As the PHY/MAC-layer IR-HARQ and RLC-layer ARQ error recovery procedures, adopted in LTE, may impose additional delay when their code-block retransmissions occur, the arising question is whether these significantly contribute to IP and consequently RTP packet delays, and finally degrade the overall application-layer end-to-end QoE, especially when voice is transmitted over LTE? With this regard, we propose and demonstrate a VoLTE QoS and QoE test procedure based on PHY/MAC/RLC/IP/TCP-UDP/RTP cross-layer protocol analysis and perceptual speech quality QoE measurements. We identified monotonic relationship between the paired observations: QoE and HARQ RTT, i.e. between the PESQ voice quality rating and the IP/RTP packet latency, for given BLER of the received MAC/RLC code-blocks. Specifically, we found out that, for the HARQ RTT value of about 8 ms, only up to 2 HARQ retransmissions (and consequently no RLC-ARQ one) is appropriate during any voice packet, otherwise delay accumulation might not be accordingly “smoothed out” by jitter/playback buffers along the propagation path.

由于LTE中采用的PHY / MAC层IR-HARQ和RLC层ARQ错误恢复程序在发生代码块重传时可能会施加额外的延迟，因此出现的问题是，它们是否对IP造成重大影响，并因此导致RTP数据包延迟，最终降低整个应用层的端到端QoE，尤其是在通过LTE传输语音时？鉴于此，我们提出并演示了基于PHY / MAC / RLC / IP / TCP-UDP / RTP跨层协议分析和感知语音质量QoE测量的VoLTE QoS和QoE测试程序。对于接收到的MAC / RLC代码块的给定BLER，我们确定了成对的观测值之间的单调关系：QoE和HARQ RTT，即PESQ语音质量等级和IP / RTP数据包延迟之间的单调关系。具体来说，我们发现，对于大约8毫秒的HARQ RTT值，