MCMS. A Flexible 4 x 16 MIMO Testbed with 250 MHz 6 GHz Tuning Range

Transcription

1 A Flexible 4 x 16 MIMO Testbed with 250 MHz 6 GHz Tuning Range Steve Ellingson Mobile & Portable Radio Research Group (MPRG) Dept. of Electrical & Computer Engineering Virginia Polytechnic Institute & State University ellingson@vt.edu 2005 IEEE Int l Antennas & Propagation Symposium

2 A One-Slide MIMO Primer Generalized Shannon Bound: Mean SNR per RX antenna Capacity [b/s] Bandwidth [Hz] Matrix of Channel Coefficients [ N R x N T ] N T =1 or N R =1 rank{hh }=1 C log 2 N N T >1 and N R >1 and rank{hh }>1 C N Up to min{n T,N R } independent MIMO subchannels, each with SNR the associated eigenvalues of HH

3 An Example of a Nice MIMO Channel Ideal N T =2 Measured N T =2 Ideal N T =8 Measured N T =8 Eigenvalues of HH Capacity (Γ =10) TX site behind building View from RX site 2.4 GHz N R =8 Actually, uncommon that results turn out this well

4 Examples of Problematic MIMO Channels 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

5 Equipment Used to Obtain This Data: Front View of Rack (2001) Rear 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

6 Instrument Wish List ( 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 MHz Cover as many MIMO candidate bands as possible

7 Matrix Channel Measurement System () Project History NSF/MRI proposal Jan 2002 Joint effort with Aeroflex Corp. Project start: October month proof-of-concept Ohio State University 15-month development Aeroflex, OSU, & Virginia Tech Aeroflex delivery: December 2004; now at Virginia Tech Operational, although some development continues

8 High-Level Block Diagram Embedded PC cpci Multi- Channel Transmitter (MCT) Dig I/O QDUC RFUC Dig I/O QDUC RFUC Dig I/O QDUC RFUC Dig I/O QDUC RFUC Clock & LO Synthesis & Distribution Matrix Channel Under Test Clock & LO Synthesis & Distribution Aggregation & Corner Turning Dig I/O cpci Quad DSP Embedded PC Multi- Channel Receiver (MCR)

9 Multichannel Receiver (MCR) Size: 55.9 cm (W) x 59.7 cm (D) x 99.0 cm (H) Weight: 90 kg (~200 lbs.)

10 RF Downconverter / Digitizer ()

11 MCR Digital Chassis Digital IF Boards Gb/s LVDS from Daisy Chain #1 (320 Mb/s LVDS Serial Bus) Control In, Data Out BW < 1.5 MHz: Streaming mode BW > 1.5 MHz: Burst mode Corner Turner Board MCR Digital Chassis Daisy Chain #2 Daisy Chain #3 Daisy Chain #4 32-bit High-Speed DIO Board

12 Digital IF Board From LVDS RX LVDS RX FS = 52 MSPS (I/Q) fc = 0 MHz BW = 40 MHz Altera Stratix EP1S10 O I SHIFT E FS = 26 MSPS (I/Q) fc = 0 MHz BW = 20 MHz FS/4 A Q FIR, 2 FIR, 2 A 16K FIFO A A NCOM CIC+FIR, R Analog Devices AD6620 LVDS RX LVDS TX Daisy Chain FS = 104 MSPS (Real) fc = 78 MHz BW = 40 MHz FS = var. (I/Q) fc = 0 MHz BW = var.

13 MCR Signal Path Demo Time Domain 52 MSPS complex Output of Fs/4 Downconversion is 16-bits (+/-32K) Filter Specs: 63-tap FIR, 12-bit coeff., 12-bit in, 16-bit out, 20 MHz LP ~70 db -F S /4 Spectral Shift (104 / 4 = 26 MHz) +27 MHz shifts to +1MHz Frequency Domain Blue: 1 Yellow: 100, average

14 MCT: Direct Digital IF Synthesis 200 MSPS sample clock From PC: I-Q (symbols) or arbitrary waveform or sinusoid parameters fc = 78 MHz Ch.1 RF UC Ch.2 RF UC Ch.3 RF UC Ch.4 RF UC Example: Synthesized BW =12 MHz DSSS signal with RRC filtering, upconverted to 1250 MHz 4-channel quadrature digital upconverter (QDUC) board using the Analog Devices AD9857

15 Measuring Wired MIMO Channels Eigenvalues of HH Wired Full Rank Wired Keyhole MCT MCR MCT MCR combiner splitter

16 Measuring Actual MIMO Channels 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 Eigenvalues of HH 4 x 4: Optical LOS Exists 4 x 4: Optical LOS Blocked using 1 m x 2 m metal plate

17 Portability 24V Battery Pack MCR MCT stowed MCR set up (June 2005 Demo)

18 MCR Front Panel Observing HDTV 497 MHz center 6 MHz BW IEEE b (11 Mb/s DSSS/CCK) 2.41 GHz center 20+ MHz BW Examples of signals observed in the laboratory using a simple scanner whip antenna attached directly to an input jack

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20 Efforts Underway / Planned Fixes & 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

21 Acknowledgements S. Ellingson OSU, now VT PI / Systems Engineer G. Hampson OSU, now CSIRO Electronics W. Theunissen OSU Electronics B. Reynolds Aeroflex Aeroflex Program Manager P. Bohley Aeroflex Integration S. Fisher Aeroflex Electronics W. Koehler Aeroflex Software Students S. Horst OSU, now Ga Tech RF Design W. Taylor VT RF Design M. Nuhfer VT Software