KR100362872B1 - Channel effect compensation apparatus in frequency hopping/orthogonal frequency division multiplexing system - Google Patents

Abstract

The present invention relates to a frequency hopping / orthogonal frequency division multiplexing system, and more particularly to an equalizer for compensating for channel effects.

The present invention is a receiver of a frequency hopping / orthogonal frequency division multiplexing system for receiving an orthogonal frequency division multiplex signal including a pilot symbol, and receives a synchronized frame to perform multiple demodulation of the orthogonal frequency division on a symbol basis from the symbol. A fast Fourier transform unit that separates and outputs subcarriers, and detects subcarriers of a pilot symbol among the symbols to measure a channel state, and compensates and outputs a channel effect for each of the subcarriers of a used data symbol using the measured information It is characterized by consisting of an equalizer.

Description

CHANNEL EFFECT COMPENSATION APPARATUS IN FREQUENCY HOPPING / ORTHOGONAL FREQUENCY DIVISION MULTIPLEXING SYSTEM}

The present invention relates to a channel effect compensation device of a frequency hopping / orthogonal frequency division multiplexing system, and more particularly, to an apparatus for compensating for channel effect using pilot symbols inserted in symbol units.

In general, a frequency hopping code division multiplex access (FH / CDMA) mobile communication system is a set of frequencies according to a certain form determined by a pseudo-random code. It is to jump carrier frequency within. An Orthogonal Frequency Division Multiplex (OFDM) communication system carries data on a plurality of orthogonal subcarriers. The transmitter of the OFDM communication system carries data on a plurality of orthogonal subcarriers and transmits the data to the receiver so that a more accurate decoding operation must be performed to maintain orthogonality of the received data. In addition, the performance of the equalizer to compensate for the attenuation and propagation time delay variation for each frequency in the channel should also be improved.

Recently, an FH / OFDM system that combines an FH / CDMA mobile communication system and an OFDM communication system has emerged. In such an FH / OFDM mobile communication system, a plurality of subcarriers having orthogonality exist in one frequency band in which frequency is hopping. Since the randomly hopping frequency bands are affected by different channels during transmission, the equalization method used in the conventional OFDM communication system cannot perform the exact equalization required by the characteristics of the FH / OFDM communication system.

As described above, in the frequency hopping / orthogonal frequency division multiplexing mobile communication system in which a frequency hopping code division multiple access mobile communication system and an orthogonal frequency division multiplexing communication system are combined, the conventional equalization method is frequency hopping / orthogonal frequency division multiplexing. There is a problem that accurate demodulation cannot be performed in a communication system. Therefore, a new equalization method is required to perform accurate demodulation in frequency hopping / orthogonal frequency division multiplexed mobile communication systems.

Accordingly, an object of the present invention is to provide a transmitter for inserting and transmitting a pilot data symbol in a frame data sequence frequency hopping in units of frames in order to compensate for channel effects of a receiver during data transmission.

Another object of the present invention is to provide a frequency effect compensation apparatus for receiving data in which pilot symbols are inserted in a data sequence on a frame basis and compensating for frequency effects by using the pilot symbols of the received data.

In order to achieve the above object, the present invention provides an orthogonal frequency division multiple modulation for outputting an orthogonal frequency division multiple symbol that receives a predetermined signal and modulates and outputs a predetermined signal in a transmitter of a frequency hopping / orthogonal frequency division multiple system. And a guard interval insertion unit for inserting a guard interval into the hopped quadrature frequency division multiple symbol, and a pilot symbol insertion unit for inserting and outputting pilot symbols at a predetermined interval into the orthogonal frequency division multiple symbol string into which the guard interval is inserted. And a digital / analog converter for converting the orthogonal frequency division multiple symbol string into which the pilot symbol is inserted into an analog orthogonal frequency division multiplexing signal, and outputting a digital hopping code generator for generating a frequency hopping code. Receive a divided multiple signal, receive the frequency hopping code, And a frequency hopping unit for hopping a frequency division multiplexed signal into a random frequency band.

Another object of the present invention is a receiver of a frequency hopping / orthogonal frequency division multiplexing system for receiving an orthogonal frequency division multiplex signal including a pilot symbol, and receives orthogonal frequency division multiplexing on a symbol unit by receiving a data string of a synchronized frame. A fast Fourier transform unit demodulates and outputs the subcarriers separated from the symbol, and detects the subcarriers of the pilot symbol among the symbols, and measures a channel state. The channel for each of the subcarriers of the used data symbol is measured using the measured information. Characterized in that it consists of an equalizer for compensating the output.

1 is a block diagram illustrating a frequency hopping / orthogonal frequency division multiplexing system transmitter according to an exemplary embodiment of the present invention.

2 illustrates a data structure in which a pilot symbol is inserted according to an embodiment of the present invention.

3 is a block diagram illustrating a frequency hopping / orthogonal frequency division multiplexing system receiver according to an exemplary embodiment of the present invention.

4 is a diagram illustrating an equalizer structure of a frequency hopping / orthogonal frequency division multiplexing system receiver according to a first embodiment of the present invention.

5 is a diagram illustrating an equalizer structure of a frequency hopping / orthogonal frequency division multiplexing system receiver according to a second embodiment of the present invention.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. First, in adding reference numerals to the components of each drawing, it should be noted that the same reference numerals have the same reference numerals as much as possible even if displayed on different drawings. In the following description of the present invention, if it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted.

In the present invention, a new pilot symbol is inserted and transmitted in a frequency band frequency hopping by the transmitter for accurate decoding, and the receiver detects the pilot symbol to compensate channel effects for data in each hopping frequency band.

First, a transmitter configuration of a frequency hopping / orthogonal frequency division multiplexing mobile communication system according to an embodiment of the present invention will be described with reference to FIG.

The quadrature frequency division multiplexing modulator 101 converts the input data into an inverse fast Fourier transform and outputs the same. The data t input to the orthogonal frequency division multiplexing modulator 101 is signal mapped data. Specifically, the orthogonal frequency division multiplexing modulator 101 converts serially input data into parallel, converts parallel data into inverse fast Fourier transform, and then converts the serial data into serial data and outputs the serial data. The data output from the orthogonal frequency division multiplexing modulator 101 is called an orthogonal frequency division multiplexing symbol. The guard interval inserting unit 103 receives the orthogonal frequency division multiple symbol in units of frames in order to prevent interference between OFDM effective symbols due to multipath, copies a predetermined period of the orthogonal frequency division multiple symbol in the unit of frame, Insert the copied section in front and print it. The pilot pattern inserting unit 110 receives an orthogonal frequency division multiple symbol in units of frames output from the guard period inserting unit 103 and inserts and outputs a pilot symbol. The pilot pattern inserting unit 110 generates the pilot symbols in the orthogonal frequency division multiple symbol output from the pilot symbol inserting unit 107 and the guard interval inserting unit 103 to generate and output the pilot symbols. It consists of a mux 105 to insert and output the pilot symbol. Since the frequency hopping is performed in units of frames, the pilot symbols are inserted at predetermined positions in the units of frames. For example, in the present invention, as shown in FIG. 2, the data can be inserted at the front of the data after the FSP or at another position. In all other frames, the insertion positions of pilot symbols must be identical. This is because the transmitting side and the receiving side must know the position of the pilot symbol. If the position of the pilot symbol is randomly inserted in each frame by a predetermined code, the transmitting side should provide the information about this to the receiving side. Alternatively, the transmitting side should insert a pilot symbol in each frame with a random code known to the receiving side. The digital / analog converter 111 converts an OFDM symbol output from the pilot symbol inserting unit 107 into an analog signal and outputs the analog signal. The frequency hopping code generator 113 generates a code for randomly hopping the frequency and outputs the code to the frequency hopping unit 115. The frequency hopping code may use a PN code or a Read Solomon code. The frequency hopping unit 115 receives an orthogonal frequency division multiplex symbol (hereinafter, referred to as an "orthogonal frequency division multiplexing signal") converted into an analog signal and receives the frequency hopping code from the frequency hopping code generator 113. The orthogonal frequency division multiplexing signal is randomly frequency hopping to output the transmission signal s (t).

2 is a diagram illustrating a data structure in which a pilot symbol is inserted according to an embodiment of the present invention, and shows that a pilot symbol and a frame synchronous pattern (FSP) are inserted in front of a frame including N data. Giving. Two or more pilot symbols may be inserted at regular intervals instead of only one pilot symbol. However, if a large number of pilot symbols are inserted, the call quality may be degraded due to a lot of data loss. Therefore, the number of pilot symbols should be appropriately determined. In the present invention, for example, as shown in FIG. 2, the pilot symbols are inserted and output after the FSP.

3 is a block diagram illustrating a frequency hopping / orthogonal frequency division multiplexing system receiver according to an exemplary embodiment of the present invention. Hereinafter, a configuration of a receiver and a reception operation of a signal s (t) transmitted in FIG. 1 will be described with reference to FIG. 3.

The received signal s (t) is output to the reverse frequency hopping section 203. The reverse frequency hopping part 203 receives the frequency hopping code from the frequency hopping code generating part 201 which generates the same code as the frequency hopping code generated by the frequency hopping code generating part 113 of the transmitter described in FIG. It takes the input and outputs it by making reverse frequency hopping. The reverse frequency hopping unit 203 is for restoring the quadrature frequency division multiplexed signal that has been frequency hopping in the transmitter to the original frequency. The analog / digital converter 205 receives the transmission signal input from the reverse frequency hopping unit 203 and converts the digital signal into a digital frame, that is, an orthogonal frequency division multiple symbol as shown in FIG. 207). The FFT window position recovery unit 207 receiving the frame detects a frame sync pattern (FSP) from the frame and finds a starting point of the frame to restore the position of the FFT window. The FFT window position restored data is input to the serial / parallel converter 205. The serial / parallel conversion unit 205 receives the input data in symbol units and processes the received data in parallel into N sample data and outputs the parallel data to the FFT 207. The FFT 207 receives sample data output from the serial / parallel conversion unit 205 and performs fast Fourier transform to output N subcarriers. The equalizer 209 receives the N subcarriers output from the FFT 207 and performs an equalization process in the frequency domain and outputs the same to the parallel / serial converter 211. The parallel / serial converter 211 converts N equalized N parallel subcarriers output from the equalizer 209 in series and outputs data d (t).

4 is a view showing the equalizer structure of FIG. 3 according to the first embodiment of the present invention.

Referring to FIG. 4, the FFT 207 receives n sample data in parallel from the serial / parallel conversion unit 205 and performs Fourier transform on n subcarriers k (1), k (2), .. outputs., k (n) to the selector 303. The selector 303 receives a predetermined selection signal from an upper layer, and if the selection signal is a pilot symbol selection signal, n subcarriers k (n) {n = 1, 2, ... , n} is outputted to the channel estimator 305, and if the selection signal is a data selection signal, the n subcarriers k (n) {n = 1, 2, ..., n} are supplied to the channel compensator 309. Will output The channel estimator 305 receives a pilot symbol k (n) {n = 1,2, ..., n} consisting of n subcarriers from the selector 303 and estimates channel states of respective subcarriers. The channel coefficients h (1), h (2), ..., h (n) are output to the channel estimation coefficient storage unit 307 and stored. The channel estimation coefficient storage unit 307 receives the selection signal, and stores the n channel estimation coefficients input by the channel estimation unit 305 when the selection signal is a pilot symbol selection signal, and the selection signal selects data. If it is a signal, the stored channel estimation coefficient is output to the channel compensator 309. The channel compensator 309 receives n subcarriers k (n) carrying data from the selector 303, receives channel estimate coefficients from the channel estimation coefficient storage unit 307, and receives the n subcarriers k (n). ) Is multiplied by the corresponding channel estimation coefficient to compensate for the channel effect and outputs data d (t).

FIG. 5 is a diagram illustrating an equalizer structure of a frequency hopping / orthogonal frequency division multiplexing system receiver according to a second embodiment of the present invention. In FIG. 4, when a channel effect occurs in a pilot symbol used to compensate for channel effects, FIG. In other words, it has a configuration for more accurate channel estimation.

The FFT 207 receives n parallel data from the serial / parallel conversion unit 205 and performs Fourier transform to select n subcarriers k (1), k (2), ..., k (n). Will output The selector 303 receives a predetermined selection signal from an upper layer, and if the selection signal is a pilot symbol selection signal, n subcarriers k (n) {n = 1, 2, ... , n} are output to the weighted averager 304, and if the selection signal is a data selection signal, the n subcarriers k (n) {n = 1,2, ..., n} are transmitted to the channel compensator 309. Output

The weighted averager 304 receives the input subcarriers k (n), calculates a weighted average of arbitrary subcarriers and carriers before and after the subcarriers, and outputs the weighted average to the channel estimator 305. In the above, a weighted average of three subcarriers such as itself, front and back, and three subcarriers can be calculated, but a weighted average of two carriers, front and back, can be obtained from the center, or a weighted average of more carriers can be obtained. This is done for all carriers. In this operation, if a specific subchannel signal of the pilot symbol signals received by the receiver as shown in FIG. 4 has a large noise component unlike an adjacent signal, that is, a channel effect occurs due to multipath or interference, etc. 4 is for preventing performance degradation caused by equalization of received data using subchannel characteristics of pilot symbols having a channel effect. In other words, even if the received data symbol has no channel effect, the equalizer is prevented from compensating for the channel effect of the data symbol in which the channel effect has not occurred by using the subchannel characteristics of the pilot symbol in which the channel effect occurs. This is to prevent performance degradation for all of the subchannels of the data symbols corresponding to any subchannels of the generated pilot symbols.

Hereinafter, the weighted average calculation method of the weighted averager 304 will be described. In describing the weighted average calculation method, three cases will be described.

(1) First, when two adjacent pilot symbols are referred to, that is, a weighted average of an arbitrary subcarrier of a pilot symbol and two subcarriers adjacent to the arbitrary subcarrier is obtained. When the weighting coefficient of any subcarriers to be weighted average is called a and the weighting coefficients of two adjacent subcarriers is b, 'b + a + b = 2b + a = 1' must be established. For example, when a = 3/4, it should have a value of b = 1/8.

(2) A weighted average is obtained by referring to four second adjacent subcarriers. In other words, when a is a target subcarrier, a weighted average value is obtained by referring to b and c on both sides of the a. In this case, similarly to the first, the sum of the weighting values must establish 'c + b + a + b + c = 2c + 2b + a = 1'.

(3) Third, an average of three subcarriers including two subcarriers adjacent to the target subcarrier is obtained, wherein the weighting coefficients of the three subcarriers are the same. This is represented by Equation 1 below.

The results of experiments using the three examples are shown in Table 1.

Pilot average power One One One One Peripheral Pilot Reference Never (One) (2) (3) Eb / No for BER 104 10.7 dB 9.9 dB 9.4 dB 9.1 dB Improve performance - 0.8 dB 1.3 dB 1.6 dB

As shown in Table 1, it can be seen that the performance is improved in the equalizer of the present invention.

The channel estimator 305 receives a pilot symbol k '(n) {n = 1, 2, ..., n}, which consists of n subcarriers output from the weighted averager 304, for each subcarrier. The channel state is estimated and the channel coefficients h (1), h (2), ..., h (n) are output to the channel estimation coefficient storage unit 307 and stored. The channel estimation coefficient storage unit 307 receives the selection signal, and stores the n channel estimation coefficients input by the channel estimation unit 305 when the selection signal is a pilot symbol selection signal, and the selection signal selects data. If it is a signal, the stored channel estimation coefficient is output to the channel compensator 309. The channel compensator 309 receives a data symbol consisting of n subcarriers k (n) from the selector 303, receives a channel estimate coefficient from the channel estimation coefficient storage unit 307, and receives the n subcarriers k ( n) is multiplied by the corresponding channel estimation coefficient to compensate for the channel effect and outputs data d (t).

As described above, the present invention has an advantage that a receiver can perform more accurate equalization by inserting and transmitting a pilot signal in symbol units in a frequency hopping quadrature frequency division multiplexing system.

In addition, by obtaining a weighted average value of the pilot symbols and estimating channel conditions, performance degradation due to noise introduced into the pilot symbols can be reduced.

Claims (13)

delete delete delete delete delete delete delete delete delete A receiver in a frequency hopping / orthogonal frequency division multiplexing system for receiving an orthogonal frequency division multiplex signal containing pilot symbols, A fast Fourier transform unit for receiving the synchronized frames and performing orthogonal frequency division multiple demodulation on a symbol basis to separate and output subcarriers from the symbol; Equalizer for measuring the channel state by detecting the sub-carriers of the pilot symbol of the symbol, and using the measured information to compensate for the channel effect for each of the sub-carriers of the used data symbol, and outputs; The equalizer, A selector for receiving subcarriers output from the demodulator, receiving a predetermined signal, and separating and outputting original data subcarriers and pilot subcarriers; A weighted average that receives pilot subcarriers from the selector, obtains a weighted average of a predetermined number of subcarriers adjacent to each subcarrier, and outputs a weighted average subcarriers; A channel estimator for estimating channel states of the weighted average subcarriers and outputting a channel estimation coefficient; A channel estimation coefficient storage unit for receiving the predetermined signal, receiving and storing channel estimation coefficients according to the signal, or outputting a prestored channel estimation coefficient; And a channel compensator for compensating and outputting channel effects of the subcarriers of the data by multiplying the subcarriers of the data by channel estimation coefficients when the subcarriers of the data are input from the selector. Compensator. 12. The apparatus of claim 10, wherein the weighted averager performs each of the subcarriers. 11. The channel effect compensator of a frequency hopping / orthogonal frequency division multiplex system according to claim 10, wherein the weighted averager outputs a weighted average of three subcarrier powers. 13. The apparatus of claim 12, wherein the sum of weighted average values of the three subcarrier powers is '1'.