In this paper, a spectrally efficient protocol for cooperative transmit diversity is proposed. By allowing multiple nodes to transmit simultaneously, relaying transmission only consumes limited bandwidth resource. To facilitate the performance analysis, the lower and upper bounds of the outage probability are first developed. Then the high signal-to-noise ratio (SNR) behavior of the cooperative protocol is studied, our analytical results show that the proposed strategy can achieve full diversity. To achieve the performance gain promised by cooperative diversity, an iterative soft interference cancelation minimum mean-squared error (SIC-MMSE) equalizer is then proposed, which utilizes the structure of the cooperative strategy and can provide fast convergence speed.