Abstract
Full-duplex (FD) wireless - simultaneous transmission and reception on the same frequency - is a promising technique that can significantly improve spectrum efficiency and reduce communication latency in future wireless networks. To enable FD operation, the powerful self-interference (SI) signal leaking from the transmitter (TX) into the receiver (RX) needs to be suppressed and canceled to an extreme degree at the antenna interface as well as in the RF/analog and digital domains. Various approaches to achieve TX-RX isolation at the antenna interface and SI cancellation (SIC) in the RF/analog and digital domains have been demonstrated, with a focus on using bench-top off-the-shelf components. Recent advances in integrated circuit (IC) implementations of various types of shared antenna interfaces and cancellers in the RF and/or analog baseband (BB) domains have further pushed the frontier of realizing FD wireless in small-form-factor/hand-held devices. Moreover, it is still important to fundamentally study the SIC performance that can be achieved by different types of cancellers. In this paper, we present a first-of-its-kind comprehensive overview on the implementation and comparison of various state-of-the-art integrated shared antenna interfaces and SI cancellers in both the RF and analog BB domains. We define two figures of merit (FOM) for the IC-based shared antenna interfaces and SI cancellers, which capture various design considerations and performance tradeoffs including the achievable isolation/SIC, bandwidth, noise figure degradation, TX/SI power handling, and power consumption. In particular, we focus on two types of integrated shared antenna interfaces including electrical-balance duplexers and circulators. We also discuss two types of SI cancellers based on the time-domain and frequency-domain approaches, which respectively employ parallel delay lines and bandpass filters to emulate the SI channel. Based on realistic measurements, we perform extensive numerical evaluations to illustrate and compare the achievable RF SIC performance in different scenarios, as well as discuss various design tradeoffs. Finally, we provide an overview of the IC-based implementations and performance evaluations of both types of cancellers based on our recent work.
Highlights
E XISTING wireless systems such as Wi-Fi and cellular networks operate in half-duplex mode, where radios transmit and receive in different time slots or frequency channels
In the first part of this paper, we focus on integrated shared antenna interface and integrated SI cancellers in the RF and analog baseband (BB) domains, which can provide TX-RX isolation and SI cancellation (SIC), respectively, and largely alleviate the dynamic range requirements at the RX
We present a detailed overview of two types of SI cancellers using different approaches: (i) time-domain cancellers employing parallel delay line (DL) taps, FIGURE 1
Summary
E XISTING wireless systems such as Wi-Fi and cellular networks operate in half-duplex mode, where radios transmit and receive in different time slots (i.e., time-division duplexing, TDD) or frequency channels (i.e., frequency-division duplexing, FDD). Gyrator and using periodically loaded inductors to realize transmission lines, both the chip area and power consumption of the circulator can be largely reduced Using these techniques, an integrated circulator that achieves >40 dB isolation across 92 MHz bandwidth for a wide range of antenna impedance up to a VSWR of 2.33 was presented in [24], [25]. Received signals from the antenna directly propagate to the receiver through the transmission lines The prototype using this technique provides an isolation of >25 dB from 0.3–1.6 GHz. In addition, unlike typical shared antenna interfaces that operate at RF, duplexing operation for enabling FD wireless has been demonstrated at baseband frequencies [80], [81]. The transfer functions of a time-domain and frequency-domain SI
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