NTT DOCOMO用于5G的3.5GHz频段天线

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本文作者Tatsuhiko Yoshihara，Sho Yoshida，Teruo Kawamura：NTT DOCOMO无线接入网络发展部。Hiroyuki Kawai：NTT DOCOMO研发战略部。一引言NTT DOCOMO developed new base-station 3.5-GHz antennas for small cell, indoor, and macro cell use, as summarized below.（1）Small cell base stations are being rolled out in outdoor areas with high volumes of traffic such as areas surrounding train stations to provide stable communications at higher speeds. To be effective, the formation of small cell service areas must consider the purpose of use and a variety of installation conditions (building walls, rooftops, etc.). For this reason, NTT DOCOMO developed three types of compact antennas for small-cell base stations.（2）Use of the 3.5-GHz band is also vital in indoor areas such as largescale commercial facilities to support ever-increasing volumes of traffic. To meet this indoor need, NTT DOCOMO developed a compact antenna for mounting on ceilings to form a service area on the floor of a building.（3）The 3.5-GHz band will also be introduced in macro cell base stations to provide high-speed communications for more than just high-traffic areas such as train station neighborhoods. To form a broad service area with a macro cell, NTT DOCOMO developed a base-station antenna with high antenna gain for installation in existing building and steel-tower base stations.In this article, we describe the features of these new base-station antennas developed by NTT DOCOMO to meet a variety of usage scenarios and installation conditions.二5G小小区覆盖场景下的3.5GHz频段天线Major specifications of antennas for small cells are listed in Table 1. Three types of antennas were developed taking into account diverse installation platforms such as building walls and roofs and interference with adjacent small cells. These antennas have vertical/horizontal polarization in common, and compared with small-cell antennas supporting the 1.5 and 1.7 GHz bands, they are compact in size. The following summarizes the features of each of these antennas.表1 用于小小区覆盖场景的3.5GHz频段天线的主要规格

1、棒状天线（两种类型）This is a rod-shaped antenna that is vertically installed to form a radiation pattern with no directivity (omnidirectional radiation pattern) in the horizontal plane. It can be installed on a building wall or steel pillar to form a service area in its periphery. Two types of rod antennas have been developed: one with electrical tilting that can reduce interference with adjacent small cells, and the other with no tilting for a compact configuration.2、平面天线This is a box-shaped antenna having a planar radiating surface and unidirectional radiation pattern. Its high antenna gain makes it applicable to forming spot-like service areas from high locations such as building roofs. In addition to mechanical tilting to reduceinterference between small cells, this antenna features a low sidelobe design to further reduce interference.三5G室内覆盖场景下的3.5GHz频段天线Major specifications of the antenna for indoor use are listed in Table 2. When forming a new service area using the 3.5-GHz band, it must be kept in mind that antenna units supporting the 1.5/1.7/2-GHz bands have already been installed indoors. Installation space is therefore limited, which means that replacing existing antenna units is desirable.This newly developed antenna unit therefore supports the 1.5-, 1.7-, 2-, and 3.5-GHz bands in one unit with support of the 3.5-GHz band achieved through Multiple Input Multiple Output (MIMO) operation using four antenna elements. The antenna unit has the same size as existing antenna units supporting the 1.5/1.7/2-GHz bands making antenna unit replacement simple. The 3.5-GHz band can therefore be introduced without changing the overall look of indoor facilities.表2 用于室内覆盖场景的3.5GHz频段天线的主要规格

The polarization configuration of the four antenna elements used for the 3.5-GHz band was studied by comparing a“vertically polarized element×4”configuration with a“vertically polarized element×2 and horizontally polarized element×2”configuration. Since the size of the newly developed antenna unit is the same as existing ones, sufficient spacing between antenna elements cannot be secured, and as a result, the configuration having only vertically polarized elements exhibits high antenna correlation compared with the configuration having both vertically and horizontally polarized elements. This high antenna correlation causes throughput to drop. For this reason, we adopted the latter configuration providing higher throughput (low antenna correlation).四5G宏小区覆盖场景下的3.5GHz频段天线Major specifications of antennas for macro cells are listed in Table 3. Three types of antennas were developed here according to the service area to be formed: two types (gain-oriented and installation-oriented) for use with three sectors and one type (installation-oriented) for use with six sectors. To install and operate these antennas together with other base-station antennas supporting the 700-and 800-MHz bands, 1.5-, 1.7- and 2-GHz bands, etc., it may be difficult to secure space for setting up a new steel pillar for an antenna supporting the 3.5-GHz band on a building roof or elsewhere in an urban area. Accordingly, to make it easy to install a new antenna on the same steel pillar mounting existing antennas, we also developed an installation-oriented type of antenna with roughly half the volume of the gainoriented type. In these antennas for macro cells, remote control signals can be used to drive internal phase shifter devices and control tilting. We adopted the global standard specified by the Antenna Interface Standards Group (AISG) as the interface here for remote control of the tilt angle.表3 用于宏小区覆盖场景的3.5GHz频段天线的主要规格

五结论、展望This article described the features of new base-station antennas developed for small cell, indoor, and macro cell use to support the newly available 3.5-GHz band. Base-station antennas are important facilities closely tied to area formation in a cellular system. Going forward, NTT DOCOMO is committed to developing advanced antennas to provide users with an even better network experience including enhanced radio capacities and faster communication speeds.喜欢关注我们 ↓↓↓就请关注我们→我们是专门关注5G的第一大新媒体平台：5G标准化、技术、产品、业务、市场最新现状与趋势。

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