Symbiotic radio (SR) is an emerging green technology for the Internet of Things (IoT). One key challenge of the SR systems is to design efficient and low-complexity detectors, which is the focus of this paper. We first drive the mathematical expression of the optimal maximum-likelihood (ML) detector, and then propose a suboptimal iterative detector with low complexity. Finally, we show through numerical results that our proposed detector can obtain near-optimal bit error rate (BER) performance at a low computational cost.
As a complement of terrestrial networks, non-terrestrial networks (NTN) have advantages of wide-area coverage and service continuity. The NTN is potential to play an important role in the 5G new radio (NR) and beyond. To enable the massive machine type communications (mMTC), the low earth orbit (LEO) satellite is preferred due to its lower transmission delay and path loss. However, the LEO satellite may generate notable Doppler shifts to degrade the system performance. Recently, orthogonal time frequency space (OTFS) modulation has been proposed. It provides the opportunity to allocate delay Doppler (DD) domain resources, which is promising for mitigating the effect of high mobility. Besides, as the LEO satellite constellation systems such as Starlink are thriving, the space spectrum resources have become increasingly scarce. Therefore, non-orthogonal multiple access (NOMA) is considered as a candidate technology to realize mMTC with limited spectrum resources. In this paper, the application of OTFS enabled NOMA for mMTC over the LEO satellite is investigated. The LEO satellite based mMTC system and the OTFS-NOMA schemes are described. Subsequently, the challenges of applying OTFS and NOMA into LEO satellite mMTC systems are discussed. Finally, the potential technologies for the systems are investigated.
The industrial Internet of Things (IIoT) is an important engine for manufacturing enterprises to provide intelligent products and services. With the development of IIoT, more and more attention has been paid to the application of ultra-reliable and low latency communications (URLLC) in the 5G system. The data analysis model represented by digital twins is the core of IIoT development in the manufacturing industry. In this paper, the efforts of 3GPP are introduced for the development of URLLC in reducing delay and enhancing reliability, as well as the research on little jitter and high transmission efficiency. The enhanced key technologies required in the IIoT are also analyzed. Finally, digital twins are analyzed according to the actual IIoT situation.
The fifth generation (5G) communication has been a hotspot of research in recent years, and both research institutions and industrial enterprises put a lot of interests in 5G communications at some new frequency bands. In this paper, we investigate the radio channels of 5G systems below 6 GHz according to the 5G communication requirements and scenarios. Channel measurements were conducted on the campus of Beijing Jiaotong University, China at two key optional frequency bands below 6 GHz. By using the measured data, we analyzed key channel parameters at 460 MHz and 3.5 GHz, such as power delay profile, path loss exponent, shadow fading, and delay spread. The results are helpful for the 5G communication system design.
