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Everything in the world is being connected, and things are becoming interactive. The future of the interactive world depends on the future Internet of Things (IoT). Software-defined networking (SDN) technology, a new paradigm in the networking area, can be useful in creating an IoT because it can handle interactivity by controlling physical devices, transmission of data among them, and data acquisition. However, digital signage can be one of the promising technologies in this era of technology that is progressing toward the interactive world, connecting users to the IoT network through device-to-device communication technology. This article illustrates a novel prototype that is mainly focused on a smart digital signage system comprised of software-defined IoT (SD-IoT) and invisible image sensor communication technology. We have proposed an SDN scheme with a view to initiating its flexibility and compatibility for an IoT network-based smart digital signage system. The idea of invisible communication can make the users of the technology trendier to it, and the usage of unused resources such as images and videos can be ensured. In addition, this communication has paved the way for interactivity between the user and digital signage, where the digital signage and the camera of a smartphone can be operated as a transmitter and a receiver, respectively. The proposed scheme might be applicable to real-world applications because SDN has the flexibility to adapt with the alteration of network status without any hardware modifications while displays and smartphones are available everywhere. A performance analysis of this system showed the advantages of an SD-IoT network over an Internet protocol-based IoT network considering a queuing analysis for a dynamic link allocation process in the case of user access to the IoT network.

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A low-complexity frame synchronisation method for IEEE 802.15.4 systems is proposed. An autocorrelation function is utilised for reducing computational complexity for fine timing estimation instead of a cross-correlation function. To provide accurate estimation results, residual errors are compensated in the step of detecting start-offrame delimiter symbols. The complexity of the proposed method for fine timing estimation is <1/4 compared with the conventional crosscorrelation-based algorithm.Introduction: Low power consumption is a crucial aspect or requirement for wireless sensor communication systems such as those of IEEE 802.15.4 [1]. Particularly, in baseband processing, computational complexity is directly related to the power consumption [2]. Usually receivers detect desired packets using a frame synchronisation function that induces high computational complexity due to correlation of all incoming signals [3]. Thus, it is important to reduce the complexity of the synchronisation for low power consumption. According to previous works [2-6], the autocorrelation function (ACF) and the crosscorrelation function (CCF) have been utilised for synchronisation algorithms. The ACF-based algorithms measure signal similarity for periodically allocated identical signals in a preamble. The complexity of the ACF can be reduced by recursive calculation [2]. It means that the ACF computation is independent of the correlation length. However, the timing metric generates a plateau-shape envelope around correct frame timing. Because of the ambiguousness of the plateau, the timing metric cannot be used to decide accurate packet timing. Thus, the ACF has been just applicable to coarse timing estimation. Meanwhile, the CCF measures instantaneous signal energy between reference and incoming signals. The CCF produces an impulse-shape envelope at frame start timing, so the timing metric is available to fine timing estimation. However, number of CCF calculations depends on the correlation length. In this Letter, the ACF-based fine frame synchronisation method is proposed for direct sequence spread spectrum systems at the 2.4 GHz band [1]. Based on the characteristics of cyclic spreading sequences, a modified ACF algorithm is provided to find the transition timing from the preamble to start-of-frame delimiter (SFD). To guarantee estimation accuracy, an error compensation method is also provided. With the proposed method, the computational complexity of the fine timing estimation is significantly reduced by 1/4N O in comparison with the CCF, while performance degradation for frame detection is at most 0.5 dB under two-path Rayleigh fading channels.

We analyze the effect of the loopback signal on the equalization digital on-channel repeater (EDOCR) used for single frequency network (SFN), and propose a simple loopback canceller. Simulation results show that the proposed loopback canceller improves the convergence performance of the decision feedback equalizer (DFE) in the EDOCR by eliminating the loopback signal in advance instead of the DFE.