HARQ (20141217) and lteharq, key LTE technologies for wireless communication network learning

HARQ (20141217) and lteharq, key LTE technologies for wireless communication network learning

Today, let's take a look at a key technology used in LTE, HARQ (hybrid auto retransmission technology)

Because information is lost during channel transmission, in order to ensure information integrity, it is necessary to re-transmit the information until all information is received.

First, let's take a look at HARQ's theory:

HARQ can be divided into synchronous and asynchronous Based on the retransmission occurrence time;

Synchronous HARQ refers to the transmission (Retransmission) of HARQ at a fixed time. Because the receiving end knows the transmission time in advance, no additional signaling overhead is required to represent the serial number of the HARQ process, in this case, the HARQ process number can be obtained from the sub-frame number.

Asynchronous HARQ means that HARQ retransmission can occur at any time. Because the receiving end does not know the transmission time, the HARQ process processing sequence number needs to be sent together with the data.

HARQ can be divided into non-adaptive and self-adaptive based on whether the data characteristics change during re-transmission:

Adaptive transmission: the sender changes transmission parameters based on the actual channel status information;

Non-adaptive transmission: the transmission parameters are known to the receiver. Therefore, the signals containing the transmission parameters do not need to be transmitted again in the non-adaptive transmission system.

Advantages of synchronous HARQ: 1. Low overhead; 2. Low acceptor operation complexity in non-adaptive systems; 3. Improved channel reliability.

Advantages of asynchronous HARQ: 1. In a fully adaptive system, discrete and continuous sub-carrier distribution methods can be used for scheduling with great flexibility;

2. Support multiple HARQ processes of a sub-frame;

3. Flexibility of retransmission scheduling.

 

The LTE downlink system adopts asynchronous and adaptive HARQ technology, and the uplink system adopts synchronous non-adaptive HARQ technology;

The uplink system adopts the non-adaptive HARQ synchronization technology, mainly because of the complexity of the uplink and the uncertainty of interference from other residential areas. The base station cannot accurately estimate the signal-to-dry ratio (SINR) of each user) value,

Next, let's focus on the asynchronous adaptive HARQ technology used by the downlink system. First, let's look at a downstream HARQ timeline:

The downstream transmission end uses PDSCH for scheduling. The ACK or NACK corresponding to PDSCH is sent on PUCCH or PUSCH;

The downstream transmission receiver uses PDCCH for scheduling;

TX: sender

RX: Acceptor

 

Assume that the transfer information is 1234

After each transmission, only one bit is left, for example, 1, 2, 3, and 4. After a long time, it takes four re-uploads to complete the transmission of all the information (ideally ).

During each transmission, we generally use (trace Chase) or (Soft merge Soft Combining) to merge all data.

When transmitting big data, an incremental redundant IR (IncrementalRedundancy) must be added to reduce the large amount of overhead consumed during re-transmission, that is, the data that was not received before is transmitted, the received data is no longer transmitted.

 

 

 

Okay. Let's talk about this for HARQ. I hope you can share your comments with us. Next time, we will continue to learn key LTE technologies.