Low-Complexity Multi-size Cyclic-Shifter for QC-LDPC Codes

Abstract

The decoding process of a quasi-cyclic low-density parity check code requires a unique type of rotator. These rotators, called multi-size cyclic-shifters (MSCSs), rotate input data with various sizes, where the size is the amount of data to be rotated. This paper proposes a lowcomplexity MSCS structure for the case when the sizes have a nontrivial common divisor. By combining the strong points of two previous structures, the proposed structure achieves the smallest area. The experimental results show that the area reduction was more than 14.7% when the proposed structure was applied to IEEE 802.16e as an example.

Low‐complexity, high‐speed multi‐size cyclic‐shifter for quasi‐cyclic LDPC decoder

“…The delay times of the RIP structure and the BN + F3 structure are and , respectively. The FC structure in [9] combined the BN + F3 structure and the pre‐rotator structure, achieving the smallest number of MUXs, , and the moderate delay time, .…”

“…In the proposed structure, the sub‐MSCS block in the coarse part uses the RIP structure instead of the BN + F3 structure exploited in [9]. The 2‐input MUX number of the proposed coarse part can be calculated by substituting for N in the second row of Table 1.…”

“…Because of the delay, the BN structure generates a larger circuit than the RIP structure after synthesis. In the experimental results of [9], the RIP structure was found to be the smallest and almost the fastest one among the above structures. The fine‐coarse (FC) structure proposed in [9] combined the BN structure and the pre‐rotator structure, leading to an even smaller MSCS block.…”

“…The above structures were compared in [9], where the BN structure was theoretically found to have the lowest complexity but a longer delay. Because of the delay, the BN structure generates a larger circuit than the RIP structure after synthesis.…”

“…The kth sub-MSCS block gathers the kth outputs of the pre-rotators and rotates them by s c with the rotation size of z g = z/g. The cross-group movement, the make-up for the inside-group rotation at the pre-rotators, is performed by the s c + 1 rotation in the kth sub-MSCS block of k + s f ≥ g. In the proposed structure, the sub-MSCS block in the coarse part uses the RIP structure instead of the BN + F3 structure exploited in [9]. The 2-input MUX number of the proposed coarse part can be calculated by substituting N g for N in the second row of Table 1.…”