Low complexity blind transport format detection
Provided is a method, apparatus and computer program product for detecting a transport format of a multiplexed transport channel used for transferring binary data. A path metric value is determined, which estimates likelihood for a hypothetical trellis path to end at a predetermined state, for every state of a trellis stage of a possible end bit position of a data block of the transport channel. Then, for each possible end bit position a number of path metric values which indicate higher likelihood for the hypothetical trellis path to end at said predetermined state than an initial state is calculated, and the best end bit positions which lead to highest values of the calculated number are selected and error checking is performed for the selected best end bit positions to detect the transport format. The proposed selection of best end bit positions leads to a reduced number of decoding operations.
1. A method of detecting a transport format of a multiplexed transport channel used for transferring binary data, said method comprising the steps of:
determining, using at least one of a discrete circuit and a programmed processor, for every state of a trellis stage of a possible end bit position of a data block of said transport channel a path metric value which estimates likelihood for a hypothetical trellis path to end at a predetermined state;
calculating for each possible end bit position the number (δ s ) of path metric values which indicate higher likelihood for the hypothetical trellis path to end at said predetermined state than an initial state;
selecting a predetermined number of best end bit positions which lead to highest values of said number (δ s ) of path metric values by rejecting end bit positions which lead to path metric values smaller than a predetermined threshold value, and sorting non-rejected end bit positions in a list from highest to lowest path metric values; and
performing error checking for said selected best end bit positions to detect said transport format.
2. A method according to claim 1 , further comprising declaring said data block wrong, if all end bit positions are rejected.
3. A method according to claim 1 , wherein said predetermined number is three.
4. A method according to claim 1 , further comprising selecting an end bit position which corresponds to a greater block size, if two or more end bit positions lead to the same said number (δ s ) of path metric values.
5. A method according to claim 1 , wherein said error checking comprises sorting possible transport formats in decreasing order of transport block number, and starting the checking operation with the transport format with the highest number of data blocks.
6. A method according to claim 5 , further comprising deciding that a transport format is detected if all error checking operations of said transport format lead to the result that the checked blocks are correct.
7. A method according to claim 5 , further comprising deciding that a data block is wrong if all transport formats associated with said selected best end bit positions have been checked without success.
8. An apparatus for detecting a transport format of a multiplexed transport channel used for transferring binary data, said apparatus comprising:
determination means for determining for every state of a trellis stage of a possible end bit position of a data block of said transport channel a path metric value which estimates likelihood for a hypothetical trellis path to end at a predetermined state;
calculation means for calculating for each possible end bit position the number (δ s ) of path metric values which indicate higher likelihood for the hypothetical trellis path to end at said predetermined state than an initial state;
selection means for selecting a predetermined number of best end bit positions which lead to highest values of said number calculated by said calculation means; and
checking means for performing error checking for said selected best end bit positions to detect said transport format.
9. An apparatus according to claim 8 , wherein said determination means comprises a Viterbi decoder.
10. An apparatus according to claim 8 , wherein said calculation means comprise a counter controlled by an output signal of a comparator arranged to compare respective path metric values determined by said determination means for a current state and for said initial state.
11. An apparatus according to claim 8 , wherein said apparatus comprises a receiver device for a wireless communication system.
12. A computer readable medium having computer-executable instructions stored thereon that, when executed by a processor, cause the processor to detect a transport format of a multiplexed transport channel used for transferring binary data by:
determining for every state of a trellis stage of a possible end bit position of a data block of said transport channel a path metric value which estimates likelihood for a hypothetical trellis path to end at a predetermined state;
calculating for each possible end bit position the number (δ s ) of path metric values which indicate higher likelihood for the hypothetical trellis path to end at said predetermined state than an initial state;
selecting a predetermined number of best end bit positions which lead to highest values of said number (δ s ) of calculated path metric values by rejecting end bit positions which lead to path metric values smaller than a predetermined threshold value, and sorting non-rejected end bit positions in a list from highest to lowest path metric values; and
performing error checking for said selected best end bit positions to detect said transport format.
13. A computer readable medium of claim 12 , wherein said instructions, when executed by a processor, further cause the processor to declare said data block wrong, if all end hit positions are rejected.