## 5 Random Linear Network Coding for 5G New Radio
### Opportunities and Challenges for Mobile Video Delivery in 5G  
**PDCP Coded Duplication in 5G NR:** Due to PDCP duplication feature, PDCP protocol becomes an interesting option for the RLNC sublayer within the NG-RAN user plane protocol stack. Empowering PDCP layer with RLNC sublayer could provide a possibility for \"coded duplication\" where, instead of a simple duplication of PDCP PDUs, one could transmit two different sets of RLNC coded packets created from the appropriately defined source block. Next, we briefly describe the concept of coded duplication but leave the more detailed investigation for our future work.  
Figure 8 illustrates the concept of PDCP Coded Duplication. PDCP protocol receives PDCP service data units (SDUs), i.e., IP packets, and organizes one or more PDCP SDUs into a source block of length \(K\) source packets. The source block is processed by RLNC sublayer to produce \(N\) coded packets encapsulated into a sequence of coded PDCP PDUs. The set of PDCP PDUs carrying the coded packets  
Figure 7: 5G NG-RAN Protocol Stack and 5G QoS Architecture.  
of the same source block are enumerated using the same PDCP sequence number and transmitted using PDCP duplication feature via separate protocol legs. The coded duplicated content propagates down the two independent legs, undergoing possibly different segmentation at the two RLC entities followed by different MAC frame delivery success. Note that due to RLNC coding at PDPC layer, RLC layer ARQ and MAC layer HARQ could be altogether avoided in coded PDCP duplication.  
At the receiving side, instead of removal of PDCP duplicates, the receiving PDCP entity would collect the coded content from all incoming PDCP PDUs tagged with the same sequence number and received through both legs. The coded packets are extracted from PDCP PDU until the content of the source block is reconstructed, as illustrated in Figure 8. Finally, note that coded PDCP duplication operates across two parallel packet erasure channels, which offers different possibilities for matching layered UEP RLNC schemes and parallel erasure channels, empowered with appropriate resource allocation of coded packets to coded duplicated PDCP PDUs.  
**QoS Control for 5G Mobile Video Delivery:** The 5G QoS architecture described in the previous subsection will provide advanced mechanisms for QoS control in mobile video delivery. 5 GC will classify QoS flows based on their QFI and provide per flow forwarding treatment in terms of e.g., packet loss rates and packet delay, thus providing mobile video flows with desired delivery parameters.  
One of the key elements of 5G QoS architecture is a novel SDAP protocol defined at NG-RAN user plane interface. SDAP is additional resource allocation entity in 5G NR that will complement MAC scheduler. While the \"lower layer\" MAC scheduler aims to dynamically schedule resource blocks to different UEs in order to maintain guaranteed or best possible DRB parameters, the \"upper layer\" SDAP scheduler aims to assign QoS flows to different DRBs in order to satisfy their QFI-defined parameters. Note that different DRBs defined at the interface towards the UE may be configured using different NG-RAN protocol configurations. In this sense, coded PDCP duplication described above may provide a flexible approach to trade off reliability and latency and fine tune QFI-defined requirements in terms of packet loss rates and packet delay for a given DRB.