When a wireless system is changing people's lives, its technology itself is also developing and evolving. From 2G, 3G, 4G to 5G now, the application of each new technology has brought a great enhancement in air interface capacity of the wireless system. The 5G air interface uses Massive MIMO to maximize the space division multiplexing of spectrum resources through beamforming, which greatly improves the spectrum efficiency and cell capacity. However, a large number of flexible beams increase the complexity of the wireless system. If there is no efficient beam management and planning, the entire wireless system will be adversely affected. The increasingly complex wireless environment and urban construction growth also pose challenges to 5G coverage. Typical coverage scenarios include general wide coverage, high-rise building coverage, hot venues coverage, and highway coverage. How can 5G achieve better coverage in different scenarios while reducing intra-system interference and enhancing user experience?
As the coverage of a cell is determined by the coverage of cell broadcast, controlling the coverage of a broadcast beam is the key to 5G coverage. To achieve high-quality 5G coverage, ZTE has proposed the SSB 1+X beaming networking solution, in which '1' represents a wide beam configured for basic horizontal coverage and 'X' refers to narrow/wide beams configured on demand for vertical coverage extension. In this solution, different SSB (SS/PBCH blocks) beams are used in different cells to stagger inter-neighbor interference for horizontal coverage. According to coverage requirements, more beams are used for spatial coverage in the vertical dimension to achieve the best 5G coverage (Fig. 1).
The SSB 1+X beam networking solution is designed to improve coverage, save sources, reduce power consumption and control interference, and can finally get the best user experience with high performance-to-price ratio.
The SSB 1+X beam networking solution uses the minimum horizontal SSB beam and on-demand vertical beams to achieve 3D full space coverage and in-depth coverage extension and adapt to various coverage scenarios in complex environments.
The solution improves horizontal beam gain through the SSB power boosting and increases SSB 1 beam gain by 6 dbm. In this way, the horizontal wide SSB 1 beam provides the same coverage as the horizontal SSB 8 beams, and more SSB beams are reserved for vertical coverage.
In the 5G system, the beams corresponding to SSB are distinguished through time polling. Multiple SSB beams correspond to multiple SSB time-domain positions. One slot can be configured with two SSB beams, and one SSB occupies four OFDM symbols in the time domain. One SSB occupies 20 PRB resources in the frequency domain. In the general wide coverage scenario, SSB 8 beams are configured horizontally, and SSB beams occupy four slots. The corresponding system messages SIB and Paging also need to broadcast 8 times, and thus occupy 8 times the wireless resources.
The SSB 1+X beam networking solution adopts horizontally SSB 1 beam configuration mode to meet the coverage requirements. Therefore, the horizontal configuration of SSB 1 beam requires only four OFDM symbols in one slot in the time domain, and system messages SIB and Paging only need one set of wireless resources, which greatly saves the wireless resources occupied by sending messages.
After data analysis, the SSB 1+X beam networking solution can save about 6% of the total wireless resources compared with the horizontal SSB 8 beams solution. In particular, for the initial access phase, the SSB 1+X beam networking solution can save wireless resources by 34%.
Reduce Power Consumption
The SSB 1+X beam networking solution occupies less wireless resources, thus greatly reducing 5G power consumption.
The SSB 8 beams solution is compared with the SSB 1+X beam networking solution according to the period of 20 ms. When SSB 8 beams are configured, the mark-space ratio of wireless resources is 76.92%. When the SSB 1 beam is configured, the mark-space ratio of wireless resources is 11.30%. The lower the mark-space ratio, the less resources the system needs. The difference of the mark-space ratio between SSB 8 beams and the SSB 1 beam is 65.62%. The SSB 1+X beam networking solution can save the power consumption of AAU by nearly 10% compared with the SSB 8 beams solution.
With the expansion of 5G deployment in China, the SSB 1+X beam networking solution used by hundreds of thousands of 5G sites nationwide will greatly reduce long-term 5G operation and maintenance costs for operators.
The broadcast interference between neighboring cells in a 4G network has always been a key issue to improve network performance. Neighbor cell interference also exists in 5G network deployment. Through continuous algorithm demonstrations, the SSB 1+X beam networking solution proposed by ZTE can solve the problem of adjacent interference.
5G adopts horizontally the configuration of SSB 1 beam, while different SSB beams are sent through time polling. Therefore, different SSB beams are configured for neighboring cells, and the transmission time of SSB beams between neighboring cells is staggered through the time polling. This can avoid broadcast interference between neighboring cells.
In addition to broadcast interference between neighboring cells, interference also exists when conflicts occur between broadcast beams and service beams in neighboring cells. The interference also has a negative impact on user experience. To avoid the interference, ZTE has put forward the inter-neighbor rate matching configuration function based on the 3GPP 5G protocol. If there is a conflict in neighboring cells between service channels and SSB beams, the rate matching function at the symbol level is enabled for service beams to avoid the interference and improve user experience.
With the large-scale deployment in 2020, 5G network coverage and optimization will face great challenges. The SSB 1+X beam networking solution will help operators optimize 5G network, improve its performance, and achieve high-quality 5G growth.