5G consists of a host of technologies that include mmWave frequencies and multiple antennas. Because mmWave signals must overcome losses not encountered at lower frequencies, the industry is moving to multiple antennas and phased-array technology that direct signals to their destination with higher power than today's omnidirectional signals. Testing such systems is difficult, but a startup out of NYU Tandon School of Engineering may just make channel emulation practical and affordable.
Started by post-doctoral research fellow Aditya Dhananjay and NYU faculty members Sundeep Rangan and Dennis Shasha, Millilabs has developed a system that uses off-the-shelf hardware that emulates both the transmission channel and the phased-array antennas needed to produce MIMO signals.
Because 3G and 4G signals are omnidirectional and operate at frequencies below 6 GHz, signal power is strong enough to overcome many transmission losses. Not so with mmWave signals starting at 24 GHz. EE Times spoke with Aditya Dhananjay about Millilabs and its technology.
Using PXI instruments, the Millilabs emulator (Figure 1) incorporates National Instruments FPGA cards that emulate the conditions that signals might encounter in a live situation. The system uses analog-to-digital converter (ADC) cards to emulate signals sent from an antenna. After signal processing is done with two FPGA cards, the digital signals go to digital-to-analog converters (DACs), which emulate signals from the receiving antennas.
Millilabs has developed a system that emulates multiple beamforming signals and their signal paths. Source: Millilabs/NYU.
According to Dhananjay, the FPGAs can adjust the following conditions:
- Noise figure
- Number of antenna elements. While the current system emulates up to 1,024 antennas, there is theoretically no limit.
- Spacing of antenna elements, such as λ/4 and λ/2
- Polarization (horizontal, vertical, and circular)
- Errors in phased arrays
- Beamforming vector and noise imperfections
- Phase noise
- System clocks (CMOS and crystal sources)
Dhananjay explained why this development is significant: "With traditional emulation, the cost of building an emulator scales linearly with the number of antenna elements. For example, emulating a 64-antenna system will need 64 times the amount of hardware than a single-antenna system. The MilliLabs Emulator supports beamforming with hundreds of antenna elements, which is our key technology."
By emulating antennas and the transmission channel, the Millilabs system eliminates the need for antenna arrays and their associated wires. Designers need only provide the analog or digital signals from a transmitter and provide a receiver (Figure 2).
The Millilabs emulator emulates both the channel and the transmit/receive phased-array antennas. Source: Millilabs."By virtue of the joint channel and front-end emulation, the hardware cost doesn't change as you increase the number of antennas," said Dhananjay. "The relative cost savings depends on the number of antennas compared to traditional systems."
You can read more of the technical details in NYU emulator advances 5G technology towards reality by Steve Taranovich.
—Martin Rowe covers test and measurement for EE Times and EDN. Contact him at
[email protected] 
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