Method and system for cyclic redundancy check
View Patent ↗The present disclosure describes a method, performed by a data processor comprising a cyclic redundancy check (CRC) module configured for calculating CRC remainders for encoded data and a comparator comprising a shift register, for making a cyclic redundancy check of an encoded data record of bit length L, in which at least A bits of the record represent content data and at least B bits represent check data. A system for performing a cyclic redundancy check is also described.
1. A system for processing electromagnetic signals representing convolutionally encoded data streams, the system comprising:
at least one processor configured to execute a trellis search of a convolutionally encoded data stream of bit length L, where L is an integer;
a survivor memory unit comprising:
at least one (D×N)-bit data register configured to store decision bit data representing results of the trellis search provided by the at least one processor for a first D bits of the convolutionally encoded data stream, where D is an integer greater than zero and less than L, and N is an integer equal to a number of states used by the at least one processor to execute the trellis search, the decision bit data stored in the (D×N)-bit data register being re-orderable by the at least one processor according to the results of the trellis search for the first D bits of the convolutionally encoded data stream; and
a memory store configured to store decision bits representing results of the trellis search provided by the at least one processor for a subsequent L−D bits of the convolutionally encoded data stream; and
a cyclic redundancy check (CRC) module configured to perform a cyclic redundancy check on a decoded data record outputted from the survivor memory unit, the CRC module comprising:
a CRC remainder calculator configured to calculate a CRC remainder based on a first A bits of the decoded data record received from the survivor memory unit, the first A bits of the decoded data record comprising the decision bit data outputted from the (D×N)-bit data register and a first portion of the decision bits outputted from the memory store; and
a comparator to compare the CRC remainder calculated by the CRC remainder calculator with a final B bits of the decoded data record.
2. The system of claim 1 , wherein the survivor memory unit further comprises at least one LIFO register for output of the stored decision bit data.
3. The system of claim 1 , wherein the final B bits of the decoded data record comprise a second portion of the decision bits outputted from the memory store.
4. The system of claim 1 , further comprising a shift register coupled between the survivor memory unit and the CRC module, the shift register configured to delay provision of the final B bits of the decoded data record to the comparator.
5. The system of claim 1 , wherein: A≧B.
6. The system of claim 1 , wherein:
25 ≦L≦ 70; and
B= 16.
7. The system of claim 1 , further comprising a descrambler module configured to descramble the last B bits of the decoded data record in parallel with the cyclic redundancy check performed by the CRC module.
8. The system of claim 1 , wherein the at least one processor comprises an add-compare-select unit configured to perform the trellis search and to provide the results of the trellis search to the survivor memory unit.
9. The system of claim 1 , further comprising a plurality of (N×M)-bit registers configured for storage of trace-forward data provided by the at least one processor, where M is an integer equal to a number of delay elements in a convolutional encoder used to encode the data stream of bit length L.
10. The system of claim 9 , wherein the survivor memory unit comprises a trace-back logic unit configured to perform trace-back operations on the decision bits stored in the memory store based on the trace-forward data stored in at least one of the plurality of trace-forward registers.
11. The system of claim 9 , further comprising a tail-biting check unit configured to perform tail-biting analyses using the trace-forward data stored in at least one of the plurality of trace-forward registers.