Since ancient times most of the communication technologies first found their ways into defense applications. The research and development in communication technologies has had distinct differentiation in terms of defense use and commercial use. Technologies for defense use have been covert until their inventors and governments thought to make them available for public use. On the other hand, commercial use technologies had a difficult time making inroads into the defense sector due to their open architecture, standardization, security concerns, etc. However, this environment is rapidly changing with the adoption of commercial wireless communication technologies across the globe. The sheer size of user base and the overall impact of modern technology motivates researchers to improve the existing wireless communication technologies to meet and exceed the growing demands of users. In less than 25 years, advancements in cellular technologies have grown data rates from a few tens of kbps to a Gbps. Commercial off-the-shelf (COTS) products have become a familiar name in the defense industry resulting in benefits like shorter development cycles, ready availability, lower cost and ease of technology refresh. Earlier roadblocks like standardization and open architecture have become advantages as they allow defense R&D to benefit from best practices of the commercial industry and make appropriate technology modifications to suit the needs of defense applications.
Wireless communication for defense applications
Due to the complexity and diversity of defense requirements, there are numerous types of communication systems required. Communications systems as traditional as high-frequency (HF) two-way radios to more elaborate systems such as satellite communications (SATCOM), RADAR and airborne early warning and control (AEW&C) systems are being used. With new technologies in place, current warfare is now being termed as network centric warfare wherein a robustly networked defense force improves information sharing which enhances the quality of information and shared situational awareness. This shared situational awareness enables collaboration and self-synchronization, and enhances sustainability and speed of command. All of these dramatically increase mission effectiveness. In network centric warfare, both speed of information sharing and quality of information form an integral part of the information domain and this is where a choice of communication technology plays an important role. Commercial cellular communication technologies like GSM and WCDMA were limited in terms of data rates, bandwidths, IP connectivity etc. These limitations are being addressed by continuous enhancements in the 4th generation of cellular technology; LTE. In release 12 of 3GPP LTE standards, enhancements specific to public safety and mission critical applications were identified and these have taken shape in the latest release 14 of 3GPP LTE standards.
What makes LTE relevant?
LTE offers multiple deployment bandwidths:1.4 MHz, 3 MHz, 5 MHz, 10 MHz, 15 MHz and 20 MHz, which makes it a flexible choice depending on the application. LTE being an all IP technology offers high level of security as desired for defense applications. One of the most important aspects of LTE in this regards is OFDM and OFDMA. Orthogonal frequency division multiplexing (OFDM) has been the backbone of current commercial wireless systems because it delivers high data throughput in real-world environments, along with spectral efficiency and link flexibility. OFDM’s low symbol rate and multicarrier structure, combined with coding and forward error correction, allow it to operate effectively in channel conditions degraded by interference, jamming, and frequency selective fading.
Because of its multicarrier structure, OFDM is readily extendable to simultaneous multiple-access capability by mapping subcarriers to users in a scheme called orthogonal frequency division multiple access (OFDMA). This multiple access approach is especially attractive because multiple users can be supported in a flexible fashion with only minor changes in the air interface. In addition, Multiple-Input Multiple-Output (MIMO) techniques can be used with OFDM and OFDMA systems to further improve data throughput in the presence of multipath environments.
These underlying benefits of LTE makes it attractive for flexible deployment in defense applications, both terrestrial and marine. One of the important elements of network centric warfare is video streaming for improved situational awareness. Defense users could potentially take advantage of sophisticated existing hardware and software solutions that offer proven commercial performance in different physical environments from wide open terrain to complex obstructed urban environments. COTS solutions can be configured to meet many different commercial requirements in terms of number of users, required average and peak data rates, cell sizes and configurations, and overall coverage areas.
They not only include network infrastructure but a range of handsets and terminals that implement sophisticated roaming features that can comprise automatic switching to nearby LAN resources when available. This is a powerful benefit when optimizing the use of valuable metropolitan area network (MAN) resources. While these technologies were not designed with defense applications in mind, particularly in the areas of security and resistance to jamming, they are designed to handle environments with interference and competing spectral users. They could potentially serve as a base layer, to which additional layers for security and robustness or redundancy may be added.
In addition to the above-mentioned capabilities of LTE, newer releases from 3GPP have made this technology even more powerful by adding higher order of MIMO, beam-forming, carrier aggregation, and space-time coding (STC).
LTE gets Mission Critical
As defined by 3GPP, mission critical stands for quality or characteristic of a communication activity, application, service or device, that requires low setup and transfer latency, high availability and reliability, ability to handle large numbers of users and devices, strong security and priority and pre-emption handling. This definition very well captures the applicability of LTE for defense.
In release 12 of 3GPP LTE standards, two specific enhancements in LTE were identified to address public safety applications, namely, Proximity Services (ProSe) and Group Communication System Enablers for LTE (GCSE_LTE). Proximity services consists of two main elements: network assisted discovery of users with a desire to communicate with those who are in close physical proximity, and the facilitation of direct communication between such users with, or without, supervision from the network. The definition of proximity services includes some features that are exclusively for public safety applications in public safety spectrum. In the feature “User equipment to network relay” one mobile acts as a relay for another and provides access to network services outside the normal network coverage area. In the feature “User equipment to user equipment relay” one mobile acts as a relay point between two others and allows communication to take place without going via the network even if the communicating mobiles are out of range for direct communication.
Release 14 of 3GPP LTE standards has defined features and enhancements specifically for mission critical applications. Under the heading of mission critical, features like mission critical push to talk (MCPTT), mission critical video over LTE (MCVideo) and mission critical data over LTE (MCData) have been introduced. Under this heading, multiple study topics have been identified such as mission critical security enhancements, mission critical system migration and interconnect between MCPTT systems, mission critical communication interworking with LTE and non-LTE systems, protocol enhancements for MCPTT over LTE and security of the mission critical service.
3GPP has been cognizant of the mission critical requirements which is to develop systems that are highly robust and can address the specific communication needs of emergency services. The study item on mission critical communication interworking with LTE and non-LTE systems emphasizes the use case to make LTE work with public safety standards – such as P25, TETRA and legacy LMR. These public safety standards have so far provided a set of features that were not previously supported in commercial cellular systems.
The MCPTT Service is intended to support communication between several users (a group call), where each user can gain access to the permission to talk in an arbitrated manner. However, the MCPTT Service also supports Private Calls between pairs of users. The MCPTT Service builds on the existing 3GPP transport communication mechanisms provided by the Evolved Packet System (EPS) architectures to establish, maintain, and terminate the actual communication path(s) among the users. The MCPTT Service also builds upon service enablers like GCSE_LTE and ProSe.
MCVideo defines a service for Mission Critical video communication using LTE transport networks. Mission Critical refers to meeting the needs of agencies providing Public Safety services such as, but not limited to, Police, Fire and Ambulance services. Surveillance cameras could also use the MCVideo service in which case, in addition to the existing video storage and monitoring activity already used for the surveillance camera, authority may be given to users in the MCVideo system to connect to, control, receive and forward video either to an individual or to a group. Although the service is designed for transport over commercial and dedicated LTE networks it is not expected to be limited to use over LTE.
MCData service is aimed to provide a means to manage all data connections of mission critical users in the field and provide relevant resources to the ones who need it. For example mission critical users already use event manager software along with the voice system. The migration to LTE networks will allow mission critical users to operate current and new data services whilst relying on the fundamental capabilities of mission critical communication such as defined for MCPTT and Mission Critical Services Common Requirements (MCCoRe). The MCData Service provides a set of communication services that will be directly used by the user or functions that will be called by external applications in control rooms. The MCData Service will reuse functions including end-to-end encryption, key management, authentication of the sender, etc. defined in MCCoRe in order to provide group communications for data services. In addition, the MCData Service will provide a set of generic capabilities such as: messaging, file distribution, data streaming, IP proxy, etc. Also, the MCData Service will provide specific services such as conversation management, data base enquiries, internet access, robots control.
Conclusion
In summary, improvements in LTE data rates and reduction in latency can address the important aspects of information domain; quality and speed of information sharing. Leading defense products companies have already added LTE products like ruggedized user equipment or terminals, ruggedized network components like LTE eNodeB, micro cell, pico cell and LTE core. Although 3GPP defined the mission critical features and capabilities with public safety applications in mind, this doesn’t forbid the use of LTE for defense applications. Mission critical aspects of LTE has further increased its applicability to the defense sector as it demands high reachability, availability and reliability of the service, low latency, real-time operating capabilities, highly secured operations, inter-operability with other services and systems, private and group communications, handling of emergencies and ability to provide prioritization, pre-emption, queuing and assured quality of service.
References
[1] OFDMA Introduction and Overview for Aerospace and Defense Applications – Application Note, Literature number 5991-4596EN
[2] 3GPP TS 22.179: “Mission Critical Push To Talk (MCPTT) over LTE; Stage 1”.
[3] 3GPP TS 22.280: “Mission Critical Services Common Requirements (MCCoRe)”.
[4] 3GPP TS 22.282: “Mission Critical Data services over LTE”.
[5] 3GPP TR 23.782 V15.0.0 “Study on mission critical communication interworking between LTE and non-LTE systems”.
