KR20080079822A - Transmitting method for recoverying a carrier frequency in wireless communications system and apparatus therefor - Google Patents

Abstract

A transmitting method and a transmitting apparatus for recovering a carrier frequency in a wireless communication system are provided to allow a receiver to recover a receiving carrier frequency accurately by sensing power from a specific carrier frequency when the receiving carrier frequency is different from a transmitting carrier frequency. A transmitting apparatus for recovering a carrier frequency in a wireless communication system includes a signal mapper(402), a series/parallel converter(404), a DC tone generator(414), and an IFFT(Inverse Fast Fourier Transform) block(406). The signal mapper generates modulation symbols including data to be transmitted. The series/parallel converter parallel converts the modulation symbols and maps the modulation symbols to subcarriers corresponding to allocated transmission resources. The DC tone generator generates a DC tone having predetermined power and maps the DC tone to the subcarrier corresponding to a receiving carrier frequency used by at least one receiver serving the DC tone. The IFFT block converts a frequency domain signal to which the modulation symbols and the DC tone are mapped into a time domain signal.

Description

TRANSMIT METHOD FOR RECOVERYING A CARRIER FREQUENCY IN WIRELESS COMMUNICATIONS SYSTEM AND APPARATUS THEREFOR}

1 illustrates a transmit and receive frequency band of a scalable OFDM system in accordance with an embodiment of the present invention.

Figure 2 is a block diagram showing a frequency recovery structure using a pilot in accordance with a preferred embodiment of the present invention.

3 illustrates a transmit and receive frequency band of a scalable OFDM system according to a preferred embodiment of the present invention.

4 is a block diagram illustrating a transmitter structure for a scalable OFDM system according to a preferred embodiment of the present invention.

5 is a block diagram showing a frequency recovery structure using carrier power according to an embodiment of the present invention.

The present invention relates to the restoration of a carrier frequency in a wireless communication system, and more particularly, to a method and apparatus for restoring a carrier frequency when the transmission and reception system uses a different carrier frequency.

As the communication system evolves, the types of services to be provided in the communication system are diversified. Accordingly, there is a need for a broadband communication system that provides broadband services. In general, since frequency support is a limited resource in the communication system, a frequency band in which a broadband communication system can also be used is limited. The design is also difficult because backward compatibility with already installed communication systems must be considered.

Conventional broadband communication systems are designed on the assumption that they use different frequency bands. As communication technology advances, the demand for increasing frequency bands for broadband services is inevitable. Accordingly, the license cost for the use of the frequency band is increased, and various methods proposed for providing broadband services are not served and are delayed due to the increase in the license cost.

Accordingly, there is a need for a scheme for smoothly providing broadband services while overcoming the limitation of the frequency band, that is, solving the problem of increasing the license cost for the frequency band. As one of these methods, a legacy communication system and a broadband communication system overlaid on a specific frequency band may be considered. In this case, the mobile station existing in the broadband communication system overlaid in the specific frequency band and the mobile station of the existing communication system may have different carrier frequencies from base stations capable of receiving service. frequencies) to receive data.

Therefore, in the receiver of the broadband communication system that can use a different carrier frequency between the transceiver as described above, there is a need for a technique for efficiently recovering the desired carrier frequency.

The present invention provides a method and apparatus for effectively recovering carrier frequencies in a wireless communication system using frequency overlay.

The present invention provides a method and apparatus for efficiently recovering a carrier frequency in a communication system using different carrier frequencies between transceivers.

The present invention provides a method and apparatus for recovering carrier frequency in a scalable Orthogonal Frequency Division Multiplexing (OFDM) system.

According to a first aspect of the present invention, there is provided a transmission method for restoration of a carrier frequency in a wireless communication system.

Mapping modulation symbols including data to be transmitted to subcarriers corresponding to the allocated transmission resources;

Mapping a DC tone having a predetermined power to a subcarrier corresponding to a reception carrier frequency used by at least one serviceable receiver;

And converting the frequency domain signal to which the modulation symbols and the DC tone are mapped into an inverse fast fourier transform (IFFT) into a signal in a time domain, and transmitting the same over a system band centered on a transmission carrier frequency. .

According to a second aspect of the present invention, there is provided a transmitting apparatus for restoring a carrier frequency in a wireless communication system.

A signal mapper for generating modulation symbols containing data to be transmitted;

A serial / parallel converter for converting the modulation symbols in parallel and mapping them to subcarriers corresponding to allocated transmission resources;

A DC tone generator for generating a DC tone having a predetermined power and mapping the DC tone to a subcarrier corresponding to a reception carrier frequency used by at least one serviceable receiver;

And a IFFT block for converting the modulation domain and the DC tone mapped frequency domain signal into a signal in a time domain so that the frequency domain signal can be transmitted through a system band centered on a transmission carrier frequency.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In describing the present invention, when it is determined that the detailed description of the related known function or configuration may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted. Terms to be described later are terms defined in consideration of functions in the present invention, and may be changed according to intentions or customs of users or operators. Therefore, the definition should be made based on the contents throughout the specification.

The main subject of the present invention, which will be described later, is to recover a carrier frequency in a broadband wireless communication system, and a transmitter transmits power on a corresponding carrier frequency for a receiver using a carrier frequency different from that of the transmitter. In the following, an extensible OFDM system will be used as a representative wireless communication system using different carrier frequencies in a transceiver, but the present invention is not limited to this system structure.

1 illustrates a transmit and receive frequency band of a scalable OFDM system according to an embodiment of the present invention.

Referring to FIG. 1, the transmitter 102 has a transmission carrier frequency of F _{c_tx} and transmits a signal through a system band corresponding to a system bandwidth allocated around F _{c_tx} . Here, the illustration of the guard band included for each of the minimum frequency unit available is omitted. The signal includes user data and control information for at least one receiver serviced by the transmitter 102. Here, the first receiver 104 supports the extended bandwidth (hereinafter referred to as EB) and receives the signal from the transmitter 102 through the entire system band, and narrow bandwidth (hereinafter referred to as NB). And a second receiver 106 receiving a signal from the transmitter 102 over an allocated receive band that is part of the system band.

The first receiver 104 has a reception carrier frequency equal to F _{c_tx} , which is the center frequency of the system band, to receive data from the transmitter 102 through the entire system band, and the transmitter 102 is loaded on F _{c_tx} . It detects the power of the sending DC (Direct Current) tone and accurately receives signals of the entire system band from the analog part.

On the other hand, the second receiver 106 uses F _{c_rx} , which is the center frequency of the allocated reception band, as a reception carrier frequency in order to receive data from the transmitter 102 through some of the allocated reception bands of the system band. Receive a signal in the band. However, since the carrier power does not exist in the intermediate frequency of the reception band, the second receiver 106 cannot perform frequency recovery in the analog terminal using the carrier power. For this purpose, the second receiver 106 needs a means for accurately detecting the position of F _{c_rx} .

Means for facilitating the receiver to easily recover the received carrier frequency when the transmit and receive carrier frequencies are different from each other, wherein the transmitter transmits a pilot consisting of a known code or sequence over predetermined frequencies in a system band, and the receiver transmits the pilot The frequency offset of the received carrier frequency is corrected by detecting.

2 is a block diagram showing a frequency recovery structure using a pilot according to a preferred embodiment of the present invention.

Referring to FIG. 2, the received signal 220 through the antenna 202 includes a signal of the entire system band and is provided to the mixer 204 and the oscillator 214. The oscillator 214 corrects the frequency of the received signal 220 according to the frequency offset control signal 224 from the phase detector 212, thereby converting the local oscillation signal 228 having the corresponding local oscillation frequency. Occurs. The mixer 204 mixes the local oscillation signal 228 with the received signal 220 to produce a baseband signal centered around the desired receive carrier frequency.

A low pass filter (hereinafter referred to as LPF) 206 filters the baseband signal from the mixer 204 according to the bandwidth of the desired receive band to remove the unwanted band signal. The output signal of the low pass filter 206 is converted into a digital signal through an analog to digital converter (hereinafter referred to as A / D) 208 and then transmitted to the carrier reconstructor 210.

The carrier restorer 210 performs frequency correction on the digital signal by multiplying Exp (j2pi * f _offset ), which is an exponential value of f _offset 226 which is a frequency offset provided from the phase detector 212. The signal corrected by the carrier restorer 210 is provided as a fast Fourier transform (FFT) block (not shown) so that it can be interpreted in the frequency domain.

Meanwhile, the frequency corrected signal includes a pilot of a known pattern. The phase detector 212 uses a pilot included in the frequency corrected signal to determine whether the frequency corrected signal has been correctly received in an allocated reception band, and if not correctly, a frequency offset indicating a corresponding frequency error ( 226). Reflecting the frequency offset 226 in the received signal may be performed by at least one of the oscillator 214 and the carrier recoverer 210. When the oscillator 214 performs, the frequency offset control signal 224 according to the frequency offset 226 is provided to the oscillator 214, the oscillator 214 is frequency correction according to the frequency offset control signal 224 The local oscillation signal 228 is output to the mixer 204. When the carrier decompressor 210 performs, the frequency offset 226 is provided to the carrier decompressor 226, and the carrier decompressor 226 multiplies the received signal by an exponent value equal to the frequency offset 226. Perform frequency correction.

In the case of using the carrier reconstructor 226, it is difficult to precisely and accurately correct frequency due to the fixed point, but frequency correction can be processed in the baseband stage. For this reason, there is no need to exchange additional control signals for mutual control between the digital baseband and the analog baseband in hardware compared to the case of using the oscillator 214.

However, the structure as shown in FIG. 2 causes a problem of increasing the complexity of the receiver in that additional components 210 and 212 for carrier recovery are required. In order to solve this problem, in the preferred embodiment of the present invention, the transmitter transmits an arbitrary power at a position corresponding to the reception carrier frequency. Since the receiver can detect a signal in a frequency band centered on a known reception carrier frequency, a simpler frequency recovery using a phase locked loop (hereinafter referred to as a PLL) can be performed.

3 illustrates the transmit and receive frequency bands of a scalable OFDM system according to a preferred embodiment of the present invention.

Referring to FIG. 3, the transmitter 302 has a transmission carrier frequency of F _{c_tx} and transmits a signal through a system band corresponding to the system bandwidth allocated around F _{c_tx} . Here, the illustration of the guard band included for each of the minimum frequency unit available is omitted. The signal includes user data and control information for at least one receiver serviced by the transmitter 302. The following describes a receiver 304 that supports narrow bandwidth (NB) and receives a signal from the transmitter 302 over an allocated receive band that is part of the system band.

In order to receive data from the transmitter 302 through some of the allocated reception bands of the system band, the receiver 304 uses the signal of the reception band using F _{c_rx} as a reception carrier frequency, which is the center frequency of the allocated reception band. Receive In order to support the receiver 304 having such a narrow bandwidth, the transmitter 302 carries DC power not only at the center frequency of the system band, F _{c_tx,} but also at the reception carrier frequency F _{c_rx} , which is used by the receiver 304. When the receiver 304 can use the lower half band or the upper half band of the system band, the transmitter 302 carries DC power not only on the transmission carrier frequency F _{c_tx} but also on the center frequency of each half band.

Then, the receiver 304 accurately receives the signal of the desired reception band in the analog terminal by detecting the power of the DC tone transmitted by the transmitter at F _{c_rx} which is the intermediate frequency of the allocated reception band.

4 is a block diagram illustrating a transmitter structure for a scalable OFDM system according to a preferred embodiment of the present invention.

Referring to FIG. 4, a transmitter includes a signal mapper 402, a serial to parallel converter 404, a DC tone generator 414, IFFT block 406, parallel to serial converter (hereinafter referred to as P / S) 408 and digital to analog converter (hereinafter referred to as D / A) 410 do.

The signal mapper 402 inputs an encoded bit stream including user data and control information for all of the receivers serving to receive modulation symbols according to a modulation scheme corresponding to the encoded bit stream. Converts to the complex values represented and outputs them. S / P 404 converts the serial data containing the modulation symbols into parallel data and forwards it to the corresponding input taps of IFFT block 406. Here, each input tap represents each subcarrier constituting a system band, and the parallel data is mapped to subcarriers corresponding to transmission resources allocated by a scheduler (not shown).

The IFFT block 412 receives the DC tone from the DC tone generator 414 as an input tap corresponding to the received carrier frequency of each of the receivers serving and IFFT-converts the parallel data to output a time domain signal. To this end, the DC tone generator 414 knows in advance the reception carrier frequencies corresponding to the center frequencies of the reception bands of the serving receivers, and has a DC having a virtual carrier power determined in advance or determined according to transmission power. A tone is generated and mapped to the input taps of IFFT block 406 corresponding to the received carrier frequencies. That is, in the present invention, the power of the DC tone is set to a non-zero constant value.

The time domain signal generated by the IFFT block 406 is converted into a serial signal by the parallel / serial converter 408, and then converted into an analog signal by the digital / analog converter 410 and then the transmitter carrier frequency of the transmitter is converted. It is carried in the system band centered and transmitted over the air through the antenna 412.

5 is a block diagram showing a frequency recovery structure using carrier power according to an embodiment of the present invention. As shown, frequency recovery is handled using a PLL at the analog stage of the receiver.

5, the received signal 520 through the antenna 502 includes signals of the entire system band (or the receivable band of the antenna 502), and the mixer 504 and the phase locked loop (PLL) ( 510. The PLL 510 outputs a frequency offset control signal for the oscillator 518 by the operation described below.

The oscillator 518 generates a local oscillation signal 528 having a corresponding local oscillation frequency according to the frequency of the received signal 520. The mixer 504 mixes the local oscillation signal 528 with the received signal 520 to generate a baseband signal centered on the received carrier frequency. A low pass filter (LPF) 506 filters the baseband signal from the mixer 504 according to the bandwidth of the desired receive band to remove the unwanted band of signals. The output signal of the lowpass filter 506 is converted into a digital signal through an analog-to-digital converter (A / D) 508, and then a fast Fourier transform (FFT) block (not shown) to be interpreted in the frequency domain. Is provided.

The operation of the PLL 510 will be described in detail as follows. The PLL 510 includes a phase detector 512, a loop filter 514, and a numerically controlled oscillator (NCO) 516.

The received signal 520 is input to the phase detector 512. The phase detector 512 detects a DC tone included in the received signal 520 and receives e (t) 524 which is a phase error indicating a difference between a frequency position at which the DC tone is detected and a reception carrier frequency set in the receiver. Decide The loop filter 514 loop-filters the e (t) 524 and converts it into an e _loop (t) 526 which is a DC voltage signal, and the NCO 516 converts the voltage of the e _loop (t) 526. A locally generated signal y (t) 522 having a frequency according to the signal is generated and provided to the phase detector 512. The phase detector 512 provides the y (t) 522 to the oscillator 518, while the y (t) 522 is the received carrier frequency and the phase error e (t) for the received signal 520. 524 is used to calculate. Oscillator 518 generates a local oscillation signal 528 having a frequency suitable for converting the received signal 520 into a baseband signal in accordance with the signal provided from the phase detector 512 to provide to the mixer 504. do.

Meanwhile, in the detailed description of the present invention, specific embodiments have been described, but various modifications are possible without departing from the scope of the present invention. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be defined not only by the scope of the following claims, but also by those equivalent to the scope of the claims.

In the present invention operating as described in detail above, the effects obtained by the representative ones of the disclosed inventions will be briefly described as follows.

According to the present invention, when the transmission carrier frequency and the reception carrier frequency are different, such as in an expandable OFDM system, the receiver can accurately restore the reception carrier frequency through a simpler structure by sensing power at a specific carrier frequency.

Claims (6)

In the transmission method for the recovery of the carrier frequency in a wireless communication system, Mapping modulation symbols including data to be transmitted to subcarriers corresponding to the allocated transmission resources; Mapping a DC tone having a predetermined power to a subcarrier corresponding to a reception carrier frequency used by at least one serviceable receiver; And converting the frequency domain signal to which the modulation symbols and the DC tone are mapped into an inverse fast fourier transform (IFFT) into a signal in a time domain, and transmitting the resultant signal through a system band centered on a transmission carrier frequency. Transmission method. The method of claim 1, wherein the DC tone, A transmission method characterized by having a predetermined constant power. The transmission method according to claim 1, wherein the at least one reception carrier frequency is different from the transmission carrier frequency. In the transmitting device for the recovery of the carrier frequency in a wireless communication system, A signal mapper for generating modulation symbols containing data to be transmitted; A serial / parallel converter for converting the modulation symbols in parallel and mapping them to subcarriers corresponding to allocated transmission resources; A DC tone generator for generating a DC tone having a predetermined power and mapping the DC tone to a subcarrier corresponding to a reception carrier frequency used by at least one serviceable receiver; And an inverse fast fourier transform (IFFT) block for transforming the frequency domain signal to which the modulation symbols and the DC tone are mapped to a signal in a time domain so that the frequency domain signal is transmitted through a system band centered on a transmission carrier frequency. A transmitting device, characterized in that. The method of claim 4, wherein the DC tone, And a power having a predetermined constant value. The transmission device according to claim 4, wherein the at least one reception carrier frequency is different from the transmission carrier frequency.

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