TECHNICAL FIELD

The present invention relates to an OFDM/OFDMA (Orthogonal Frequency Division Multiplexing/Orthogonal Frequency Division Multiplexing Access) transmission system, more particularly, to the method and apparatus for generating a pilot tone capable of eliminating an interference by users within a different cells or sectors in an OFDMA system, and the channel estimation method and apparatus corresponding to it.

BACKGROUND ART

OFDM or OFDMA which is based it is a multicarrier modulation scheme which parallelly transmits data by using a multiple orthogonal subcarriers instead of a single carrier having a broad band. It is based on the fact that each subchannel of a narrowband has the flat fading characteristic in the frequency selective fading channel having the very large ISI (Inter-Symbol Interference).

In OFDM, as the symbol is determined on the frequency domain, it is necessary to have an equalizer for frequency domain in order to compensate for the channel distortion of the received symbol. For this, in addition to sending data symbol, the transmitter of the OFDM transmission system transmits the pilot symbol used for the channel estimation for the equalization of data symbol by estimating the characteristics of the channel transmitting a signal.

FIG. 1is a block diagram that shows the configuration OFDM receiver of the related art, showing schematically only the unit that restores data from the baseband signal obtained from the received signal.

A burst symbol extracting unit100extracts the OFDM symbol from the baseband signal obtained from the received signal by the RF (Radio Frequency) processing unit (not shown). As to the OFDM symbol which is extracted by the burst symbol extracting unit100, it is applied to an equalizer108, after the CP (Cyclic Prefix) which is inserted by a CP deleting unit102from the transmitter is eliminated and FFT (Fast Fourier Transform) is performed by an FFT unit104. The equalizer108compensates for the channel distortion according to the channel characteristic value which is estimated by a channel estimating unit106for the FFT data signal.

After being demodulated in a demodulator110, the signal compensated the channel distortion performs Viterbi decoding by a decoder112and data are restored by the determination of a deciding unit114. The channel estimating unit106performs the channel estimation by using the pilot tone. Pilot tones are arranged between OFDM data tones. In the meantime, when the channel is estimated, the pilot tone is interfered by the pilot tones from the cell of the adjacent base station or other user of the sector. Therefore, the pilot tone interference cancellation technology capable of the exact channel estimation in spite of the interference signal is required.

DISCLOSURE OF INVENTION

Technical Problem

Accordingly, an object of the present invention is to solve at least the problems and disadvantages of the related art. The present invention is to provide the pilot tone generating method and apparatus in an orthogonal frequency division multiple access system capable of generating the pilot tone for the exact channel estimation without the interference of the pilot tone of the adjacent base station that affects the pilot tone.

Another object of the present invention is to provide the channel estimation method and apparatus using the pilot tone generating method and apparatus in the orthogonal frequency division multiple access system.

Technical Solution

In order to accomplish the object, according to an aspect of the present invention, provided is a pilot tone generating method in an orthogonal frequency division multiple access system which uses for subcarriers having an orthogonality and transmits data by frame, which comprises the steps of: (a) inserting a data tone and a pilot tone into the frame; (b) PRBS (Pseudo Random Binary Sequence) masking for the data tone; and (c) masking an orthogonal code for the pilot tone.

In accordance with an aspect of the present invention, at the step (b), masking the orthogonal code for eight pilot tones forming a rectangular window form, when the frame is a down-link subframe. The masking of the orthogonal code is performed by moving the rectangular window from left to right, from top to bottom, by pilot tone inserted into the frame. A set of the orthogonal code for eight pilot tones is an eight-bit orthogonal code set having an orthogonality for a different code. At the step (b), masking the orthogonal code for four pilot tones forming a tile of an up-link subframe, when the frame is the up-link subframe. A set of the orthogonal code for four pilot tones is a four-bit orthogonal code set having an orthogonality for a different code. At the step (c), the masking is performed by allocating the same orthogonal code to sectors within each cell and allocating a different orthogonal code to the each cell, when FRF (Frequency Reuse Factor)-3 is applied. At the step (c), the masking is performed by allocating a different orthogonal code to each sector within a cell, when FRF (Frequency Reuse Factor)-1 is applied. After the step (c), an aspect of the present invention further comprises the step (d) transmitting the masked orthogonal code information. At the step (d), the orthogonal code information is included in a DCD TLV (Downlink Channel Descriptor Type, Length, Value) field of a NBR-ADV message (Neighbor Advertisement Message).

According to another aspect of the present invention, provided is a pilot tone generating apparatus of an orthogonal frequency division multiple access (OFDMA) system, which comprises a data and pilot inserting unit for inserting a data tone and a pilot tone into a frame of the OFDMA system; a PRBS (Pseudo Random Binary Sequence) masking unit for masking a PRBS for the data tone; and an orthogonal code masking unit for masking an orthogonal code for the pilot tone.

The orthogonal code masking unit masks the orthogonal code for eight pilot tones forming a rectangular window form when the frame is a down-link subframe, and masks the orthogonal code for four pilot tones forming a tile of an up-link subframe when the frame is the up-link subframe. The orthogonal code masking unit masks the orthogonal code by moving the rectangular window from left to right, from top to bottom, by pilot tone inserted into the frame. The orthogonal code masking unit masks the orthogonal code by allocating the same orthogonal code to sectors within each cell and allocating a different orthogonal code to the each cell, when FRF (Frequency Reuse Factor)-3 is applied. The orthogonal code masking unit masks the orthogonal code by allocating a different orthogonal code to each sector within a cell, when FRF (Frequency Reuse Factor)-1 is applied.

According to still another aspect of the present invention, provided is a channel estimation method by using a pilot tone in a receiver receiving an orthogonal frequency division multiple signal by frame, which comprises the steps of: (a) extracting a pilot tone, which corresponds to a channel for estimating, masked with an orthogonal code from a received signal; (b) unmasking the extracted pilot tone; and (c) estimating a channel by calculating an average of the unmasked pilot tones.

At the step (b), unmasking the masked orthogonal code for eight pilot tones forming a rectangular window form when the frame is a down-link subframe. The unmasking of the orthogonal code is performed by moving the rectangular window from left to right, from top to bottom, by channel. At the step (b), unmasking the masked orthogonal code for four pilot tones forming a tile of up-link subframe, when the frame is the up-link subframe. At the step (b), the unmasking is performed by using the orthogonal code information received before the step (a). The orthogonal code information is an orthogonal code masking information which is included in a NBR-ADV message (Neighbor Advertisement Message) field.

According to still another aspect of the present invention, provided is a channel estimation apparatus for estimating a channel by using a pilot tone in an orthogonal frequency division multiple access system, which comprises a pilot tone extracting unit for extracting, a pilot tone, which is inserted within a frame with data tone, masked with an orthogonal code; a pilot tone unmasking unit for unmasking of the pilot tone extracted from the pilot tone extracting unit by using an orthogonal code information; and a channel estimation operating unit for estimating a channel by calculating an average of the pilot tones which is unmasked in the unmasking unit.

The unmasking unit unmasks the masked orthogonal code for eight pilot tones forming a rectangular window form when the frame is down-link subframe, and unmasks the masked orthogonal code for four pilot tones forming a tile of an up-link subframe when the frame is the up-link subframe. The pilot tone unmasking unit unmasks the masked orthogonal code by moving the rectangular window from left to right, from top to bottom, by channel.

Advantageous Effects

According to the present invention, even when the interference signal exists, the relatively exact channel estimation is possible by using an orthogonal code so that the portable Internet (WiBro/WiMax) system performance can be improved. Particularly, in a channel estimation, an interference between users that is the interference by the users of other cell or sector can be eliminated. Further, a much more performance improvement can be implemented as the signal can be coherently combined in a diversity combining. Additionally, the interference power can be accurately measured as far as possible, so that the performance of CINR (Carrier Interference to Noise Ratio) measurement can be improved.

The present invention can be applied to the OFDM system including the WiBro system. And even if the orthogonal code is moved to the time and frequency axis, the orthogonality is still maintained so that a successive channel estimation is possible. Further, the size of the orthogonal code window is determined by the coherence time and the coherence bandwidth. By measuring the power loaded in a coding word except the desired orthogonal code word, the interference power can be easily calculated.

