Several modulation in direct-sequence spectrum-spread systems

Performances of BPSK, balanced-quaternary modulation, dual-quaternary modulation and complex-quaternary modulation in direct-sequence spectrum-spread (DS-SS) system are discussed in this paper. Based on the criterion the power of original signal is the same, it is shown that complex-quaternary modulation has the best performance, and dualquaternary modulation degrades 2dB. Moreover, the frequency efficient of the two modulations is 2 bit/Hz. Balancedquaternary has the same performance as BPSK with frequency efficient 1 bit/Hz.