Direct sum construction of DC-free adder channel codes

The design of uniquely decodable DC-free multi-user coding schemes with good rate sums for the multiple access adder channel is described in this paper. It is shown that by using the direct sum construction on short multi-user codes, it is possible to devise longer DC-free multi-user coding schemes with rate sums which increase quite rapidly at each iteration of the construction. Asymptotically, there is no penalty in requiring the coding schemes to be DC-free. In addition, the schemes can be efficiently soft decision decoded using a relatively low complexity sectionalised trellis.