The impact and benefits of channel state information (CSI) are analyzed in terms of degrees-of-freedom (DoFs) in a K-user interference network operating over time-selective channels, where the error variance of CSI estimation is assumed to scale with an exponent of the received signal-to-noise ratio (SNR). The original interference alignment (IA) scheme is used with a slight modification in the network. Then, it is shown that the DoFs promised by the original IA can be fully achieved under the condition that the CSI quality order, represented as a function of the error variance and the SNR, is greater than or equal to 1. Our result is extended to the case where the number of communication pairs, K, scales with the SNR, i.e., infinite K scenario, by introducing the user scaling order. As a result, this letter provides vital information to the system designer in terms of allocating training resources for channel estimation in practical cellular environments using IA.

We have demonstrated radio-over-fiber transmission of wireless signals at millimeter-wave bands. The system incorporated 25 km of an optical intermediate frequency feeder and 60 GHz OFDM signal transmission at 155 Mbps with a BER of less than 10-6 was achieved within the system cell of a radius of 2.6 m under the channel condition of Line-of-Sight.