Evaluation Of Medium Access Control Protocol - Myassignmenthelp.Com

Question: Discuss about the Evaluation Of Medium Access Control Protocol. Answer: INTRODUCTION This report depicts a comparison between existing radio based and wireless networks with underwater acoustic networks. The various challenges faced by underwater acoustic networks are analysed. Some of these challenges are slow signal propagation speed, very small channel capacity, low channel quality and high dynamics of channel quality, and long propagation delays. As a result, various Medium Access Control strategies are used to counter attack these challenges. Still, underwater acoustic network is a hot research topic because it has many applications. Radio-frequency based wireless networks (RWNs): Radio-frequency based wireless networks are which uses radio-frequency as a base for communication. The frequency range of these networks lies between 535 KHz to 300 GHz. Few examples of radio frequency based wireless networks are radio and television broadcast systems, Wi-Fi, Bluetooth, satellite communication system and many more. These higher frequencies provide competence in propagation, and provide immunity from noise. The radio frequency signals inseminate between two station antennas named as sending and receiving stations. As the propagation medium is air therefore there is a loss in amplitude. Radio frequency based networks are classified according to their frequency range as follows, Less than 1GHz This frequency range is used for cordless phones, amateur television and ZigBee along with IEEE 802.15.4. Between 1GHz and 5GHz The ISM band falls under this category having a frequency range of 2.4GHz.WiMAX, GPS, microwave ovens also function in this range. Above than 5GHz Very less networks operate in this frequency range as they experience maximum attenuation and scattering. Few examples are IEEE 802.11a and 802.11n along with Wi-Fi. Advantages of radio frequency based wireless networks are: They have low propagation delays They have high frequency range Good operation in foggy weather conditions Long channel capacity High channel reliability Disadvantages of radio frequency based wireless networks are: Less security At times low throughput UNDERWATER ACOUSTIC NETWORKS An underwater acoustic network (UAN) can be defined as a communication network which is used to monitor particular ocean infrastructures. These networks are made by forming two-way acoustic links between the instruments located in the sea and the sensors. Acoustic waves enable communications over long-range links, as they suffer from relatively low absorption hence they are used in underwater acoustic networks.The range of these links is very small approx. 100 kms. When compared with radio-frequency based wireless networks, underwater acoustic networks have limited bandwidth which depends on the range as well as frequency. Also the propagation speed of these channels is lower than radio frequency channels and it keeps on fluctuating. The acoustic signals have time-varying multipath due to which they face interference and large Doppler shifts which are observed less in radio channels. The throughput of these networks is less because of the large delays in transactions. As radio-frequency based wireless networks are to the terrestrial environment, similarly for ocean environment underwater acoustic networks are designed. These networks provide a continuous check of the particular area of the sea. Advantages of underwater acoustic networks: They monitor and find environmental parameters inside the ocean. They help in understanding the complexities o underwater environment. Disadvantages of underwater acoustic networks: Low propagation speed Less power sufficient Limited bandwidth Various Medium Access Control Protocols are designed for under water acoustic networks. For long propagation delays there are three protocols described as follows. Frequency Division Multiple Access (FDMA)- In this protocol, the available frequencies are divided into sub bands and hence these sub bands are assigned to individual users. FDMA are accessible to fading because the channels bandwidths are small. The long propagation delays are reduced because of the division of frequencies. FDMA channels are faulty to bursty traffic. Time Division Multiple Access (TDMA)- In this protocol, rather than division of frequency bands the time intervals are divided. A particular time interval is appointed to individual users. TDMA along with FDMA trims the effects of intercell interference. Using TDMA, battery consumption is diminished. For TDMA channels in underwater acoustic networks it desires synchronization. But the time slots are kept so that the collisions in propagation delays are avoided. Code Division Multiple Access (CDMA)- In CDMA, the frequency band is accessed by multiple users. Different users are discriminated by the codes. The CDMA channels have large bandwidth and hence frequency fading is reduced. This protocol reduces the battery consumption as well and improves the throughput of the network. The reservation based MAC protocols for UWANs are: Message-based protocols for distributed topologies Under the category of message-based protocols or distributed topologies is signal-based reservation. As message-based reservation causes collision and to reduce these collisions a Tone-Lohi channel is used. T-Lohi reserves the channels and carrier sensing so that the reservation result can be verified. A node transfers data and then the channel is listened for the duration of contention round. The reservation is successful when no other tone is heard at the end of the contention round. T-Lohi is load stable and hence reduces the energy consumption and improves fairness of heavy traffic loads. There are various scheduling based UWAN MAC protocols. They are: ALOHA with Collision Avoidance In ALOHA-CA the nodes calculated the busy duration caused by the frames at every other node to avoid collisions. This method does not provide the information useful to calculate schedules for collision avoidance. The protocols performance is affected by propagation delays. Spatio-temporal conflict graph (ST-CG) The scheduling constraints are determined by this protocol which develops a TDMA-based scheduling as a NP- complete problem. Further, this problem is solved by Traffic based One-step Trial Approach algorithm. The long propagation delays are exploited by few MAC protocols, Bidirectional Concurrent MAC This protocol lets a pair of nodes to transfer to one another at the same time whenever a handshaking is successful. Along with this, many rounds of bidirectional transmissions whenever a burst happens. 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. Staggered TDMA This protocol adapts propagation delay estimate to allow communication overlapping to decrease channel idle time. The scheduling decisions to resist reception conflict are also made. Distributed Traffic-based Scheduling MAC This protocol is based on an analytical model to optimize bandwidth allocation in multi-hop UWANs. The majority of the underwater acoustic networks MAC protocols are sender initiated protocols. Few receiver initiated protocols are: 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. Underwater Practical MAC This protocol gives two access modes for high and low traffic loads, letting the nodes to switch between then in accordance to the traffic loads. This MAC protocol uses ALOHA at the low load mode for irrational data transmission. The receiver broadcasts an initial packet to the neighbours, then the neighbours response. At last, the receiver broadcasts an announcement frame comprising the schedule. This protocol is also used to calculate propagation delays between nodes. Conclusion Underwater acoustic networks have many applications. The various flaws in the design of underwater acoustic networks were power limitations, bandwidth limitations along with long propagation delays. But at the same time, most of these factors were taken care by the medium access layer protocols. MAC strategies which are suggested to handle few flaws of underwater acoustic networks are signal-based reservations, scheduling-based MAC, long propagation delays. It has been observed that since this technology is evolving but still there are many challenges which need to be solved. 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 [1]D. Dobkin,RF Engineering for Wireless Networks: Hardware, Antennas, and Propagation. USA: Elsevier, 2011. [2]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. [3]G. Fan, H. Chen, L. Xie and K. 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