In TDD-CDMA (time division duplex-code division multiple access) systems, the chip-synchronous transmission in the uplink is obtainable and thus, leading to free MAI (multiple access interference) in flat Rayleigh fading channels plus AWGN (additive white Gaussian noise). This motivates us to develop a novel cooperative transmission strategy which allows single-antenna devices to benefit from spatial diversity using orthogonal signature sequences. The proposed cooperation is applicable to any constant-envelope modulation and achieves the fullest diversity level, the low implementation complexity and the full data rate. The closed-form outage probability expression was also derived and compared to the simulation results to evaluate its validity. A variety of numerical results demonstrated the cooperation's superiority over single transmission under the same transmit power constraint
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