Jŏngjŏm FSO

A single transceiver module for the Jŏngjŏm FSO system.

Jŏngjŏm (Menghean: 정점 / 頂點, "Peak" or "Zenith") is a type of free-space optical (FSO) communication system used by the Menghean Navy and exported to some of Menghe's allies. It consists of four FSO send-receive units which can wirelessly exchange data using visible or, in later versions, infrared light. Compared with a radio frequency system, the Jŏngjŏm FSO is almost impossible to jam or intercept, making it a secure way of transmitting data while operating under highly restrictive EMCON conditions. However, it is limited to line-of-sight transmission and suffers severe attenuation from rain, clouds, and heavy fog.

Background

As far back as the 1930s, the Menghean Navy (then the Imperial Menghean Navy) placed a heavy emphasis on fighting under conditions of radio silence, as radio transmissions could be intercepted and read by enemy forces. Even if transmissions were encrypted, the very presence of an encrypted radio signal could inform hostile forces about the bearing to a Menghean ship or fleet. Menghean forces conducted a number of successful surprise attacks early in the Pan-Septentrion War by approaching under strict radio silence, and during the later years of the Menghean War of Liberation, Communist forces used captured torpedo boats and light vessels to raid coastal bases.

During this early period, Menghean naval ships relied on signal flags and semaphore flags for daytime communication and signal lamps for nighttime communication. As late as the 1990s, many Menghean warships, such as the Ansa-class frigates, included at least one signal lamp on a high platform to maximize signaling range over the horizon.

Though safe against radio interception, these systems had a very low data transfer rate, as they required crews to transmit sinmun components one at a time. The Menghean Navy Code of Signals includes a set of two- and three-flag combinations to use as shorthand for common messages, but allows little flexibility beyond this, and is only visible in daytime. All of these systems also relied on a human observer to identify, write down, and decode signals, making errors and misreadings common. And while impossible to intercept at long ranges, they could all be read (and potentially decoded) if used within visual range of an enemy installation.

Beginning in the early 2000s, Menghe began investigating free-space optical communication as an alternative means of transmitting data. Many Menghean private-sector tech companies, including the large Samsan Group, had been pursuing FSO technology as a means of securely transmitting large volumes of data at college campuses, linking remote mountain villages to the national internet network, or quickly re-establishing communications after a natural disaster. In 2003, the Menghean Ministry of National Defense concluded a contract with Samsan Defense to develop an FSO system for the Menghean Navy's warships and shore installations, with development work accelerating after relations with Maverica, Innominada, and the Entente Cordiale broke down in 2005.

The Jŏngjŏm FSO system first entered service in 2011, aboard the Yechŏn-class frigate HO-332 Dŏkju. From that year onward, it was installed on nearly all new-build warships above missile boat size, and retrofitted to many existing warships such as the Chŏndong-class destroyers during mid-life refits or minor maintenance periods. It has also been exported to many Namhae Front navies.

Description

Each Jŏngjŏm transceiver consists of a set of six individual laser emitters, a low-resolution camera to aim the transceiver, an alignment laser, and a central receiver lens. When two transceivers are pointed at one another, they select a bandwidth and establish a two-way or duplex datalink with simultaneous high-rate data transfer in both directions. Because this requires a direct alignment of both transceivers, the base of the transceiver module has precision motors controlling elevation and bearing, and is stabilized so as to maintain contact even as the ship is pitching and rolling.

Because each transceiver can only communicate with a single counterpart, a typical Jŏngjŏm installation contains four transceivers in a diagonal cross formation. This ensures that two transceivers are available to point at any given bearing. Large ships that may serve as formation leaders, such as aircraft carriers, may have a second ring of transceivers, for a total of eight.

A typical Jŏngjŏm installation also includes a set of passive laser receivers arranged in a ring, usually just above the transceiver group. This allows an outside platform to "ping" a ship with a laser signal, giving its bearing and requesting permission to establish two-way FSO communications.

The actual effective range of the Jŏngjŏm FSO system is classified. Independent sources estimate a figure of 2-3 kilometers for the useful range of military-grade FSO transceivers, though Menghean practice, such as the installation of Jŏngjŏm modules high on sensor masts and the introduction of the Dungan airborne relay, suggest the Menghean Navy is interested in maintaining two-way links at distances of up to 20-30 kilometers. Actual range is highly dependent on atmospheric conditions, as rain, clouds, fog, sea spray, and smoke can all seriously attenuate or entirely block the signal.

The frequencies of the six laser emitters are also classified, but at a minimum, they are known to include both visible and infrared options, and high-power and low-power options, to allow crews to select frequencies that transmit best in a given set of atmospheric conditions.

Advantages

• Because the signal is only transmitted in a narrow laser beam, FSO signals are nearly impossible to intercept; a third listening receiver would have to be almost perfectly in between the two transceivers, or almost perfectly behind one of them.
• On this basis, a formation operating under strict EMCON conditions can still use FSO signals freely without revealing its location.
• FSO signals are nearly impossible to jam by conventional electronic warfare.
• FSO signals allow for a very high rate of data transfer, even compared to UHF or SHF radio datalinks.

Disadvantages

• Even in clear conditions, FSO communications are strictly limited in range by the visual horizon.
• Even at short ranges, FSO communications can suffer severe attenuation from inclement weather.
• Each transceiver can only establish a two-way link with one other ship, making it difficult to coordinate a large formation without the use of relays.
• The electric motors on each transceiver must be very precise in order to maintain alignment while both sender and receiver are moving and rolling.
• High-power beam options can cause eye damage to sailors on the receiving ship, which may also explain the Menghean Navy's preference for mounting Jŏngjŏm systems high on a sensor mast.

Later expansions

Jŏngjŏm-W

Jŏngjŏm-W (with W denoting wisŏng or satellite) is an FSO system capable of transmitting data between a surface ship and a satellite. Compared with Jŏngjŏm, it is larger and heavier, usually with only one or two mountings for a shipborne installation. It is typically reserved for large ships serving as formation leaders. It is much less flexible than a conventional SATCOM dome, as it suffers severe attenuation in foggy or overcast conditions, but on a clear day or night it can communicate more securely and more effectively.

Jŏngjŏm-J

Jŏngjŏm-J (with J denoting jamsuham or submarine) is a system used on some Menghean submarine classes. It consists of a single FSO send-receive unit on top of a periscope mast, which can be extended while the submarine is surfaced or at periscope depth. It is less widely used than the surface ship systems, as it takes up the footprint of a full periscope mast and requires another ship or aircraft to be near the submarine.

Dungan

Dungan ("obtuse angle") is a communications pod for aircraft which consists of a Jŏngjŏm-compatible send-receive unit and its associated computing systems. It can be mounted on any Menghean hardpoint with 250mm-spaced bomb suspension lugs, even without a connection to the aircraft's own electronics, and can be fitted to helicopters, fixed-wing aircraft, and UAVs. With two such systems fitted, any helicopter, plane, or UAV can relay signals from one ship to another, extending the FSO link beyond either ship's visual horizon. Because of atmospheric attenuation, however, these relay systems are still limited in their effective range, depending on weather conditions.

See also

• MChGJ-0800 (similar Menghean Army system using SHF radio waves)
• Menghean Navy Code of Signals