MN603 Wireless Networks and Security for Medium Access Control

Human underwater activities in oceans are growing fast in recent years and a huge number of sensors, actuators and various types of vehicles have been deployed underwater. Underwater things equipped with communication functions are able to construct the Internet of Underwater Thing (IoUT). Thus, underwater wireless networking has been becoming a hot research topic for more than one decade. Similar to radio-frequency based wireless networks (RWNs) used in terrestrial environments, the medium access control (MAC) protocol is one of the most important parts for underwater wireless networks. Since radio signal cannot propagate well in underwater environments, currently acoustic communication is widely used. However, due to peculiar features of underwater acoustic channels such as slow signal propagation speed (about 1.5 km/s in seawater), very small channel capacity, low channel quality and high dynamics of channel quality, MAC protocol design for underwater acoustic networks (UWANs) faces many new challenges. Especially, the long propagation delay is a key factor that makes the MAC design strategy widely adopted by RWNs
unsuitable for UWANs.

For further reading could refer to the article “State-of-The-Art Medium Access Control (MAC) Protocols for Underwater Acoustic Networks: A Survey Based on A MAC Reference Model”. The link for the article is:

http://ieeexplore.ieee.org/document/8093608/

The assessment requires the students to compare the existing radio-frequency (RF) based wireless networks (RWNs) with the Underwater Acoustic Networks and evaluate the Medium Access Control (MAC) Protocols for Underwater Acoustic Networks. The you are required to submit a report which addresses the following issues:

1. Comparison of (RWNs) with (UWANs)

2. Evaluate Medium Access Control (MAC) Protocols for Underwater Acoustic Networks (UWANs) considering proposed strategies based on:

a. Long Propagation Delays
b. Signal-based reservation
c. Scheduling based MAC
d. Receiver initiated protocols

Underwater acoustic networks (UAN) are an evolving technology as they have wide range of applications. Also human underwater actions are growing rapidly because of which many sensors and different types of vehicles are expanding underwater. Underwater communication is capable of forming the Internet of Underwater Thing (IoUT).Radio frequency based networks are very important for earth like environment similarly underwater acoustic networks are a base to analyse the ocean environment.

Underwater acoustic communication networks basically examine a particular area of an ocean and then research it properly. A two-way acoustic link is formed between the machines placed in the ocean with the sensors placed outside the sea. It’s not possible to use radio waves in underwater as they do not forms communication over long-range therefore acoustic waves are used. Along with this they also have low absorption powers hence they are perfect to use in underwater acoustic networks. But there are many drawbacks of these networks and researches are made to resolve them. Few of the challenges faced are limited bandwidth which depends on two factors: range and frequency, the propagation speed is also low and it continuously oscillates. The large delays in transmission lead to low throughput. Under the water the battery’s power plays a key role and these networks are less power sufficient.

These networks examine and analyses a particular part of the ocean continuously. In radio channels, there is time-static multipath and hence the Doppler shifts and interference is very less while underwater acoustic signals are very much prone to these shifts. Underwater acoustic networks make us understand the complications faced in underwater environment. They also find the environmental frameworks inside the ocean.

Radio-frequency based wireless networks (RWNs)

Radio-frequency based wireless networks can be defined as networks that uses radio-frequency as a key element for communication. These networks have good frequency range which is defined between 500 KHz to 300 GHz band. Most of the wireless networks are based on radio-frequency like Wi-Fi, Bluetooth, radio and television system or satellite communication and many more. Because of the high frequency they have high propagation capacity. The propagation medium is only air and hence disruption of noise is more also there is a loss in amplitude. But these networks provide immunity from the noise. Antennas form a basic part of radio frequency signals and have a sending antenna and a receiving antenna. Radio frequency based networks can be described as follows,

1. Networks having frequency less than 1GHz

Very few networks lie in this range and the devise which lies in this range were used years ago. Devices which use this frequency range are amateur television, cordless phones and ZigBee. Also few IEEE standards fall under this category.

2. Networks having frequency between 1GHz and 5GHz

WiMAX, GPS operates in this range along with microwave ovens. The ISM band also has a frequency of 2.4GHz.

3. Networks having frequency above 5GHz

Maximum attenuation and scattering is experienced in this range and the exposure to air is more. IEEE 802.11a, 802.11n and Wi-Fi falls under this category.

Radio frequency based wireless networks are preferred over underwater acoustic networks because,

• They have high frequency range
• They operate good even in foggy weather situations
• Their channel capacity is long
• The channel reliability is high
• They have low propagation delays

Although radio-frequency based wireless networks have many advantages but along with that they have very less security. And in severe conditions they give low throughput.

2. Medium Access Protocols are constructed to reduce the challenges of underwater acoustic networks.

Long propogation delay based mac protocols

ALOHA-

In ALOHA protocol, each time the nodes transfers a packet of data it can do it immediately without any delay. Whenever the packet is received at the other end, the receiver confirms that he has got the packet by sending an acknowledgement. The communication is said to be successful when the sender receives the acknowledgement. Even if there is heavy traffic ALOHA performs well and solves the problem of long propagation delays as it is a fast process.

Handshaking

Although handshaking is a complex protocol but it gives good throughput as it reduces the propagation delay. Also, before sending a data frame this protocol engages a request-to-send/clear-to-send frames. The basic advantage is that because of these frame all other interferences are blocked and hence the propagation delay is less. A particular node does not execute any other action until this on –doing transmission is not complete. It provides a propagation delay which is less than the length of the data frame and hence the throughput is good.

Propagation-Delay-Tolerant Collision Avoidance Protocol

This protocol follows the concept of handshaking. It fixes the time which is wasted in setting the links for data frames by organising the actions of sensors. PCAP follows a concept which seems like it has a pipeline for transmission and hence the propagation delay is reduced. As a node involve itself I transmitting man other data frames rather than wasting its time waiting for signals to propagate. Basically, PCAP allows stations to schedule activities for multiple data frames, and hence reduces the time wasted in waiting for signals to travel over high-delay channels.

Reservation Based MAC Protocols for UWANs 

Tone-Lohi MAC Protocol

T-Lohi protocol catches and calculates the challenger nodes during the reservation and traffic-adaptive back off algorithm. Along with this it employs a wake up tone to reserve the data transmission. Every node contains a hardware wake-up tone detector; on this basis the nodes spend their minimal energy. It contains a reservation period which comprises of multiple contention slots. T-Lohi reserves the channels and carrier sensing so that the reservation result can be verified. T-Lohi is load stable and hence reduces the energy consumption and improves fairness of heavy traffic loads.

Scheduling Based MAC Protocols

ACME Network Protocol (ACME Net)

This protocol is particularly a type of master-slave protocol. ACME Net is established on scheduled transmission schedules which aim that the data packets can be transferred from slave to master node consecutively. This protocol uses the concept of CDMA in which the nodes are scheduled in a way that a group of data packets can be send and received simultaneously. These schedules are backed up with instructions to maintain the power levels and modulation rates at nodes.

Hybrid Protocol

In hybrid protocol, the whole network is divided into clusters and the transmission of these clusters I scheduled by TDMA algorithm. The nodes reserves the whole channel  by a spreading technology and hence the channel efficiency is high. Along with TDMA at times it uses CDMA as well which is used to enable spatial reuse of slots throughout the network.

Underwater Distributed TDMA 

This scheduling protocol makes a use of scattered maximal independent set algorithm so that the maximum number of nodes which can transfer without collision in the same time interval can be determined.

Receiver-Initiated MAC Protocols

Spatially Fair MAC

This protocol is used to handle spatial unfairness which occurs due to distinct distances. SF-MAC accepts a receiver-based protocol without any information of distance availability. It guarantees the node by submitting a Receiver to Sender as soon as possible to transfer the data first. The receiver abducts the RTS frames to evaluate the earliest transmitter by the usage of potential transmission duration.

Feri MAC

FERI MAC applies a receiver initiated handshaking protocol. The main aim of this protocol is to enhance the channel utilization and the energy efficiency. The collisions are avoided by RTR and ATS messages exchanging making it more effective in defending the receiver from packet collisions. This protocol also reduces the overhead of handshaking control messages by applying parallel reservation and packet train.

Conclusion

Underwater acoustic networks are an evolving technology and have wide range of applications. In comparison to radio frequency based wireless networks these networks have disadvantages like power limitations, bandwidth limitations along with long propagation delays. Therefore, MAC protocol strategies are implemented on these networks to overcome these problems.

Over the next decade, significant improvements are anticipated in the design and performance of UWA networks as more experience is gained through at-sea experiments and network simulation tools.

References

N. Ullah, B. Choi and K. Kwak, "Throughput and delay analysis of MAC protocol based on frame slotted aloha for low energy critical infrastructure sensor networks", Electronics Letters, vol. 51, no. 13, pp. 1035-1037, 2015.

K. Kredo and P. Mohapatra, "Medium access control in wireless sensor networks", Computer Networks, vol. 51,   no. 4, pp. 961-994, 2007

H. Belloc, On. Freeport, N.Y.: Books for Libraries Press, 1967.

D. Dobkin, RF Engineering for Wireless Networks: Hardware, Antennas, and Propagation. USA: Elsevier,    2011.

S. Climent, A. Sanchez, J. Capella, N. Meratnia and J. Serrano, "Underwater Acoustic Wireless Sensor Networks: Advances and Future Trends in Physical, MAC and Routing Layers", Sensors, vol. 14, no. 1, pp. 795-833, 2014.

R. Otnes, Underwater Acoustic Networking Techniques. Berlin: Springer, 2012.

H. Ng, W. Soh and M. Motani, "A Bidirectional-Concurrent MAC Protocol With Packet Bursting for Underwater Acoustic Networks", IEEE Journal of Oceanic Engineering, vol. 38, no. 3, pp. 547-565, 2013.

S. Jiang, "State-of-The-Art Medium Access Control (MAC) Protocols for Underwater Acoustic Networks: A Survey Based on A MAC Reference Model", IEEE Communications Surveys & Tutorials, pp. 1-1, 2017.

M. Rahman, Y. Lee and I. Koo, "An adaptive network allocation vector timer-based carrier sense multiple access with collision avoidance medium access control protocol for underwater acoustic sensor networks", International Journal of Distributed Sensor Networks, vol. 13, no. 1, p. 155014771668776, 2017.

P. Etter, Underwater acoustic modeling and simulation. Boca Raton, FL: Taylor & Francis, 2013.

J. Loo, J. Lloret Mauri and J. Ortiz, Mobile Ad Hoc Networks. .

G. Fan, H. Chen, L. Xie and K. Wang, "A hybrid reservation-based MAC protocol for underwater acoustic sensor networks", Ad Hoc Networks, vol. 11, no. 3, pp. 1178-1192, 2013.

S. Shahabudeen, M. Motani and M. Chitre, "Analysis of a High-Performance MAC Protocol for Underwater Acoustic Networks", IEEE Journal of Oceanic Engineering, vol. 39, no. 1, pp. 74-89, 2014.

D. Pyeon, I. Jang, H. Yoon and D. Kim, "RM-MAC: a reservation based multi-channel MAC protocol for wireless sensor networks", Wireless Networks, vol. 22, no. 8, pp. 2727-2739, 2015.