KR20020045309A - Complex adaptive channel equalizer for digital VSB receiver - Google Patents

Abstract

PURPOSE: A device for equalizing a complex adaptive channel of a VSB(Vestigial Sideband) receiver is provided to output an I channel signal and a Q channel signal as complex signals, and to update coefficients of each signal for minimizing differences between a transmitted symbol value and an output value of an adaptive channel equalizer, thereby improving a capacity of a digital VSB receiving system. CONSTITUTION: The first multiplier(110) multiplies a received signal by the first local carrier signal to demodulate the multiplied signal to an I channel signal. The first LPF(Low Pass Filter)(120) removes a high frequency component from the I channel signal. The first A/D converter(130) performs a discrete cosine transform process for the I channel signal. The second multiplier(140) multiplies a received signal by the second local carrier signal to demodulate the multiplied signal to a Q channel signal. The second LPF(150) removes a high frequency component from the Q channel signal. The second A/D converter(160) performs a discrete cosine transform process for the Q channel signal. A complex adaptive channel equalizer(170) equalizes the I channel signal and the Q channel signal as complex signals having a real number and an imaginary number. An adder(180) adds an output of the complex adaptive channel equalizer to a discrete symbol, and outputs the added symbol to the complex adaptive channel equalizer.

Description

Complex adaptive channel equalizer for PSS receiver

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a complex adaptive channel equalizer using not only I-channel signals but also Q-channel signals in order to improve the performance of digital VSB receiving systems, particularly in highly variable channels.

In the United States, the 8VSB transmission system was adopted as a standard for terrestrial digital broadcasting in 1995, and has been broadcasting since the second half of 1998. In Korea, the terrestrial digital VSB broadcasting based on the American method is being tested.

Amplitude modulation with a single carrier using a baseband signal yields an output signal with the same information in the upper and lower bands around the carrier in the frequency spectrum. It is undesirable to transmit this output signal in the transmission channel in terms of frequency band utilization efficiency. Therefore, a modulation scheme for transmitting only one sideband of an upper sideband or a lower sideband is required. The method is a single sideband (SSB) or vertical sideband (VSB) modulation. These two methods are very similar, but the VSB method differs greatly in transmitting additional parts of the remaining sidebands so that the demodulator can easily demodulate.

An apparatus for generating a digital VSB signal for terrestrial digital broadcasting is shown in FIG.

Referring to FIG. 1, the VSB baseband input signal [x (t)] is converted into a carrier signal [ ] A first multiplier 10 for modulating with Hilbert, a Hilbert transformer 20 for Hilbert transforming the VSB baseband input signal [x (t)], and a Hilbert transformed signal with a carrier signal [ A second multiplier 20 modulated by] and an adder 40 which adds and outputs a signal modulated by the first multiplier 10 and a signal modulated by the second multiplier 30.

The complex response channel equalizer of the conventional digital VSB receiver configured as described above will be described with reference to the accompanying drawings.

First, the VSB baseband input signal [x (t)] is input to the first multiplier 10 on an I channel, and the first multiplier 10 carries a carrier signal [ ] Modulates the input signal and outputs it to the adder 40.

The VSB baseband input signal [x (t)] is Hilbert transformed by the Hilbert converter 20 to obtain a signal of the Q channel [x ^ h (t)], and the Q channel signal is a second signal. In the multiplier 30 Is modulated into] and input to the adder 40.

The adder 40 is a carrier [ , The two channel signals I and Q modulated by] are added and output. The output signal v (t) of the adder 40 is expressed by the following equation.

Here, as shown in (a) and (b) of FIG. 2, the modulated I and Q channel signals are related to each other in the frequency spectrum. Except for a part of the center, the lower band wave has the same I and Q channel signal. The upper wave has the same size and opposite sign.

Therefore, when the I, Q channel components are added to each other, only a part of the lower wave and the upper wave remain as shown in FIG. That is, the bandwidth of the signal is cut in half.

That is, when the VSB baseband input signal x (t) is the Fourier transform as X (w), the relationship between the frequency spectrum of the VSB signal is shown in FIG. FIG. 2C has a frequency spectrum obtained by adding waveforms of I and Q channel signals a and b.

In Equation 1, a modulated signal may be demodulated to a baseband at a receiver. ], The demodulated signal r (t) is given by Equation 2.

r (t) = x (t) + hfc

In Equation 2, hfc is a high frequency component and is removed by passing a low pass filter. Therefore, if the high frequency component hfc is removed, only the baseband signal [x (t)] remains. However, if there is a ghost in the channel of the radio wave reflection between the transmitter and the receiver by the mountain or the tall building, the modulated signal of Equation 1 can be rewritten as Equation 3.

In Equation 3, g is the magnitude of the gosk, τ is the delay time of the ghost, and θ is the phase of the ghost.

When demodulating the baseband in Equation 3, the demodulated signal is r (t) as Equation 4.

Accordingly, if the ghost phase θ is not zero, the demodulated signal has a Hilbert transformed component [x ^ h (t−τ)] of the signal [x (t−τ)].

(A) and (b) of FIG. 3 are channel impulse responses when the ghost phase θ is 0 and-pi / 2, respectively, where a near ghost channel having a ghost delay time? In the case where the ghost is large in size, the attenuation of the main signal is increased by x ^ h (t-τ), which may cause the ghost signal to become a main signal (FIG. 3C).

The impulse response of the ghosted channel on the complex plane for each of these Figs. 3 (a) (b) (c) is shown in Figs. 4 (a) (b) (c), respectively.

As described above, in the digital VSB system, the channel change due to the ghost phase is very large, and thus the adaptive channel equalizer may not sufficiently follow the channel change. Therefore, an effective adaptive channel equalizer is needed to solve this problem.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems. In order to improve the performance of the digital VSB receiving system in a channel that is highly variable in the digital VSB receiving system, a complex number using not only an I channel signal but also a Q channel signal is used. It is an object of the present invention to provide a complex adaptive channel equalizer of a VSB receiver which outputs a signal and updates the coefficient of each signal in a direction that minimizes the difference between the transmitted symbol value and the output value of the adaptive channel equalizer. .

1 is a block diagram showing a VSB signal generator in a conventional digital VSB system.

2A to 2C are frequency spectra of conventional VSB signals.

Figure 3 (a ~ c) is a graph of the impulse response of the ghosted channel in the conventional digital VSB system.

Figure 4 (a ~ c) is a graph of the impulse response of the channel with the ghost on the conventional complex number plane.

5 is a block diagram showing a complex adaptive channel equalizer of a digital VSB receiver according to the present invention;

Figure 6 (a) is a detailed block diagram of a complex adaptive channel equalizer during amplitude modulation.

(b) is a detailed block diagram of a complex adaptive channel equalizer in residual sideband modulation.

<Explanation of symbols for the main parts of the drawings>

10,30,110,140 ... Multiplier 20 ... Hilbert Converter

40,180,175,176,170c ... adder170 ... complex adaptive channel equalizer

170 ~ 174,170a, 170b ... counter

In order to achieve the above object, the complex adaptive channel equalizer of the VSB receiver according to the present invention,

A multiplier for multiplying the received signal by the first and second local carrier signals and demodulating the I and Q channel signals, respectively;

A low pass filter for removing high frequency components of the demodulated I, Q channel signals;

A complex adaptive channel equalizer which equalizes the I-channel signal and the Q-channel signal, which are the signals from which the high frequency component is removed, with a complex signal having a real side and an imaginary side, respectively, in response to a channel response;

And an adder for outputting the complex adaptive channel equalizer to the complex adaptive channel equalizer by adding discrete symbols to the outputs of the plurality of adaptive channel equalizers so that the difference between the input signals is minimized.

Hereinafter, with reference to the accompanying drawings as follows.

5 is a block diagram illustrating a complex adaptive channel equalizer of a digital VSB receiver according to the present invention, and FIG. 6 (a) (b) is a detailed block diagram of a complex adaptive channel equalizer in the case of a QAM and VSB receiver.

Referring to FIG. 5, the first local carrier signal [ ] A multiplying the I channel signal [r _I (t)] The first multiplier 110, a first low-pass filter for removing high-frequency components of the demodulated I-channel signal [r _I (t)] for demodulating a (LPF 120, a first analog-to-digital converter (A / D) 130 for converting the I-channel signal from which the high frequency component is removed into a discrete signal, and a second to the received signal signal v (t). Local carrier signal [ ] Q channel signal [r _Q (t)] The second multiplier 140, a second low-pass filter (150 to eliminate high frequency components of the demodulated Q-channel signal [r _Q (t)] for demodulating by multiplying the ), A second analog-to-digital converter 160 for converting the Q-channel signal from which the high frequency component has been removed to a discrete signal, and the I-channel signal and the Q-channel signal converted to the discrete signal are respectively real and imaginary. An output of the complex adaptive channel equalizer 170 which equalizes the channel response with a complex signal, and the output of the multiple adaptive channel equalizer 170 such that the output of the complex adaptive channel equalizer 170 is minimal from an input signal And an adder 180 that adds the discrete symbols d _I (n) and outputs the complex adaptive channel equalizer 170.

In addition, when the complex adaptive channel equalizer 170 is a quadrature amplitude modulation (QAM) method, referring to (a) of FIG. And a second adder 175 for adding the signals counted by the counters 171 and 173 to output complex signals of the I channel, and adding the signals counted by the counters 172 and 174 to output the complex signals of the Q channel. It consists of a third adder 176.

In the case of the VSB method, referring to FIG. 6B, the counters 170a and 170b that receive and count the I-channel signals and the Q-channel signals, respectively, are counted by the counters 170a and 170b. And a fourth adder 170c for adding the real signal and the Q channel signal to the imaginary side to output a complex I-channel signal.

The adaptive channel equalizer of the VSB receiver according to the present invention configured as described above will be described with reference to the accompanying drawings.

Referring to FIG. 5, a signal v (t) such as Equation 1 received from a transmitter to a receiver is input to the first and second multipliers 110 and 140. The first multiplier 110 adds a first local carrier signal [ Multiplied by] to demodulate the I-channel signal [r_I (t)], and the second multiplier 140 adds the received local signal to the second local carrier signal [ Multiply by] to demodulate the Q-channel signal [r_Q (t)].

When the output I-channel signal r_I (t) of the first multiplier 110 passes through the first low pass filter 120, an I-channel signal [x (t)] from which high-frequency components are removed is obtained. The channel signal is converted into a discrete signal r_I (n) by the first analog-to-digital converter 130 and input to the complex adaptive channel equalizer 170.

When the output Q channel signal r_Q (t) of the second multiplier 140 passes through the second low pass filter 150, the Q channel signal [x ^ h (t)] from which the high frequency component is removed is obtained. The Q channel signal is converted into a discrete signal r_Q (n) by the first analog-to-digital converter 160 and output.

Here, if there is a ghost having a magnitude g, a delay τ, and a phase θ in the channel, the demodulated I-channel signal r_I (t) can be written as Equation 5 below, and the demodulated Q-channel signal r_Q (t) Can be written as in Equation 6.

Therefore, when the I-channel signal and the Q-channel signal are interpreted as complex signals having the real side and the imaginary side, respectively, the demodulated signal r (t) can be written as in Equation (7).

r (t) = r_I (t) + jr_Q (t)

In addition, a ghost having a magnitude g, a delay τ, and a phase θ can be written as Equation 8.

g e ^ jθ [x (t-τ) + jx ^ h (x-τ)]

4 is a channel impulse response on the complex plane when the ghost phase θ is 0, -π / 2, and when there is a near ghost, and complex adaptation is performed to remove ghosts present on the complex plane. Channel equalizer 170 must be defined on the complex plane. The coefficient of the complex adaptive channel equalizer 170 defined on the complex plane can be written as Equation 9 on the complex plane.

c ^ j (n) = c_I ^ j (n) + jc_Q ^ j (n), [j = -n, ...., 0, ...., n]

Since the value r (n) obtained by converting the input signal r (t) of the complex adaptive channel equalizer 170 into a discrete signal in the analog / digital converter 130 or 160 can be written as in Equation 10, complex adaptive The output y (n) of the channel equalizer 170 can be written as Equation (11).

r (n) = r_I (n) + jr_Q (n)

Since Equation 11 requires I channel output y (n), the output of complex adaptive channel equalizer 170 can be rewritten as Equation 12.

That is, in the case of VSB, unlike the case of Quadrature Amplitude Modulation (QAM), although it is an adaptive channel equalizer defined on a complex plane, the output y_Q (n) of the channel Q is not necessary. Therefore, there is an advantage that the complexity is 1/2 compared to the QAM as shown in FIG.

To this end, when the complex adaptive channel equalizer 170 is a QAM receiver, referring to FIG. 6A, the counters 171 and 173 receive and count I channel signals r_I (t). The counters 172 and 174 receive the Q channel signals r_Q (t) and count them.

The second adder 175 receives the signal counted by the counter 171 as a positive signal and adds the signal counted by the counter 172 as a negative signal and adds the negative signal as an I-channel signal [y_I (n)]. The third adder 176 adds the signal counted by the counters 173 and 174 to output the Q channel signal y_Q (n).

In contrast, the complex adaptive channel equalizer 170 of the VSB receiver of the present invention, as shown in (b) of FIG. 6, the counter 170a receives an I-channel signal and counts the counter 170b. After counting the Q-channel signals, the adder 170c adds the counted I-channel signals to the positive real side and the counted Q-channel signals to a complex signal making the negative imaginary side the I-channel. Output the signal [y_I (n)]. This is about half the complexity of the VSB method compared to the QAM method.

Here, the coefficient of the complex adaptive channel equalizer 170 is updated in a direction to minimize Mean-Squared Error (MSE) as shown in Equation (13).

remind Is an ensemble average, and d _I (n) is a discrete symbol value transmitted from a transmitter, and a signal [x (t)] is received by the first adder 180 and added to the discrete symbol d _I (n) for channel transmission. Suitably converted to continuous values and input to the complex adaptive channel equalizer 170 as an error value [e_I (n)]. That is, the coefficients of the complex adaptive channel equalizer 180 are updated to minimize the difference between the transmitted symbol values and the output values of the adaptive channel equalizer.

As shown in Equation 13, the update of the coefficient proceeds irrespective of the output y _Q (n) of the channel Q.

In order to apply the Least Mean-Square (LMS) algorithm to Equation 13, Equation 13 is partially divided with respect to c _I (n) and c _Q (n), as shown in Equation 14.

The coefficient update equation using this is as shown in equation (15).

In Equation 15, μ is a step size.

In Equation 15, the necessary value for the coefficient update of the complex adaptive channel equalizer is necessary to obtain the error value e _I (n) of the I channel, which is d _I (n) at the receiver. If it is known in advance, the value may be used as it is. Otherwise, various blind equalization methods used in the real adaptive channel equalizer may be applied as it is.

As described above, the present invention has the effect of improving the performance of the reception system in a channel that is more variable than the conventional real adaptive channel equalizer by applying a complex adaptive channel equalizer to the digital VSB receiving system.

Claims (1)

A multiplier for multiplying the received signal by the first and second local carrier signals and demodulating the I and Q channel signals, respectively; A low pass filter for removing high frequency components of the demodulated I, Q channel signals; A complex adaptive channel equalizer which equalizes the I-channel signal and the Q-channel signal, which are the signals from which the high frequency signal has been removed, with a complex signal having a real side and an imaginary side, respectively; And an adder for outputting the complex adaptive channel equalizer to the complex adaptive channel equalizer by adding discrete symbols to the output of the plurality of adaptive channel equalizers so that the difference between the input signal and the input signal is minimized. Complex Adaptive Channel Equalizer of Receiver.