Template for Papers ECOC 2015

End-to-end analogue downand uplink radio transmission with real-time signal processing is experimentally demonstrated using a technologically lean and energy-conscious remote radio head. Powering through the fronthaul at an optical feed of 290 mW enables a centralised power supply. Introduction In the upcoming years we anticipate a continuous increase in wireless data rates. Hence, small cell techniques increasing network density have an important role to play1. This entails that baseband processing is off-loaded to the CO while simple remote radio head (RRH) technology remains at the cell site. However, as load conditions in wireless networks are shifting rapidly with the mobility of its users, RRHs that are distributed across the network infrastructure need to be dynamically taken into operation to optimize the interplay of macroand small cells. Such a scenario is unfavourable for practical deployment: even in case of strongly localized cells, each site needs to be supplied with data and energy, thus being subject to high cost. In this work we experimentally demonstrate a remotely powered RRH with low-cost VCSEL transmitter and energy-conscious RF amplification. End-to-end real-time transmission of OFDM radio signals with PRBS and HDTV payload is shown over a radio and fronthaul loss budget of 84 and 10 dB, respectively. Low-Power Remote Radio Head In the proposed radio access scheme conventional high-power RRHs of macro-cells are assisted by additional low-power distributed RRHs during on-peak, especially in overloaded spots where the user density is peaking regularly. With the introduction of numerous small cells associated to fewer macro-cells the complexity of these additional RRHs becomes a critical parameter since cost attributed to RRH subsystems is shared among a smaller number of network users. Simplicity is therefore of paramount importance and can be facilitated by: (1) Analogue radio-over-fibre transmission as an attractive solution to handle high CPRIequivalent data rates at the fronthaul2 while also assuring lean small-cell RRHs based solely on low-noise amplification (LNA) and an linear optical transceiver. (2) Energy reclamation at the RRH fronthaul interface allows to centralize power supply units of RRHs at the CO. Downand uplink performance of a small-cell RRH has been evaluated in the setup shown in Fig. 1. At the CO the downlink I/Q data signal is up-converted to a RF carrier at 2.05 GHz. A post-amplified Mach-Zehnder modulator (MZM) transmits the signal at 1547.72 nm with a power of 10 dBm over the 4 km SMF-based fronthaul. At the RRH the signal is boosted by energyconscious LNA towards the radio equipment (RE) where real-time block error ratio (BLER) estimation is performed on a payload size of 9024 bits/packet. OFDM with an IEEE 802.11a compliant format having a modulation bandwidth of 20 MHz and 64 subcarriers was employed. The real-time DSP at transmitter and receiver performs OFDM (de-)modulation with insertion of pilots, synchronization sequences and cyclic prefix. Moreover convolutional coding with code generator polynom (1718, 1338) and code rate /2 is employed. The DSP stack was implemented using the NI USRP-2953R software-defined radio and was fed by either PRBS for real-time BLER measurement or by Fig. 1: Experimental setup and DSP stack for evaluating a low-power RRH that is supplied with energy through its fronthaul. RRH Pump α LNA Radio path attenuator RE VCSEL PIN small-cell RRH CO