What is Radio Retransmission in LTE?
- The radio retransmission mechanism is called Hybrid Automatic Request (H-ARQ).
- H-ARQ allows to retransmit fastly erroneous blocks between the eNodeB and the UE.
- It avoids long retransmission between 2 TCP layers.
The H-ARQ process runs in the eNodeB and in the UE.
The H-ARQ is based on ACK/NACK messages carried by PUCCH or PUSCH. The LA1.X implementation is a hard HARQ technique:
- It reserves the same RB resources & MCS used for the initial transmission.
- Using information that was sent in the previous transmissions of the same block to increase the probability of decoding.
- If data block not received correctly, soft values are stored in order to reuse them after the retransmission of the block.
- When data is retransmitted, a different puncturing scheme is used so that the transmitted bit do not carry the same information as the first time.
- If puncturing schemes are disjoint between two transmission, number of coded bits transmitted after the second transmission is twice as high, thus coding rate has been divided by 2. After the third transmission, coding rate has been divided by 3. Probability to decode the block is increased after each transmission.
- If puncturing schemes are not disjoint, soft values corresponding to the samed bits are added. Decisions’ average reliability increases.
What Is Radio Retransmission in LTE?
Radio retransmission in LTE happens when your device or the network detects that a data packet was not received correctly. Instead of dropping that data, LTE tries to send it again to make sure nothing is lost during transmission.
Why Retransmission Is Needed
Wireless signals can get affected by noise, interference, or weak coverage. When this happens, some data might not reach your device properly. So, the system checks for errors and if any are found, it resends the data to ensure accuracy.
How Retransmission Works
- HARQ (Hybrid Automatic Repeat Request): Quickly resends small blocks of data with extra bits to help fix errors. This happens at the MAC layer.
- RLC Retransmission: If HARQ fails after several tries, the RLC layer takes over and resends the full packet to keep things reliable.
What You Experience
Thanks to retransmissions, you don’t see glitches or missing data when streaming or downloading. The system quietly fixes errors in the background so your experience stays smooth and consistent.