A Big Mesh: Military Tactics and the Future of Mobile Communications
An analysis of the historical link between the military's use of retransmission stations ("retrans") and the advent of the mesh network.
(Video screen shot of a US Army mountain patrol in Eastern Afghanistan, October, 2011)
Unalone and Unafraid
A few years ago in the Hindu-Kush Mountains, a small US Army patrol found themselves over 100km away from their base of operations. Surrounded by undulating mountains that would make seasoned climbers nervous, the patrol discovered that their communications voice lifeline was ineffective due to the terrain. With the radio link broken, the patrol moved to a location within range of a friendly radio retransmission station. After tuning their radios to the established retransmission frequency, the patrol's radio crackled to life. The patrol sent a signal calling the headquarters at the base of operations and received an immediate reply. Unlike typical long-range transmissions on an encrypted network, the voices were crystal clear. A wave of relief washed over the patrol with the return of a reliable means with which to send reports, request air/fire support, or call for early extraction. While this is a personal example, this scenario is repeated constantly in remote combat zones around the world.
Understanding the Network
Radio retransmission (or "retrans" for short) is a common military technique used to provide long-range, secure, line-of-sight (LOS) voice communications in remote and austere environments. Units establish retrans stations by slaving together two amplified radios which function to receive any signals on one frequency within range and subsequently retransmit them on a separate frequency. Due to the lower signal strength of tactical VHF radios, the retransmitted signal is typically amplified to ensure the signal is received at all nodes operating in the area. The station location is often on a prominent terrain feature to ensure maximum reach, especially in areas prone to breaks in communication or "dead space" such as mountainous terrain. These stations can be fixed/permanent structures for long-term operations or mobile/temporary sites for short-term operations. While the use of radio retrans is usually a very deliberate and planned event, the discovery of this capability was quite accidental.
(USS George Washington enroute to France, 1919)
A Fortunate Accident
In March 1919, President Woodrow Wilson embarked on the US Navy troop transport ship USS George Washington to France with the intent of formally bringing World War I to an end at the Treaty of Versailles. During the return journey, the George Washington participated in an Independence Day celebratory broadcast to the New Brunswick Naval Radio Station in New Brunswick, New Jersey. The radio station (callsign NFF) utilized a high powered transmitter with an incidental configuration that would immediately rebroadcast signals received on the wavelength used by the George Washington. While the intent was to simply communicate with the ship, the result was transmission of both sides of the radio transmissions via a very low frequency (VLF) of 22kHz, which has the ability to propagate at a range beyond 5,000km. Of note, the amateur radio enthusiast magazine QST published a letter in January 1920 received from Mr. James Corum of Deering, North Dakota, which stated he received the two-way Independence Day conversation between NFF and the George Washington at his home, no less than 1,423 miles away!
Network? Yes. Mesh? Sort of.
The configuration of these networks that enable each radio to talk to any other radio through the retrans station or directly to one another as in machine to machine (M2M) applications qualifies it as a hybrid mesh network. The topology of this network is dynamic. When all radios are within range of one another and the retrans station, the network mimics a flood topology. As elements move around the battlefield and enter/exit dead space, the network mimics a routing topology. However, instead of utilizing an algorithm to determine the best route to transmit data, the network utilizes user judgment and a "relay" system. In a relay system, an end user volunteers to become an ad-hoc retrans station. The user receives the voice transmission from the sender, records it manually, and the retransmits the data to the receiver. Additionally, all senders and receivers require verbal acknowledgement, similar to a network handshake.
Current military applications
This requirement to accommodate constant communications and data links on a dynamic/fluid battlefield sparked the development of wireless data networks exhibiting the characteristics of a true mesh topology. Each device in this network serves as a node by transmitting its own data as well as forwarding traffic unrelated to its own functions (voice, data, TCP/IP, etc). In the absence of an established communications infrastructure (or in spite of it due to its security vulnerabilities), this capability is critical to optimizing processes such as the movement of supplies forward to the battlefield and casualties back to ambulance exchange points and beyond.
(A CAISI terminal (front) between two communications control tents)
A real world example of a mesh network implemented in support of military operations is the Army's Combat Service Support Automated Information Systems Interface (CAISI). CAISI is a mesh network integrating key logistical systems such as the Unit Level Logistics System-Ground (ULLS-G) and the Medical Communications for Combat Casualty Care (MC4). CAISI serves as the actual framework of the mesh network, allowing these systems to communicate data to and through each other. This critical ability to bring instant connectivity to the fight allows Army logisticians to focus less on establishing communications and more on allowing Army warfighters to accomplish their mission.
The Future of Mobile Communications
These mesh networks show the value of M2M capabilities via a mesh topology in an austere environment. This is clearly not a critical system to mobile communications in the developed world. If you picked up your mobile phone and texted your bestie across the country, you could expect an instant reply. Modern communications networks rely on fixed infrastructure consisting of interconnected cellular towers, microwave data transmission, fiber optic cable, etc. These systems are dependable and fast, but what if we suddenly lost that infrastructure, or it was significantly degraded or overloaded? As far-fetched as it sounds, extremist groups utilizing unconventional tactics understand the value of disrupting communications networks via the use of electromagnetic pulse (EMP). While its ability to completely "turn out the lights" is debatable, the ability to impact highly sensitive electronic components especially within close range of a nuclear detonation is certain. The phones already in use with the general population would likely be worthless. Caches of simple mobile phones with the integrated mesh network technology embedded could be stored with electromagnetic shielding in National Guard armories, FEMA offices, or local emergency management centers for distribution in the event of a disaster or emergency. In order to reestablish communications networks and subsequently coordinate emergency response efforts, a flood mesh network of mobile phones would satisfy the need for individual communications while facilitating an ad hoc wireless network for data transfer. This topology would also facilitate mass communication to all mobile phones, thereby keeping the public informed and providing guidance along the way.
Besides a failure of infrastructure, it is reasonable to speculate that the data requirements of society could exceed the capability of its communications networks. In this case, M2M capabilities in the mobile network would ease the burden on the fixed infrastructure. The possibility of satellite networks replacing the ground infrastructure of mobile networks exists as a possibility. It would suffice for routing large amounts of data via point to point communications where the transmitters have sufficient hardware and power, but it is impractical for everyday usage with current technology due to limitations in transmitter size and battery life.
While your smartphone is likely safe from your operating system receiving an update for mesh network protocols, the future use of mesh networks as simple means to increase the efficiency of data transfer in mobile networks is a very real possibility. Your mobile phone contract could eventually include a clause permitting transmission of unrelated data via your phone in the interest of high-speed local data transfer or even volunteering participation in transmissions from the emergency broadcast system such as amber alerts, public safety announcements, etc. Make sure you read the fine print.