ECE 4710: Lecture #1 1 Communication Systems  Designed to transmit information between two points  Electrical systems do this via electrical signals  Time-varying voltage (or current) in electrical circuit »“Wired” communication  Time-varying EM wave propagating through air/space »“Wireless” communication  Transmission of information implies that message is not known ahead of time  random  Randomness (entropy) is proportional to information content

ECE 4710: Lecture #1 2 Communication Systems  Design and selection of information bearing waveforms is critical to successful communication  Waveform design/selection depends on:  Signal Bandwidth ( B s )  Information Data Rate ( R d )  Transmission Center Frequency ( f c )  Signal Power/Energy ( P s )  Resistance to Noise/Interference ( N )  Complexity/Cost to Design Tx/Rx Circuits

ECE 4710: Lecture #1 3 Communication History Year EventInventor/Comment 1837TelegraphSamuel Morse 1864 EM Theory James Maxell 1876TelephoneA.G. Bell 1901Radio TransmissionG. Marconi 1921Mobile Radio 1928TelevisionP.T. Farnsworth 1933Frequency Modulation (FM)E.H. Armstrong 1945First ComputerUniv. of Penn. 1948Information TheoryClaude Shannon 1948TransistorShockley et al. 1950Error CodingHamming

ECE 4710: Lecture #1 4 Communication History Year EventInventor/Comment 1958Integrated CircuitJack Kilby (TI) 1965 Satellite Communications 1971 Microprocessor Intel 1972Cellular Radio ConceptMotorola/Bell Labs 1981Personal ComputerIBM st Generation (1G) CellularAnalog AMPS 1989GPS SatellitesU.S. Military 19912G Digital CellularGSM in Europe 1995WWW and Internet 19982G CDMA CellularQualcomm/Sprint PCS 20033G Cellular StandardsWhole World

ECE 4710: Lecture #1 5 Analog vs. Digital  Information Source  Analog: continuous range of states »Microphone: output voltage signal with continuous range of amplitudes (infinite number of voltages)  Digital: finite set of possible states »Computer Keyboard: finite set of characters  Waveform = signal voltage vs. time  Analog  continuous amplitude   Digital  discrete set of amplitudes 

ECE 4710: Lecture #1 6  Typically uses BOTH analog AND digital waveforms  Analog: carrier waveform (sinusoid) for transmission  Digital: discrete values for amplitude, frequency, or phase used to represent information bits  Binary Digital Waveform  2 states for each digital symbol, e.g. 0, 1  M -ary Digital Waveform  M -states for each symbol  # Bits/Symbol = log 2 ( M ) Digital Communication System M = 4 states  2 bits/symbol

ECE 4710: Lecture #1 7 Deterministic vs. Random  Waveform Classification  Deterministic: waveform modeled or represented completely as a function of time, e.g. s ( t ) = A cos (   t +  )  Random/Stochastic: cannot be completely specified as a function of time  Recall that randomness = information  Waveforms must be random to carry significant information  Source/Information Waveform: each symbol can be deterministic but information stream is random  Noise is also a random signal  Probability/Statistics must be used to analyze performance of any communication system

ECE 4710: Lecture #1 8  Digital communication systems have MANY advantages over analog systems including:  Data encryption for security/privacy  Combine multiple information types (voice, video, data) on a single transmission channel  Resistant to noise, fading, and interference »Small error probability even with large interference  Error detection and correction using digital codes  Implementation using all digital circuits Digital Communication System

ECE 4710: Lecture #1 9 Basic Communication System ˜ Information Source Baseband Signal Processing Modulation & Carrier Circuits Transmission Channel Demodulation & Carrier Circuits Baseband Signal Processing Information Sink Noise n (t) m (t) s (t) r (t) m (t) Transmitter (Tx)Receiver (Rx) Goal: Design system to transmit information, m(t), with as little deterioration as possible within design constraints of signal power, signal bandwidth, and system cost

ECE 4710: Lecture #1 10 System Components  Baseband signals  signal centered at f = 0  m(t) : input information signal (voice, data, video, etc.)  m(t) : received information signal distorted/corrupted by noise, interference, non-linearities, etc.  Baseband Signal Processing  Encoding of information  “Source coding”  Filtering to minimize signal bandwidth  Error coding to protect information  “Channel Coding” ˜

ECE 4710: Lecture #1 11 System Components  Tx Carrier Circuit  Converts processed baseband signal into frequency band that is appropriate for transmission through channel  Tx output s(t) is called a “bandpass” signal »Carrier frequency, f c, is center frequency of bandpass signal  m(t)  s(t) conversion or mapping is called “modulation”  Channel : Two major categories  Wire  coaxial, twisted pair, & fiber optic cables  Wireless  mobile radio (cellular, 3G, 4G, etc.), terrestrial radio/TV broadcasts, satellite radio/TV broadcasts, WiFi, bluetooth, etc.  Introduces significant attenuation, noise, and possibly distortion and other impairments (e.g. interference)

ECE 4710: Lecture #1 12 System Components  Channel Impairments  Attenuation, multipath echoes, fading, noise, interference, etc.  Channel characteristics can be fairly stable (wired) or change rapidly as function of time (mobile radio) »Time-varying channel is difficult to model  Noise »Man-made: computers, motors, car ignition, other users (cellular phone) »Natural: thermal “background” noise, lightening, etc.

ECE 4710: Lecture #1 13 System Components  Receiver Carrier Circuit (Rx)  Takes corrupted signal from channel, amplifies, filters, etc. and then converts down to baseband signal  demodulation (mod/dem = modem)  Rx Baseband Signal Processing  Cleans up distorted baseband signal and delivers estimate of the source information signal  m(t)  Filtering, bit detection, error detection/correction  Performance measures  Analog  output signal-to-noise ( S / N ) ratio  Digital  probability of bit error or “Bit Error Rate (BER)” ˜