Gain-Switched Optical Frequency Combs for Future Mobile Radio-Over-Fiber Millimeter-Wave Systems

Abstract

The millimeter-wave (mm-wave) frequency band has emerged as a means to overcome current radio frequency spectral limitations and represents an interesting solution to fulfill the bandwidth and networking requirements of fifth generation (5G) mobile communications and beyond. Photonic generation of these frequencies holds advantages over electronic methods in terms of cost and effective network distribution. Due to their coherent nature, optical frequency combs (OFC) are a promising solution for the efficient generation of mm-wave frequencies. The work outlined examines the use of OFCs in a mm-wave radio-over-fiber (RoF) heterodyne system with regard to the specific requirements of a 5G candidate waveform, universally filtered orthogonal frequency division multiplexing. Through experimentation and simulation, the key limitations of linewidth, effective path length difference, and relative intensity noise (RIN) are explored. Results are presented, in terms of error vector magnitude (EVM), for a wide range of system parameters highlighting important considerations to be taken in designing future mm-wave RoF systems employing OFCs. Performance of ∼5% EVM using single sideband modulation is achieved for optimized system conditions and an RIN level of −132 dB/Hz.

Optical Heterodyne Analog Radio-Over-Fiber Link for Millimeter-Wave Wireless Systems

“…Mixing of these phase noise correlated mmwave frequency components, will result in the cancellation of the RF phase noise, of the IF signal, upon frequency down-conversion. Achieving phase noise cancellation, in this manner, effectively removes the requirement for phase correlated or ultra-low linewidth laser sources which have been shown to be a necessity for heterodyne A-RoF applications [18]. The presented architecture permits a significant reduction in the complexity of the C-BBU transmitter and RRH antenna site designs.…”

“…The use of OFCs, for mm-wave signal generation, gives precise control over the center frequency of the mm-wave signal to be transmitted from the antenna unit. Previous work on OFC based optical heterodyning analog RoF [18] has shown how the coherence length of correlated optical tones requires strict path matching between these carriers throughout the system. Effective path length difference and fiber dispersion in the system results in decorrelation at the receiverproducing mm-wave carriers with relatively high levels of phase noise.…”

“…The optically compatible A-RoF fronthaul network can facilitate the distribution of mmwave carriers to various RRH sites through the same fiber network leading the way for centralization of the resources. However, in such systems, the phase noise (PN) of the photogenerated mm-wave carriers has been shown to be a performance limiting factor [18], especially for the small baud rate/subcarrier spacing multicarrier signals as envisioned in 5G and beyond 5G wireless systems. Hence, it is necessary to either reduce the phase noise of mm-wave carriers or compensate it in some way for the successful system implementation.…”

16-QAM Vector Terahertz-Wave Signal Generation by Simple MZM-Based Optical Frequency Comb

“…This problem can be resolved by coherent detection techniques with good frequency selectivity and advanced digital signal processing (DSP) algorithms to recover the transmitter signal accurately, in particular the receiver-based and DSP-based carrier recovery algorithms, which makes the signal processing time longer and meanwhile make system more complex. The employment of the optical frequency comb in photonic vector THz-wave signal generation effectively solves the aforementioned problems [27][28][29][30][31][32]. Optical frequency comb generation based on one single laser source driven by radio frequency source and serval optical modulator is verified to be very cost-effective, which has the advantage of simple structure, high operational stability, tunable wavelength, and optical frequency comb lines with strong coherence.…”

A 60 GHz RoF generation system based on optical beat of narrowband Bragg filters

“…Among the most recent studies for the generation of frequencies close to 60 GHz [18][19][20][21] is the use of frequency-division orthogonal multiplexing (OFDM, multi-carrier modulation) proved by a RoF tunnel certificate operating two wireless radio links [22]. This millimeter wave is generated by the gain-switching laser that is a result of the beating of two uncorrelated optical tones [23] on the one hand or by using Mach-Zehnder modulators (MZM) [24,25] on the other.…”