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CHAPTER-1

WIRELESS COMMUNICATION - LASER COMMUNICATION

1.1 INTRODUCTION:

Communication technology has experienced a continual development to higher and higher carrierfrequencies, starting from a few hundred kilohertz atMarconi's time to several hundred terahertzes since we employ lasers in fiber systems. The main driving forcewas that the usable bandwidth - and hencetransmission capacity - increases proportional to thecarrier frequency. Another asset comes into play infree-space point-to-point links. The minimumdivergence obtainable with a freely propagating beam of electromagnetic waves scales proportional to thewavelength. The jump from microwaves to lightwaves therefore means a reduction in beam width byorders of magnitude, even if we use transmit antennasof much smaller diameter. The reduced beamwidthdoes not only imply increased intensity at the receiversite but also reduced cross talk between closelyoperating links and less chance for eavesdropping.

For the past quarter century, wireless communication has been hailed as the superior method for transmitting video, audio, data and various analog signals. Laser offers many well-known advantages over twisted pair and coaxial cable, including immunity to electrical interference and superior bandwidth. For these and many other reasons, wireless transmission systems have been increasingly integrated into a wide range of applications across many industries.

Now, a new generation of products that employs pure digital signaling to transmit analog information offers the opportunity to raise the standard once again, bringing wireless transmission to a whole new level.

Digital systems offer superior performance, flexibility and reliability, and yet don’t cost any more than the older analog designs they replace. This Education Guide examines how digital signaling over laser is accomplished and the resulting benefits, both from a performance and economic perspective.

1.2 LASER APPLICATIONS:

Why Laser Instead of RF?

  • Power Consumption :

RF network needs to constantly listen, depending on the duty cycle. This takes power. A laser node however does not need to listen, and can sleep while waiting for a laser pulse.

  • Range:

A RF enabled node has a limited range. A laserhas a range in the kilometers. This means anode can be far away from the central network nodes.

  • Low cost and reliable:

Laser communication system is basically cheaper in comparison to lying of optical fiber and maintaining it. Wireless communication system hasinitial value but it is quite reliable and of many usage at a time as digital as well as voice transmission through a singletransmitter. Hence quite more effective

CHAPTER -2

LASER COMMUNICATION WITH CONTROL SYSTEM

2.1PROJECT GOALS

The goal of our project is to develop a low powered, inexpensive, and versatile opticalwireless communication system. Such a system should be able to send transmissionmessages using lasers, and should be low powered, especially compared to radiofrequency based wireless communications. Our goal is to create and design a versatilesystem so that the system can be used for different types of wireless networks, includingIP based networks and wireless sensor networks.

Our primary objective is to develop a working system that can achieve wirelesscommunication over laser. This entails the design and development of the hardware, datalink, and physical layers of the system. This includes the data network protocols,including the method of using the laser to transmit information over air. We also need todesign the higher level network protocols, such that data frames can be transferred overthe data link layers. A secondary goal will be to compare and contrast the power consumption of the opticalwireless communication system against a typical RF wireless communication system. Weseek to demonstrate that for some wireless applications, an optical wireless system holds

Certain advantages in terms of power and other characteristics. It is our goal as well todevelop a framework for further research and analysis into such a system, and makingone actually viable.

Overall we seek to develop a working communication system where two nodes cantransfer data (in the form of bytes) to each other using laser pulses, and demonstrate thatsuch a system can indeed work. In this paper, we will explain the motivation for such asystem, where a laser based network has advantages over traditional RF ones, and howwe implemented our prototype network.

2.2 PROJECT BACKGROUND

Wireless communications has become increasingly important in technology,communication, and computer science. From cell phones to wireless internet to homedevices, everything is being converted from wired into wireless. A major research andfocus area in fact has been the wireless sensor network. This network relies on lowpowered self-contained nodes that sense the environment, such as temperature orhumidity. These nodes must be able to transfer and receive information wirelessly. Indeed, a lot of research and funding has been put into developing wireless systems. Most of the focus has gone to radio frequency wireless communication.

All spacecrafts flying at present communicates with ground by means of a radio communication link. This link consists of an onboard radio transmitter/receiver coupled to a single or two antennas. The ground station has a similar system. The radio-beam that leaves the antenna will attenuate over distance following the r-2, just like light from a flashlight. For satellites in low earth orbit, i.e. altitudes between 200 and 2000km, the onboard antenna system is typically a simple dipole or quadropole antenna,

Enabling omnidirectional communication, i.e. without pointing the

Antenna towards the receiver. This approach is viable because the distance is small, and, because the data rate typically is moderate.

For higher orbit, e.g. geostationary satellites, the downlink antennas are typically highly directional, e.g. dish- or cluster-antennas. Such antenna systems have the benefit of “focusing” the radio energy into a narrow beam before the wave’s leaves the antenna. As soon as the waves leaves the antenna dominated space (far field approximation) the beam is still attenuated according to the r- 2 law, but as the intrinsic energy is higher in certain directions, more energy/m-2 will be observed in these directions. Obviously, such antennas must be pointed at the ground station in order to work, and this pointing action requires either the satellite to track the station or to have a moving gimbal mounted antenna system. The spacecraft uplink antenna does not need high directionality (gain), because the ground

Segment usually utilizes large antennas and powerful transmitters such that an ample radio energy density (W/m-2) arrives at the spacecraft receiver antenna. Conversely, the spacecraft are bound to use low power transmitters, partly because electrical power is a scarce resource in space, partly because high power transmitters are heavy, large, and have a short life. Deep space probes, that are spacecrafts that are bound for the Moon and beyond, are forced to use highly directional antennas both for up- and downlink because of the large distance between the spacecraft and the ground station. E.g. spacecrafts bound for Mars will have 2- 4m diameter dish antennas on the spacecraft, and the ground segment uses 70m antennas! The size of the antenna determines, together with the frequency of the radio waves, the

Directionality (i.e. gain) of the antenna (3dB beam width = 70/antenna diameter degrees).

The larger the antenna, and the higher the frequency, the higher gain. Therefore, there has been a constant drive for use of higher frequencies to enable smaller antenna systems onboard the spacecraft. At present, 20-30 GHzis practical. Finally, the required data rate that the communication link has to support depends on the total attenuation of the link because certain energy must be received per bit. Hence, if the powers received are low, it will take longer time to achieve the necessary energy, and vise

2.3 SYSTEM OVERVIEW & DESCRIPTION

2.3.1 Overview

• Background

• Project goals

• Motivation and Challenges

• Project implementation

• Data flow

• Encoding scheme

• Framing scheme

2.3.2 Background

There has been a shift from wired to wireless

A lot of research has been put into Radiofrequency (RF) wireless. But not much on optical wireless

2.3.3Project goals

Develop a wireless optical communication

System using laser

A)Low-powered

b) Inexpensive

c) Versatile

2.3.4Motivations and Challenges

Laser offers the following benefits

1. Long range

2. Low-powered, low interference

3. Narrow beam very hard to detect & intercept

4. High speed

Laser has the following disadvantage

1. Non-mobile

2. Line of sight issue

3. Challenges

4. Design a reliable coding scheme

5. Optimize for bandwidth and latency

.

2.3.5Project Implementation

Composed of two Parts

1. Laser boards – the data link and physical layer

2. Transmitter & receiver scale - the network and application layer

2.3.6 Data Flow

1. Framed bytes

2. Encoded bits

3. Framed bytes

2.3.6Result – what did we accomplish

1. Implemented a basic laser communication

System

2. Can send data from one Scale to another

3. Input data can be from a file or from command

Line

4. Can use the system to trigger command line

Execution remotely

2.3.8 Future works

1.Improve latency and bandwidth

2. Support full-duplex communication

3.Support multiple senders/receivers

4. Improve encoding and framing schemes

5.Error detection/correction

6. Extensive power-usage analysis of the system

7.More fully develop laser network stack

CHAPTER-3

COMPONENTS

3.1 COMPONENTS USED:

  • PCB
  • STEP DOWN TRANSFORMER 5V/500mA
  • VOLTAGE REGULATOR LM7805
  • RECTIFIER DIODES 1N4001
  • ELECTROLYTIC CAPACITORS
  • LED DISPLAY
  • LEDs
  • IC 7447, 8870, 91214.
  • Tr. BC-548
  • Laser diode
  • OPERATIONAL AMPLIFIER
  • PVC WIRES
  • RESSISTANCE 10K
  • CAPACITOR 104PF
  • DPDT S/W
  • IC 7805
  • MICRO SWITCH
  • CRYSTAL 12 MHZ
  • RESET 100K
  • MIKE
  • SPEAKER 5 OHM

3.2 DESCRIPTION ABOUT THE COMPONENTS

3.2.1 PCB:

PCBs are boards whereupon electronic circuits have been etched. PCBs are rugged, inexpensive, and can be highly reliable. They require much more layout effort and higher initial cost than either wire-wrapped or point-to-point constructed circuits, but are much cheaper and faster for high-volume production. Much of the electronics industry's PCB design, assembly, and quality control needs are set by standards that are published by the IPC organization.

After the printed circuit board (PCB) is completed, electronic components must be attached to form a functional printed circuit assembly, or PCA (sometimes called a "printed circuit board assembly" PCBA). In through-hole construction, component leads are inserted in holes. In surface-mount construction, the components are placed on pads or lands on the outer surfaces of the PCB. In both kinds of construction, component leads are electrically and mechanically fixed to the board with a molten metal solder.

There are a variety of soldering techniques used to attach components to a PCB. High volume production is usually done with machine placement and bulk wave soldering or reflow ovens, but skilled technicians are able to solder very tiny parts (for instance 0201 packages which are 0.02" by 0.01") by hand under a microscope, using tweezers and a fine tip soldering iron for small volume prototypes. Some parts are impossible to solder by hand, such as ball grid array (BGA) packages.

Often, through-hole and surface-mount construction must be combined in a single PCA because some required components are available only in surface-mount packages, while others are available only in through-hole packages. Another reason to use both methods is that through-hole mounting can provide needed strength for components likely to endure physical stress, while components that are expected to go untouched will take up less space using surface-mount techniques.

After the board has been populated it may be tested in a variety of ways:

  • While the power is off, visual inspection, automated optical inspection. JEDEC guidelines for PCB component placement, soldering, and inspection are commonly used to maintain quality control in this stage of PCB manufacturing.
  • While the power is off, analog signature analysis, power-off testing.
  • While the power is on, in-circuit tests, where physical measurements (i.e. voltage, frequency) can be done.
  • While the power is on, functional test, just checking if the PCB does what it had been designed for.

To facilitate these tests, PCBs may be designed with extra pads to make temporary connections. Sometimes these pads must be isolated with resistors. The in-circuit test may also exercise boundary scan test features of some components. In-circuit test systems may also be used to program nonvolatile memory components on the board.

In boundary scan testing, test circuits integrated into various ICs on the board form temporary connections between the PCB traces to test that the ICs are mounted correctly. Boundary scan testing requires that all the ICs to be tested use a standard test configuration procedure, the most common one being the Joint Test Action Group (JTAG) standard. When boards fail the test, technicians may disorder and replace failed components, a task known as "rework".

Manufacturing

a)Materials:Conducting layers are typically made of thin copper foil. Insulating layers dielectric are typically laminated together with epoxy resinprepare. The board is typically coated with a solder mask that is green in color. Other colors that are normally available are blue, and red. There are quite a few different dielectrics that can be chosen to provide different insulating values depending on the requirements of the circuit. Some of these dielectrics are polytetrafluoroethylene, FR-4, FR-1, CEM-1 or CEM-3. Well known prepreg materials used in the PCB industry are FR-2 (Phenolic cotton paper), FR-3 (Cotton paper and epoxy), FR-4 (Woven glass and epoxy), FR-5 (Woven glass and epoxy), FR-6 (Matte glass and polyester), G-10 (Woven glass and epoxy), CEM-1 (Cotton paper and epoxy), CEM-2

(Cotton paper and epoxy), CEM-3 (Woven glass and epoxy), CEM-4 (Woven glass and epoxy), CEM-5 (Woven glass and polyester).

Typical density of a raw PCB (an average amount of traces, holes, and via's, with no components) is 2.15g / cm3

Patterning (etching) : The vast majority of printed circuit boards are made by bonding a layer of copper over the entire substrate, sometimes on both sides, (creating a "blank PCB") then removing unwanted copper after applying a temporary mask (eg. by etching), leaving only the desired copper traces. A few PCBs are made by adding traces to the bare substrate (or a substrate with a very thin layer of copper) usually by a complex process of multiple electroplating steps.

There are three common "subtractive" methods (methods that remove copper) used for the production of printed circuit boards:

1. Silk screen printing uses etch-resistant inks to protect the copper foil. Subsequent etching removes the unwanted copper. Alternatively, the ink may be conductive, printed on a blank (non-conductive) board. The latter technique is also used in the manufacture of hybrid circuits.

  1. Photoengraving uses a photomask and chemical etching to remove the copper foil from the substrate. The photomask is usually prepared with a photoplotter from data produced by a technician using CAM, or computer-aided manufacturing software. Laser-printed transparencies are typically employed for phototools; however, direct laser imaging techniques are being employed to replace phototools for high-resolution requirements.
  1. PCB milling uses a two or three-axis mechanical milling system to mill away the copper foil from the substrate. A PCB milling machine (referred to as a 'PCB Prototyper') operates in a similar way to a plotter, receiving commands from the host software that control the position of the milling head in the x, y, and (if relevant) z axis. Data to drive the Prototyper is extracted from files generated in PCB design software and stored in HPGL or Gerber file format.

"Additive" processes also exist. The most common is the "semi-additive" process. In this version, the unpatterned board has a thin layer of copper already on it. A reverse mask is then applied. (Unlike a subtractive process mask, this mask exposes those parts of the substrate that will eventually become the traces.) Additional copper is then plated onto the board in the unmasked areas; copper may be plated to any desired weight. Tin-lead or other surface platings are then applied. The mask is stripped away and a brief etching step removes the now-exposed original copper laminate from the board, isolating the individual traces.

The additive process is commonly used for multi-layer boards as it facilitates the plating-through of the holes (to produce conductive vias) in the circuit board.

Lamination

Some PCBs have trace layers inside the PCB and are called multi-layer PCBs. These are formed by bonding together separately etched thin boards.

Drilling

Holes through a PCB are typically drilled with tiny drill bits made of solid tungsten carbide. The drilling is performed by automateddrilling machines with placement controlled by a drill tape or drill file. These computer-generated files are also called numerically controlled drill (NCD) files or "Excellon files". The drill file describes the location and size of each drilled hole. These holes are often filled with annular rings to create vias. Vias allow the electrical and thermal connection of conductors on opposite sides of the PCB.