JP2002033684A - Demodulator for wireless communication wave - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a demodulator for a wireless communication for a receiver that can enhance received quality without increasing the circuit scale. SOLUTION: The demodulator is characterized in the provision of a configuration where the energy of delay waves is used for demodulation by synthesizing signal components of the delay waves with weights as to the delay waves whose delay time is d-symbols or below and the delay waves whose delay time is d-symbols or more are cancelled through discrimination feedback.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital radio communication wave demodulator using a decision feedback equalizer.

[0002]

2. Description of the Related Art In recent years, a demand for wireless transmission of multimedia information has been increasing. Along with this, the speed of wireless data transmission has been increasing. For example, in a wireless LAN, 11 Mbps transmission has already been put to practical use. In wireless transmission, due to frequency selective fading of the transmission path,
Intersymbol interference occurs, which causes waveform distortion in the received signal and deteriorates transmission quality. In particular, as the transmission speed increases, the waveform distortion due to intersymbol interference increases even if the delay spread due to multipath is small.

[0003]

One method of compensating for intersymbol interference is waveform equalization using a decision feedback equalizer. However, in this method, a delayed wave of the received signal is canceled as an interference wave, so that only the energy of the first arriving wave can be used for demodulation of the signal, and the delay spread is large. Performance had deteriorated.

In a receiver using a decision feedback equalizer, a delay wave is conventionally canceled as an interference wave and is not used for demodulation. Therefore, in an environment where delay spread is large, signal energy used for demodulation is large. Has become smaller,
The reception quality has deteriorated.

An object of the present invention is to provide a radio communication wave demodulation device capable of improving the reception quality without increasing the circuit scale in a receiver in order to solve the above-mentioned drawbacks of the prior art. It is.

[0006]

In order to solve this problem, a radio communication wave demodulator according to the present invention weights and combines signal components of each delayed wave with respect to a delayed wave having a delay time of d symbols or less. Accordingly, the delay wave energy is also used for demodulation, and a delayed wave having a delay time d symbol or more is canceled by decision feedback. More specifically, the wireless communication wave demodulation apparatus according to the present invention includes a transmission line characteristic extracting unit for extracting characteristics of a wireless transmission line, and a symbol from the past d + 1 symbol (d ≧ 1) to L (d + 1 ≦ L) symbol. , Using the impulse response of the transmission path extracted by the transmission path characteristic extracting means,
A first waveform equalizer for performing waveform equalization on an interference wave caused by an L symbol from a symbol, and an equalization signal output from the first waveform equalizer for a signal from a past d symbol to a past one symbol. For each combination of symbols, a second waveform equalizer that performs waveform equalization on the interference wave caused by the past d symbols, and a vector error between the output of the second waveform equalizer and the original signal point. Vector error calculating means for calculating, vector error synthesizing means for weighting the output of the vector error calculating means for the past m symbols with the value of the impulse response, and synthesizing, and vector error output from the vector error adding means And a minimum value detecting means for detecting a minimum value from the combined values.
The minimum value detecting means detects a combination that gives the minimum value, and the symbol at the time of the past d symbols at this time is configured as decoded data at the time of the past d symbols.

[0007]

FIG. 1 is a block diagram of a demodulator according to an embodiment of the present invention. In this embodiment, it is assumed that the received signal is QPSK modulated. In FIG.
The received signal received by the antenna 5 is converted by the down-conversion unit 1 into a received complex baseband signal. The received complex baseband signal is subjected to A / D conversion by the A / D converter 2.
The data is converted and input to the transmission path characteristic estimator 3 and the data equalizer 4. The transmission path characteristic estimating unit 3 constituting the "transmission path characteristic extraction means" estimates the impulse response of the wireless transmission path from the received complex baseband signal. In packet transmission, estimation of an impulse response is normally performed by an RLS (Recursive Least Square: recursive least squares) algorithm or the like using a known repetition pattern added in advance to the head of the packet on the transmission side. In high-speed transmission of 10 Mbps or more, the packet length is shorter than the fading period, so that the impulse response may be regarded as stationary within one packet. For this reason, in the data part, the transmission path characteristic estimating unit 3 holds the impulse response estimated at the packet head part. The data equalizer 4 is a block according to the present invention, and uses the impulse response of the transmission path estimated by the transmission path characteristic estimating unit 3 to demodulate data in the equalizer 4 by a method described later.

FIG. 2 is a block diagram of the equalizer 4 in FIG.
It is. In this embodiment, d =
It is set to 1. Let the received complex baseband signal be r (t),
Includes all filters for wireless transmission lines and transceivers
Let h (t) be the impulse response of the entire transmitting and receiving system,
Data determination timing t = nT (T is a symbol period, n is
The sample values r (nT) and h (nT) in
Each r_nAnd h _nAnd In FIG. 2, r_nYou
And h_nAre data etc. as 201 and 202 respectively
Input to the converter 4. Here, the transmission data signal is a
_nThen, equation (1) holds.

(Equation 1) Here, n _n is the noise component. Also, it is assumed that the delay time in the wireless transmission path is finite. That is, h _n =
0 (n <0, n> L).

In FIG. 2, a received complex baseband signal r _n is input to a complex multiplier 11 and multiplied by h ₀ ^*, thereby performing pilot synchronous detection. The signal subjected to the packet synchronous detection is expressed by equation (2).

(Equation 2) The pilot synchronously detected signal is applied to the subtractor 12. Delay wave replica creation circuit 10 in subtractor 12
The decision feedback equalization is performed on the delayed wave delayed by two or more symbols by subtracting the delayed wave replica delayed by two or more symbols created by the above. The delayed wave replica creation circuit 10, the complex multiplier 11, and the subtractor 12 constitute "first waveform equalizing means". The decision feedback equalization signal EQ _n is expressed by the following equation (3).

(Equation 3) Here, a _ni hat is the determination data corresponding to a _ni . The decision feedback equalization signal EQ _n is branched into four and input to the subtractors 20 to 23, respectively. The subtracter 20-23 constitutes "a second waveform equalizing means", the signal vector corresponding to the QPSK data of 4 kinds of one-symbol delay wave is subtracted from the decision feedback equalization signal EQ _n. Subtractor 20 ~
The output signal u _n of _{^{23 (k) = (x n}} (k), y n (k)) (k
= 0 to 3) is expressed by equation (4).

(Equation 4)

[0010]

[Outside 1] Is equal to

In this embodiment, QPSK is used as the modulation method, and d = 1 is set for the past symbol d. Therefore, four subtractors 20 to 23 are required. Generally, when a p-value modulation method is used,

[Outside 2] In, the total number of combinations for all of k _m,
That is, p ^d subtracters are required.

Now, it is assumed that the decision data a _ni hat (i = 2 to L) for the delayed wave component of two or more symbols is correct. At this time, u _n ^(k) is expressed by equation (5).

(Equation 5) Here, the transmission data of the one-symbol delayed wave is represented by a _n-1 ^(k) ,
Preceding wave vector error BM0 (k, m) when the transmission data has been assumed that a _n ^(m) of the seek. BM0 (k, m) is expressed by equation (6).

(Equation 6) In equation (6), there are four cases for k and m, respectively. Therefore, it is necessary to perform 16 calculations to find BM0 (k, m) for all cases.

However, as described later, BM0 (k,
With respect to m), it is only necessary to find k that gives the minimum value.
In this case, only four types of calculations need to be performed. This will be described below with reference to FIG. Preceding wave u _n a ^(k) u _n ^{(k, m)} when the transmission data has been assumed that a _n ^(m) with when, u _n ^{(k, m)} is expressed by equation (7).

(Equation 7) When considering securing the ^{_{k, u n (k, m}} ) and the signal point a _n
^(m) h ₀ ^m is defined as m ₀ , which minimizes the vector error BM ₀ (k, m) from h ₀ ^* . That is, the vector error B when the transmission data of the one-symbol delayed wave is a _n-1 ^(k)
M0 (k, m) minimum value BM0 (k, m ₀₎ of the.

FIG. 3 shows that a vector (vector indicated by a broken line in FIG. 3) and a signal point a obtained by performing an operation of replacing the I component and the Q component with their absolute values on u _n ^{(k, m0)} are obtained.
_n ⁽⁰⁾ the distance between the h ₀ h ₀ ^* is found to be BM0 (k, m _0).

In FIG. 2, in the absolute value calculators 30 to 33, operations for replacing the I and Q components with their absolute values are performed on u _n ^(k) , and further, subtracters 40 to 43 and an absolute value calculator Signal points a _n ⁽⁰⁾ h _{0 at} 50 to 53
BM0 by determining the distance between the ^{_{h 0 * (k, m 0}} )
Have gained. That is, the absolute value calculation units 30 to 33, the subtractors 40 to 43, and the absolute value calculation units 50 to 53 constitute "vector error calculation means" at time n. BM0
(K, m ₀ ) is multiplied by | h ₁ | by the multipliers 60 to 63.

BMs from error calculators 80 to 83 to be described later
1 (k) is | h in multipliers 70 to 73₀| Multiplied
Then, the outputs of the adders 60 to 63 are output by the adders 90 to 93.
| H ₁│ ・ BM0 (k, m₀) And finally
PM (k, m) expressed by equation (8)₀) Is obtained. Multiplier 6
0-63, multipliers 70-73 and adders 90-93
It constitutes "vector error combining means".

(Equation 8) In equation (8), k that minimizes PM (k, m ₀ )
When (k = 0 to 3) is k _0, and a _n-1 ^(k0) of the preceding symbol of the decoded data. The minimum value detection unit 101 constituting the “minimum value detection means” obtains k that minimizes PM (k, m ₀ ). If this value is k ₀ , the decoding unit 1
02, a _n-1 ^(k0) is ^converted to the decision data 20 of the one symbol delayed wave.
3 and decrypted.

[0017] In selector 100, four u _n ^(k)
U _n ^(k0) is selected from. In addition, the error calculator 8 constituting the “vector error calculator” at time n−1
In 0-83, vector error BM1 of four signal points with u _n ^{(k0) (k)} is calculated.

The decoding method by evaluating the minimum value of the equation (8) can be described as follows. That is, | h ₀ | and | h ₁ |
Since | h ₀ | is larger than | h ₁ | because the magnitude of the symbol delayed wave is represented, the energy of the transmission data one symbol before is equal to the current energy because the magnitude of the delayed wave is smaller than the preceding wave. It is more included in the received signal one symbol before than the received signal. Conversely, when | h ₀ | is smaller than | h ₁ |, since the magnitude of the delayed wave is larger than that of the preceding wave, the energy of the transmission data one symbol before is larger than that of the current reception signal. More included. Therefore, all combinations (16 patterns) are assumed for the current and one symbol previous transmission data, and the current vector error for each combination is |
h ₁ |, and the vector error one symbol before is weighted by | h ₀ |. This allows
It can be used for demodulation without discarding the energy of the preceding wave and the one-symbol delayed wave.

FIG. 4 shows a result obtained by computer simulation of a packet error rate (PER) when the delay dispersion is changed. The transmission speed was 22 Mbps (QPSK) and 11 Mbps (BPSK). From FIG. 4, even when only two waves of the preceding wave and the one-symbol delayed wave are combined,
It can be seen that there is a PER improvement effect compared to the case where demodulation is performed only by decision feedback equalization.

[0020]

As described above, in the present invention, in a radio communication wave receiver, for a delayed wave having a delay time of d symbols or less, the preceding wave and the signal components of each delayed wave are weighted and combined. As a result, the energy of the delayed wave is also used for demodulation, and the path having a delay time longer than that is canceled by decision feedback, so that the reception quality can be improved without increasing the circuit scale.

[Brief description of the drawings]

FIG. 1 is a block diagram of a demodulation device according to one embodiment of the present invention.

FIG. 2 is a circuit diagram showing a configuration example of an equalizer used in the embodiment of FIG.

FIG. 3 is a vector diagram for explaining the operation of the present invention.

FIG. 4 is a characteristic diagram showing a comparison between demodulation in a conventional decision feedback equalizer and demodulation in the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Down-conversion part 2 A / D converter 3 Transmission-path characteristic estimation part 4 Data equalizer 10 Delay-wave replica creation circuit 11 Complex multiplier 12 Subtractor 20, 21, 22, 23 Subtractor 30, 31, 32, 33 Absolute value calculators 40, 41, 42, 43 Adders 50, 51, 52, 53 Absolute value calculators 60, 61, 62, 63 Multipliers 70, 71, 72, 73 Multipliers 80, 81, 82, 83 Error Calculation unit 90, 91, 92, 93 adder 100 selection unit 101 minimum value detection unit 102 decoding unit

Claims (1)

[Claims] 1. A transmission line characteristic extracting unit for extracting a characteristic of a wireless transmission line from a received wireless communication wave for demodulation of a wireless communication wave, and a past d + 1 symbol (d ≧ 1) using decoded data. And a delay wave replica generating circuit for generating a replica of a symbol determined from L to d (d + 1 ≦ L) symbols, and using the impulse response of the transmission path extracted by the transmission path characteristic extracting means. Past d from
A first waveform equalizer that performs waveform equalization on an interference wave from +1 symbol to L symbol, and an equalization signal output from the first waveform equalizer, from past d symbols to past one symbol. A second waveform equalizing means for performing waveform equalization on the interference wave caused by the past d symbols for all combinations of the symbols, and a vector error between the output of the second waveform equalizing means and the original signal point. , A vector error combining means for weighting the output of the vector error calculating means for the past d symbols with the value of the impulse response, and combining the vectors, and a vector output from the vector error combining means. Minimum value detection means for detecting the minimum value from the error composite value; and minimum value detection means of all combinations between the past d symbols. Detecting a combination that gives the Oite minimum, the symbol time in the past d symbol at this time, and a decoding unit to the decoded data point in the past d symbols, the wireless communication wave demodulator.