JP2587432B2 - Effective area judgment signal detection circuit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION The present invention relates to an effective area determination signal detection circuit, and in particular, to a high multi-level quadrature amplitude modulation system in which a signal point arrangement on a phase plane is stepped. The present invention relates to an effective area determination signal detection circuit used in a demodulation device in a digital wireless communication system adopting the above.

(Prior Art) As is well known, in digital wireless communication, a high-valued quadrature amplitude modulation (QAM) method is adopted from the viewpoint of effective frequency utilization. This includes various types such as the 64QAM system and the 256QAM system. However, in this QAM system, as shown in FIG. 5, for example, the signal point arrangement on the phase plane is square, so that the peak power-to-average power ratio of the modulated wave increases as the number of values increases, and the transmission power increases. It becomes susceptible to non-linear distortion of an amplifier or the like.

Therefore, for example, as shown in FIG. 6, a quadrature amplitude modulation scheme (STEPPED-SQUARE) in which the signal points on the phase plane are arranged in a step-like manner to reduce the peak power.
QAM system: hereinafter, simply referred to as “SS-QAM” system) (Japanese Patent Laid-Open No. 61-77452). Fig. 6 shows 256SS-
The signal point arrangement of the QAM method is shown. The outer shape connecting the outermost signal points is a regular octagon, and the signal points near the vertices of each square of the normal QAM method are deleted.

By the way, in order to correctly demodulate a QAM modulated wave, an automatic amplitude control signal (AGC), a carrier recovery signal, a DC offset control signal, and a tap control signal of a transversal equalizer for equalizing fading distortion and the like in a propagation path. An error signal indicating the deviation of the signal point from the ideal value is required to generate the like, but only the outside of the position of the signal point having the highest signal level is used while the control loop of the demodulator is not correctly pulled in. An effective error signal is obtained by a maximum level error method (MLE). That is, FIG. 7 shows the signal point constellation of the 256QAM system similar to that of FIG. 5, but the outer part (shaded area in the figure) of the square area connecting the signal point positions of the outermost shell is defined as an effective area. In this method, only an error signal obtained when a signal is input to the controller is used for various controls as an effective signal, and the others are discarded.

In short, in the QAM method, a signal indicating that a signal has entered an effective area, that is, how to detect an effective area determination signal is a problem. However, the conventional effective area determination method in the 256SS-QAM method is as follows. It has been done. FIG. 8 shows a conventional effective area determination signal detection circuit. In FIG. 8, reference numerals 21 and 22 denote A / D converters, and reference numeral 23 denotes a signal conversion circuit.

P that are orthogonal to each other and obtained by a demodulation device (not shown)
The baseband signals of the channel and the Q channel are input to A / D converters 21 and 22 via input terminals 51 and 52, respectively.
The clock signal applied to the input terminal 53 is supplied to the A / D converters 21, 22 and the signal conversion circuit 23 as an operation clock for determining the identification timing.

A / D converters 21 and 22 convert the input baseband signal into 5
The signal is converted into a 1-bit data signal and a 1-bit error signal, and is supplied to a signal conversion circuit 23. As is apparent from FIG. 6, in the 256SS-QAM system, since the P channel and the Q channel have 18 levels, the data signal needs 5 bits.

The signal conversion circuit 23 is composed of an individual logic circuit using a plurality of logic gates or a ROM or the like, and uses the data signal of a total of 10 bits of the P channel and the Q channel to determine the position of the outermost shell signal point (the black circle in FIG. 9). 24) a to x
9 is detected, and this is indicated by a triangle (△) in FIG.
The signals are converted into signals a 'to x' of 24 signal point positions. That is, it is assumed that the signal is received equivalently in the square signal point constellation as shown in FIG.
In the same manner as in FIG. 3, it is detected that a signal has entered the effective area from the 10-bit data signal and the 2-bit error signal, and the output terminal 54 is set to “1” to output an effective area determination signal. ing.

(Problems to be Solved by the Invention) However, in the conventional effective area determination signal detection method in the SS-QAM method, once a normal
This is a method of converting to the signal point arrangement of the QAM method. This conversion is performed at a stage where the error rate is extremely large even if the control loop pull-in is uncertain or pull-in, so that correct conversion is not performed. Therefore, there is a problem that a correct valid area determination signal cannot be detected and the demodulation operation becomes extremely unstable.

The present invention has been made in view of such a conventional problem, and an object of the present invention is to perform a correct detection of an effective area determination signal in a demodulation system under the SS-QAM scheme, thereby stabilizing a demodulation operation. An object of the present invention is to provide an effective area determination signal detection circuit which enables the detection.

(Means for Solving the Problems) In order to achieve the above object, an effective area determination signal detection circuit of the present invention has the following configuration.

That is, the effective area determination signal detection circuit according to the present invention is a signal processing method for use in a demodulation device in a digital wireless communication system employing a high multi-level quadrature amplitude modulation scheme in which signal point arrangement on a phase plane is stepped. An effective area determination signal detection circuit for detecting an outer part of the position of the outermost signal point of the point arrangement as an effective area; the effective area determination signal detection circuit includes P-channels orthogonal to each other and acquired by a demodulator. And a signal addition circuit for performing an addition process between the baseband signals of the Q and Q channels; a signal subtraction circuit for performing a subtraction process between the baseband signals of the P and Q channels; and receiving the output of the signal addition circuit (P + Q A) a first signal discriminating circuit for discriminating that a signal has been detected outside the outermost signal point position of the axis and discriminating a signal point; A second signal discriminating circuit for discriminating that a signal has been detected in a portion outside the outermost signal point position of the (P-Q) axis and discriminating a signal point; each base of a P channel and a Q channel; A third and a fourth signal discriminating circuit for discriminating that a signal has been detected in a portion outside the position of the outermost signal point on the P axis or the Q axis for each of the band signals and discriminating the signal points; A logical sum circuit that performs a logical sum process between the outputs of the fourth to fourth identification circuits and outputs an effective area determination signal.

(Operation) Next, the operation of the effective area determination signal detection circuit of the present invention configured as described above will be described with reference to FIG.

FIG. 1 shows the signal point constellation of the 256SS-QAM method described above. In the present invention, the effective area determination signal is directly detected without being converted to the signal point constellation of the normal QAM method as in the related art. Things.

That is, the output of the signal addition circuit is the axis (P +
Q), and the output of the signal subtraction circuit is an orthogonal projection to the axis (PQ) of each signal point position.
Q) and the 25 signal levels on the axis (PQ) are identified in the first and second signal identification circuits to detect that a signal has been received outside the square decision area (I). it can. Further, by identifying the 18 signal levels on the axes P and Q in the third and fourth signal discriminating circuits, it is possible to detect that a signal has been received outside the square determination area (II). Therefore, a signal indicating that the signal has been received outside the position of the outermost signal point, that is, an effective area determination signal is obtained from the output of the OR circuit.

As described above, according to the effective area determination signal detection circuit of the present invention, the effective area indicating that the signal has been received in the outer part (effective area) of the outermost signal point position of the signal point constellation of the SS-QAM scheme. Since the area determination signal can be obtained directly without converting to the signal point constellation (square) of the normal QAM system as in the conventional case, the error rate is not affected even if the control loop of the demodulation device is uncertain or pulled in. Even in a very large stage, a correct effective area determination signal can be detected, and the demodulation operation can be stabilized.

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

FIG. 2 shows an effective area determination signal detection circuit according to one embodiment of the present invention. In FIG. 2, reference numeral 11 denotes a signal addition circuit;
Is a signal subtraction circuit, 13 to 16 are signal identification circuits, and 17 is a 4-input OR circuit.

The P-channel baseband signal applied to the input terminal 1 is supplied to one input of each of a signal addition circuit 11 and a signal subtraction circuit 12 and to a signal identification circuit 15. The Q channel baseband signal applied to the input terminal 2 is supplied to the other input of the signal addition circuit 11 and the other input of the signal subtraction circuit 12, and to the signal identification circuit 16. Further, the clock signal applied to the input terminal 3 is supplied to the signal identification circuits 13 to 16 as an operation clock for defining the identification timing.

The signal point arrangement of the 256SS-QAM system is as shown in FIG. 6, and the outer peripheral shape connecting the outermost signal points is a regular octagon. The present invention is intended to directly detect signal points located on each side of a regular octagon. That is, since the two axes P and Q orthogonal to each other can be defined for a pair of opposing sides, the axis (P + Q) and the axis (P-Q) that can be defined for the remaining two pairs of sides are the third.
As shown in the figure, it is arranged orthogonally at a position inclined 45 degrees from the axis P,
The four axes P, Q, (P + Q) and (P-
Q) The signal point position is identified above, so that the outer portion (effective area) of each circumference of the regular octagon can be directly determined.

The signal addition circuit 11 performs an addition process between the baseband signals of the P channel and the Q channel, and provides an output 5 to the signal identification circuit 13 as a result. The result output 5 is the axis P of each signal point position.
+ Q, which is a 25-level signal level.

The signal subtraction circuit 12 performs a subtraction process between the baseband signals of the P channel and the Q channel, and outputs the result 6 to the signal identification circuit 14. The result output 6 is the axis P of each signal point position.
This is an orthogonal projection to -Q, which is a signal level of 25 values.

As shown in FIG. 4 (a), the signal discriminating circuits 13 and 14 discriminate the signal point positions of each signal level from the eye pattern at each of the input 25-value signal levels, and If the signal is detected in the outer part of, the determination output is set to the “1” level, otherwise, it is set to the “0” level. The judgment outputs 7 and 8 are supplied to the OR circuit 17.

On the other hand, the signal discriminating circuits 15 and 16 discriminate the signal point positions of each signal level from the eye pattern at each of the 18 input signal levels, as shown in FIG.
When a signal is detected outside the position of the outermost signal point, the determination output is set to “1” level, and otherwise, the determination output is set to “0” level. The judgment outputs 9 and 10 are given to the OR circuit 17.

Thus, in the OR circuit 17, the four judgment outputs 7, 8, and
The logical sum of the same 9 and 10 is obtained, and the effective area determination signal V is sent to the output terminal 4.

The OR circuit 17 is provided in order to obtain as much effective error signal information as possible, since the probability that a signal point enters an effective area is reduced in a modulation scheme having a large number of values such as the 256SS-QAM scheme. is there. That is, the error signal information of the signal points entering the effective area by the OR circuit 17 is used for generating AGC, APC, DC offset control signal, tap control signal, etc. of P channel and Q channel.

Here, the valid area determination signal V is obtained when the received signal is outside the square area (I) or (II) shown in FIG. 1, that is, when the signal is received in the shaded area in FIG. Only at the “1” level, and the effective area detection is notified.

(Effect of the Invention) As described above, according to the effective area determination signal detection circuit of the present invention, signal reception is performed in an outer part (effective area) of the outermost signal point position of the SS-QAM signal point arrangement. Since the effective area determination signal indicating that the operation has been performed can be directly obtained without converting the signal point constellation (square) of the ordinary QAM method as in the related art, the control loop of the demodulation device is uncertain or uncertain. Even if the error rate is drawn, the correct valid area determination signal can be detected even at a stage where the error rate is extremely large, and there is an effect that the demodulation operation can be stabilized.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining the principle of detection of an effective area determination signal according to the present invention;
FIG. 2 is a block diagram showing a configuration of an effective area determination signal detection circuit according to one embodiment of the present invention, and FIG. 3 is a diagram showing P axis-Q axis and (P +
Q) Axis- (PQ) axis relationship diagram, FIG. 4 is an explanatory diagram of the operation of the signal identification circuit, FIG. 5 is a signal point arrangement diagram of the 256QAM system, and FIG. 6 is a signal point arrangement of the 256SS-QAM system. Figure 7 is 256QAM
FIG. 8 is an explanatory diagram of an effective area determination method in the system, FIG. 8 is a block diagram of a configuration of a conventional effective area determination signal detection circuit, and FIG. 9 is an operation explanatory view of a conventional effective area determination. 11 ... Signal addition circuit, 12 ... Signal subtraction circuit, 13-16 ...
Signal discriminating circuit, 17… OR circuit, 21, 22… A / D converter, 23 …… Signal converting circuit.

Claims (1)

(57) [Claims] 1. An outermost signal point of said signal point arrangement used in a demodulator in a digital radio communication system employing a high multi-level quadrature amplitude modulation system in which a signal point arrangement on a phase plane is stepped. An effective area determination signal detection circuit for detecting an outer part of the position as an effective area; the effective area determination signal detection circuit detects baseband signals of a P channel and a Q channel which are orthogonal to each other and acquired by a demodulation device. A signal addition circuit for performing an addition process between the signals; a signal subtraction circuit for performing a subtraction process between each baseband signal of the P channel and the Q channel; an outermost signal point on the (P + Q) axis receiving an output of the signal addition circuit A first signal discriminating circuit for discriminating that a signal has been detected at a position outside the position and discriminating a signal point; and receiving an output of the signal subtracting circuit, an outermost shell signal on the (PQ) axis A second signal discriminating circuit for discriminating that a signal has been detected in a portion outside the point position and discriminating a signal point; an outermost P-axis or Q-axis for each of the baseband signals of the P channel and the Q channel; A third and a fourth signal discriminating circuit for discriminating that a signal has been detected outside the shell signal point position and discriminating a signal point; and a logical sum between outputs of the first to fourth discriminating circuits. An OR circuit for performing processing and outputting an effective area determination signal; and an effective area determination signal detection circuit.