This document provides an introduction to MIMO communications techniques and their applications in 3G and 4G wireless systems. It discusses the historical use of multiple antennas, advantages of MIMO such as increased data rates and spectral efficiency. It describes adaptive antenna techniques including beamforming and transmit/receive diversity. MIMO is defined as using multiple antennas at both the transmitter and receiver to increase spectral efficiency and data rates by transmitting independent data streams through parallel channels. The document provides examples of MIMO channel capacity and its advantages over SISO.

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