Systematic t-Unidirectional Error-Detecting Codes over Zm

Some new classes of systematic t-unidirectional error-detecting codes over Z_m are designed. It is shown that the constructed codes can detect two errors using two check digits. Furthermore, the constructed codes can detect up to m^r-2 + r-2 errors using r ges 3 check bits. A bound on the maximum number of detectable errors using r check digits is also given.