1. Lecture Slides 26-September-2017
TLEN 5830 Wireless Systems
Lecture Slides
26-September-2017
Signal Encoding

2. Additional reference materials
Required Textbook: Antennas and Propagation for Wireless Communication Systems, by Simon R. Saunders and Alejandro Aragon-Zavala, ISBN ; March 2007 (2nd edition). Optional References: Wireless Communications and Networks, by William Stallings, ISBN , 2002 (1st edition); Wireless Communication Networks and Systems, by Corey Beard & William Stallings (1st edition); all material copyright 2016 Wireless Communications Principles and Practice, by Theodore S. Rappaport, ISBN (2nd edition) Acknowledgements:

3. Channel Correction Mechanisms: Brief Overview
Forward error correction
Adaptive equalization
Adaptive modulation and coding
Diversity techniques and MIMO
OFDM
Spread spectrum
Bandwidth expansion

4. Forward Error Correction
Transmitter adds error-correcting code to data block
Code is a function of the data bits
Receiver calculates error-correcting code from incoming data bits
If calculated code matches incoming code, no error occurred
If error-correcting codes don’t match, receiver attempts to determine bits in error and correct

5. 5.15 Forward Error Correction Process

6. Adaptive Equalization
Can be applied to transmissions that carry analog or digital information
Analog voice or video
Digital data, digitized voice or video
Used to combat intersymbol interference (from?)
Involves gathering dispersed symbol energy back into its original time interval
Techniques
Lumped analog circuits
Sophisticated digital signal processing algorithms

7. Time diversity – techniques aimed at spreading the data out over time
Diversity is based on the fact that individual channels experience independent fading events
Space diversity – techniques involving physical transmission path, spacing antennas
Frequency diversity – techniques where the signal is spread out over a larger frequency bandwidth or carried on multiple frequency carriers
Time diversity – techniques aimed at spreading the data out over time
Use of diversity
Selection diversity – select the best signal
Combining diversity – combine the signals

8. Multiple Input / Multiple Output (MIMO) Antennas
Use antenna arrays for
Diversity – different signals from different antennas
Multiple streams – parallel data streams
Beamforming – directional antennas
Multi-user MIMO – directional beams to multiple simultaneous users
Modern systems
4 × 4 (4 transmitter and 4 reciever antennas)
8 × 8
Two dimensional arrays of 64 antennas
Future: Massive MIMO with many more antennas

9. Multiple Input / Multiple Output (MIMO) Antennas
This is a good summary slide for MIMO

10. Adaptive modulation and coding (AMC)
The modulation process formats the signal to best transmit bits
To overcome noise
To transmit as many bits as possible
Coding detects and corrects errors
AMC adapts to channel conditions
100’s of times per second
Measures channel conditions
Sends messages between transmitter and receiver to coordinate changes

11. Bandwidth expansion A signal can only provide a limited bps/Hz
More bandwidth is needed
Carrier aggregation
Combine multiple channels
Example: Fourth-generation LTE combines third-generation carriers
Frequency reuse
Limit propagation range to an area
Use the same frequencies again when sufficiently far away
Use large coverage areas (macro cells) and smaller coverage areas (outdoor picocells or relays and indoor femtocells)
Millimeter wave (mmWave)
Higher carrier frequencies have more bandwidth available
30 to 300 GHz bands with millimeter wavelengths
Yet these are expensive to use and have problems with obstructions

12. Bandwidth expansion: Carrier Aggregation

13. Key Data Transmission Terms

14. Encoding and Modulation Techniques

15. Signal Encoding Criteria
What determines how successful a receiver will be in interpreting an incoming signal?
Signal-to-noise ratio (or better Eb/N0)
Data rate
Bandwidth
An increase in data rate increases bit error rate
An increase in SNR decreases bit error rate
An increase in bandwidth allows an increase in data rate
Importantly, another factor can be utilized to improve performance
and that is the encoding scheme

16. Factors Used to Compare Encoding Schemes
Signal spectrum
With lack of high-frequency components, less bandwidth required
Clocking
Ease of determining beginning and end of each bit position
Signal interference and noise immunity
Certain codes exhibit superior performance in the presence of noise (usually expressed in terms of a BER)
Cost and complexity
The higher the signal rate to achieve a given data rate, the greater the cost

17. Basic Encoding Techniques
Digital data to analog signal
Amplitude-shift keying (ASK)
Amplitude difference of carrier frequency
Frequency-shift keying (FSK)
Frequency difference near carrier frequency
Phase-shift keying (PSK)
Phase of carrier signal shifted

18. Modulation of Analog Signals for Digital Data

19. Phase-Shift Keying (PSK)
Two-level PSK (BPSK)
Uses two phases to represent binary digits

20. Phase-Shift Keying (PSK)
Differential PSK (DPSK)
Phase shift with reference to previous bit
Binary 0 – signal burst of same phase as previous signal burst
Binary 1 – signal burst of opposite phase to previous signal burst

21. Differential Phase-Shift Keying

22. Quadrature Phase-Shift Keying (PSK)
Four-level PSK (QPSK)
Each element represents more than one bit

23. QPSK Constellation Diagram

24. QPSK and OQPSK Modulators

25. Phase-Shift Keying (PSK)
Multilevel PSK
Using multiple phase angles with each angle having more than one amplitude, multiple signal elements can be achieved
D = modulation rate, baud or symbols/sec
R = data rate, bps
M = number of different signal elements = 2L
L = number of bits per signal element

26. Performance Bandwidth of modulated signal (BT) ASK, PSK BT = (1+r)R
FSK BT = 2Δf+(1+r)R
R = bit rate
0 < r < 1; related to how signal is filtered
Δf = f2 – fc = fc - f1

27. Performance Bandwidth of modulated signal (BT) MPSK MFSK
L = number of bits encoded per signal element
M = number of different signal elements

28. Bit Error rate (BER)
Performance must be assessed in the presence of noise
“Bit error probability” is probably a clearer term
BER is not a rate in bits/sec, but rather a probability
Commonly plotted on a log scale in the y-axis and Eb/N0 in dB on the x-axis
As Eb/N0 increases, BER drops
Curves to the lower left have better performance
Lower BER at the same Eb/N0
Lower Eb/N0 for the same BER

29. Theoretical Bit Error Rate for Various Encoding Schemes

30. Theoretical Bit Error Rate for Multilevel FSK, PSK, and QAM

31. Quadrature Amplitude Modulation
QAM is a combination of ASK and PSK
Two different signals sent simultaneously on the same carrier frequency

32. QAM Modulator

33. 16-QAM Constellation Diagram

34. Additional reference materials
Required Textbook: Antennas and Propagation for Wireless Communication Systems, by Simon R. Saunders and Alejandro Aragon-Zavala, ISBN ; March 2007 (2nd edition). Optional References: Wireless Communications and Networks, by William Stallings, ISBN , 2002 (1st edition); Wireless Communication Networks and Systems, by Corey Beard & William Stallings (1st edition); all material copyright 2016 Wireless Communications Principles and Practice, by Theodore S. Rappaport, ISBN (2nd edition)