In this paper we investigate a new class of codes, the 2-D tail-biting convolutional codes (2-D TBCCs). The class of two-dimensional convolutional codes (2-D CCs) is a littleresearched subject in coding theory, and tail-biting versions were hardly mentioned, unless they can be represented as a product of two 1-D codes. These codes have interesting geometry since they are the 2-D analog of the 1-D TBCC which their graph is a ring. The result being a code invariant to shifts in 2-D space. We apply algebraic methods in order to find bijective encoders, create parity check matrices and inverse encoders. Next, we discuss minimum distance and weight distribution properties of these codes. We observe that some of these codes exhibit very good codes performance. We then present several novel iterative suboptimal algorithms for soft decoding 2-D CCs, which are based on belief propagation and generalized belief propagation. The results show that the suboptimal algorithms achieve respectable results, in some cases coming as close as 0.4dB from optimal (maximum-likelihood) decoding.
I. INTRODUCTIONMulti-dimensional convolutional codes (m-D CCs, where m stands for the dimension) extend the notion of 1-D CCs [1] to m-D information sequences and generator polynomials. However, in contrast to the one dimensional case, little research has been done in the field of m-D CCs. Significantly, the algebraic theory for m-D CCs has been laid out by Foransini and Valcher [2] and Weiner [3]. Lobo et al. [4]have also investigated the subject, concentrating on a subfamily of these codes dubbed "Locally Invertible m-D CCs". Some progress in the field was also made by Charoenlarpnopparut et al.,[5], who suggest a method to realize a 2-D CC encoder, and a construction for its parity check matrix.We believe 2-D TBCCs to be interesting from an academic point of view, as these codes were largely unexplored to-date, and are a non-trivial generalization of 1-D TBCCs. From the results point of view, we have shown that among 2-D TBCCs there are good codes for medium sized blocks compared to existing codes, so these codes have practical potential. We hope these codes will find applications as error correcting codes for medium length blocks, for example in wireless applications.Tail biting [1] is a well known technique to efficiently convert CCs into block codes. In this paper we extend the notion to m-D CCs, and derive some algebraic properties for them with focus on rate 1/n codes. We show: how to test whether an encoder is bijective, how to test whether it has a polynomial inverse; and how to construct a polynomial inverse and a parity check matrix in case they exist. Then we use a tree-search algorithm to find the distance properties of