Generic Multimedia Codec Payload Format for Unequal Error Protection
Original Publication Date: 2003-Nov-25
Included in the Prior Art Database: 2003-Nov-25
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Today's multimedia codecs generate frames consisting of bit groups with different grades of sensitivity for transmission errors, also known as "priority classes". For instance, an AMR (Adaptive Multirate Codec) generates media frames consisting of 3 bit groups: class A bits, class B bits and class C bits. Class A bits are very sensitive to transmission errors: if there is an error in the class A bits received at the decoder side, this may cause a very annoying sound after decoding. Thus a very tight error protection and detection is required for class A bits. On the contrary, class C bit errors can at most affect the background noise. "Unequal Error Protection" (UEP) allows protecting each priority class differently with an appropriate grade of error protection. Possible error protections can range from simply adding a checksum for error detection, adding different grades of redundancy to allow "forward error correction" (FEC), retransmission of frames with errors (ARQ, Automatic ReQuest of Retransmission) etc. The use of UEP means that the media frames need to be split in groups of bits belonging to the same priority class, and then a different error protection mechanism is applied to each such group. This frame splitting as well as the application of error protections is most efficient when applied at the lower OSI (Open System Interconnection) layers (physical and/or link layer). E.g. for UEP of the UMTS (Universal Mobile Telecommunications System) radio interface this means splitting the media stream into multiple Radio Bearers (RB), whereby each RB has different protection mechanisms. The equipment that performs the frame splitting task for UEP must know the first and last bit of each priority class in the media frames received from the encoder. For the more complex codecs such as H.263, MPEG-4, etc these boundaries are varying from frame to frame.