Abstract
Considering the coverage and short-packet communication requirements, this paper proposes a hybrid automatic repeat request (HARQ) assisted short-packet communications for cooperative Internet of Things (IoT) networks, where the signals are transmitted through short-packets. Since the short-packet communications will bring a higher packet error rate than long-packet communications, HARQ is adopted to improve transmission reliability by allowing retransmit the signals which cannot be detected correctly. For lighting the burden of the transmitter, the retransmitted signals are only sent from the relay. According to the detection capability of the user, selection combining (SC) scheme and maximum ratio combining (MRC) scheme are designed to detect the multiple transmitted signals. Besides, a set of closed-form expressions of the average packet error rate (APER) and effective throughput (ET) are derived over Nakagami-$m$ channels in the proposed SC and MRC schemes. For providing more insights into system performance, the asymptotic results are also provided. Simulation results demonstrate that HARQ will significantly improve reliability and transmission efficiency. Also, the MRC scheme outperforms the SC scheme in terms of APER and ET metrics, however, when the transmit power at the relay is high enough or the packet length is big enough, they achieve nearly the same performance.
Highlights
W ITH the development of the 5G and beyond 5G networks, Internet of Things (IoT) is coming to provide ubiquitous connectivity for smart office, smart industry, intelligent transportation, and so on [1]–[3]
Simulations are conducted and the results show that hybrid automatic repeat request (HARQ) is beneficial to improve reliability and transmission efficiency; in addition, the maximum ratio combining (MRC) scheme outperforms selection combining (SC) scheme in terms of average packet error rate (APER) and effective throughput (ET); the packet-length can be optimized for achieving higher ET
Results show that HARQ improves the reliability and transmission efficiency when compared with the non-HARQ scheme, and increasing the maximum transmission round L will further improve system performance
Summary
W ITH the development of the 5G and beyond 5G networks, Internet of Things (IoT) is coming to provide ubiquitous connectivity for smart office, smart industry, intelligent transportation, and so on [1]–[3]. Yang et al.: HARQ Assisted Short-packet Communications for Cooperative Networks over Nakagami-m Fading Channels ering the limited power in IoT, an energy harvesting IoT system was proposed in [12], where relays are utilized to help the base station transmits signals to IoT devices. Chen et al [17] proposed a wireless-powered IoT network with finite packet-length coding, where the effectivethroughput (ET) and effective-amount-of-information are adopted as performance metrics and maximized by optimizing the delay and packet error rate. For mitigating the packet error caused by shortpacket communications, an HARQ scheme is employed, where the signal will be retransmitted only from the relay to lighten the burden of the transmitter when the user cannot detect its message correctly. We consider a cooperative network where a decode-and-forward relay denoted as R cooperates with the transmitter T for providing reliable short-packet communications for the user denoted as U. Two schemes can be adopted to utilize the retransmitted signals, which are detailed as follows
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