Quasi-Perfect Lee Codes from Quadratic Curves over Finite Fields

Golomb and Welch conjectured in 1970 that there only exist perfect Lee codes for radius t = 1 or dimension n = 1, 2. It is admitted that the existence and the construction of quasi-perfect Lee codes have to be studied since they are the best alternative to the perfect codes. In this paper we firstly highlight the relationships between subset sums, Cayley graphs, and Lee linear codes and present some results. Next, we present a new constructive method for constructing quasi-perfect Lee codes. Our approach uses subsets derived from some quadratic curves over finite fields (in odd characteristic) to derive two classes of 2quasi-perfect Lee codes are given over the space Znp for n = p+1 2 (with p ≡ 1,−5 mod 12 and k is any integer, or p ≡ −1, 5 mod 12 and k is an even integer) and n = p k −1 2 (with p ≡ −1, 5 mod 12, k is an odd integer and p > 12), where p is an odd prime. Our codes encompass the quasi-perfect Lee codes constructed recently by Camarero and Martı́nez. Furthermore, we solve a conjecture proposed by Camarero and Martı́nez (in ”quasi-perfect Lee codes of radius 2 and arbitrarily large dimension”, IEEE Trans. Inf. Theory, vol. 62, no. 3, 2016) by proving that the related Cayley graphs are Ramanujan or almost Ramanujan. The Lee codes presented in this paper have applications to constrained and partial-response channels, in flash memories and decision diagrams. Index Terms Lee distance, quasi-perfect codes, subset sums, Cayley graphs, Ramanujan graphs, quadratic curves.