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 1
Transportation of MIMO Radio Signals over RoF-Distributed Antenna System and its Performance Analysis in the Presence of Incomplete Synchronization in Optical TDM
Dec 26, 2014
Radio on Fiber-Distributed Antenna System (RoF- DAS) is known to improve coverage and performance of wireless communications. Currently, various multiplexing schemes in RoF-DAS for transport Multiple Input Multiple Output (MIMO) signals in a fiber link are studied. The RoF-DAS over Wave- length Division Multiplexing - Passive Optical Network (WDM- PON) with optical Time Division Multiplexing (TDM) is actively researched. This system uses optical switcher to multiplex a set of MIMO radio signals in a fiber and transfer to the Remote Antenna Unit (RAU). Since a pair of switches multiplex and demultiplex MIMO radio signals, two switches are required to synchronize completely. Therefore, there is a problem that high performance switches are required to perform the clock extraction. This paper proposes asynchronous optical TDM. In this proposal, synchronization mismatch is compensated by estimating the amount of drifting and cancel it out at the RAU. The bit error ratio (BER) performance is evaluated by using computer simulation.
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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
1
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
2
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
3
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
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
5
MIMO technique
6
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.
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
7
a b c d e
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
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)
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
10
Block Diagram
11
CCS (Centralized Control Station) RAUs (Remote Antenna Units)
Signal Processor
E/O O/ETDM
MultiplexingBPF
TDMDemultiplexing
Delay Matrix
Estimator
RoF
Feedback 𝑻−1
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
12
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
13
Simulation (SNR=35dB &
16QAM)
14
Simulation (𝜏 = 0.4)
8.5dB
15
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.
16
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