Eng Sem I #11 Telecommunications Introduction PDF

PROPAGATION OF RADIO "Electromagneticwave3Dfromside" by Lookang many thanks to Fu-Kwun Hwang and author of Easy Java Simulation = Francisco Esquembre - Own work. Licensed under CC BY-SA 3.0 via Commons - https://commons.wikimedia.org/wiki/File:Electromagneticwave3Dfrom...

PROPAGATION OF RADIO "Electromagneticwave3Dfromside" by Lookang many thanks to Fu-Kwun Hwang and author of Easy Java Simulation = Francisco Esquembre - Own work. Licensed under CC BY-SA 3.0 via Commons - https://commons.wikimedia.org/wiki/File:Electromagneticwave3Dfromside.gif#/ media/File:Electromagneticwave3Dfromside.gif COMMON FREQUENCY BANDS There are hundreds of frequency bands for different wireless technologies. Some examples: Cell phones: 824 to 849 MHz Global Positioning System: 1227 to 1575 MHz Garage Door Openers: Around 40 MHz Baby Monitors: 49 MHz MIR Space Station: 145 to 437 MHz Deep Space Communications: 2290 to 2300 MHz  Human voice also has its own frequency band. Voice’s frequency band is from 0 Hz to 4000 Hz. Middle C is 261.6Hz ANOTHER The commonly stated range of human IMPORTANT hearing is 20 Hz to 20 kHz FREQUENCY BAND WHY IS AM RADIO AT A LOWER BAND THAN FM RADIO? Mostly, due to history. AM was invented before FM. Transmitting at higher frequencies means that electronic equipment has to be faster. Fast enough to oscillate and detect highly- changing signals. When AM radio invented electronic capabilities were fairly limited (compared to nowadays). Hence lower frequencies were allocated. Later when FM radio was developed, it was assigned unused frequencies at a higher band. DUPLEXING In some wireless systems, a radio unit will have capabilities to both transmit and receive (unlike a car radio but like a cell phone) at the same time. These radios are called full-duplex. In other systems, a radio unit can either transmit or receive at a given time. These radios care called half-duplex. DUPLEXING (CONT’D) Both CB radios and walkie-talkies are half-duplex devices. Two people communicating on a CB radio use same frequency, so one person can talk at a time, otherwise the signals would overlap and interfere with each. More on interference later. In full-duplex systems, both radios can transmit and receive at the same time. For example, they use different frequencies to transmit and receive. DUPLEXING (CONT’D) CB Radio: Half-Duplex Cellular: Full-Duplex RADIO WAVES Radio waves carry music, conversations, pictures, and data invisibly through the air over millions of miles. Radios can transmit and/or receive radio waves. RADIO WAVE EMISSION FORM AN AERIAL THEY’RE EVERYWHERE  All wireless technologies use radio waves to communicate. Some examples: Some other examples: AM/FM Radios Cordless Phones Garage Door Openers Cell Phones Radio-Controlled Toys GPS Receivers Television Broadcasts Wi-Fi Ham Radio Etc. SOME OTHER (NOT-SO-OBVIOUS) EXAMPLES Radar (police, air traffic control, military applications) Microwave ovens Navigation systems Airplanes (contain dozen different radio systems) Baby monitors SIMPLE, CHEAP RADIO Take a fresh 9V battery and a coin Find AM radio and tune to an area of dial where there is static Hold battery near antenna Quickly tap two terminals of battery using coin Radio crackles due to connection/disconnection by coin. Battery/coin combo is a radio transmitter! HOW? As the electrons in the electric current wiggle back (alternate) and forth along the antenna, they create invisible electromagnetic radiation in the form of radio waves. These waves travel out at the speed of light, taking the shape of the alternation with them. This electromagnetic radiation can be picked up by an aerial where the radio signal induced an electric current identical in shape to the one in the transmitting antenna.  SINE WAVES By sending sine wave electric current to antenna, you can transmit sine wave into space. All radios today, however, transmit continuous sine waves to transmit information (audio, video, data). Why sine waves? To allow many different people/devices to use radio waves at the same time. A receiver usually locks into one frequency, ignoring all others.  SINE WAVES: FREQUENCY When one cycle of a sine wave lasts T seconds, we say that the sine wave as frequency 1/T Hertz (Hz). 1 Hz = 1 cycle/second Wavelength is the distance of a full cycle in meters Lamda symbol MORE ON SINE WAVES If there was a way to see radio waves, we would find there are literally thousands of different radio waves (sine waves) traveling thru the air (TV broadcasts, cell phone conversations, AM/FM broadcasts, etc.) Each different radio signal uses a different sine wave frequency. Use of different frequencies help separate different radio signals. MORE ON FREQUENCY When you listen to AM broacast, your radio is tuning into sine waves oscillating at a frequency around 1,000,000 cycles per second. For example, 880 on the AM dial corresponds to listening to a radio (sine) wave that has frequency 880,000 Hz = 880 KHz. FM signals operate in range of 10,000,000 Hz. So, 90.9 on FM dial corresponds to 90,900,000 Hz = 90.9 MHz. KILO, MEGA, GIGA, ETC. 1 Hz (One Hertz) 1000 Hz = 1 KHz (kilohertz) 1,000,000 Hz = 1 MHz (megahertz) 1,000,000,000 Hz = 1 GHz (gigahertz) 1,000,000,000,000 Hz = 1 THz (terahertz) MORE ON RADIO BASICS Any radio setup has two parts: Transmitter and Receiver Transmitter takes some form of message (someone’s voice, pictures for TV set, etc.) encodes it into a sine wave and transmits it with radio waves. Combination of encoded message on a radio wave is commonly referred to as a signal. Receiver receives radio waves and decodes messages from the sine waves. Both transmitter and receiver use antennas to radiate and capture radio waves.  TRANSMITTER DESCRIPTION Radio Transmitter Radio Waves Combine Antenna Information (voice message) Sine Wave Transmitter generates its own sine wave using oscillators. RECEIVER DESCRIPTION Radio Transmitter Antenna Separate Information (voice message) Sine Wave MODULATION If you have a sine wave and a transmitter that is transmitting the sine wave into space using an antenna (more antennas later), you have a radio station. Problem with plain old sine wave: does not contain information. Sine wave has to modulated in some way so that it contains information, e.g., voice message. MODULATION MODULATION DIGITAL MODULATION DIGITAL MODULATION (PHASE SHIFT KEYING) DIGITAL MODULATION (FREQUENCY SHIFT KEYING) WHAT ABOUT ANTENNAS? Almost every radio you see (cell phones, car radio, etc.) has an antenna. Antennas come in all shapes and sizes. Shapes and sizes depend on the frequency the antenna is trying to receive. Ranges from long stiff wire (as in car radios) to large satellite dishes (as used by NASA). For satellites that are millions of miles away NASA uses antenna dishes that 200 feet wide. MORE ON ANTENNAS Often radio stations use extremely tall antenna towers to transmit their signals. Antenna at radio transmitter: launch radio signals into space. Antenna at radio receiver: pick up as much of the transmitter’s power as possible and feed it to the tuner. ANTENNAS (CONT’D) Size of optimum radio antenna is related to frequency of the signal antenna is trying to transmit and/or receive. Reason for this: different frequencies of radio travel differently (propagation)- Line of sight Ground Waves Sky Waves Space Wave Radio travels at the speed of light is 300,000 meters/sec (or 186,000 miles/sec) ANTENNAS (CONT’D) ANTENNA TYPES Primary Antenna types in DAS configurations are: Omni Directional Broadcasts in all directions Examples are whip, helical and dipole Directional Broadcast in a single direction Examples are Yagi, and parabolic ANTENNAE TYPES Directional Broadcast in a single direction Examples are Yagi, Panels, and parabolic antennas ANALOG VERSUS DIGITAL AM and FM is analog technology. Most new wireless systems are based on digital technology. What’s the difference? ANALOG VERSUS DIGITAL (CONT’D) Analog signals take on a continuous range of values. Digital signals are quantized to take on one of a set of possible values. Quantization RADIO CHANNEL There is another very important player in the wireless game: the physical environment over which radio waves travel. Radio waves can take many different paths to get from transmitter to receiver. Transmitter Receiver RADIO CHANNEL Essentially, the radio waves interact with the physical environment along each of these paths. There are typically (unless you are in free- space) many paths from the transmitter to the receiver. Each path is called a multipath. MULTIPATHS The lengths of multipaths are different. As a result, sine waves along one path reach the receiver at different times than the same signal along a different path. 2 i pa th l t Mu Receiver Transmitter Multipath 1  WORST CASE EXAMPLE OF 2 MULTIPATHS Received radio wave along multipath 1 Received radio wave along multipath 2 The antenna combines (sums) these two multipaths. In the example above, the output of the antenna will be: No Signal !! + =  ANOTHER ASPECT OF MULTIPATHS Whenever a radio wave bounces off or passes through a physical obstruction, the amplitude of the sine wave changes. Also amplitude of sine wave shrinks the further the radio wave travels, regardless of whether there are obstructions or not. Reflection A aA -A -aA Originally Received transmitted radio wave, a < 1 radio wave  IMPACT OF MULTIPATHS When all the radio waves on the multiple paths reach the receiver’s antenna, they combine together. Some multipaths cancel each other out, some add up together constructively, some partially cancel each other, etc. Signal fades in and out A and is Radio Channel: distorted Impact of Physical -A Environment Overall combined Transmitted received signal at radio wave receive antenna LIMITED RADIO SPECTRUM Assume one transmitter is sending a signal using a sine wave of frequency f1. Ideally, we would like there to be only one transmitter sending a signal at this frequency. Problem with this: since there is only limited frequency (see radio spectrum), only a limited number of transmitters can send radio waves at a given time. Because of limited radio spectrum, it becomes necessary to reuse frequencies and allocate certain frequencies to certain users (Radio Stations, Satellite, TV, Mobile Phone Networks, Military, etc.) OTHER ISSUES WITH WIRELESS Attenuation Attenuation is simply a reduction of signal strength during transmission. Radio waves don't travel the same distance in all directions. Walls, doors, elevator shafts, people, and other obstacles offer varying degrees of attenuation, which cause the Radio Frequency (RF) radiation pattern to be irregular and unpredictable. Noise In radio reception, noise is the superposition of disturbing influences on the signal that can cause reception issues. It can be caused either by thermal noise and other electronic noise from receiver input circuits or by interference from other radio sources picked up by the receiver's antenna. If no noise were picked up with radio signals, even weak transmissions could be received at virtually any distance by making a radio receiver that was sensitive enough. SOME QUESTIONS A. Why do radio waves transmit away from antenna into space at speed of light? B. How can radio waves transmit millions of Km? C. Doesn’t antenna only create magnetic field in its vicinity? D. How can the magnetic field variation be registered millions of miles away? ANSWER A. When current enters antenna, it creates a magnetic field around the antenna. This magnetic field creates an electric field (voltage and current) in another wire placed close to the antenna. This is electromagnetic radiation, and it travels at the spee d of light. B. In space, magnetic field created by antenna induces electric field in space with is radiated as electromagnetic waves. C. This electric field induces another magnetic field in space, which induces another electric field, and so on D. These electric and magnetic fields (electromagnetic fields) induce each other in space at the speed of light in a direction away from the antenna and cause an electric current in far away antenna. TRANSMISSION MEDIUMS Bound Media: Un Bound Media: Twisted pair Microwave Co-axial cable Infrared Fibre optic Satellite MODAL DISPERSION (MULTIMODE) SINGLE MODE (MONOMODE) FIBRE OPTICS Advantages: Disadvantages: Thinner Expensive to maintain. Higher Carrying Capacity (≈ 100Mbps) The termination of a fibre optic cable is complex and Less Signal Degradation requires special tools. Non-Flammable Need Repeaters over long Light Weight distances (every 2km) No electromagnetic They are more fragile than interference coaxial cable High Security UNBOUND MEDIUMS Unbound mediums use the Electromagnetic Spectrum Radio Microwaves Infrared (IR) Light X-Rays In general, the greater the frequency the more data can be transmitted per second (throughput) MICROWAVE POINT2POINT Line of Sight transmission (Point to Point) High Frequencies => More Data Microwave links are commonly used by television broadcasters to transmit programmes across a country, for instance, or from an outside broadcast back to a studio. Affected greatly by environmental constraints, including rain fade. Have very limited penetration capabilities through obstacles such as hills, buildings and trees (Line of Sight) WIRELESS INFRASTRUCTURE Wireless Infrastructure consist of antenna systems and the infrastructure needed to support them. During this session we will discuss the types of wireless infrastructures: The Distributed Antenna System. Backhaul Antenna Systems. These wireless infrastructures are vastly used today and are critical to the deployment of wireless services. DISTRIBUTED ANTENNA SYSTEMS Overview Distributed Antenna Systems (DAS) are the deployment of various antenna configurations used to extend the coverage of wireless or mobile signals inside and outside of structures where RF signals do not reach and traffic density is often very irregular. Most people think of a DAS as an indoor antenna systems and most of our focus will be on indoor DAS applications, we will review campus and wide area DAS applications in minor detail. The size of the systems typically varies from a small repeater or enhancer system covering 2 or 3 floors of a small office block to large-scale systems using a Base Transceiver Station (BTS) to cover many floors or areas of a building complex or campus environment.  DISTRIBUTED ANTENNA SYSTEMS Campus CampusDistribution Distribution In InBuilding BuildingServices Services Cellular CellularBack BackHaul Haul CELLULAR SERVICE NETWORK TOPOLOGIES Point-to-Point Single node to single node connection Well suited for long distances, backhauls and dedicated service extension and where narrow beam antennas are used Point-to-Multipoint Allows multiple facilities to share a connection back to a common source node Highly flexible with minimal or no changes required to install connections to additional facilities Range is more limited due to a wider distributed power area Mesh (also referred to peer-to-peer or multipoint-to-multipoint) Highly flexible and provides for easy network expansion Provides self-healing architecture Reduces implementation and operating cost Facilitates mobile operations DISTRIBUTED ANTENNA SYSTEMS (CONT.) The two technologies that Distributed Antenna Systems will support are; Data Networks such as 802.11 Networks, WiMax Networks, and Blue Tooth Networks. Telecommunications Networks such as PCS, GSM, GPRS, iDEN, UMTS (3G), etc. 802.11 What is an 802.11? IEEE standard that specifies medium-access and physical- layer specifications for 1Mbps and 2Mbps wireless connectivity between fixed, portable, and moving stations within a local area. 802.11a transmits radio signals in the 5 GHz range at a bandwidth of 54 Mbps. 802.11 b transmits radio signals in the 2.4 GHz range at a bandwidth of 11 Mbps. 802.11 g transmits radio signals in the 2.4 GHz range at a bandwidth of 54 Mbps. 802.11n transmits radio signals in the 2.4 and 5 GHz range at a bandwidth of 245 Mbps. 802.11y transmits radio signals in the 3.7 GHz range at a bandwidth of 54 Mbps. WIMAX What is WiMax? 802.16 (WiMax) is a group of broadband wireless communications standards for metropolitan area networks (MANS). The original 802.16 standard, published in December 2001, specified fixed point-to-multipoint broadband wireless systems operating in the 10-66 GHz licensed spectrum. An amendment, 802.16a, approved in January 2003, specified non-line-of-sight extensions in the 2-11 GHz spectrum, delivering up to 70 Mbps at distances up to 31 miles. IEEE 802.15 (BLUETOOTH) What is Bluetooth? Bluetooth is the name for a short-range radio frequency (RF) technology that operates at 2.4 GHz and is capable of transmitting voice and data. The effective range of Bluetooth devices is 32 feet (10 meters). Bluetooth transfers data at the rate of 1 Mbps, which is from three to eight times the average speed of parallel and serial ports, respectively. Specification created in 1999 jointly by Ericsson, IBM, Intel, Nokia, and Toshiba IEEE 802.15 (BLUETOOTH) Named after 10th century Danish Viking King Harald “Bluetooth Blaatand This is a technology that enables wireless communication between Bluetooth-compatible devices. It is used for short-range connections between desktop and laptop computers, PDAs (like the Palm Pilot or Handspring Visor), digital cameras, scanners, cellular phones, and printers. TELECOMMUNICATIONS NETWORKS Mobile Wireless or “Cellular Networking” is a frequency re- use strategy used by all of the mobile telephone systems (and some PBX/LAN’s) Below are some of the more common Mobile Wireless Networks being deployed today: GSM HSDPA (3rd Generation or G3) UMTS (4th Generation or G4) DAS will support these systems in an indoor environment and Wireless Backhaul Antenna Systems are used to support them in an outdoor environment.