Direct sum DC-free coding schemes for multi-user adder channel

The design of uniquely decodable multi-user coding schemes with good rate sums for the DC-free multiple access adder channel is described. By using the direct sum construction on short multi-user codes, it is possible to devise longer DC-free 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