Presentation is loading. Please wait.

Presentation is loading. Please wait.

Communication System Overview Gwo-Ruey Lee. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Outlines Communication System Digital Communication.

Similar presentations


Presentation on theme: "Communication System Overview Gwo-Ruey Lee. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Outlines Communication System Digital Communication."— Presentation transcript:

1 Communication System Overview Gwo-Ruey Lee

2 Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Outlines Communication System Digital Communication System Modulation

3 Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Communication System Input Transducer Transmitter Channel Receiver Output Transducer 1/6

4 Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Communication System Input transducer  Messages can be categorized as analog (continuous form)or digital (discrete form).  The message produced by a source must be converted by a transducer to a form suitable for the particular type of communication system employed. 2/6

5 Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Communication System Transmitter  The purpose of the transmitter is to couple the message to the channel.  Modulation  For ease of radiation  to reduce noise and interference  For channel assignment  For multiplexing or transmission of several message over a single channel  To overcome equipment limitation 3/6

6 Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Communication System Channel  Different forms  The signal undergoes degradation from transmitter to receiver  Noise, fading, interference…… 4/6

7 Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Communication System Receiver  The receiver is to extract the desired message from the received signal at the channel output and to convert it to a form suitable for the output transducer  Demodulation 5/6

8 Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Communication System Output Transducer  The output transducer completes the communication system  The device converts the electric signal at its input into the form desired for the system user 6/6

9 Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Digital Communication System 1/6

10 Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Digital Communication System Source Encoder/ Decoder  The purpose of source coding is to reduce the number of bits required to convey the information provided by the information source.  The task of source coding is to represent the source information with the minimum of symbols.  High compression rates (Good compression rates) make be achieved with source encoding with lossless or little loss of information. Source Coding  Fixed-length coding  Pulse-code modulation (PCM)  Differential Pulse-code modulation (DPCM)  Variable-length coding  Huffman Coding/ entropy coding 2/6

11 Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Digital Communication System Channel Encoder/ Decoder  A way of encoding data in a communications channel that adds patterns of redundancy into the transmission path in order to lower the error rate.  The task of channel coding is to represent the source information in a manner that minimizes the error probability in decoding.  Error Control Coding  Error detection coding  Error correct coding 3/6

12 Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Digital Communication System Error Control Coding  Linear block code  Convolutional code  RS code Modulation Coding  Trellis code  Turbo code 4/6

13 Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Digital Communication System Synchronization  Symbol/ Timing synchronization  Frequency synchronization  Carrier frequency synchronization  Sampling frequency synchronization  Two basic types of synchronization  Data-aid algorithm  Training sequences  Preambles  Non-data-aid algorithm  Blind 5/6

14 Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Digital Communication System Channel Estimation  A channel estimate is only a mathematical estimation of what is truly happening in nature.  Allows the receiver to approximate the effect of the channel on the signal.  The channel estimate is essential for removing inter symbol interference, noise rejection techniques etc.  Two basic types of channel estimation methods  Data-aid algorithm  Training sequences  pilots  Non-data-aid algorithm  Blind 6/6

15 Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Modulation Analog Modulation  AM  FM  PM Pulse Modulation  PAM / PPM / PCM / PWM Digital Modulation  ASK  FSK  PSK  QAM Amplitude FrequencyPhase Carrier: 1/10

16 Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Modulation Mapping  The process of mapping the information bits onto the signal constellation plays a fundamental role in determining the properties of the modulation Modulation type  Phase shift keying (PSK)  Quadrature Amplitude Modulation (QAM) 2/10

17 Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Modulation M-ary Phase Shift Keying  Consider M-ary phase-shift keying (M-PSK) for which the signal set is where is the signal energy per symbol, is the symbol duration, and is the carrier frequency.  This phase of the carrier takes on one of the M possible values, namely,, where. 3/10

18 Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Modulation An example of signal-space diagram for 8-PSK 4/10

19 Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Modulation Phase shift keying  BPSK  QPSK with Gray code  M-ary PSK where 5/10

20 Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Modulation BER versus SNR curves in AWGN channel using BPSK, QPSK, 8-PSK,16-PSK. 6/10

21 Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Quadrature Amplitude Modulation  The transmitted M-ary QAM signal for symbol n can be expressed as  where E is the energy of the signal with the lowest amplitude, and, and are amplitudes taking on the values  Note that M is assumed to be a power of 4.  The parameter a can be related to the average signal energy ( ) by Modulation 7/10

22 Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. An example of signal-space diagram for 16-square QAM. Modulation 8/10

23 Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. QAM Modulation 9/10

24 Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. BER versus SNR curves in AWGN channel using BPSK/QPSK, 16QAM, 64QAM, 256QAM. Modulation 10/10

25 Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Communication System Overview Readings  Any book about communications

26 Random Process/ Stochastic Process

27 Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Outlines Basic Concepts Stationary Process Transmission over Linear Time-Invariant (LTI) Systems 1/10

28 Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Basic Concepts Why study random processes?  Due to the uncertainty of 1. noise and 2. the unpredictable nature of information itself. Information signal usually is randomlike  We can not predict the exact value of the signal  Signal must be distributed by its statistical properties.  Ex: mean, variance….. 2/10

29 Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Basic Concepts Random Variable (r.v.)  Consider an experiment with sample space. The element of are the random outcomes,, of the experiment. If to every, we assign a real value, such a rule is called a random variable (r.v.) Real line 3/10

30 Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Basic Concepts Random Process (r.p.)  A random process is the mapping of the outcomes in into a set of real valued functions of time, called sample function. r.v. 1. : ensemble 2. : sample function (or a realization) 3. : r.v. 4. : numerical value 4/10

31 Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Basic Concepts Classification of random process  From the perspective of time  Random process:  for, t has a continuous of values  Random sequence:  for, t can take on a finite or countably infinite number of values   From the perspective of the value of  Continuous:  can take on a continuous of values  Discrete :  Values of are countable 5/10

32 Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Basic Concepts Classification of random process  Continuous random process  Discrete random process  Continuous random sequence  Discrete random sequence 6/10

33 Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Basic Concepts 1 st -order distributions function  It describes the instantaneous amplitude distribution of a random process  Mean: 2 nd -order distributions function  It distributes the structure of the signal in the time domain  Autocorrelation Function (A.F.) 7/10

34 Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Basic Concepts  Autocovariance  Cross-correlation  If and are orthogonal   If and are statistically uncorrelated  8/10

35 Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Basic Concepts  Crosscovariance  The autocorrelation function of a real WSS process is 9/10

36 Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Basic Concepts  The cross-correlation function of two real WSS process and is  If and are orthogonal   If and are statistically uncorrelated   Power Spectral Density (PSD)  PSD represents the distribution of signal strength (ie, energy or power) with frequency  The PSD of WSS process is the Fourier transform (FT) of the A.F. 10/10

37 Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Stationary Process Stationary  A random process whose statistical properties do not change over time Stationary Process  Strictly-Sense Stationary (SSS)  Wide-Sense Stationary (WSS)  Strictly-Sense Cyclostationary  Wide-Sense Cyclostationary 1/9

38 Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Stationary Process Strictly-Sense Stationary (SSS)  A nth-order strictly-sense stationary process is a process in which for all, all, and all  Note: Mth-order stationary of the above equation holds for all.  Example: 2 nd -order SSS process  1 st -order SSS process 2/9

39 Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Stationary Process A example of 2 nd -order stationary 3/9

40 Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Stationary Process Wide-Sense Stationary (WSS)  A random process is wide-sense stationary process (WSS) if  Its mean is constant  Its A.F. depends only on the time difference. 4/9

41 Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Stationary Process The relationship between SSS and WSS  SSS  WSS (True)  SSS  WSS (Fault)  1 st -order SSS   2 nd -order SSS   For Gaussian process : SSS  WSS  Since the joint-Gaussian pdf is completely specified by its mean and A.F. 5/9

42 Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Stationary Process Strictly-Sense Cyclostationary  A nth-order strictly-sense cyclostationary process is a process in which for all, all, and integer m ( mT is integer multiples of period T ) 6/9

43 Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Stationary Process Wide-Sense Cyclostationary  A random process with and is wide-sense cyclostationary if  Its mean satisfies  Its a.F. satisfies 7/9

44 Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Stationary Process Ergodic Process  A random process is strictly ergodic process if all time and ensemble (statistical) average are interchangeable including mean, A.F. PSD, etc.  A random process is wise-sense ergodic if it it ergodic in the mean and the A.F.  mean ergodic  A.F. ergodic 8/9

45 Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Stationary Process The relationship between ergodic and stationary  Ergodic  stationary (True)  Ergodic  stationary (Fault) 9/9

46 Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Transmission over LTI Systems Linear Time-Invariant (LTI) Systems 1/3

47 Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Transmission over LTI Systems Assumptions: and are real-valued and is WSS. The mean of the output The cross-correlation function 2/3

48 Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Transmission over LTI Systems The A.F. of the output The PSD of the output 3/3

49 Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Random Process/ Stochastic Process Readings  Communication Systems, 4 th edition, Simon Haykin, Wiley  Chapter 1 – 1.1 ~1.7, 1.8


Download ppt "Communication System Overview Gwo-Ruey Lee. Wireless Access Tech. Lab. CCU Wireless Access Tech. Lab. Outlines Communication System Digital Communication."

Similar presentations


Ads by Google