Development of a hybrid modified MELP/LPC-10e speech coder

Low bit rate speech coding is vital for communication in today's military environments. Currently, the Link-16 waveform uses the LPC-10e speech coder to perform this task at 2.4 kbs. However, Link-16 speech communication can potentially be improved with an upgrade to the newer Mixed Excitation Linear Predictive (MELP) speech coder, which produces higher quality speech and was chosen as the new military standard 2.4 kbs speech coder. Taking advantage of MELP's capabilities requires upgrading the systems which use Link-16. However being a more complex speech coder, MELP may introduce unwanted computational delays in the system. Moreover, because not all communications equipment will be upgraded simultaneously, there remains a need to retain backwards compatibility with LPC-10e. ALPHATECH proposes to develop a modified hybrid MELP-LPC-10e speech coder/decoder that will implement MELP within Link-16 and retain backward compatibility with LPC-10e, even improving LPC-10e speech. This Phase-I effort will focus on: (1) modifying the MELP vocoder by simplifying or removing certain analysis steps to reduce computation time without affecting the speech quality, (2) developing a hybrid decoder that can seamlessly decode both encoding schemes, and (3) testing the new speech coder to ensure it meets the required Quality of Service (QoS) standards.