Project management Essay Example | Topics and Well Written Essays - 2500 words - 5

Project management - Essay Example In order for the project therefore to succeed, there is need for the project firm to recruit the most appropriate workers for every obligation undertaken in the said project. In addition to this, the already recruited workers need to be provided with the necessary skills pertaining each and every operation they will need to undertake. Workers motivation is another major factor to the success of the workers activities. It is a necessary requirement for the organization’s growth irrespective the nature of the project undertaken. The worker’s needs are changing every day and with the traditional techniques of motivation the project might not be successful as required as these would not be sufficient in proving the necessary motivation. Machine, Man, money and materials happen to be the four necessary resource requirements for such projects. Among these, the Manpower is the most essential since it controls the other three resources. The manpower also needs to be utilized in the most appropriate manner. Man would never be in a position to operate like machine since they have physical as well as mental needs. Man works well on creation of good working environment and provision of the necessary skills pertaining the job they are operating. If cases where the organization fails to meet the needs of the workers, including the necessary training there would be less productive results. Haughey (2010) holds that planning any project is crucial to the project success. The project plan would be the first essential thing that the recruitment manager would need to have while starting to undertake the project. Planning the project in time would help in reducing time, financial resources and other operational challenges. Devastation feelings, lack of confidence, low level of skills as well as dark future perspective and financial insecurity are some of he factors

Internet of things and sun spot Essay Example | Topics and Well Written Essays - 4250 words

Internet of things and sun spot - Essay Example From this research it is clear that there are two main functions of the internet of things. The first is to incorporate sensors into a wide range of items, creating an interconnected network that will ultimately span all types of different things. For example, in the future, this could involve every item, whether it is a piece of electronic equipment or an article of clothing, having an electronic tag. Additionally, there would be sensors for a wide range of environmental variables, such as those on weather balloons that record the way in that factors such as temperature and wind change. The second objective can only be achieved after the first has been successful to some degree. This is the development of intelligent systems based on these inputs. Thus, the more sensors and identifiers there are, the more information is available, and the more efficient the system is. Within a structure, whether it is a house or a business there are a large number of different systems that could pot entially interact with each other, but do not. For example, most buildings have a lighting system, a heating system and internal devices such as microwaves, televisions and computers. Linking some of these systems to each other would have many benefits including the increase of energy efficiency. There are many different examples of the ways in which systems could interact with one another in order to provide a more energy efficient environment. One example of this would be linking the heating system to internal and external environmental sensors so that the base heating level of the structure is able to be adjusted according to the temperature outside. This would mean that the house would be cooled on hot days, and warmed on cooler days. The result of this would be that the structure would be kept at a relatively constant temperature regardless of other factors. The concept of an intelligent home is one of the end products of such a system. Currently, the level of technology would this a very expensive proceeding, but nevertheless this has been demonstrated on a small scale. An intelligent home is one where the owner can control all activities from a single point, such as turning on or off lights using a remote control, or adjusting the house wide temperature. However, the most important factor of a intelligent home is that it can make use of the knowledge that it receives from a wide range of sources to do many mundane activities that are part of general housekeeping. For example, this could include turning lights off when no-one is in the room, adjusting ambient temperature to the occupants preference, having coffee ready for when the person wakes up, and setting the alarm clock based on their

Primary source analyze Article Example | Topics and Well Written Essays - 1250 words

Primary source analyze - Article Example Therefore, free trade is tied to the Europe’s colonies fate. The author argues that the special trade of the mother nations tends to reduce or at least putting down below what these nations would then rise to both the industry and enjoyments of all the countries generally, particularly the American colonies. He continues to argue that by rendering the colony produce preciously in other nations, it diminishes its consumption and henceforth cramps the industry of all the other nations that both enjoy less when they emolument a lot for what they are enjoying, and producing less when they get less for the things they are producing. The people targeted by this source are historians mostly who want ton know how the British ruled America1. It is viewed that the surplus produce of America, however, which is the main source of all that increase of industry and enjoyments that Europe got from the colonization and discovery of America. The source is rendered much less sufficient by the select trade of mother countries. This primary source is a book written by He Ao (Ho Ao) in 1520. The author was a bureaucrat who referred to the Europeans as the Feringis. The event of this source took place in the fifteenth century when the Europeans invaded China. He portrayed that they were not trust worthy individuals; they were unruly and were a threat to the security of a nation. The sentiments stated by He Ao were mutual among to officials in following centuries, even when China prospered in the commercial exchanges of a gradually connected universe2. The author argues that the Feringis were the most crafty and cruel. Their arms were the most superior than that of other foreign individuals. This source was created during the colonial periods. It is seen that the Europeans came to Canton where some of them stayed in the post station while others had bad behavior and had intercourse with the local people. The source also states that if the Chinese people

Case Research Paper Example | Topics and Well Written Essays - 500 words

Case - Research Paper Example The high costs associated with the implementation of the Sarbanes-Oxley prompts the clients (companies) to pay lesser fees to the audit firms as they try to mi9nimoize their total costs. Ethical issues may, therefore, arise. There is a significant variation in the amount of fees paid by General Electric to auditors before and after the implementation of the Sarbanes-Oxley. The comparison is therefore between the fees before (2000 and 2002) with those of (2004, 2006, 2008, and 2010). In the period between 2000 and 2002, all the fees paid by General Electric to Auditors (in millions), except the financial information systems fees took an upward trend. The audit fees increased by $14.8 while the audit-related fees and the tax fees increased by $7.8 and $7.4 respectively (textbooks.com). After the implementation of the Sarbanes-Oxley, the figures increased still but not uniformly as before. The audit fees and the audit related fees rose significantly between 2004 and 2008 and then dropped to in 2010. The increment is however not bigger than the change in the tax fees, which were reduced drastically after the implementation of the Sarbanes-Oxley. Taking a similar analysis for the Fortune 100 companies yields even more interesting comparison. There is no significant variation in the amount of fees paid by Fortune 100 companies to auditors before and after the implementation of the Sarbanes-Oxley. In the period between 2000 and 2002, all the fees paid by Fortune 100 companies to auditors (in millions), except the financial information systems fees take an upward trend. The audits fees increase by $1.0 while the audit-related fees and the tax fees increased by $1.9 and $3.4 respectively. As in the case General Electric, after the implementation of the Sarbanes-Oxley, the figures still increased (amazon.com). The increase here is more uniform and consistent unlike the case of General Electric. The audit fees

Virtual Reality Research Paper Example | Topics and Well Written Essays - 2500 words - 1

Virtual Reality - Research Paper Example Virtual reality is turning out to be the topic with many opposing viewpoints. It has become the focal point of discussion among the general public for several reasons. Conceivably, this is mostly because of all the potentials which virtual reality develops (Hoffman, 2004). However, despite the disagreement this new technology has awakened, society should not stay dubious. Virtual reality if used in an optimistic way can bring a large technological development. Military and space technology, the entertainment industry, and the physical sciences contributed to the drive to make advanced computers user friendly. Initially, complex simulators presented low-definition displays through binocular headsets. Addition of position sensors introduced "motion parallax", with depth cues that created the illusion of being within a three-dimensional graphical display. The invention of a `DataGlove, whose movements could be sensed by the computer and then reconstructed in the display, enabled the observer and computer to interact with instructions given by the observer via simple hand movements such as pointing. The overall effect was that the observer experienced a computer-generated artificial or virtual reality (VR), whose credibility depended largely on the agreement between the simulated imagery and the familiar sensible world (Zimmer, 2004). Virtual reality applications are finding their way into the mainstream of society. Initially, the use of VR (virtual reality) was seen as valuable only to scientists and engineers whose highly specialized needs more than overcame the poor quality of the computer generated 3D images. For example, scientists can engage in molecular research by moving within molecules to examine their structures. Doctors and other medical personnel can practice elaborate or dangerous procedures before attempting them on human subjects. With special imaging software, the

US Supreme Court Decision Essay Example for Free

US Supreme Court Decision Essay An examination of the United States Supreme Court case Romer v. Evans, which was decided on May 20, 1996, is to be put forth in this paper. The case was argued on October 10, 1995. At issue was Amendment 2 to the State Constitution of Colorado â€Å"which precludes all legislative, executive, or judicial action at any level of state or local government designed to protect the status of persons based on their homosexual, lesbian or bisexual orientation, conduct, practices or relationships† (Romer v. Evans, 1995). The U. S. Supreme court held it violates the Equal Protection Clause. The opinion in favor was filed by Justice Kennedy, while the dissenting opinion was filed by Justice Scalia. The referendum, Article II sec 30b of the Colorado Constitution, read as follows: NO PROTECTED STATUS BASED ON HOMOSEXUAL, LESBIAN, OR BISEXUAL ORIENTATION. Neither the State of Colorado, through any of its branches or departments, nor any of its agencies, political subdivisions, municipalities or school districts, shall enact, adopt or enforce any statute, regulation, ordinance or policy whereby homosexual, lesbian or bisexual orientation, conduct, practices, or relationships shall constitute or otherwise be the basis of, or entitle any person or class of persons to have or claim any minority status, quota preferences, protected status or claim of discrimination. This Section of the Constitution shall be in all respects self-executing (Romer v. Evans, 1996). While many believed the law would prevent non-federal discrimination lawsuits based on sexual orientation as well as prevent the passage or the enforcing of existing laws prohibiting such discrimination, Amendment 2’s purpose was â€Å"generally inconsistent with mainstream American values† (Debbage Alexander, pg. 264). The State of Colorado argued the â€Å"measure does no more than deny homosexuals special rights† (Romer v. Evans, 1995). This is a decades old argument that right-wing Christian groups have used â€Å"to appeal to a wider, more secular audience by characterizing the gay rights movement as one aimed at getting special rights and protected status for gays and lesbians incorporated into civil rights law† (Debbage Alexander, pg. 273). Justice Kennedy writes in the opinion in favor, â€Å"The States principal argument that Amendment 2 puts gays and lesbians in the same position as all other persons by denying them special rights is rejected as implausible† (Romer v. Evans, 1995). Justice Kennedy further states how â€Å"Amendment 2 confounds this normal process of judicial review. It is at once too narrow and too broad. It identifies persons by a single trait and then denies them protection across the board† (Romer v. Evans, 1995). The final paragraph of Justice Kennedy’s opinion declares: â€Å"We must conclude that Amendment 2 classifies homosexuals not to further a proper legislative end but to make them unequal to everyone else. This Colorado cannot do. A State cannot so deem a class of persons a stranger to its laws. Amendment 2 violates the Equal Protection Clause, and the judgment of the Supreme Court of Colorado is affirmed† (Romer v. Evans, 1995). While Justice Scalia writes in his dissenting opinion, Amendment 2 is a â€Å"modest attempt by seemingly tolerant Coloradans to preserve traditional sexual mores against the efforts of a politically powerful minority to revise those mores through the use of the laws† (Romer v. Evans, 1995). While Justice Scalia has the right to his own personal beliefs regarding homosexuality and its validity as a protected class, many others do not share them. As Richard Mohr observes in Romer v. Evans: A Blow for Justice, â€Å"All or nearly all legal burdens on gays appeal directly or indirectly to prejudice†. His article goes on to describe how in 1996 this ruling should affect two major gay issues: gays in the military and gay marriage. When opponents cannot give logical reasons for their opposition it presupposes â€Å"strongly held beliefs for which one can offer no reasons or explanations are by definition prejudicial ones† (Mohr, para. 5). With the decision of the U.S. Supreme Court, Romer v. Evans â€Å"marked an immensely important day for the gay rights movement and a major setback for anti-gay rights activists of all persuasions† according to Sharon Debbage Alexander’s article in the Winter 2002 issue of Texas Forum on Civil Liberties Civil Rights. Furthermore, this case has become one of the most significant decisions issued by the U.S. Supreme Court in regards to gay rights. The majority of those who have analyzed Romer v. Evans purport the â€Å"fact that the case was won using a rational basis test adds to the strength of the decision for gay rights† (Debbage Alexander, pg. 297). Since the decision of Romer v. Evans, President Barack Obama has overturned the â€Å"Don’t Ask, Don’t Tell† policy within our Armed Forces and gay marriage is currently under consideration in two cases that have been heard at the U.S. Supreme Court. After winning Boy Scouts of America v. Dale in 2000 protecting the groups First Amendment expressive association rights, recently the governing body of the Boy Scouts of America voted to allow openly gay scouts within its membership, but not as Scout Leaders. The important issue of gay rights in America has finally reached the forefront of public policy and debate. As in Romer v. Evans, I hope that the United States Supreme Court will rule against the State of California’s Proposition 8 and DOMA, the Defense of Marriage Act, to find both laws unconstitutional. In so far as to bring equality for all to these United States of America.

The Underwater Wireless Communications Information Technology Essay

The Underwater Wireless Communications Information Technology Essay Wireless communication technology today has become part of our daily life; the idea of wireless undersea communications may still seem far-fetched. However, research has been active for over a decade on designing the methods for wireless information transmission underwater. The major discoveries of the past decades, has motivated researches to carry out better and efficient ways to enable unexplored applications and to enhance our ability to observe and predict the ocean. The purpose of this paper is to introduce to the readers the basic concepts, architecture, protocols and modems used in underwater wireless communications. The paper also presents the difficulties faced in terms of power management and security, and the latest developments in the underwater wireless industry. Towards the end, we also discuss a wide range of applications of underwater wireless communication. Index Terms: Underwater Wireless Communication (UWCs), Medium Access Control (MAC), Underwater Acoustic Sensor Networks (UAWSNs). I. INTRODUCTION In last several years, underwater sensor network (UWSN) has found an increasing use in a wide range of applications, such as coastal surveillance systems, environmental research, autonomous underwater vehicle (AUV) operation, many civilian and military applications such as oceanographic data collection, scientific ocean sampling, pollution, environmental monitoring, climate recording, offshore exploration, disaster prevention, assisted navigation, distributed tactical surveillance, and mine reconnaissance. By deploying a distributed and scalable sensor network in a 3-dimensional underwater space, each underwater sensor can monitor and detect environmental parameters and events locally. Hence, compared with remote sensing, UWSNs provide a better sensing and surveillance technology to acquire better data to understand the spatial and temporal complexities of underwater environments. Some of these applications can be supported by underwater acoustic sensor networks (UWASNs), which consist of devices with sensing, processing, and communication capabilities that are deployed to perform collaborative monitoring tasks. Fig 1 gives a generalized diagram of an UWASN. Wireless signal transmission is also crucial to remotely control instruments in ocean observatories and to enable coordination of swarms of autonomous underwater vehicles (AUVs) and robots, which will play the role of mobile nodes in future ocean observation networks by virtue of their flexibility and reconfigurability. Present underwater communication systems involve the transmission of information in the form of sound, electromagnetic (EM), or optical waves. Each of these techniques has advantages and limitations. Acoustic communication is the most versatile and widely used technique in underwater environments due to the low attenuation (signal reduction) of sound in water. This is especially true in thermally stable, deep water settings. On the other hand, the use of acoustic waves in shallow water can be adversely affected by temperature gradients, surface ambient noise, and multipath propagation due to reflection and refraction. The much slower speed of acoustic propagation in water, about 1500 m/s (meters per second), compared with that of electromagnetic and optical waves, is another limiting factor for efficient communication and networking. Nevertheless, the currently favorable technology for underwater communication is upon acoustics. On the front of using electromagnetic (EM) waves in radio frequencies, conventional radio Figure1. Scenario of a UW-ASN composed of underwater and surface vehicles does not work well in an underwater environment due to the conducting nature of the medium, especially in the case of seawater. However, if EM could be working underwater, even in a short distance, its much faster propagating speed is definitely a great advantage for faster and efficient communication among nodes. Free-space optical (FSO) waves used as wireless communication carriers are generally limited to very short distances because the severe water absorption at the optical frequency band and strong backscatter from suspending particles. Even the clearest water has 1000 times the attenuation of clear air, and turbid water has more than 100 times the attenuation of the densest fog. Nevertheless, underwater FSO, especially in the blue-green wavelengths, offers a practical choice for high-bandwidth communication (10-150 Mbps, bits per second) over moderate ranges (10-100 meters). This communication range is much needed in harbor inspection, oil-rig maintenance, and linking submarines to land, just name a few of the demands on this front. In this paper we discuss the physical fundamentals and the implications of using acoustic waves as the wireless communication carrier in underwater environments in Section II, then we discuss an Overview of Routing Protocols for Underwater Wireless Communications in Section III. Section IV we discuss about the two networking architectures of UWSNS. Section V we discuss about acoustic modem technology and will describe Link Quest Incs Cutting-Edge Acoustic Modems in detail.. Section VI gives a comparison between ground based sensors with that of a Mobile UWSNs, Section VII we throw some light on the various applications of UWC. And finally we conclude the paper in Section VIII followed by references. II. ACOUSTIC WAVES Among the three types of waves, acoustic waves are used as the primary carrier for underwater wireless communication systems due to the relatively low absorption in underwater environments. We start the discussion with the physical fundamentals and the implications of using acoustic waves as the wireless communication carrier in underwater environments. Propagation velocity: The extremely slow propagation speed of sound through water is an important factor that differentiates it from electromagnetic propagation. The speed of sound in water depends on the water properties of temperature, salinity and pressure (directly related to the depth). A typical speed of sound in water near the ocean surface is about 1520 m/s, which is more than 4 times faster than the speed of sound in air, but five orders of magnitude smaller than the speed of light. The speed of sound in water increases with increasing water temperature, increasing salinity and increasing depth. Most of the changes in sound speed in the surface ocean are due to the changes in temperature. Approximately, the sound speed increases 4.0 m/s for water temperature arising 1C. When salinity increases 1 practical salinity unit (PSU), the sound speed in water increases 1.4 m/s. As the depth of water (therefore also the pressure) increases 1 km, the sound speed increases roughly 17 m/ s. It is noteworthy to point out that the above assessments are only for rough quantitative or qualitative discussions, and the variations in sound speed for a given property are not linear in general. Fig.2. a vertical profile of sound speed in seawater as the lump-sum function of depth Absorption: The absorptive energy loss is directly controlled by the material imperfection for the type of physical wave propagating through it. For acoustic waves, this material imperfection is the inelasticity, which converts the wave energy into heat. The absorptive loss for acoustic wave propagation is frequency-dependent, and can be expressed as e ®(f)d, where d is the propagation distance and  ®(f) is the absorption coefficient at frequency f. For seawater, the absorption coefficient at frequency f in kHz can be written as the sum of chemical relaxation processes and absorption from pure water where the first term on the right side is the contribution from boric acid, the second term is from the contribution of magnesium sulphate, and the third term is from the contribution of pure water; A1, A2, and A3 are constants; the pressure dependencies are given by parameters P1, P2 and P3; and the relaxation frequencies f1 and f2 are for the relaxation process in boric acid and magnesium sulphate, respectively. Fig. 3 shows the relative contribution from the different sources of absorption as a function of frequency. Fig.3. Absorption in generic seawater Multipath: An acoustic wave can reach a certain point through multiple paths. In a shallow water environment, where the transmission distance is larger than the water depth, wave reflections from the surface and the bottom generate multiple arrivals of the same signal. The Fig 4 illustrates the adverse effects of Multipath Propagation. In deep water, it occurs due to ray Fig 4: Shallow water multipath propagation: in addition to the direct path, the signal propagates via reflections from the surface and bottom. bending, i.e. the tendency of acoustic waves to travel along the axis of lowest sound speed. The channel response varies in time, and also changes if the receiver moves. Regardless of its origin, multipath propagation creates signal echoes, resulting in intersymbol interference in a digital communication system. While in a cellular radio system multipath spans a few symbol intervals, in an underwater acoustic channel it can spans few tens, or even hundreds of symbol intervals! To avoid the intersymbol interference, a guard time, of length at least equal to the multipath spread, must be inserted between successively transmitted symbols. However, this will reduce the overall symbol rate, which is already limited by the system bandwidth. To maximize the symbol rate, a receiver must be designed to counteract very long intersymbol interference. Path Loss: Path loss that occurs in an acoustic channel over a distance d is given as A= dka (f) d, where k is the path loss exponent whose value is usually between 1 and 2, and a(f) is the absorption factor that depends on the frequency f. This dependence severely limits the available bandwidth: for example, at distances on the order of 100 km, the available bandwidth is only on the order of 1 kHz. At shorter distances, a larger bandwidth is available, but in practice it is limited by that of the transducer. Also in contrast to the radio systems, an acoustic signal is rarely narrowband, i.e., its bandwidth is not negligible with respect to the center frequency. Within this limited bandwidth, the signal is subject to multipath propagation, which is particularly pronounced on horizontal channels. III ROUTING PROTOCOLS There are several drawbacks with respect to the suitability of the existing terrestrial routing solutions for underwater wireless communications. Routing protocols can be divided into three categories, namely, proactive, reactive, and geographical. Proactive protocols provoke a large signaling overhead to establish routes for the first time and each time the network topology is modified because of mobility, node failures, or channel state changes because updated topology information must be propagated to all network devices. In this way, each device can establish a path to any other node in the network, which may not be required in underwater networks. Also, scalability is an important issue for this family of routing schemes. For these reasons, proactive protocols may not be suitable for underwater networks. Reactive protocols are more appropriate for dynamic environments but incur a higher latency and still require source-initiated flooding of control packets to establish paths. Reactive protocols may be unsuitable for underwater networks because they also cause a high latency in the establishment of paths, which is amplified underwater by the slow propagation of acoustic signals. Geographical routing protocols are very promising for their scalability feature and limited signaling requirements. However, global positioning system (GPS) radio receivers do not work properly in the underwater environment. Still, underwater sensing devices must estimate their current position, irrespective of the chosen routing approach, to associate the sampled data with their 3D position. IV ARCHITECTURE In general, depending on the permanent vs on-demand placement of the sensors, the time constraints imposed by the applications and the volume of data being retrieved, we could roughly classify the aquatic application scenarios into two broad categories: long-term non-time-critical aquatic monitoring and short-term time-critical aquatic exploration. Fig 5: An illustration of the mobile UWSN architecture for long-term non-time-critical aquatic monitoring applications Fig. 5 illustrates the mobile UWSN architecture for long-term non-time-critical aquatic monitoring applications. In this type of network, sensor nodes are densely deployed to cover a spacial continuous monitoring area. Data are collected by local sensors, related by intermediate sensors, and finally reach the surface nodes (equipped with both acoustic and RF (Radio Frequency) modems), which can transmit data to the on-shore command center by radio. Since this type of network is designed for long-term monitoring task, then energy saving is a central issue to consider in the protocol design. Moreover, depending on the data sampling frequency, we may need mechanisms to dynamically control the mode of sensors (switching between sleeping modes, wake-up mode, and working mode). In this way, we may save more energy. Further, when sensors are running out of battery, they should be able to pop up to the water surface for recharge, for which a simple air-bladder-like device would suffice. Clearly, in the mobile UWSNs for long-term aquatic monitoring, localization is a must-do task to locate mobile sensors, since usually only location-aware data is useful in aquatic monitoring. In addition, the sensor location information can be utilized to assist data forwarding since geo-routing proves to be more efficient than pure flooding. Furthermore, location can help to determine if the sensors float crossing the boundary of the interested area. Fig 6: An illustration of the mobile UWSN architecture for short-term time-critical aquatic exploration applications In Fig. 6, we show a civilian scenario of the mobile UWSN architecture for short-term time-critical aquatic exploration applications. Assume a ship wreckage accident investigation team wants to identify the target venue. When the cable is damaged the ROV is out-of-control or not recoverable. In contrast, by deploying a mobile underwater wireless sensor network, as shown in Fig. 2, the investigation team can control the ROV remotely. The self-reconfigurable underwater sensor network tolerates more faults than the existing tethered solution. After investigation, the underwater sensors can be recovered by issuing a command to trigger air-bladder devices. As limited by acoustic physics and coding technology, high data rate networking can only be realized in high-frequency acoustic band in underwater communication. It was demonstrated by empirical implementations that the link bandwidth can reach up to 0.5Mbps at the distance of 60 meters. Such high data rate is suitable to deliver even multimedia data. Compared with the first type of mobile UWSN for long-term non-time-critical aquatic monitoring, the mobile UWSN for short-term time-critical aquatic exploration presents the following differences in the protocol design. Real-time data transfer is more of concern Energy saving becomes a secondary issue. Localization is not a must-do task. However, reliable, resilient, and secure data transfer is always a desired advanced feature for both types of mobile UWSNs. V ACOUSTIC MODEM TECHNOLOGY Acoustic modem technology offers two types of modulation/detection: frequency shift keying (FSK) with non-coherent detection and phase-shift keying (PSK) with coherent detection. FSK has traditionally been used for robust acoustic communications at low bit rates (typically on the order of 100 bps). To achieve bandwidth efficiency, i.e. to transmit at a bit rate greater than the available bandwidth, the information must be encoded into the phase or the amplitude of the signal, as it is done in PSK or Quadrature Amplitude Modulation (QAM). The symbol stream modulates the carrier, and the so-obtained signal is transmitted over the channel. To detect this type of signal on a multipath-distorted acoustic channel, a receiver must employ an equalizer whose task is to unravel the intersymbol interference. A block diagram of an adaptive decision-feedback equalizer (DFE) is shown in Figure 7. In this configuration, multiple input signals, obtained Fig 7: Multichannel adaptive decision-feedback equalizer (DFE) is used for high-speed underwater acoustic communications. It supports any linear modulation format, such as M-ary PSK or M-ary QAM. from spatially diverse receiving hydrophones, can be used to enhance the system performance. The receiver parameters are optimized to minimize the mean squared error in the detected data stream. After the initial training period, during which a known symbol sequence is transmitted, the equalizer is adjusted adaptively, using the output symbol decisions. An integrated Doppler tracking algorithm enables the equalizer to operate in a mobile scenario. This receiver structure has been used on various types of acoustic channels. Current achievements include transmission at bit rates on the order of one kbps over long ranges (10-100 nautical miles) and several tens of kbps over short ranges (few km) as the highest rates reported to date. VI Mobile UWSNs and Ground- Based Sensor Networks A mobile UWSN is significantly different from any ground-based sensor network in terms of the following aspects: Communication Method: Electromagnetic waves cannot propagate over a long distance in underwater environments. Therefore, underwater sensor networks have to rely on other physical means, such as acoustic sounds, to transmit signals. Unlike wireless links among ground-based sensors, each underwater wireless link features large latency and low-bandwidth. Due to such distinct network dynamics, communication protocols used in ground-based sensor networks may not be suitable in underwater sensor networks. Specially, low-bandwidth and large-latency usually result in long end-to-end delay, which brings big challenges in reliable data transfer and traffic congestion control. The large latency also significantly affects multiple access protocols. Traditional random access approaches in RF wireless networks might not work efficiently in underwater scenarios. Node Mobility Most sensor nodes in ground-based sensor networks are typically static, though it is possible to implement interactions between these static sensor nodes and a limit amount of mobile nodes (e.g., mobile data collecting entities like mules which may or may not be sensor nodes). In contrast, the majority of underwater sensor nodes, except some fixed nodes equipped on surface-level buoys, are with low or medium mobility due to water current and other underwater activities. From empirical observations, underwater objects may move at the speed of 2-3 knots (or 3-6 kilometers per hour) in a typical underwater condition [2]. Therefore, if a network protocol proposed for ground-based sensor networks does not consider mobility for the majority of sensor nodes, it would likely fail when directly cloned for aquatic applications. Although there have been extensive research in groundbased sensor networks, due to the unique features of mobile UWSNs, new research at almost every level of the protocol suite is required. VII