A novel type of code design for the CP-CDMA system: comb spectrum grouped codes

The motivation of the present paper is to develop better CDMA codes for reducing the hardware complexity of the conventional CP-CDMA (cyclic-prefix CDMA). This technology combines the frequency orthogonality of OFDM to CDMA code design for grouping the codes and allows a significant reduction of the calculations in channel equalization. The proposed method is referred to as an OFDG code, which divides the codes of M chips in length into N groups, which are orthogonal one another in the frequency domain. Each of the groups contains K codes which are mutually orthogonal in the time domain. The design principle is introduced and a solution, called the CS code, is obtained by the use of two operations on the conventional orthogonal code set: (1) an operation of cyclic repetition; and (2) an operation of angle rotation. In comparison with CP-CDMA, the points taken for channel equalization of CP-CS CDMA can be reduced by a factor of 1/N. Simulation results confirm the effectiveness of this approach.