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1、5G NR Cell Search and Synchronization5G(NR)网络中的小区搜索和同步July 28, 2019admin5G, Future Network Optimization, Interviews, LTE, NewRadio, NR, Tech FundasCell search is the procedure by which a UE acquires time and frequency synchronization with a cell and decode the Cell ID of that cell. In 5G NR, Cell se
2、arch concept is similar to what it is in LTE in terms of decoding Primary Sync Signal (PSS) and Secondary Sync Signal (SSS) to the Physical Cell ID (PCI).小区搜索是终端在时间和频率上与小区同步和解码小区ID的过程。在5G (NR)网络中, 终端小区搜索的过程与LTE网络中的终端与小区主同步信号(PSS)和辅同步信号(SSS)同步， 解码物理小区(PCI)相同。There are 2 methods by which a UE can acce
3、ss a 5G-NR cell.在5G(NR)网络中UE有两种方法接入：1. Non Stand Alone Mode (NSA) Deployment: EUTRA - NR Dual Connectivity EN-DC2. Standalone SA Deployment: NR Only Cell3. NSA组网模式：4G.5G双连接方式4. SA组网模式：5G小区接入方式In EN-DC, Cell Search information like frequency (NR-ARFCN), Cell ID, RACH parameters, etc. are provided by
4、network in RRC Reconfiguration message via LTE eNB. The UE can attempt RACH to access the NR cell.在NSA(ENDC)组网中，终端通过LTE eNB中RRC配置信息获取NR-ARFCN,小区ID,接入参 数等接入NR小区；In Standalone , NR Cell Search procedure follows below steps:在SA网络中，NR小区接入通过以下几步： UE tunes to a specific frequencyUE tries to detect PSS, SS
5、S, If UE fails to detect this, it goes to tune to next frequency Once UE successfully detect PSS/SSS, UE tries to decode PBCHOnce UE successfully decoded PBCH, it tries to PDCCH and PDSCH for RMSI and OSI UE调到小区频点UE检测PSS,SSS,如果失败，转往下一频点； 一旦PSS/SSS检测成功，UE尝试解码PBCH；一旦PBCH解码成功，尝试获取PDCCH和PDSCH上的RMSI和OSI消
6、息；PSS and SSS DecodeNR MobileFrequency TuningPBCH DecodeRM SI and OSI DecodeSweepinggNBUE scans the frequency band on sync raster based on which frequency band the UE is performing cell search on and is defined by 3GPP 38.104 section 5.4.33 to tune specific frequency. The synchronization raster indi
7、cates the frequency positions of the synchronization block that can be used by the UE for system acquisition when explicit signalling of the synchronization block position is not present. The synchronization raster and the subcarrier spacing of the synchronization block is depend on separately for e
8、ach band.3GPP 38.104第节定义,UE开机后按照小区频段的同步步长(SYNC RASTER)进行小 区搜索，根据结果调整到特定频率；同步步长(SYNC RASTER)指示了频率中同步块的位置， UE根据其获取系统信息，得到同步信令是否存在的确认；每个频段的同步块的步长和子载 波间隔各不相同。In further step UE decode primary and secondary synchronization signals to get Physical Cell ID PCI, and PBCH DMRS, located on the synchronization
9、 raster. PSS, SSS, and NR-PBCH are transmitted in a Synchronization Signal Block (SS Block). SSB is consist of 4-symbol, 1-symbol PSS, a 1-symbol SSS, and a 2-symbol PBCH.Time synchronization in terms of symbol-level and slot-level and frequency synchronization are realized via PSS/SSS.UE解码同步步长(rast
10、er)上的主同步信号(PSS)和辅同步信号(SSS)后获得物理小区ID(PCI) 和PBCH DMRSo其中PSS、SSS和NR-PBCH在同步信号块(SS块)上传输。SSB由4符号组 成:PSS占用1个符号、SSS占用1个符号和2 PBCH占用2个符号组成，通过PSS /SSS可实 现符号(级)时间同步、时隙(级)时间同步和频率同步。NR supports up to 1008 PCIs, twice as many as that of LTE. 336 unique cell-identity groups each group containing three unique and i
11、t can be calculated by following formula:5G(NR)中有PO 1008个是LTE的一倍；共有336个小区组，每个组有3个小区；计算公式如 下：座=3嘴+%Where N(1)iD= Secondary Synchronization Signal (SSS) and its range is from 0, 1.335 N(2)id = Primary Synchronization Signal (PSS) and its range is from 0,1, 2 辅同步信号(SSS)取值(0, 1,.335) 主同步信号(PSS)取值(0,1,2)
12、SSBs is transmitted in a batch by forming an SS Burst (one SSB per beam) that is used during beam sweeping by changing beam direction for each SSB transmission. Beam Sweeping mechanism is used by UE to measure and identifies the best beam for a UE.SSBs是通过传输一批SS Burst (SSB/波束)在波束扫描过程中，通过改变每个SSB传输 的波束
13、方向来进行批量传输。UE通过波束扫描是用来测量和选定最佳波束。A collection of SS Bursts is referred to as an SS Burst Set. Both SS Burst and SS Burst Set may contain one or more elements, while the maximum number of SSBs in an SS Burst is frequency-dependent and it can 4 (below 3 GHz), 8 (3 to 6 GHz), or 64 (6 to 52.6 GHz). The p
14、eriodicity of the SSB is configured by the network, while the default transmission periodicity for initial cell selection, the SS burst set periodicity is default at 20 ms for all frequency range i.e., 2 NR frames. This interval is four times longer than that in LTE (5 ms) and aims at reducing the u
15、always-onn transmission overheads. The frame and slot timings are defined by the identifiers of SBSs and acquired by the UE.一组SS Bursts被称为SS Burst集。SS Burst和SS集都可以包含一个或多个粒子，而 SS集中SSBs的最大数量与频率有关,可以为4( RMSI配置、DMRS位置等。成功解码PBCH后，UE接收物理下行控制信 道(PDCCH)和物理下行共享信道(PDSCH)等内容，这些信道中包括基本系统信息(RMSI)、其 他系统信息(OSI)。PD
16、CCH配置的RMSI由PBCH承载。RMSI的控制资源集(CORESET)配置与 SSB突发集中的SS块相关联。PBCH中的一位信息比特用于RMSI,的SCS发送信号，以及 用于初始接入的OSI和其他随机接入过程中的消息。Related Post: NR-Cell Physical Layer Cell ID NR-Master Information Block (NR-MIB) NR-Primary Synchronization Signal (PSS) NR-Secondary Synchronization Signal (SSS) 5G NR Reference Signals (DMRS, PTRS, SRS and CSI-RS) 5G NR Sounding Reference Signal (NR-SRS)