Exploratory Advanced Research Program

FHWA White Paper On Mobile Ad Hoc Networks

Technology Landscape Assessment

Current Applications

As of 2016, research on MANETs has not been widely adopted or applied in the civilian wireless networking field. However, MANETs have had an important presence in two fields: military and disaster recovery.⁽²⁾ In many situations, a military deployment involves operating a technology in harsh, infrastructure-less, and potentially hostile environments in which safe, reliable, and efficient communication is a challenge. For over a decade, military tactical units have used MANETs for autonomous maneuvering of unmanned vehicles and robots,⁽¹⁵⁾ and for critical radio communications to provide timely situational awareness for current and upcoming operation phases and to maintain data and connection integrity.^[10] In most cases, the military uses a combination of networks, including cognitive radio and satellites. The military will typically use more sophisticated nodes compared to commercial off-the-shelf (COTS) nodes that are commonly used elsewhere.⁽¹⁶⁾ Following the example of the military, police forces have recently started using tactical MANETs for crowd management and surveillance. One example of the use of a tactical MANET was during the 2016 Boston Marathon to provide secure communication support to law enforcement up to 30 miles apart.^[11]

As with military environments, disaster recovery environments are ideally served by MANETs because of their lack of infrastructure, topological barriers—such as collapsed tunnels—and potentially hazardous conditions.⁽¹⁷⁾ Some of the primary concerns for disaster recovery applications include accurately predicting movements among nodes to locate team members and the fast delivery of emergency messages.⁽¹⁸⁾

Improvements to Current Wireless Technologies

As research on MANET applications develops, the wireless technologies underpinning MANETs also improve. On the physical layer, improvements include more advanced nodes, such as lighter and faster drones, more powerful and efficient smart phones, and overall more durable devices. Additionally, improvements in battery technology have allowed all types of devices to establish and maintain a network over a longer duration. Sensors within each device, such as more efficient accelerometers and wireless receivers within smart phones, have greatly improved over the past 10 years.

In addition to changes in sensors and nodes, major strides have been made in the efficiency, quantity, and quality of data transmission between nodes, as well as securing the data in transmission. With respect to vehicles, DSRC has become the standard for communication among vehicles, particularly in vehicle-to-everything (V2X) communications. DSRC is a one-way or two-way short-range to medium-range wireless communication channel. This type of medium was primarily designed for vehicular communication systems and can be seen in V2X-types of communications. Along with other wireless communication technologies, DSRC is used in intelligent transportation systems (ITS) to ensure safe and interoperable connectivity across all transportation system modes,^[12] although to date most development has been concentrated on automobiles. While open to device manufacturers, application developers, and other users, safety applications are given priority over other applications.^[13]

Overall, there is a low latency—the delay in node-to-node communication—during communication exchanges using DSRC. DSRC channels have a high level of interoperability with common standards adopted by manufactures, including some level of safety message authentication and privacy.^[14] Because of this, DSRC is a potential medium for forming VANETs. Currently, however, DSRC is used mainly to broadcast information for crash avoidance purposes in the United States, which represents a precursor to a full MANET capability. Although multi-hop capabilities are included in Cooperative Intelligent Transport Systems standards for vehicle-to-vehicle (V2V) and V2I in Europe, this capability has not yet been widely developed in the United States. This means that for the United States, adoption of DSRC for MANETs will require further development of multi-hop capabilities.^[15] Researchers and practitioners have discussed using “epidemic distribution” to distribute digital credentials and certificate revocation lists, which would make DSRC channels part of the MANET paradigm.

One of the most prevalent improvements in wireless standards is the fifth generation of mobile technology (5G), which builds on all previous generations (1, 2, 3, and 4), LTE/LTE-A, and other Radio Access Technologies.⁽¹⁹⁾ 5G aims to be a HetNet that joins LTE to other wireless networks as a single system.^[16] Among other characteristics, 5G technology combines existing technology to support operations on smaller wavelength (millimeter waves) spectrums with a higher bandwidth that can potentially produce data rates of tens of megabits per second for tens of thousands of users.⁽¹⁹⁾ This next generation wireless technology is expected to provide a higher reliability, lower latency, and better address scalability issues when compared to previous standards. The degree to which 5G achieves each of these goals, however, remains to be seen. Researchers familiar with the technology argue that, in practice, only one or two of these targets can be achieved at once. For example, to achieve higher reliability at an extremely large scale, users must sacrifice latency. Thus, having both low latency and high reliability is not practical at a relatively large scale.^[17]

Multiple public and private organizations are working together to develop 5G standards to serve a wide range of applications. Because of the number of collaborating groups and level of complexity for the new technology, 5G standards are not expected to be adopted until 2020 or beyond. Once completed, 5G is expected to address many challenges, including network heterogeneity, which consists of, among other things, the melding of 802.11-based radio access technologies such as Wi-Fi and DSRC, and varying current and evolving technologies, such as LTE.

Some of the potential applications for 5G technology include improved data communication on high-speed trains; improved three dimensional connectivity among aircraft, such as drones (FANETs); and automated traffic control and driving. Overall, the examples mentioned here are not meant to be exhaustive but rather a glimpse into 5G opportunities.

Limitations, Challenges, and the Federal Role

Two decades of research into MANET technology has resulted in a deep understanding of the field’s strengths and limitations, along with the creation of numerous COTS products that can be used to create a MANET. While there has been limited Government application, new research shows potential adoption in fields such as industrial networks, smart grids, and ITS.⁽²⁾ However, there remain technical and policy-related challenges to the technology’s adoption and implementation.

Technical Challenges

Device interoperability through network standardization is critical for the wider adoption and adequate market diversification of MANETs.⁽²⁾ In addition to standards and interoperability, performance optimization can be a significant challenge for MANETs. The ability to efficiently communicate between nodes through optimal routing protocols is complicated by the potential for propagation issues, such as multipath and background noise. As researchers and developers address these challenges, scalability has become more important and could be a barrier to further MANET adoption. Simply adding more nodes to a network will not create a highly functional MANET. Increased traffic density in a network can lead to a broadcast storm problem, where node density above a certain value results in increased packet collisions.⁽²⁰⁾

MANETs are also limited in their ability to provide Quality of Service (QoS)—the ability of a node or router to classify and transmit incoming data in a manner that matches rules or behaviors particular to the application that created the data.^[18] In general, mobile wireless networks are prone to smaller and more variable capacity than wired networks, resulting in high data loss rates and weak QoS. In some cases, MANETs use media access control layers, which have little to no QoS support. Recent research projects have started addressing QoS loss but have seen limited results.⁽²¹⁾ Further, while battery technologies improve in both capacity and efficiency in weight and size, integrating batteries and optimizing battery-use within MANETs continues to be a challenge by limiting network range, run-time, and node mobility.

Policy Challenges

Because MANETs have an infrastructure-free design, their adoption could be seen as a potential threat by more infrastructure-dependent mobile operators.⁽⁶⁾ While this issue might not arise in areas where there is no existing infrastructure, conflict may arise in areas dependent on physical infrastructure. Creating a clear business-case for adoption by mobile phone carriers may ease any conflicts.

While MANETs could allow for significant benefits in safety, efficiency, and mobility, they may lead to significant risks regarding data confidentiality, integrity, or availability (CIA). Confidentiality concerns the level of access users have to data on a network; integrity concerns the legitimacy and accuracy of data; availability concerns how users can access data on the network.⁽²²⁾ One of the most impactful risks that includes all CIA elements involving MANETs is network security. At a network-wide level, MANETs create a constantly changing environment that can require fast authentication protocols, limited physical node security, and vulnerable channels of information that can be eavesdropped on or interfered with.⁽²¹⁾ A vulnerable network is susceptible to security attacks that can replicate, modify, or delete data exchanged between nodes. For example, a malicious node can tamper a routing protocol by modifying route information to an unwanted node or by ending the route prematurely. Network security is particularly concerning when there are high-speed physical nodes in a MANET. While there are some common privacy and safety elements that can be used in MANETs, such as Elliptic Curve Cryptography, Public Key Infrastructures, and Digital Certificates,⁽²³⁾ there are still technical and privacy issues that are not fully addressed by existing solutions.

A performance evaluation gap exists for each type of application, especially as scalability becomes a concern. One role that the Federal Government can play is to identify feasible transportation MANET applications and promote the creation of realistic simulation models for diverse scenarios and real testbeds for experimental evaluation. Overall, interest is growing in mixed-network adaptations, centered primarily on HetNets.

One of the Government’s current activities in MANETs, which is led by the U.S. Federal Communications Commission, focuses on spectrum band management for DSRC deployment; that is, determining which groups can have access to the network, and how much traffic these groups create. The Government has stimulated the development of standards for DSRC by creating a reference implementation model that is being merged with the ITS architecture. In addition, the Government has funded initial certification efforts to ensure interoperability and security. With 75 MHz of spectrum dedicated primarily to DSRC,^[19] there is potential for the USDOT to further develop and apply MANET standards and technologies in the connected vehicle field. This would require more agreement on the transmission of interoperable data, without which there is little incentive to create and deploy the physical media necessary to transmit and receive these data. For example, during the development of a crash avoidance technology using DSRC, much time was consumed by getting all parties to agree on a data unit to share. There is a great opportunity to better coordinate among relevant stakeholders and use the 75 MHz of spectrum for further innovative developments in transportation safety and efficiency.

Outside of Government, there are other organizations that address wireless standards and interoperability, which the Government can collaborate with. The Wi-Fi Alliance, for example, is a consortium of companies and contributors that certify new technologies that effectively use 802.11 standards, in both 2.4 and 5 GHz.^[20] Additionally, IEEE is a professional association that created the 802 standards for wireless technologies. IEEE consists of over 400,000 engineers, scientists, and allied professionals worldwide who contribute to over 1,300 international technological standards.^[21]

^[10] https://www.trellisware.com/wp-content/uploads/2017/02/TW-225-01-CheetahNet-Mini-Datasheet.pdf. Last Accessed 10-5-17.

^[11] Workshop Discussion with U.S. Navy Subject Matter Expert, October 2017.

^[12] For more information, see: https://www.its.dot.gov/factsheets/dsrc_factsheet.htm. Accessed 7-3-17.

^[13] Personal Interview with USDOT Subject Matter Expert, March 2017.

^[14] Ibid.

^[15] For more information, see: http://local.iteris.com/cvria/html/applications/app2.html#tab-3. Accessed 8-25-17.

^[16] Personal Interview with USDOT Subject Matter Expert, March 2017.

^[17] Ibid.

^[18] For more information, see: http://www.juniper.net/techpubs/en_US/learn-about/LA_QoS.pdf. Accessed on 4-20-17.

^[19] There are other primary users in this spectrum range, and co-existence arrangements have been negotiated for DSRC and satellite uplinks, for example. Other uses such as industrial, scientific, and medical services also overlap the DSRC spectrum.

^[20] For more information, see: http://www.wi-fi.org/certification. Accessed on 4-7-17.

^[21] For more information see: http://www.ieee.org/about/today/at_a_glance.html. Accessed on 4-7-17.