Theoretical value, that's it!
Recently, under the organization of the IMT-2020 (5G) Promotion Group, Huawei successfully completed the low latency high reliability (URLLC) technology laboratory test with a 1ms latency. The test results show that using 5G R15 and R16 low latency and high reliability key technologies, 5G millimeter wave devices achieve a two-way end-to-end delay of 1ms at a reliability level of 99.999%.
As one of the 5G capability triangles, eMBB has begun to prove its value, and the next thing to shine is URLLC. As a communication with ultra-low latency and ultra-high reliability, URLLC can meet some services with high latency sensitivity and reliability requirements, and can be widely used in AR/VR, industrial, medical, unmanned driving and other scenarios. It can be said that Huawei's test proves that 5G can achieve the theoretical value of 1ms two-way end-to-end latency, opening up a new blue ocean for the 5G industry.
If we look at the history stretched, the communications industry in the 21st century is a "history of struggle" that strives to reduce latency. From 20ms to 1ms, in order to reduce the delay of this 19ms, the communications industry spent 17 years.
From 20ms to 2.7ms
The story begins with the standardization of LTE networks in 2004. Of course, in that era, the national communications industry represented by China Mobile, Huawei, ZTE, etc. had not yet entered the core circle of standard setting.
As a very successful generation of mobile communication technology, LTE in the process of standard formulation and industrial commercialization, the main focus is on MBB services, that is, to improve network speed and spectrum use efficiency. From 3GPP R8 all the way to R13, the industry has been moving forward along the "faster" path. Later, the 3GPP found that it was not enough to emphasize only fast, but also to pay attention to the time delay of the air interface.
Because the delay not only affects the network speed, but also brings challenges to the user experience. At that time, the network latency of LTE was a bidirectional delay of 20ms, but this was only a theoretical value. The actual situation should be judged according to the wireless environment, only long and not short.
In 2015, at the 67th meeting of 3GPP RAN, a research project (SI) to reduce the time delay of LTE networks was established. In March 2016, at the 71st meeting of 3GPP RAN, the research project work was officially approved.
By improving the Resource Scheduling Request and Assignment and Transmission Interval, the upstream network transmission delay is greatly reduced. Based on the simulation results, the bidirectional transmission delay of the LTE air interface is reduced to about 8ms. Subsequently, the 3GPP RAN 72 conference, a project was established to work on improving the transmission interval of LTE networks and thus reducing network latency. By the time LTE R15 arrives, all the big moves are used, and the LTE's network latency can theoretically be reduced to 2.7ms in both directions.
For MBB business, a theoretical delay of 2.7ms is sufficient. But for vertical industry production needs, 2.7ms is still too long.
From 2.7ms to 1ms
In the field of mobile communication standard development, the ITU is mainly responsible for proposing indicators and pointing out the problems that need to be solved in 5G, and the 3GPP is responsible for completing the design and definition of specific technical standards and specifications.
In order to complete the "5G Flower" proposed by ITU and meet the extremely high reliability and low latency requirements of URLLC, 3GPP defines the requirements of 0.5ms upstream and 0.5ms downstream for the latency of URLLC services, that is, 1ms of bidirectional latency.
The task is clear, and the next step is how to achieve it, from 2.7ms to 1ms.
With the joint efforts of the industry, by using a 5G system configuration scheme with a subcarrier spacing of 30KHz, upstream dispatch-free, and two-symbol micro-time slot, the requirements of less than 1ms of bidirectional delay can be achieved. If 5G high-frequency communication is used, the subcarrier interval of 120KHz can be used, and the delay can be lower.
In this test and verification, Huawei's base station equipment meets the technical requirements of low latency and high reliability in terms of function and performance. This time, not only the reliability and latency of 5G mmWave devices are tested, but also the key technical functions and performance of URLLC of 5G 2.6G band devices are verified, including low latency upstream and downstream non-slot scheduling, commercial live network frame structure and upstream free scheduling, high reliability and low bit rate MCS table/CQI table, PDCCH high aggregation level, PDSCH/PUSCH time slot level repeated transmission, etc. As well as delay and reliability performance in different signal-to-noise ratio environments.
Through the flexible combination of various standard technologies and implementation means, 5G networks can fully meet the diversified needs of all walks of life, and lay a solid foundation for 5G to enter the core production business of industries such as industry, and promote the rapid development of the digital economy. (Yue Ming)