Exploring Antenna Remoting Using RFoF: Revolutionizing Communication Technology

Across industries, applications and deployment fields, wireless communication is happening more often but the need to transmit radio frequency (RF) signals over extended distances in cables (“wires”) with minimal loss is growing at a significant pace. 

This is especially challenging now that higher frequency bands are deployed to take advantage of higher capacity and faster data rates at the cost of resiliency. For example, high frequencies used in 5G cellular communication, such as mmWave, can produce significantly more throughput but are also more easily interrupted by any natural or man-made obstacles where line of sight is required. This shift is also happening in military communications, where there is a clear transition from communication on the Ku-band (12.5-18 GHz) to the Ka-band (26.5-40 GHz) to take advantage of higher data transfer rates.  At higher frequencies, antennas are required to maintain line of sight – while connectivity between the antenna and the communication equipment is done over coax cables or waveguides. The role of fiber optics will dominate the higher frequencies of cabled transport.

Another growing complexity for resilient over-the-air communication is mobility. Maintaining a high-frequency signal is hard enough in a stationary environment, but in military and broadcasting use cases, there is often a need for the antenna to be far from where the information is being collected (i.e. a control center).

The deployment of antenna remoting, leveraging RF over Fiber (RFoF) technology, is emerging as a pivotal solution to address these challenges. This article explores antenna remoting in RFoF, discussing its significance, underlying principles, and diverse range of applications across various industries.

What is RFoF and Antenna Remoting?

RFoF technology converts RF into optical signals for transmission over fiber optic cables, and subsequently reconverts it back to RF signals at the receiving end. The process involves using electro-optic modulation techniques to convert the RF signal into an optical waveform suitable for transmission over single-mode or multi-mode fiber optic cables, which offer low attenuation and high bandwidth capabilities. At the receiving end, the optical signal is converted back into an RF signal using photodetection techniques such as direct detection or coherent detection. This conversion process restores the original RF waveform, preserving signal integrity and fidelity (i.e. signal to noise ratio) over long distances that simply cannot be accomplished by its most common alternatives coaxial cable or waveguides (Fig. 1).

Figure 1: RF Attenuation - Coaxial Cable vs. Fiber (to 40GHz)

What are the Different Types of Antenna Remoting?

There are two ways to deploy antenna remoting regardless of its application. The first is Simplex (Fig. 2), where the traffic to or from the antenna is unidirectional, serving purposes such as radio telescopy or jamming in electromagnetic warfare.

The second is Duplex (Fig. 3), which facilitates bi-directional communication with the antenna, essential for applications requiring both transmitting and receiving functions. This implementation involves separating the transmitting and receiving elements to minimize interference and optimize signal integrity. This is the most common form of antenna remoting in wireless communication use cases and military applications.

Figure 2: Simplex Antenna Remote Example – GNSS timing signal to indoors equipment

Figure 3: Duplex Antenna Remoting Example – providing indoor wireless coverage

What are the Key Performance Metrics for Antenna Remoting?

Since the conversion from electrical to optical and back happens for wide frequency ranges and diversified dynamic ranges, the link requirements should be properly defined. To ensure proper deployment and effectiveness of antenna remoting, it is important for signal transport designers to consider these key parameters:

Frequency

In antenna remoting, this references frequency of the RF signals being transmitted and received determines the characteristics of the optical and electrical components used in the system. It is crucial that the frequency of the RF signals falls within the operating range of the optical transmitters, receivers, and fiber optic cables to achieve optimal signal transmission and fidelity.

Power

Power refers to the strength or amplitude of the RF signals being transmitted and received, typically measured in watts (W) or decibels relative to a reference power level (dBm). The power level of RF signals impacts the performance and range of antenna-remoting systems. Adequate power levels are necessary to overcome signal attenuation and ensure reliable transmission over long distances. Additionally, controlling the power levels of RF signals helps prevent signal saturation or distortion, which maintains signal integrity and fidelity.

Dynamic Range

Dynamic range refers to the range of signal amplitudes that an antenna-remoting system can effectively transmit and receive without distortion or degradation. It is essential to ensure that the dynamic range of the system accommodates the wide range of signal amplitudes encountered in practical applications. A wide dynamic range allows the system to handle both weak and strong signals, enabling reliable communication over varying signal conditions and distances.

Noise Figure

Noise figure (dB) quantifies the amount of additional noise introduced by the components of an antenna-remoting system. Lower noise figures indicate better performance. Minimizing noise figures is crucial for maintaining signal-to-noise ratio (SNR) and maximizing the sensitivity and accuracy of the system, particularly in low-power or weak signal environments.

Error Vector Magnitude (EVM)

EVM measures the accuracy of the modulated RF signal transmissions relative to their ideal or reference waveforms. High EVM values indicate greater deviation from the ideal waveform and may result from impairments such as noise, distortion, or modulation errors. Minimizing EVM is essential for ensuring signal quality and fidelity in antenna-remoting systems, particularly in digital communication applications where data integrity and reliability are paramount.

Antenna Remoting Use Cases

Given its increased resiliency and security over other methods of RF transmission such as coaxial cable and waveguides, antenna remoting is used for many important applications today across many industries such as military, satellite, broadcast, and telecommunications as well as astronomy. Here are some of the most common use cases:

Global Navigation Satellite System (GNSS)

Antenna remoting is an ideal choice for GNSS timing applications because it ensures accurate and synchronized timing information across distributed systems by preserving signal integrity, minimizing delay, and offering scalability and redundancy. Fiber optic cabling enables GNSS timing signals to reach the server’s timing cards, base station radios and direction-finding arrays, ensuring reliable synchronization critical for telecommunications, financial transactions, and scientific research.

One of the most significant modern use cases of antenna remoting in the United States for GNSS timing is data centers. The United States has the most data centers in the world with 5,375 as of 2023, nearly double the 2,701 in 2022. This demand has led to more facilities in remote locations with challenging connectivity environments. Antenna remoting not only enables them to receive precise timing but also affords operators a way to monitor all RFoF equipment across their network of data centers.

Satellite Communication (SATCOM)

In SATCOM applications involving stationary large fields, such as satellite ground stations or satellite earth stations, antenna remoting facilitates the transmission of RF signals between ground-based antennas and the SATCOM equipment located within the facility. For example, in a satellite Earth station with multiple antennas pointing towards different satellites, antenna remoting enables operators to transmit RF signals from each antenna to the SATCOM equipment for processing and communication. This setup allows for efficient utilization of space and resources within the satellite ground station while maintaining reliable communication links with orbiting satellites.

Astronomy

In astronomy applications, particularly those involving very large deep space antenna arrays, antenna remoting can transport a wide dynamic range of signals from celestial objects. Fiber optic cables are used to connect the antennas to the data processing equipment located within observatories and/or research facilities. For radio astronomy projects involving large arrays of antennas distributed over vast distances, antenna remoting allows operators to synchronize and control the antennas remotely. Astronomers can capture detailed images of distant galaxies, pulsars, and other cosmic phenomena while ensuring precise timing and synchronization of data acquisition.

Command and Data Link (CDL)

Antenna remoting is utilized in CDL systems to establish secure and reliable communication between command centers, field units, unmanned aerial vehicles (UAVs) and unmanned surface vessels (USVs). Fiber optic cables connect the antennas to the CDL equipment located within military vehicles, aircraft, or ground stations.

Particularly for USVs, antenna remoting has become more important than ever because an error with the links could take days or even weeks to repair the communication. Typically, these vessels use Waveguides to transmit Ku-Band CDL communications payloads between radomes mounted above ship decks and equipment rooms within ship hulls. However, the waveguides are inflexible and prone to mechanical stress, necessitating meticulous maintenance, especially during prolonged sea deployments. Additionally, moisture and contaminants degrade the RF performance of the coaxial cables within the waveguide, making RFoF the ideal alternative given its resilience to these natural environmental conditions.

Secure Wi-Fi

Antenna remoting is used to provide secure Wi-Fi in Sensitive Compartmented Information Facilities (SCIFs) to maintain the integrity and confidentiality of classified communications. By isolating Wi-Fi access points outside the SCIF perimeter and transmitting signals over fiber optic cables, antenna remoting over fiber prevents unauthorized access and eavesdropping on sensitive information while enabling wide spectrum monitoring for all electromagnetic sources. This approach reduces electromagnetic emissions footprint outside the SCIF and ensures that wireless communications remain contained within the secure confines of the SCIF, minimizing the risk of interception. Antenna remoting also offers flexibility and scalability, allowing for optimal placement of Wi-Fi access points to provide comprehensive coverage and controlled flexible allocation of bandwidth services to different areas in a building, all while accommodating changes in user requirements. 

Military Field Deployable

In military field deployable applications, antenna remoting provides secure and resilient communication solutions for command and control, surveillance, and reconnaissance operations in remote or hostile environments. Fiber optic cables connect antennas mounted on military vehicles, aircraft, or ground stations to centralized command centers or tactical communication networks. It can also be used to divert enemy surveillance (exploring and mapping electromagnetic footprint) from knowing the location of vehicles or command centers for the purpose of attacking. It is as much of a defensive measure as it is one about flexible and easily deployable communication infrastructure.

Conclusion

By extending the reach of RF signals, preserving signal integrity, and enabling mobility and flexibility, RFoF systems are unlocking new possibilities across a wide range of industries, from telecommunications and satellite communication to military operations and scientific research.

As the demand for high-speed, reliable, and scalable communication solutions continues to grow, antenna remoting stands poised to play an increasingly pivotal role in shaping the future of global connectivity.

About the author

Meir Bartur, Ph.D., is the President & CEO of the Optical Zonu Corporation. Dr. Bartur has over 30 years of experience in leadership, product development, and technology innovation. As a Senior Member of the IEEE and recognized leader in the development of low cost fiber optic solutions for FTTx, he contributed both to the IEEE ITU PON standards. Before founding Optical Zonu, he directed Advanced Product Development and Strategic Technology for access transceivers at MRV Communications’ (MRVC), as well as business relations with its major clients. Prior to that, he held posts as VP of Engineering & Technology at SSDI (Solid State Devices Inc), VP of Engineering at MEC (Molecular Electronics Corp), and systems engineering Captain in the Israeli Air Force.