KR20000007189A - Coherent data demodulator and method of code division multiple access communication system - Google Patents

Abstract

PURPOSE: A data demodulator and a method are provided to perform a coherent data demodulation by compensating a change of a phase generated during passing a channel. CONSTITUTION: The data demodulator comprises: a demultiplexer to separate each to a pilot symbol and a data symbol by receiving a channel formed by a data symbol section; a pilot symbol channel measuring device to output a cosine theta and a sin theta to show the phase theta about a transmitting standard signal by measuring the channel of the pilot symbol; a data symbol channel measuring device to output a D1 cosine pi and a D1 sin pi.

Description

Coherent Data Demodulation Apparatus and Method in Code Division Multiple Access Communication System

The present invention relates to a code division multiple access (CDMA) system, and more particularly, to a data demodulation device for performing coherent data demodulation by correcting a phase change occurring over a channel. It is about a method.

In general, a communication system should compensate for various interferences and distortions experienced by a transmission signal through a channel so that the reception end can receive the signal from the transmitter without error. In particular, in the case of a wireless communication system using the CDMA scheme, since multiple subscribers simultaneously use a common frequency band, an interference signal experienced through a channel has a large influence on the overall system performance. Since the performance of the system is further degraded by fading due to multipath, which is one of them, the CDMA communication system adopts many methods to maximize the performance by minimizing such distortion and interference.

One of them has a pilot channel with no data loaded on the transmission channel, so that the coherent data demodulation is possible by measuring and correcting the phase change of the transmission signal generated through the channel at the receiving end. Way. However, this method has a disadvantage in that the number of subscribers can be reduced by that in the CDMA communication system whose performance is limited by the interference signal because the interference signal is increased by the pilot channel.

As an alternative, a pilot symbol scheme has been proposed. The pilot symbol method is a time division of a pilot channel and transmits a pilot symbol only for a predetermined period, and the other part transmits other data. Therefore, the amount of interference signal by the pilot component can be reduced by the amount of data that can be carried in the pilot channel, which is very efficient. However, this pilot symbol method cannot be adapted to rapid channel changes because the phase component of the channel measured in one pilot symbol interval is used equally in the multiple data symbol intervals until the next pilot symbol interval. There is a problem that many exist to bring down the performance.

The present invention is to provide an improved pilot symbol data demodulation method to solve such a problem, to minimize the amount of interference component by the pilot channel and to compensate for the disadvantages of the pilot symbol scheme of the CDMA scheme This is to maximize the efficiency of the system.

1 is a diagram showing the principle of measuring the phase of a channel with a pilot signal.

2 illustrates a structure of a channel having a pilot symbol scheme.

3 is a diagram illustrating a coherent data demodulation device according to an embodiment of the present invention.

Data demodulation device according to the present invention for achieving the above object is

A demultiplexer for receiving a channel consisting of a pilot symbol interval and a data symbol interval having a plurality of data components and separating the pilot symbol and the data symbol into a pilot symbol and a data symbol, respectively;

A pilot symbol channel measurer for measuring a channel of the pilot symbol and outputting cos θ and sin θ representing a phase θ with respect to a transmission reference signal as first reference phase signals, respectively;

A data symbol channel measurer measuring a channel of a data symbol having a first data component and outputting a phase ψ for the transmission reference signal and D1cosψ and D1sinψ representing the first data component D1;

A data component extractor for extracting the first data component D1 by receiving D1cosψ and D1sinψ which are channel measurement results of the first reference phase signal and the data symbol channel measurer;

Data for determining the sign of the extracted first data component D1, and outputting the corrected phase cosψ and sinψ by removing a first data component of D1cosψ and D1sinψ, which is a channel measurement result of the data symbol channel measurer, based on the determination result. It consists of a symbol phase generator.

On the other hand, the data demodulation method according to another feature of the present invention

Receiving a channel consisting of a pilot symbol interval and a data symbol interval having a plurality of data components and separating the channel into pilot symbols and data symbols, respectively;

Measuring a channel of the pilot symbol and outputting cos θ and sin θ representing a phase θ with respect to a transmission reference signal as first reference phase signals, respectively;

Measuring a channel of the data symbol having a first data component and outputting D1cosψ and D1sinψ representing a phase ψ and the first data component D1 for a transmission reference signal;

Extracting the first data component D1 by receiving D1cosψ and D1sinψ which are the channel measurement results of the first reference phase signal and the data symbol;

Determining the sign of the extracted first data component D1, and outputting the corrected phase cosψ and sinψ by removing the data component of the D1cosψ and D1sinψ based on the determination result.

Hereinafter, with reference to the drawings will be described an embodiment of the present invention;

First, the principle of measuring the phase of the channel at the receiving end with the pilot signal will be described with reference to FIG.

In Fig. 1, the pilot signal Ps of the transmission signal always has the same phase because no data is loaded, but the data signal Ds changes with a phase value relative to the pilot signal in the IQ diagram according to the modulation scheme. . In order to detect the data signal at the receiving end, the phase change of the received pilot signal Pr should be detected to compensate for the phase error of the received data signal Dr.

For example, assume a CDMA communication system having a quadrature phase shift keying (QPSK) modulation scheme. As shown in Fig. 1, it is assumed that the transmission pilot signal Ps is located on the I axis, and the transmission data signal Ds is present in the first quadrant with a phase difference of θ with respect to this pilot signal. When such a transmission data signal passes through a channel and there is a phase change by dθ, the reception data signal Dr has a phase difference of θ + dθ with respect to the transmission pilot signal Ps. On the other hand, since the pilot signal at the receiving end also undergoes a phase change of dθ, after obtaining this dθ value from the receiving pilot signal Pr, if the dθ component of the received data signal Dr is removed, the phase error of the data signal at the receiving end is eliminated. To compensate.

The following describes the principles of the present invention applied to the pilot symbol scheme.

2 is a diagram illustrating a structure of a channel having a pilot symbol scheme. As shown in FIG. 2, the pilot symbol scheme uses only a pilot symbol (PS) section of a channel for channel measurement, and the rest, that is, a data symbol section. Is used for various data (eg, power control signals, etc.) required for communication. In the conventional pilot symbol method, since the channel measurement value (phase measurement value) obtained in the pilot symbol interval Ts is used for all data symbol intervals before the next pilot symbol, it is necessary to follow the channel change occurring in each data interval. The performance of the coherent demodulation system is degraded.

Meanwhile, in the embodiment of the present invention, as described below, the phase value of the data symbol section may be continuously measured based on the phase value obtained in the pilot symbol section.

First, assume that channel measurement values (phase measurement values) Ref ^I and Ref ^Q measured in the pilot symbol period Ts are equal to Equation 1.

Ref ^I = cosθ, Ref ^Q = sinθ

Here, θ represents the phase change in the received pilot symbol interval with respect to the transmission reference signal (eg, the pilot signal). At this time, since the phase θ is difficult to measure directly, the sinθ and cosθ values are measured instead. The method of obtaining these values is not described herein because it depends on the structure of the transmission channel and is outside the scope of the present invention.

On the other hand, in the data 1 section T _D 1, as shown in Equation 2, channel measurement values D ^I and D ^Q obtained by adding a constant data component to this phase component are obtained.

D ^I = D1 × cosψ, D ^Q = D1 × sinψ

Here, ψ (ψ = θ + dθ) represents the phase change of the received data signal with respect to the transmission reference signal in the data 1 interval T _D 1, and D1 represents a data component in the data 1 interval, Has a constant sign, 1 or -1. Therefore, as can be seen from Equation 2, the channel measurement values D ^I and D ^Q in the data 1 section are determined not only according to ψ but also according to the sign of the data component D1.

Therefore, if only the data components D1, D2,... Can be eliminated from the values obtained during the data periods T _D 1, T _D 2,... As a result, the same effect as using a substantially continuous pilot channel can be obtained.

First, it is assumed that the phase change as a whole cannot be ignored, but the phase components of adjacent sections in one pilot symbol group hardly change. That is, if the phase θ in the pilot symbol interval with respect to the reference signal and the phase ψ in the data1 interval (T _D 1) are approximately equal (that is, dθ ≒ 0), Ref ^I and Ref ^Q and D ^I and D ^Q are Z ^I and Z ^{Q, which} are multiplied values, can be obtained by the following equations (3) and (4).

Z ^I = Ref ^I × D ^I = cosθ × (D1 × cosψ) ≃D1 × cos ² θ

Z ^Q = Ref ^Q × D ^Q = sinθ × (D1 × sinψ) ≃D1 × sin ² θ

By adding Equations 3 and 4, respectively, the data component D1 can be obtained as shown in Equation 5.

Z = Z ^I + Z ^Q = D1 × (cos ² θ + sin ² θ) = D1

Therefore, as shown in Equation 6, the sign of the Z value is obtained and multiplied by the D ^I and D ^Q to obtain a phase value from which the data component value is removed.

Y ^I = D ^I × sgn [Z] = (D1 × cosψ) × sgn [Z] = cosψ

Y ^Q = D ^Q × sgn [Z] = (D1 × sinψ) × sgn [Z] = sinψ

Here, sgn [] is a function for determining the sign of the input value. That is, sgn [Z] becomes +1 when the Z value is a positive value, and −1 when the Z value is a negative value. Therefore, as shown in Equation 5, since the Z value coincides with the sign of the data component D1, Y ^I and Y ^Q in Equation 6 can obtain phase information irrespective of the sign of the data component.

Therefore, even in the data 1 section T _D 1, the phase values cos ψ and sin ψ can be obtained irrespective of the data component _D 1, and the phase error of the received data signal can be recovered based on the phase values. . Similarly, the phase information irrespective of the data components can be obtained even in the data 2 section (T _D2 ) by using the phase values (cosψ, sinψ) obtained in the data section 1, so that the same effect as using a continuous pilot channel can be obtained. Can be.

3 is a diagram illustrating a coherent data demodulation device according to an embodiment of the present invention. As shown in FIG. 3, a coherent data demodulation device according to an embodiment of the present invention includes a demultiplexer 100, a pilot symbol channel measurer 200, a data symbol channel measurer 300, a data component extractor 400, And a code discriminator 500 and a data component remover 600.

The demultiplexer 100 accepts a channel having a pilot symbol structure as shown in FIG. 2 and separates the pilot symbol and the data symbol. Pilot symbols and data symbols separated from the demultiplexer 100 are input to the pilot symbol channel measurer 200 and the data symbol channel measurer 300, respectively.

The pilot symbol channel measurer 200 measures the channel of the pilot symbol and outputs cos θ and sin θ in which the phase θ of the transmission reference signal is measured. The data symbol channel measurer 300 measures the channel of the data symbol and outputs D ^I (D ^I = D ¹ cos ψ) and D ^Q (D ^Q = D 1sinψ), respectively, shown in Equation 2. Where D1 represents the data component of the data symbol

Denotes the phase of the data symbol signal with respect to the transmission reference signal.

The data component extractor 400 receives the output channel signal of the pilot symbol channel measurer 200, which is an initial reference phase signal, and the channel signal output from the data symbol channel measurer 300, and extracts the data component D1. That is, as shown in equations (3) and (4), Z ^I and Z ^{Q, which} are values obtained by multiplying channel measurement values of pilot symbols and channel measurement values of data symbols, are obtained. In this case, if the data symbol is adjacent to the pilot symbol, Z ^I and Z ^Q are respectively D1 × cos ² θ Wow D1 × sin ² θ Therefore, by adding Z ^I and Z ^Q , the data component D1 can be extracted.

The data component D1 of the data symbol extracted from the data component extractor 400 is input to the code discriminator 500 to determine a sign, and the determined result sgn [D1] is input to the data component remover 600. do. That is, the data component extractor 400 determines the sign of the data component from the most significant bit (MSB) of the input data component D1 and outputs the determination result to the data component remover 600.

The data component remover 600 receives the discrimination result sgn [D1] from the code discriminator 500 and the channel measurement values D1cos ψ and D1sinψ from the data symbol channel measurer 300 and removes the data components. The phase cos ψ and sin ψ of the symbol are obtained, respectively. These phase cos ψ and sin ψ are used to recover the phase error of the received data signal. In FIG. 3, the code discriminator 500 and the data component remover 600 form a data symbol phase generator that outputs the corrected phase.

On the other hand, the phase signal cosψ and sinψ of the data symbol output from the data component remover are provided to the data component extractor 400 as a reference phase signal to obtain a signal from which the data component of the phase signal of the next data symbol is removed therefrom. The hardware structure for this can be easily understood by those skilled in the art from FIG. 3 and will not be described herein any further.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and of course, many other modifications and changes are possible.

As described above, the present invention provides an improved pilot symbol data demodulation method that can continuously measure the phase value of the data symbol interval based on the phase value obtained in the pilot symbol interval. The efficiency of the CDMA system can be maximized by minimizing the amount of interference components and compensating for the shortcomings of the pilot symbol scheme to adapt to rapid channel changes.

Claims (7)

A demultiplexer which receives a channel consisting of a pilot symbol interval and a data symbol interval having a plurality of data components and separates the pilot symbol and the data symbol into a pilot symbol and a data symbol, respectively; A pilot symbol channel measurer for measuring a channel of the pilot symbol and outputting cos θ and sin θ representing a phase θ with respect to a transmission reference signal as a first reference phase signal, respectively; A data symbol channel measurer for measuring a channel of a data symbol having a first data component and outputting a phase ψ for the transmission reference signal and D1cosψ and D1sinψ representing the first data component D1; A data component extractor for extracting the first data component D1 by receiving D1cosψ and D1sinψ which are channel measurement results of the first reference phase signal and the data symbol channel measurer; Determining the sign of the extracted first data component D1, and outputting the corrected phase cosψ and sinψ by removing a first data component of D1cosψ and D1sinψ, which is a channel measurement result of the data symbol channel measurer, based on the determination result A data demodulation device for a code division multiple access communication system comprising a data symbol phase generator. In claim 1, The data demodulation device Outputting the corrected phase cosρ and sinρ by removing the second data component D2 from D2cosρ and D2sinρ, which are channel measurement results of the data symbol having the second data component, using the corrected phase cosψ and sinψ as second reference phase signals. And a data demodulation device for a code division multiple access communication system. In claim 1, The data symbol phase generator is A code discriminator for determining a sign of the first data component through the most significant bit of the first data component D1 extracted from the data component extractor; A data demodulation device of a code division multiple access communication system including a data component remover which receives D1cosψ and D1sinψ which are channel measurement results of the data symbol channel measurer as inputs, and removes the first data component D1 based on the code discrimination result. . In claim 1, The data component extractor D1cosθcosψ and D1sinθsinψ, which are the product of cosθ and sinθ, which are the channel measurement results of the pilot symbol channel meter, and D1cosψ and D1sinψ, which are the channel measurement results of the data symbol channel meter, respectively, are obtained, and then the first data component D1 is extracted by adding these values. And a data demodulation device for a code division multiple access communication system. Receiving a channel consisting of a pilot symbol interval and a data symbol interval having a plurality of data components, and separating the pilot symbol intervals into pilot symbols and data symbols, respectively; Measuring a channel of the pilot symbol and outputting cos θ and sin θ representing a phase θ with respect to a transmission reference signal as first reference phase signals, respectively; Measuring a channel of a data symbol having a first data component to output a phase ψ for the transmission reference signal and D1cosψ and D1sinψ representing the first data component D1; Extracting the first data component D1 by receiving D1cosψ and D1sinψ which are the channel measurement results of the first reference phase signal and the data symbol; Determining a code of the extracted first data component D1, and outputting a corrected phase cosψ and sinψ by removing a first data component of the D1cosψ and D1sinψ based on the determination result. How to demodulate data in the system. In claim 5, The data demodulation method Providing the corrected phase cosψ and sinψ as a second reference phase signal; And outputting the corrected phases cosρ and sinρ by removing the second data component D2 from D2cosρ and D2sinρ, which are channel measurement results of the data symbol having the second data component, based on the second reference phase signal. A method for demodulating data in a code division multiple access communication system. In claim 5, Extracting the data component Obtaining D1cosθcosψ and D1sinθsinψ, which are the product of cosθ and sinθ, the channel measurement results of the pilot symbols, and D1cosψ and D1sinψ, respectively, of the channel measurement results of the data symbols; And adding the D1cosθcosψ and D1sinθsinψ.