CSE 4215/5431: Mobile Communications Winter 2011 Suprakash Datta datta@cs.yorku.ca Office: CSEB 3043 Phone: 416-736-2100 ext 77875 Course page: http://www.cs.yorku.ca/course/4215 Some slides are adapted from the book website 11/17/2018 CSE 4215, Winter 2010

Last class Introduction to mobile communications Similarities and differences with wired communication Review of the TCP/IP architecture 11/17/2018 CSE 4215, Winter 2010

Today On the first lab The physical layer for mobile communications 11/17/2018 CSE 4215, Winter 2010

Lab 1: Evaluating mobility models Why do we need mobility models? What should the criteria be? 11/17/2018 CSE 4215, Winter 2010

The Physical Layer Let’s start with the very basic notions 11/17/2018 CSE 4215, Winter 2010

Signals, channels and systems What is a signal? Baseband signal Modulation Bandwidth Transmission/reception What is a channel? Noise Attenuation,Loss What is a communication system? 11/17/2018 CSE 4215, Winter 2010

Types of signals (a) continuous time/discrete time (b) continuous values/discrete values analog signal = continuous time, continuous values digital signal = discrete time, discrete values Periodic signal - analog or digital signal that repeats over time s(t +T ) = s(t ) -¥< t < +¥ where T is the period of the signal signal parameters of periodic signals: period T, frequency f=1/T, amplitude A, phase shift  sine wave as special periodic signal for a carrier: s(t) = At sin(2  ft t + t) 11/17/2018 CSE 4215, Winter 2010

Sine Wave Parameters

Bandwidth Of a signal Of a channel Bandwidth vs bit rate 11/17/2018 CSE 4215, Winter 2010

The underlying mathematics Universität Karlsruhe Institut für Telematik Mobilkommunikation SS 1998 The underlying mathematics Fourier representation of periodic signals 1 1 t t ideal periodic signal real composition (based on harmonics) What about aperiodic signals ? 11/17/2018 CSE 4215, Winter 2010 Prof. Dr. Dr. h.c. G. Krüger E. Dorner / Dr. J. Schiller 10

Frequency domain 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 11/17/2018 CSE 4215, Winter 2010

Transmitting rectangular signals Observations 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 11/17/2018 CSE 4215, Winter 2010

Bit rates, channel capacity Impairments, such as noise, limit data rate that can be achieved For digital data, to what extent do impairments limit data rate? Channel Capacity – the maximum rate at which data can be transmitted over a given communication path, or channel, under given conditions 11/17/2018 CSE 4215, Winter 2010

Nyquist Bandwidth For binary signals (two voltage levels) C = 2B With multilevel signaling C = 2B log2 M M = number of discrete signal or voltage levels 11/17/2018 CSE 4215, Winter 2010

Signal-to-Noise Ratio Ratio of the power in a signal to the power contained in the noise that’s present at a particular point in the transmission Typically measured at a receiver Signal-to-noise ratio (SNR, or S/N) A high SNR means a high-quality signal, low number of required intermediate repeaters SNR sets upper bound on achievable data rate 11/17/2018 CSE 4215, Winter 2010

Shannon Capacity Formula Equation: Represents theoretical maximum that can be achieved In practice, only much lower rates achieved Formula assumes white noise (thermal noise) Impulse noise is not accounted for Attenuation distortion or delay distortion not accounted for 11/17/2018 CSE 4215, Winter 2010

Example of Nyquist and Shannon Formulations Spectrum of a channel between 3 MHz and 4 MHz ; SNRdB = 24 dB Using Shannon’s formula 11/17/2018 CSE 4215, Winter 2010

Example of Nyquist and Shannon Formulations How many signaling levels are required? 11/17/2018 CSE 4215, Winter 2010

Modulation Why? How? 11/17/2018 CSE 4215, Winter 2010

Frequencies for wireless communication Universität Karlsruhe Institut für Telematik Mobilkommunikation SS 1998 Frequencies for wireless communication VLF = Very Low Frequency UHF = Ultra High Frequency LF = Low Frequency SHF = Super High Frequency MF = Medium Frequency EHF = Extra High Frequency HF = High Frequency UV = Ultraviolet Light VHF = Very High Frequency Frequency and wave length  = c/f wave length , speed of light c  3x108m/s, frequency f twisted pair coax cable optical transmission 1 Mm 300 Hz 10 km 30 kHz 100 m 3 MHz 1 m 300 MHz 10 mm 30 GHz 100 m 3 THz 1 m 300 THz VLF LF MF HF VHF UHF SHF EHF infrared visible light UV 11/17/2018 CSE 4215, Winter 2010 Prof. Dr. Dr. h.c. G. Krüger E. Dorner / Dr. J. Schiller 20

Frequencies for wireless communication Universität Karlsruhe Institut für Telematik Mobilkommunikation SS 1998 Frequencies for wireless communication VHF-/UHF-ranges for mobile radio simple, small antenna for cars deterministic propagation characteristics, reliable connections SHF and higher for directed radio links, satellite communication small antenna, beam forming large bandwidth available Wireless LANs use frequencies in UHF to SHF range some systems planned up to EHF limitations due to absorption by water and oxygen molecules (resonance frequencies) weather dependent fading, signal loss caused by heavy rainfall etc. 11/17/2018 CSE 4215, Winter 2010 Prof. Dr. Dr. h.c. G. Krüger E. Dorner / Dr. J. Schiller 21

Frequencies and regulations Universität Karlsruhe Institut für Telematik Mobilkommunikation SS 1998 Frequencies and regulations ITU-R holds auctions for new frequencies, manages frequency bands worldwide (WRC, World Radio Conferences) Examples Europe USA Japan Cellular phones GSM 880-915, 925-960, 1710-1785, 1805-1880 UMTS 1920-1980, 2110-2170 AMPS, TDMA, CDMA, GSM 824-849, 869-894 TDMA, CDMA, GSM, UMTS 1850-1910, 1930-1990 PDC, FOMA 810-888, 893-958 PDC 1429-1453, 1477-1501 FOMA 1920-1980, 2110-2170 Cordless phones CT1+ 885-887, 930-932 CT2 864-868 DECT 1880-1900 PACS 1850-1910, 1930-1990 PACS-UB 1910-1930 PHS 1895-1918 JCT 245-380 Wireless LANs 802.11b/g 2412-2472 802.11b/g 2412-2462 802.11b 2412-2484 802.11g 2412-2472 Other RF systems 27, 128, 418, 433, 868 315, 915 426, 868 11/17/2018 CSE 4215, Winter 2010 Prof. Dr. Dr. h.c. G. Krüger E. Dorner / Dr. J. Schiller 22

Multiplexing Multiplexing in 4 dimensions Universität Karlsruhe Institut für Telematik Mobilkommunikation SS 1998 Multiplexing Multiplexing in 4 dimensions space (si) time (t) frequency (f) code (c) Goal: multiple use of a shared medium Important: guard spaces needed! channels ki k1 k2 k3 k4 k5 k6 c t c s1 t s2 f f c t s3 f 11/17/2018 CSE 4215, Winter 2010 Prof. Dr. Dr. h.c. G. Krüger E. Dorner / Dr. J. Schiller 23

Frequency multiplexing Universität Karlsruhe Institut für Telematik Mobilkommunikation SS 1998 Frequency multiplexing Separation of the whole spectrum into smaller frequency bands A channel gets a certain band of the spectrum for the whole time Advantages no dynamic coordination necessary works also for analog signals Disadvantages waste of bandwidth if the traffic is distributed unevenly inflexible k1 k2 k3 k4 k5 k6 c f t 11/17/2018 CSE 4215, Winter 2010 Prof. Dr. Dr. h.c. G. Krüger E. Dorner / Dr. J. Schiller 24

Time division multiplexing Universität Karlsruhe Institut für Telematik Mobilkommunikation SS 1998 Time division multiplexing A channel gets the whole spectrum for a certain amount of time Advantages only one carrier in the medium at any time throughput high even for many users Disadvantages precise synchronization necessary k1 k2 k3 k4 k5 k6 c f t 11/17/2018 CSE 4215, Winter 2010 Prof. Dr. Dr. h.c. G. Krüger E. Dorner / Dr. J. Schiller 25

Time and frequency multiplex Universität Karlsruhe Institut für Telematik Mobilkommunikation SS 1998 Time and frequency multiplex Combination of both methods A channel gets a certain frequency band for a certain amount of time Example: GSM Advantages better protection against tapping protection against frequency selective interference but: precise coordination required k1 k2 k3 k4 k5 k6 c f t 11/17/2018 CSE 4215, Winter 2010 Prof. Dr. Dr. h.c. G. Krüger E. Dorner / Dr. J. Schiller 26

Code multiplex Each channel has a unique code Universität Karlsruhe Institut für Telematik Mobilkommunikation SS 1998 Code multiplex k1 k2 k3 k4 k5 k6 Each channel has a unique code All channels use the same spectrum at the same time Advantages bandwidth efficient no coordination and synchronization necessary good protection against interference and tapping Disadvantages varying user data rates more complex signal regeneration Implemented using spread spectrum technology c f t 11/17/2018 CSE 4215, Winter 2010 Prof. Dr. Dr. h.c. G. Krüger E. Dorner / Dr. J. Schiller 27

Example Lack of coordination requirement is an advantage. 11/17/2018 CSE 4215, Winter 2010

Aside: Digital Communications What is coding? What is source coding? What are line codes? What is channel coding? 11/17/2018 CSE 4215, Winter 2010

Transceivers How are signals sent and received in wireless communications? 11/17/2018 CSE 4215, Winter 2010

Antennas: isotropic radiator Universität Karlsruhe Institut für Telematik Mobilkommunikation SS 1998 Antennas: isotropic radiator Radiation and reception of electromagnetic waves, coupling of wires to space for radio transmission Isotropic radiator: equal radiation in all directions (three dimensional) - only a theoretical reference antenna Real antennas always have directive effects (vertically and/or horizontally) Radiation pattern: measurement of radiation around an antenna z y z ideal isotropic radiator y x x 11/17/2018 CSE 4215, Winter 2010 Prof. Dr. Dr. h.c. G. Krüger E. Dorner / Dr. J. Schiller 31

Antennas: simple dipoles Universität Karlsruhe Institut für Telematik Mobilkommunikation SS 1998 Antennas: simple dipoles Real antennas are not isotropic radiators but, e.g., dipoles with lengths /4 on car roofs or /2 as Hertzian dipole  shape of antenna proportional to wavelength Example: Radiation pattern of a simple Hertzian dipole Gain: maximum power in the direction of the main lobe compared to the power of an isotropic radiator (with the same average power) /4 /2 y y z simple dipole x z x side view (xy-plane) side view (yz-plane) top view (xz-plane) 11/17/2018 CSE 4215, Winter 2010 Prof. Dr. Dr. h.c. G. Krüger E. Dorner / Dr. J. Schiller 32

Antennas: directed and sectorized Universität Karlsruhe Institut für Telematik Mobilkommunikation SS 1998 Antennas: directed and sectorized Often used for microwave connections or base stations for mobile phones (e.g., radio coverage of a valley) y y z directed antenna x z x side view (xy-plane) side view (yz-plane) top view (xz-plane) z z sectorized antenna x x top view, 3 sector top view, 6 sector 11/17/2018 CSE 4215, Winter 2010 Prof. Dr. Dr. h.c. G. Krüger E. Dorner / Dr. J. Schiller 33

Antennas: diversity Grouping of 2 or more antennas Antenna diversity Universität Karlsruhe Institut für Telematik Mobilkommunikation SS 1998 Antennas: diversity Grouping of 2 or more antennas multi-element antenna arrays Antenna diversity switched diversity, selection diversity receiver chooses antenna with largest output diversity combining combine output power to produce gain cophasing needed to avoid cancellation /2 /2 /4 /2 /4 /2 + + ground plane 11/17/2018 CSE 4215, Winter 2010 Prof. Dr. Dr. h.c. G. Krüger E. Dorner / Dr. J. Schiller 34

Antenna Gain Antenna gain Effective area Power output, in a particular direction, compared to that produced in any direction by a perfect omnidirectional antenna (isotropic antenna) Effective area Related to physical size and shape of antenna 11/17/2018 CSE 4215, Winter 2010

Antenna Gain Relationship between antenna gain and effective area G = antenna gain Ae = effective area f = carrier frequency c = speed of light (» 3 ´ 108 m/s)  = carrier wavelength 11/17/2018 CSE 4215, Winter 2010

Back to modulation Digital modulation Analog modulation Motivation Universität Karlsruhe Institut für Telematik Mobilkommunikation SS 1998 Back to modulation Digital modulation digital data is translated into an analog signal (baseband) ASK, FSK, PSK - main focus in this chapter differences in spectral efficiency, power efficiency, robustness Analog modulation shifts center frequency of baseband signal up to the radio carrier Motivation smaller antennas (e.g., /4) Frequency Division Multiplexing medium characteristics Basic schemes Amplitude Modulation (AM) Frequency Modulation (FM) Phase Modulation (PM) 11/17/2018 CSE 4215, Winter 2010 Prof. Dr. Dr. h.c. G. Krüger E. Dorner / Dr. J. Schiller 37

Modulation and demodulation Universität Karlsruhe Institut für Telematik Mobilkommunikation SS 1998 Modulation and demodulation analog baseband signal digital data digital modulation analog modulation radio transmitter 101101001 radio carrier analog baseband signal digital data analog demodulation synchronization decision radio receiver 101101001 radio carrier 11/17/2018 CSE 4215, Winter 2010 Prof. Dr. Dr. h.c. G. Krüger E. Dorner / Dr. J. Schiller 38

Digital modulation Modulation of digital signals known as Shift Keying Universität Karlsruhe Institut für Telematik Mobilkommunikation SS 1998 Digital modulation Modulation of digital signals known as Shift Keying Amplitude Shift Keying (ASK): very simple low bandwidth requirements very susceptible to interference Frequency Shift Keying (FSK): needs larger bandwidth Phase Shift Keying (PSK): more complex robust against interference 1 1 t 1 1 t 1 1 t 11/17/2018 CSE 4215, Winter 2010 Prof. Dr. Dr. h.c. G. Krüger E. Dorner / Dr. J. Schiller 39

Advanced Frequency Shift Keying Universität Karlsruhe Institut für Telematik Mobilkommunikation SS 1998 Advanced Frequency Shift Keying bandwidth needed for FSK depends on the distance between the carrier frequencies special pre-computation avoids sudden phase shifts  MSK (Minimum Shift Keying) bit separated into even and odd bits, the duration of each bit is doubled depending on the bit values (even, odd) the higher or lower frequency, original or inverted is chosen the frequency of one carrier is twice the frequency of the other Equivalent to offset QPSK even higher bandwidth efficiency using a Gaussian low-pass filter  GMSK (Gaussian MSK), used in GSM 11/17/2018 CSE 4215, Winter 2010 Prof. Dr. Dr. h.c. G. Krüger E. Dorner / Dr. J. Schiller 40

Example of MSK 1 1 1 1 data bit even 0 1 0 1 even bits odd 0 0 1 1 Universität Karlsruhe Institut für Telematik Mobilkommunikation SS 1998 Example of MSK 1 1 1 1 data bit even 0 1 0 1 even bits odd 0 0 1 1 signal h n n h value - - + + odd bits low frequency h: high frequency n: low frequency +: original signal -: inverted signal high frequency MSK signal t No phase shifts! 11/17/2018 CSE 4215, Winter 2010 Prof. Dr. Dr. h.c. G. Krüger E. Dorner / Dr. J. Schiller 41

Advanced Phase Shift Keying Universität Karlsruhe Institut für Telematik Mobilkommunikation SS 1998 Advanced Phase Shift Keying BPSK (Binary Phase Shift Keying): bit value 0: sine wave bit value 1: inverted sine wave very simple PSK low spectral efficiency robust, used e.g. in satellite systems QPSK (Quadrature Phase Shift Keying): 2 bits coded as one symbol symbol determines shift of sine wave needs less bandwidth compared to BPSK more complex Often also transmission of relative, not absolute phase shift: DQPSK - Differential QPSK (IS-136, PHS) Q I 1 Q I 11 01 10 00 A t 11 10 00 01 11/17/2018 CSE 4215, Winter 2010 Prof. Dr. Dr. h.c. G. Krüger E. Dorner / Dr. J. Schiller 42

Quadrature Amplitude Modulation Universität Karlsruhe Institut für Telematik Mobilkommunikation SS 1998 Quadrature Amplitude Modulation . Quadrature Amplitude Modulation (QAM) combines amplitude and phase modulation it is possible to code n bits using one symbol 2n discrete levels, n=2 identical to QPSK Bit error rate increases with n, but less errors compared to comparable PSK schemes Example: 16-QAM (4 bits = 1 symbol) Symbols 0011 and 0001 have the same phase φ, but different amplitude a. 0000 and 1000 have different phase, but same amplitude 0000 0001 0011 1000 Q I 0010 φ a 11/17/2018 CSE 4215, Winter 2010 Prof. Dr. Dr. h.c. G. Krüger E. Dorner / Dr. J. Schiller 43

Hierarchical Modulation Universität Karlsruhe Institut für Telematik Mobilkommunikation SS 1998 Hierarchical Modulation DVB-T modulates two separate data streams onto a single DVB-T stream High Priority (HP) embedded within a Low Priority (LP) stream Multi carrier system, about 2000 or 8000 carriers QPSK, 16 QAM, 64QAM Example: 64QAM good reception: resolve the entire 64QAM constellation poor reception, mobile reception: resolve only QPSK portion 6 bit per QAM symbol, 2 most significant determine QPSK HP service coded in QPSK (2 bit), LP uses remaining 4 bit Q 10 I 00 000010 010101 11/17/2018 CSE 4215, Winter 2010 Prof. Dr. Dr. h.c. G. Krüger E. Dorner / Dr. J. Schiller 44