Finite session codes in asynchronous channel

This paper introduces a new code for asynchronous channel without a common clock between sender and receiver. In communication systems like magnetic recording systems, the existing solutions use the Run Length Limited (RLL) code to prevent errors due to time jitter. In addition, a long communication period is chopped into sessions so that other errors due to environmental noise cannot propagate over a session. However, some recent works have proposed a new code which can outperform RLL. Although this code is optimal for sessions with infinite length, this paper shows that the new code is suboptimal for finite sessions. In this paper, an algorithm is proposed to construct the optimal code for finite sessions. Another algorithm with lower complexity is proposed to construct the suboptimal code. These results can also give a lower bound on the capacity of an asynchronous channel with finite sessions.