Presentation on theme: "Lecture 1: Introduction Chapter 1 Introduction to Wireless Communication Systems."— Presentation transcript:
Lecture 1: Introduction Chapter 1 Introduction to Wireless Communication Systems
2 Introduction “It is dangerous to put limits on wireless.” - Guglielmo Marconi, 1932 There has been tremendous growth in wireless in the past 10 years. Even more in Europe and Asia than North America Driven by technological advances – digital and RF circuit fabrication improvements, large scale circuit integration, miniaturization technologies, digital switching
3 Driven by business investment – although overinvestment has created bad profitability recently. Driven by consumer demand – Regardless of current business profitability, the growth rate in terms of numbers of customers is substantial. The ability to communicate wirelessly is of obvious benefit to many. What are some of the benefits?
4 I. History Wired Communications Gauss and Weber build telegraph system in Germany Morse connects Baltimore and Washington by telegraph First transatlantic telegraph cable laid Alexander Bell demonstrates telephone New York can telephone Denver Wireless Communications --Not so “new” Had slow growth at first compared to other inventions. But now is growing very rapidly.
6 Marconi sends first radio message across Atlantic Hulsmeyer detects ships with radar US & Europe telephones linked by HF radio AM mobile police radios for public safety widely used Edwin Armstrong demonstrates FM radio system, became the primary modulation technique. First microwave radar First commercial communication satellite AT&T proposes cellular phone system to Federal Communications Commission (FCC)
7 FCC allocates spectrum for analog cellular service (AMPS) GSM digital cellular service introduced in Europe FCC auctions new Personal Communication Service (PCS) licenses in U.S. for digital services million cellular phone users in U.S. In some countries, mobile users outnumber conventional wireline customers.
8 million subscribers worldwide (as compared to 1 billion wired phone lines. Over 1% of worldwide wireless subscribers have abandoned wired telephone service for home use. 2005 − Over 130 million cellular phone users in U.S. (out of population of 300 million including children).
9 II. Frequencies RF - Radio Frequency 1 MHz to 1 GHz - general classification, not absolute 100 MHz to 1 GHz - more widely used definition Microwave 1 GHz to 300 GHz - general 1 GHz to 100 GHz - more widely used Trends towards use of higher frequencies greater signal bandwidth (BW) per channel more users and/or higher data rates but more difficult to design - more $$, more engineering required
10 III. Wireless Applications Mature Home Appliances - What devices are used that are wireless? Communications fixed microwave (point-to-point or Line Of Sight) - nearly 20,000 in U.S satellite to fixed ground stations (TV, phone, defense, etc.) analog cellular : AMPS (FM) since 1980's paging
11 Emerging WLAN: Wireless Local Area Networks Mobile computers/ Wireless Local Loop (WLL) local phone service via wireless connection prominent in non-industrialized nations cheaper to install than wired lines new IEEE standard has been developed for WLL. Wireless-enabled Personal Digital Assistants (PDAs)
12 Wireless Device Connectivity between computer peripherals (printers, monitors, keyboards, etc.) - Bluetooth Satellite to mobile ground units - Land Mobile Satellite (LMS) Motorola/Iridium Digital Cellular/PCS PCS = Personal Communication Services Several types of services and capabilities are offered
13 Radio Frequency Identification Tags (RFID’s) on merchandize in warehouses and stores. Sensor networks – small devices wirelessly communicating among themselves to monitor environments using a variety of sensors.
14 FCC controls all usable Radio Spectrum - allocates specific frequency bands for specific uses Military Public safety and public service - Police, fire, utilities, medical Commercial - To customers, between commercial mobiles Unlicensed Amateur Etc.
16 SMR Bands - Specialized Mobile Radio Three 20 MHz bands from MHz Large number of radio system licenses nationwide paging/messaging voice dispatch - taxi, Police/Fire/Ambulance data (UPS/Fedex) Extended SMR Nextel/Motorola partnership Nationwide coverage providing digital cellular/data service Created by buying SMR licenses from a large number of private radio service providers
17 ISM Bands - Industrial/Scientific/Medical MHz, MHz, & MHz “Garbage” bands spread spectrum modulation Transmit (Tx) power level < 1 W Remote meter reading Wireless medical monitors Digital cordless telephones Big new application: Wireless Local Area Networks (WLAN’s)
18 Cellular Phone AMPS: Advanced Mobile Phone System MHz Reverse Channel: Transmit from mobile to fixed base station MHz Forward Channel: Transmit from base station to mobile FCC mandated duopoly in Major Trading Areas (MTAs) MTA = 51 largest U.S. cities two providers per MTA
19 PCS Band GHz FCC Spectrum Auctions - $10 Billion!! 1st time spectrum sold for $$ in U.S. It is has been hard for companies to recover this investment A & B blocks for Major Trading Areas (MTAs) duopoly like AMPS C, D, E, & F blocks - Basic Trading Areas (BTAs) BTA = 492 large rural areas (includes MTAs) Digital cellular phone service + PCS PCS = special services like messaging, caller ID, voice mail, FAX, data, etc. Compete with analog cellular and SMR services combined
20 V. Mobile Radiotelephony The focus of this course: mobile wireless communications. Our predominant focus will be on mobile cellular communications Historically voice communications, but also incorporating data into newer generation systems.
21 But we will also take a substantial look at Wireless LAN’s Have grown quickly over the past couple of years. Are an important replacement opportunity for traditional wiring in buildings. Some are trying to make them a competitor to cellular for data communications. Cellular can or will provide 10’s to 100’s of kilobits per second. But if one can connect to a Wireless LAN (either at home/office or in public “hot spot” areas), 10’s of Megabits per second are readily available
22 And below all of these technologies are important radio transmission issues we need to study Radio signal propagation – signal strengths varies with distance from the transmitter, but may also vary by large amounts over a few centimeters Digital modulation – putting data on analog wireless signals. Compensation for fading – making channels more reliable Frequency reuse and sharing (multiple access techniques) – making best use of spectrum to support multiple users. Sharing in the time, frequency, and code domains.
23 Early mobile phone systems used a high power Tx to cover a large spatial area (R = 50 km) Half-duplex (HDX) operation two-way communication using same radio channel transmit or receive only at a given time (HDX) “push-to-talk” system - CB radio
24 Allocated spectrum determines maximum # of simultaneous users e.g., 10 MHz allocated BW with 100 kHz channels = 100 simultaneous users/market Demand was great in large cities and this led to poor service (many blocked calls) Spectrally inefficient system allocated spectrum supports small # of users
25 In 1976, Bell Mobile Phone Service only had 12 channels for all of New York City (10 million people), which could acceptably only support 543 customers. Acceptable service - Certain probability of not being able to make a call (i.e., be "blocked") Given the # of customers, average calling load per customer, # of channels → can compute blocking
26 Cellular Concept - break coverage area (market) into many small cell (many transmitters) where each non- adjacent cell will reuse different portions (not all) of allocated spectrum Increase spectrum efficiency many users share same channels Increase in required system infrastructure (base stations) more capital costs to provide adequate coverage
27 BASE STATION
28 Advanced Mobile Phone System (AMPS) spectrum allocated by FCC in 1983 Full duplex (FDX) operation : simultaneous two-way communication two 30 kHz channels (forward & reverse) Two providers for each market - duopoly limited competition Analog frequency modulation (FM) used exclusively Frequency Division Multiple Access (FDMA) one channel per pair of users
29 USDC: U.S. Digital Cellular proposed in 1991 (D-AMPS or IS-54) Replace single user analog channel with digital channels that support 3 users/30 kHz channel BW User capacity is 3 times greater than AMPS - more provider revenue ($$) Digital modulation & speech coding allow Time Division Multiple Access (TDMA) 3 users share one channel by using different time slots This service is provided under the title "Digital Cellular"
30 VI. Mobile Radio Terminology Table 1.4, pg everyone is responsible for these definitions Mobile: high speed motion (e.g. cell phone in car) Portable: low speed motion (cordless phone in home, walking) Mobile Unit = subscriber unit = user communication device Transmitter (Tx) and Receiver (Rx) Base Station: Tx/Rx on tower at center of cell that provides service to group of mobile users
31 Forward/Reverse Channels (a.k.a. downlink/uplink) Forward: From base station to mobile Reverse: From mobile to base station Simplex (SX), Half Duplex (HDX), & Full Duplex (FDX) Frequency Division Duplexing (FDD) - Using two separate frequency bands to provide both sides of the duplex operation Example: AMPS uses MHz for reverse channel and MHz for forward channel PSTN: Public Switched Telephone Network
33 VII. Paging Systems One-way communication (SX) Send short message to mobile unit (pager) Wide area coverage Page broadcast from many base stations simultaneously to remote units no information as to user location Reliable communication everywhere (need good Signal to Noise performance) Requires large Tx power and low data rate (~ 2-8 kbps) Noise has less of an effect when the data rate is lower. Coverage needed even inside buildings w/ dB signal attenuation Needs an extensive network of transmitters to transmit the signal everywhere
35 VIII. Cordless Telephone Systems Primarily in-home use Use ISM bands – 900 MHz most popular for a while, now 2.4 GHz is common and 5.8 GHz is available. Low power, limited range (~ 100 m) and coverage, and limited mobility
36 IX. Cellular Telephone Systems
37 Large geographic coverage Limited frequency spectrum – a surprisingly low amount of spectrum has been allocated for a service with such popularity. High user mobility High system capacity - Large # of simultaneous users obtained by limiting coverage of each base station to small area (cell) frequency spectrum can be reused by other non- adjacent cells in network
38 Base station serves mobile users in each cell bridge between mobile unit and MSC connected to MSC via phone line (for example, T1 of 24 channels or T3 of 672 channels) or Line of Sight microwave link
39 MSC: Mobile Switching Center controls base stations, call initiation & routing, handoffs, etc. connects cellular system to Public Switched Telephone Network (PSTN) cellular network brains: call initiation/setup base station handoffs controlling power levels in mobile units billing information roaming user ID and verification Typically handles 5000 simultaneous calls supporting 100,000 cellular subscribers (at most 5% of subscribers are assumed to be active at anyone time)
40 Common Air Interface (CAI) Standard mechanism used by all mobiles. Defines 4 different channels to be used by a mobile unit Forward/reverse voice channels - FVC/RVC Full Duplex communication Forward/reverse control channels - FCC/RCC call initiation & setup makes up 5% of total # of available channels One cell contains 10 to 60 voice channels and only 1 to 3 control channel pairs (F+R) MSC broadcasts call request from PSTN over all FCC's of all base stations – to find the mobile user
41 There are two ways to keep mobiles “connected” to the best base station 1. Mobile unit monitors FCC's looking for strongest base station (closest) and incoming call if FCC signal < acceptable level - mobile looks for another base station neighboring base stations must use same frequencies for FCC/RCC handoff from one base station to another occurs when FCC signal is less than an acceptable level
42 2. Base stations (current server + adjacent stations) monitor RCC and report mobile unit signal strength to MSC (analog AMPS system) if RCC signal < acceptable level - MSC initiates handoff to one of neighboring base stations neighboring base stations must use different frequencies for FCC/RCC
43 Cellular Phone Call Timing Mobile Identification Number (MIN) is the subscriber's telephone number Electronic Serial Number (ESN) is device identifier. Station Class Mark (SCM) identifies the class of the device, based on its maximum transmit power level.