project ii explore the physical broadcast channel pbch of 5g

5G NR: Synchronization Signal/PBCH block SSBCell search is the procedure for a UE to acquire time and frequency synchronization with a cell and to detect Physical layer Cell ID PCI of th

111Equation Chapter 1 Section 1 HANOI UNIVERSITY OF SCIENCE

AND TECHNOLOGY

SCHOOL OF ELECTRICAL AND ELECTRONIC ENGINEERING

- -  

PROJECT II

TOPIC: Explore the Physical Broadcast Channel PBCH of 5G

Teacher: Doctor Nguyễn Thu Nga

Student: Đào Nhật Nam Student ID: 20193232

Hà Nội, 2023

1 5G NR: Synchronization Signal/PBCH block (SSB) 4

2 PBCH payload generation 6

3 Scrambling 6

4 Transport block CRC attachment 7

5 Channel Coding 8

6 More about Scrambling 9

7 Modulation 9

8 Resource Element Mapping 9

9 Reference materials……… …….15

Nowadays, there is a huge demand in Viet Nam to recruit advance-skilled engineers with extensive knowledge and ability to solve difficult problem Since modern technology is becoming more popular in life, the top priority is using software as a effective tool As a student of Ha Noi University of Science and Technology, i not only have to use the most modern technologies, but also understand their operation Before presenting this report, i want to express our sincere thanks to Doctor Nguyễn Thu Nga for the guidance to teach us to implement this project Due to limited knowledge and lack of experiences, mistakes are unavoidable on this project As a result, I am looking forward to receiving comments and evaluations from the instructor

1 5G NR: Synchronization Signal/PBCH block (SSB)

Cell search is the procedure for a UE to acquire time and frequency

synchronization with a cell and to detect Physical layer Cell ID (PCI) of the cell During cell search operations which are carried out when a UE is powered ON, mobility in connected mode, idle mode mobility (e.g reselections), inter-RAT mobility to NR system etc., the UE uses NR synchronization signals and PBCH to derive the necessary information required to access the cell

Similar to LTE, two types of synchronization signals are defined for NR; Primary Synchronization Signal (PSS) and the Secondary Synchronization

Signal (SSS) The Synchronization Signal/PBCH block (SSB) consists of PSS, SSS and Physical Broadcast Channel (PBCH)

=> Physical Broadcast Channel (PBCH): This physical channel carries

system information for UEs requiring to access the network It only carries what is termed Master Information Block, MIB, messages.

PBCH transport process

Broadcast channel (PBCH)

Data arrives to the coding unit in the form of a maximum of one transport block every 80ms The following coding steps can be identified:

- Payload generation

- Scrambling

- Transport block CRC attachment

- Channel coding

- Rate matching

2 PBCH payload generation

Denote the bits in a transport block delivered to layer 1 by , where A is the payload size generated by higher layers The lowest order

information bit a0 is mapped to the most significant bit of the transport block (Lssb=64 as defined in 4.1)

(https://www.etsi.org/deliver/etsi_ts/138200_138299/138213/16.02.00_60/ts_1382 13v160200p.pdf )

3 Scrambling

For PBCH transmission in a frame, the bit sequence is scrambled

defined as 7.1.2

(https://www.etsi.org/deliver/etsi_ts/138200_138299/138212/16.02.00_60/ts_1382 12v160200p.pdf )

Example

The scrambling sequence C(i) is given by Clause 5.2.1[4, TS38.211] and initialized with cell at the start of each SFN satisfying

for , and , where is the number of candidate SS/PBCH blocks in a half frame; and v is determined using the 3rd and 2nd LSB

of the SFN in which the PBCH is transmitted

4 Transport block CRC attachment

Error detection is provided on BCH transport blocks through a Cyclic Redundancy Check (CRC)

The entire transport block is used to calculate the CRC parity bits The input bit sequence is denoted by and the parity bits by

, where A is the payload size and L is the number of parity bits

The parity bits are computed and attached to the BCH transport block by setting L

to 24 bits and using the generator polynomial , resulting in the sequence

, where B = A+ L

to the channel encoder, where and K = B

5 Channel Coding

Information bits are delivered to the channel coding block They are denoted by

, where K is the number of bits, and they are encoded via Polar

coding, by setting ,and .After encoding the bits are denoted by , where N is the number of coded bits

6 More about Scrambling

NOTE: Lmax is the maximum number of SS/PBCH blocks in an SS/PBCH period This value is determined by subcarrier spacing and frequency range

7 Modulation

8 Resource Element Mapping

Overall description on the resource allocation for SS/PBCH block and Time-frequency structure of an SS/PBCH block and followings are the summary of the specification

 SS/PBCH block consists of 240 contiguous subcarriers (20 RBs)

The subcarriers are numbered in increasing order from 0 to 239 within the SS/PBCH block

The UE may assume that the contents(value) of the resource elements denoted as 'Set to 0' in are set to zero (This mean that the contents of the gray colored resource element in the SSB diagram shown below is filled with zeros)

k_ssb corresponds to the gap between Subcarrier 0 of SS/PBCH

block and Common Resource Block

o is obtained from the higher-layer parameter OffsetToPointA

o offset-ref-low-scs-ref-PRB corresponds to the

FrequencyInfoDL.absoluteFrequencyPointA Data type is ARFCN-ValueNR and the range of the value is INTEGER (0 3279165) in integer

There are two types of SS/PBCH Block

o Type A (Sub 6)

 k_ssb(k0 in older spec) = {0,1,2, ,23}

 4 LSB bits of k_ssb value can informed to UE via ssb-subcarrierOffset in MIB

 The MSB bit is informed to UE via a bit within the PBCH Data ( )

 is expressed in terms of 15 Khz subcarrier spacing

 u (numerology) = {0,1}, FR1 (sub 6 Ghz)

 is expressed in terms of 15 Khz subcarrier spacing

o Type B (mmWave)

 k_ssb(k0 in older spec) = {0,1,2, ,11}

 the whole k_ssb value can be informed to UE via ssb-subcarrierOffset in MIB

 is expressed in terms of the subcarrier spacing provided

by the higher-layer parameter

subCarrierSpacingCommon in MIB

 u (numerology) = {3,4}, FR2 (mmWave)

 is expressed in terms of 60 Khz subcarrier spacing

Following table shows the time domain (OFDM symbol number) and frequency

domain (Subcarrier Number) within SS/PBCH block

This table can be represented in Resource Grid as shown below Note that the position of PBCH DM-RS varies with v and the value v changes depending on Physical Cell ID

*Rate matching:

PBCH Decoding Process

When power on 5G/NR UE (NR Standalone UE) or When LTE is adding NR Cell

as a secondary cell, the first thing happening in UE is the process described below This is summary and the implementation on UE may vary a little bit from this

i) Search Frequency in which SSB (PSS + SCC + PBCH) is transmitted ii) Search PSS ==> By detecting PSS, UE can figure out This is done

in time domain by calculating correlation between each reference NID(2) sequences with the received signal With the correlation calculation, we can figure out the exact timing offset (i.e, exact symbol start timing of PSS) in addition to finding out the best NID(2) This timing value (let's call it as 'offset') is the crucial information to construct the accurate resource grid that

is used in step iii) and onwards

iii) Construct the resource grid from the received signal and the detected

timing from step ii)

iv) Search SSS by correlating the extracted SSS REs and calculating the

correlation between the extracted SSS and Reference SSS ==> By detecting SSS, UE can figure out

v) From and , UE can calculate Physical Cell ID ( ) Search PBCH DMRS

==> from PBCH DMRS UE can

 Estimate channel ==> Calculate the channel matrix H This will be used for equalization

 estimate noise

 figure out

vi) (based on Channel and Noise estimation) Perform Equalization(MMSE)

for PBCH extraction

==> Once this equalization is done properly, UE can

 figure out RE for PBCH

 figure out PBCH CSI

vii) Demodulate PBCH ==> figure out PBCH bits

viii) Decode PBCH ==> Figure out MIB

9 REFERENCE MATERIALS

[1] 3GPP

[2] Share technote

[3] Wikipedia, sources from internet