Overview of technical challenges

Millimeter-Wave Based Device-toDevice Communications - Research
Activities at Aalto
Dr. Linsheng Li
Department of Radio Science and Engineering,
Aalto University
13.04.2015
OUTLINE
• Background
• Overview of technical challenges
• On-going research activities
OUTLINE
• Background
• Overview of technical challenges
• On-going research activities
Overview of the project
• Title of research project:
– Device-to-device communications at millimetre-wave
frequencies
• Principal Investigators & contributors：
– Prof. Katsuyuki Haneda， Aalto University School of
Electrical Engineering(PI)
• Sinh Nguyen, Linsheng Li and Jan Järveläinen
– Prof. Andreas F. Molisch， University of Southern
California (USC), Communications Sciences Institute(PI)
• Rui Wang, Umit Bas and Daoud Burghal
• Duration of the project:
– 24 months (two years) starting from 15 November 2014.
Background: Millimeter-Wave (Mm-Wave)
Radios
• > 1 GHz bandwidth available for high-data-rate radio
communications
• Higher free space loss with a fixed physical size of receive
antenna aperture
Free space loss
4m
Transmit
omnidirectional
antenna
Transmit
omnidirectional
antenna
Background: Millimeter-Wave (Mm-Wave)
Radios
• Directional radio transmission required to ensure link
budget
– Small-cell operation preferable; effective spatial coexistence of
multiple links
Antenna array
2 mm @ 60GHz
2 mm
Ideal beam pattern
Device-to-Device (D2D) Communications
at Millimeter-Wave Radio Frequency
• D2D comm. improves the spectral efficiency per area in
cellular comm.
Legacy (< 5GHz)
frequency has
wider coverage
Indoor
Use of legacy bands
as a fall back option of
mm-wave bands
Mm-wave (>30GHz)
frequency has smaller
coverage
Directional isolation allows
effective D2D comm at
mm-wave
OUTLINE
• Background
• Overview of technical challenges
• On-going research activities
D2D Comm. at Mm-Wave Frequency:
Technical Challenges (1)
• How far mm-wave radios can reach in comparison to
legacy radios? Outdoor-to-indoor penetration/isolation?
We address this challenge
by extensive mm-wave
radio channel sounding.
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?
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D2D Comm. at Mm-Wave Frequency:
Technical Challenges (2)
• How should the mm-wave radios coordinate with legacy
cellular?
We address this challenge
by considering the legacy
cellular as a fall-back
option to mm-wave radios.
D2D Comm. at Mm-Wave Frequency:
Technical Challenges (3)
• Directional antennas allow highly isolated links. At the
beginning, how efficient it is to find a device to communicate?
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?
We address this challenge by
developing an efficient
neighbor discovery method.
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D2D Comm. at Mm-Wave Frequency:
Technical Challenges (4)
• What is the feasible beamforming architecture at mm-wave?
Tradeoff between complexity (energy losses) and flexibility?
Hybrid analog-digital beamforming
RFchain
RFchain
RFchain
RFchain
RFchain
RFchain
Baseband control
Fully digital beamforming
Baseband control
We address this challenge by developing a
hybrid analog-digital beamforming architecture.
OUTLINE
• Background
• Overview of technical challenges
• On-going research activities
On-going research activities
• Channel measurements and modeling
– Accurate channel measurement is the essential step
to get a quantitative model of the environment effects
and channel characteristics.
– Vector network analyzer based channel sounder for
60GHz have been used to carry out outdoor/indoor
channel measurement. The sounder for 28GHz has
been designed and tested in the laboratory. Channel
measurement will be carried out in the airport in May
2015.
– A switched array channel sounder is under
development for 60GHz channel sounding.
Measurement equipment
Tx
Rx
60 GHz Indoor and O2I measurement
Indoor cafeteria
O2I cafeteria
Deterministic field prediction
• Spatio-temporal channel propagation prediction
requires accurate description of environment
• Laser scanning  Point cloud environment data
No surface description  ray tracing cannot be used
Point Cloud-Based Propagation Prediction
– Synthesis of Power Delay Profile (PDP)
Path power [dB] = |Es|2 + GTx + GRx - FSPL
Power delay profile:
bandwidth limited form
Discrete channel impulse response
-70
-70
-90
-100
-110
-120
-130
0
S=0.5, R=50
S=0.2, R=50
-80
Amplitude [dB]
Amplitude [dB]
-80
-90
-100
-110
-120
5
10
15
Delay [ns]
20
25
30
Channel transfer function over 5 GHz BW
L
H i    l exp( j2f i l )
l 1
-130
0
5
10
15
Delay [ns]
20
25
30
PDP derivation from channel transfer
functions
2
 L

PDP( )  E   H l exp( j2f l ) 
 l 1

18
Point-cloud based Channel Simulation
PDP for Tx4
 11, S  0.6
-60
Measured
Predicted
Amplitude [dB]
-70

-80
-90
-100
-110
-120
0
10
20
30
Delay [ns]
40
Measured
Predicted
Mean delay
5.3 ns
5.2 ns
RMS delay
spread
3.1 ns
2.5 ns
50
8
On-going research activities
• Neighbor discovery
– For D2D communication, the first step is to discover
its neighbors, i.e., which other devices it can
communicate with.
– Solution methods for mm-waves are significantly
different from those at lower frequencies, due to the
high directionality of the channels.
– Measurements complemented with point-cloud
simulations will be of use for this analysis.
On-going research activities
• Beamforming and beamtracking
– Due to the highly dynamic nature of the D2D channel
and the sensitivity to the interaction with the body of
the person holding the device, adaptive beamforming
is necessary.
– Hybrid analog-digital beamforming based on an
antenna array at 60 GHz working in multipath
environments is under development.
– Analysis with spatial degrees-of-freedom of multipath
channel is under development.
Hybrid analog-digital beamforming scheme
.
.
.
DAC
.
.
.
Baseband
(digital
beamforming)
DAC
Analog
beamforming
.
.
.
Antenna array
Hybrid analog-digital beamforming scheme
Research plan