Cooperative transmission, where spatially distributed users form a multi-antenna system and assist in forwarding the information from source to destination node, achieves the diversity gain of a multiple-input multiple-output (MIMO) system. Cooperative network based on OFDM has been proposed to cope with the channel frequency-selectivity but due to high peak-to-average power ratio (PAPR) of OFDM, expensive power amplifier are required. In this paper, we present cooperative network based on OFDM combined with time division multiplexing (OFDM/TDM) using minimum mean square error frequency-domain equalization (MMSE-FDE) in a frequency-selective fading channel. We theoretically analyze the network performance with respect to the bit error rate (BER). The conditional signal-to-interference plus noise ratio (SINR) expressions are derived based on Gaussian approximation of the residual inter-slot interference (ISI) after MMSE-FDE for the given set of channel gains. The average BER performance for OFDM/TDM is evaluated by Monte-Carlo numerical computation method using the derived theoretical expressions and confirmed by computer simulation. The results show that the lower BER is achieved with cooperative OFDM/TDM in comparison with OFDM based cooperative network because OFDM/TDM exploits both cooperative and frequency diversity gains.