Optical SCM transmission multiplexing IF and local signals for adaptive array

There has been much interest in the application of adaptive array antennas to wireless communication systems. To keep base station (BS) requirements simple, it is advantageous to separate the array antenna in a BS from a signal processing unit in a central station (CS) and link them by optical fiber. Several approaches have been proposed. In these approaches, due to ambient temperature changes, phase differences among antenna branches cannot be kept constant between a CS and a BS so that the antenna radiation pattern changes. We introduce a new configuration for optical subcarrier multiplexing (SCM) radio-on-fiber (ROF) transmission, which can avoid the above difficulties. In this system, the SCM signal comprises all antenna branch signals and all local signals for original frequency conversions. While the proposed system is simple, the phase difference among antenna branches can be maintained to be constant in spite of fiber length fluctuation. Furthermore, only a pair of optical transceivers and optical fibers for downstream and upstream lines is required between a CS and a BS. We show the results of several experimental investigations.