KR100864823B1 - Apparatus and method for hierarchical modulation using pilot, apparatus and method for receiving hierarchically modulated signal - Google Patents

Abstract

A hierarchical modulation apparatus and method using a pilot, an apparatus for receiving a hierarchical modulated signal, and a method thereof are disclosed. A hierarchical modulation device using a pilot of the present invention includes: a first encoder for encoding a first layer signal sequence; A second encoder for encoding a second layer signal sequence; A pilot insertion unit inserting a pilot signal into the signal sequence encoded by the second encoder; And a hierarchical modulator for modulating and combining the signals output from the first encoder and the pilot inserter, respectively.

Description

Apparatus and method for hierarchical modulation using pilot, apparatus and method for receiving hierarchically modulated signal

1 shows a block diagram of a hierarchical modulation device according to the present invention.

2 illustrates a constellation of transmitting a pilot to an additional layer signal sequence in a hierarchically modulated π / 4-DQPSK signal.

3 illustrates an example in which pilots are periodically inserted into a hierarchical signal sequence.

4 illustrates a block diagram of a receiver for receiving a hierarchical modulated signal in accordance with the present invention.

5 is a flowchart illustrating a process of demodulating a hierarchical modulated signal according to the present invention.

6 is a flowchart illustrating another embodiment of step 54 of FIG. 5.

7 is a block diagram of a receiver for receiving a hierarchical modulated signal according to another embodiment of the present invention.

The present invention relates to an orthogonal frequency division multiplexing transmission system, and more particularly, to an apparatus and method for hierarchical modulation or demodulation using a pilot signal in an OFDM transmission system.

Hierarchical modulation means that at least two signals modulated by different modulation schemes are added together and modulated synchronously for transmission.

In layer modulation, a base layer signal is a signal transmitted from an existing system, and an enhancement layer signal is transmitted to provide a service added to the base layer signal.

In order to receive and demodulate the hierarchically modulated signal, an in-phase demodulation method is required, and for this purpose, it is necessary to transmit an additional pilot signal.

An object of the present invention is to provide a method and apparatus for demodulating a modulated signal by inserting and modulating a pilot signal in an additional layer signal in order to secure in-phase demodulation performance for the hierarchically modulated signal.

According to an aspect of the present invention, there is provided a hierarchical modulation device including: a first encoder configured to encode a first layer signal sequence; A second encoder for encoding a second layer signal sequence; A pilot insertion unit inserting a pilot signal into the signal sequence encoded by the second encoder; And a hierarchical modulator for modulating and combining the signals output from the first encoder and the pilot inserter, respectively.

In order to achieve the above technical problem, the hierarchical modulation method of the present invention comprises the steps of: first encoding a first layer signal sequence; Second encoding the second layer signal sequence; Inserting a pilot signal into the second coded signal sequence; And modulating and combining the signal sequence output in the first encoding and inserting the pilot signals.

In order to achieve the above technical problem, a signal receiver of the present invention is a receiver for receiving a hierarchically modulated signal of a first layer signal sequence and a second layer signal sequence into which a pilot is inserted, using the reference symbol included in the received signal. A channel estimator for estimating channels of subcarrier signals with respect to the received signal; An equalizer for outputting subcarrier signals for the pilot using an estimated channel value; A determination unit which determines which constellation point in the constellations the subcarrier signals outputted from the equalizing unit correspond to; A channel estimation updater re-estimating subcarrier signal channels for the pilot using the determination result, and updating an estimate of subcarrier signal channels using the reestimated subcarrier channel values; And a demodulator for equalizing other subcarrier signals excluding subcarrier signal channels for the pilot using updated channel estimate values and demodulating the hierarchically modulated first and second layer signal sequences.

According to an aspect of the present invention, there is provided a method of receiving a hierarchically modulated signal of a first layer signal sequence and a second layer signal sequence into which a pilot is inserted, by using a reference symbol included in the received signal. Estimating channels of subcarrier signals for the subcarrier signals; Outputting subcarrier signals for the pilot using the estimated channel value; Determining which constellation points in the constellation the subcarrier signals for the pilot correspond to; Re-estimating subcarrier signal channels for the pilot using the determination result; Updating the estimate of subcarrier signal channels using the reestimated subcarrier channel values; And equalizing other subcarrier signals other than subcarrier signal channels for the pilot using updated channel estimate values and demodulating the hierarchically modulated first and second layer signal sequences.

According to an aspect of the present invention, there is provided a method of receiving a hierarchically modulated signal of a first layer signal sequence and a second layer signal sequence into which a pilot is inserted, by using a reference symbol included in the received signal. Estimating channels of subcarrier signals for the subcarrier signals; Outputting subcarrier signals for the pilot using the estimated channel value; Determining which constellation points in the constellation the subcarrier signals for the pilot correspond to; Re-estimating subcarrier signal channels for the pilot using the determination result; Replacing channel estimate values for carriers corresponding to the pilot subcarrier signals with the reestimated subcarrier channel values; Updating the estimates of the subcarrier signal channels by correlating the channel estimates for nearby subcarrier signals using the replaced subcarrier channel values; And equalizing other subcarrier signals other than subcarrier signal channels for the pilot using updated channel estimate values and demodulating the hierarchically modulated first and second layer signal sequences.

According to an aspect of the present invention, there is provided a receiver for receiving a signal in which a first layer signal sequence and a pilot-inserted second layer signal sequence are hierarchically modulated, wherein the first layer signal sequence and the pilot are inserted from a received signal. A layer separator for separating the two-layer signal sequence; First layer demodulation means for demodulating the first layer signal sequence; And second layer demodulation means for estimating subcarrier signal channels for the pilot and demodulating the second layer signal sequence by equalizing other subcarrier channels except for the subcarrier signal channels for the pilot using the estimated channel values. It is characterized by.

1 shows a block diagram of a hierarchical modulation device according to the present invention.

The illustrated hierarchical modulation device includes a first encoder 10, a second encoder 11, a pilot inserter 12, and a hierarchical modulator 13.

The first encoder 10 encodes the base layer signal sequence, and the second encoder 11 encodes the additional layer signal sequence. As the encoding method, convolutional coding, trellis coding, turbo coding Low Density Parity Check (LDPC) coding, or concatenated encoding in which two or more of them are connected to each other may be adopted.

The pilot inserting unit 12 inserts a pilot signal into the encoded second layer signal sequence. The pilot signal to be inserted will be described later.

The hierarchical modulator 13 modulates signals output from the first encoder 10 and the pilot inserter 12 and maps the signals to the corresponding signal space. For example, the base layer may be a quadrature phase-shift keying (QPSK) signal space, and the additional layer may be a binary phase-shift keyed signal space.

2 is a diagram illustrating subcarriers of an additional layer signal sequence and subcarriers of an inserted pilot when hierarchical modulation is applied to a terrestrial digital audio broadcasting (DAB) or digital multimedia broadcasting (DMB) system of π / 4-D (Differential) QPSK transmission scheme. It illustrates the constellation.

In the drawing, a rectangle represents each subcarrier signal of an odd-numbered OFDM symbol, starting with a phase reference symbol (PRS) transmitted first among DAB transmission frames. The circle represents each subcarrier signal of the even-numbered OFDM symbol from the PRS. In addition, the hatched squares or circles represent pilot signals.

 The pilot signal is necessary for channel estimation and equalization for in-phase demodulation due to hierarchical modulation characteristics. In order to ensure compatibility with the existing system, the hierarchical modulation can change only the additional layer signal without changing the existing π / 4-DPSK signal, so that the pilot signal can be inserted only in the additional layer signal. In this case, unlike the form used in most communication or broadcasting systems, the pilot signal is a form in which random data that is not previously promised between the transmitting side and the receiving side is modulated and is relatively small compared to the base layer signal. Have power.

Therefore, in order to obtain proper channel estimation performance at the receiver by using such a pilot signal, decision directed channel estimation is required to detect a base layer signal and use it for channel estimation.

Accordingly, the pilot signal to be transmitted as the additional layer signal preferably has correlation with the base layer signal corresponding to the same subcarrier, and most preferably, as shown in FIG. 1. That is, if the base layer signal of the subcarrier through which the pilot is transmitted in the even-numbered OFDM symbol period is located in the second quadrant of FIG. 1, transmitting the signal corresponding to the constellation point of reference number 21 as the pilot signal is the base layer signal. This has the same effect as the transmission power of increases, resulting in a reduction in the determination error of the base layer signal.

As another example of selecting a pilot signal, the subcarrier to which the pilot signal is transmitted may increase the transmission power of the base layer signal by a constant value or a predetermined ratio and may not transmit the additional layer signal. That is, since the additional layer signal acts as noise due to the lower power than the base layer signal, increasing the transmission power of the base layer signal and not transmitting the additional layer signal may improve channel estimation performance. In this case, as a result of increasing the transmit power of the base layer signal by a constant value or by a certain ratio, it may not match one of the constellation points of other subcarrier signals in which the pilot is not transmitted in FIG. It also includes transmitting at a transmit power of and not transmitting additional layer signals.

As another example of selecting a pilot signal, the pilot signal may be a base layer signal whose power is lowered to a predetermined value or a base layer signal whose magnitude is lowered by a predetermined ratio.

The pilot subcarriers having the constellation of the above-described type may be periodically inserted into the additional layer signal and transmitted as shown in FIG. 3. As shown in FIG. 3, it can be seen that the pilot is periodically inserted every 10 subcarriers.

The pilot may also be inserted aperiodically, for example, if the data length actually to be transmitted in the additional layer signal sequence is smaller than the maximum allowable length, the data may be transmitted and inserted in the remaining area.

4 is a block diagram of a receiver for receiving a hierarchical modulated signal according to the present invention. The illustrated receiver includes a channel estimator 40, an equalizer 41, a determiner 42, a channel estimate updater 43, and a hierarchical demodulator 44.

5 is a flowchart illustrating a process of demodulating a hierarchical modulated signal according to the present invention.

The operation of the receiver of FIG. 4 will be described with reference to the flowchart shown in FIG. 5.

The channel estimator 40 estimates a channel for all subcarriers using a PRS transmitted first in a DAB frame such as a preamble included in the received signal (step 50). Since the PRS is a signal having a fixed transmission pattern, a channel estimation value can be easily obtained from the PRS signal. As the channel estimation method, one of conventional channel estimation methods including least square estimation or maximum likelihood estimation may be adopted.

The equalizer 41 compensates for the channel distortion of the subcarrier signals corresponding to the pilot in the currently received OFDM symbol by using the channel value estimated by the channel estimator 40 (step 51).

The determination unit 42 determines which constellation point the subcarrier signals of the pilot correspond to based on the constellation as shown in FIG. 2 (step 52).

The channel estimation updating unit 43 estimates the channels of the pilot subcarrier signals again based on the determination result, and reflects the reestimated channel values of the pilot subcarrier signals through interpolation or the like to thereby estimate the channels of all the subcarrier signals estimated in step 50. Update the values (step 54).

In this case, the channel estimation noise may be reduced by processing the channel state of the pilot subcarrier signal through linear or nonlinear signal processing for the reestimation result. A moving average method may be used as an example of linear signal processing, and a median filtering method may be used as an example of nonlinear signal processing.

The hierarchical demodulator 44 demodulates in-phase demodulated data subcarriers of OFDM symbols other than the pilot subcarrier using the channel values updated by the channel estimation updater 43 (step 55).

6 is a flowchart illustrating another embodiment of step 54 of FIG. 5.

In step 60, channel estimation values for carriers corresponding to pilot subcarrier signals are replaced with decision-based channel estimates. Channel estimation noise may be attenuated by linear or nonlinear processing of the replaced values as described above, and then the channel estimate for the subcarrier signal may be updated by correlating channel estimation values between adjacent subcarriers (step 61).

7 is a block diagram of a receiver for receiving a hierarchical modulated signal according to another embodiment of the present invention. The receiver shown is a hierarchical splitter 71, a base layer demodulator 72, a channel estimator 73, an equalizer 74, a determiner 75, a channel estimate updater 76 and an additional layer demodulator. (77).

The layer separator 71 separates the base layer signal sequence and the additional layer signal sequence from the received signal. The base layer demodulator 72 demodulates the base layer signal sequence according to a demodulation scheme corresponding to the modulation scheme of the transmitting side.

Demodulation of the additional layer signal sequence is performed as follows. First, the channel estimator 73 estimates channels for all subcarriers using the PRS included in the received signal. Since the PRS is a signal having a fixed transmission pattern, a channel estimation value can be easily obtained from the PRS signal.

The equalizer 74 compensates for channel distortion of subcarrier signals corresponding to pilots in the currently received OFDM symbol by using the channel value estimated by the channel estimator 73.

The determination unit 75 determines which constellation point the pilot subcarrier signals correspond to based on the constellations of the subcarriers as shown in FIG. 2.

The channel estimation updating unit 76 re-estimates the channels of the pilot subcarrier signals based on the determination result, and updates the channel values of all the estimated subcarrier signals by reflecting the reestimated channel values of the pilot subcarrier signals through interpolation or the like. do.

In this case, the channel estimation noise may be reduced by processing the channel state of the pilot subcarrier signal through linear or nonlinear signal processing for the reestimation result. A moving average method may be used as an example of linear signal processing, and a median filtering method may be used as an example of nonlinear signal processing.

The additional layer demodulator 77 demodulates in-phase demodulated data subcarriers of the OFDM symbol other than the pilot subcarrier using the channel values updated by the channel estimation updater 76.

The invention can also be embodied as computer readable code. The computer-readable recording medium includes all kinds of recording devices in which data that can be read by a computer system is stored. Examples of computer-readable recording media include ROM, RAM, CD_ROM, magnetic tape, floppy disks, optical data storage devices, and the like, and also include those implemented in the form of carrier waves, for example, transmission over the Internet. The computer readable recording medium can also be distributed over network coupled computer systems so that the computer readable code is stored and executed in a distributed fashion.

According to the present invention, reception performance can be improved by additionally transmitting a pilot signal while maintaining compatibility with an existing system in an OFDM-based communication or broadcasting system employing hierarchical modulation.

As described above, optimal embodiments have been disclosed in the drawings and the specification. Herein, specific terms have been used, but they are used only for the purpose of illustrating the present invention and are not intended to limit the scope of the present invention as defined in the claims or the claims. Therefore, those skilled in the art will understand that various modifications and equivalent other embodiments are possible therefrom. Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

Claims (16)

A first encoder which encodes a first layer signal sequence; A second encoder for encoding a second layer signal sequence; A pilot insertion unit inserting a pilot signal into the signal sequence encoded by the second encoder; And And a hierarchical modulator for modulating and combining the signals output from the first encoder and the pilot inserter, respectively. The pilot insertion portion And inserting the pilot signal into the encoded second layer signal sequence at predetermined intervals or after the encoded second layer signal sequence. delete A first encoder which encodes a first layer signal sequence; A second encoder for encoding a second layer signal sequence; A pilot insertion unit inserting a pilot signal into the signal sequence encoded by the second encoder; And And a hierarchical modulator for modulating and combining the signals output from the first encoder and the pilot inserter, respectively. The pilot signal is And a signal having a correlation with the first layer signal sequence. The method of claim 1 or 3, wherein the pilot signal is And the first layer signal sequence whose power is amplified or reduced in size. First encoding the first layer signal sequence; Second encoding the second layer signal sequence; Inserting a pilot signal into the second coded signal sequence; And Modulating and combining the signal sequence output from the first encoding and inserting the pilot signal, The pilot signal is And inserting the second coded signal string at a predetermined interval or after the second coded signal string. delete First encoding the first layer signal sequence; Second encoding the second layer signal sequence; Inserting a pilot signal into the second coded signal sequence; And Modulating and combining the signal sequence output from the first encoding and inserting the pilot signal, The pilot signal is And a signal having a correlation with the first layer signal sequence. The method of claim 5 or 7, wherein the pilot signal is And the first layer signal sequence whose power is amplified or reduced in size. A receiver for receiving a signal in which a first layer signal sequence and a pilot-inserted second layer signal sequence are hierarchically modulated; A channel estimator for estimating channels of subcarrier signals with respect to the received signal using a reference symbol included in the received signal; An equalizer for outputting subcarrier signals for the pilot using an estimated channel value; A determination unit which determines which constellation point in the constellations the subcarrier signals outputted from the equalizing unit correspond to; A channel estimation updater re-estimating subcarrier signal channels for the pilot using the determination result, and updating an estimate of subcarrier signal channels using the reestimated subcarrier channel values; And And a demodulator for equalizing other subcarrier signals excluding subcarrier signal channels for the pilot using updated channel estimate values and demodulating the hierarchically modulated first and second layer signal sequences. 10. The method of claim 9, wherein the subcarrier signals for the reestimated pilot are A signal receiver characterized in that the channel estimation noise is reduced by linear or nonlinear processing. 1. A method of receiving a signal in which a first layer signal sequence and a pilot-inserted second layer signal sequence are hierarchically modulated; Estimating channels of subcarrier signals for the received signal using a reference symbol included in the received signal; Outputting subcarrier signals for the pilot using the estimated channel value; Determining which constellation points in the constellation the subcarrier signals for the pilot correspond to; Re-estimating subcarrier signal channels for the pilot using the determination result; Updating the estimate of subcarrier signal channels using the reestimated subcarrier channel values; And Equalizing other subcarrier signals excluding subcarrier signal channels for the pilot using updated channel estimate values and demodulating the hierarchically modulated first and second layer signal sequences. 12. The method of claim 11, wherein the subcarrier signals for the reestimated pilot are A method for receiving signals, characterized in that the channel estimation noise is reduced by linear or nonlinear processing. 1. A method of receiving a signal in which a first layer signal sequence and a pilot-inserted second layer signal sequence are hierarchically modulated; Estimating channels of subcarrier signals for the received signal using a reference symbol included in the received signal; Outputting subcarrier signals for the pilot using the estimated channel value; Determining which constellation points in the constellation the subcarrier signals for the pilot correspond to; Re-estimating subcarrier signal channels for the pilot using the determination result; Replacing channel estimate values for carriers corresponding to the pilot subcarrier signals with the reestimated subcarrier channel values; Updating the estimates of the subcarrier signal channels by correlating the channel estimates for nearby subcarrier signals using the replaced subcarrier channel values; And Equalizing other subcarrier signals excluding subcarrier signal channels for the pilot using updated channel estimate values and demodulating the hierarchically modulated first and second layer signal sequences. 14. The method of claim 13, wherein the subcarrier signals for the reestimated pilot are A method for receiving signals, characterized in that the channel estimation noise is reduced by linear or nonlinear processing. A receiver for receiving a signal in which a first layer signal sequence and a pilot-inserted second layer signal sequence are hierarchically modulated; A hierarchical separation unit that separates the first layer signal sequence and the second layer signal sequence into which the pilot is inserted from a received signal; First layer demodulation means for demodulating the first layer signal sequence; And Second layer demodulating means for estimating subcarrier signal channels for the pilot and demodulating the second layer signal sequence by equalizing other subcarrier channels except for the subcarrier signal channels for the pilot using the estimated channel values. Characterized by signal receiver. The method of claim 15, wherein the second layer demodulation means A channel estimator estimating channels of subcarrier signals with respect to the second layer signal sequence using a reference symbol included in the second layer signal sequence; An equalizer for outputting subcarrier signals for the pilot using an estimated channel value; A determination unit which determines which constellation point in the constellations the subcarrier signals outputted from the equalizing unit correspond to; A channel estimation updater re-estimating subcarrier signal channels for the pilot using the determination result, and updating an estimate of subcarrier signal channels using the reestimated subcarrier channel values; And And a second layer demodulator for demodulating the second layer signal sequences by equalizing other subcarrier signals except for the subcarrier signal channels for the pilot using updated channel estimate values.

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