# An Efficient Relayed Broadcasting Based on the Duplication Estimation Model for IoT Applications
## 1 Introduction  
The recent advances in Internet of Things (IoT) technologies have introduced many emerging applications [1; 2; 3; 4]. We consider that a relay-based broadcasting is one of the key enabling technologies for IoT services, which can be used to propagate traffic to many unspecified nodes located beyond the transmission range of a source node. In this type of traffic spreading called flooding or relayed broadcasting (In this study, we use two terms: \"flooding\" and \"relayed broadcasting\" interchangeably), all of the nodes work as receivers and at the same time, rebroadcast the received frames to adjacent nodes. In particular, we consider several typical IoT services (data service, public safety [5], and social network [6]) that can be realized by the relayed broadcasting as shown in Figure 1. For example, files can be distributed or shared among a large number of users in a conference hall (Figure 1a) or an emergency alarm can be propagated to many users to provide immediate first aid in a hospital or disaster relief environment (Figure 1b). As shown in Figure 1c, the flooding can also be used to provide social messages or location-based marketing information to users in a community or shopping mall. In addition, the flooding can be effectively used to disseminate traffic in wireless sensor networks (WSN) and vehicular ad hoc networks or in device-to-device communication [7; 8]. A common feature of these services is that the data should be delivered in a timely manner to as many users as possible, even if the network is temporarily set up without the aid of an appropriate infrastructure. Meanwhile,most IoT devices are equipped with the wireless local area network (WLAN) interface [9] and their number is growing continuously. They operate in unlicensed bands which are free of charge. As a result, it can be expected that the flooding in WLANs can be an attractive and cost-effective way to enable various IoT services. Despite the various advantages of flooding, it is faced with a fundamental problem in that a large number of duplicate frames are unnecessarily transmitted, which can lead to severe collisions and/or interference; this is referred to as a _broadcast storm problem_[10]. Accordingly, the reliability of the frame transmission degrades and the dissemination time of the traffic increases. The primary cause of this problem is the absence of a centralized control mechanism, which incurs a significant signaling overhead and is difficult to implement in WLANs. Furthermore, as the density of the nodes increases, this problem becomes worse if the transmission is not properly suppressed. To solve this problem, it is essential to establish a reasonable criterion for suppressing the transmission of duplicate frames. Various criteria have been proposed in the literature, like a threshold value for the number of duplicate frames or the probability depending on the number of adjacent nodes. However, they have not successfully dealt with the trade-off between transmission reliability and traffic dissemination time because they could not tightly ensure the reliability without increasing the delivery time or they intended to decrease the traffic dissemination time at the cost of reliability. Furthermore, the values of these criteria were set in a heuristic way without systematic and theoretical grounds and it is difficult to estimate their optimal values in various dynamic network environments. In this paper, we introduce an effective criterion for flooding suppression called the _duplication ratio_ to provide the reliable and fast propagation of traffic. The duplication ratio is related to the probability that adjacent nodes have already received a specific frame, and it is modeled as a function of the number of duplicate receptions. It is used to determine the probability that each node attempts or abandons the relaying of a frame, thus the flooding of frames is suppressed in a distributed and probabilistic manner depending on the duplication ratio.