CN1574821A - TDS-OFDM receiver and signal processing method thereof - Google Patents

Abstract

A TDS-OFDM receiver capable of processing signals by using pilot signals hidden in the frequency domain and a signal processing method thereof. The multi-carrier receiver includes: a Fourier transform unit for transforming a time-domain signal into a frequency-domain signal; a pilot detection unit for detecting a pilot signal hidden in a frequency-domain signal; an offset/channel estimation unit for for estimating frequency offset, time offset and channel state; an offset compensation unit for compensating the estimated frequency offset and time offset; and an equalizer for equalizing frequency domain signals based on the estimated channel state.

Description

Time Domain Synchronous Orthogonal Frequency Division Multiplexing Receiver and Its Signal Processing Method

Technical field

The present invention relates generally to a digital broadcasting system, and in particular to a Time Domain Synchronous Orthogonal Frequency Division Multiplexing (TDS-OFDM) capable of improving reception performance using pilot signals hidden in subcarriers in the frequency domain Receiver and its signal processing method.

Background technique

Orthogonal Frequency Division Multiplexing (OFDM) is one of the multi-carrier modulation methods, which has good performance in multipath or mobile environment.

OFDM systems improve frequency utilization by using multiple carriers with orthogonality between carriers. The OFDM system uses multiple carriers in wired and wireless communications and is suitable for high data rate transmission. If a single-carrier system is used to transmit high-speed data whose symbol duration is short in a wireless communication channel with multipath fading, the inter-symbol interference will be aggravated and the complexity of the receiving end will be significantly increased.

When a multi-carrier system expands the symbol duration of each sub-carrier by the number of sub-carriers, the system can maintain a data transmission rate and is therefore robust against multipath.

In the OFDM system, multi-carriers with orthogonality between carriers are used to improve frequency utilization, and the transmitting end and receiving end modulate/demodulate the multi-carriers respectively, which brings about the inverse discrete Fourier transform (IDFT ) and the discrete Fourier transform (DFT) have the same effect. Therefore, modulation and demodulation can be performed at high speed by using inverse discrete Fourier transform (IDFT) and discrete Fourier transform (DFT).

TDS-OFDM systems insert synchronization information such as pseudo-noise (PN) sequences into the time domain. Specifically, the TDS-OFDM system uses a synchronization signal in the time domain to obtain synchronization in the time domain and frequency domain, and to perform channel equalization. However, the TDS-OFDM system has disadvantages regarding a limited receiving system and performance degradation.

The present applicant has disclosed on Korean Patent Application No. 10-2002-59363 titled "Multi-carrier transmission system having pilot signal added in frequency domain and signal processing method thereof, Multi-carrier transmission system having pilot signal added frequency domain and signal processing method thereof", wherein a pilot signal is added to the time-domain OFDM signal for transmission.

FIG. 1 is a block diagram showing a transmission system disclosed in Korean Patent Application No. 10-2002-59363.

As shown in FIG. 1, the transmission system includes a pilot insertion unit 220 that adds a pilot signal to a time-domain OFDM signal. Referring to FIG. 2, the pilot insertion unit 220 adds the very low power I pilot signal P _I and Q pilot signal P _Q to the I signal and the Q signal with the same 1 symbol time as the I signal and the Q signal. The power P _I of the I pilot signal is set in such a way that the accumulation of the power of a predetermined number of I pilot signals becomes larger than the average power of the I signal. The power P _Q of the Q pilot signal can be set in the same way as that of the power of the I pilot signal. When pilot signals Hidden_Pilot P _I and P _Q are added to I and Q signals which are OFDM signals, signals are formed as shown in FIG. 3 . Mapping data and pilot signals Hidden_Pilot _PI and P _Q are loaded to each of the IDFT point subcarriers.

Through the IDFT unit 230, the OFDM signal with the pilot signals Hidden_Pilot _PI and P _Q is modulated into an OFDM signal in the time domain. The modulated OFDM signal in the time domain is transmitted to the wireless channel environment through the guard interval insertion unit 240 , the synchronization information insertion unit 250 and the shaping filter unit 260 .

Therefore, a receiving system is required to process the pilot signals Hidden_Pilot PI and P _Q hidden in _the subcarriers in the frequency domain.

Contents of invention

In order to meet the above needs, an object of the present invention is to provide a TDS-OFDM receiver and a signal processing method thereof for obtaining synchronization and performing channel equalization by using hidden pilot signals in subcarriers in a frequency domain.

The TDS-OFDM receiver includes: a Fourier transform unit for transforming time-domain signals into frequency-domain signals; a pilot detection unit for detecting pilot signals hidden in frequency-domain signals; an offset/channel estimation unit for for estimating frequency offset, time offset and channel state; an offset compensation unit for compensating the estimated frequency offset and time offset; and an equalizer for equalizing frequency domain signals based on the estimated channel state.

The pilot detection unit detects the hidden pilot signal based on the correlation value between the frequency domain signal and the reference pilot signal. The hidden pilot signal is a pseudo-noise (PN) sequence.

A signal processing method for a multi-carrier receiver includes: transforming a time domain signal into a frequency domain signal; detecting a pilot signal hidden in the frequency domain signal; estimating frequency offset, time offset and channel state; compensating the estimated frequency offset and time offset; and equalizing the frequency domain signal based on the estimated channel state.

Detecting the pilot signal is performed based on a correlation value between the frequency domain signal and the reference pilot signal.

Therefore, by estimating frequency offset, time offset, and multipath with higher accuracy using pilot signals hidden in the frequency domain, reception performance is improved compared to general receivers.

Description of drawings

Read the following detailed description in conjunction with accompanying drawing, above-mentioned purpose, other features and advantages of the present invention will become clearer, wherein:

FIG. 1 is a block diagram showing a conventional multi-carrier transmitter;

FIG. 2 is a diagram showing a data signal and an added pilot signal in the frequency domain;

3 is a diagram showing a data signal with a pilot signal in the frequency domain;

4 is a block diagram showing a multi-carrier receiver according to an embodiment of the present invention;

5 is a flowchart showing a signal processing method of a multi-carrier receiver according to an embodiment of the present invention; and

FIG. 6 is a diagram showing a correlation between a received signal and a reference pilot signal according to an embodiment of the present invention.

Detailed ways

The present invention is described in detail with reference to the accompanying drawings.

4 is a block diagram showing a Time Domain Synchronous Orthogonal Frequency Division Multiplexing (TDS-OFDM) receiver among multi-carrier receivers, which processes signals using pilot signals hidden in subcarriers in the frequency domain.

The TDS-OFDM receiver includes: radio frequency (RF) unit 411, offset compensation unit 413, drift retransmission (SRRC) filter for reliability compensation 414, synchronization signal/guard interval detection unit 415, offset estimation unit 417 , synchronization signal/guard interval removal unit 419 , Fourier transform unit 421 , pilot detection unit 431 , offset/channel estimation unit 433 , equalizer 435 and forward error correction (FEC) unit 437 .

The RF unit 411 converts the received signal into a baseband signal.

The offset compensating unit 413 compensates the offset with respect to the received signal based on the estimated frequency offset and time offset.

The SRRC filter 414 is the same filter used at the transmit end and shapes the pulses of the received signal.

The synchronization signal/guard interval detection unit 415 detects a guard interval (GI) inserted to prevent interference between adjacent symbols and a pseudo noise (PN) sequence included in a received signal as a synchronization signal.

The offset estimation unit 417 estimates a frequency offset and a time offset based on the detected synchronization signal.

The sync signal/guard interval removal unit 419 removes the detected sync signal and GI.

The Fourier transform unit 421 Fourier transforms the received signal from which the synchronization signal and the GI are removed, into a signal in the frequency domain.

The pilot detection unit 431 detects the pilot signals PI and _PQ hidden in the subcarriers _based on the correlation between the signal in the frequency domain and the reference pilot signal known to the receiving end.

The correlation of PN sequences, which are general pilot signals, has characteristics that the correlation value between the same PN sequences has a peak value, and the correlation value between different PN sequences is "0". Using the correlation property of the PN sequence, the pilot signals P _I and P _Q hidden in the subcarriers in the frequency domain can be detected.

The offset/channel estimation unit 433 re-estimates a frequency offset and a time offset based on the correlation detected at the pilot detection unit 431 , and supplies the re-estimated frequency offset and time offset to the offset compensation unit 413 . The offset/channel estimation unit 433 also estimates a channel state based on the correlation value, and supplies the channel state information to the equalizer 435 .

The equalizer 435 removes multipath interference in the received signal based on the provided channel state information.

The FEC unit 437 detects errors through an error detection system provided for the equalized data signal, and corrects the detected errors.

FIG. 5 is a flowchart showing a signal processing method of a TDS-OFDM receiver according to an embodiment of the present invention. The signal processing method is described in detail with reference to FIGS. 5 and 6 , in which reception performance is improved using pilot signals hidden in subcarriers in the frequency domain.

The offset unit 417 estimates a frequency offset and a time offset using a PN sequence, which is a synchronization signal in the time domain and included in a received signal. In step S511, the offset compensation unit 417 compensates the estimated frequency offset and time offset.

In step S513 , the Fourier transform unit 421 Fourier transforms the received signal from which the synchronization signal and GI are removed, into a frequency domain signal.

In step S521, the pilot detection unit 431 detects the pilot signals P _I and P _Q hidden in the subcarriers through the correlation between the frequency domain signal and the reference pilot signal.

Fig. 6 shows the received signal comprising the pilot signals _PI and _PQ in the first subcarrier in the frequency domain. Referring to FIG. 6, the first subcarrier has signals I+P I and Q+ _{P Q} generated by adding an I pilot signal and a Q signal to the I and Q signals, respectively.

The pilot detection unit 431 obtains the correlation between the signals I+P _I and Q+P _Q in the first subcarrier and the reference pilot signals RP _I and RP _Q. The reference pilot signals RP _I and RP _Q are pilot signals in the first subcarrier.

If the pilot signals _PI and _PQ buried in the received signal are the same as the reference pilot signals _RPI and _RPQ , the correlation value becomes a peak value according to the correlation characteristic of the PN sequence. If the pilot signals _PI and _PQ are not identical to the reference pilot signals _RPI and _RPQ , the correlation value becomes "0" according to the correlation characteristic of the PN sequence.

For example, the presence of this peak indicates that the pilot signals PI and _PQ buried in the first subcarrier _are the same as the reference pilot signals RP _I and _RPQ . Therefore, by removing the reference pilot signals RP _I and RP _Q from the first subcarrier, only the data signals I and Q remain.

As described above, the pilot signals Hidden_Pilot PI and P _Q hidden in subcarriers from the _first to N (N represents the number of subcarriers) can be detected using the correlation characteristic of the PN sequence.

In step S523, the offset/channel estimation unit 433 re-estimates the frequency offset and the time offset based on the correlation value, and also estimates the channel state.

If the peak value as the correlation value does not exist in the first subcarrier but comes from the second subcarrier, the offset/channel estimation unit 433 estimates the frequency offset as a value corresponding to the interval between the first subcarrier and the second subcarrier. frequency offset. The offset/channel estimation unit 433 additionally estimates a time offset and a channel state through changes in the phase component of the correlation value.

In step S525, the offset compensation unit 413 uses the re-estimated frequency offset and time offset to compensate the remaining frequency offset and time offset not compensated by the time domain synchronization signal.

In step S527, the equalizer 435 equalizes the data signals I and Q from which the pilot signal is removed.

In step S529, the FEC unit 437 detects and corrects errors in the equalized data signal.

Therefore, frequency offset, time offset, and channel state are estimated using the time-domain synchronization signal and the frequency-domain pilot signal, so reception performance is improved.

According to an embodiment of the present invention, frequency offset, time offset, and multipath are estimated with higher accuracy by using a pilot signal hidden in the frequency domain, so reception performance is improved compared to a general receiver.

While some embodiments of the present invention have been shown and described, it should be understood by those skilled in the art that, without departing from the principles and spirit of the present invention and the scope defined by the appended claims and their equivalents, the Changes are made in this example.

Claims (6)

1. A multi-carrier receiver for processing signals by transforming a time domain signal into a frequency domain signal using a Fourier transform, comprising: a Fourier transform unit, configured to transform a time-domain signal into a frequency-domain signal; a pilot detection unit, configured to detect a pilot signal hidden in a frequency domain signal; an offset/channel estimation unit for estimating frequency offset, time offset and channel state; an offset compensation unit for compensating the estimated frequency offset and time offset; and The equalizer is used for equalizing the frequency domain signal based on the estimated channel state. 2. The receiver of claim 1, wherein the pilot detection unit detects the hidden pilot signal based on a correlation value between the frequency domain signal and the reference pilot signal. 3. The receiver of claim 1, wherein the concealed pilot signal is a pseudo-noise (PN) sequence. 4. A signal processing method for a multi-carrier receiver by transforming a time-domain signal into a frequency-domain signal by Fourier transform, comprising: Transform time-domain signals into frequency-domain signals; Detect pilot signals hidden in frequency domain signals; Estimate frequency offset, time offset and channel state; compensate for the estimated frequency offset and time offset; and The frequency domain signal is equalized based on the estimated channel state. 5. The method of claim 4, wherein detecting the pilot signal is performed based on a correlation value between the frequency domain signal and a reference pilot signal. 6. The method of claim 4, wherein the concealed pilot signal is a pseudo-noise (PN) sequence.

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