We experimentally demonstrate a multiband intermediate frequency-over-fiber/mmWave (IFoF/mmWave) fiber/wireless mobile fronthaul link for gigabit capacity over the unlicensed V-band (57–64 GHz). Digital synthesis of the multiband radio waveforms is performed at the baseband unit using digital subcarrier multiplexing technique, whereas digital predistortion is exploited to cope with the analog IFoF channel impairments without any further baseband processing at the digital-free remote radio head. Commercial optoelectronic components and analog V-band radio and antenna equipment for 7-km fiber and 5-m wireless transmission are employed to successfully demonstrate both uplink and downlink connectivity. An aggregate capacity up to 24 Gb/s was demonstrated with a 6-band 1 Gbaud 16-QAM on a 7.2-GHz analog bandwidth over the combined fiber/wireless channel showing error vector magnitude (EVM) values below the 3GPP requirements (<12.5%) for 5G systems. Multiformat assignment on each subcarrier was also realized by using M-PSK and 16-QAM schemes to achieve 18-Gb/s connectivity for both uplink and downlink, while demonstrating flexible resource allocation capabilities. By replacing the stand-alone optical modulator with an InP-based externally modulated laser chip for the implementation of the IFoF transmitter, a 16-Gb/s aggregate capacity was showcased on a 7-km fiber link and 5-m wireless channel with a 4-band 16-QAM encoded at 1 Gbaud. Successful operation with robust EVM performance was demonstrated using also the 6-band scheme of 1 Gbaud QPSK bands.

A 5G mmWave Fiber-Wireless IFoF Analog Mobile Fronthaul Link With up to 24-Gb/s Multiband Wireless Capacity

A thru-match-reflect/line-match-reflect (TMR/LMR) self-calibration procedure based on the 16-term error model is shown. The error model takes into account all the leakage paths of a wafer prober, test fixture, and network analyzer. Simple closed-form calibration equations are presented. The method is very robust-zero leakage paths and symmetrical or matched-error networks can be handled equally well as more general cases. The algorithm is suitable for nonleaky network analyzers as well. The calibration is comprised of two-port measurement of the following standards: T(L), M-M, R-R, R-M, M-R. Two matched loads (M) are the only standards that have to be known in addition to the thru (T) or line (L). The reflection coefficient of the two identical reflection standards (R) is found in addition to the error parameters as in the normal TMR method. Experimental measurements with the LMR 16 have been made. All the possible combinations of five calibration standards for the 16-term error model are tabulated. The limitations of the super-thru-short-delay algorithm are defined for the first time.

LMR 16-a self-calibration procedure for a leaky network analyzer

Analogue Radio over Fibre together with subcarrier multiplexing and wavelength division multiplexing is proven to be more cost-efficient when compared to CPRI fronthaul solutions. Furthermore, the results of the allocation of RF channels to better exploit the available modulation bandwidth of commercial transceivers show that the uniformly spaced channel plan is bandwidth efficient but susceptible to interference. The ITU-T G.692 plan results in much higher tolerance to interference but it is more bandwidth consuming. Finally, the proposed ‘mind the gap’ RF channel plan shows an acceptable compromise between bandwidth consumption and robustness against intermodulation interference.

Subcarrier Multiplexing RF Plans for Analog Radio Over Fiber in Heterogeneous Networks

The deployment of new radio access technologies always provides a good opportunity and timing to optimize the existing mobile front- and backhaul (commonly called “anyhaul”). The legacy systems (Long-Term Evolution (LTE), High-Speed Packet Access (HSPA), third-generation mobile (3G), second-generation mobile (2G)) already extensively utilize the transmission and transport capacities of the mobile anyhaul. With the current launch of 5G (fifth-generation mobile) and recent LTE-A (Advanced Long-Term Evolution), additional new transmission capacities are required again. Depending on the traffic and network topology, additional cell sites are built, and even more locations are connected with fiber optics. The existing microwave and millimeter-wave links are rotated toward those aggregation points that already have optical-fiber access. Due to the increased cell-site density, the average distance of the radio access links can be reduced by network and topology optimization. The reduced hop lengths combined with adaptive modulation and automatic power control bring an opportunity for capacity increase in shortened radio links. Links newly deployed for 5G find a wide spectrum in the millimetric V, E, W, and D frequency bands. This paper discusses the availability and hop-length targets of the anyhaul links that should be carefully kept by proper planning and monitoring.

https://www.mdpi.com/2076-3417/9/23/5240/pdf

Availability and Fade Margin Calculations for 5G Microwave and Millimeter-Wave Anyhaul Links

Current research efforts on 5G RAN strongly focus on pico-cells deployment based on mmWave radio, optical/wireless convergence to support massive-MIMO and a cloud-centric operation of BBUs. Industrial and academic institutions concur that it is of great importance to develop evolutional paradigms that ensure the functional combination of the above technologies into a 5G cellular architecture and its associated ecosystems providing new vertical services. This paper aims to explore the role of Analog RoF solutions moving beyond CPRI implementations for future 5G architectures, highlighting the impact of digital-signal-processing to proposed network implementations. A DSP-assisted IFoF concept to support 60-GHz multi-band wireless connectivity is successfully demonstrated through preliminary experiments showing 12 Gb/s downlink connectivity with centralized processing at BBU side.

Analog Radio-over-Fiber Solutions for 5G Communications in the Beyond-CPRI Era

Important parameters of waveguide diplexer components as lowpass filter and combiner, have been improved. Concave shaping of vertical walls of a corrugated filter decreases reflection coefficients by 10 dB in the 14.5-15.35 GHz band. Placement of inserts at the antenna port of a combiner increases bandwidth by more than 50%.

Improvement of waveguide diplexer components

Input-reduced noise current density of a distributed amplifier excited by a photodiode is minimised. It has been found that for low noise the admittance of the transmission line between the amplifier and the pin photodiode has to be small. To prove this statement we have obtained an analytical formula for the input-reduced noise current density of the simplest possible distributed amplifier. Effect of the diode capacitance and resistance on the input-reduced noise as a function of characterstic impedance of the input line is studied. Then our statement is verified numerically for the case of a more complicated distributed amplifier.

Noise minimization in photodiode-driven distributed amplifiers

We verify by system analysis that in a multi subcarrier radio over fiber system, the error vector magnitude (EVM) as a function of the subcarrier input power (P in ) is independent of the channel selection if our new channel allocation scheme is used.

Frequency invariance in a new allocation scheme for optical communications

The Costas loop with decision direction can be used for 4QAM demodulation. In this paper we make the decision directed Costas loop more resistant against noise by application of the folding method, that is, carrier recovery after transforming the constellation diagram so that the constellation points coincide. Excellence of our Costas variant is that it can operate under heavy noise conditions.

https://archive.aessweb.com/index.php/5003/article/download/3883/6109

János Ladvánszky

Papers

Subcarrier Multiplexing RF Plans for Analog Radio Over Fiber in Heterogeneous Networks

Improvement of waveguide diplexer components

Noise minimization in photodiode-driven distributed amplifiers

Frequency invariance in a new allocation scheme for optical communications

A Costas Loop Variant for Large Noise