TCP Performance Degradation of In-Sequence Delivery in LTE Link Layer

LTE networks have been rapidly commercialized for 4G cellular communications systems in all over the world as well as Korea. Because many internet applications use TCP as their transport layer protocol, TCP throughput measurements and its performance improvements in LTE networks is very important. In this paper, we analyze the impact of “in-sequence delivery” in LTE link layer on TCP RTT increment. When HARQ or ARQ in LTE link layer is working frequently for error recovery, it increases TCP RTT and decreases TCP throughput seriously. Therefore, in order to get better TCP throughput with the same packet error probability, we should decrease TCP RTT when HARQ or ARQ in LTE link layer is working for error recovery. We propose "out-of-sequence delivery" in LTE link layer in order to decrease TCP RTT. From our test results, "out-of-sequence delivery" outperforms “insequence delivery”. While "out-of-sequence delivery" makes LTE link layer design simpler, but its throughput gain is considerable.