We have carried out research and development of next generation (5G) wireless communication systems in dense user environments utilizing advanced photonic technologies. Especially, we have focused on a heterogeneous wireless communication system, which includes 4G, 3G, WiFi and millimeter-wave wireless links, with broadband, low latency, low-power consumption and low-cost. In this report, photonic-based millimeter-wave wireless links of ultra-small cells (atto-cells) in a big football stadium are discussed. Advantages of an asymmetric millimeter-wave link combined with terminal localization techniques are also pointed out. Some basic experimental results on the millimeter-wave wireless links in an actual big football stadium are also reported.
Due to its larger capacity and lower energy consumption, High-speed train (HST) system is playing very important role in mass transportation. Various Communication systems for HST have been deployed mainly for train control and safety purpose. Growing demand of broadband wireless communication for passengers on the train requires new data transmission technique suitable for high speed and dense user environment. In this paper, distributed antenna systems (DASs) with combination of W-band millimeter communication and radio over fiber (RoF) technology is presented.
The communication system can basically avoid transmission rate decrease due to handover employing RoF based signal distribution architecture. Since ITU-R assigned wide band frequency bands (92.0-94.0, 94.1-100.0, 102-109.5GHz) for mobile system and relatively low propagation loss of the frequency bands, a high data transmission rate more than 1Gb/s per train and cost effective system can be realized. The technical challenges in providing DAS-based communication systems for HSTs include system architecture, RF system design and propagation issue of W-band frequency in a railway environment. Propagation studies in the specific railway environment such as tunnel, cutting and viaduct are investigated. Wide-band single carrier, OFDM and sub-channel single carrier is considered a candidate of the system. Designed and evaluated characteristics of GaAs compound MMICs, system level consideration of RF/IF/RoF link and EVM measurement of wide band modulation signals are discussed and outlined.