Although a photonic integration project, HAMLET has been conceived using a top-down approach in an effort to address the challenge for the development of a powerful photonic integration technology for microwave photonics. Within the set of possible applications, future 5G systems stand out due to their technical challenge and commercial potential.
Very short after the first deployments of 4G wireless networks enabled by long-term evolution (LTE) systems, the 5G vision for “desktop-like experience on the go”, “lifelike media everywhere”, “an intelligent web of connected things”, and “real-time remote control of machines” is setting a new set of requirements for the wireless network. High system capacity and uniform user experience regardless of the user location are two very central requirements within this set. As far as the former is concerned, high available bandwidth, areal reuse and spectral efficiency are the parameters that define it. The need for high bandwidth dictates the migration of operation to high frequencies (beyond 6 GHz), where available frequency slots (i.e. contiguous spectrum of more than 500 MHz) remain available and can constitute a frequency band for the operation of 5G systems. Among the possible options, which include bands around 18.5 GHz, 28 GHz, 39 GHz or even 60 GHz, the 28 GHz band with 2 GHz available bandwidth (27.5-29.5 GHz) appears as enjoying the support by very large industrial players and getting a general acceptance as the most prominent candidate for the frequency band of the first generation of 5G systems.
The use of a high frequency band, the need for high levels of areal reuse, and the need for uniform user experience, make the use of small cells necessary, which requires in turn a very dense network of antennas. Figure on the right shows the photograph of an urban environment with indicative allocation of 5G cells and antennas, which is by comparison at least 3-4 times denser than the current allocation of 4G cells and antennas. The large number of the cells and the emergence of novel system concepts, like the coordinated multi-point transmission (CoMP), the cloud-radio access network (cloud-RAN) concept and the relevant RAN virtualization, make also necessary the decoupling between the baseband processing unit (BBU) and the antenna unit of each base-station (BS), and the centralization of the BBUs in large pools, as shown on the same figure. Each pool will control a large number (40 or even 100) of remote antenna units (RAUs), allowing for better coordination between the RAUs, and higher system capacity. The connectivity between the RAUs and the BBU pool will rely on an optical fronthaul network based on a simple star topology or on a more efficient – in terms of cell number scaling, installation costs and resilience – ring topology with WDM.
This is where HAMLET provides the solution, using its hybrid integration technology to develop novel transceivers that will interface seamlessly the optical fronthaul and radio access of the remote antenna units.
At the downlink, the optical data will be forwarded to the HAMLET transceiver, using digital radio-over-fiber transmission, where they will be detected and processed. Appropriate framing will be applied with the use of FPGA transponder and these data will be used to modulate a GP-EAM . Appropriate time delays will be applied to the optical signal with the use of an extensive optical beam forming network (up to 1:64). Arrays of up to 64 photodiodes, will convert it to electrical signals that will be used to drive the phased array antenna elements.
At the uplink, the data will be received at the HAMLET transceiver, using the phased array antenna elements, where they will be amplified and used to modulate an array of up to 64 GP-EAMs . Appropriate time delays will be applied to the optical signals with the use of an extensive optical beam forming network (up to 1:64). A photodiode will detect the combined optical signal, convert it to electrical data and use it to drive a GP-EAM, sending the data to the optical network.