Must OFDM signal be time-division in a multiple-transmitter and SFN system when the signal is free of spread-spectrum? The OFDM baseband signal can be demodulated since  each subcarrier is orthogonal to another. But In SFN system, i.e., Single Frequency Network, all OFDM signals from several transmitters are in the same frequency domain, which breaks the orthogonality.

So without some technology like CDMA, the OFDM sigals from each transmitter must be time-divided.

Is that right?
In a multi-user scenario where every transmitter uses the same center frequency and bandwidth, but transmits different data, time-division multiplex has to be applied. Otherwise, interference between the multiple transmit signals will make successful reconstruction of a specific transmit signal at the receiver virtually impossible.

However, in typical SFNs, all transmitters are part of a broadcast network and transmit identical data. Examples are Digital Audio Broadcast (DAB) and terrestrial Digital Video Broadcast (DVB-T). In such networks, the guard interval of OFDM symbols can compensate for the propagation delay between different transmitters and there is no need for time-division multiplex.

Also, I don't think CDMA and OFDM can be combined. As a multiple-access scheme, OFDM(A) allows sharing of the same frequency band by frequency multiplex while CDMA applies code multiplex.