LTE system message content and its receiving process

First, the system message concept and its contents si:system information; sibs:systeminformationblocks, except SystemInformationBlockType1, Other system messages are hosted on SystemInformation (SI) messages, and the mapping information for sibs and SI messages is included in SIBType1 scheduling While the SIBs is hosted on the Dl-sch channel, an SI can contain multiple cycles of the same sibs, and a SIB block is only in one SI message, and the SIB Type2 information is always included in the first item of the schedulinglist. A fixed receive cycle of 80ms Subframe5 sent, each SFN% 2 is 0 of the frame repeat sent, Mib:masterinformationblock, hosted on the PBCH channel, the fixed reception period of 40ms, repeated in the cycle, the MIB carries the necessary basic information ; Contains information: Sfn,hich-config and DL Bandwidth information (band-width); SIB1 content:--cellaccessrelatedinfo:plmn (Public land Mobile Network), TAC ( Trackingareacode), Cellid ...--cellselectioninfo: ...--schedulinginfolist: Period and its corresponding SIB type--si-windowlength-- Systeminfovaluetag Note: An SI can contain multiple sib, and multiple si have a common si window length; SIB2 content: Common channel configuration, upstream carrier frequency, bandwidth, Radio Resource, MBSFN (multimedia Broadcast Multicast Services single frequency network), Rach required information SIB3 ... SIB12: Public resources and re-election of various information;
Second, the system message acquisition process the entire system receives the process to need: Obtains the MIB, obtains the Sib type1 the Si infolist, obtains the SIB information from the SI, in the LTE system the MIB carries on the PBCH, but the sib type1 and other Si all sends on the Pdsch; 1 , about MIB reception see <<lte's cell search and PBCH reception >>
2, about the SIB received 2.1, access to SIB1 in the agreement has been in the time to explain the SIB1 on the Pdsch cycle 80ms,subframe5 and other related information, then also need frequency domain, code block size and so on to decode the necessary information, this need to parse DCI (downlink Control information), the DCI carries the PDCCH channel, and the decoding PDCCH needs to obtain the information of the CFI on Pcfich first;
2.1.1, the acquisition of CFI information on the Pcfich channel carries about the subframe in the pdcch of the OFDM symbol number is the CFI information; the current CFI value is 1, 2, 3, the encoding type belongs to block code, The protocol specifies 1-4 corresponding encoded 32-bit sequence, the CFI encoding sequence is scrambling (according to Cellid to obtain the corresponding scrambling code initial value), QPSK modulation, pre-coding and so on finally mapped to the corresponding re; about resource occupancy: frequency points based on the total number of points on the downlink (obtained from the MIB) And cellid calculations are obtained, while the mapping of OFDM uses the way of Reg (resource element groups) [5.2.4 of 36.211];
2.1.2, Pdcch decoding method Dci:downlink control INFORMATION;DCI hosted on the PDCCH channel, with a variety of formats, the DCI contains decoding Dsch channel information, such as carrier frequency information and MCS (modulation and Coding scheme), DCI has a variety of formats, different formats are used in different scenarios and different rnti, while decoding BCH, it is necessary to use Si-rnti to decode, the different formats of DCI are not exactly the same size, easy to use pdcch blind solution; The DCI's coded modulation sending process: CRC16 (CRC will be scrambling with different si-rnti-0xffff), 1/3 truncated convolution coding, rate matching, scrambling/modulation, and finally mapping to PDCCH's Reg resource;
Reg use: Cce:consecutive control channel elements, the Protocol stipulates a number of pdcch formats, respectively, using 1, 2, 4, 8 cces, corresponding to 9, 18, 36, 72 regs, the corresponding pdcch bits of 72 , 144, 288, 576; with different rnti PDCCH decoding, the protocol is divided into two types of search space: Public search space and UE-specific search space public search space: There are 1, 2, 4, 8 kinds of configuration; UE-specific search space: only 4, 8 configuration; At the same time, the number of attempts of various scenes of PDCCH is also limited; UE decoding PDCCH, the need to try different modes of the possible CCE/DCI format scenarios, using the corresponding rnti to solve the CRC is correct decoding;
2.1.3, Pdsch decoding according to the corresponding DCI information can be obtained pdsch the corresponding OFDM symbol, and decoding it, pdsch--using the Turbo code, the code block degree of 6144,CRC length of 24, and W is significantly different: when divided into multiple code blocks, A 24-bit CRC is added to each code block;
2.2, obtain the SI block containing other sib after getting SIB1, it can parse the corresponding SI period and window size (si-periodicity, si-windowlength) information, equivalent to have obtained the time domain information, the remaining receiving process is similar to the SIB1 process;