KR100690622B1 - Method for restoring error in wireless device - Google Patents

Abstract

The present invention relates to an error recovery method of a wireless device, and in particular, by applying incremental redundancy (IR) to improve the error recovery process of the wireless LAN to increase the success rate of packet reception and retransmission currently used in the wireless LAN The purpose of this is to shorten the packet transmission time by reducing the number of retransmissions by increasing the channel decoding efficiency of the receiver during retransmission. According to an aspect of the present invention, there is provided a packet transmission method of a wireless device, the method comprising: preparing a packet to be transmitted, determining an initial packet transmission rate, transmitting a packet at the determined transmission rate, and transmitting the packet. And if the acknowledgment (ACK) signal is not received, determine the channel coding rate and the channel code set and retransmit the packet.

Description

How to recover from a wireless device {METHOD FOR RESTORING ERROR IN WIRELESS DEVICE}

1 is an exemplary view showing parameters of an IEEE 802.11 WLAN.

2 is a flowchart illustrating a packet transmission process according to an embodiment of the present invention.

FIG. 3 is a flowchart illustrating an operation of determining a first channel speed in FIG. 2; FIG.

4 is a flowchart illustrating a packet receiving process according to an embodiment of the present invention.

FIG. 5 is a diagram illustrating a code combining process in FIG. 4; FIG.

The present invention relates to a wireless device, and more particularly, to a method for error recovery in a local area network (LAN).

The IEEE 802.11 Medium Access Control (MAC) standard, commonly called WLAN, was completed in 1999.

The most widely used WLAN standards are IEEE 802.11a and IEEE 802.11g.

The coding rate and modulation scheme of the convolutional encoder for each channel speed used in the WLAN standards IEEE 802.11a and IEEE 802.11g are as shown in FIG. 1, and the reception speed is lower from the low speed to the high speed.

The modulation schemes used in IEEE 802.11a and IEEE 802.11g include Binary Phase Shift Keying (BPSK), Quadrature Phase Shift Keying (QPSK), Quadrature Amplitude Modulation (16-QAM), and Quadrature Amplitude Modulation. ) And 64-QAM, and the symbols are smaller in order of BPSK, QPSK, 16-QAM, and 64-QAM, and the bit error ratio (BER) is higher in order of BPSK, QPSK, 16-QAM, and 64-QAM.

In addition, IEEE 802.11a and IEEE 802.11g use an Orthogonal Frequency Division Multiplexing (OFDM) physical layer, and channel coding is a convolutional coding having coding rates of 1/2, 2/3, and 3/4. ).

The lower the channel coding rate, the higher the decoding success rate at the receiving end, but the throughput is reduced due to the channel coding overhead.

In addition, error recovery in the current IEEE 802.11 standard relies on packet retransmission. Initially defined retransmission methods remain intact in the recent amendments to IEEE 802.11 amendments.

In the packet transmission, the receiver must confirm receipt of all MAC Management Protocol Data Units (MMPDUs) and MAC Protocol Data Units (MPDUs) by means of an Acknowledgment (ACK) signal. If the transmitter does not receive an acknowledgment (ACK) within a predetermined time, the transmitter repeatedly performs retransmission of the corresponding packet (MPDU, MMPDU) up to a limit number of times. At this time, the packet header indicates retransmission.

According to the prior art, only the contention window size value used as a parameter for determining a random backoff time according to the number of transmissions during packet retransmission is changed. Some products use a method of lowering the channel rate when retransmitting packets, but in this case, disregarding the information from the first and previous retransmitted packets.

For this reason, the redundancy of the packet obtained by the receiving end is not used for channel decoding. Therefore, in case of poor channel environment, the retransmission success rate decreases or the number of retransmissions increases in the environment where the channel information is poor. There was a problem of increasing time.

Meanwhile, the channel coding scheme includes a turbo code first introduced by Berrou et al. In 1993 and is currently adopted in the IMT-2000 standard.

Turbo code is currently being discussed in standard proposals such as IEEE 802.11n to support high-speed processing in WLAN, and is likely to be supported in the next generation WLAN.

In general, a turbo code decoder has a characteristic of improving performance according to decoding iterations, and the decoding times are uniformly applied regardless of the number of packet retransmissions.

Therefore, as the number of retransmissions increases, it is necessary to determine that the channel environment deteriorates and to adjust the number of decoding in order to increase the decoding success rate according to the information that can be secured. That is, it is necessary to further improve efficiency by adapting and changing the WLAN radio in a wireless environment having a lot of interference, obstacles, or distance, and having a low signal-to-noise ratio.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for recovering an error of a wireless device, which is designed to improve the conventional problems.

A first object of the present invention is to increase the packet reception success rate by improving the error recovery process of the wireless LAN by applying incremental redundancy (IR).

A second object of the present invention is to shorten the packet transmission time by reducing the number of retransmissions by increasing the channel decoding efficiency of a receiver during retransmissions currently used in a WLAN.

In order to achieve the above object, the present invention configures a radio transmitter and a radio receiver to have the following features.

First, the radio transmitter according to the present invention is configured to have the following features.

The wireless transmitter according to the present invention selects a channel speed based on a packet error rate (PER) at the time of transmitting a packet for the first time instead of retransmitting the packet, and according to the channel coding rate and modulation scheme according to the number of retransmissions during packet retransmission. And determining a channel code set to determine a channel code set.

The wireless transmitter according to the present invention is configured to transmit the channel code set differently according to the channel speed and the number of retransmission attempts during packet retransmission.

The wireless transmitter according to the present invention is configured to select a channel code set according to the number of retransmissions in the puncturer when applying a turbo encoder.

In addition, the wireless receiver according to the present invention is configured to have the following features.

The wireless receiver according to the present invention is configured to record a measurement value that can be used to calculate a signal-to-noise ratio (S / N) at the time of packet reception, and calculate a weight to use for code combining by using the measured value. It is characterized by.

The measured values include received signal strength indication (RSSI), received channel power indicator (RCPI), noise flow, and the like.

When the retransmitted packet is received, the wireless receiver according to the present invention is configured to perform channel decoding on the retransmitted packet preferentially and to perform code combining on the retransmitted packet when the channel decoding fails. It is characterized by.

In the above process, code combining may be performed by using a weight recorded at the time of packet reception. That is, the WLAN receiver may increase channel decoding success rate by executing channel decoding under a lower channel coding rate by using information of a packet previously received during code combining.

The wireless receiver according to the present invention is characterized in that when the turbo decoder is applied, the decoding success rate is increased when the number of retransmissions is large by adjusting the decoding iterations of the turbo decoder according to the number of retransmissions.

In conclusion, the present invention applies an incremental redundancy (IR) to increase the extraction performance of the original packet during decoding of the receiver to reduce the number of radio retransmissions in the entire system, thereby reducing the radio channel usage time Characterized in that the configuration to increase.

The present invention configured to have the above characteristics can be used in a device using a wireless communication link, and is applied to a method for retransmitting a wireless packet for error recovery.

In particular, the present invention improves the efficiency of applying a turbo code to a wireless device.

Hereinafter, the present invention will be described in detail with reference to the drawings.

In the present invention, a wireless device will be described using, for example, a wireless LAN device to which IEEE 802.11, in particular, IEEE 802.11a and IEEE 802.11g standards are applied.

In the present invention, assuming that there are a total of N channel speeds, the selectable channel speeds are defined as follows.

At this time, each channel rate is matched one-to-one with the modulation scheme and channel coding rate as shown in FIG.

In the present invention, a process of transmitting MPDU and MMPDU by dividing the WLAN transmitter (Tx) and the WLAN receiver (Rx) will be described.

First, the MPDU and MMPDU transmission operation of the WLAN transmitter (Tx) is the same as the operation flow chart of Figure 2, which will be described as follows.

First step: prepare an MPDU or MMPDU (hereinafter referred to as MPDU, MMPDU is referred to as "PDU") to send.

Step 2: Clear the number of retransmissions (RETRY_COUNT) to "0".

)를 결정한다. 이는 채널 속도 결정 알고리즘을 이용하며, 이의 상세한 동작은 하단에서 설명하기로 한다. Step 3: Speed of First Packet Transmission Channel

Is determined. It uses a channel rate determination algorithm, the detailed operation of which will be described later.

)로 PDU를 송신한다.Fourth step: Channel speed determined in the third step (

Transmit the PDU.

Step 5: The transmitter checks whether an acknowledgment (ACK) is transmitted from the receiver within a predetermined time.

If the acknowledgment is not received, the transmitter performs a packet retransmission by increasing the value of the retransmission count (RETRY_COUNT) by "1".

Step 6: After retransmitting the number of retransmissions (RETRY_COUNT) to "1" for packet retransmission, check whether the number of retransmissions (RETRY_COUNT) is greater than the retransmission limit (RETRY_LIMIT).

At this time, if the retransmission number is not greater than the retransmission limit number, the flow moves to step 7.

Step 7: Determine a channel speed and a code set to be used for channel coding of a packet to be retransmitted according to a hybrid radio adaptation algorithm. That is, the channel-coded packet to be transmitted is prepared according to a hybrid radio adaptation process.

Step 8: Transmit the PDU with the determined modulation scheme and channel code set, and proceed to Step 5.

In the fifth step, if the ACK (acknowledgment) signal is received from the receiver at the time of the first packet transmission or the packet retransmission, the PDU transmission process is terminated.

If retransmission is repeated and the number of retransmissions (RETRY_COUNT) according to packet retransmission is greater than the retransmission limit count (RETRY_LIMIT) in the sixth step, it is determined that the corresponding PDU transmission has failed, and the transmission process is terminated.

Meanwhile, the WLAN transmitter determines a channel speed for packet transmission, which will be described with reference to the operation flowchart of FIG. 3.

"이라 가정한다. 여기서, m은 1~N 중 하나의 값이다. First, set the channel rate used for the packet sent after the previous modulation or the channel rate set as the default in the case of the first packet transmission after the device operation.

", Where m is a value from 1 to N.

로 정의한다. When the current time is "t", the measurement time window for calculating the packet error rate PER is

Defined as

"라고 할 때 m은 "prev"로 설정한다. Set m to default when the first packet transmission is confirmed after the machine is started. If the packet is retransmitted rather than the first packet transmission after the machine is started, set the channel rate of the first packet to ".

M is set to "prev".

) 동안 패킷 오류율(Packet Error Ratio : PER)을 계산한다. Measurement time determined during packet transmission

Calculate Packet Error Ratio (PER).

의 정해진 배수가 되는 시간마다 실행한다. 예로,

The packet error rate (PER) is constantly updated. Update behavior is

Runs every time a fixed multiple of. For example,

At this time, counter values for obtaining the packet error rate (PER) are also updated for each packet transmission and reception.

The channel rate is determined based on the updated packet error rate. The channel rate determined at the time of packet transmission according to the packet error rate (PER) calculated during the measurement window is maintained or changed to a lower channel rate. Determines whether to switch to channel speed.

, 상한값을

라 하면

이면 채널속도를 높이는데,

이면

로 설정하고, m=N이면 현재의 채널속도를 유지한다. 반면에,

이면 채널속도를 낮추는데, m>1이면

로 설정하고, m=1이면 현재의 채널속도를 유지한다.That is, the lower limit of the packet error rate, which is the standard for changing the channel rate,

, The upper limit

If

If you increase the channel speed,

Back side

If m = N, current channel speed is maintained. On the other hand,

If the channel speed is lowered, if m> 1

If m = 1, the current channel speed is maintained.

In addition, the hybrid wireless adaptation algorithm of the WLAN transmitter (TX) is configured by applying a hybrid ARQ (Automatic Repeat reQuest) along with a channel speed fallback for changing the channel speed.

The present invention can individually decode a channel for each retransmitted packet, perform code combining when an error occurs during individual decoding, and incremental redundancy (IR) in which additional information is provided during retransmission. Use Incremental Redundancy.

The rules of the hybrid radio adaptation algorithm are as follows.

,

)1. Prepare two channel coding sets containing different parity bits by dividing when the number of retransmissions is odd and even according to the channel coding rate corresponding to the current channel rate.

,

)

를, 짝수이면

를 전송한다. 2. If the number of retransmission attempts is odd

If even

Send it.

와

를 전송한 후 다시 재전송을 시도할 때에는 채널속도를 한 단계 낮춘 후, 그 변경된 채널속도에 대하여

와

를 준비한다. 이어서, 재전송 시도횟수가 홀수이면

를, 짝수이면

를 전송한다. 3. At the current channel speed

Wow

If you try to retransmit after sending, lower the channel rate by one step and then change the channel rate.

Wow

Prepare. Then, if the number of retransmission attempts is odd

If even

Send it.

If the current channel speed is the lowest channel speed, the current channel speed is maintained.

For example, if the initial transmission channel rate is 36 Mbps, and the channel rate (modulation method) shown in Fig. 1 is applied, the channel rate is changed as follows according to the number of retransmissions.

, 3/4 채널 코딩율을 갖는 16-QAM 변조 방식 적용. On first transmission:

16-QAM modulation scheme with 3/4 channel coding rate.

, 3/4 채널 코딩율을 갖는 16- QAM 변조 방식 적용. At the second transmission (retransmission):

16-QAM modulation scheme with 3/4 channel coding rate.

, 1/2 채널 코딩율을 갖는 16-QAM 변조 방식 적용. 3rd transmission (retransmission):

16-QAM modulation scheme with 1/2 channel coding rate.

, 1/2 채널 코딩율을 갖는 16-QAM 변조 방식 적용. 4th transmission (retransmission):

16-QAM modulation scheme with 1/2 channel coding rate.

, 3/4 채널 코딩율을 갖는 QPSK 변조 방식 적용. At the fifth transmission (retransmission):

, QPSK modulation scheme with 3/4 channel coding rate.

과

의 선택은 Puncturer에서 서로 다른 추가(redundant) 정보가 있는 코드셋을 선택하거나 랜덤 펑쳐링(random puncturing)을 사용함으로써 가능하다. And, in the case of the turbo code that can be adopted in the next generation WLAN standard

and

The selection of is possible by selecting codesets with different redundant information in Puncturer or by using random puncturing.

Meanwhile, a packet reception operation in the WLAN receiver will be described with reference to FIG. 4.

First step: Received Signal Strength Indication (RSSI), Received Channel Power Indicator (RCPI), Noise Flow (Noise Floor) The weight (W_N) using the signal-to-noise ratio (S / N) is obtained based on the signal and noise strengths that can be measured at the LAN antenna connector.

The weight W_N must satisfy the following characteristics.

1. The weight increases as the received signal strength (RSSI) increases.

2. The weight increases as the RCPI increases.

3. The weight decreases as the noise floor increases.

The IEEE 802.11 standard does not cover noise floors, but values such as the noise histogram report are supported so that the noise floor can be measured in most WLAN devices. Here, the noise floor may be understood as the noise level of the signal received from the antenna, and the noise floor may be varied by the bandwidth-power relationship according to the bandwidth to be measured.

Step 2: Determine whether there is an error.

Step 3: When there is no error, an acknowledgment (ACK) is transmitted to the transmitter and the reception process for the packet is terminated.

If an error occurs, go to step 4.

Step 4: Check whether the packet is a previously received packet, ie, the packet is retransmitted, for the packet in error.

)를 적용한다. At this time, if it is confirmed that there is a packet previously received for the corresponding packet in which an error occurs, the weight reflecting the signal-to-noise ratio (S / N) calculated when the previously received packets are received (

).

Fifth step: As shown in FIG. 5, the packet P is estimated by code combining using N received packets to which each weight is applied.

로 표시된다.

는 i 번째 패킷 수신 시에 산출된 가중치(weight)를 의미하며, I는 1~N의 값을 갖는다. Here, the input of the code combiner is obtained by multiplying each bit of the reception packet by the weight at the reception.

Is displayed.

Denotes a weight calculated at the reception of the i-th packet, and I has a value of 1 to N.

Step 6: Check whether an error has occurred in the estimated packet after code combining / channel decoding.

Accordingly, when it is confirmed that there is no error in the estimated packet P, an acknowledgment (ACK) is transmitted to the transmitter.

If an error occurs, wait for the packet to be retransmitted from the transmitter without any action.

In addition, the WLAN receiver executes the following additional algorithm when decoding the turbo code.

Turbo code uses turbo feedback. The turbo decoder uses the already decoded output value as prior information in the next iteration.

When iteration is performed several times, since additional reliability information is generally statistical and independent, the gain is increased by increasing the number of iterations, but the gain thereafter is small.

However, as the number of iterations increases, the decoding success rate increases, but the decoding time increases. Therefore, an increase in the number of retransmissions means that the current wireless environment is not good, and thus the number of iterations is increased even though the decoding time is increased.

That is, the WLAN receiver according to the present invention increases the channel decoding success rate by increasing the number of repetitions of the turbo decoder as the number of retransmissions increases during channel decoding.

The WLAN receiver has a table defined by the following function. This is a table that determines the number of repetitions according to the number of retransmissions, and is defined for each channel speed.

는 송신기가 i번째 패킷 전송 시에 수신단에서 해당 패킷에 대하여 사용할 터보 디코더의 반복(iteration) 횟수이며,

개만큼 즉, 재전송 시도횟수의 제한만큼의 요소로 이루어진다. here,

Is the number of iterations of the turbo decoder that the transmitter will use for the packet at the receiving end when transmitting the i th packet,

Number of elements, that is, the limit of the number of retransmission attempts.

이면

이다. According to the channel rate, the table defined by the above equation has the same or smaller number of iterations for the same packet transmission as the channel rate is larger. In other words,

Back side

to be.

For example, if the number of decoding iterations is three times in the second retransmission for the 54 Mbps transmission, the number of decoding repetitions is three or more in the second retransmission for the 48 Mbps transmission.

Therefore, as the number of repetitions increases, the time taken for decoding increases, so that the number of repetitions decreases at a high channel rate at which the receiving end of a packet must be processed quickly.

As described in detail above, the present invention has an effect of increasing the retransmission success rate even in an environment where the channel environment is not good by using additional information (redundancy) for the packet secured by the receiver at the time of channel decoding.

Claims (15)

In the packet transmission method of a wireless device, Preparing packets for transmission, Determining an initial packet transmission rate; Transmitting a packet at the determined transmission rate; And if the acknowledgment (ACK) signal is not received for the transmitted packet, determining a channel coding rate and a channel code set and retransmitting the packet. 2. The method of claim 1, wherein the initial packet rate determination step Calculating the packet error rate (PER) during the measurement time; If the packet error rate is smaller than the minimum error rate, the transmission rate is increased, and if the packet error rate is larger than the maximum error rate, the process of reducing the transmission rate of the wireless device characterized in that the process. 3. The error recovery method of claim 2, wherein the transmission rate is sequentially changed by one level. 3. The method of claim 2, wherein the current channel rate is equal to the maximum channel rate when the packet error rate is less than the minimum error rate, or the current channel rate is equal to the minimum channel rate when the packet error rate is greater than the maximum error rate. Error recovery method of a wireless device comprising the process of maintaining the speed. The method of claim 1, wherein the packet retransmission step If the acknowledgment signal is not received, increasing the number of retransmissions by "1"; Comparing whether the reset retransmission number is greater than a limit number; Determining a channel code set and a channel speed according to the number of retransmission attempts if the number of retransmissions is not greater than the limit number; And transmitting the determined channel code set to the retransmission packet at the determined channel rate. The method of claim 5, wherein the channel code set reflects one of two parity bits set according to whether the number of retransmissions is odd or even. 7. The method of claim 6, wherein the two parity bits are When the turbo code is applied, the error recovery method of the wireless device, characterized in that the selection in the puncturer or random puncturing (random puncturing) method. 6. The method of claim 5, wherein the determination of the channel rate according to retransmission lowers the channel rate as the number of retransmissions increases. In the packet receiving method of a wireless device, Measuring and recording the weight upon packet reception; Checking for packet reception errors; In the checking step, estimating the packet by performing channel decoding and code combining on the basis of the information of the previous packet when it is determined that the packet reception error; Checking whether an error occurs in the estimated packet; And in the error occurrence checking step, responding to an acknowledgment (ACK) signal when an error does not occur. The method of claim 9, wherein the weighting step A method for recovering an error of a wireless device, characterized by obtaining a weight using a signal-to-noise ratio (S / N) based on a received signal strength (RSSI) or a received channel power strength (RCPI) measured by an antenna. The method of claim 10, wherein the weight increases as the received signal strength (RSSI) or the received channel power strength (RCPI) increases. The method of claim 9, wherein the weighting step Error recovery method of a wireless device, characterized in that the weight is obtained using the signal-to-noise ratio (S / N) based on the noise floor measured at the antenna stage. 13. The method of claim 12 wherein the weight decreases as the noise floor increases. 10. The error recovery method of claim 9, wherein the channel decoding is performed by the turbo decoder, wherein the iteration value for the number of transmissions is set equal to or smaller as the transmission speed increases. 10. The method of claim 9, wherein code combining is performed only on retransmitted packets when channel decoding fails.

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