Bladerf micro phase coherency for 4 channel coherent reception

[venky0108]

Hi,

I am trying to setup 4 channel phase coherent receiver with two Bladerf A4 SDR boards for Angle of Arrival(AoA) estimation setup. In the setup process following setup are performed:

1)Clock In of Board 1 & Clock out of Board 2 are connected for sharing the clock
2)Sample synchronization through Trigger functionality.Board 1 is made trigger master and Board 2 is made Trigger slave, J51-1 & J51-3 of both boards are connected
3)Four RX channels of SDR boards is fed with same signal through power divider.

Observations:

1)Frequency offset of the four channels are measured and they are same

Channel Mean Standard Deviation Min value Max Value range
Freq offset ch1 -478.7109375 38.80481412 -585.9375 -366.2109375 219.7265625
Freq offset ch2 -475.78125 38.89318775 -585.9375 -366.2109375 219.7265625
Freq offset ch3 -478.7109375 38.80481412 -585.9375 -366.2109375 219.7265625
Freq offset ch4 -475.78125 38.89318775 -585.9375 -366.2109375 219.7265625
Freq offset ch1 -476.953125 42.06525257 -585.9375 -366.2109375 219.7265625
Freq offset ch2 -472.8515625 38.76055174 -512.6953125 -366.2109375 146.484375
Freq offset ch3 -476.953125 42.06525257 -585.9375 -366.2109375 219.7265625
Freq offset ch4 -472.8515625 38.76055174 -512.6953125 -366.2109375 146.484375
Freq offset ch1 -472.8515625 39.8523658 -512.6953125 -366.2109375 146.484375
Freq offset ch2 -472.8515625 41.95083356 -512.6953125 -366.2109375 146.484375
Freq offset ch3 -472.8515625 39.8523658 -512.6953125 -366.2109375 146.484375
Freq offset ch4 -472.8515625 41.95083356 -512.6953125 -366.2109375 146.484375


2)Phase offset between channel 1 & 2, 1&3 , 1& 4, 3 & 4 are measured. Phase offset is not same with respect to channel .

Channel Mean Standard Deviation Min value Max Value range
phase offset ch1 & ch2 -138.96 2.144388025 -141 -128 13
phase offset ch1 & ch3 145.888 891.5005617 -4040 4011 8051
phase offset ch1 & ch4 119.64 901.8573759 -4002 4049 8051
phase offset ch3 & ch4 33.856 1.129275874 25 34 9
phase offset ch1 & ch2 -138.392 2.18319399 -140 -128 12
phase offset ch1 & ch3 8.896 684.6637694 -3582 3904 7486
phase offset ch1 & ch4 74.288 682.0492629 -635 3944 4579
phase offset ch3 & ch4 34.016 0.85775521 25 35 10
phase offset ch1 & ch2 -136.304 3.427474872 -140 -127 13
phase offset ch1 & ch3 -70.096 791.8313702 -4096 4197 8293
phase offset ch1 & ch4 -149.824 774.8225094 -4192 603 4795
phase offset ch3 & ch4 34.096 0.294591242 34 35 1

ch1 & Ch3 , Ch1 & Ch4 phase offset are random with huge standard deviation

[lengistonjorry]

Achieving phase coherency with a BladeRF Micro for four-channel coherent reception involves precise synchronization of the local oscillators across all channels. This is essential for applications such as direction finding, beamforming, and MIMO systems, where phase alignment directly impacts performance. The BladeRF Micro's architecture allows for such synchronization by using a shared reference clock and meticulous calibration procedures to align the phase of each channel. By ensuring that all channels operate in phase, it is possible to accurately combine signals received from multiple antennas, thereby enhancing the overall system capability to analyze and interpret the incoming signals coherently. Proper implementation involves both hardware configuration and software adjustments for Snapchat planets, often leveraging the BladeRF API and FPGA capabilities to achieve the desired phase alignment across the channels.







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