Turbo Decoder Design based on an LUT-Normalized Log-MAP Algorithm

• Published in: Entropy (Basel, Switzerland) Vol. 21; no. 8; p. 814
• Main Authors: Li, Jun, Wang, Xiumin, He, Jinlong, Su, Chen, Shan, Liang
• Format: Journal Article
• Language: English
• Published: Basel MDPI AG 20.08.2019; MDPI
• Subjects: Algorithms; Approximation; Bit error rate; Codes; Complexity; cyclone IV; Decoding; Error correction; Logic; LTE-advanced; normalization functional unit; normalized-Log-MAP algorithm; Simulation; Turbo codes; turbo decoder; Wireless communication systems
• ISSN: 1099-4300; 1099-4300
• DOI: 10.3390/e21080814

Turbo codes have been widely used in wireless communication systems due to their good error correction performance. Under time division long term evolution (TD-LTE) of the 3rd generation partnership project (3GPP) wireless communication standard, a Log maximum a posteriori (Log-MAP) decoding algorithm with high complexity is usually approximated as a lookup-table Log-MAP (LUT-Log-MAP) algorithm and Max-Log-MAP algorithm, but these two algorithms have high complexity and high bit error rate, respectively. In this paper, we propose a normalized Log-MAP (Nor-Log-MAP) decoding algorithm in which the function max* is approximated by using a fixed normalized factor multiplied by the max function. Combining a Nor-Log-MAP algorithm with a LUT-Log-MAP algorithm creates a new kind of LUT-Nor-Log-MAP algorithm. Compared with the LUT-Log-MAP algorithm, the decoding performance of the LUT-Nor-Log-MAP algorithm is close to that of the LUT-Log-MAP algorithm. Based on the decoding method of the Nor-Log-MAP algorithm, we also put forward a normalization functional unit (NFU) for a soft-input soft-output (SISO) decoder computing unit. The simulation results show that the LUT-Nor-Log-MAP algorithm can save about 2.1% of logic resources compared with the LUT-Log-MAP algorithm. Compared with the Max-Log-MAP algorithm, the LUT-Nor-Log-MAP algorithm shows a gain of 0.25~0.5 dB in decoding performance. Using the Cyclone IV platform, the designed Turbo decoder can achieve a throughput of 36 Mbit/s under a maximum clock frequency of 44 MHz.