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A Flexible 4 x 16 MIMO Testbed with250 MHz – 6 GHz Tuning Range
Steve EllingsonMobile & Portable Radio Research Group (MPRG)Dept. of Electrical & Computer EngineeringVirginia Polytechnic Institute & State [email protected]
2005 IEEE Int’l Antennas & Propagation Symposium
MCMS
A One-Slide MIMO Primer
Capacity[b/s]
Bandwidth[Hz]
Mean SNR per RX antenna
Matrix ofChannel
Coefficients[ NR x NT ]
Generalized Shannon Bound:
NT=1 or NR=1 → rank{HH′}=1 → C ∝ log2NNT>1 and NR>1 and rank{HH′}>1 → C ∝ N
Up to min{NT,NR} independent MIMO “subchannels”, each with SNR ∝ the associated eigenvalues of HH′
MCMS http://www.ece.vt.edu/swe/mcms
Ideal NT=8Ideal NT=2
MeasuredNT=8
• 2.4 GHz• NR=8 • Actually, uncommon that results
turn out this well…
An Example of a Nice MIMO Channel
Eigenvalues of HH′ Capacity (Γ =10)
MeasuredNT=2
TX site behind building
View fromRX site
MCMS http://www.ece.vt.edu/swe/mcms
Examples of Problematic MIMO Channels
MCMS http://www.ece.vt.edu/swe/mcms
Persistent (minutes…)Near-Keyhole Condition
Transient (seconds…)“Hard” Keyhole Condition
• From nearby location during the same measurement campaign• Related anomalies: defective (two-ray) fading, hard shadowing,…• Very difficult to back out causes from the captured data…
Equipment Used to Obtain This Data:
Rear View of Rack (2001)Front View of Rack (2001)
• Three racks of custom built equipment, not including a PC and required test equipment. Not portable, very slow, so:
• Not really suitable for chasing down interesting MIMO channel anomalies
MCMS http://www.ece.vt.edu/swe/mcms
Instrument Wish List (→ MCMS Features)Bona Fide (not Synthetic) 4 x 16– Not common to see effective channel rank greater than 4– Availability of 16 receive elements allows:
Concurrent high-res spatial analysis (e.g., AOA clustering)Multiple arrays of smaller number of elements (simultaneous locations, multiple types of arrays)
– Bona fide (vs. “synthetic”) arrays important for understanding antenna design issues; in particular, mutual coupling
40 MHz Instantaneous Bandwidth – Time resolution, wideband modulations
Battery powered (hours of operation) + 2-person lift– Mobile/field operation
Tuning Range 250-6000 MHz – Cover as many MIMO candidate bands as possible
MCMS http://www.ece.vt.edu/swe/mcms
NSF/MRI proposal Jan 2002 – Joint effort with Aeroflex Corp.
Project start: October 2002
9-month proof-of-concept phase @ Ohio State University
15-month development phase @ Aeroflex, OSU, & Virginia Tech
Aeroflex delivery: December 2004; now at Virginia Tech
Operational, although some development continues
Matrix Channel Measurement System (MCMS)Project History
MCMS http://www.ece.vt.edu/swe/mcms
Clock & LO Synthesis & Distribution
Qua
dD
SPEm
bedd
ed
PC
Dig I/O
Dig IFDig IFDig IFDig IFDig IFDig IFDig IFDig IFDig IFDig IFDig IFDig IFDig IFDig IFDig IFDig IF
MCMS High-Level Block Diagram
Multi-ChannelTransmitter(MCT)
Multi-ChannelReceiver(MCR)
cPCI
Embedded PC
Clock & LO Synthesis & Distribution
Dig I/O QDUC RFUCDig I/O QDUC RFUCDig I/O QDUC RFUCDig I/O QDUC RFUC
RFDCRFDCRFDCRFDCRFDCRFDCRFDCRFDCRFDCRFDCRFDCRFDCRFDCRFDCRFDCRFDC
Agg
rega
tion
& C
orne
r Tur
ning
cPC
I
Mat
rix C
hann
el U
nder
Tes
t
MCMS http://www.ece.vt.edu/swe/mcms
Multichannel Receiver (MCR)
MCMS http://www.ece.vt.edu/swe/mcms
Size: 55.9 cm (W) x 59.7 cm (D) x 99.0 cm (H)Weight: 90 kg (~200 lbs.)
RF Downconverter / Digitizer (RFDC)
MCMS http://www.ece.vt.edu/swe/mcms
MCR Digital Chassis
Daisy Chain #1(320 Mb/s LVDSSerial Bus)
Control In,Data Out
1.248 Gb/s LVDSfrom RFDC
Daisy Chain #2Daisy Chain #3Daisy Chain #4
MCR Digital Chassis
32-bitHigh-SpeedDIO Board
Digital IF Boards
“CornerTurner”Board
BW < 1.5 MHz:“Streaming” mode
BW > 1.5 MHz: “Burst” mode
MCMS http://www.ece.vt.edu/swe/mcms
Digital IF Board
LVDSRX
LVDSRX
O
E
I
QSHIFTFS/4
FIR,↓2
FIR,↓2
NCOM CIC+FIR,↓R
LVDSRX
LVDSTX
16K FIFO
A
A A
Altera Stratix EP1S10
Analog Devices AD6620
A
FS = 104 MSPS (Real)fc = 78 MHzBW = 40 MHz
FS = 52 MSPS (I/Q)fc = 0 MHzBW = 40 MHz
FS = 26 MSPS (I/Q)fc = 0 MHzBW = 20 MHz
FS = var. (I/Q)fc = 0 MHzBW = var.
From R
FDC D
aisy
Cha
in
MCMS http://www.ece.vt.edu/swe/mcms
-FS/4 Spectral Shift(104 / 4 = 26 MHz)
+27 MHz shifts to +1MHz
Filter Specs:•63-tap FIR,•12-bit coeff.,•12-bit in,•16-bit out,•20 MHz LP
Frequency Domain
Time Domain52 MSPS complexOutput of Fs/4 Downconversionis 16-bits (+/-32K)
Blue: 1Yellow: 100, averageYellow: 100, average
MCR Signal Path Demo
MCMS http://www.ece.vt.edu/swe/mcms
~70 dB
MCT: Direct Digital IF Synthesis
4-channel quadrature digital upconverter (QDUC) board using
the Analog Devices AD9857
Ch.1
From PC:I-Q
(symbols) or
arbitrary waveform
orsinusoid
parameters
Ch.2
Ch.3
Ch.4
RFUC
RFUC
RFUC
RFUC
200 MSPSsample clock
Example: Synthesized BW =12 MHz DSSS signal with RRC filtering,
upconverted to 1250 MHz
fc = 78 MHz
MCMS http://www.ece.vt.edu/swe/mcms
Measuring Wired MIMO Channels
“Wired” Full Rank
MCT MCR MCT MCR
com
bine
r
split
ter
“Wired” Keyhole
Eigenvalues of HH′
MCMS http://www.ece.vt.edu/swe/mcms
Measuring Actual MIMO Channels
Eigenvalues of HH′
4 x 4: Optical LOS Exists 4 x 4: Optical LOS Blockedusing 1 m x 2 m metal plate
• Indoor: Cluttered laboratory, approx 5 m x 10 m • About 2 meters between arrays• Transmit Array: 4 λ/4 monopoles, V-pol, 0.25λ spacing• Receive Array: same
MCMS http://www.ece.vt.edu/swe/mcms
MCMS Portability
MCMS stowed MCR set up(June 2005 Demo)
MCT
MCR
24V Battery Pack
MCMS http://www.ece.vt.edu/swe/mcms
HDTV497 MHz center6 MHz BW
IEEE 802.11b(11 Mb/s DSSS/CCK)2.41 GHz center20+ MHz BW
MCR “Front Panel” Observing
Examples of signals observed in the laboratory using a simple scanner whip antenna attached directly to an RFDC input jack
MCMS http://www.ece.vt.edu/swe/mcms
Efforts Underway / PlannedFixes & Improvements Pending:– RF upconverter tuning – Hammerhead DSP integration– Dynamic mode selection (consolidation to single FPGA code)– User software
Measurement Campaigns– 2.4 GHz x 40 MHz MIMO “channel library” (started)– Rank collapse phenomenology (hallways, corners) (imminent)– Site planning / array design project (planned)
Aeroflex Spinoff Projects
MCMS http://www.ece.vt.edu/swe/mcms
Acknowledgements
S. Ellingson OSU, now VT PI / Systems EngineerG. Hampson OSU, now CSIRO ElectronicsW. Theunissen OSU Electronics
B. Reynolds Aeroflex Aeroflex Program ManagerP. Bohley Aeroflex IntegrationS. Fisher Aeroflex ElectronicsW. Koehler Aeroflex Software
StudentsS. Horst OSU, now Ga Tech RF Design W. Taylor VT RF DesignM. Nuhfer VT Software
MCMS http://www.ece.vt.edu/swe/mcms
