PGT316 Mobile and Wireless Communications

Transcription

1 PGT316 Mobile and Wireless Communications Lecture 1: Introduction to Mobile Communications System Ts. Dr. Khairul Najmy bin Abdul Rani

2 Wireless Technology Overview 2

3 Contents Definition, History, Objective of Communications, and Block Diagrams of Communication Systems Analog/Digital Communication Systems Overview of Open Systems Interconnection (OSI) Model and Physical (PHY) Layer Functionalities Overview of Wireless Communication Evolutions Signal and Properties Bandwidth of Signal and Medium Amplitude/Power Signal Bandwidth Bit Rate vs Symbol Rate Baseband and Bandpass Transmissions 3

4 Definition of Communication Literally A process where information is exchanged between individuals through a common system of symbols, signs, or behavior. (source: Technically The transfer of information from one place to another. Should be bandwidth and power efficient, reliable, and secure. 4

5 Communications Every living entity communicates. We speak and listen to communicate. Transmit Information Flow Receive Receive Transmit We act and watch to communicate. 5

6 efficiency History of Communications Luxury desired? 1990 to now, Digital comm (TV, Cellular, DSP App) 1972, Analog cellular phone Basic Human Need 1966, Optical link (Laser & Fiber) 1962, First Satellite (Telstar 1) 1936, FM Radio 1923, First TV (color TV in 1953) 1904, AM Radio 1902, transatlantic S (Marconi) 1886, radio transmission (Heinrich Hertz) 1876, voice telegraph (Alexander Bell) 1843, telegraph (Samuel Morse) distance 900BC 776BC, Olympic 6

7 Objective of Communications TRANSMISSION MEDIUM SOURCE TX RX SINK Communications Network To transmit a signal from one point (Source) to another point (Sink) in the communications network with minimal losses, noise, distortion, and interference effects. 7

8 Communications Technology and Systems Difficulties arise due to long distances. z z z No Information Flow Light and voice cannot travel far in natural living environment. Technology is needed. Communication systems are needed. 8

9 Two types: Communication Systems Analog communication systems Example: conventional terrestrial TV and radio broadcasting systems, 1G mobile phone systems, old PSTN, etc. Digital communication systems (current trends) Example: terrestrial digital TV and radio broadcasting systems, 2G/3G/4G/5G mobile phone systems, Integrated Services Digital Network (ISDN), Wireless Local Area Networks (WLANs), etc. 9

10 Analog Communications System SOURCE ANALOG MODULATOR TRANSMISSION CHANNEL ANALOG DEMODULATOR SINK Block Diagram of an Analog Communications System Illustration of an Analog Communication System Subsystem Analog Modulator Analog Demodulator Function Modulate analog baseband signals into analog bandpass signals Demodulate analog bandpass signals into analog baseband signals Output AM and FM signals Analog baseband signal 10

11 Digital Communications System Noise Source Transmitted Info. signal Transmitter Channel Received signal Receiver Received info. User Source Data, speech, video, etc. Source encoder Transmitter Channel encoder Modulator User Receiver Channel Data, speech, video, etc. Source decoder Channel decoder Demodulator 11

12 Subsystem Function Output Convert analog signal into digital Digital data Source Encoder signal for digital processing (Pulse Code Modulation) Channel Encoder Add redundant bits to digital data to reduce bit errors that are caused by channel noise (error control coding) Digital codewords Digital Modulator Map digital codewords into analog ASK, FSK, and bandpass waveforms PSK signals Channel: Digital Communications System (cont.) Wired: unshielded twisted-pair (UTP) telephone line, coaxial cable, waveguide, and fiber-optic cables. Wireless: air vacuum, and seawater. In general, the channel attenuates the signal. Channel noise may arise from natural electrical disturbances or from artificial sources. 12

13 Features of Digital Communications System The transmitter sends a waveform from a finite set of possible waveforms during a limited time. Channel distorts, attenuates the transmitted signal, and adds noise to it. The receiver decides which waveform was transmitted from the noisy received signal. The probability of erroneous decision or bit error rate (BER) is an important measure for the performance of digital communication systems. (BER = number of errors / total transmitted bits) In analog systems, the performance measure is usually taken to be the Signal-to-noise Ratio (SNR) usually measured in decibel (db) unit at the receiver (Rx) output. 13

14 bandwidth efficiency power efficiency Features of Digital Communications System (cont.) We can measure the GOODNESS of a communication system in many ways (but ultimately related to power efficiency and bandwidth efficiency): How close is the estimate m (t) to the original signal m(t) Better estimate = higher quality transmission Signal to Noise Ratio (SNR) for analog m(t) Bit Error Rate (BER) for digital m(t) How much power is required to transmit s(t)? Lower power = longer battery life, less interference How much bandwidth B is required to transmit s(t)? Less B means more users can share the channel How much information is transmitted? In analog systems information is related to B of m(t). In digital systems information is expressed in bits/sec. 14

15 Features of Digital Communications System (cont.) Regenerator receiver Original pulse Regenerated pulse Propagation distance Different kinds of digital signals are treated identically. Data Image Speech Video A bit is a bit! 15

16 Communication Networks: Current Source Terminal Terminal Circuit switched Voice Network Gateway Destination Terminal Terminal Terminal Gateway Data Network Terminal Terminal Packet-Switched Terminal 16

17 Communication Networks: Future Source Terminal Terminal Converged Network Destination Terminal Terminal Packet-Switched Packet-switched describes the type of network in which relatively small units of data called packets are routed through a network based on the destination address (Internet Protocol or IP address) contained within each packet. Breaking communication down into packets allows the same data path to 17 be shared among many users in the network.

18 Data Communications: Functionalities Source Terminal Terminal Network Destination/Sink Terminal Terminal How does it transfer data? 18

19 Data Communications: OSI Model OSI Model Host layers Media layers Data unit Layer Function Data Application Network process to application Presentation Session Data representation and encryption Inter-host communication Segments Transport End-to-end connections and reliability Packets Network Path determination and logical addressing (IP) Frames Data link Physical addressing (MAC & LLC) Bits Physical Media, signal and binary transmission 19

20 PHY Layer Functionalities Transmission (Tx) system Channel or Medium Receiver (Rx) system Formatting, ADC Source coding Channel coding Signal shaping Modulation Amplification, etc. Noise Distortion fading Attenuation Formatting, DAC Source decoding Channel decoding Equalization Demodulation, etc. 20

21 TCP/IP Model TCP/IP technically applies to network communications in which the Transport Control Protocol (TCP) transport is used to deliver data across Internet Protocol (IP) networks. Known as a connection-oriented protocol, TCP works by establishing a virtual connection between two devices via a series of request and reply messages sent across the physical (PHY) network. 21

22 OSI vs. TCP/IP Models 22

23 Wireless Communications System: Evolutions R&D / Experimental Continuous R&D for revised/new standards Standardization Revised/new standards Trial run Trials: revised/new standard Commercial service 23

24 Wireless Communications System: Evolutions (cont.) 3G: WCDMA 1980s 90s R&D / Experimental Continuous R&D for revised/new standards Standardization Revised/new standards Late 1990s HSDPA HSUPA HSPA + LTE LTE Adv 2000: Rel : Rel : Rel : Rel : Rel : Rel : Rel : Rel 10 Trial run 2000 Trials: revised/new standard Commercial service

25 Wireless Communications System: Evolutions (cont.) WLAN 1960s 90s R&D / Experimental ALOHANET Standardization Continuous R&D for revised/new standards Revised/new standards HIPERLAN b a (2 Mbps) (54 Mbps) HIPERLAN g (54 Mbps) n (>100 Mbps) Commercial service 25

26 Current Wireless Systems Increasing efficiency, bandwidth and data rates 4G/IMT-Advanced LTE- Advance Rel 10 and Beyond WiMAX m ac ad 3.9G/4G 3.5G 3G 2.5G W-CDMA FDD HSCSD HSPA+ HSDPA/HSU PA FDD & TDD W-CDMA TDD GPR S LTE FDD & TDD Rel-8/9 EDGE Evolutio n TD-SCDMA LCR-TDD e Mobile WiMAX TM E-GPRS EDGE imode WiBRO 1 EV-DO Release 0->A->B IS-95C CDMA2000 IS-95B CDMA d Fixed WiMAX TM n g a 2G GSM IS-136 TDMA PDC IS-95A CDMA b 26

27 Current Wireless Data Systems range/cost Wireless WAN < 15 KM IEEE GPP EDGE(GSM) Wireless MAN < 5 km IEEE IETSI HIPERMAN & HIPERACCESS Wireless LAN < 150 m IEEE ETSI HIPERLAN Wireless PAN < 10 m IEEE ETSI HIPERPAN Bluetooth Zigbee 27

28 Signals Signal is a variation of a physical quantity (voltage or current) with respect to time or space. The unexpectedness of the signal carries information. Analog signals are composed of analog waveforms. They are continuous and vary in amplitude, frequency, phase, or combination of them. Digital signals are composed of a finite set of waveforms with discrete states (in frequency, amplitude, or phase). x(t) x(t) Analog t Digital t 28

29 Example of signals. Signals (cont.) 29

30 Example of signals. Signals (cont.) 30

31 Possible of multi-dimensions: 1-D, 2-D, 3-D, etc. Occur naturally in analog form. May need to convert to digital form for various reasons: 1. Processing (digitally) 2. Storage 3. Transmission Signals (cont.) 31

32 Signals (cont.) Sinusoidal Rectangular Pulse Sinc Function Triangular Function 32

33 Signals (cont.) Delta Function Step Function Exponential Function Gaussian Function 33

34 Periodic Signals A signal which repeats itself after a specific interval of time is called periodic signal. Periodic analog signals can be classified as simple or composite. A simple periodic analog signal, a sine wave, cannot be decomposed into simpler signals. A composite periodic analog signal is composed of multiple sine waves. 34

35 Non-Periodic Signals A signal which does not repeat itself after a specific interval of time is called non-periodic signal. In communications, periodic analog signals and nonperiodic digital signals are usually used. Periodic and non-periodic signals A periodic signal A non-periodic signal 35

36 Deterministic vs. Random Signals Deterministic signal: No uncertainty (uniformity or consistency) with respect to the signal value at any time. Random signal: Some degree of uncertainty in signal values before it actually occurs. For example, thermal noise in electronic circuits due to the random movement of electrons 36

37 Perspective or representation: Time-domain Frequency-domain Signals and Spectra 37

38 Signals and Spectra (cont.) Fourier Transform x(t) X(f) Inverse Fourier Transform 38

39 Signals and Spectra (cont.) X f F j ft x t x t e 2 dt Fourier Transform x(t) Inverse Fourier Transform X(f) x t F 1 j ft X f X f e 2 df 39

40 Fourier Transforms: Background Fourier analysis is named after Jean Baptise Joseph Fourier ( ) who claimed that any continuous periodic signal could be represented as the sum of properly chosen sinusoidal waves. His paper was disapproved by Joseph Louis Lagrance ( ) who claimed that a summation of sinusoids cannot form a signal with a corner. 40

41 Example: Single-Tone Sinusoidal Signals Time domain v(t): Fourier Transform V(f) 0 f t V(f) 0 V(f) f 0 f 41

42 Example: Composite Signals A single-tone sine wave is not useful in communications; therefore, a composite signal made of many sine waves are usually sent. According to Fourier analysis, any composite signal is a combination of simple sine waves with different frequencies, amplitudes, and phases. 0 f o 3f o 5f o 7f o f Frequency domain Time domain 42

43 Time and Frequency Domains of Non-Periodic Signal Non-periodic t V(f) 0 Spectrum is continuous f If the composite signal is non-periodic, the decomposition gives a combination of sine waves with continuous frequencies. 43

44 Bandwidth (BW) of Signals Periodic time frequency BW Periodic time frequency BW Non Periodic time BW frequency The BW of a composite signal is the difference between the highest and the lowest frequencies 44 contained in that signal.

45 Example: Bandwidth of Signals If a periodic signal is decomposed into five sine waves with frequencies of 100, 300, 500, 700, and 900 Hz, what is its bandwidth? Draw the spectrum, assuming all components have a maximum amplitude of 10 V. Bandwidth = Highest frequency Lowest frequency = = 800 Hz 45

46 Bandwidth of Medium Wide BW More Signal or Information Low BW Less Signal or Information All physical structure have a limited frequency response. It is important to know bandwidth or capacity to 46 transfer information.

47 Amplitude: Power I V International System of Units (SI) unit of power is Watt (W). P 2 I R V 2 R 47

48 Decibel (db) Ops! Back to the basics! db = 10 log 10 OR db = 20 log 10 P P V V Note: db is a relative power unit! 48

49 dbm and dbw dbm = 10 log 10 P (in mw) 1 mw dbw = 10 log 10 P (in W) 1 W Note: dbm & dbw is an absolute power unit! 49

50 dbμv and dbmv dbμv = 20 log 10 V (in μv) 1 μv dbmv = 20 log 10 V (in mv) 1 mv Note: db V & dbmv is an absolute power unit!! 50

51 Digital Signals Representation Level 2 Level 1 Amplitude 8 bits sent in 1 s, Bit rate = 8 bps s Time A 1 can be encoded as a positive voltage and a 0 as zero voltage. Digital Signal with two levels Level 4 Level 3 Level 2 Level 1 Amplitude bits sent in 1 s, Bit rate = 16 bps Digital Signal with four levels 1s Time A digital signal can have more than two levels. In this case, we can send more than 1 bit for each level. 51

52 Example: Digital Signals Representation A digital signal has eight levels. How many bits are needed per level? We calculate the number of bits from the formula n = log 2 L, where n = number of bits per level and L= number of levels. Example: n = log 2 L = log 2 8 = 3 Each signal level is represented by 3 bits. 52

53 Bit Rate vs Symbol (or Baud) Rate Bit rate is the number of bits that are conveyed or processed per unit of time. It is quantified using the bits per second (bit/s or bps) unit. Symbol rate or baud rate, is the number of symbol changes (waveform changes or signalling events) made to the transmission medium per second using a digitally modulated signal or a line code. It is measured in baud (Bd) or symbols/second. In line code, the symbol rate is the pulse rate in pulses/second. Each symbol can represent or convey one or several bits of data. 53

54 Time and Frequency Domains of Periodic and Non-Periodic Digital Signals t 1 st harmonic 2 nd harmonic Periodic V(f) 0 Fundamental Spectrum consists of impulses at discrete frequencies f t V(f) Spectrum is continuous Non-periodic A digital signal is a composite analog signal with an infinite BW f

55 Baseband Transmission A digital signal is a composite analog signal with an infinite bandwidth. 55

56 BW of Baseband or Low-Pass Channel Baseband transmission of a digital signal that preserves the shape of the digital signal is possible only if we have a low-pass channel with an infinite or very wide bandwidth. The required bandwidth is proportional to the bit rate; if we need to send bits faster, we need more bandwidth. The ideal baseband transmission bandwidth can be estimated by the formula of BW = R/2, where BW is bandwidth and R is bit rate. For example, the maximum bit rate of a 100 khz 56 baseband bandwidth is approximately 200 kbps.

57 Bandpass Channel If the available channel is a bandpass channel, we cannot send the digital signal directly to the channel. Here, we need to convert the digital signal to an analog signal before transmission via a process called modulation. 57

58 References Behrouz A. Forouzan, Data Communications and Networking, 4th Edition, McGraw Hill, Leon W. Couch II, Digital and Analog Communication Systems, Pearson Education 7th Edition., N.J., William Stalling, Data and Computer Communications, 8th Edition, Prentice Hall,