This paper proposes a novel radio access scheme that uses duplicated transmission via multiple frequency channels to achieve mission critical Internet of Things (IoT) services requiring highly reliable wireless communications; the interference constraints that yield the required reliability are revealed. To achieve mission critical IoT services by wireless communication, it is necessary to improve reliability in addition to satisfying the required transmission delay time. Reliability is defined as the packet arrival rate without exceeding the desired transmission delay time. Traffic of the own system and interference from the other systems using the same frequency channel such as unlicensed bands degrades the reliability. One solution is the frequency/time diversity technique. However, these techniques may not achieve the required reliability because of the time taken to achieve the correct reception. This paper proposes a novel scheme that transmits duplicate packets utilizing multiple wireless interfaces over multiple frequency channels. It also proposes a suppressed duplicate transmission (SDT) scheme, which prevents the wastage of radio resources. The proposed scheme achieves the same reliable performance as the conventional scheme but has higher tolerance against interference than retransmission. We evaluate the relationship between the reliability and the occupation time ratio where the interference occupation time ratio is defined as the usage ratio of the frequency resources occupied by the other systems. We reveal the upper bound of the interference occupation time ratio for each frequency channel, which is needed if channel selection control is to achieve the required reliability.

We propose, in this article, the Hierarchical Behavior-Knowledge Space as an extension of Behavior-Knowledge Space. Hierarchical BKS utilizes ranked level individual classifiers, and automatically expands its behavioral knowledge in order to satisfy given reliability requirement. From the statistical view point, its decisions are as optimal as those of original BKS, and the reliability threshold is a lower bound of estimated reliability. Several comparisons with original BKS and unanimous voting are shown with some experiments.

Local Area Networks(LANs)are now being used all over the world. The need for cost-effective and high-speed communication services, such as LAN interconnections and large-volume file transfer of all types of data is rapidly increasing. At the same time, Internet services are spreading rapidly, and well soon see the construction of a cost-effective open computer network (OCN). Frame-relay and cell-relay technologies which can achieve higher-speed and higher-performance switching than packet switching, are therefore attracting much attention. Frame-relay technologies are also important because they provide an infrastructure for high-speed data communication as fast as 1. 5 Mbit/sec. Demand for these frame-relay network services have been increasing rapidly. We propose a cost-effective and highly reliable node architecture that we have developed at NTT. Our basic concept for this is based on the all-band switching node architecture which can provide both STM and ATM switches on the same hardware and software platforms, and can accommodate any type of node, such as STM nodes, and ATM nodes for B-ISDN. Our proposed architecture forms highly reliable frame-relay network infrastructure. By using a scale-flexibility building-block architecture, we can construct a small-scale node and a large-scale node cost-effectively. Next, the key technologies of highly reliable node architecture are presented. These are methods of changing over following function-units without frame-loss and/or cell-loss. We present two examples: frame-relay protocol processing units(PPUs)with an N+M-redundant architecture that consists of a number of acting PPUs(ACT)and a number of standby PPUs(SBY)waiting to become active, and duplicate ATM Mux/DemuX blocks(ATM MDXs)with a cell shaping buffer.