JPH06177788A - Phasing distortion compensating system - Google Patents

Abstract

PURPOSE:To reduce deterioration of phasing distortion compensation due to noise by averaging the addition of a reception pilot symbol in calculating the phasing distortion. CONSTITUTION:A 4 multi sub-carrier 16 QAM signal with a pilot symbol inserted is inputted from an input terminal 1 of a receiver and converted into a digital signal, and then stored in memories 9 and 10 by one slot and divided into four types of sub-carrier by a separation circuit 11. A phasing distortion detection circuit 12 takes out a reception pilot symbol from the sub-carrier data arrangement to combine them, and then adds the reception pilot symbol inserted at the same time by ch, dividing the addition value by 2 of the sub- carrier number to obtain the average. Then, the phasing amount is calculated based on the average value. A phasing distortion waveform estimating circuit 13 performs the interpolation of the one-system phasing distortion data inputted from the circuit 12, and outputs them.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a system for compensating for fading distortion in digital mobile communication, and more particularly to improving deterioration of compensation performance due to noise.

[0002]

2. Description of the Related Art In a digital mobile communication system, in order to improve the efficiency of modulation / demodulation in TDM (time division multiplex) transmission of digital signals, four values are output through carrier suppressed AM modulation of two carriers having a phase difference of π / 2. Simultaneous modulation and demodulation 1
Multi-subcarrier 16QA in which 6QAM (Quadrature Amplitude Modulation) is performed in multiple stages using a plurality of subcarriers
Practical application of the M method is in progress.

In such a modulation / demodulation system having a large number of multi-values, the error of the transmission signal greatly increases due to the distortion caused by fading in the transmission process. Therefore, how to accurately compensate the fading distortion on the receiving side becomes an important issue.

In order to compensate for this fading distortion, in the conventional multi-subcarrier 16QAM system, a known pilot symbol is inserted into the data to be transmitted at the transmitting side, and a pilot signal in the received data is received at the receiving side. The degree of symbol distortion is checked, and the received data distortion is compensated according to the degree.

Specifically, the fading distortion compensation is performed as follows.

First, multi-subcarrier 16QAM-
Explaining the configuration of the TDM receiver, this receiver has, as shown in FIG.
, A synthesizer 3 that generates a carrier for synchronous detection, an analog multiplier 2 that multiplies a received signal by an in-phase carrier generated by the synthesizer 3, and an analog that multiplies a received signal by an orthogonal carrier generated by the synthesizer 3. Multiplier 4, low-pass filters 5 and 6 that remove harmonic components from the outputs of multipliers 2 and 4, AD converters 7 and 8 that convert the filtered signal into a digital signal, and digitally converted Memories 9 and 10 that store data for one slot
, A subcarrier separation circuit 11 that separates the stored data into data for each subcarrier and recovers a symbol clock from the stored data, and a pilot symbol that detects distortion of the pilot symbols included in the data. The fading distortion detection circuit 12 that outputs the data of the distortion series, the fading distortion waveform estimation circuit 13 that generates the estimated distortion series of all the received symbols by interpolating the distortion series of the pilot symbols, and this fading estimated distortion A fading distortion compensating circuit 14 for compensating the fading distortion of the received symbol using the decoding and serial / parallel conversion circuit 15 for decoding the fading distortion-compensated received symbol into multi-valued digital data and performing serial / parallel conversion for output.
And a digital signal output terminal 16.

From the input terminal 1 of this receiver, 4 multi-subcarrier 16QAM signals 16QAM-modulated by 4 types of subcarriers are input.

The data carried by each subcarrier is
I- and Q-symbol data representing points on the constellation (FIG. 4) obtained by 16QAM modulation, and I-symbol data and Q-symbol data are orthogonal subcarriers whose phases are shifted by π / 2. Transmitted by. Each of 16 points on this constellation represents 4-bit transmission data, and in the example of FIG. 4, a point of I = 1 and Q = 1 is 0101 of transmission data, and I = 3. , Q = 3 indicates 0000.

The signal input to the input terminal 1 is branched into two, one of which is multiplied by the in-phase carrier generated by the synthesizer 3 and the other of which is multiplied by the quadrature carrier generated by the synthesizer 3, It is detected synchronously. The detected data has harmonics removed by filters 7 and 8 and is converted into a digital signal, and then stored in memories 9 and 10 for each slot.

The I and Q symbol data stored in the memories 9 and 10 are separated by the separation circuit 11 into data for each of four types of subcarriers. The format of the TDM frame output from the separating circuit 11 is shown in FIG. On the transmitting side, pilot symbols P for checking the magnitude of fading are inserted at intervals of 8 symbols of data symbols D for data transmission, and the pilot symbols P are separated by a separation circuit 11. It appears in the data array of each of the subcarriers.
This pilot symbol has I and Q symbols (for example, I = 3 and Q = 3) that are agreed in advance for both transmission and reception.
Is used.

[0011] By the way, in mobile communication, fading unique to mobile communication called Rayleigh fading occurs. This is a phenomenon that occurs because a space that is hard to receive radio waves and a space that is easy to receive radio waves are distributed while intersecting with each other due to reflection of radio waves by a building and moving while receiving the radio waves. This Rayleigh fading has a great influence on mobile communications, and the transmission signal is therefore subject to flat level fluctuations on the frequency axis.

When the transmission pilot symbol (3, 3) is subjected to Rayleigh fading distortion (If, Qf) on the transmission line, the size of the reception pilot symbol is expressed by the equation (1).
Can be obtained by complex multiplication of. (3 + j · 3) × (If + j · Qf) = 3 × (If−Qf) + j · 3 × (If + Qf) (1) FIG. 5 illustrates how the pilot symbols are level-varied due to fading distortion. There is. At the time of transmission, in subcarriers 1 and 4, pilot symbols of size 3 are inserted into both Ich and Qch at every 8 bits, and subcarriers 2 and 3 are also inserted.
In, in the middle of the pilot symbol insertion time in subcarriers 1 and 4, pilot symbols of size 3 are inserted in both Ich and Qch (a).

When this signal undergoes transmission path distortion (b) due to fading in the process of transmission, reception pilot
From equation (1), the symbol size is 3 × for Ich.
(If-Qf), and 3 × (If +
Qf) (c).

On the other hand, when obtaining the magnitude of fading distortion from the magnitude (Ir, Qr) of the received pilot symbol, the received pilot symbol is complexly divided by the transmitted pilot symbol as shown in equation (2). To do. (Ir + j · Qr) / (3 + j · 3) = 0.5 × (Qr + Ir) /3+j·0.5× (Qr−Ir) / 3 (2) In FIG. 6, the pilot symbol insertion positions are different. Two series of fading distortion sequences (b) in which subcarrier 1 and subcarrier 2 and subcarrier 3 and subcarrier 4 are combined and the magnitude of the waveform of fading distortion is calculated from the magnitudes of the received pilot symbols. Is shown. From the equation (2), the magnitude of fading distortion is I
In ch, 0.5 × (Qr + Ir) / 3, and Q
In ch, it is calculated as 0.5 × (Qr−Ir) / 3.

The fading distortion detection circuit 12 is a separation circuit 11
Received pilot symbols are detected from the data array for each subcarrier while synchronizing with the clock regenerated in step 1, and subcarriers 1 and 2 and subcarriers 3 and 4 are combined according to the procedure of FIG. Then, the magnitude of fading distortion is calculated from the magnitudes of the received pilot symbols, and the calculation data of the two series of fading distortion sequences is output.

The fading distortion waveform estimating circuit 13 interpolates the two series of fading distortion sequence data input from the fading distortion detecting circuit 12 to fill in the data between the respective distortion sequences and to obtain the two sequences of all received symbols. Output as fading estimation distortion.

The fading distortion compensating circuit 14 performs complex division on the received symbols of each subcarrier using the corresponding fading estimated distortion input from the fading distortion waveform estimating circuit 13 to compensate for the fading distortion of each received symbol. The distortion-compensated received symbol is decoded by the decoding and parallel / serial conversion circuit 15 from I and Q symbols into 4-bit digital data based on the constellation of FIG. 4, and then each decoded subcarrier is decoded. Data is converted into a serial signal and output from the output terminal 16.

[0018]

However, since the signal received by the multi-subcarrier 16QAM-TDM receiver is distorted by random thermal noise in the receiver, the fading distortion detection circuit 12 produces fading. It means that the fading distortion is detected by using the pilot symbol in which the distortion and the thermal noise distortion are superimposed and added. Therefore, the calculation data of the fading distortion sequence output from the fading distortion detection circuit 12, the accuracy is reduced by the amount affected by the thermal noise, which results in the deterioration of distortion compensation performance in the conventional fading distortion compensation method. Has become.

The present invention solves these conventional problems, and an object of the present invention is to provide a fading distortion compensating method in which the performance of fading distortion compensation is improved by removing the influence of thermal noise as much as possible.

[0020]

Therefore, according to the present invention, a pilot symbol is inserted into transmission data transmitted using a plurality of subcarriers, and the side receiving the pilot symbol detects the distortion based on the pilot symbol distortion. In a fading distortion compensation method that calculates the amount of fading distortion and compensates the distortion of the received data according to this amount of distortion, insert pilot symbols in the transmission data transmitted by two or more subcarriers at the same time, and receive On the side, the fading distortion amount is calculated by using the added value of the pilot symbols inserted at the same time.

[0021]

Therefore, since the distortion amount is calculated using the added value of the signal, the influence of noise on the calculation result is reduced, and the deterioration of the fading distortion compensation performance is suppressed.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The configuration of a multi-subcarrier 16QAM-TDM receiver that implements the fading distortion compensation system of the present invention is as shown in FIG.
It is no different from the conventional one (Fig. 7).

The fading distortion compensation method of the present invention is characterized in that, in the calculation of the fading distortion amount performed by the fading distortion detection circuit 12, the pilot symbols received at the same time are added and the magnitude thereof is averaged. . As a result, the fading distortion sequence calculation data output from the fading distortion detection circuit 12 corresponds to one series, and the fading estimation distortion output from the fading distortion waveform estimation circuit 13 also corresponds to one series. This point is different from the conventional configuration (FIG. 7).

When signals having the same directionality are added as in the present invention, the ratio of random noise components contained in the signals decreases. This is because the original signal component has the same directionality and therefore increases in size twice when added, but the random noise component does not have the size doubled even when added because the directionality does not match. Because. Statistically, it is known that random noise is reduced by 3 dB each time the number of sums increases.

In the fading distortion compensation method of the present invention, the time of insertion of pilot symbols to be inserted on a subcarrier at a constant interval is made to coincide on a plurality of subcarriers during transmission.

The 4-multi-subcarrier 16QAM signal in which the pilot symbols (3, 3) are inserted is input from the input terminal 1 of the receiver, synchronously detected, harmonics are removed, and converted into a digital signal. After that, it is stored in the memories 9 and 10 one slot at a time, and then by the separation circuit 11,
It is separated into data for each of four types of subcarriers.

The received pilot symbols contained in the separated data for each subcarrier are shown in FIG. 2 (a). The pilot symbols of subcarrier 1 and subcarrier 4 and the pilot symbols of subcarrier 2 and subcarrier 3 are inserted at the same time on the transmission side, and the pilot symbols of subcarriers 2 and 3 are It is inserted in the middle of the time of inserting pilot symbols into subcarriers 1 and 4.

In the fading distortion detection circuit 12, the separation circuit
While synchronizing with the clock regenerated in 11, the received pilot symbols are taken out from the data array of all subcarriers and combined into one, and the received pilot symbols inserted at the same time are Ich,
Addition is performed for each Qch, and the added value is divided by 2 which is the number of subcarriers to obtain an average (FIG. 2B). Then, based on this average value (Irc, Qrc), the fading distortion amount is calculated by the equation (3). (Irc + j · Qrc) / (3 + j · 3) = 0.5 × (Qrc + Irc) /3+j·0.5× (Qrc−Irc) / 3 (3) From this equation (3), the fading distortion amount of Ich is 0. .5
X (Qrc + Irc) / 3, and the fading distortion amount of Qch is calculated as 0.5 * (Qrc-Irc) / 3.

The fading distortion detection circuit 12 calculates data of one series of fading distortion sequences thus obtained (see FIG. 2).
(c)) is output.

The fading distortion waveform estimating circuit 13 interpolates the one series of fading distortion sequence data input from the fading distortion detecting circuit 12 and outputs it as the fading estimated distortion of all received symbols.

The fading distortion compensating circuit 14 compensates the fading distortion of the received symbol by complexly dividing the received symbol by the fading estimated distortion input from the fading distortion waveform estimating circuit 13. The distortion-compensated received symbol is decoded and parallel / serial conversion circuit 15,
It is decoded into 4-bit digital data, converted into a serial signal, and output from the output terminal 16.

As described above, in the fading distortion compensation method of the present invention, the influence of noise components is suppressed by adding and averaging the received pilot symbols when the fading distortion is calculated. Therefore, deterioration of fading distortion compensation performance due to thermal noise is reduced.

If the pilot symbols inserted into subcarriers 1 and 4 or subcarriers 2 and 3 at the same time are of different types, weighting is performed when adding the received pilot symbols, The same process can be performed by complexly dividing the addition result of the reception pilot symbols by the addition result of the transmission pilot symbols.

[0034]

As is apparent from the above description of the embodiments, the fading distortion compensating system of the present invention can suppress the deterioration of fading distortion compensating performance due to noise.

[Brief description of drawings]

FIG. 1 is a block diagram showing an example of a receiving apparatus that implements a fading distortion compensation method of the present invention,

FIG. 2 is a diagram showing a received symbol (a) in the system of the present invention;
Explanatory diagram showing the relationship between the symbol addition value (b) and the distortion estimation waveform (c),

FIG. 3 is a frame format of TDM transmission using multiple subcarriers,

FIG. 4 is a constellation diagram of 16QAM symbols,

FIG. 5 is an explanatory diagram showing the relationship among transmission data (a), transmission distortion (b), and received symbol (c) in digital transmission,

FIG. 6 is an explanatory diagram showing a relationship between a received symbol (a) and a distortion estimation waveform (b) under a conventional fading distortion compensation method,

FIG. 7 is a block diagram showing a configuration of a receiving device used for implementing a conventional fading distortion compensation method.

[Explanation of symbols] 1 input terminal 2, 4 multiplier 3 synthesizer 5, 6 low-pass filter 7, 8 AD converter 9, 10 memory 11 subcarrier separation circuit 12 fading distortion detection circuit 13 fading distortion waveform estimation circuit 14 Fading distortion compensation circuit 15 Decoding and parallel / serial conversion circuit 16 Output terminal

Claims (1)

[Claims] 1. A pilot symbol is inserted into transmission data to be transmitted using a plurality of subcarriers, and a fading distortion amount is calculated on the side of receiving the pilot symbol based on the distortion of the pilot symbol. In a fading distortion compensating method for compensating distortion of received data according to amount, pilot symbols are inserted at the same time in transmission data transmitted by two or more subcarriers, and at the receiving side, at the same time. A fading distortion compensation method, characterized in that the fading distortion amount is calculated using the added value of the pilot symbols.