Monday, January 7, 2019

Mobile communcation

We understand by mobile communication as the use of technology that allows us to communicate with others in different locations without the use of cables. Mobile communication makes our life easier, saves time and effort.

Security:

Mobile device security, has become increasingly important in mobile computing of particular concern is the security of personal and business information now stored on smartphones.

Types of Wireless Communication

The different types of wireless communication mainly include, IR wireless communication, satellite communication, broadcast radio, Microwave radio, Bluetooth, Zigbee etc.

Satellite Communication

Satellite communication is one type of self contained wireless communication technology, it is widely spread all over the world to allow users to stay connected almost anywhere on the earth. When the signal (a beam of modulated microwave) is sent near the satellite then, satellite amplifies the signal and sent it back to the antenna receiver which is located on the surface of the earth. Satellite communication contains two main components like the space segment and the ground segment.The ground segment consists of fixed or mobile transmission, reception and ancillary equipment and the space segment, which mainly is the satellite itself.

Infrared Communication

Infrared wireless communication communicates information in a device or systems through IR radiation . IR is electromagnetic energy at a wavelength that is longer than that of red light. It is used for security control, TV remote control and short range communications. In the electromagnetic spectrum, IR radiation lies between microwaves and visible light. So, they can be used as a source of communication

Broadcast Radio

The first wireless communication technology is the open radio communication to seek out widespread use, and it still serves a purpose nowadays. Handy multichannel radios permit a user to speak over short distances, whereas citizen’s band and maritime radios offer communication services for sailors. Ham radio enthusiasts share data and function emergency communication aids throughout disasters with their powerful broadcasting gear, and can even communicate digital information over the radio frequency spectrum.

Microwave Communication

Microwave wireless communication is an effective type of communication, mainly this transmission uses radio waves, and the wavelengths of radio waves are measured in centimeters. In this communication, the data or information can be transfers using two methods. One is satellite method and another one is terrestrial method.

Wi-Fi

Wi-Fi is a low power wireless communication, that is used by various electronic devices like smart phones, laptops, etc.In this setup, a router works as a communication hub wirelessly. These networks allow users to connect only within close proximity to a router. WiFi is very common in networking applications which affords portability wirelessly. These networks need to be protected with passwords for the purpose of security, otherwise it will access by others

Bluetooth Technology

The main function of the Bluetooth technology is that permits you to connect a various electronic devices wirelessly to a system for the transferring of data.Cell phones are connected to hands free earphones, mouse, wireless keyboard. By using Bluetooth device the information from one device to another device. This technology has various functions and it is used commonly in the wireless communication market.

Advantages of Wireless Communication

· Any data or information can be transmitted faster and with a high speed

· Maintenance and installation is less cost for these networks.

· The internet can be accessed from anywhere wirelessly

· It is very helpful for workers, doctors working in remote areas as they can be in touch with medical centers.

Disadvantages of Wireless Communication

· An unauthorized person can easily capture the wireless signals which spread through the air.

· It is very important to secure the wireless network so that the information cannot be misused by unauthorized users

· Mobile Phone Communication. How it works?

A mobile phone is an electronic device used for mobile telecommunications over a cellular network of specialized base stations known as cell sites. A cell phone offers full Duplex Communication and transfer the link when the user moves from one cell to another. As the phone user moves from one cell area to another, the system automatically commands the mobile phone and a cell site with a stronger signal, to switch on to a new frequency in order to keep the link.

History of Mobile Communication

Cellular Era

To overcome the constraints of bandwidth scarcity and to give coverage to larger sections, BELL lab introduced the principle of Cellular concept. By frequency reuse technique this method delivered better coverage, better utility of available frequency spectrum and reduced transmitter power. But the established calls are to be handed over between base stations while the phones are on move.

Even though the US based BELL lab introduced the cellular principle, the Nordic countries were the first to introduce cellular services for commercial use with the introduction of the Nordic Mobile Telephone (NMT) in 1981.

First Generation Systems

All these systems were analog systems, using FDMA technology. They are also known as First Generation (1G) systems. Different systems came into use based on the cellular principle. They are listed below.

Year	Mobile System
1981	Nordic Mobile Telephone(NMT)450
1982	American Mobile Phone System(AMPS)
1985	Total Access Communication System(TACS)
1986	Nordic Mobile Telephony(NMT)900

Disadvantages of 1G systems

They were analog and hence are were not robust to interference.
Different countries followed their own standards, which were incompatible.

To overcome the difficulties of 1G, digital technology was chosen by most of the countries and a new era, called 2G, started.

Advantages of 2G

Improved Spectral Utilization achieved by using advanced modulation techniques.
Lower bit rate voice coding enabled more users getting the services simultaneously.
Reduction of overhead in signaling paved way for capacity enhancement.
Good source and channel coding techniques make the signal more robust to Interference.
New services like SMS were included.
Improved efficiency of access and hand-off control were achieved.

Name of the Systems	Country
DAMPS-Digital Advanced Mobile Phone System	North America
GSM-Global System for Mobile communication	European Countries and International applications
JDC - Japanese Digital Cellular	Japan
CT-2 Cordless Telephone–2	UK
DECT-Digital European Cordless Telephone	European countries

History of GSM

GSM standard is a European standard, which has addressed many problems related to compatibility, especially with the development of digital radio technology.

Milestones of GSM

1982 - Confederation of European Post and Telegraph (CEPT) establishes Group Special Mobile.
1985 - Adoption of list of recommendation was decided to be generated by the group.
1986 - Different field tests were done for radio technique for the common air interface.
1987 - TDMA was chosen as the Access Standard. MoU was signed between 12 operators.
1988 - Validation of system was done.
1989 - Responsibility was taken up by European Telecommunication Standards Institute (ETSI).
1990 - First GSM specification was released.
1991 - First commercial GSM system was launched.

Frequency Range of GSM

GSM works on four different frequency ranges with FDMA-TDMA and FDD. They are as follows −

System	P-GSM (Primary)	E-GSM (Extended)	GSM 1800	GSM 1900
Freq Uplink	890-915MHz	880-915MHz	1710-1785Mhz	1850-1910MHz
Freq Downlink	935-960MHz	925-960MHz	1805-1880Mhz	1930-1990MHz

· Mobile phone is primarily designed for Voice communication. In addition to the standard voice function, new generation mobile phones support many additional services, and accessories, such as SMS for text messaging, email, packet switching for access to the Internet, gaming, Bluetooth, camera with video recorder and MMS for sending and receiving photos and video, MP3 player, radio and GPS.

presented by

P.VIJAYALAKSHMI

18JG5A0501

22-12-2018.

Sunday, January 6, 2019

Leftist Heap

Priority Queues:Leftist Heaps

New Heap Operation: Merge

Given two heaps, merge them into one heap

– first attempt: insert each element of the smaller into the larger. runtime:

– second attempt: concatenate binary heaps’ arrays and run buildHeap. runtime:

Leftist Heaps Idea:

Focus all heap maintenance work in one small part of the heap Leftist heaps:

1. Binary trees

2. Most nodes are on the left

3. All the merging work is done on the right

Definition: Null Path Length

null path length (npl) of a node x = the number of nodes between x and a null in its subtree

npl(x) = min distance to a descendant with 0 or 1 children

Definition: Null Path Length • npl(null) = -1 • npl(leaf) = 0 • npl(single-child node) = 0

Equivalent definition: npl(x) = 1 + min{npl(left(x)), npl(right(x))}

Another useful definition: npl(x) is the height of the largest perfect binary tree that is both itself rooted at x and contained within the subtree rooted at x.

Leftist Heap Properties

*Order property – parent’s priority value is ≤ to childrens’ priority values – result: minimum element is at the root – (Same as binary heap)

* Structure property – For every node x, npl(left(x)) ≥ npl(right(x)) – result: tree is at least as “heavy” on the left as the right (Terminology: we will say a leftist heap’s tree is a leftist tree)

Observations

Are leftist trees always… – complete? – balanced? Consider a subtree of a leftist tree… – is it leftist

Right Path in a Leftist Tree is Short (#1)

Claim:The right path (path from root to rightmost leaf) is as short as and in the tree.

Proof: (By contradiction) R x L D2 D1 Pick a shorter path: D1 < D2 Say it diverges from right path at x npl(L) ≤ D1-1 because of the path of length D1-1 to null npl(R) ≥ D2-1 because every node on right path is leftist Leftist property at x violated!

Right Path in a Leftist Tree is Short (#2):

Claim:If the right path has r nodes, then the tree has at least 2r-1 nodes.

Proof: (By induction) Base case : r=1. Tree has at least 21-1 = 1 node Inductive step : assume true for r-1. Prove for tree with right path at least r. 1. Right subtree: right path of r-1 nodes ⇒ 2r-1-1 right subtree nodes (by induction) 2. Left subtree: also right path of length at least r-1 (prev. slide) ⇒ 2r-1-1 left subtree nodes (by induction) ⇒ Total tree size: (2r-1-1) + (2r-1-1) + 1 = 2r-1

Why do we have the leftist property?

Because it guarantees that: • the right path is really short compared to the number of nodes in the tree • A leftist tree of N nodes, has a right path of at most log2(N+1) nodes Idea – perform all work on the right path

Merge two heaps (basic idea)

• Put the root with smaller value as the new root. • Hang its left subtree on the left.

• Recursively merge its right subtree and the other tree.

• Before returning from recursion: – Update npl of merged root. – Swap left and right subtrees just below root, if needed, to keep leftist property of merged result.

Merging two leftist heaps:

Recursive calls to merge(T1,T2): returns one leftist heap containing all elements of the two (distinct) leftist heaps T1 and T2

Merge continued

Leftest Merge example

Sewing up the example

Operations on Leftist Heaps

• merge with two trees of total size n: O(log n)

• insert with heap size n: O(log n) – pretend node is a size 1 leftist heap – insert by merging original heap with one node heap

• deleteMin with heap size n: O(log n) – remove and return root – merge left and right subtrees

LI-FI TECHNOLOGY

Introduction to Li-Fi:

Li-Fi is the abbreviation of light fidelity and was expressed by Harald Hass who was a German physicist. In Li-Fi the information is transferred through light signals instead of radio waves and mostly Wi-Fi plays an efficient role for wireless information coverage within the buildings whereas by using Li-Fi we can provide the excel density data coverage in a particular area without any radio interference issue. It furnishes well bandwidth, assurance than Wi-Fi and excels speed. In the coming generation, this technology will be used for transmitting data or information to smartphones, laptops etc. through the light in a room.

The affordable, speed change in the optical form of Wi-Fi is the Li-Fi and it is based on VLC i.e. Visible Light Communication where VLC is a medium of information communication which avails quick pulses of light to send the data wirelessly. The main constituents of a Li-Fi system are:

An excel brightening white LED which plays the role of a transmitter.
A silicon photodiode with a good response to visible light acts as a receiver.

LED’s can be switched on and off through which different unions of digital chains consisting of 1’s and 0’s are produced. The LED can be used as a transmitter or a source, the response of LED appears consistent to the human eye due to the quick flickering of LED.

Working of Li-Fi:

In a typical setup, the transmitter (LED) is connected to the data network (Internet through the modem) and the receiver (photo detector/light sensor) on the receiving end receives the data as light signal and decodes the information, which is then displayed on the device connected to the receiver. The receiver (photo detector) registers a binary ‘1’ when the transmitter (LED) is ON and a binary ‘0’ when the transmitter (LED) is OFF. Thus flashing the LED numerous times or using an array of LEDs (perhaps of a few different colours) will eventually provide data rates in the range of hundreds of Mbps. The Li-Fi working is explained in a block diagram.

Hence all that is required, is some or an array of LEDs and a controller that controls/encodes data into those LEDs.All one has to do is to vary the rate at which the LEDs flicker depending upon the data input to LEDs. Further data rate enhancements can be made in this method, by using array of the LEDs for parallel data transmission, or using mixtures of red , green and blue LEDs to alter the light’sfrequency, with each frequency encoding a different data channel. Figure 7 shows working/deployment of a Li-Fi system connecting the devices in a room.

*History:

Li-Fi technology was first introduced by a German professor,physist and communications technology innovator, Herald Hass, at a TED talk in july 2011.in his talk, Herald demonstrated how energy can be transmitted from a light bulb by inducing subtle changes in the amplitude of the light bulb in such high speed that they are not visible to the human eye. Herald demonstrated Li-Fi to audience by playing a high definition vedio of a flower that was solely transmitted using a LED table lamp with an LED bulb.

Today, Li-Fi has been deployed in more than 20 countries.

* Comparison Between Li-Fi and, Wi-Fi and other Radio Communication technologies Both Wi-Fi and Li-Fi:

can provide wireless Internet access to users, and both the technologies transmit data over electromagnetic spectrum. Li-Fi is a visible light communication technology useful to obtain high speed wireless communication. The difference is: Wi-Fi technology uses radio waves for transmission, whereas Li-Fi utilizes light waves. Wi-Fi works well for general wireless coverage within building/campus/compound, and Li-Fi is ideal for high density wireless data coverage inside a confined area or room and is free from interference issues unlike the Wi-Fi. Table I shows a comparison of transfer speed of various wireless technologies. Table II shows a comparison of Li-Fi with Wi-Fi.

*Advantages of Li-Fi :

Li-Fi, which uses visible light to transmit signals wirelessly, is an emerging technology poised to compete with Wi-Fi. Also, Li-Fi removes the limitations that have been put on the user by the Radio wave transmission such as Wi-Fi as explained above vide 4.1. Advantages of Li-Fi technology include:

a)Efficiency: Energy consumption can be minimised with the use of LED illumination which are already available in the home, offices and Mall etc. for lighting purpose. Hence the transmission of data requiring negligible additional power, which makes it very efficient in terms of costs as well as energy.

b) High speed: Combination of low interference, high bandwidths and high-intensity output, help Li-Fi provide high data rates i.e. 1 Gbps or even beyond.

c) Availability: Availability is not an issue as light sources are present everywhere. Wherever there is a light source, there can be Internet. Light bulbs are present everywhere – in homes, offices, shops, malls and even planes, which can be used as a medium for the data transmission.

d) Cheaper: Li-Fi not only requires fewer components for its working, but also uses only a negligible additional power for the data transmission.

e) Security: One main advantage of Li-Fi is security. Since light cannot pass through opaque structures, Li-Fi internet is available only to the users within a confined area and cannot be intercepted and misused, outside the area under operation.

f) Li-Fi technology has a great scope in future. The extensive growth in the use of LEDs for illumination indeed provides the opportunity to integrate the technology into a plethora of environments and applications.

*Limitations of Li-Fi:

Some of the major limitations of Li-Fi are:

· Internet cannot be accessed without a light source. This could limit the locations and

· situations in which Li-Fi could be used. It requires a near or perfect line-of-sight to transmit data.

· Opaque obstacles on pathways can affect data transmission

· Natural light, sunlight, and normal electric light can affect the data transmission speed

· Light waves don’t penetrate through walls and so Li-Fi has a much shorter range than Wi-Fi

· High initial installation cost, if used to set up a full-fledged data network

.· Yet to be developed for mass scale adoption.

*Applications of Li-Fi:

Some of the future applications of Li-Fi could be as follows:

a) Education systems: Li-Fi is the latest technology that can provide fastest speed for Internet access. So, it can augment/replace Wi-Fi at educational institutions and at companies so that the people there can make use of Li-Fi with the high speed.

b) Medical Applications: Operation theatres (OTs) do not allow Wi-Fi due to radiation concerns. Usage of Wi-Fi at hospitals interferes/blocks the signals for monitoring equipments. So, it may have hazardous effect to the patient's health, due to improper working of medical apparatus. To overcome this and to make OT tech savvy Li-Fi can be used to access internet and also to control medical equipments. This will be beneficial for conducting robotic surgeries and other automated procedures.

c) Cheaper Internet in Aircrafts: The passengers travelling in aircrafts get access to low speed Internet that too at a very high price. Also Wi-Fi is not used because it may interfere with the navigational systems of the pilots. In aircrafts Li-Fi can be used for data transmission. Li-Fi can easily provide high speed Internet via every light source such as overhead reading bulb, etc. present inside the airplane.

d) Underwater applications: Underwater ROVs (Remotely Operated Vehicles) operate from large cables that supply their power and allow them to receive signals from their pilots above. But the tether used in ROVs is not long enough to allow them to explore larger areas. If their wires were replaced with light — say from a submerged, highpowered lamp — then they would be much freer to explore. They could also use their headlamps to communicate with each other, processing data autonomously and sending their findings periodically back to the surface. Li-Fi can even work underwater where Wi-Fi fails completely, thereby throwing open endless opportunities for military underwater operations.

e) Disaster management: Li-Fi can be used as a powerful means of communication in times of disaster such as earthquake or hurricanes. The average people may not know the protocols during such disasters. Subway stations and tunnels, common dead zones for most emergency communications, pose no obstruction for Li-Fi.

f) Applications in sensitive areas: Power plants need fast, inter-connected data systems so that demand, grid integrity and core temperature (in case of nuclear power plants) can be monitored. The Radio communication interference is considered to be bad for such sensitive areas surrounding these power plants. Li-Fi can offer safe, abundant connectivity for all areas of these sensitive locations. Also, the pressure on a power plant 12 ‘s own reserves (power consumption for Radio communications deployments) will be lessened.

g)Traffic management: In traffic signals Li-Fi can be used to communicate with passing vehicles (through the LED lights of the cars etc) which can help in managing the traffic in a better manner resulting into smooth flow of traffic and reduction in accident numbers. Also, LED car lights can alert drivers when other vehicles are too close.

h) Mobile Connectivity: Mobiles, laptops, tablets, and other smart phones can easily connect with each other. The short-range network of Li-Fi can yield exceptionally high data rates and higher security.

i) Replacement for other technologies: Li-Fi doesn‘t work using radio waves. So, it can be easily used in the places where Bluetooth, infrared, Wi-Fi, etc. are banned.

*Conclusion :

Although there’s still a long way to go to make this technology a commercial success, it promises a great potential in the field of wireless internet. A significant number of researchers 15 and companies are currently working on this concept, which promises to solve the problem of lack of radio spectrum, space and low internet connection speed. By deployment of this technology, we can migrate to greener, cleaner, safer communication networks.

The very concept of Li-Fi promises to solve issues such as, shortage of radio-frequency bandwidth and eliminates the disadvantages of Radio communication technologies. Li-Fi is the upcoming and growing technology acting as catalyst for various other developing and new inventions/technologies. Therefore, there is certainty of development of future applications of the Li-Fi which can be extended to different platforms and various walks of human life.

Technomics