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

Additional reference materials Required Textbook: Antennas and Propagation for Wireless Communication Systems, by Simon R. Saunders and Alejandro Aragon-Zavala, ISBN 978-0-470-84879-1; March 2007 (2nd edition). Optional References: Wireless Communications and Networks, by William Stallings, ISBN 0-13-040864-6, 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 0-13-042232-0 (2nd edition) Acknowledgements:

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

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

5.15 Forward Error Correction Process

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

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

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

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

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

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

Bandwidth expansion: Carrier Aggregation

Key Data Transmission Terms

Encoding and Modulation Techniques

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

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

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

Modulation of Analog Signals for Digital Data

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

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

Differential Phase-Shift Keying

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

QPSK Constellation Diagram

QPSK and OQPSK Modulators

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

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

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

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

Theoretical Bit Error Rate for Various Encoding Schemes

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

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

QAM Modulator

16-QAM Constellation Diagram

Additional reference materials Required Textbook: Antennas and Propagation for Wireless Communication Systems, by Simon R. Saunders and Alejandro Aragon-Zavala, ISBN 978-0-470-84879-1; March 2007 (2nd edition). Optional References: Wireless Communications and Networks, by William Stallings, ISBN 0-13-040864-6, 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 0-13-042232-0 (2nd edition)