Enhancing CESMO

Generic radar screen
The CESMO tactical datalink protocol helps aircraft geolocate the position of hostile ground-based air surveillance and fire control/ground-controlled interception radars to help improve survivability.

The uptake of NATO’s CESMO tactical datalink protocol is proceeding apace with ongoing enhancements to deepen its abilities to share electronic intelligence to support air operations.

This year’s Association of Old Crows’ Electronic Warfare Europe exhibition and conference was held on 14th and 15th May in the town of Lillestrøm, southeast Norway. Delegates were updated on the progress of the North Atlantic Treaty Organisation’s (NATO’s) Cooperative Electronic Support Measure Operations (CESMO) Tactical Datalink (TDL) protocol.

CESMO helps aircraft share hostile emitter location information so the latter can be avoided or engaged. The SEWWG (NATO SIGINT and Electronic Warfare Working Group) is CESMO’s custodian. Military aircraft are routinely equipped with Radar Warning Receivers (RWRs) and Electronic Support Measures (ESMs). ESMs and RWRs protect aircraft by detecting, identifying and locating hostile ground-based air surveillance and fire control/ground-controlled interception radars. An RWR tends to give aircrew a relatively simple warning with details of a radar’s bearing relative to the aircraft. An ESM supplies more detailed information on the radar’s identity and location. The electronic support measure will also furnish specifics on the waveforms the radar is using although, to an extent, RWR and ESM functions overlap.

How CESMO works

RWRs and ESMs can use two mechanisms to detect and locate red force radars, chiefly Angle-Of-Arrival (AOA) and Time of Arrival (TOA). AOA determines the Line-of-Bearing (LOB) from one point to another, in this case between an aircraft and a hostile radar. Consider three aircraft flying in the vicinity of a ground-based air surveillance radar. One aircraft is flying towards the radar on a north-south bearing, the second is flying on an east-west radial away from it and the third is flying on a south-north bearing towards it. Each plane is equipped with an RWR which determines the radar’s line-of-bearing relative to the aircraft. All three planes detect the same radar transmission. The RWR on the first aircraft determines a southern LOB to the radar. The RWR on the second determines a westerly LOB while the third aircraft’s RWR determines a northerly line-of-bearing. By using this information, the radar’s position is determined as the point where all three bearings cross.

TOA works slightly differently. We will stick with our three aircraft, all of which are continuing to fly the same courses in the vicinity of the hostile radar. One aircraft is 100 nautical miles/nm (185.2 kilometres/km) from the radar flying on north-south bearing. The second is 150nm (277.8km) from the radar flying away on an east-west radial. The third is 50nm (92.6km) away flying on a south-north bearing. Triangulation relies on the fact that radar transmissions move at light speed (161,595 nautical miles-per-second/299,274 kilometres-per-second).

Radar transmissions will take different times to reach each aircraft’s RWR. For the first plane it will take the transmissions 0.6 milliseconds to get there. For the second it will take 0.9 milliseconds and for the third 0.1 milliseconds. Calculating the time difference taken by the radar transmissions to reach each aircraft relative to their position computes the radar’s location. This data is fused with the aircraft’s position as derived from its navigation equipment and sent from each aircraft via their standard communications links. The data reaches a central computer housing the CESMO software. Once the data arrives, the software computes the point where the lines-of-bearing from each RWR meet.

Once the CESMO software ascertains the radar’s location it retransmits this to other friendly aircraft at risk of detection. The radar can then be avoided or engaged with kinetic, electronic and/or cyberattack. CESMO information is sent back out across the same communications links. Data is carried on standard very/ultra-high frequency (30 megahertz to three gigahertz) links and tactical datalinks like NATO’s Link-16. Traffic is carried in IP (Internet Protocol) format messages absorbing under 16 kilobits-per-second of bandwidth. Furthermore, CESMO is a node-less network as there is no single, central point of network control. Should one platform sharing its information be lost this will not cause the collapse of the CESMO network.

Updating CESMO

As Armada reported in June 2023, new messaging standards are being introduced into the CESMO architecture. The new standards widen the remit of the data shared across a CESMO network and cover electronic attack and Emission Control (EMCON) information. Tactical messaging can now be moved across CESMO links with information on how an emitter is to be engaged. EMCON messages enable the distribution of frequencies off limits for electronic attack.

Delegates were told by representatives from the Bundeswehr (German armed forces) that recent exercises involving CESMO and the German armed forces had seen traffic carried across Link-16 and Satellite Communications (SATCOM) links. Other conduits employed include tactical radio TDLs, local area networks and SINA (Secure Inter Network Architecture) wide area networks. The representatives added that CESMO is “designed to work with limited bandwidth radios with long latencies when the reception of messages cannot always be ensured.”

CESMO will experience further capability enhancements, according to the Bundeswehr representatives. These enhancements include the handling of CESMO across NATO’s Link-22 TDL (2MHz to 29.9MHz, 225MHz to 399.975MHz). Link-22 is mainly used to support naval operations. Other protocols that will handle CESMO traffic including NATO’s JREAP (Joint Range Extension Application Protocol) and Systematic’s SitaWare Command and Control (C2) software. SitaWare is used extensively to support C2 in all domains across NATO and allied nations. JREAP allows TDL traffic to be moved across beyond line-of-sight links like SATCOM.

The Bundeswehr representatives said that two CESMO enhancements covering track classification and messaging have already been performed. The SEWWG is planning to make at least two updates per year. These updates will cover airborne electronic attack coordination, emitter association and disassociation messaging, time difference of arrival coordination and platform activity messaging. Nonetheless, the representatives emphasised that the more nations join the CESMO initiative, the more updates and enhancements can be made.

by Dr. Thomas Withington