Wireless systems which can simultaneously transmit
and receive (STAR) are gaining significant academic and
commercial interest due to their wide range of applications such
as full-duplex (FD) wireless communication and FMCW radar.
FD radios, where the transmitter (TX) and the receiver (RX)
operate simultaneously at the same frequency, can potentially
double the data rate at the physical layer and can provide many
other advantages in the higher layers. The antenna interface of
an FD radio is typically built using a multi-antenna system, or
a single antenna through a bulky magnetic circulator or a lossy
reciprocal hybrid. However, recent advances in CMOS-integrated
circulators through spatio-temporal conductivity modulation
have shown promise and potential to replace traditional bulky
magnetic circulators. However, unlike magnetic circulators,
CMOS-integrated non-magnetic circulators will introduce some
nonlinear distortion and spurious tones arising from their clock
circuitry. In this work, we present an FD radio using a highly
linear CMOS integrable circulator, a frequency-flat RF canceler,
and a USRP software-defined radio (SDR). At TX power level of
+15 dBm, the implemented FD radio achieves a self-interference
cancellation (SIC) of +55 dB from the circulator and RF canceler
in the RF domain, and an overall SIC of +95 dB together with
SIC in the digital domain. To analyze the non-linear phenomena
of the CMOS circulator, we calculated the link level data-rate
gain in an FD system with imperfect SIC and then extended
this calculation to count the effect of TX-RX non-linearity of the
circulator. In addition, we provide a qualitative discussion on
the spurious tone responses of the circulator due to the clocking
imperfections and non-linearity.
Index Terms—Circulator, CMOS, conductivity modulation,
full-duplex, non-reciprocity, self-interference cancellation.
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An Experiment-Based Comparison between Fully Digital and Hybrid Beamforming Radio Architectures for Many-Antenna Full-Duplex Wireless Communication
Full-duplex (FD) communication in many-antenna base stations (BSs) is hampered by self-interference (SI). This is because a FD node’s transmitting signal generates significant interference to its own receiver. Recent works have shown that it is possible to reduce/eliminate this SI in fully digital many-antenna systems, e.g., through transmit beamforming by using some spatial degrees of freedom to reduce SI instead of increasing the beamforming gain. On a parallel front, hybrid beamforming has recently emerged as a radio architecture that uses multiple antennas per FR chain. This can significantly reduce the cost of the end device (e.g., BS) but may also reduce the capacity or SI reduction gains of a fully digital radio system. This is because a fully digital radio architecture can change both the amplitude and phase of the wireless signal and send different data streams from each antenna element. Our goal in this paper is to quantify the performance gap between these two radio architectures in terms of SI cancellation and system capacity, particularly in multi-user MIMO setups. To do so, we experimentally compare the performance of a state-of-the-art fully digital many antenna FD solution to a hybrid beamforming architecture and compare the corresponding performance metrics leveraging a fully programmable many-antenna testbed and collecting over-the-air wireless channel data. We show that SI cancellation through beam design on a hybrid beamforming radio architecture can achieve capacity within 16% of that of a fully digital architecture. The performance gap further shrinks with a higher number of quantization bits in the hybrid beamforming system.
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- NSF-PAR ID:
- 10315825
- Date Published:
- Journal Name:
- Electronics
- Volume:
- 11
- Issue:
- 1
- ISSN:
- 2079-9292
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Wireless systems which can simultaneously transmit and receive (STAR) are gaining significant academic and commercial interest due to their wide range of applications such as full-duplex (FD) wireless communication and FMCW radar. FD radios, where the transmitter (TX) and the receiver (RX) operate simultaneously at the same frequency, can potentially double the data rate at the physical layer and can provide many other advantages in the higher layers. The antenna interface of an FD radio is typically built using a multi-antenna system, or a single antenna through a bulky magnetic circulator or a lossy reciprocal hybrid. However, recent advances in CMOS-integrated circulators through spatio-temporal conductivity modulation have shown promise and potential to replace traditional bulky magnetic circulators. However, unlike magnetic circulators, CMOS-integrated non-magnetic circulators will introduce some nonlinear distortion and spurious tones arising from their clock circuitry. In this work, we present an FD radio using a highly linear CMOS integrable circulator, a frequency-flat RF canceler, and a USRP software-defined radio (SDR). At TX power level of +15 dBm, the implemented FD radio achieves a self-interference cancellation (SIC) of +55dB from the circulator and RF canceler in the RF domain, and an overall SIC of +95dB together with SIC in the digital domain. To analyze the non-linear phenomena of the CMOS circulator, we calculated the link level data-rate gain in an FD system with imperfect SIC and then extended this calculation to count the effect of TX-RX non-linearity of the circulator. In addition, we provide a qualitative discussion on the spurious tone responses of the circulator due to the clocking imperfections and non-linearity.more » « less
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- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3390/electronics11010059
