KR100449225B1 - Transmission Diversity Apparatus In Radio Communication System - Google Patents

Abstract

The present invention relates to a transmission diversity apparatus in a wireless communication system which can obtain a diversity gain capable of improving system capacity and performance while maintaining the standard of the IEEE802.11a system for the wireless Internet. The present invention relates to a transmission diversity apparatus. FEC encoder that encodes the signal; Fast Fourier transformer (IFFT) for converting the signal into a time domain signal, guard section insertion section for inserting a guard section for multipath fading into the output signal of the inverse fast Fourier transformer, digital signal output from the guard section insertion section Digital to analog signal A diver capable of improving the capacity and performance of the system by implementing a receiver as a high frequency transmitter that up-converts the signal output from the / analog converter and the digital / analog converter to high frequency and then transmits the signal to the transmitting antenna to radiate radio signals in the space. It provides a city device.

Description

Transmission Diversity Apparatus In Radio Communication System

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transmission diversity apparatus in a wireless communication system. In particular, in the IEEE802.11a system for the wireless Internet, a diversity gain capable of improving system capacity and performance while maintaining an orthogonal frequency division multiplexing (OFDM) standard The present invention relates to a transmit diversity apparatus in a wireless communication system capable of obtaining the same.

In general, in response to an increasing demand for high-speed multimedia data services, element-specific techniques for improving signal quality and spectrum efficiency of a wireless communication system for the purpose of providing high-speed data transmission service in a recent mobile radio channel. Development is underway. That is, efficient coding techniques, modulation schemes, signal processing techniques for improving the quality and spectral efficiency of wireless communication, and techniques for sharing limited spectrum among other high-capacity users.

The information capacity of a wireless communication system can be significantly increased by using multiple transmit / receive antennas. An effective approach for increasing the data rate for wireless channels is to use coding techniques suitable for multiple transmit antennas. This coding technique is a space-time coding (STC) technique. Space-time coding is a coding technique using multiple transmit antennas. Space-time coding is a technique that introduces time and spatial correlation to signals transmitted from other antennas to provide code gain without sacrificing the full diversity effect and bandwidth at the receiver.

In general, space-time code schemes are classified into space-time trellis code (STTC) and space-time block code (STBC). Decoded by the Viterbi algorithm of decoding of the STTC, the complexity of the decoder increases according to the diversity order and the transmission rate when the number of transmit antennas is fixed. In contrast, STBC uses a very simple maximum likelihood decoding algorithm at the receiver.

On the other hand, orthogonal frequency division multiplexing (OFDM) has been applied to various fields as an effective method for overcoming multipath fading and high-speed data transmission in a mobile radio channel. A typical example is IEEE802.11a, an OFDM system for wireless Internet. Much research is being conducted on a system combining a transmission diversity scheme using STTC in such an OFDM system.

In an OFDM system having transmit diversity, two or more different signals are simultaneously transmitted through different antennas, where the received signals are overlapped signals transmitted with the same transmit power. If the channel parameters corresponding to each transmit / receive antenna pair are not properly obtained, performance deterioration is inevitable. Therefore, considering the above, the design of a training sequence for channel estimation is of paramount importance in an OFDM system having transmit diversity. However, applying transmit diversity to a system with specifications without considering transmit diversity is not so simple.

1 and 2 show the configuration of a transmitter and a receiver applied to a conventional IEEE802.11a system.

First, the transmitter shown in FIG. 1 encodes data input from a forward error correction (FEC) encoder 11 and interleaves the encoded data in an interleaver 12. An inverse fast Fourier transformer (IFFT) 13 performs an inverse fast Fourier transform to convert a signal in the frequency domain into a signal in the time domain. Next, a guard interval is inserted in the guard interval inserter 14 so that the signal output from the IFFT 13 is robust to multipath fading, and then the guard interval in the digital / analog converter 15 is inserted. (GI) converts the added digital signal into a corresponding analog signal. This signal is converted into an RF signal at the transmitter 16 and then amplified and transmitted through the transmit antenna 17.

Next, in the receiver shown in Fig. 2, a signal is passed through a channel including multipath fading and noise. The signal received through the receiving antenna 21 is converted into a digital signal by the analog / digital converter 23 after passing through the receiver 22. Next, the guard interval removing unit 24 removes the guard interval from the converted digital signal. In the fast Fourier transformer (FFT), a signal in the frequency domain is performed by performing fast Fourier transform on a time domain signal. Convert to The output of the FFT 25 is de-interleaved at the deinterleaver 26 and then decoded by the FEC decoder 27.

3 shows a frame structure of a typical IEEE802.11a system.

One frame consists of ten short training sequences, two long training sequences, one signal block, and several data blocks. Basically, transmit diversity should transmit data through each antenna simultaneously using multiple transmit antennas.

The concept of transmit diversity with two transmit antennas 31 and 32 and one receive antenna 33 is shown in FIG. When the frame of FIG. 3 is simultaneously transmitted through two antennas as shown in FIG. 4, since the signals transmitted from the transmitting antennas 31 and 32 are superimposed on the receiving side, the frames of FIG. 3 are substantially received from each transmitting antenna 31 and 32. It is very difficult to distinguish the channel characteristics corresponding to the path to the antenna 33.

In general, in order to apply the STTC to the IEEE802.11a system, it is inevitable to change the standard, and in the wireless communication system using the conventional OFDM scheme, the termination of trellis for decoding the STTC in the OFDM block Since additional symbols are required for termination, transmission efficiency is reduced.

Accordingly, the present invention has been proposed to solve various problems occurring in the wireless communication system (especially, IEEE802.11a system) for the wireless Internet using the two transmission antennas as described above.

SUMMARY OF THE INVENTION An object of the present invention is to provide a transmit diversity apparatus in a wireless communication system which can obtain a diversity gain capable of improving system capacity and performance while maintaining the standard of the IEEE802.11a system for the wireless Internet.

That is, an object of the present invention is to provide a transmission diversity apparatus which can obtain diversity gain without changing the standard of the IEEE802.11a system standard for wireless Internet.

"Transmission diversity device in a wireless communication system" according to the present invention for achieving the above object,

In a wireless communication system comprising a transmitter for transmitting the OFDM data and a receiver for receiving the transmitted data,

The transmitter,

An FEC encoder for encoding transmission data;

An interleaver for interleaving the output data of the FEC encoder;

An STBC encoder for encoding data output from the interleaver into a space-time block code to provide a substantial transmit diversity gain;

An inverse fast Fourier transformer (IFFT) for converting a signal in the frequency domain output from the STBC encoder into a signal in the time domain;

A guard section inserting section for inserting a guard section corresponding to multipath fading into an output signal of the inverse fast Fourier transformer;

A digital / analog converter for converting the digital signal output from the protection section insertion unit into an analog signal;

And converting the signal output from the digital-to-analog converter into a high frequency and transmitting the signal to a transmitting antenna to radiate a radio signal in a space.

In addition, another embodiment of the "transmission diversity apparatus in a wireless communication system" according to the present invention for achieving the above object,

In a wireless communication system comprising a transmitter for transmitting the OFDM data and a receiver for receiving the transmitted data,

The receiver,

A receiving antenna for receiving the signal transmitted from the transmitter;

A high frequency receiver for down converting the high frequency received by the reception antenna;

An analog / digital converter for converting an analog signal output from the high frequency receiver into a digital signal corresponding thereto;

A guard section removing unit for removing a guard section from the signal output from the analog / digital converter;

A fast Fourier transformer (FFT) for converting a signal in the time domain output from the guard interval removing unit into a signal in the frequency domain;

An STBC encoder for generating space-time block codes;

A training sequence generator for generating a training sequence;

A select switch for selecting one of the outputs of the STBC encoder and training sequence generator;

A channel estimator for combining a signal output from the selection switch and an output signal of the fast Fourier transformer to estimate a channel;

A STBC decoder for decoding the STBC from the signal in the frequency domain output from the fast Fourier transformer in accordance with the signal output from the channel estimator;

A de-interleaver for de-interleaving data output from the STBC decoder;

Characterized in that the FEC decoder for decoding the data output from the de-interleaver to the original data.

1 is a block diagram showing the configuration of a transmitter applied to a conventional IEEE802.11a system,

2 is a block diagram showing the configuration of a receiver applied to a conventional IEEE802.11a system,

3 is a frame structure diagram of a general IEEE802.11a system,

4 is an explanatory diagram for describing a concept of transmit diversity in which two conventional transmit antennas and one receive antenna are used.

5 is a block diagram showing the configuration of a transmitter in a transmission diversity apparatus in a wireless communication system according to the present invention;

6 is a block diagram showing a configuration of a receiver among apparatuses for transmitting diversity in a wireless communication system according to the present invention;

7 is a view showing an embodiment format of a long training sequence in the present invention,

8 is a frame structure diagram according to the present invention for applying STBC to IEEE802.11a,

FIG. 9 is a diagram illustrating an embodiment of the STBC encoder of FIG. 5;

FIG. 10 is a diagram showing a guard interval of a long training row on IEEE802.11a.

11 is a view showing a guard interval of the long training row in the present invention.

<Explanation of symbols for the main parts of the drawings>

103, 206 .... STBC encoder

207 ..... Training Sequence Generator

208 ..... selection switch

209 ..... Channel estimator

210 ..... STBC decoder

Hereinafter, described in detail with reference to the accompanying drawings, preferred embodiments of the present invention according to the technical spirit as described above.

5 is a block diagram showing the configuration of a transmitter in a transmission diversity apparatus in a wireless communication system according to the present invention.

As shown therein, an FEC encoder 101 for encoding transmission data; An interleaver (102) for interleaving the output data of the FEC encoder (101); An STBC encoder (103) for encoding data output from the interleaver (102) into a space-time block code to provide a substantial transmit diversity gain; First and second inverse fast Fourier transformers (IFFTs) (104) (105) for converting signals in the frequency domain output from the STBC encoder (103) into signals in the time domain; First and second guard interval inserts (106) (107) for inserting guard intervals corresponding to multipath fading into output signals of the first and second inverse fast Fourier transformers (104); First and second digital-to-analog converters (108) (109) for converting the digital signals output from the first and second guard interval insertion units (106) (107) into analog signals; First and second radio signals transmitted from the first and second digital-to-analog converters 108 and 109 to high frequency and then transmitted to the transmitting antennas 112 and 113 to radiate radio signals in space. It consists of the second high frequency transmission unit (110, 111).

The transmitter of the transmission diversity apparatus according to the present invention configured as described above has considered the case where the number of transmission antennas is two.

The first input data is interleaved in the interleaver 102 via the FEC encoder 101, and then encoded through the STBC encoder 103, and then each data block is passed through the first and the first IFFT 104 and 105. Converted to a signal in the time domain. Then, the signal converted into the time domain is inserted by the first and second guard interval inserting parts 106 and 107, respectively, and then by the first and second digital / analog converters 108 and 109, respectively. It is converted into an analog signal. Then, the first and second high frequency transmitters 110 and 111 are upconverted to high frequencies, respectively, and then transmitted through the two transmit antennas 112 and 113, respectively.

The signal thus transmitted is received and processed by the receiver as shown in FIG.

6 is a block diagram showing the configuration of a receiver among apparatuses for transmitting diversity in a wireless communication system according to the present invention.

As shown therein, a reception antenna 201 for receiving a signal transmitted from a transmitter; A high frequency receiver 202 for down converting the high frequency received by the reception antenna 201; An analog / digital converter (203) for converting an analog signal output from the high frequency receiver (202) into a digital signal corresponding thereto; A guard section removing unit 204 for removing a guard section from the signal output from the analog-digital converter 203; A fast Fourier transformer (FFT) 205 for converting a signal in the time domain output from the guard interval removing unit 204 into a signal in the frequency domain; An STBC encoder 206 for generating space-time block codes; A training sequence generator 207 for generating a training sequence; A selection switch (208) for selecting one of the outputs of the STBC encoder (206) and the training sequence generator (207); A channel estimator (209) for estimating a channel by combining the signal output from the selection switch (208) and the output signal of the fast Fourier transformer (205); An STBC decoder (210) for decoding the STBC from the signal in the frequency domain output from the fast Fourier transformer (205) according to the signal output from the channel estimator (209); A de-interleaver (211) for de-interleaving data output from the STBC decoder (210); It is composed of an FEC decoder 212 that decodes the data output from the de-interleaver 211 into original data.

The receiver configured as described above receives a signal output from the transmitter at the reception antenna 201 and down-converts the signal received at the high frequency receiver 202. The converted signal is converted into a digital signal corresponding to the analog / digital converter 203, and the guard interval removing unit 204 removes the guard interval from the digitally converted signal. Thereafter, the fast Fourier transformer 205 converts the signal in the time domain into the signal in the frequency domain again through the fast Fourier transform.

On the other hand, the signal selected by the operation of the selection switch 208 is transmitted to the channel estimator 209, and the channel estimator 209 combines the transmitted signal with the output signal of the fast Fourier transformer 205 to estimate the channel. The STBC decoder 210 decodes the received data by using the channel parameter obtained by the estimation. The STBC decoded signal is deinterleaved in the deinterleaver 211 and finally decoded through the FEC decoder 212.

On the other hand, in order to apply the diversity scheme using STBC, the receiver needs to know channel information from each transmitting antenna to the receiver. Therefore, the structure of the transmitter should be designed to suit this principle.

To this end, the present invention proposes a method for selectively applying transmit diversity while maintaining the IEEE802.11a standard.

That is, IEEE802.11a has two long training sequences T1 and T2 for channel estimation and fine frequency synchronization (see FIG. 3). Therefore, to apply STBC, the method of utilizing these two long trains is one problem. In order to solve this problem, it is assumed that channel change between two OFDM symbols can be ignored. In this case, a long training train may be configured as shown in FIG. 7. Where _ and _ correspond to T1 and T2, respectively.

Such a structure is a rotation of the existing STBC encoding method and is somewhat modified. In this case, the antenna 1 112 has a frame structure conforming to the IEEE802.11a standard, and the antenna 2 113 has a frame having a structure different from that of antenna 1 for applying STBC. The signal block is used for both antennas as it is, and the STBC is applied again from the data block. In this manner, the frame structure for applying STBC to IEEE802.11a is shown in FIG.

9 shows an embodiment configuration of the STBC encoder 103 in the transmitter.

Reference numeral 103a denotes a buffer for buffering and outputting an input signal, 103b denotes a switch for switching, and reference numeral 13c denotes a block reformatter for reformatting the data block.

In FIG. 9, when the switch 103b is opened, that is, the 'A' path represents a system structure using the existing IEEE802.11a standard, and when the switch 103b is closed, the 'B' path is the 'A' path. It will have a different data structure than the frame structure of.

Thus, the 'B' path is optional for STBC. If transmit diversity is applied, two data blocks are input to the STBC encoder, and the path of 'B' must reformat the data to be transmitted to antenna 2 (113). The data block of path 'A' is input to the buffer 103a to wait. As a result, the data of path 'A' and path 'B' are aligned in time at the output of the STBC encoder.

On the other hand, there is a matter of attention in the long training column structure from antenna 2 (113).

Since the Guard Interval of the long training row on the IEEE802.11a is virtually the same for both T1 and T2, as shown in Fig. 10, either the latter part 'a' of T1 or the second part 'b' of T2 is used as the protection interval. This is also valid for antenna 1 as it is.

However, as shown in FIG. 11, since the structure of the long training train is different from that of antenna 1 from antenna 2 113, a guard interval must be made from the long training train in front of two long training trains.

Next, in order to examine the case where STBC is applied to the data interval, a general OFDM symbol having an IFFT size of N is considered. The input data forms a data block to fit the IFFT size. At this time, the odd data block The even-numbered data vector Assume that if Is the K-th data block symbol vector, Denotes a (K + 1) th data block symbol vector and is represented by Equations 1 and 2 below.

During the first timeslot at transmit antenna 1 (112) Is transmitted and during the second timeslot Is sent. And during the first timeslot in transmit antenna 2 (113) Is transmitted and during the second timeslot Is sent. This is similar to the general STBC as described above. The STBC transmission code matrix is expressed by Equation 3 below.

Where * means complex conjugate.

On the other hand, for convenience, the case where the number of transmit antennas is 2 and the number of receive antennas is 1 will be described. Let us assume that the channel frequency response of each of the transmit antennas 1 and 2 from the transmit antennas 1 and 2 is H1 and H2. here to be.

In addition, assuming that the channel response is constant during two timeslots, the received signal in the corresponding timeslot is represented by Equations 4 and 5, respectively.

If the receiver can accurately estimate the frequency response of the channel, detection of the signal is possible by combining R1 and R2 and the channel frequency responses H1 and H2.

[4] and [Equation 5] by substituting [Equation 6] and [Equation 7] can be arranged to obtain the diversity gain of the following [Equation 8] and [Equation 9] .

According to the present invention described above, it is possible to obtain diversity gain by providing transmit diversity using STBC without changing the standard of the existing IEEE802.11a system.

In addition, since the transmit diversity device can be modularized and added to the existing wireless Internet system, compatibility with the existing system can be maintained.

Claims (3)

In a wireless communication system comprising a transmitter for transmitting the OFDM data and a receiver for receiving the transmitted data, The transmitter, An FEC encoder for encoding transmission data; An interleaver for interleaving the output data of the FEC encoder; An STBC encoder for encoding data output from the interleaver into a space-time block code to provide a substantial transmit diversity gain; An inverse fast Fourier transformer (IFFT) for converting a signal in the frequency domain output from the STBC encoder into a signal in the time domain; First and second guard interval inserting portions for inserting guard intervals corresponding to multipath fading into an output signal of the inverse fast Fourier transformer; First and second digital-to-analog converters for converting the digital signals output from the first and second guard interval insertion units into analog signals; And first and second high frequency transmitters which up-convert the signals output from the first and second digital / analog converters to high frequencies, and then transmit the signals to the first and second transmit antennas to radiate radio signals in space. Transmission diversity apparatus in a wireless communication system characterized in that. The method of claim 1, wherein the STBC encoder, A buffer for buffering and outputting an input signal; A switch for switching; And a block reformatter configured to reconstruct a data block of the input signal through the switch. In a wireless communication system comprising a transmitter for transmitting the OFDM data and a receiver for receiving the transmitted data, The receiver, A receiving antenna for receiving the signal transmitted from the transmitter; A high frequency receiver for down converting the high frequency received by the reception antenna; An analog / digital converter for converting an analog signal output from the high frequency receiver into a digital signal corresponding thereto; A guard section removing unit for removing a guard section from the signal output from the analog / digital converter; A fast Fourier transformer (FFT) for converting a signal in the time domain output from the guard interval removing unit into a signal in the frequency domain; An STBC encoder for generating space-time block codes; A training sequence generator for generating a training sequence; A select switch for selecting one of the outputs of the STBC encoder and training sequence generator; A channel estimator for combining a signal output from the selection switch and an output signal of the fast Fourier transformer to estimate a channel; A STBC decoder for decoding the STBC from the signal in the frequency domain output from the fast Fourier transformer in accordance with the signal output from the channel estimator; A de-interleaver for de-interleaving data output from the STBC decoder; And a FEC decoder configured to decode the data output from the de-interleaver into original data.