HARP EU FP7 project, # 318489
A New Signal Model for MIMO Communication with
Compact Parasitic Arrays
6th International Symposium on Communications, control and signal
processing (ISCCSP)
May, 21-23, 2014, Athens, Greece
Vlasis I. Barousis (AIT, Broadband Wireless & Sensor Networks Lab (B-WiSE), Peania, Greece)
Constantinos B. Papadias (AIT, Broadband Wireless & Sensor Networks Lab (B-WiSE), Peania, Greece)
Ralf R. Müller (Institute for Digital Communications, Universität Erlangen-Nürnberg, Erlangen, Germany)
Outline
HARP EU FP7 project, # 318489
• Brief description of single RF parasitic arrays
• Brief description of the existing signal model for compact parasitic arrays
• Weak point of the existing model
• A new signal model approach
• Example: Parasitic array design for MIMO transmission of 16-QAM signals
• Extension to massive regime
• Conclusions and Outlook
No.2/12
Brief description of single RF parasitic
arrays
HARP EU FP7 project, # 318489
xNT
x2
ZS
parasitic
elements
x1
ZS
vs
x1
xNT 1
.
.
.
....
active
element
xNT 1
Coupling
matrix
Z
tunable
loadings
....
vs
Dynamic
matching
• There is only a single feeding port: Significant hardware savings
• The remaining elements are connected to tunable analog loads
• Strong coupling among is needed: All elements participate to the radiation
mechanism
K. Gyoda and T. Ohira, “Design of electronically steerable passive array radiator (ESPAR) antennas,” in Proc. IEEE
International Symposium of Antennas & Propagation Society, vol. 2, pp. 922-925, 2000.
No.3/12
Brief description of the existing signal
model for compact parasitic arrays
HARP EU FP7 project, # 318489
P0    s0 0  
Active element
s   s0 s1 sM 1 

T
d
.
.
.
.
L
Varactor
PT ( )   sm m ( )
m 0
Parasitic
elements
PM1 ( )  sM1M1  
xN-1
.
.
.
vs, x1
M 1
In parasitic arrays we use the
coupling as a benefit that enables
us to emulate MIMO transmission
with a single RF chain, by switching
to different patterns at every
symbol period.
• We encode the symbols for transmission directly to the radiation pattern
• How? We assign each symbol to a different radiation mode of the array
• We come up with a set of pre-defined patterns, each corresponding to a
different combination of symbols
O. Alrabadi, C. Divarathne, P. Tragas, A. Kalis, N. Marchetti, C. Papadias, and R. Prasad, “Spatial multiplexing with a
single radio: Proof-of- concept experiments in an indoor environment with a 2.6-GHz prototype,” IEEE
Communications Letters, vol. 15, no. 2, pp. 178–180, 2011.
No.4/12
Weak point of the existing model
HARP EU FP7 project, # 318489
• Given a parasitic array, MIMO transmission over the air is possible when the
Parasitic
next steps are followed:
elements
NT 1
1. Estimate  n  m0
2. Estimate the set of Q desired radiation patterns
Pq   
NT 1
s
n 0
q
n
q
 n  , s
q q
  s0 s1
q
sNT 1 
T
 
q
Q
Active
3. Compute the set of loading values x
element
q1
• In real-world designs the accurate estimation of all desired
patterns is not guaranteed (especially for non-dipole arrays)
There is a need to be more flexible and design non-dipole arrays: A new
model is needed that bypasses the need to describe the radiation patterns
No.5/12
A new signal model approach
HARP EU FP7 project, # 318489
Arbitrary array
ZG1
Parasitic array
ZG1
vT1
vs
ZG2
ZG2
vT2
vT2
.
.
.
.
R0
R0
vT1
ZGN
vTN
.
.
.
.
vs
ZG2
Coupling
matrix
X2
.
ZT
.
.
.
ZGN
.
.
.
.
Coupling
matrix
ZT
XN
ZGN
vTN
Z G  diag  ZG1 , ZG 2 ,
vT  vT 1 vT 2
, ZGN 
vTN 
T
i   ZT  ZG  vT
1
Z G  diag  Z S , x1 ,
vT  v S 0
, xN 1 
0
T
General system model: y  Hi  n
The actual signals for transmission are assigned directly to the currents
and NOT to radiation patterns
No.6/12
A new signal model approach
HARP EU FP7 project, # 318489
New array design methodology:
• Assume the desired set of possible symbol vectors
S  s1 s2
•
•
sQ  , s q  i q
Design an array that gives the appropriate coupling matrix
Specifications
• The loadings should be tuned within a reasonable range of values
• Matching with the source
Design Rule:
A parasitic array can support a
precoding set of length Q, when
q
   0, q 1, Q
Re Zin
V. I. Barousis and C. B. Papadias, “Arbitrary precoding with single-fed Parasitic arrays:
Closed-form expressions and design guidelines,” IEEE Wireless Communications Letters, Vol. PP, no. 99, Feb. 2014.
No.7/12
Example: Parasitic array design for
MIMO transmission of 16-QAM signals
HARP EU FP7 project, # 318489
Active
element
Parasitic
element
Substrate
Input
Z1
Complex
voltage
output
Z2
Tunable matching
R+jX
• Frequency: 2.6 GHz
• Non-symmetrical design
• FR4 rectangular substrate with
dielectric constant of 4.45
• The shape is adjusted to give
an appropriate coupling matrix:
• Optimize the length of the
active port
• Optimize the difference of
the length of the elements
• Optimize the substrate
dimensions
No.8/12
Example: Parasitic array design for
MIMO transmission of 16-QAM signals
HARP EU FP7 project, # 318489
The loading values are limited
in very reasonable bounds
The same trend applies to all
cases
1
Real part
Imaginary part
0
0.6
-10
0.4
0.2
(a)
0
-100
-50
0
loading value ()
50
100
1
Real part
Imaginary part
CDF
0.8
0.6
-20
-30
-40
-50
-60
i1=[-3+j3;-3+j3]
i2=[-3+j3;-3+j]
i3=[-3+j3;-3-j3]
i4=[-3+j3;-3-j]
0.4
-70
2
0.2
0
-300
Reflection coefficient (dB)
CDF
0.8
(b)
-200
-100
0
100
ESPAR's input impedance ()
2.2
2.4
2.6
Frequency (GHz)
2.8
3
200
No.9/12
Extension to massive regime: Design
challenges
HARP EU FP7 project, # 318489
• Requirements
– Low front-end hardware complexity, i.e. number of RF chains
– Small dimensions: Maximize the performance metrics (e.g. directivity,
scanning range) for a given limited space.
• Design challenges
– Small inter-element spacing (e.g.  10 or even smaller)
– How does this affect the array’s bandwidth?
– Multiple active elements are needed: How should they be arranged over
the “grid” of the array?
– Random vs. grid deployment
No.10/12
Conclusions
HARP EU FP7 project, # 318489
• For long, front-end hardware complexity has been a major challenge in
MIMO transceivers
• In massive MIMO, it becomes a decisive issue
• The proposed front-end hardware architecture is an attractive trade-off
between performance and complexity
• Further effort is needed to design compact massive arrays with low
hardware complexity.
No.11/12
Outlook: Single RF Multiport arrays
HARP EU FP7 project, # 318489
Power
amplifier
Circulator
iin
Carrier
signal
i1
Load
modulator #1
Resistor
Load
modulator #2
.
.
.
Load
modulator #M
i2
iM
.
.
.
Each passive load modulator adjusts the input
current according to a signal constellation
• For massive MIMO, send a sinusoid on the active element.
• Feed the passive elements not inductively, but galvanically.
No.12/12
Outlook: Single RF Multiport arrays
HARP EU FP7 project, # 318489
• For large number of elements, the
source becomes matched by the
law of large numbers.
• Details will be presented next
week at the IEEE Communications
Theory Workshop in Curacao.
M. A. Sedaghat, R. R. Mueller, G. Fischer, "A Novel Single-RF Transmitter for Massive MIMO," In
Proc. 18th International ITG Workshop on Smart Antennas (WSA), pp.1-8, 12-13 March 2014,
Erlangen, Germany.
No.13/12
HARP EU FP7 project, # 318489
Thank you!

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