CDMA in Metamaterials Using Polyphase Codes.

Small code sets are required for asynchronous code division multiple access (CDMA) communication in dispersive channels such as metamaterials, for applications including communications in conductive environments and wireless power transfer. Desirable properties of such codes include low autocorrelation sidelobes, low cross correlations, and low bandwidth. Pairs of polyphase codes in bases 2, 3, 4, 5 and 6 are investigated using a rapid numerical sieve with a spectral cost function. Optimum codes are selected from complex conjugate pairs with equal spectral costs, and codes with minimum bandwidth are identified for lengths up to 12 for all except base 2. Coded signaling and CDMA are investigated by simulation and experiment at high frequency (HF) in example metamaterial, a magneto-inductive waveguide.