LTE & 5G Retransmission

In this post, we will have a look at LTE & 5G Retransmission Mechanisms: HARQ & RLC.

Both LTE and 5G have HARQ and RLC Retransmission mechanism. The HARQ is related to MAC/PHY layer while the RLC Retransmission is related to RLC Layer The HARQ Retransmissions usually are much quicker while the RLC retransmissions should take a longer time to get triggered.

When Maximum HARQ retransmission count is reached, the connection is still retained, and UE remains connected. However, the eNB or gNB can reduce MCS to make the service more robust. On the other hand, when Maximum RLC Retransmission count is reached, the connection is dropped.

LTE & 5G Retransmission Mechanisms: HARQ & RLC Explained

In 5G networks, retransmissions are an essential mechanism for ensuring reliable data transmission. Similar to LTE, 5G also utilizes the Hybrid Automatic Repeat Request (HARQ) protocol for retransmission purposes. However, 5G introduces some enhancements and optimizations to improve the efficiency and performance of the retransmission process. Here are some key aspects of 5G retransmissions:

  1. HARQ-ACK Bundling: In 5G, multiple HARQ-ACK (Acknowledgment) messages can be bundled together and transmitted in a single transmission. This bundling technique helps to reduce overhead and improve efficiency.
  2. Mini-Slots and Slot Bundling: 5G introduces the concept of mini-slots, which are shorter transmission time intervals within a regular time slot. Mini-slots allow for more frequent HARQ feedback, reducing latency and enabling faster retransmissions. Additionally, multiple mini-slots can be bundled together to form larger transmission opportunities, further enhancing efficiency.
  3. Improved HARQ Feedback: 5G supports more precise and granular feedback for HARQ processes. The feedback information can include explicit indications about the exact packets or transport blocks that need retransmission, enabling more targeted retransmission strategies.
  4. Adaptive Modulation and Coding (AMC): 5G systems employ advanced modulation and coding schemes that can dynamically adapt based on the channel conditions. By adjusting the modulation and coding parameters, 5G can optimize data transmission for improved reliability and capacity.
  5. Link Adaptation and Beamforming: 5G incorporates advanced techniques like beamforming and massive MIMO (Multiple-Input Multiple-Output) to enhance signal quality and coverage. These technologies improve the overall link quality, reducing the need for retransmissions.
  6. Channel State Information (CSI) Reporting: 5G devices can provide detailed feedback on the channel conditions, allowing the network to make more informed decisions about resource allocation and retransmission strategies.

Overall, 5G retransmissions aim to provide more efficient and reliable data transmission, reducing latency and improving the user experience. The enhancements introduced in 5G networks help to optimize the retransmission process, making it more adaptive to varying network conditions and improving overall network performance.

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Ali Khalid

5G NR | VoLTE | LTE-A | Massive MIMO | NB-IoT | NDO Network Specialist at Ericsson, Australia
Ali Khalid is a Senior LTE/VoLTE RNPO, NB-IoT and 5G Solution Architect who has successfully led and delivered a number of projects in different regions across the globe including Pakistan, Bahrain, UAE, Qatar, Oman, KSA, Nigeria, Turkey, Poland and Japan. He is currently working in Strategic Competence Unit (SCU), a highly experienced global team at Ericsson, Australia. In case of any questions or feedback, please feel free to drop a comment below or connect with him on LinkedIn.

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