Implementation of millimeter wave band DDD radio system

In the 5G mobile communication system, we consider the minimal cell base stations are installed in closely packed areas where optical fiber infrastructures cannot easily access in many cases such as wall surfaces of the buildings or utility poles including streetlamps. This is widely accepted as the last-mile problem. To solve the problem, it is effective to implement a millimeter-wave radio system with extra-wide bandwidth and maximum frequency usage efficiency for the final approach up to the base station. In order to provide the radio with higher frequency usage efficiency, we are making efforts to develop a DDD (Directional Division Duplex) system, which is one of the full duplex system. The DDD system has features of simultaneous communications of the same frequency channel and the same polarized wave by the combination of "an extra-high speed multi-level QAM modulation/demodulation digital signal processing equipped with self-interference canceller" and "high-isolation antennas disposed separately for transmission and reception using the characteristics of millimeter wave". Thereby, it is possible to double the frequency usage efficiency in contrast with a that of existing duplex system such as TDD (Time Division Duplex) or FDD(Frequency Division Duplex). We have prototyped the 40 GHz band point-to-point radio with the DDD system, and evaluated its performance in the indoor environment. The results of our experiment clearly indicate that the DDD system would show good performance even under the real outdoor environment.