Design and implementation of high-performance radix-4 turbo decoder for multiple 4G standards

Abstract

Recently, turbo codes have been adopted for high-speed data transmission of the 4G communications systems such as Mobile WiMAX (IEEE 802.16e standard) and 3GPP-LTE in the form of the double-binary and the single-binary, respectively. Especially, double-binary convolutional turbo code (CTC) shows superior advantages over the classical single-binary turbo codes. However, compared with the classical single-binary turbo code, nonbinary turbo code is much more complex in hardware implementation and its decoding requires more memory especially for storing the extrinsic information to be exchanged between the two soft-input soft-output (SISO) decoders. Additionally, due to its iterative decoding behavior, implementing a high-performance turbo decoder for next-generation mobile communication systems becomes challenging. Also, as the need to support multiple standards in a single mobile handheld device increases, the efficient implementation of the advanced channel decoders, which is the most area-consuming and computationally intensive block in baseband modem, becomes more important. In order to deal with these issues in resource limited handheld systems, this dissertation presents several solutions from every aspect - algorithm, architecture, and implementation. As an algorithmic solution, two techniques are proposed, which are especially suitable for nonbinary / high-radix single-binary turbo decoding. The first one, an energy-efficient SISO decoder based on border metric encoding, eliminates the complex dummy calculation at the cost of a small-sized memory that holds encoded border metrics. Due to the infrequent accesses to the border memory and its small size, the energy consumed for SISO decoding is reduced hugely. As the second one, to reduce the memory size required for double-binary turbo decoding, a new method to convert the symbolic extrinsic information to the bit-level information and vice versa is presented. By exchanging the bit-level extrinsic informa...