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  • 1. Tutorial ─ MIMO Communications with Applications to (B)3G and 4G Systems Introduction Juha Ylitalo Tutorial #2: MIMO Communications with Applications to (B)3G and 4G Systems ─ Introduction © J. Ylitalo & M. Juntti, University of Oulu, Dept. Electrical and Inform. Eng., Centre for Wireless Communications (CWC) 1
  • 2. Introduction • Short historical note • Advantages of multi-antenna techniques • Adaptive antennas – - Beamforming: spatial focusing of correlated signals – - Rx/Tx diversity: combining of decorrelated signals – - MIMO: increasing spectral efficiency/ data rates • Simple example: SINR improvement • Definition of MIMO • Spatial correlation matrix • Example: Diversity & MIMO in WCDMA Tutorial #2: MIMO Communications with Applications to (B)3G and 4G Systems ─ Introduction © J. Ylitalo & M. Juntti, University of Oulu, Dept. Electrical and Inform. Eng., Centre for Wireless Communications (CWC) 2
  • 3. Historical Note • Multiple antenna transmission used by Marconi in 1901 – Four 61m high tower antennas (circular array) – Morse signal for "S" from England to Signal Hill, St. John, Newfoundland, distance 3425km • • • • Submarine sonar during 1910's Acoustic sensor arrays 1910's RF radars 1940's Ultrasonic scanners from 1960's Tutorial #2: MIMO Communications with Applications to (B)3G and 4G Systems ─ Introduction © J. Ylitalo & M. Juntti, University of Oulu, Dept. Electrical and Inform. Eng., Centre for Wireless Communications (CWC) 3
  • 4. Advantages of Multiple Antenna Techniques • • • • • • • Resistivity to fading (quality) Increased coverage Demonstration by Lucent Increased capacity with 8 Tx /12 Rx antennas: Increased data rate 1.2 Mbit/s in 30kHz Improved spectral efficiency Reduced power consumption Reduced cost of wireless network Some challenges: - RF: Linear power amplifiers, calibration - Complex algorithms: DSP requirements, cost - Network planning & optimisation Tutorial #2: MIMO Communications with Applications to (B)3G and 4G Systems ─ Introduction © J. Ylitalo & M. Juntti, University of Oulu, Dept. Electrical and Inform. Eng., Centre for Wireless Communications (CWC) 4
  • 5. Adaptive Antennas • An adaptive antenna system consists of several antenna elements, whose signals are processed adaptively in order to exploit the spatial dimension of the mobile radio channel. Weight Adaptation RF IF RF IF + RF IF Baseband processing Tutorial #2: MIMO Communications with Applications to (B)3G and 4G Systems ─ Introduction © J. Ylitalo & M. Juntti, University of Oulu, Dept. Electrical and Inform. Eng., Centre for Wireless Communications (CWC) 5
  • 6. Adaptive Antenna Operation • Conventional BTS: – radiation pattern covers the whole cell area • “Smart” Antenna BTS: – adaptive radiation pattern, "spatial filter" – transmission/reception only to/from the desired user direction – minimise antenna gain to direction of other users Conventional BTS radiation pattern Tutorial #2: MIMO Communications with Applications to (B)3G and 4G Systems ─ Introduction Smart Antenna BTS © J. Ylitalo & M. Juntti, University of Oulu, Dept. Electrical and Inform. Eng., Centre for Wireless Communications (CWC) 6
  • 7. Beamforming (beam steering) • Beamforming = phasing the antenna array elements • Only Direction-of-Arrival (DOA) parameter needed in both TX and RX: simple and robust • Suits especially well to FDD systems 0 Array Gain [dB] -5 DOA = 0 deg. 1 DOA = 30 deg. M=8 2 -10 -15 -20 -25 -30 -50 0 Azimuth [deg] Tutorial #2: MIMO Communications with Applications to (B)3G and 4G Systems ─ Introduction 50 © J. Ylitalo & M. Juntti, University of Oulu, Dept. Electrical and Inform. Eng., Centre for Wireless Communications (CWC) 7
  • 8. RX Diversity • De-correlated (statistically independent) signals received • spatial and polarisation diversity arrangements dB • combining of fading signals: – Maximum Ratio Combining (MRC) – Interference Rejection Combining (IRC) 10 Received signal power 5 0 -5 -10 4MRC 2MRC -15 0 0.5 RX 1 1.5 2 2.5 Seconds, 3km/h RX RX RX Tutorial #2: MIMO Communications with Applications to (B)3G and 4G Systems ─ Introduction WCDMA WCDMA Transceiver Transceiver Combined received signal © J. Ylitalo & M. Juntti, University of Oulu, Dept. Electrical and Inform. Eng., Centre for Wireless Communications (CWC) 8
  • 9. Transmission Diversity • Multiple antennas available at the BTS • Terminal: only one antenna Uncorrelated fading -> downlink suffers from lack of diversity Downlink: Use TX instead of RX diversity • TX diversity gain: Signal #1 Base station – Gain against fading – Feedback modes: coherent combining ("beamforming") gain (1) Gain against fading Signal #2 (2) Coherent combining gain (only feedback modes) • Downlink capacity improvement RX diversity in terminal is coming soon enabling RX diversity at UE, MIMO, … Tutorial #2: MIMO Communications with Applications to (B)3G and 4G Systems ─ Introduction © J. Ylitalo & M. Juntti, University of Oulu, Dept. Electrical and Inform. Eng., Centre for Wireless Communications (CWC) 9
  • 10. SISO, SIMO, MISO, MIMO • Single-Input, Single-Output channel suffers from fading • Single-Input, Multiple-Output channel: RX diversity • Multiple-Input, Single-Output channel: TX diversity, Beamforming SISO Data stream radio channel Data stream SIMO Data stream Data stream radio channel MISO Data stream Combiner Data stream radio channel Tutorial #2: MIMO Communications with Applications to (B)3G and 4G Systems ─ Introduction © J. Ylitalo & M. Juntti, University of Oulu, Dept. Electrical and Inform. Eng., Centre for Wireless Communications (CWC) 10
  • 11. Definition of MIMO • Multiple-Input, Multiple-Output channel • Mapping of a data stream to multiple parallel data streams and de-mapping multiple received data streams into a single data stream • Aims at high spectral efficiency / high data rate M antennas Data stream N antennas MIMO Serial/ parallel mapping Parallel/ serial mapping radio channel Rxx HMN Data stream Ryy Requires rich scattering environment Tutorial #2: MIMO Communications with Applications to (B)3G and 4G Systems ─ Introduction © J. Ylitalo & M. Juntti, University of Oulu, Dept. Electrical and Inform. Eng., Centre for Wireless Communications (CWC) 11
  • 12. TX diversity& Beamforming vs. MIMO Maximum Gain: Transmit Diversity/ BF V1 Same signal on all antennas, i.e. conventional Tx diversity/ BF V2 s1, s2, s3, s4 V3 V4 a) Maximum Capacity: Parallel channel transmission s1 V1 s2 V2 s3 V3 s4 V4 Different signals on Tx antennas. i.e. true MIMO b) BLAST (PARC) type of transmission scheme is considered as MIMO, whereas WCDMA STTD is a hybrid, considered as a Tx diversity scheme Tutorial #2: MIMO Communications with Applications to (B)3G and 4G Systems ─ Introduction © J. Ylitalo & M. Juntti, University of Oulu, Dept. Electrical and Inform. Eng., Centre for Wireless Communications (CWC) 12
  • 13. Channel capacity (Shannon) • Represents the maximum error-free bit rate • Capacity depends on the specific channel realization, noise, and transmitted signal power. • Single-input single-output (SISO) channel y (t ) = α ⋅ x(t ) + n(t ) ⎛ P 2⎞ C = log2 ⎜1 + 2 α ⎟ ⎟ ⎜ σ n ⎠ ⎝ • Multi-input multi-output (MIMO) channel y(t ) = Hx(t ) + n(t ) ⎡ ⎛ ⎞⎤ 1 H ⎟ C = log 2 ⎢det⎜ I + 2 HQH ⎥ ⎟⎥ ⎢ ⎜ σn ⎠⎦ ⎣ ⎝ Q is the covariance matrix of the transmitted vector Tutorial #2: MIMO Communications with Applications to (B)3G and 4G Systems ─ Introduction © J. Ylitalo & M. Juntti, University of Oulu, Dept. Electrical and Inform. Eng., Centre for Wireless Communications (CWC) 13