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Analysis of High-Reliable and Low-Latency Communication Enablers for New Radio Unlicensed
How to enable B5G/6G URLLC (Ultra Relia-ble Low Latency Communications) to meet the require-ments of low latency, ultra-high-speed and real-time indus-trial automatic control for multi-sensor IIoT (Industrial Internet of Things), it is one of the most important chal-lenges of multi-sensor IIoT. The RTT (Round-Trip Time) is significantly reduced by SPS (Semi-Persistent Scheduling) or short TTI (Transmission Time Interval) method, yet these methods may cost extra frequency and time resources. To reduce latency without the cost of extra spectrum and time resources, such research is almost blank in both aca-demia and industry for B5G/6G URLLC scenario of mul-ti-sensor IIoT. We hence propose the latency reduction method for the B5G/6G URLLC scenario of multi-sensor IIoT. Our research fills this research gap. The proposed reduction method includes a storage planning method for global data and local data, a dynamic data configuration method and an execution time minimization method. Based on these methods, we can obtain the minimum data space of the program and the data storage arrangement approaching to the minimum WCET (Worst-Case Execution Time). Under the main frame of SPS and short TTI method, our proposed method can further reduce latency without re-ducing spectrum and time resources utilization by mini-mizing data storage and access delay. The experimental results show that our method didn’t reduce spectrum and time resources utilization, and when our method was applied in SPS and short TTI method, our method further reduced the physical layer computing latency by about 21% to 28%.
The use of wireless communications in Industrial Internet of Things (IIoT) enables unparalleled levels of flexibility and instantaneous reconfiguration for autonomous industrial processes. In this paper, the focus is on optimizing and evaluating Wi-Fi 6 and 5G New Radio (NR) licensed and unlicensed wireless networks for meeting the packet latency and reliability requirements of critical IIoT applications. The study is based on extensive system simulations using a 3GPP-defined IIoT indoor factory framework and application traffic models. Each radio technology is individually optimized leveraging the pros and cons of that technology to maximize the carried load in the network while fulfilling the delay requirements at a specified reliability level of 99.999 %. In addition to a performance comparison, the paper also provides deployment guidance for applying each radio technology in the considered IIoT setting. With proposed latency aware scheduling and when operated in interference free spectrum, Wi-Fi 6 can support <1 ms applications at a very low load, whereas the performance gap with respect to 5G NR reduces as delay requirements are relaxed to 10-100 ms. Conditioned on the fulfilment of the application latency and reliability requirements, unlicensed 5G NR shows nearly 2x the spectral efficiency of Wi-Fi 6 in all available configurations. Licensed 5G NR shows generally the best performance, especially for delay requirement <1 ms, supporting 2-4x the spectral efficiency achievable by unlicensed technologies.
In this chapter we present a compact overview of the 3GPP designed New Radio (NR) system with emphasis on the Radio Access Network (RAN) part, and related innovations that enable mission critical communication for Industrial Internet of Things (IIoT) including the use of 5G seamlessly in an Industrial Ethernet scenario. We focus on Ultra-Reliable Low-Latency Communication (URLLC), including its evolution towards enhanced URLLC (eURLLC), and Time-Sensitive Communications (TSC). The chapter is organized by first shortly introducing the addressed IIoT use cases and requirements addressed by the NR (e)URLLC and TSC enablers. To understand how 5G enables wireline-like performance while retaining the flexibility of wireless deployment, we then provide a brief overview of the NR RAN protocol stack and architecture options followed by a summary of main enablers for (e)URLLC in 3GPP NR Release-15 and 16. Then, the seamless integration of 5G into an IIoT factory setup with TSC is explained and main enablers introduced in 3GPP NR Release-16 are introduced. Finally, the chapter is closed with an outlook of further enhancements being considered for Release-17 standardization. Throughout the chapter, we provide pointers to the most relevant 3GPP Technical Reports (TRs) and Technical Specifications (TS), as well as selected publications where more details can be found.
In this paper, the achievable latency-reliability performance of a standalone cellular network over the 5 GHz unlicensed spectrum is analysed. Fulfilling strict latency-reliability requirements comes with significant challenges for unlicensed operation, especially due to mandatory channel access procedures. Using MulteFire as the reference system-model, an analysis of a highly realistic multi-cell network with bi-directional traffic shows that latency of 23 ms with a reliability level of 99.99% is achievable for low-loads, while latency is increased to 79 ms at high-loads. Different techniques are described to improve the system performance. First, a pre-emptive scheme to cope with continuous uplink listen before talk (LBT) failures for uplink control transmissions is proposed. It provides a latency reduction of 24% at low-loads with two transmission opportunities and 11% for high-loads with three opportunities. Secondly, the possibility of skipping LBT performance under given conditions is evaluated. This results in a lower uplink LBT failure rate which translates to a latency reduction of 8% for low-loads and up to 14% for high-loads, at 99.99% reliability. Thirdly, as an alternative to grant-based uplink, grant-free uplink is evaluated. Grant-free uplink achieves better performance than grant-based uplink at low-loads, offering 50% lower uplink latency. At high-loads, the gain of grant-free uplink decreases due to the high number of simultaneous transmissions.
The fifth-generation (5G) radio networks will support ultra-reliable low-latency communications (URLLC). In the uplink, the latency can be reduced by removing the time-consuming and error-prone scheduling procedure and, instead, using the grant-free (GF) transmissions. Reaching the strict URLLC reliability requirements with GF transmissions is, however, particularly challenging due to the wireless channel uncertainties and interference from other URLLC devices. As a consequence, the supported URLLC capacity and, hence, the spectral efficiency are typically low. Multi-cell reception, i.e., joint reception and combining by multiple base-stations (BS), is a technique known from long-term evolution (LTE), with the potential to greatly enhance the reliability. This paper proposes the use of multi-cell reception to increase the URLLC spectral efficiency while satisfying the strict requirements using GF transmissions in a 5G new radio (NR) scenario. We evaluate the achievable URLLC capacity for an elaborate multi-cell reception parameter space and multi-cell combining techniques. In addition, we demonstrate that rethinking of the radio resource management (RRM) in the presence of multi-cell reception is needed to unleash the full potential of multi-cell reception in the context of UL GF URLLC. It is observed that multi-cell reception, compared to a single-cell reception, can provide URLLC capacity gains from 205% to 440% when the BSs are equipped with two receive antennas and 53% to 22% when BSs are equipped with four receive antennas, depending on whether the retransmissions are enabled.
In this article, we aim to address the question of how to exploit the unlicensed spectrum to achieve URLLC. Potential URLLC PHY mechanisms are reviewed and then compared via simulations to demonstrate their potential benefits to URLLC. Although a number of important PHY techniques help with URLLC, the PHY layer exhibits an intrinsic trade-off between latency and reliability, posed by limited and unstable wireless channels. We then explore MAC mechanisms and discuss multi-channel strategies for achieving low-latency LTE unlicensed band access. We demonstrate, via simulations, that the periods without access to the unlicensed band can be substantially reduced by maintaining channel access processes on multiple unlicensed channels, choosing the channels intelligently, and implementing RTS/CTS.
In wireless networks with smaller cell sizes and dense network deployments the spectral efficiency is limited by inter-cell interference. To improve signal-to-noise-plus-interference-ratio, interference can be mitigated using advanced receivers like an interference rejection combining (IRC) receiver. The performance of a practical IRC-receiver is dependent on the quality of the channel and interference covariance estimation. Interference covariance can be estimated for example by using reference signals. As the interference structure is dependent on several components, such as scheduler decisions made and precoders used by other cells, receiver evaluations are performed on system level. Because of full network system level simulations are very complex and highly computationally intensive, simplifications in modeling are needed. Typically time-frequency resolution can be reduced and only the fast-fading coefficients of the interfering links are generated. The lack of symbol samples requires a model to estimate the losses of realistic IRC receivers. In this paper, we show system level results for practical IRC algorithms.
In this study we analyze the downlink OFDMA system level performance for three different channel quality indicator (CQI) reporting schemes. The effect of terminal measurement and estimation errors, quantization from formatting and compression, and uplink reporting delays and detection errors are included. We find that a simple threshold-based CQI scheme provides an attractive trade-off between downlink system level performance and uplink CQI signaling overhead, as compared to using a best-M scheme. When applied to the UTRAN LTE system in a 10 MHz bandwidth, we find that a frequency domain packet scheduling gain of 40% is achievable with a CQI word size of only 30-bits. Finally, the effect of applying a so-called outer loop link adaptation algorithm is reported.
MulteFire Release 1.0 Technical Paper: A New Way to Wireless
- M Alliance
Multi-cell reception for uplink grant-free ultra-reliable low-latency communications
- T H Jacobsen
- R Abreu
- G Berardinelli
- K I Pedersen
- I Z Kovcs
- P Mogensen