5G NR UE POWER ON

The UE is switched on, initializing all hardware components including the baseband processor, RF front-end, and antenna system.?

1. Baseband Execution:

Baseband Firmware Boot: The baseband processor firmware is loaded and executed. This firmware controls the signal processing and protocol stack operations.?A reset sequence is initiated to set the baseband processor and other hardware components to a known state.

2. Boot Loader Execution:

Bootloader Start/Firmware initialization: The bootloader, a small program stored in non-volatile memory (such as ROM or flash), is the first piece of code executed by the baseband processor.

Hardware Check/ firmware verification: The bootloader performs initial hardware checks to verify the integrity and functionality of critical components, such as memory, RF front-end, and peripheral interfaces.

Initialization of Peripherals: Essential peripherals, such as clocks, timers, and communication interfaces (SPI, I2C, UART), are initialized.

Initialization of OS and Kernel: The baseband processor's operating system kernel is initialized. This includes setting up task schedulers, memory management, and system services.

RF Front-End Initialization: Initialization of the?drivers of the RF front-end, including the transceiver, filters, and amplifiers. antenna and interfaces are loaded.

RF Calibration: Calibration of RF components to ensure accurate frequency and power settings. This may involve automatic gain control (AGC) and frequency tuning.

Antenna Configuration: The antenna system is configured, including any beamforming or MIMO (Multiple Input Multiple Output) settings.

Self-Tests and Diagnostics: The firmware runs self-tests and diagnostics to ensure all components are functioning correctly and within specified parameters.

Memory Initialization: Initialization of volatile and non-volatile memory for storing configuration parameters, temporary data, and operational states.

Protocol Stack Initialization: Layers of the protocol stack (PHY, MAC, RLC, PDCP, RRC, and NAS) are initialized to handle communication with the network.

3. Initial Frequency and Band Detection

Frequency Scanning: The UE performs an initial scan over available frequencies to detect 5G NR cells and possibly EUTRA cells if applicable. This helps the UE?to identify the carrier frequencies used by the?network. There are two types of frequency scan or acquisition?as below

SLS (Store List search):?After powering on, the UE will start scanning the frequencies that were already stored in its memory. This frequency is stored by UE in its previous attachment.

DBS (Deviated Band Search):?In this case, UE does not have any idea about which frequency it has to try to camp on. It will start doing the blind search means scanning all the frequencies of the whole band.

4. SSB (Synchronization Signal Block) Detection:

SSB is the combination of PSS (Primary Synchronization Signal), SSS (Secondary Synchronization Signal, PBCH/MIB(Master Information Block) and PBCH-DMRS?(Demodulation Reference Signal). In NR, we have a minimum requirement of 20RBs.?SSB takes the 20RBs in the frequency domain and each SSB occupies 4 consecutive OFDM signals in the time domain and PSS, SSS and PBCH are always together in consecutive OFDM signals. The 0th?OFDM symbol is occupied by PSS and 2nd?OFDM symbol is occupied by SSS and PBCH occupies the 1st, and 3rd?complete OFDM Symbol and the 0th?and 2nd?partial OFDM symbols.??PBCH total we have 576 REs out of which PBCH DMRS we have 1/4th?REs.?PBCH occupies 576REs. PBCH DMRS occupies 576/4 which is 144 REs.

Cell Search and Synchronization:

Cell Search: ?The UE performs cell search by detecting synchronization signals (SSS and PSS) which are periodically broadcast by gNB as a part of SSBs. This allows the UE to adjust the internal clock and frequency reference to align with the timing and frequency of the detected cells.

Primary Synchronization Signal (PSS):

Purpose: The PSS is used by the UE to achieve symbol timing synchronization and to identify the 5G cell.

Length: The PSS sequence in 5G NR has a length of 127.

Content: The PSS contains one of three possible sequences, allowing the UE to determine the physical layer cell identity within a group of three(0,1,2).

Detection: ??The received time domain signals are converted to the frequency domain using the FFT. The ?UE applies a matched filter using the known PSS sequences corresponding to the three possible cell identities (N-ID2). The matched filter involves correlating the signal with the locally generated PSS sequence. The correlation results are analyzed to detect peaks The position of the peak indicates the timing of the PSS and the magnitude indicates the signal strength. The signal that produces the highest correlation peak is detected and the corresponding peak is detected and the corresponding (N-ID2) is identified

Secondary Synchronization Signal (SSS)

Purpose: The SSS is used by the UE to achieve frame timing synchronization and to complete the identification of the cell ID.

Length: The SSS sequence in 5G NR also has a length of 127.

Content: The SSS contains one of 336 possible sequences. The SSS provides additional information to determine the full cell ID and helps in establishing frame boundaries.?

Detection: The received signal containing SSS is converted into the frequency domain using the FFT. ?The UE performs correlation with each of the possible SSS sequences matched filtering is used to correlate the received signal with the locally generated sss sequences. The correlation results are analyzed to detect peaks. The sequence with the highest peaks detected provided the (N-ID1) ?cell group identity

Physical cell iD Detection

n Physical cell ID (PCI). The physical cell ID is calculated

PCI= 3 N-ID2+ N-ID1

5. PBCH ?Processing:

System Information Acquisition:?The UE reads the Master Information Block (MIB) from the Physical Broadcast Channel (PBCH) to obtain basic system information.

Master Information Block (MIB): The UE decodes the MIB from the Physical Broadcast Channel (PBCH). The MIB contains critical information such as the system frame number (SFN) and the physical configuration of the cell.?The MIB will give the basic cell information.

?System information Block:?The UE reads System Information Blocks (SIBs) to acquire necessary configuration parameters, including cell access parameters, scheduling information, and random access configuration.?The ?SIB will detailed cell information and scanning information.

?System Information Blocks (SIB1): The UE reads SIB1, which provides detailed system information necessary for cell access. SIB1 includes parameters like cell identity, tracking area code (TAC), and scheduling information for other SIBs.

?6. Frequency and Band selection

Frequency Scanning: Based on the information in the SIBs, the UE performs further scanning if necessary to detect additional frequency bands or cells, especially if the network conditions or UE's location change.

?7. Initial Access and Random Access Procedure?:

The UE initiates a Random Access Channel (RACH) procedure to request an initial connection with the gNB.?It enables the connection establishment.

Random Access Preamble (Message 1): The UE transmits a random access preamble on the Physical Random Access Channel (PRACH) to initiate contact with the gNB.

Short Preamble Format:

Purpose: Used in scenarios where low latency is critical, such as in dense urban deployments or scenarios requiring fast handovers.

Structure: The short preamble consists of a smaller number of sub-carriers and a shorter duration.

Subcarrier Spacing: Typically uses a higher sub-carrier spacing (e.g., 30 kHz, 60 kHz, 120 kHz).

Preamble Length: Varies depending on the sub-carrier spacing. There are various short preamble formats ??

Format 0:?The sub-carrier spacing is 15KHz. The preamble length is 139, transmitted over 0.5 ms. ?Typically used for general coverage scenarios with moderate latency requirements

Format 1: The sub-carrier spacing is 30KHz ?Preamble length is 139, transmitted over 0.25ms. Typically used for low latency and small cell scenarios.

Format 2:?The sub-carrier spacing is 60 KHz. ?The preamble length is 139 sub-carriers, transmitted over 0.125 ms. Designed for very low latency and high-density small cell scenarios.

Format 3:?The subcarrier spacing is 120 KHz. ?The length of the sub-carrier is 139 ?and transmitted over o.0625ms. ?Used in Ultra-low latency applications.

Long Preamble Format:?

The 3GPP specifications (e.g., 3GPP TS 38.211) define several long preamble formats. Here are the main long preamble formats used in 5G NR:`

Purpose: Used for scenarios requiring higher coverage and better signal robustness, such as rural or wide-area deployments.

Structure: The long preamble consists of more subcarriers and a longer duration.

Subcarrier Spacing: Typically uses a lower subcarrier spacing (e.g., 1.25 kHz, 15 kHz).

Preamble Length: Varies with subcarrier spacing. For example, a 15 kHz subcarrier spacing has a preamble length of 1 ms.

Format A1:?The subcarrier spacing is 1.25 KHz, number of subcarriers is 839 subcarriers, transmitted over 1 ms. Primarily used in scenarios that require a wide area of coverage with relatively long delay spreads, suitable for large cell sizes.

Format A2:?The subcarrier spacing is 1.25 KHz, number of subcarriers is 839 subcarriers, transmitted over 2ms.Similar to Format A1 but with a longer preamble duration, providing better robustness in very large cells or environments with high delay spreads.

Format A3: ?The subcarrier spacing is 1.25 KHz, number of subcarriers is 839 subcarriers, transmitted over 3ms. Suitable for extreme coverage scenarios where signal robustness is critical, such as rural or remote areas with very large cell sizes

Format ?B1:?The subcarrier spacing is 5 KHz, number of subcarriers is 839 subcarriers, transmitted over 0.25 ms. ?Designed for medium coverage scenarios, balancing between coverage and latency requirements.

Format B2: ?The subcarrier spacing is 5 KHz, number os subcarriers is 839 subcarriers, transmitted over 0.5 ms. ?Suitable for scenarios needing higher robustness compared to B1, used in medium to large cells.

Format B3:?The subcarrier spacing is 5 KHz, number os subcarriers is 839 subcarriers, transmitted over 0.75 ms. ??For larger cells where signal robustness is a higher priority, providing a balance between latency and coverage.

Random Access Response (Message 2): The gNB responds with a Random Access Response (RAR) containing timing advance, initial uplink grant, and temporary C-RNTI (Cell Radio Network Temporary Identifier).

RRC Connection Request (Message 3): The UE uses the uplink grant to send an RRC Connection Request message, indicating its intention to establish an RRC connection.

RRC Connection Setup (Message 4): The gNB sends an RRC Connection Setup message, providing the UE with configuration details for the RRC connection.

8. UE Registration and Authentication

The UE registration verifies and registers the UE to the network

NAS (Non-Access Stratum) Procedures: The UE performs NAS registration with the core network, including authentication and security setup. This process involves exchanging messages with the AMF (Access and Mobility Management Function).

Security Mode Command: The gNB sends a Security Mode Command to the UE, initiating the establishment of encryption and integrity protection keys.

Security Mode Complete: The UE responds with a Security Mode Complete message, confirming the successful establishment of security parameters.

The UE is ready to proceed with other procedures like Registration, Service Request, or data transfer in a secure manner.

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