Big Video Challenges 5G

观点 作者:浮生吾记 2016-11-23 09:23:07
5G是全球移动通信人都在关注的热点,浮生也很想在更大的范围内,与业界同仁交流我们的想法,寻求思维的碰撞。借着5G与视频这个话题,我们迈出了国际化的第一步。 The 5G tests in China, the release of V5G in the USA, and the launch of S5G in Japan, make 2016 the first year of 5G. Similarly, video services, such as Virtual Reality (VR) and live video streaming, frequently draw the attention of the industry. Recently Japan announced its commercial use of 5G, which will offer each user 20 GB data traffic every month. Will the advanced 5G technology meet the demand for increasingly High Definition (HD) videos with a so large data traffic package available? Video services have become the favorite among users. Compared with text, images, and voice, videos attract the widest audience. A video can clearly record the whole process of an event or a story and vividly reflect each dynamic detail in a three-dimensional form, bringing unique experience to its audience. In the past, the transmission of higher definition videos was limited by the technical level. With the technological development of video production and telecom networks, the falling costs of the production and spread of video media make online video transmission possible. Driven by the pursuit of higher definition video experience, people are now turning their demands towards the extremely clear, bright, and smooth ultra-HD videos. For a wireless communication network, mobile video services have become a basic wireless service following voice and data services. According to an analysis of global data traffic, video services have largely been credited with data traffic increase in recent years. The video services, especially HD videos, greatly stimulate traffic consumption and thus witness the rapid growth of data consumption. According to predictions in the development of global video traffic from 2016 to 2020 conducted by Cisco, mobile traffic will increase by ten times and video traffic will account for more than 75% of the Internet traffic. In developed areas, the two items will grow 20 times faster and more than 80% respectively. The reason for this growth is users' preference for video streaming services. Driven by the increasing popularity of online video contents, such as news, advertisements, and social media, HD videos are everywhere in mobile networks. With the global launch of LTE networks, the cost of HD smart terminals is rapidly declining. The screen resolution of the current mobile smart terminals reaches or exceeds 720P; some terminals even support a resolution of 1080P or 2000P. The network bandwidth of mobile operators faces a huge challenge for video services.

2016-11-23_114751

User video experience is closely related to operators' networks. The introduction and deployment of 4K, 8K, and VR/AR video services in operators' networks mean a growth by dozens in bandwidth. For example, compared with HD video services, 4K videos provide three improvements: (1) image resolution: 3840 × 3840, four times that of HD videos (1920 × 1080); (2) image smoothness: 50/60 fps, even 100/120 fps, higher than that of HD videos (25/30 fps); and (3) color accuracy: increase of the color gradation of pixels from 8 bits to 10 bits. Based on the combination of different frame rates and color gradations, 4K videos can be divided into three categories: ordinary 4K, standard 4K, and 4K+. Coded with H.265, the bit rate of 4K videos is two to ten times that of HD videos and the required bandwidth is 22.5 MHz to 75 MHz. 8K and VR videos have higher requirements for bandwidth, approx 90 MHz to 300 MHz for 8K videos (four times that of 4K videos) and 300 MHz to 1.2 GHz for VR videos (4 to 16 times that of 4K videos) respectively. The following table shows that, with the H.265 coding scheme, the bit rates of ordinary 4K videos, standard 4K videos, and 4K+ videos are about 15 Mbps, 30 Mbps, and 50 Mbps respectively, two to ten times that of mainstream HD videos. The bit rates of 8K and VR videos are four times and four to sixteen times that of 4K videos respectively. 2016-11-23_114751 How should mobile equipment manufacturers and operators respond to such great challenges? Both Softbank and ZTE give their answer: Pre5G Massive MIMO. 5G is some way from commercial use due to reasons of standards and technologies. Fortunately, Pre5G can provide a near 5G user experience or much better user experience than 4G in terms of such indicators as throughput and delay, and therefore is an inevitable stage in the development of wireless networks to 5G. In the Pre5G stage, some new technologies for improving air-interface capacity and some futuristic solutions will be used, meeting the increasingly pressing demands for video service user experience. 5G is evolving based on LTE mobile broadband networks in the Pre5G stage. Mobile Internet videos rapidly develop with the target of 1080P continuous coverage and 2K hotspot coverage, 4K and VR videos may be provided at the hotspots in the Cloud RAN architecture, and 4K 60/90 fps VR videos (H.265) can be played at an average download rate of 40 to 50 Mbps in Pre5G networks. How can the amazing Pre5G provide so high bandwidth for mobile videos? Highlight 1: Massive MIMO improves the spectrum efficiency comprehensively, allowing 4G users to enjoy 5G before its commercial use. Massive MIMO is the expansion and extension of MIMO and has a basic feature that several dozen to several thousand antenna arrays configured on the eNodeB side serve multiple users simultaneously according to the Space Division Multiple Access (SDMA) principle. The huge array gain and interference suppression gain of massive antenna arrays contribute to the great improvement in the total spectrum efficiency of a cell and the spectrum efficiency of cell-edge users. As we all know, in a rich-scattering environment, the probability of interference among data streams depends on the total number of spatial degrees of freedom and the number of streams transmitted simultaneously. If the spatial degree of freedom is very big, there is almost no correlation among streams, and therefore data can be transmitted independently of each other. If the number of antennas configured on the eNodeB side approaches infinity and the correlation coefficient of the channel vectors corresponding to any two users approaches zero, it indicates that the two channels of any two users tend to be orthogonal. This nature makes multiple-user communication (including broadcast channels and multiple access) possible. Pre5G Massive MIMO can provide 16 downlink data streams through 64 channels. In addition, with the introduction of beamforming, a terminal receiver can receive in-phase superposed signals, thus bringing an obvious array gain. Highlight 2: Space Division Multiplexing (SDM) of UE-specific reference signals upgrades two-user SDM to 16-user SDM; interference randomization of uplink control channels resolves the interference with uplink control channels of multiple users, which has been incorporated in 3GPP standards. One remarkable aspect of 5G is antenna arrays. The introduction of antenna arrays can improve system capacity, increase the radiation efficiency of wireless signals, reduce equipment costs, and enhance the anti-interference performance of the system due to the usage of low-power devices on each antenna. According to 3GPP protocols, the SDM based on UE-specific reference signals can support eight antenna ports at the most. However, the protocols do not specify how to implement MU-MIMO. Based on the existing 4G protocols, Pre5G Massive MIMO achieves SDM transmission for a large number of commercial terminals in the existing networks. The SDM based on UE-specific reference signals can be achieved for up to 16 users, making users enjoy the advantages of 5G antenna arrays. Highlight 3: Downlink beamforming and multi-user pairing almost eliminate the interference among SDM users; correlation-based SDM pairing can effectively improve the high-beamforming gain of antenna arrays; and the preferential allocation of spectrum resources to SDM users can further improve the spectrum efficiency. In terms of downlink beamforming and multi-user pairing, ZTE realizes three innovations: ZF transmission beamforming, correlation-based SDM pairing, and effective allocation of frequency spectrum resources. (1) ZF transmission beamforming One of the 5G characteristics is a large number of antenna arrays, and therefore beams can be isolated from each other just with the simplest MRT in downlink beamforming (the weight of downlink beamforming is equal to the conjugate value of the channel state detected in the uplink). However, limited by the cost and volume, the existing commercial eNodeBs cannot afford too many antennas, and therefore low interference between beams cannot be realized with MRT if two SDM users are close to each other. If some SDM users are adjacent to a target user, interference occurs during beamforming for the target user because some power leaks to the adjacent SDM users, and then the whole system becomes an interference-limited system. Owing to ZF beamforming used in ZTE eNodeBs, antenna pattern null can be realized for the adjacent SDM users, which means that the beamforming for a target user cannot cause interference with other SDM users. ZF beamforming eliminates the interference among SDM users and the traffic of any user can reach the peak value as long as the SNR is high enough. (2) Correlation-based SDM pairing With ZF transmission beamforming, when two users with a high correlation are paired for SDM, most of the downlink transmission power is used to offset the mutual interference among beams, and only a small part of the power can reach the target user. To give full play to the high beamforming gain of antenna arrays, users with a high correlation should not be paired for SDM. Therefore, terminal pairing is one of the important technologies of Pre5G Massive MIMO. (3) Allocation of frequency spectrum resources In traditional 4G networks, the frequency spectrum resources are allocated based strictly on the priority determined by the PF algorithm. With the introduction of SDM, the ratio of SDM must be as high as possible to obtain higher spectrum efficiency. Therefore, the allocation of frequency spectrum resources must be revised. The users that have a higher allocation priority but are not scheduled for a long time and therefore do not participate in SMD are allocated with the resources first. The remaining resources are divided into two parts: P% of them for SMD and the value of (1 - P%) for Frequency-Division Multiplexing (FDM). To improve the proportion of SDM, most of the remaining resources can be allocated to SDM. After the application of the preceding innovations, the spectrum efficiency is increased to 17.5 bit/Hz/s from 5 bit/Hz/s and 16-stream MU-MIMU is realized for the first time. ZTE will continually make innovations and breakthroughs and invest in the wireless market to embrace the era of big videos.

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