EM-Based High Speed Wireless Sensor Networks for Underwater Surveillance and Target Tracking

Table 1

Advantages, disadvantages, and challenges of underwater networking using acoustic and EM waves [12–14].

Particulars	Acoustic wave	EM wave
Advantages	(i) Significantly lower signal attenuation; (ii) Longer transmission area in the range of km; (iii) Can function in the absence of line-of-sight (LOS) path between transmitting and receiving nodes	(i) Large bandwidth; (ii) High data rates in the range of few Mbps; (iii) Faster response due to higher propagation speed and significantly lower delay; (iv) LOS for communication is not essential; (v) No need of clear water; (vi) No noticeable impact of underwater environment, such as temperature, turbidity, salinity, bubbles, and pressure gradients and thus improving robustness in unpredictable underwater environment; (vii) Not affected by sediments and aeration; (viii) Immune to other noise except electromagnetic interference (EMI); (ix) Lower Doppler shift; (x) More reliable communication; (xi) Can cross water-to-air or water-to-earth boundaries easily; (xii) No impact on marine life; (xiii) Lower cost of nodes; (xiv) Good performance in shallow water; (xv) Higher attenuation is beneficial in an environment of multiuser interference
Disadvantages	(i) Significantly slower response as propagation speed is much lower (1500 m/s) than that of EM wave; (ii) Significantly lower data rate (up to 20 kbps) as bandwidth is low; (iii) Surface repeater is required as strong reflections and attenuation occurs in crossing water/air boundary; (iv) Poor performance in shallow water; (v) Less reliable and robust communication as easily affected by turbidity, ambient noise, temperature, salinity, and pressure gradients; (vi) Adverse impact on the marine life and ecosystem; (vii) Higher cost of network nodes	(i) Easy to be affected by EMI; (ii) Higher attenuation, which increases with the salinity of water; (iii) Limited communication range in high data rate applications (e.g., 50 m for 150 kbps and less than 10 m for Mbps range); (iv) Dense deployment of nodes is required for higher frequency range
Challenges	(i) Higher and variable latency; (ii) Difficult time synchronization due to variable delay; (iii) Higher bit error rate; (iv) Multipath propagation and fading; (v) Easy signal corruption due to ambient noise; (vi) Mobility of nodes	(i) Timing synchronization is difficult as the symbol duration is smaller for higher data rates; (ii) Multipath propagation and fading; (iii) Mobility of nodes