We report high-capacity intermediate-frequency-over-fiber (IFoF) transmission using parallel intensity/phase modulators (IM/PM). Thanks to the parallel IM/PM transmitter, we can avoid all the null frequencies caused by dispersion-induced RF power fading. Compared to other techniques to avoid RF power fading, the parallel IM/PM transmitter offers a simple solution because it does not rely on any sophisticated digital signal processing. We transmitted 14 $\times$ 1.2-GHz orthogonal-frequency-division-multiplexed signals over a 20-km single-mode fiber using the parallel IM/PM transmitter and achieved a Common Public Radio Interface equivalent data rate of 1.032 Tb/s. Thus, an IFoF system with the parallel IM/PM transmitter shows great potential to be applied to high-capacity mobile fronthaul links in the upcoming fifth-generation mobile system and beyond.

1.032-Tb/s CPRI-Equivalent Rate IF-Over-Fiber Transmission Using a Parallel IM/PM Transmitter for High-Capacity Mobile Fronthaul Links

Cloud radio access network (C-RAN) becomes a promising scenario to accommodate high-performance services with ubiquitous user coverage and real-time cloud computing in 5G area. However, the radio network, optical network and processing unit cloud have been decoupled from each other, so that their resources are controlled independently. Traditional architecture cannot implement the resource optimization and scheduling for the high-level service guarantee due to the communication obstacle among them with the growing number of mobile internet users. In this paper, we report a study on multi-dimensional resources integration (MDRI) for service provisioning in cloud radio over fiber network (C-RoFN). A resources integrated provisioning (RIP) scheme using an auxiliary graph is introduced based on the proposed architecture. The MDRI can enhance the responsiveness to dynamic end-to-end user demands and globally optimize radio frequency, optical network and processing resources effectively to maximize radio coverage. The feasibility of the proposed architecture is experimentally verified on OpenFlow-based enhanced SDN testbed. The performance of RIP scheme under heavy traffic load scenario is also quantitatively evaluated to demonstrate the efficiency of the proposal based on MDRI architecture in terms of resource utilization, path blocking probability, network cost and path provisioning latency, compared with other provisioning schemes.

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Experimental demonstration of multi-dimensional resources integration for service provisioning in cloud radio over fiber network

As a counterpart of analog radio-over-fiber technology, digital radio-over-fiber (D-RoF) system, such as common public radio interface (CPRI), is a matured and robust solution to support RF signal delivery in traditional mobile fronthaul networks. In view of recent progresses in delta-sigma modulation, data compression, and advanced error correcting coding, the efficiency of D-RoF is significantly improved, which motivates researchers to re-evaluate the role of D-RoF in future mobile fronthaul networks to support 5G and beyond wireless communications. In this paper, we demonstrate two critical technologies to improve the transmission efficiency and flexibility of D-RoF systems. A fast-statistical-estimation based data compression algorithm is proposed to reduce the number of quantization digits in a D-RoF-based mobile fronthaul with low complexity and high quality. Combined with resampling and advanced modulation formats, data-transmission efficiency of a 25-Gbit/s D-RoF testbed is improved by around five times compared with uncompressed CPRI systems. On the other hand, we also experimentally demonstrate a point-to-multi-point (PTMP) D-RoF system with multiband modulation, which exhibits higher flexibility and better compatibility with multiple services and different radio-access technologies compared to existing schemes based on time interleaving. An experiment of 13.3-Gbit/s 4-band PTMP bidirectional D-RoF MFH is demonstrated. Combined with data compression, error free delivery of 6.4-Gbit/s 1024-QAM 5G-New-Radio-like signals is realized.

Key Technologies for Next-Generation Digital RoF Mobile Fronthaul With Statistical Data Compression and Multiband Modulation

In this paper, we experimentally and numerically evaluate the performance of a common public radio interface (CPRI) over a time division multiplexed passive optical network (TDM-PON) system for accommodating densely deployed small cells in centralized-radio-accessnetwork- based future radio access. A prototype of the CPRI over TDM-PON is developed by using Ethernet-based TDM-PON. Experimental results showed that its synchronization accuracy and latency meet the requirements of a mobile front-haul using CPRI by the implemented delay jitter reduction and low-latency bandwidth allocation techniques. An in-phase and quadrature (IQ) data compression technique is also implemented on the system to enable a higher accommodation of remote radio heads. Experiments confirmed that the compression technique meets open radio equipment interface standards in terms of latency and signal quality degradation. Numerical results showed that the technique with a 0.45 compression ratio increases the number of supportable remote radio heads from 3 to 7 for a mobile front-haul with a 100 μs latency limitation.

Performance evaluation of mobile front-haul employing ethernet- based TDM-PON with IQ data compression [Invited]

We first experimentally demonstrated a digital mobile fronthaul (MFH) architecture using delta-sigma modulation as the new digitization interface to replace the conventional common public radio interface (CPRI). Both one-bit and two-bit delta-sigma modulations were demonstrated, and the digitized signals were transmitted over on-off keying (OOK) or 4-level pulse-amplitude-modulation (PAM4) optical intensity modulation-direct detection (IM-DD) links. 32 LTE component carriers (CCs) were digitized and transmitted over a 25-km single-λ 10-Gbaud OOK/PAM4 link, so that 32 LTE carrier aggregation (CA) specified by 3GPP release 13 can be supported. Compared with the conventional digitization interface based on CPRI, the fronthaul capacity is increased by four times. Error vector magnitude (EVM) less than 5% or 2.1% for all LTE CCs was obtained using one-bit and two-bit delta-sigma modulators, so that high-order modulations (256QAM/1024QAM) can be supported. As a waveform-agnostic digitization interface, delta-sigma modulation can digitize not only 4G-LTE but also 5G waveforms, and its 5G compatibility was verified by filter-bank-multicarrier (FBMC) signals. The tolerance to bit error ratio (BER) of the proposed delta-sigma modulation-based digital MFH was evaluated, and no significant EVM degradation was observed for BER up to 3 χ 10−5. A comparison with analog MFH reveals that the proposed digital MFH based on delta-sigma modulation can offer improved resilience against noise and nonlinear impairments, and it increases the fronthaul capacity by four times compared with the conventional CPRI-based digital MFH without significant EVM penalty.

Digital mobile fronthaul based on delta-sigma modulation for 32 LTE carrier aggregation and FBMC signals

This paper reviews the required specifications to optical fronthaul links for C-RAN and presents key technologies of optical transmissions and a CPRI data compression for next-generation optical access networks.

Keiji Tanaka

Papers

Next-generation optical access networks for C-RAN