Underwater Acoustic Networks (UWANs)
Questions:
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
The network that is considered in this paper is the Underwater Acoustic Networks (UWANs) and the Radio Frequency that is based on Wireless Networks. The UWANs (Underwater Acoustic Networks) are considered as a primary tool so that they can monitor on the marine environments and also act well on the environment. To propagate signals under the water, electromagnetic waves of Radio Frequency (RF) do not work well [8]. For the propagation of signals under water, the UWANs are the most important carrier of communication. The UWAN network uses acoustic signals that are different from the radio frequency signals in different ways. The speed of the propagation acoustic signals is about 1500 m/s including five orders of magnitude which are much slower than the radio frequency signals. The range of transmission of the acoustic signals can travel up to several kilometers that are much longer than the RF signals. An acoustic signal also have bandwidths that are relatively low and also accommodates the transmission of signal that are less than the speed of 60 kbps.
The main function of the MAC (Medium Access Control) protocol that is transferred over shared channel is mainly to coordinate all the transmissions from one node to another so that there are no collisions. There is propagation delays of concurrent transmission in network of RF wireless which is mainly due to more than one nodes on the channel that mat collide. The MAC protocols of the UWANs avoid collision mainly by enforcing more transmitter in the carrier of receiver so that they can sense the range for transmission.
The (UWA) Underwater Acoustic Networks are mainly formed by the process of establishing an acoustic link which is a two way in between different instruments that includes Acoustic Underwater (AUV) Vehicles and many sensors. The Underwater Acoustic (UWA) Networks are connected to surface that can be further have connection to the backbone including Internet via RF link [13]. The configuration of the UWA builds interactive environment where the scientists are able to extract the data of real time from different distant instruments of underwater. After evaluating data that are obtained, all the controlled messages can be delivered to the individual instruments and network that can be adapted to change the situation. The data in the UWN are all transferred to controlled station when the data is available and by this loss of data can be prevented till the time of failure.
The operation of the AUV (Autonomous Underwater) can be increased by the network of underwater. There are many wireless communication in an AUV that are feasible by acoustic range of a particular single modem that varies from a distance of 10 km to 90 km. By changing the data messages and the control through a network which covers very large areas, there is an increased range of the AUV (Autonomous Underwater). There should be an effect of time delay in propagation [12]. The speed of propagation in network of Underwater Acoustic (UWA) channel generally has five orders with a magnitude that is lower than the radio channel. The huge amount of delay that mostly occurs between the transactions can reduce the system’s throughput considerably is the delay is not taken in account. The instruments that are send at the bottom of the ocean are mostly powered by battery. The network of underwater has a characteristics of having power efficiency. The network protocol should be given special attention.
Radio Frequency (RF) Based Wireless Networks
On the other hand, in comparison with the UWA (Underwater Acoustic), the radio frequency signals are signals that are referred to electromagnetic signals that are mainly wireless and then use them as a communication form in wireless electronics [11]. There are radio waves that are in the form of electromagnetic waves which have radio frequencies that are identified and mainly range between 3 kHz to maximum of 300GHz. The rate of collision is referred to as the frequency. Propagation of radio frequency mainly occurs in a very high speed which is considered to happen at a speed of light and also do not need any kind of medium such as air or water for its transmission. Radio frequencies can be achieved naturally from lightening, stars, and sun rays in the space which radiates radio frequency. Humans mainly create artificial radio frequency waves which oscillate at different frequencies [9]. Many of the industries use radio frequencies for the purpose of communication that includes broadcasting of televisions, mobile platforms networks, remote control, computer networks, remote monitoring, and radar systems. According to the range of operating frequency, there are many radio components which include filter, power amplifiers, and mixers. These items cannot be particularly categorized in the wireless list for the reason that only provides physical layer in their support.
Data link layer often supports more than one protocol of wireless communication which includes RF modules, SoCs, and the transceivers. The radio frequency is generally considered as a technique that uses data of high rate. The user who is using a radio frequency can have a communication within a very short range having a rate of communication of about 100 Mb/s. The electronic waves which come under the radio frequency are mainly considered to have a better communication in the underwater system [10]. While comparing the underwater with the radio frequencies, the trends of electromagnetic waves that are less sensitive to the reflection and refraction are considered to be in a shallower region in the water. The speed that is in the electromagnetic waves is much more than the acoustic waves. There are speed of the electromagnetic waves that mainly depends on the parameters which includes density of volume charged, permittivity, permeability, and conductivity.
The parameters that are stated above mainly depend on what kind of value of water in the conductivity of electricity that is related with them. The conductivity of electricity mainly depends on the speed or the rate of propagation of wave and the coefficient of absorption that depends on the frequency of the operation directly [1]. There are some disadvantages of underwater communication as well. The disadvantage is that underwater communication depends on the electromagnetic waves to make high attenuation that results in conductivity in water. The attenuation value increases with increasing the value of electromagnetic waves. The communication of the underwater can have a band of maximum of 2.4 GHz that is considered to be an impractical one.
Long Propagation Delays – MAC protocols that are used for Underwater Acoustic Network (UWANs) also faces some challenges such as energy efficiency, quality of all the services, utilization of the medium, validation protocol, and also supports mobility. There are many characteristics of the underwater channel which includes propagation delay, crowded and small channels, and also channels that are vulnerable and changing. Networks that are based on radio frequency are basically based on networks that have terrestrial environment of working and Medium based accesses (MAC) are also considered as an important factor for the acoustics underwater channels [5]. Because of the peculiar challenge of the nature in the underwater channels which includes high dynamics, capacity of low channel, MAC designed strategies which have low reliability, high dynamics, and protocols of RWNs that are not widely used as in UNAWs.
The magnitude of the speed of acoustic under the sea is mainly five times slower that speed of light. There is certain list of parameters that generally affects the speed of acoustic under the sea. The list of parameters includes salinity, depth, and temperature that results in a better propagation speed. There are propagation delays which has variable in speed and has long propagation delay that creates problem such as authority of certainty [2]. The Doppler Effect proves more effective in the area of mobile UWANs because the magnitude is related directly to the ratio of transmitter speed and the receiver end. Doppler Effect is more effective in the area of UWAN. This is because the magnitude of the Doppler Effect is related directly with the ratio between the speed of transmitter and receiver’s end and also depends on the speed of the signal. This results in shifting the frequency and the motion at an induced rate of the distortion which results in contributing the dynamics of the quality of the channel. The feature that is involved with the acoustic channel of underwater, there is lot of challenges that is involved in the UWAN’s MAC protocol. The challenge that is faced is medium utilization [7]. The challenges reflect how the efficiency factor of the medium works and also transmit the data of the user. By small channel capacity and utilization of the medium at high rate is very important factor but long propagation faces many difficulties with its delay. MAC is not able to avoid the collision at receiver’s end and the sender’s end after acquiring the message properly which in mainly undesirable in delaying the long propagation.
Comparison of UWANs and RF Based Wireless Networks
Single-Based Reservation – The RF frequency which is mainly based on the wireless network are mostly used for the terrestrial network on contrary medium of access control that is considered as an important factor for the wireless network underwater. There should be fact which is to be considered about the RF frequency is that the radio signal is not able to propagate easily with the environment in underwater. Mainly to overcome this issue, the acoustic communication channel is used. Because of different feature of underwater acoustic, the propagation rate of signals is mainly slow under the water and also has a very small amount of channel capacity and also the dynamics value is high. The design of MAC protocol is designed in a way by which it can overcome the design of the acoustic network of underwater [4]. All the challenges can be addresses by the MAC protocol. The delay propagation is taken as a most important part that makes the MAC strategy design easy and can be adopted widely by the RWNs which is mostly unsuitable for the network of UWAN. The main aim of the MAC protocol is to give many users so that they can efficiently share a common medium of protocol. The collision that happens at the receiver’s end mainly tends to failure of the reception.
Scheduling based MAC – The survey that is done with the UWAN of the MAC protocol is divided easily into many categories which include typically RWN which is a newly designed protocol. The modification that is needed by the RWN MAC based protocol provides unfamiliar features that are related with the specific features of the UWAN which gives them the proper way to handle the problems. The first type of feature is differentiated in multiplexing and also non-multiplexing. The second feature can be differentiated in reservation, cross layered design and also scheduling. The sender is required to take proper decisions while scheduling about the time in which the transmission will take place and also aims for deciding the impact which overcomes the delay of propagation. The time is required for a node of transmission which mainly assures an output that is collision free and also time involved for saving the energy [6]. Proper decision mainly depends on the availability and the accuracy of the information that is needed. Scheduling of RF channels that are based on RWN (Radio wireless networks) is generally considered different from the transmission order that supports QoS which avoids collision including traffic scheduling. There are many such mechanism of algorithm that is used for making the changes in protocols to improve the adaptability quality in different protocols and also the efficiency of the energy.
Receiver Initiated Protocols – There are mainly two schemes that are made by the controlled channel with ALOHA and the other with the RTS that are monitored and analyzed properly. The ALOHA sends proper control via the DCC so that they can provide information in a proper way about the channel receiver which gets selected in the transmission over DCH and then the data gets transmitted. The RTS cannot send the data unless a method of shaking hand is not established in the RTS or the CTS []. The receiver also has to select the DCH version. Generally a back off is added to the value of ALOHA which easily reduces the transmission node when packets are arrived.
Conclusions
The communication that is done underwater usually involves monitoring of long-term that is selected in the area of ocean. The traditional approaches which are involved in ocean-column and the ocean-bottom monitoring deploys recording of data, recovering of instruments and also oceanographic sensors. This kind of approach mainly creates logs that receive the recorded information. If there is a failure in the recovery, all data are lost. The most ideal way to mitigate this solution is to create a real-time communication in between the instruments of underwater and also controls the configuration of network.
This report consists detail process of Acoustic underwater networks. There is also a detailed study about the Radio frequencies that are carried out with the electromagnetic waves. This report sheds light on the working of UWA (Underwater Acoustic) Channels. There is a comparison between the UWA (Underwater Acoustic) and the Radio Frequency networks. This report also describes MAC protocols of the Underwater Acoustic channels with four categories.
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