# A Novel Self-Forming Virtual Sub-Nets Based Cross-Layer MAC Protocol for Multihop Tactical Network
## 1 Introduction  
Tactical networks are mobile ad hoc networks (MANETs) of self-organized, self-configured software-defined radios (SDRs) to guarantee mission-critical information exchange. Their autonomous behavior (including mobility, node failures, and link failures) strains connectivity, which requires decentralized solutions to assure network survivability and communications reliability. At the same time, there is a critical demand for communication capacity with services diversity. Examples include the need for wideband communications to transfer large volumes of data, narrowband communications for extendedcommunication ranges, and bounded channel access latency to share mission-critical information [1]. Other important perilous issues with regards to networked communication include communication-on-the-move and interoperability. A distributed system should address these issues with self-forming, self-healing, and self-organizing capabilities. The developed system should be intelligent enough to cater to tactical communication rudiments, be technically radical, and not rely on a central controlling hub. In tactical networks, SDRs are provisional in mission-critical areas such as battlefields and catastrophic environments to meet immediate tactical needs. These SDRs autonomously communicate and keep track of each other to enable seamless single-hop and multihop communication by configuring and reconfiguring themselves through coordination with their neighbors. SDRs ensure flexibility for every particular scenario, and the communication among radios can be optimized using a specific waveform that can switch dynamically. It is capable of operating various wireless communication protocols without changing or updating the hardware. Since the radios keep changing their positions, neighbors must know the routes or at least the next hop toward a distant destination. In many cases, there is also a need for alternate paths to compensate for failed communications [2]. Therefore, it is evident that the reliability of routes and the opportunity to make quick routing decisions are critical features. In ad hoc networks, a message from a source node to a destination node may traverse many hops, multiplying network capacity consumption and usually in a larger network, resulting in a long chain of links. However, it is not just the hopping of data packets that contributes to capacity utilization but also the overhead associated with routing the data. For instance, many mainstream ad hoc routing protocols depend on frequent network-wide broadcasts to gain a picture of the network as it continues to change [3; 4; 5]. These protocols may not be appropriate for tactical radio networks, as network-wide broadcasts can noticeably increase response latency in emergencies. In tactical radio networks, quality-of-service (QoS) guarantees (confined transmission latency, minimum guaranteed data rate, bounded call setup delay, etc.) are rated higher than spectral efficiency and increased bandwidth. The contention-based (carrier sense multiple access (CSMA)) techniques for emergencies result in collisions that trigger retransmissions, further magnifying call setup delays and power loss [6; 7; 8]. However, the noncontention-based approaches (such as time division multiple access (TDMA)) provide reliable communication but induce delays in the transmission where each node has its fixed slot that reduces spectral efficiency. Whereas frequency-division-multiple-access (FDMA) based approaches encounter cross-talk and signal interferences that are not adequate in military applications and should be handled precisely. However, a hybrid of TDMA/FDMA approaches can combine their strengths to overcome each other's inadequacies. Due to the dynamic nature of MANETs, higher layer functionalities are added depending on the complexity of the application or service. Since higher layers increase overhead and latency, the cross-layer approach is used to mitigate layering's adverse effect in the mission-critical environment.