1. Physical Layer Fundamentals Physical MAC Physical LLC Data Link Network Transport Session Presentation Application OSI Ref ModelWireless Network Network

2. Physical Layer Fundamentals Mobile Radio Propagation  Large-scale  Small-scale  Link budget analysis Modulation Techniques

3. Mobile Radio Propagation Small power will decrease with distance Signals will be distorted  Reflection, diffraction, scattering Radio propagation models Link budget analysis

4. Free Space Propagation Model Received power at distance d (d 0 is a reference distance, d> d 0 )

5. Path Loss Formula Path loss is used for link budget analysis

6. Long-term Fading Model Long-term fading model can be used for link budget analysis Surrounding environmental clutter causes Log-normal shadowing model (n is the path loss exponent)

7. Link Budget Analysis Problem: Determine the transmitting power budget with the desired area coverage based on the propagation characteristic (cell design), appropriately assign the power margin for all possible power loss so that the received power can meet the design requirement Coverage: the received power should NOT below a minimum threshold with certain probability. Need to find this probability.

8. Short-term Fading Channels Fading causes the signal power attenuation Recall: long-term fading tends to be persistent, caused by fixed infrastructure, say, building, hills, trees, etc. Short-term fading affects channel in short period time, not persistent, caused mostly by multipath, moving objects etc. Short-term fading may cause  Rapid change in signal power  Random frequency shift  Time dispersion

9. Factors Causing Short-term Fading Multipath propagation  Reflecting objects and small scatters Speed of the mobils  Relative motion between transmitter and receiver- Dopler Shift Speed of surrounding objects The transmission bandwidth of the signal

10. Modulation/Demodulation Modulation: maps blocks of bits to well- defined waveforms or symbols (a set of signals for better transmission), then shifts transmission to the carrier frequency band (the band you have right to transmit) Demodulation: the inverse of modulation Demodulation vs. Detection: Detection is to recover the modulated signal from the distorted noisy received signals

11. Signal Types Basic form: A signal is a time function Continuous signal: varying continuously with time, e.g., speech Discrete signal: varying at discrete time instance or keeping constant value in certain time interval, e.g., morse coe, flash lights Periodic signal: Pattern repeated over time Aperiodic signal: Pattern not repeated over time

12. Information Carriers

13. Transmission Signal Constellation  Binary ASK, FSK, PSK  QPSK  QAM

14. Shannon Capacity How much you can transmit All channels are noisy. All wireless channels are interference-limited 1948 paper by Clyde Shannon  A mathematical theory of communications  The mathematical theory of communications Signal-to-noise ratio: SNR=signal power/noise power

15. Shannon Capacity Shannon Capacity Theorem: For a noisy channel of BW B with signal-to-noise ratio (SNR), the maximum transmission rate is C=B log2 (1+SNR) Capacity increase as BW or signal power increases: Shout as you can SNR should be replaced by SIR in wireless communications: interference comes into play, shouts may be good for a while, not good for the whole system performance