Wireless, cellular and personal communications introduction
Text books/references • Wireless communications, principles and practice 2nd edition by Theodore S. Rappaport • Wireless communication by R. Blake • Wireless communication by William Stallin
Grading policy • Sessional=20% • Midterm=30% • Final=50%
Award of Sessional Marks • Quiz =5% • Assignment=5% • Presentation=5% • Class participation=5% • (Can have positive as well as negative weightage)
Historical Background • 1864. Maxwell predicted the existence of electromagnetic wave (radio wave). • 1887 Hertz demonstrated the existence of radio wave. • 1901 Marconi realized first across Atlantic wireless transmission (England to Canada) • 1906 First radio broadcast (AM radio)
Historical Background • 1946: AT&T introduced first mobile telephone service using line of sight analog FM radio transmission, 120 kHz per voice channel, limited to 50 miles from base, operator-assisted dialing • Mid-1960s: AT&T’s IMTS (Improved Mobile Telephone Service) uses 30 kHz voice channels, narrowband FM and direct dialing
Historical Background (cont) • First generation analog cellular telephony • late 1940s: AT&T develops cellular concept for frequency reuse • 1971: AT&T proposes High Capacity Mobile Phone Service to FCC • 1979: US standardizes it as AMPS (Advanced Mobile Phone System)in 800-900 MHz range
Historical Background (cont) • First generation analog cellular telephony • 1983: AT&T launches AMPS in Chicago 1985: Nordic Mobile Telephone (NMT 450) in Scandanavia, Total Access Communications System (TACS) in UK, C450 in W. Germany • Total six incompatible analog cellular systems in Europe • Motivated Europe to accelerate 2nd generation digital cellular
Historical Background (cont) • Second generation digital cellular • 1989: Europe standardized Global System for Mobile Communications (GSM) • 1992: GSM is launched • 1990: Japan standardized Japanese Digital Cellular (JDC) now called Personal Digital Cellular (PDC) • 1990: Europe standardized Digital Cellular System at 1800 MHz (DCS 1800, recently renamed GSM 1800) • 1993: DCS 1800 launched
History (cont) • 1992: TIA / IS-54 TDMA (Digital AMPS) is deployed in US • 1996: TIA/IS-95 CDMA in US • 1995: Personal Handphone System (PHS) in Japan, first widespread low-tier PCS, is hugely successful • 1996: AT&T and Sprint offer PCS in major US cities • Smaller cell sites (0.25 km vs traditional 1-8 km), smaller/lighter portable handsets, cheaper access points
History (cont) • 1998: ITU begins to study proposals for 3rd generation cellular • mid-2000s: UMTS, IMT-2000, W-CDMA, cdma2000, EDGE,... • 2010-?: 4th generation? • Self organizing, ad hoc?
Multimedia Requirements Voice Data Video Delay <100ms - <100ms Packet Loss <1% 0 <1% BER 10-3 10-6 10-6 Data Rate 8-32 Kbps 1-100 Mbps 1-20 Mbps Traffic Continuous Bursty Continuous One-size-fits-all protocols and design do not work well Wired networks use this approach, with poor results
LOCAL AREA PACKET SWITCHING WIDE AREA CIRCUIT SWITCHING ATM ATM 100 M 100,000 100,000 Ethernet 10,000 10,000 FDDI wired- wireless bit-rate "gap" Ethernet wired- wireless User User 1000 1000 bit-rate "gap" ISDN Bit-Rate Bit-Rate 2nd gen WLAN (kbps) (kbps) 100 100 28.8 modem 1st gen WLAN 32 kbps Polling 9.6 modem PCS 14.4 digital cellular 10 10 9.6 cellular 2.4 modem Packet 2.4 cellular 1 1 Radio .1 .1 .01 .01 1970 1980 1990 2000 1970 1980 1990 2000 YEAR YEAR Wireless Performance Gap
Spectrum • Radio Frequency (RF) • 1MHz to 1GHz (general classification, not absolute) • 100 MHz to 1GHz (more widely used definition) • Applications: AM radio, FM radio, TV, some cellular telephone systems, etc. • Microwave • 1 GHz to 300 GHz (general) • 1 GHz to 100 GHz (more widely used) • Most cellular telephone systems, wireless LAN, Satellite, etc. • Trends towards use of higher frequencies • Maximum bandwidth » 10% of carrier frequency • More users and higher data rate • More difficult to design leading to more $$ of investment
STANDARDS: MOBILE TELEPHONE SYSTEMS • 1st generation: analog voice • Example: Advanced Mobile Phone Service (AMPS) • 2nd generation: digital voice and narrowband data • Examples: GSM, D-AMPS (AT&T), IS-95 (Interim Standard-95) (Sprint) • 2.5 generation: GPRS • 3rd generation: digital voice and broadband data • Examples: WCDMA, cdma2000
STANDARDS: MOBILE TELEPHONE SYSTEMS contd… • IS-95 (Narrowband CDMA) • Code Division Multiple Access • All users Tx simultaneously using the same frequency and same time. • Different codes are used to separate the signals from different users. • CDMA • Each user is assigned a unique code • The code is known at both transmitter (Tx) and receiver (Rx) • All users Tx at the same frequency and time • Receiver uses codes to pick up desired signals • Also called spread sprectrum
STANDARDS: MOBILE TELEPHONE SYSTEMS contd… • WCDMA (Wideband CDMA) • Also called UMTS (Universal Mobile Telephone System) • Proposed by Ericsson • Will mainly be used in European countries • cdma2000 • Proposed by Qualcomm • Will mainly be used in North America • Both standards use CDMA • Only some detailed technical differences
Basic concepts • In most wireless communication systems, the wireless communication occurs between mobile station (MS) and base station (BS) • MS: Cell phone, wireless laptop, wireless PDA, etc. • BS: wireless access point, wireless router, etc. • Downlink • Radio channel for transmission from BS to MS • Also called forward link • Uplink • Radio channel for transmission from MS to BS • Also called reverse link
Basic concepts contd… • Simplex • Communication occurs only in one direction E.g. paging system • Half Duplex • Tx can occur in either direction, but only one way at a time E.g. Walki-Talki (police radio) • Full Duplex • Tx can occur at both direction simultaneously E.g. Telephone. Two simplex One Full Duplex
Basic concepts contd… • Base station • A fixed station a mobile radio system used for radio communication with mobile stations. Base stations are located at the center or on the edge of a coverage region and consists of radio channels and transmitter and receiver antennas mounted on a tower. • Control channel • Radio channel used for transmission of call setup, call request, call initiation and other beacon or control purposes.
Basic concepts contd… • Forward channel • Radio channel used for transmission of information from the base station to the mobile • Handoff • The process of transferring a mobile station from one channel or base station to another. • Mobile station • A station in the cellular radio service intended to for use while in motion at unspecified locations. Mobile station may be hand held personal unit or installed in vehicles.
Basic concepts contd… • Mobile switching center • Switching center which coordinates the routing of calls in a large service area. In a cellular radio system, the MSC connects the cellular base stations and mobiles to the PSTN. An MSC is also called mobile telephone switching office. • Reverse channel • Radio channel used for the transmission of information from the mobile to base station.
Basic concepts contd… • Roamer • A mobile station which operates in a service area other than that from which service has been subscribed. • Transceiver • A device capable of simultaneously transmitting and receiving radio signals.
Electromagnetic Signal • Function of time • Can also be expressed as a function of frequency • Signal consists of components of different frequencies
Time-Domain Concepts • Analog signal - signal intensity varies in a smooth fashion over time • No breaks or discontinuities in the signal • Digital signal - signal intensity maintains a constant level for some period of time and then changes to another constant level • Periodic signal - analog or digital signal pattern that repeats over time • s(t +T ) = s(t ) -¥< t < +¥ • where T is the period of the signal
Time-Domain Concepts • Aperiodic signal - analog or digital signal pattern that doesn't repeat over time • Peak amplitude (A) - maximum value or strength of the signal over time; typically measured in volts • Frequency (f ) • Rate, in cycles per second, or Hertz (Hz) at which the signal repeats
Time-Domain Concepts • Period (T ) - amount of time it takes for one repetition of the signal • T = 1/f • Phase () - measure of the relative position in time within a single period of a signal • Wavelength () - distance occupied by a single cycle of the signal • Or, the distance between two points of corresponding phase of two consecutive cycles
Sine Wave Parameters • General sine wave • s(t ) = A sin(2ft + ) • Figure 2.3 shows the effect of varying each of the three parameters • (a) A = 1, f = 1 Hz, = 0; thus T = 1s • (b) Reduced peak amplitude; A=0.5 • (c) Increased frequency; f = 2, thus T = ½ • (d) Phase shift; = /4 radians (45 degrees) • note: 2 radians = 360° = 1 period
Time vs. Distance • When the horizontal axis is time, as in Figure 2.3, graphs display the value of a signal at a given point in space as a function of time • With the horizontal axis in space, graphs display the value of a signal at a given point in time as a function of distance • At a particular instant of time, the intensity of the signal varies as a function of distance from the source
Frequency-Domain Concepts • Fundamental frequency - when all frequency components of a signal are integer multiples of one frequency, it’s referred to as the fundamental frequency • Spectrum - range of frequencies that a signal contains • Absolute bandwidth - width of the spectrum of a signal • Effective bandwidth (or just bandwidth) - narrow band of frequencies that most of the signal’s energy is contained in
Frequency-Domain Concepts • Any electromagnetic signal can be shown to consist of a collection of periodic analog signals (sine waves) at different amplitudes, frequencies, and phases • The period of the total signal is equal to the period of the fundamental frequency
Relationship between Data Rate and Bandwidth • The greater the bandwidth, the higher the information-carrying capacity • Conclusions • Any digital waveform will have infinite bandwidth • BUT the transmission system will limit the bandwidth that can be transmitted • AND, for any given medium, the greater the bandwidth transmitted, the greater the cost • HOWEVER, limiting the bandwidth creates distortions
Electromagnetic waves and energy • All electromagnetic systems send information from one point to another by transmitting electromagnetic energy from the sender to the intended receiver. This electromagnetic energy can travel in various modes: • As a voltage or current through wires • As radio emissions through air • As light through optical fiber • In all cases it follows following law • Wavelength( )= Velocity (c) Frequency (f)
Electromagnetic waves and energy • Where “c” is the propagation velocity and it depends on the medium through which it is traveling. • The fastest propagation velocity occurs in vacuum and is symbolized by the letter “c” • C=3*10^8 m/s • What is the wavelength in vacuum for a frequency of 1 million hertz? • What is the frequency when the measured wavelength is 6 m?
Electromagnetic waves and energy • The propagation velocity is less in any medium other than vacuum. • In air the propagation velocity of electromagnetic energy is about 95 to 98% of the value in vacuum. • In wire it is anywhere from 60 to 85% of c, depending on wire type, construction and insulation.
Data Communication Terms • Data - entities that convey meaning, or information • Signals - electric or electromagnetic representations of data • Transmission - communication of data by the propagation and processing of signals
Analog Signals • A continuously varying electromagnetic wave that may be propagated over a variety of media, depending on frequency • Examples of media: • Copper wire media (twisted pair and coaxial cable) • Fiber optic cable • Atmosphere or space propagation • Analog signals can propagate analog and digital data
Digital Signals • A sequence of voltage pulses that may be transmitted over a copper wire medium • Generally cheaper than analog signaling • Less susceptible to noise interference • Suffer more from attenuation • Digital signals can propagate analog and digital data
Reasons for Choosing Data and Signal Combinations • Digital data, digital signal • Equipment for encoding is less expensive than digital-to-analog equipment • Analog data, digital signal • Conversion permits use of modern digital transmission and switching equipment • Digital data, analog signal • Some transmission media will only propagate analog signals • Examples include optical fiber and satellite • Analog data, analog signal • Analog data easily converted to analog signal
Analog Transmission • Transmit analog signals without regard to content • Attenuation limits length of transmission link • Cascaded amplifiers boost signal’s energy for longer distances but cause distortion • Analog data can tolerate distortion • Introduces errors in digital data
Digital Transmission • Concerned with the content of the signal • Attenuation endangers integrity of data • Digital Signal • Repeaters achieve greater distance • Repeaters recover the signal and retransmit • Analog signal carrying digital data • Retransmission device recovers the digital data from analog signal • Generates new, clean analog signal
About Channel Capacity • Impairments, such as noise, limit data rate that can be achieved • Channel Capacity – the maximum rate at which data can be transmitted over a given communication path, or channel, under given conditions
Concepts Related to Channel Capacity • Data rate - rate at which data can be communicated (bps) • Bandwidth - the bandwidth of the transmitted signal as constrained by the transmitter and the nature of the transmission medium (Hertz) • Noise - average level of noise over the communications path • Error rate - rate at which errors occur • Error = transmit 1 and receive 0; transmit 0 and receive 1