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This letter aims to analyze and optimize the status update performance in a grant-free random access system with massive multiple-input multiple-output. We analyze the status update process, and derive a closed-form approximate expression of the average age of information (AoI). Then, in the asymptotic case where the large number of antennas at the base station causes the packet error rate to approach zero, we jointly optimize access control and pilot length to reduce the average AoI. Simulation and numerical results verify the correctness of the theoretical analysis, and show that the proposed scheme can achieve the same performance as the exhaustive search scheme and outperforms the benchmark ones.

Massive machine type communications (mMTC) have been regarded as promising applications in the future. One main feature of mMTC is short packet communication. Different from traditional long packet communication, short packet communication suffers from transmission rate degradation and a significant error rate is introduced. In this case, traditional resource allocation scheme for mMTC is no longer applicable. In this paper, we explore resource allocation for cellular-based mMTC in the finite block- length regime. First, to mitigate the load of the base station (BS), we establish a framework for cellular- based mMTC, where MTCGs reuse the resources of cellular users (CUs), aggregate the packets generated by MTCDs, and forward them to the BS. Next, we adopt short packet theory to obtain the minimum required blocklength of a packet that transmits a certain amount of information. Then, by modeling the process of MTCGs-assisted communication as a queuing process, we derive the closed-form expression of the average delay of all MTCDs. Guided by this, we propose a joint power allocation and spectrum sharing scheme to minimize the average delay. Finally, the simulation results verify the correctness of the theoretical results and show that the proposed scheme can reduce the average delay efficiently.

It is crucial to consider timely status updates for machine type communications (MTC) in some scenarios, where a controller continuously obtains state information of targets from a sender to complete control or monitoring tasks, such as vehicular networking and environmental detection. In this work, we measure the timeliness of the status by the recently proposed age of information (AoI) metric. Different from the previous works about AoI, we consider the short packet feature of MTC in our system, where status packets will suffer from a significant packet error rate. Considering that the status packets may not be decoded by the receiver correctly, this work investigates the performance of MTC under traditional protocol (the sender discards the error status packets directly) and automatic repeat-request (ARQ) protocol (the sender retransmits the error status packets), and obtains the approximated closed-form expressions of the average AoI, respectively. Based on the closed-form expressions of the average AoI, we design two suboptimal blocklengths to minimize the average AoI under the two protocols. Numerical results verify the correctness of theoretical analysis, and show that the proposed scheme can achieve almost the same optimization performance as the exhaustive search method. Moreover, in the case of different packet generation rates, we find that the ARQ/traditional protocol can achieve better performance in low/high packet generation rate scenarios, respectively.

This paper investigates the secrecy performance of relay-assisted dual-hop short-packet communications in cognitive Internet of Things (IoT). Specifically, there is a relay that uses the decode-and-forward (DF) mode to forward short-packet signals to ensure the ultra-reliable low-latency communication in cognitive IoT. To meet the security demand, the relay uses the maximum ratio combining/zero forcing beamforming (MRC/ZFB) scheme. Considering the impact of blocklength on transmission delay and secrecy performance, we derive the approximations for secrecy throughput in a closed-form under the secrecy and decoding error probability constraints. The numerical results illustrate the impact of the system parameters on the tradeoff between transmission delay and reliability, i.e., the optimal value of the blocklength. In addition, the simulation results confirm that the proposed scheme achieves better secrecy performance than the amplify-and-forward (AF) scheme and the single-hop transmission scheme in short-packet communications.

The advent of mobile Internet era brings both opportunities and challenges to understanding customer value in the field of customer relationship management. Traditional customer relationship management theory and practice focus on the transaction value created by individual customers and do not take into consideration enough to the huge potential commercial value behind the interaction and connection among people by means of online social services in the mobile Internet era. Towards this end, this study first analyses the new characteristics of customer behaviour in the mobile Internet era. Second, the study proposes the integrated customer value model in three dimensions of purchase value, interactive value, and marketing diffusion value with 13 indicators based on the complex network theory and RFM model, considering the value created by connection and interaction among customers. Finally, the study discusses the eight types of customer clusters and the corresponding differentiate customer relationship management strategies in the era of mobile Internet based on the integrated customer value model. This study enriches the theory of customer value in the field of customer relationship management and also helps company better practice the innovation and change in the management of relationship with customer in the mobile Internet era.

To investigate the performance of unmanned aerial vehicle (UAV) assisted machine type communications (MTC), this paper proposes a joint transmit power and blocklength optimization scheme for half duplex UAV relay system with short packet communications. Different from the majority of exiting works about UAV-assisted communications where the blocklength of information to be transmitted is infinite, short packet is considered in this paper to achieve ultra-reliable and low-latency communications (URLLC) in the scenarios of MTC. To fully explore the performance of short packet communications in UAV relay system, transmit power and blocklength, under the constraints of reliability and latency, are jointly optimized to maximize the total effective amount of transmitted information. Simulation results show that the proposed scheme can achieve almost the same performance as the exhaustive search method and outperforms the benchmark schemes.

This paper designs a new chance transmission scheme for the cognitive wireless network with randomly distributed wiretap nodes. Under the condition that the channel estimation error exists at receiver and the channel information of the wiretap channel is unknown, the closed expression of the system's secrecy outage probability, connection outage probability and secrecy throughput is deduced. Based on these, we obtain the trade-off between the secrecy throughput and energy efficiency. Finally, under the requirement of security and reliability, the optimal pilot length and transmit power under the transmission scheme are obtained by maximizing the compromise function. The simulation results verify the correctness of the theoretical analysis and show that the gain of the net secrecy throughput is improved after adding the pilot. Considering the energy efficiency, the transmit power has an optimal value to maximize compromise function, and we obtain the expression of most superior power.

Chickens represent by far the most important poultry species, yet the number, locations, and timings of their domestication have remained controversial for more than a century. Here we report ancient mitochondrial DNA sequences from the earliest archaeological chicken bones from China, dating back to similar to 10,000 B.P. The results clearly show that all investigated bones, including the oldest from the Nanzhuangtou site, are derived from the genus Gallus, rather than any other related genus, such as Phasianus. Our analyses also suggest that northern China represents one region of the earliest chicken domestication, possibly dating as early as 10,000 y B.P. Similar to the evidence from pig domestication, our results suggest that these early domesticated chickens contributed to the gene pool of modern chicken populations. Moreover, our results support the idea that multiple members of the genus Gallus, specifically Gallus gallus and Gallus sonneratii contributed to the gene pool of the modern domestic chicken. Our results provide further support for the growing evidence of an early mixed agricultural complex in northern China.

Peters et al. (1) raise several questions about early chicken domestication in northern China (2), including the claim that the climate would have been unsuitable for red jungle fowl. However, northern China was much warmer and more humid with much more extensive forest coverage during the early Holocene, as shown by the presence of buffalo bones (3) at Nanzhuagtou and macaque remains at Cishan (4), providing potential habitat for wild jungle fowl. We would also like to note that, in contrast to the claim by Peters et al., the data in reference 2 of ref. 1 indicate warmer conditions already during the early Holocene.