Beam search and partial traceback in the frame-synchronous two-level algorithm (TLBS)

The authors present and clarify some aspects of the frame-synchronous TL (two-level) algorithm. It is demonstrated that beam search and partial traceback can be integrated in the TL algorithm (two-level beam search or TLBS) so as to reduce the complexity of the original frame-synchronous TL. With this modification, TLBS decodes continuously and is well suited for word spotting. TLBS then becomes particularly attractive as it offers the potential for optimally solving the N-best decoding problem. The increased complexity of the TL is upper-bounded by the beam-search width and the traceback itself. The new TLBS algorithm behaves like the OP (one-pass) algorithm from a computational point of view. The complexity of TLBS becomes close to that of the OP for small search windows, and the window size is shown to be below two hundred frames (16 ms frame rate).<>