output from an opposing transmitter;
A reception baseband signal generation unit that generates a reception baseband signal by demodulating the received radio signal;
A symbol determination unit that performs symbol determination on the received baseband signal and outputs a bit string representing a determination result;
A distortion amount detecting means for detecting a distortion amount by the power amplifier from the received baseband signal and the bit string;
A receiving device comprising: notification means for notifying the transmitting device of the detected distortion amount.

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