KR100752842B1 - Tstd transmit diversity method in a hybrid arq system - Google Patents

Abstract

The present invention relates to a Time Switched Transmit Diversity (TSTD) scheme in a hybrid ARQ system. In particular, a transmission diversity scheme based on a TSTD is applied to a hybrid ARQ system to provide a frame upon request for retransmission (NAK). The present invention also relates to a transmit diversity method of controlling a packet to be retransmitted through antenna alternate switching.

According to the present invention, when an initial frame or packet is transmitted and an error of the frame or packet is detected and a request for retransmission of the frame or packet is detected at the time of error detection, the antenna is transmitted immediately before the retransmission request. Retransmission is performed through another transmit antenna. If an error is detected even after the retransmitted data is combined with the previously transmitted data and decoded, the first transmitted signal may be retransmitted. In this case, the transmission antenna is switched. By applying the TSTD to the hybrid ARQ as described above, independence between retransmission units (frames and packets) can be guaranteed even in a slow fading channel environment, thereby improving data transmission reliability.

CDMA, Power Control, ARQ, Diversity

Description

TST-based Diversity Method in Hybrid ARV System {TSTD TRANSMIT DIVERSITY METHOD IN A HYBRID ARQ SYSTEM}

1 illustrates a channel structure using a TSTD

2 is a flowchart for explaining a conventional hybrid ARQII operation

3 is a flowchart for explaining a conventional hybrid ARQIII operation.

4 is a diagram illustrating a channel structure of a hybrid ARQ system using a TSTD for explaining a concept of the present invention.

5 is a flowchart illustrating a diversity scheme in hybrid ARQII as a first embodiment of the present invention.

6 is a flowchart illustrating a diversity scheme in hybrid ARQIII according to a second embodiment of the present invention.

The present invention relates to a transmit diversity method in a hybrid ARQ system.

Particularly, the present invention applies TSTD (Time Switched Transmit Diversity) to a hybrid ARQ system, and alternately switches and retransmits antennas when retransmitting frame or packet data in response to a request for retransmission of frame or packet data from a receiver. The present invention relates to a TSTD-based ARQ system diversity method that improves data transmission / reception performance by ensuring unit (frame or packet) transmission, thereby ensuring independence between retransmission units even in a slow fading channel environment.

More specifically, the present invention performs a frame or packet transmission with a plurality of transmit antennas in a hybrid ARQ system, and when the frame or packet retransmission request (NAK response) is received by the receiver due to error detection, the retransmission request The present invention relates to a TSTD-based diversity method in a hybrid ARQ system capable of providing independence between retransmitted frames or packets by performing retransmission through another transmission antenna and another transmission antenna.

In the mobile communication system, there is a transmission diversity method as a method of obtaining a performance gain due to independent signal reception at a receiving end by installing a transmission antenna in addition to an existing single antenna.

Transmission diversity schemes include Space Time coding based Transmit Diversity (STTD) and Time Switched Transmit Diversity (TSTD). Among these, TSTD is a technique that gives spatial diversity gain by alternately transmitting signals to a plurality of transmit antennas. Currently, 3GPP adopts an open loop transmission diversity scheme, but applies it only to a shared channel (SCH).

The structure of the channel using the TSTD is shown in FIG. 1, and the operation thereof is a method of alternately transmitting channels to different transmission antennas (antenna 1 and antenna 2) in each slot. The transmission gain can be obtained because it experiences independent paths.

On the other hand, ARQ system (Automatic Repeat reQuest) (automatic retransmission method) is a technique for correcting the error in a system for transmitting a digital signal using a wireless channel environment.

This method corrects an error by requesting the sender to retransmit the data block (transmission unit: frame or packet) in which an error occurs after error detection, and an error correction channel encoding method for overcoming channel degradation. Is a hybrid ARQ system that aims to increase system stability and improve performance.

Error correction techniques using ARQ include Wait and stop ARQ, Go-back-N ARQ, Selective-repeat ARQ, and Adaptive ARQ.

Stop-and-wait ARQ is the simplest form of ARQ, where the sender sends a block and then sends a normal (ACK) or error (NAK) signal over the reverse channel by an error detection operation at the receiver. It waits until the next block is transmitted.

If the sender receives a NAK (error generated) signal from the receiver, it retransmits the previously transmitted block, and if it receives an ACK signal, it transmits the next block.

In order to reduce the overhead of stop-and-wait ARQ, continuous ARQ is a method of sending data blocks consecutively instead of one block. In the continuous ARQ, the Go-back-N method is a block from which an error occurs to all subsequent blocks. In this case, the selective ARQ may transmit a plurality of blocks continuously without a response from the receiving side. If an error block is found among the transmitted blocks, only the block in which the error occurs is retransmitted.

Adaptive ARQ is an ARQ method that dynamically changes the length of a block according to the channel state in order to maximize channel efficiency, and has an advantage of increasing efficiency compared to other ARQ methods, but has a disadvantage in that the control circuit is very complicated.

In the hybrid ARQ system, convolutional coding or turbo coding may be employed as a channel coding scheme, depending on whether the code is a Rate Compatible Punctured Code (RCPC) or a Complementary Punctured Code (CPC). It is divided into 3 (Type III). In general, when a transmission signal is retransmission of the same signal, it is defined as Type 1 (Type I).

In general, as the retransmission is repeated, the coding rate of the channel code transmitted in the hybrid ARQ system is gradually reduced in order to increase the reliability of the retransmitted signal. The hybrid ARQ scheme that adapts and operates according to the channel environment is essential for a system for providing a multimedia service.

FIG. 2 is a flowchart for explaining the operation of the hybrid ARQII, and FIG. 3 is a flowchart for explaining the operation of the hybrid ARQIII. In the hybrid ARQIII, a redundancy code to be retransmitted is self-decodable. If not, hybrid ARQ II.

Referring to the hybrid ARQII of FIG. 2, the first transport block (frame or packet, which is the same below) n1 is transmitted, and the decoding is performed by using this as an estimated value n1_est at the receiving end of the first transport block. 201, 202, the decoding is completed if there is no error (good), and if there is an error (bad), the block n2 to be retransmitted is transmitted, and this is initially transmitted as the estimated value n2_est at the receiving end of the retransmission block. It is combined with the estimated value n1_est at the receiving end of the block (203, 204).

This is decoded (205), and if the result of decoding is not good (good), the process is completed.

Referring to the case of hybrid ARQ III of FIG. 3, the first transport block n1 is transmitted and decode is performed using this as an estimated value n1_est at the receiving end of the first transport block (301, 302). If it is not good (good), and if there is an error (bad), the block n2 to be retransmitted is transmitted, and decoding is performed by setting it as an estimated value n2_est at the receiving end of the retransmission block (304). If there is no error as a result of the decoding, it is completed. Otherwise, it is combined with the estimated value n1_est at the receiving end of the first transport block and the estimated value n2_est at the receiving end of the retransmission block (305).

This is decoded (306), and the decoding is completed if there is no error (good), and if there is an error (bad), the process is performed again from step 301.

However, in the mobile communication system employing the hybrid ARQ, if the channel is a slow fading environment in which the channel changes slowly, the error correction capability of the channel encoding is poor. Therefore, the dependency on the ARQ technique is increased. However, as the length of a frame or packet, which is a retransmission unit, is shortened to support a multimedia service having a high data rate, a correlation may be generated between each retransmission unit (frame or packet).

Such a correlation in time between retransmission units may result in deterioration of system performance and may cause a problem of reducing the gain of the ARQ scheme employed. Therefore, when using a short frame or packet in a slow fading channel environment, there is a need for a technique capable of guaranteeing an independent property between each retransmission unit.

This technique can be considered to make retransmission independent in time / frequency / space. In the case of independent retransmission unit in time, it is necessary to process very short frame and packet units in time. Because of this time delay, it is difficult to guarantee retransmission unit independence in time, and it is also difficult to ensure independence of retransmission unit in frequency using the same frequency.

Therefore, a technique for ensuring independence between retransmission units in space is required.

The present invention proposes a diversity method based on a TSTD based diversity method in a hybrid ARQ system, and solves a correlation between retransmission units in a hybrid ARQ system by introducing a spatial separation method.

The present invention solves the temporal correlation that can occur between each retransmission unit (frame or packet) as the length of a frame or packet, which is a retransmission unit, is shortened in order to support a high data rate multimedia service in a hybrid ARQ system. As a method, TSTD-based transmission divers in a hybrid ARQ system that solves the temporal correlation and guarantees independence based on the alternating switching technique (diversity technique) of transmission antennas when retransmitting a frame or packet. Suggest a City method.

In the hybrid ARQ system of the present invention, the TSTD-based diversity method includes transmitting data of a predetermined transmission unit through one of the transmission antennas from a transmitting side to a receiving side in an ARQ system having a plurality of transmitting antennas. Receiving a retransmission request signal from a receiving side to a transmitting side according to a result of determining the quality thereof, retransmitting data of a predetermined transmission unit through an antenna different from the transmitting antenna according to the retransmission request signal; Diversity technique, characterized in that consisting of.

In addition, the TSTD-based diversity method in the hybrid ARQ system of the present invention is characterized in that the data of each retransmission unit is alternately switched to each transmit antenna whenever the retransmission is repeatedly performed.                     

Hereinafter, a TSTD transmission diversity method in a hybrid ARQ system of the present invention will be described with reference to the accompanying drawings.

4 is a diagram illustrating a channel structure of a hybrid ARQ system using a TSTD for explaining the concept of the present invention, in which two antennas (antenna 1 and antenna 2) are used.

Referring to FIG. 4, when there is a retransmission request for data or a packet transmitted to antenna 1, it is shown that antenna switching is performed to antenna 2, antenna 1, antenna 2, ... every time the data is retransmitted.

5 is a case of applying to hybrid ARQII as the first embodiment of the present invention.

Referring to the hybrid ARQII of FIG. 5, the first transport block (frame or packet) n1 is transmitted, and the decoding is performed using this as an estimated value n1_est at the receiving end of the first transport block (501, 502). If there is no error (good) as a result of decoding, the transmission antenna is switched (bad) in case of error (bad) (503).

Transmitting a block (frame or packet) n2 that is switched and retransmitted through another antenna and combines it with the estimated value n1_est at the receiving end of the first transport block using the estimated value n2_est at the receiving end of the retransmitting block (504,505). ).

Decode this (506), and if the result of decoding is not good (good), and if there is an error (bad) again switching the transmit antenna (507), through the switched antenna transport block (n1) ) Is retransmitted (it repeats from step 501).                     

That is, if retransmission is required by error detection after the initial transmission, when retransmitting the retransmission block n2, antenna switching is performed with a transmission antenna different from the antenna that transmitted the existing transmission block n1, and retransmission is performed through the switched antenna. If an error is detected even after decoding the retransmitted data by combining the retransmitted data with the previously transmitted data, the previous transport block n1 can be retransmitted, and again, the transmit antenna transmits the block n2 again. Switching between one antenna and another transmit antenna.

Referring to the hybrid ARQ III of FIG. 6, the first transport block n1 is transmitted and decode is performed using this as an estimated value n1_est at the receiving end of the first transport block (601, 602). If it is good (good), and if there is an error (bad), the transmission antenna is switched to a different antenna than the transmission antenna of the transport block (n1) (603).

The block n2 to be retransmitted is transmitted through the switched antenna, and decoding is performed using the estimated value n2_est at the receiving end of the retransmission block (604 and 605). That is, it can be seen that decoding is also performed on the retransmitted data.

If there is no error (good) as a result of the decoding, otherwise (bad), the estimated value n1_est at the receiving end of the first transport block and the estimated value n2_est at the receiving end of the retransmission block are combined (607).

This is decoded (608), and if the decoding result is no error (good), and if there is an error (bad), the transmission antenna is switched again (609), and the process is performed again from step 601.

The present invention applied TSTD to hybrid ARQ. Therefore, in case of using a short frame or packet in a slow fading channel environment, the temporal correlation between each retransmission unit can be solved by a spatial separation technique.

Therefore, independence can be ensured between retransmission units by alternately switching the transmit antennas during retransmission, thereby improving system performance.

Claims (3)

Transmitting data of a predetermined transmission unit from a transmitting side to a receiving side through any one transmitting antenna in an ARQ system having a plurality of transmitting antennas; Receiving a retransmission request signal from a receiver to a transmitter according to a result of receiving the transmitted data and determining the quality thereof; And retransmitting data of a predetermined transmission unit through an antenna different from the transmission antenna according to the retransmission request signal, and subsequently retransmitting the plurality of transmission antennas alternately when requesting a retransmission. TSTD-based diversity method in the ARQ system, characterized in that comprises a. The diversity method based on the TSTD in the hybrid ARQ system of claim 1, wherein the data of each retransmission unit is alternately switched for each transmit antenna whenever the retransmission is repeatedly performed. delete

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