mmWave Prototyping

Millimeter-wave (mmWave) communication is considered to be one of the key enabler for higher throughput. However, the high path loss and the severe scattering make the mmWave difficult to reach to the receiver. To address issue, the usage of beamforming and the fast procedure to align beams between the transmitter and the receiver are necessary.

Although various studies on the faster beam alignment have been reported, most studies verify their benefit by simulations. Testbeds and field trials are very important steps towards the realization and approval of those concepts, but the practical implementation of the mmWave system testbed is another challenge due to new hardware constraints for ensuring a high frequency large bandwidth transmission and deploying large antenna arrays. In this context, it is necessary to reconcile between technologies of system hardware and signal processing algorithm to accomplish the successful mmWave beam management research.

For a demonstration of mmWave communication, we constructed 28 GHz mmWave testbed. We can divide our mmWave prototyping history into three generations.

In 2019, we built the first mmWave testbed, which operates at 13.8 GHz. Back then, only few mmWave RF devices were available, so we could not reach our original target frequency, 28 GHz. Fig. (1) is a picture of the 13.8 GHz beamforming hardware. Both transmitter and receiver are composed of two analog beamformers (ADAR-1000), 1 x 8 ULA, NI USRP, and up/down converters. With this testbed, we demonstrated the location-aware beam alignment that drastically reduces beam search. Fig. (2) shows that the location-aware beam alignment makes the beams well-aligned when the receiver is moving.

Fig. 1. A picture of the first mmWave testbed

Fig. 2. Change in the beam index throughout time

In the second generation (2020), we constructed the second mmWave testbed that operates at 28 GHz. Thanks to development of RF devices, we could use new chip (ADMV-4801) and 4 x 16 UPA. As in Fig. (3), the 28 GHz beamforming testbed was carried on Jackal UGV to make mobility. With the second testbed, we demonstrated the location-aware beam tracking. The experiment results in Fig. (4) show that the throughput does not fluctuate over time due to the location-aware beam tracking. This result was published in IEEE Communications Magazine (https://ieeexplore.ieee.org/document/9530500).

Fig. 3. A picture of the second mmWave testbed

Fig. 4. Experimental environment for beam tracking test and several link-level performances for static and mobility conditions

In the third generation (2022 ~ ongoing), we developed a completely new end-to-end 5G mmWave system testbed. This testbed is configured to implement the real-world demonstration of a Vision-Aided 28 GHz mmWave transmission with a joint Tx-Rx beam tracking. A full end-to-end 5G mmWave system testbed is presented in Fig. (5). The testbed configuration is composed of PXI transciever, which includes CPU, FPGAs, ADC/DAC, IF modules, and RF modules which include phased array antenna and mmWave converter, and RGB camera for vision-information acquisition and portable battery. Through our testbed, we could generate 28.5 GHz mmWave signal and 64-QAM OFDM waveform with 800 MHz bandwidth. As shown in Fig (6), we verified our beam tracking method that it shows an improvement compared to the case without beam tracking in terms of throughput and RSS. This result was published in the 20th ACM International Conference on Mobile Systems, Applications, and Services (MobiSys 2022).

(https://dl.acm.org/doi/abs/10.1145/3498361.3538652)

Fig. 5. Full end-to-end real-time 5G 28 GHz mmWave testbed for demonstration

Fig. 6. Communication performance in terms of measured link throughput and normalized RSS throughout Tx-Rx misalignment angle

[Related publication]

J. Bang, H. Chung, J. Hong, H. Seo, J. Choi and S. Kim, “Millimeter-Wave Communications: Recent Developments and Challenges of Hardware and Beam Management Algorithms”, accepted to IEEE Commun. Mag., vol. 59, no. 8, pp. 86-92, Aug.2021.
J. Bang, S. Baek, H. Kim, H. Chung, J. Choi, S. Kim, “Vision-aided 28 GHz mmWave transmission with joint tx-rx beam tracking for 5G communications”, accepted to 2022 ACM MobiSys, Jun.2022.