CN101282204A - Adaptive Cooperative Retransmission Method Based on Adaptive Coding and Modulation - Google Patents

Abstract

The invention discloses an adaptive cooperative retransmission method based on adaptive coding and modulation. The method selects an appropriate coding and modulation scheme level according to the channel state information of the direct transmission link from the source end to the destination end and the service quality requirements of different services. and the maximum number of retransmissions to send data packets. Due to the broadcast characteristics of the wireless channel, the destination and the relay node can receive the data at the same time. If the destination fails to decode correctly, retransmission will be started. According to the selected code The modulation scheme and whether the relay node receives the data packet correctly determines whether the source end or the relay node will retransmit. The present invention combines adaptive coding and modulation technology, hybrid automatic request for retransmission technology and cooperative diversity, chooses to cooperate at the moment when the cooperation gain is obvious, avoids inappropriate or no-gain cooperation, and thus reduces as much as possible In the case of collaborative signaling overhead, the transmission quality is improved, and the overall system performance is effectively optimized.

Description

Adaptive Cooperative Retransmission Method Based on Adaptive Coding and Modulation

technical field

The present invention relates to the link adaptive technology in the communication system and the cooperation mode of each communication node, especially for the system using Adaptive Coding and Modulation (AMC) technology and Hybrid Automatic Repeat Request (HARQ) technology, each communication node Effective Collaboration Strategies.

Background technique

Wireless channels are affected by various external interference and multipath fading, and have time-varying and fading characteristics. Multiple-input multiple-output (MIMO) technology can provide diversity gain and effectively combat channel fading. In order to enable the MIMO system to obtain the desired diversity gain, a certain minimum distance must be maintained between the antennas. However, in practical systems, it cannot be realized due to the volume limitation of communication nodes. In order to overcome this defect, people have proposed cooperative communication technology. It utilizes the broadcast characteristics of the wireless channel, the signal sent by the source end node can be received by other users, therefore, the antenna array gain can be obtained by utilizing the cooperation among users. Studies have shown that cooperative communication technology can effectively improve coverage performance, improve link reliability and throughput. However, since the cooperation will bring additional signaling overhead, improper cooperation may cause performance loss. Therefore, the cooperation scheme must be designed reasonably to maximize the gains brought by the cooperation.

Adaptive coding and modulation (AMC) technology can dynamically adjust the code rate and modulation mode of channel coding to match the instantaneous channel conditions of time-varying channels, which can improve the throughput and spectrum utilization of data communication. Hybrid automatic repeat request (HARQ) technology combines two basic error control technologies, forward error correction coding and automatic repeat request (ARQ), and is an important means to ensure reliable data transmission on wireless time-varying channels. The basic principle of the HARQ technology is: at the sending end, the information data packet is first encoded with an error detection code, then encoded with a channel error correction code, and then sent to the channel. At the receiving end, the received information data packets are first decoded by channel coding to correct errors introduced during wireless channel transmission. Then check whether the information packet is decoded correctly through the error detection code. If the check result information packet is correctly decoded, the receiving end sends an acknowledgment signal (ACK) to the sending end. The sending end continues to send the next information data packet; if it is detected that the received information data contains error information, the information data packet is discarded or the information data packet is saved, and then a negative signal (NACK) is sent to the sending end. The predetermined delivery scheme resends the information of the information packet. This is repeated until the information data packet is received correctly or the maximum number of retransmissions is reached although the data packet still has errors, then a new information data packet transmission is started.

Contents of the invention

The present invention aims at the problem of performance loss caused by the extra signaling overhead existing in the existing cooperative communication technology, and provides an adaptive coding and modulation-based adaptive cooperative reconfiguration that can improve system transmission performance while minimizing node cooperative signaling overhead. pass method.

The adaptive cooperative retransmission method based on adaptive coding and modulation of the present invention includes the following steps:

(1) According to the service quality requirements of the business, the maximum allowable packet error rate (PER) after retransmission is obtained, and combined with the channel state information of the current direct transmission link from the source end to the destination end, determine the level of the channel coding modulation scheme and the maximum PER number of passes;

(2) The source end sends data to the destination end, and the destination end and the relay node receive the data at the same time;

(3) If the destination end decodes correctly, it will feed back an acknowledgment signal (ACK), and the source end and the relay node receive the acknowledgment signal (ACK) at the same time; if the destination end cannot decode correctly, it will feed back a negative signal (NACK), and the source end The terminal and the relay node receive a negative signal (NACK) at the same time;

(4) If the relay node decodes correctly, an acknowledgment signal (ACK) is fed back, and the source and destination receive the acknowledgment signal (ACK) at the same time; if the relay node cannot decode correctly, a acknowledgment signal (NACK) is fed back, The source end and the destination end receive a negative signal (NACK) at the same time;

(5) If the coding and modulation scheme level at this time is 0, that is, the direct transmission channel from the source end to the destination end is in deep fading, and the relay node decodes correctly, then the relay node will retransmit; otherwise, the source end will retransmit ;

(6) The maximum ratio combination is adopted at the destination end. If the decoding is correct after the combination, an acknowledgment signal (ACK) is fed back, and the source end and the relay node receive the acknowledgment signal (ACK) at the same time; if the destination end cannot decode correctly, then Feedback a acknowledgment signal (NACK), the source end and the relay node receive the acknowledgment signal (NACK) at the same time;

(7) Check whether the maximum number of retransmissions is reached, if not, then go to step (5); if the maximum number of retransmissions is reached, then discard this data packet and start sending the next data packet.

In the above step (1), the corresponding relationship between the channel coding modulation scheme and the channel state information is obtained through the packet error rate curve obtained by simulation.

The retransmission scheme of the relay node chooses one of the following two options:

Scheme 1: The relay node does not change the level of the current coding and modulation scheme when retransmitting.

Scheme 2: When the relay node retransmits, it reselects the coding and modulation scheme level according to the channel state information from the relay node to the destination.

The present invention combines adaptive coding and modulation technology, hybrid automatic request for retransmission technology and cooperative diversity, chooses to cooperate at the moment when the cooperation gain is obvious, avoids inappropriate or no-gain cooperation, and thus reduces as much as possible In the case of cooperative signaling overhead, the overall performance of the system is effectively optimized, and in the case of poor channel conditions, the performance gain brought by the present invention is more prominent.

Description of drawings

Fig. 1 is the topology structure of the present invention in a three-node model. Among them, S is the source end, D is the destination end, and R is the relay node; the solid line indicates the direct transmission link, and the dotted line indicates the relay link.

Fig. 2 is an implementation flow chart of the method of the present invention.

Fig. 3 is a performance comparison diagram between the present invention and the traditional scheme.

Detailed ways

Taking the most typical and general three-node model as an example to illustrate the adaptive cooperative retransmission method based on adaptive coding and modulation of the present invention, the system model is shown in FIG. 1 .

The specific implementation steps are shown in Figure 2:

Step 1: According to the service quality requirements of different services, obtain the maximum allowable packet error rate (PER) after retransmission, and determine the coding and modulation scheme level in combination with the current channel state information;

Step 2: The source end sends data to the destination end, and the destination end and the relay node receive the data at the same time;

Step 3: If the destination end decodes correctly, then feed back ACK, and the source end and relay node receive ACK at the same time; if the destination end cannot decode correctly, feed back NACK, and the source end and relay node receive NACK at the same time.

Step 4: If the relay node decodes correctly, it will feed back ACK, and the source and destination receive ACK at the same time; if the relay node cannot decode correctly, it will feed back NACK, and the source and destination will receive NACK at the same time;

Step 5: If the coding and modulation scheme level at this time is 0, that is, the direct transmission channel from the source end to the destination end is in deep fading, and the relay node decodes correctly, then the relay node will retransmit; otherwise, the source end will retransmit hair;

Step 6: The maximum ratio combination is adopted at the destination end. If the decoding is correct after combination, ACK is fed back, and the source and relay nodes receive ACK at the same time; if the destination end cannot be decoded correctly, NACK is fed back, and the source and middle nodes The successor node receives NACK at the same time;

Step 7: Check whether the maximum number of retransmissions is reached, if not, go to step 5; if the maximum number of retransmissions is reached, discard this data packet and start sending the next data packet.

It should be noted that, in the first step of the implementation process of the present invention, when the coding and modulation scheme is selected according to the channel condition, the corresponding relationship between the channel coding and modulation scheme and the channel condition can be obtained by obtaining the packet error rate curve through simulation.

It should also be noted that in some systems, in order to reduce complexity, it is stipulated that the level of the coding and modulation scheme remains unchanged during the retransmission process. In order to ensure compatibility with more systems, in the present invention, it is stipulated that the relay node can choose two retransmission schemes:

Scheme 1: The relay node does not change the level of the current coding and modulation scheme when retransmitting. Advantages: It is not necessary to estimate the channel state information from the relay node to the destination, and the complexity is low. Disadvantage: The coding and modulation scheme level may not match the channel status from the relay node to the destination.

Scheme 2: When the relay node retransmits, it reselects the coding and modulation scheme level according to the channel state information from the relay node to the destination. Advantages: The coding and modulation scheme level matches the channel state from the relay node to the destination. Disadvantages: high complexity.

Fig. 3 shows the spectrum efficiency performance comparison between the present invention and the traditional scheme (only joint consideration of adaptive coding and modulation technology and hybrid automatic request retransmission technology, but no consideration of adaptive cooperative retransmission). Among them, the average signal-to-noise ratio of the channel from the source end to the relay node and the channel from the relay node to the destination end are both γ, and the average signal-to-noise ratio of the channel from the source end to the destination end is γ/4. This is a typical network model when the relay node is located near the midpoint from the source end to the destination end. From the performance comparison, it can be concluded that for all γ values, the present invention has better performance than the traditional scheme, especially, when the γ value is relatively low, that is, the channel condition is relatively poor, the performance gain brought by the present invention is more prominent .

Claims (3)

1. the adaptive cooperation repeating method based on adaptive coding and modulating is characterized in that, may further comprise the steps:

(1) according to the quality of service requirement of business, obtain allowing Packet Error Ratio through the maximum after retransmitting, in conjunction with the channel condition information of current source end, determine chnnel coding modulation scheme rank and maximum retransmission to the direct transmission link of destination;

(2) the source end sends data to destination, and destination and via node receive data simultaneously;

(3) if the destination correct decoding, feedback acknowledgment signal then, source end and via node receive the confirmation signal simultaneously; If destination can not correct decoding, then feedback is denied that signal, source end and via node receive simultaneously and is denied signal;

(4) if the via node correct decoding, feedback acknowledgment signal then, source end and destination receive the confirmation signal simultaneously; If via node can not correct decoding, then feedback is denied that signal, source end and destination receive simultaneously and is denied signal;

(5) if the coded modulation scheme rank of this moment is 0, promptly the source end is in deep fade to the direct transmission channel of destination, and the via node correct decoding is then retransmitted by via node; Otherwise, retransmit by the source end;

(6) adopt high specific to merge at destination, if it is correct to merge back decoding, feedback acknowledgment signal then, source end and via node receive the confirmation signal simultaneously; If destination can not correct decoding, then feedback is denied that signal, source end and via node receive simultaneously and is denied signal;

(7) check whether arrive maximum retransmission, if no show then forwarded for (5) step to; If arrive maximum retransmission, then abandon this packet, begin to send next packet.

2. the adaptive cooperation repeating method based on adaptive coding and modulating according to claim 1 is characterized in that, in described (1) step, the corresponding relation of chnnel coding modulation scheme and channel condition information obtains by the Packet Error Ratio curve that emulation obtains.

3. the adaptive cooperation repeating method based on adaptive coding and modulating according to claim 1 is characterized in that, it is one of following two kinds that the retransmission scheme of described via node is selected:

Scheme 1: via node does not change present encoding modulation scheme rank when retransmitting.

Scheme 2: via node according to the channel condition information of via node to destination, is reselected the coded modulation scheme rank when retransmitting.

Images