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Millimeter-wave (mmWave) communications and cell densification are the key techniques for the future evolution of cellular systems beyond 5G. Although the current mmWave radio designs are focused on hybrid digital and analog receiver array architectures, the fully digital architecture is an appealing option due to its flexibility and support for multi-user multiple-input multiple-output (MIMO). In order to achieve reasonable power consumption and hardware cost, the specifications of analog circuits are expected to be compromised, including the resolution of analog-to-digital converter (ADC) and the linearity of radio-frequency (RF) front end. Although the state-of-the-art studies focus on the ADC, the nonlinearity can also lead to severe system performance degradation when strong input signals introduce inter-modulation distortion (IMD). The impact of RF nonlinearity becomes more severe with densely deployed mmWave cells since signal sources closer to the receiver array are more likely to occur. In this work, we design and analyze the digital IMD compensation algorithm, and study the relaxation of the required linearity in the RF-chain. We propose novel algorithms that jointly process digitized samples to recover amplifier saturation, and relies on beam space operation which reduces the computational complexity as compared to per-antenna IMD compensation.
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Synthetic Diversity for Interference Mitigation in Widely Tunable Receiver Frontends
Dynamic spectrum access relies fundamentally on the ability to tune radio transceivers to frequencies that are deemed to be available. Consequently, radio hardware must support tuning over a wide range of frequencies. For the receiver, this precludes the use of fixed frontend filters to reject out-of-band interfering signals. Instead, widely tunable receivers rely on filtering after down-conversion either at IF or baseband. This approach relies on linearity and an ideal mixer to keep the desired signal and interfering signals separated. However, practical receivers exhibit non-linearity, phase noise, and oscillator spurs that cause mixing of the signal of interest and interfering signals. As a result, portions of the interfering signals may appear in the band of the desired signal; this causes interference that cannot be mitigated by filtering. Synthetic diversity mitigates this problem by combining analog and digital processing techniques. In the analog domain, the wide-band RF signal is passed through a passive, lossless multi-port diversity network. Each output from this network is then down-converted and digitized so that multiple versions of the signal are available at digital baseband. As the desired signal and the interfering signals experience different frequency response as they pass through the diversity network, it is possible to employ beam forming methods in digital baseband processing to mitigate the interfering signals while preserving the desired signal. The performance of the proposed synthetic diversity receiver is analyzed and it is shown that excellent interference rejection can be achieved. Rejection performance can be increased even further when the circuit elements in the diversity network can be adapted.
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- Award ID(s):
- 2029836
- PAR ID:
- 10578758
- Publisher / Repository:
- IEEE
- Date Published:
- ISBN:
- 979-8-3503-1764-0
- Page Range / eLocation ID:
- 561 to 564
- Format(s):
- Medium: X
- Location:
- Washington, DC, USA
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Conference Paper:
- https://doi.org/10.1109/DySPAN60163.2024.10632814
