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Transportation of MIMO Radio Signals over
RoF-Distributed Antenna System and its
Performance Analysis in the Presence of
Incomplete Synchronization in Optical TDM
Nara Institute of Science and Technology , Japan
Network System Lab
Tatsuya Kidani, Takeshi Higashino, Minoru Okada
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Outline
• Background
• Concept of RoF-DAS using optical TDM
• Configuration of RoF-DAS using optical
TDM
• Channel Model with synchronization
mismatch
• Simulation
• Summary & Future Work
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Background
High speed and large capacity
wireless access
Adaptive control of base
station
Accommodations of various
communication standards
(Heterogeneous)
Requirements of Next Generation Network
RoF-DAS using optical TDM (Time Division
Multiplexing)
[Radio on Fiber (RoF),Distributed Antenna System (DAS)]
Source1 Source2
Source1:Cisco VNI Mobile, 2011
Source2:ZTE ZTE technology N0.1, 2011
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RoF-DAS
O/EE/O
Modulation/Demodulation
,scheduling(time,frequency),
Signal processing(MIMO, etc.)
RAU
RoF-linkCCS
Mobile Terminal
MIMO4
RoF-DAS utilizes many antennas (RAU)
geographically located at different location.
Conversion
This system can use multiple RAUs to
coordinate as MIMO system
RoF:Radio on Fiber
CCS : Centralized Control Station, RAU : Remote Antenna Unit
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Concept of RoF-DAS using
optical TDM
• Radio on Fiber (RoF)
• Distributed Antenna
System (DAS)
• Optical TDM
• Merit
– High Coverage
– Low Spatial Correlation
– Reduction of
transmission power
CCS : Centralized Control Station, RAU : Remote Antenna UnitMT : Mobile Terminal
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MIMO technique
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y :Receive Vector
𝐇𝑎𝑖𝑟 :Channel Matrix
x :Transmit Vector
n :Noise Vector
nxHy air
Transmitter H
1x
2x
Nx
Receiver
11h
12h
21h
22h
1y
2y
My
MNh
1Mh
2Mh
NMMM
NM
N
air
hhh
h
hh
hhh
,2,1,
1,
2,21,2
,12,11,1
H
MIMO technique can increase
channel capacity proportional to
the number of antennas.
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Configuration of RoF-DAS using
optical TDM
a.Optical pulse source
emits periodic pulse
train
b.RF signal modulates
the optical pulse
intensity
c.Employ optical delay
lines and the optical
signals are combined
d.O/E conversion is
performed and signal is
demultiplexed
e.RF original signal are
re-generated from TDM
demultiplexed signal
with band pass filters
(BPFs)
LN-MZM : lithium niobate - Mach-Zehnder modulatorPD : Photo Diode
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a b c d e
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Configuration of RoF-DAS using
optical TDM
• Requirement of
SW
– Accuracy
• If Synchronization
mismatch happens,
(Problem)
– Each signals is
mixed (High
Correlation)
We estimate the amount of
synchronization mismatch &
compensate it.
Prevent performance degradation8
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Channel Model with
Synchronization Mismatch
• Ideal MIMO
𝒚 = H𝒂𝒊𝒓𝒙 + 𝒏
• Channel Model with synchronization mismatch,
𝒙′ =
𝑥1 1 − 𝜏 𝑥2𝜏
𝑥2 1 − 𝜏 𝑥3𝜏
𝑥3 1 − 𝜏 𝑥4𝜏
𝑥1𝜏 𝑥4 1 − 𝜏
=
1 − 𝜏 𝜏 0 00 1 − 𝜏 𝜏 00 0 1 − 𝜏 𝜏𝜏 0 0 1 − 𝜏
𝑥1𝑥2𝑥3𝑥4
= 𝑻𝒙
𝒚′ = 𝑯𝑎𝑖𝑟𝑻𝒙 + 𝒏9
Delay Matrix
𝜏:Amount of mismatch (0 ≤ 𝜏 ≤ 1)
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Compensation of synchronization
mismatch (Proposed)
• ZF with compensation
We implemented the delay matrix estimator at
the RAU.
In this proposal, we utilities pilot sequence 𝒑,
𝐓est = 𝐓𝐩𝐩T + 𝐧RoF𝐩T
Compensated transmission signal
𝒙′′ = 𝑻𝑒𝑠𝑡−1 𝒙
𝒙𝑐𝑜𝑚 = 𝑻𝑻𝑒𝑠𝑡−1 𝒙
𝐧RoF : Noise in RoF
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Block Diagram
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CCS (Centralized Control Station) RAUs (Remote Antenna Units)
Signal Processor
E/O O/ETDM
MultiplexingBPF
TDMDemultiplexing
Delay Matrix
Estimator
RoF
Feedback 𝑻−1
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Simulation
Modulation QPSK, 16QAM, 64QAM
Number of RAUs 4
Number of RAU’s Antennas 1
Number of MTs 1
Number of MT’s Antennas 4
Clock Delay 0.1~0.9
MIMO Detection Zero-Forcing
Pilot Sequence M-sequence
Noise AWGN
Fading Channel (Air) i.i.d, Flat Rayleigh Fading
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Channel Capacity
• Shannon-Hartley theorem
𝐶 = log2 det(𝑰 +𝛾0𝑛𝑡(𝑯𝑎𝑖𝑟𝑻)
𝐻(𝑯𝑎𝑖𝑟𝑻))
(𝑯𝑒𝑠𝑡 = 𝑯𝑎𝑖𝑟𝑻)
𝛾0 : ratio between
transmission power and
noise power
𝑛𝑡 : number of antenna at CCS
𝑰 : identity matrix
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Simulation (SNR=35dB &
16QAM)
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Simulation (𝜏 = 0.4)
8.5dB
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Summary & Future Work
• Summary
–To avoid critical degradation due to the
incomplete synchronization, a new
compensation scheme is proposed.
–This scheme can estimate amount of
synchronization mismatch and also gives an
improvement in BER performance.
• Future Work
–Application of Optical OFDM (Orthogonal
Frequency Division Modulation).
–The compensation of nonlinear distortion due
to RoF characteristic.
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