A $4\times 4$ multiple-input multiple-output coherent microwave photonic (MWP) link to transmit four wireless signals with an identical microwave center frequency over a single optical wavelength based on optical independent sideband (OISB) modulation and optical orthogonal modulation with an improved spectral efficiency is proposed and experimentally demonstrated. At the transmitter, the OISB modulation and optical orthogonal modulation are implemented to generate an OISB signal using a dual-parallel Mach–Zehnder modulator (DP-MZM) driven by four microwave orthogonal frequency-division multiplexing (OFDM) signals with an identical microwave center frequency. At the receiver, the OISB signal is coherently detected at a coherent receiver where a free-running local oscillator (LO) laser source is employed. Digital signal processing is then used to recover the four OFDM signals, to eliminate the phase noise from the transmitter laser source and the LO laser source, and to cancel the unstable wavelength difference between the wavelengths of the transmitter laser source and the LO laser source. Error-free transmission of three 16 quadrature amplitude modulation (16-QAM) 1 Gbps OFDM signals and one 16-QAM 1.5 Gbps OFDM signal at a microwave center frequency of 2.91 GHz over a 10 km single-mode fiber is experimentally demonstrated.