Additive complementary pairs of codes

An additive code is an $ {{\mathrm{I\!F}}}_q $-linear subspace of $ {{\mathrm{I\!F}}}_{q^m}^n $ over $ {{\mathrm{I\!F}}}_{q^m} $, which is not a linear subspace over $ {{\mathrm{I\!F}}}_{q^m} $. Linear complementary pairs (LCP) of codes have important roles in cryptography, such as increasing the speed and capacity of digital communication and strengthening security by improving the encryption necessities to resist cryptanalytic attacks. This paper studies an algebraic structure of additive complementary pairs (ACP) of codes over $ {{\mathrm{I\!F}}}_{q^m} $. Further, we characterize an ACP of codes in analogous generator matrices and parity check matrices. Additionally, we identify a necessary condition for an ACP of codes. Besides, we present some constructions of an ACP of codes over $ {{\mathrm{I\!F}}}_{q^m} $ from LCP codes over $ {{\mathrm{I\!F}}}_{q^m} $ and also from an LCP of codes over $ {{\mathrm{I\!F}}}_q $. Finally, we study the constacyclic ACP of codes over $ {{\mathrm{I\!F}}}_{q^m} $ and the counting of the constacyclic ACP of codes. Finally, we exhibit an interesting application of ACP of codes in coding for the two-user binary adder channel.