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A Single RF Channel Smart Antenna Receiver Array with Digital Beamforming

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A Single RF Channel Smart Antenna Receiver Array with Digital Beamforming A Single RF Channel Smart Antenna Receiver Array with Digital Beamforming Darren Goshi, Yuanxun (Ethan) Wang, Tatsuo Itoh University of California, Los Angeles Electrical Engineering Dept. Los Angeles, CA University of California, Los Angeles Single RF Channel Smart Antenna System LPF ADC LNA Mixer LPF ADC Digital MUX DEMUX Beam- Former LPF ADC Antenna Single RF Array Channel IF/Baseband Processing ¾MUX reduces N-channels (LNAs, Mixers) to 1 ¾Flexibility in IF/baseband processing – analog or digital DEMUX ¾Digital Beamforming in MATLAB environment University of California, Los Angeles System Features 9 Reduction in costly RF hardware 9 Space reduction 9 Reduction in power dissipation 9 Maintains complete functionality as with typical smart antenna arrays University of California, Los Angeles Traditional DBF Smart Antenna System LNAs Mixers LPF ADC LPF ADC Digital Signal Processing / Beamforming LPF ADC ¾N-channel array requires N individual receiver chains ¾Each channel must be well matched and calibrated University of California, Los Angeles System Principles Switching waveform Г=1 (when switch is open) ¾SMILE (Spatial MultIplexing of Local Elements) scheme 9 Sequential switching samples signal at each element 9 Sampling rate greater than Nyquist rate 9 Parallel feed network retains all signal information 9 Sampling frequency limits signal modulation bandwidth University of California, Los Angeles System Principles Sampling Frequency: fBNs ≥× LPF Cutoff Frequency: BB <<−ff 22lpf s University of California, Los Angeles System Principles 0.5 0 -0.5 18 19 20 21 22 23 24 25 0.5 o 0 ¾Baseband data recovery -0.5 18 19 20 21 22 23 24 25 0.5 0 9 Non-conventional feed Array at 0 -0.5 18 19 20 21 22 23 24 25 0.5 network properly retains 0 -0.5 18 19 20 21 22 23 24 25 time µs phase information 0.5 0 -0.5 9 Allows use of advanced 18 19 20 21 22 23 24 25 0.5 o 0 beamforming and DOA -0.5 18 19 20 21 22 23 24 25 0.5 0 Array at 30 Array algorithms -0.5 18 19 20 21 22 23 24 25 0.5 0 -0.5 18 19 20 21 22 23 24 25 time µs University of California, Los Angeles 4-Element Prototype Hardware ¾LNA MUX 9 NEC32485C 4-Element Antenna Array Pseudomorphic HJ FET (LNAs) as switching element MUX 9 Low-noise switching improves overall noise figure Feed Network with compared with passive Single RF Output switch 9 No current required to LNA MUX with patch drive switching antenna element at 5.8 GHz University of California, Los Angeles Non-conventional Feed Network Non-conventional array feed network ¾Always Matched Feed Network 9 Only one active channel at each instant 9 All lines at T-junction matched to Zo 9 No loss compared with 6 dB loss of Wilkinson dividers University of California, Los Angeles Circuit Schematic From Antenna Gate Bias LNA ¾Multiplexing Hardware Circuit NE32485C HJFET 9 Tank circuit adds isolation sacrificed with non-conventional Tank Circuit feed network 9 Switch reference must be l λ/2 precisely matched to feed network Switch Zo Reference 3λ/2 Γ≈1 when off Zo Z o To Single RF Channel University of California, Los Angeles Single Source Testbed Setup Antenna chamber SMILE array LNA Horn antenna LO RF Gen Digital PC Data oscilloscope acquisition University of California, Los Angeles Two Source Testbed Setup RF Gen RF Gen Horn antenna Horn antenna SNOI SOI SMILE array LNA LO Digital PC Data oscilloscope acquisition University of California, Los Angeles Beamforming Performance Synthesized Beam Patterns ¾Digital Beamforming 9 Synthesized beamforming LNA MUX Switching accomplished in DSP 0 0 -40 40 ¾FET Switching Benefits -5 9 Fast switching with FET -10 increases possible data rate Amplitude [dB] Amplitude -15 9 Broader Symmetric Scan -20 Range -25 9 Lower sidelobes -80 -70 -60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 Theta [deg] University of California, Los Angeles Digital Data Recovery Demodulated Data 0.3 0.2 0.1 0 -0.1 -0.2 0 1 2 3 4 5 6 7 8 9 10 After Digital Beamforming 0.2 0.1 0 -0.1 -0.2 0 1 2 3 4 5 6 7 8 9 10 Time µs 200 kbps 600 kbps 1 Mbps ¾Digital Data 9 BPSK modulated carrier 9 Compare demodulation before and after applying DBF 9 Digital beamforming algorithm coherently sums all channels University of California, Los Angeles DOA Estimation and Synthesized Patterns Single Source 0 Synthesized Pattern DOA estimation -5 ¾DOA Estimation -10 9 Proper recovery of IF channel data -15 allows advanced beamforming -20 algorithms and DOA estimation -25 9 MUSIC algorithm detects proper -100 -80 -60 -40 -20 0 20 40 60 80 100 Angle Two Sources direction of signals 0 ¾Synthesized Beamforming -5 -10 9 Beam formed indirection of source -15 9 Null formed in direction of unwanted -20 signal -25 Synthesized Pattern DOA estimation -30 -100 -80 -60 -40 -20 0 20 40 60 80 100 Angle University of California, Los Angeles Spatial Filtering Before Digital Beamforming 0.3 Single Source: 0.2 0.1 0 -0.1 -0.2 -0.3 0 5 10 15 20 25 30 35 40 45 50 After Digital Beamforming 0.3 0.2 0.1 0 -0.1 -0.2 -0.3 0 5 10 15 20 25 30 35 40 45 50 Time, us ¾Single Source Data Recovery 9 Coherent summation recovers a much clearer pattern 9 Results more evident for angles farther off broadside University of California, Los Angeles Spatial Filtering Before Digital Beamforming 0.3 Two Sources: 0.2 0.1 0 -0.1 -0.2 -0.3 0 5 10 15 20 25 30 35 40 45 50 After Digital Beamforming 0.3 0.2 0.1 0 -0.1 -0.2 -0.3 0 5 10 15 20 25 30 35 40 45 50 Time µs ¾Two Source Data Recovery 9 Incoherent demodulation does not resemble a digital pattern 9Interference ‘nulling’ demonstrates spatial filtering University of California, Los Angeles Conclusion ¾Measured 20 MHz switching rate ¾DOA Estimation and Beamforming ¾Recovered up to 1 Mbps digital data ¾Demonstrated full smart antenna functionality University of California, Los Angeles Other Works ¾Slot Antenna Based SMILE Array 9 Compact design 9 Series fed PIN diode switching ¾2-D Configuration 9 Increase scanning flexibility for possible radar application University of California, Los Angeles.
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