Apoptosis requires recruitment of caspases by receptor-associated adaptors through homophilic interactions between the CARDs (caspase recruitment domains) of adaptor proteins and prodomains of caspases. We have solved the CARD structure of the RAIDD adaptor protein that recruits ICH-1/caspase-2. It consists of six tightly packed helices arranged in a topology homologous to the Fas death domain. The surface contains a basic and an acidic patch on opposite sides. This polarity is conserved in the ICH-1 CARD as indicated by homology modeling. Mutagenesis data suggest that these patches mediate CARD/CARD interaction between RAIDD and ICH-1. Subsequent modeling of the CARDs of Apaf-1 and caspase-9, as well as Ced-4 and Ced-3, showed that the basic/acidic surface polarity is highly conserved, suggesting a general mode for CARD/CARD interaction.

In this article, we propose a semi-blind full-duplex (FD) amplify-and-forward (AF) relay system with adaptive self-interference (SI) processing assisted by independent component analysis (ICA) for low-latency and high-reliability (LLHR) Internet of Things (IoT). The SI at FD relay is not necessarily canceled as much as possible like the conventional approaches, but is canceled or utilized based on a signal-to-residual-SI ratio (SRSIR) threshold at relay. According to the selected SI processing mode at relay, an ICA-based adaptive semi-blind scheme is proposed for signal separation and detection at destination. The proposed FD relay system not only features reduced signal processing cost of SI cancelation but also achieves a much higher degree of freedom in signal detection. The resulting bit error rate (BER) performance is robust against a wide range of SRSIR, much better than that of conventional FD systems, and close to the ideal case with perfect channel state information (CSI) and perfect SI cancelation. The proposed system also requires negligible spectral overhead as only a nonredundant precoding is needed for ambiguity elimination in ICA. In addition, the proposed system enables full resource utilization with consecutive data transmission at all time and same frequency, leading to much higher throughput and energy efficiency than the time-splitting and power-splitting-based self-energy recycling approaches that utilize only partial resources. Furthermore, an intensive analysis is provided, where the SRSIR thresholds for the adaptive SI H. Duan and Y. Jiang are with the

Ultra-reliable and low-latency communication (URLLC) is one of the key use cases of the fifth generation (5G) wireless communications to facilitate specific application scenarios with stringent latency and reliability demands, such as industrial automation and Tactile Internet. A full-duplex (FD) relay with simultaneous transmission and reception in the same frequency band is an effective approach to enhance the reliability of cell-edge user terminals, by significantly suppressing self-interference (SI). However, the signal processing latency at FD relay due to SI cancellation, referred to as relaying latency, takes a significant part in the end-to-end latency, and therefore should be minimized, while guaranteeing high reliability. In this article, we first present an up-to-date overview of the end-to-end latency for an FD relay system, addressed on physical layer challenges. We investigate the possible solutions in the literature to achieve the goal of URLLC. The efficient solution is to allow a simple amplify-and-forward (AF) FD relay mode with low-complexity SI radio frequency and analog cancellations, and process the residual SI alongside the desired signal at base station in an adaptive manner, rather than being cancelled at relay in digital domain. Also, the residual SI can be utilized at base station to enhance the reliability and the degree of freedom in signal processing, not necessarily being cancelled as much as possible. The FD relay assisted system with adaptive SI utilization or cancellation enables extended network coverage, enhanced reliability and reduced latency, compared to the existing overview work.

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