A half-duplex relay station (RS)-based cellular system deployment is considered, where multiple base stations (BS) cooperate in the BS-RS in-band transmission for the downlink. The duration of the relay-receive and the relay-transmit phases are fixed beforehand, so that the interference induced by other cells is stationary during a transmission interval. With the optimization of the precoders and powers allocated to the wireless backhaul (relay-receive phase)and to the RS-MS access (relay-transmit phase), it is possible to exploit the benefits of network-MIMO (N-MIMO) along with combating the pathloss and shadowing effects thanks to the RSs. Consequently, an appealing significant enhanced spectral efficiency, power efficiency and coverage homogeneity are obtained. Results are benchmarked to the case where the relay phases are optimized.