Chunqing Zhang

Passive and Active Electrical Balance Duplexers

Electrical balance duplexing enables simultaneous transmit and receive from a single antenna; however, the transmit-to-receive isolation depends on the ability of the balancing algorithm to determine the correct balancing impedance. A novel balancing algorithm based on in situ characterization of the duplexer self-interference channel is proposed. The algorithm requires no a priori knowledge of the antenna impedance or hybrid junction characteristics and automatically compensates for circuit imperfections. A novel balancing network implementation that uses active signal injection is also proposed. A hardware prototype implementing the proposed balancing algorithm and combining passive and active balancing techniques has achieved 81.5-dB isolation over an 80-MHz bandwidth.

A Widely Tunable Full Duplex Transceiver Combining Electrical Balance Isolation and Active Analog Cancellation

Electrical balance duplexers can provide high transmit-to-receive isolation whilst facilitating transmission and reception from a single antenna, can be implemented on-chip, and are widely tunable, making this an attractive technology for implementing full duplex architectures in small form factor devices. This paper presents measurements from a novel hardware prototype full-duplex transceiver architecture combining electrical balance and active analog cancellation. The prototype duplexer achieves >80dB transmit-to-receive isolation over a 20MHz bandwidth at both 890MHz and 1890MHz, exceeding the performance of antenna separation architectures where the antenna isolation is limited to the levels achievable in hand held devices.

Electrical Balance Duplexer Field Trials in High-Speed Rail Scenarios

Electrical balance duplexers (EBDs) present a potential alternative to the fixed-frequency duplexing filters used for frequency division duplexing in cellular handset radio frequency front ends. However, the transmit-to-receive (Tx–Rx) isolation can be affected by interaction between the antenna and the environment, and therefore, the EBDs balancing impedance must adaptively track time-domain antenna impedance variation. A rail scenario presents a potentially demanding use case for an EBD, as fast moving trains in the vicinity of the antenna may cause dynamically changing reflections, which can be received as self-interference. In this paper, measured dynamic antenna reflection coefficients at 745 and 1900 MHz from train mounted antennas are included in the EBD circuit simulations in order to investigate the resulting variation in Tx–Rx isolation, and determine requirements for balancing impedance adaptation. This paper also presents the results from rail-based field trials of a hardware prototype EBD, which implements real-time antenna impedance tracking. Results show that the rail scenario does result in variation in Tx–Rx isolation, but that rebalancing the EBD at the intervals of 5 ms was sufficient to maintain >50 dB isolation for ~95% of the time.

Flexible duplex transceivers for 5G and beyond wireless access

There is now significant interest in the use of signal cancellation based architectures in an attempt to replace frequency domain filtering within the duplexing function for next generation wireless transceivers. This approach can potentially eliminate the need for band specific filters, which inhibits global operation of LTE handsets due to the diverse band plan. Further, using such methods in-band full-duplex communications is also possible, thus potentially doubling the spectrum efficiency when compared with conventional techniques.