Analysis of the main process and functions of UU interfaces: What is the relationship between UU and WCDMA?

Introduction to Uu Interface

The Uu interface is an important interface in mobile communication systems. It connects user equipment (UE) and base stations (Node B). In the WCDMA system, the Uu interface is the most crucial interface. It is responsible for transmitting user data and related signaling, including broadcast paging, RRC connection processing, the execution of handover and power control decisions, the processing of wireless resource management and control information, as well as the processing of baseband and radio frequency processing information.

Protocol Layers of Uu Interface

The protocol layers of the Uu interface are mainly divided into the following three layers:

In the 5G system, a new SDAP (Service Data Adaptation Protocol) layer is added to the protocol stack of the Uu interface in the data link layer to implement the user plane function of the Uu interface. It is used to mark each packet with a flow identifier (QFI, QoS Flow ID) and perform mutual mapping between QoS flows and DRB (Data Radio Bearer) according to QoS requirements.

Main Processes of Uu Interface

The Uu interface is a wireless interface between user equipment (UE) and base stations (Node B or gNodeB), mainly used for transmitting user data and control signaling. The following are the main processes of the Uu interface:

1. System Information Acquisition

The UE acquires AS and NAS system information broadcast by E-UTRAN through system messages. This process can occur in both RRC_IDLE and RRC_Connected states.

2. Paging

The network notifies the UE of an incoming call or data arrival through a paging message. The paging message contains the identification information of the UE so that the UE can identify whether it is a paging for itself.

3. RRC Connection Establishment

The UE requests to establish an RRC connection with the base station through an RRC Connection Request message. After receiving the request, the base station allocates resources for the UE through an RRC Connection Setup message and establishes SRB1 (Signalling Radio Bearer 1).

4. Initial Authentication Activation

The base station authenticates the UE, including steps such as the transmission of authentication request messages, key confirmation and key sharing.

5. RRC Connection Reconfiguration

The base station reconfigures resources for the UE through an RRC Connection Reconfiguration message, including allocating new radio bearers or modifying the parameters of existing radio bearers.

6. RRC Connection Release

When the data transmission is completed or the connection is no longer needed, the base station releases the RRC connection resources through an RRC Connection Release message.

7. Handover to E-UTRA

When the UE is moving, it may need to handover from one base station to another. This process involves steps such as measurement reports, handover preparation and handover execution.

8. Mobility within E-UTRA

When the UE moves within the E-UTRA network, it needs to perform a tracking area update (TAU) to ensure that the network can track the location of the UE.

9. Handover from E-UTRA

When the UE hands over from the E-UTRA network to other radio access technologies (RAT), it needs to execute the corresponding handover process.

10. Measurement Report

The UE periodically sends measurement reports to the base station, including information such as signal strength and quality, so that the base station can make resource allocation and handover decisions.

11. DL Information Transmission

The base station transmits data and control information to the UE through the downlink (DL).

12. UL Information Transmission

The UE transmits data and control information to the base station through the uplink (UL).

13. UE Capability Notification

When the UE establishes a connection or is reconfigured, it notifies the base station of its own capability information, including supported frequency bands, modulation methods, etc.

The above processes are the main signaling processes of the Uu interface. They ensure that the communication between the UE and the base station can proceed smoothly and can adapt to different network conditions and user requirements.

Applications of Uu Interface

The Uu interface is a wireless interface that connects user terminal equipment (UE) and base stations (eNodeB/gNodeB), mainly used to realize the communication between UE and EUTRAN (Evolved Universal Terrestrial Radio Access Network). The following are some main applications of the Uu interface:

1. User Plane Data Transmission

The Uu interface is used to transmit user service data, such as Internet access, voice calls, video streaming, etc.

2. Control Plane Data Transmission

The Uu interface is also used to transmit control plane data, mainly RRC (Radio Resource Control) messages, to realize control functions such as UE access, handover, broadcast, and paging.

3. Hierarchical Protocol Applications

The protocol stack of the Uu interface is divided into three layers:

• Physical Layer (PHY): Responsible for processing wireless signals such as modulation, encoding, MIMO, etc., and providing wireless resources for high-level data.
• Data Link Layer (MAC/RLC/PDCP): Responsible for operations such as data segmentation, retransmission, encryption, and decryption to ensure reliable data transmission.
• Network Layer (RRC Signaling and User Plane Data): Responsible for controlling the users of interface services, including functions such as RRC connection establishment, reconfiguration, and release.

4. Applications in V2X (Vehicle-to-Everything) Communication

The Uu interface has the following application scenarios in V2X communication:

• V2N (Vehicle-to-Network) Communication: Vehicles upload real-time data to the cloud platform or obtain road information, weather warnings, map updates, etc. from the cloud platform through the Uu interface.
• Remote Management and Control: Through the Uu interface, remote diagnosis, software update (OTA) and remote intervention in emergency situations of vehicles can be realized.

5. Applications in 5G Network

The 5G Uu interface has the following characteristics and applications:

• Enhanced Spectrum Utilization: Improve spectrum efficiency and increase system capacity through massive MIMO and beamforming technologies.
• Flexible Frame Structure: Adapt to the needs of different scenarios, such as eMBB, URLLC and mMTC, and dynamically adjust subframe configurations to optimize performance.
• Efficient Signaling Mechanism: Reduce the number of unnecessary interactions between the control plane and the user plane and shorten the response time.
• Enhanced Security: Ensure the secure transmission of user data through encryption algorithms, authentication mechanisms and integrity protection measures.
• Support for Diversified Service Requirements: Not only support traditional interpersonal communication services, but also meet the requirements of various emerging application scenarios such as the Internet of Things and autonomous vehicles.

Development of Uu Interface

The Uu interface, as a wireless interface between user equipment (UE) and base stations (eNodeB/gNodeB), has experienced significant development in the evolution of mobile communication technology. The following are the key aspects of its development:

1. Evolution from 3G to 5G

• 3G Era: The Uu interface was mainly used to transmit user data and related signaling. The protocol structure included the physical layer (L1), the data link layer (L2) and the network layer (L3). Among them, the L2 layer included media access control (MAC), radio link control (RLC), packet data convergence protocol (PDCP) and broadcast/multicast control (BMC); the L3 layer included radio resource control (RRC), mobility management (MM) and connection management (CM).

• 4G Era: The Uu interface in the LTE network was similar to that in 3G in terms of protocol stack structure, but had significant improvements in technology implementation, such as the adoption of orthogonal frequency division multiplexing (OFDM) technology, supporting higher data transmission rates and lower latency.

• 5G Era: The 5G Uu interface introduced a number of key technologies on the basis of maintaining the original protocol structure, such as massive MIMO (multiple input multiple output), beamforming technology, flexible frame structure and efficient signaling mechanism, to meet the diverse service requirements of eMBB (enhanced mobile broadband), URLLC (ultra-reliable low-latency communication) and mMTC (massive machine type communication).

2. Improvement of Technical Characteristics

• Enhanced Spectrum Utilization: The 5G Uu interface improves spectrum efficiency through massive MIMO technology. Multiple antenna units are deployed at the base station to serve multiple users simultaneously, increasing system capacity. Beamforming technology concentrates energy to send signals in a specific direction, reducing interference and improving transmission rate.

• Flexible Frame Structure: The 5G Uu interface introduces a flexible frame structure that can dynamically adjust subframe configurations, such as subcarrier spacing and symbol length, according to service types to meet the needs of different scenarios such as eMBB, URLLC and mMTC.

• Efficient Signaling Mechanism: The 5G Uu interface adopts a more efficient and flexible signaling mechanism, reducing the number of unnecessary interactions between the control plane and the user plane. For example, reducing handshake steps during connection establishment or handover, shortening the response time, which is especially important for applications that require immediate response.

• Enhanced Security: The 5G Uu interface ensures the secure transmission of user data through encryption algorithms, authentication mechanisms and integrity protection measures. It also adds stronger protection measures for user privacy, such as anonymous identity identifiers to prevent tracking.

3. Expansion of Application Scenarios

• Traditional Interpersonal Communication Services: The Uu interface has always supported traditional interpersonal communication services such as voice calls and text messages.

• Internet of Things (IoT): With the development of technology, the Uu interface can meet the connection requirements of Internet of Things devices, support massive machine type communication and realize the interconnection of devices.

• Vehicle Networking (V2X): In the field of intelligent connected vehicles, the Uu interface is used for communication between vehicles and base stations to realize V2N (Vehicle - to - Network) communication, such as vehicles uploading real-time data to the cloud platform or obtaining road information, weather warnings, map updates, etc. from the cloud platform. It can also be used for remote management and control, such as remote diagnosis, software update (OTA) and remote intervention in emergency situations.

Functions of Uu Interface in WCDMA System

The Uu interface is a key interface in the WCDMA system. It connects user equipment (UE) and radio network controllers (Node B). The main functions of the Uu interface include:

• Broadcast Paging and RRC Connection Processing: The Uu interface is responsible for processing the paging of system broadcast information and the establishment, maintenance and release of radio resource control (RRC) connections.

• Execution of Handover and Power Control Decisions: The Uu interface participates in the execution of handover decisions and power control in wireless networks, ensuring that the UE can smoothly handover between different cells and maintain appropriate transmit power to optimize energy consumption and reduce interference.

• Processing of Wireless Resource Management and Control Information: The Uu interface manages wireless resources, including frequency allocation, power control, selection and scheduling of wireless resources, to improve network efficiency and performance.

• Processing of Baseband and Radio Frequency Processing Information: The Uu interface involves the baseband and radio frequency processing of wireless signals, including encoding, modulation and demodulation processes, to ensure the effective transmission of signals.

Improvements of Uu Interface in 5G NR

The Uu interface of 5G NR (New Radio) has significant improvements and optimizations in many aspects compared with the Uu interface of WCDMA (Wideband Code Division Multiple Access). The following are some main improvement points:

• Higher Data Rate: 5G NR is designed with a wider spectral bandwidth and a more efficient modulation and coding scheme, making its peak data rate much higher than that of WCDMA. This means that 5G NR can support higher-rate data transmission and meet the needs of large-data-volume applications such as future high-definition videos and virtual reality.

• Lower Latency: 5G NR introduces a new frame structure and scheduling algorithm, reducing the transmission latency. This is very important for applications that require quick responses, such as autonomous driving and telemedicine.

• Stronger Network Coverage: 5G NR supports multiple frequency bands, including low-frequency, mid-frequency, and high-frequency bands, enabling it to provide stable network coverage in various environments such as cities, suburbs, and indoors.

• Better Spectrum Utilization: 5G NR adopts advanced multiple access technologies, such as OFDM (Orthogonal Frequency Division Multiplexing) and NOMA (Non-Orthogonal Multiple Access), improving the spectrum utilization efficiency.

• More Flexible Network Architecture: 5G NR supports advanced technologies such as network slicing and edge computing, allowing the network to provide customized services according to different application requirements.

• Stronger Security Performance: 5G NR strengthens the encryption and authentication mechanisms, enhancing the security of the network.

• Wider Range of Application Scenarios: 5G NR not only supports traditional mobile broadband services but also emerging application scenarios such as the Internet of Things and industrial automation.

In summary, the Uu interface of 5G NR has significant improvements in data rate, latency, coverage, spectrum utilization, network architecture, security performance, and application scenarios compared with the Uu interface of WCDMA. These improvements enable 5G NR to better meet the needs of future communication networks and promote the digital transformation of society.

Summary

The Uu interface connects UE and base stations and plays a crucial role in both WCDMA and 5G systems. It has a hierarchical protocol, multiple processes such as system information acquisition, and is used in various application scenarios such as user plane and control plane data transmission. It has continuously evolved from 3G to 5G, and the Uu interface in 5G NR has significant improvements in many aspects.