Support of Ultra-reliable and Low-Latency Communications (URLLC) in NR

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URLLC IN NR

Ultra-reliable and Low-Latency Communications (URLLC) is one of the three use cases defined by 5G networks along with Enhanced Mobile Broadband (eMBB) and Massive Machine-Type Communications (mMTC). URLLC is designed to support mission-critical applications that require high reliability and low latency. In 5G networks, URLLC is achieved by introducing several new features that enhance the performance of the network. This paper will discuss the technical aspects of URLLC in New Radio (NR) and how it is supported in 5G networks.

Overview of URLLC in 5G

URLLC is one of the three use cases in 5G networks. It is designed to support mission-critical applications that require high reliability and low latency. Examples of such applications include factory automation, remote surgery, and autonomous driving. URLLC applications require high reliability to ensure that critical data is transmitted without errors. They also require low latency to enable real-time control and feedback.

In 5G networks, URLLC is achieved by introducing several new features that enhance the performance of the network. These features include:

1. Ultra-Reliable Low-Latency Communication (URLLC) framework: The URLLC framework defines the requirements for ultra-reliable and low-latency communication in 5G networks. It specifies the latency and reliability requirements for different applications and defines the parameters that need to be optimized to meet these requirements.
2. Radio Access Network (RAN) enhancements: 5G RAN introduces several enhancements to support URLLC, including support for flexible numerology, support for higher order modulation and coding schemes, and support for advanced interference management techniques.
3. Core Network (CN) enhancements: 5G core network introduces several enhancements to support URLLC, including support for network slicing, support for edge computing, and support for network function virtualization (NFV).
4. New Radio (NR) enhancements: NR introduces several enhancements to support URLLC, including support for Ultra-Reliable Low-Latency Communication (URLLC) services, support for enhanced Physical Downlink Control Channel (ePDCCH), support for Short TTI (Transmission Time Interval), support for adaptive beamforming, and support for carrier aggregation.

Technical Aspects of URLLC in NR

Ultra-Reliable Low-Latency Communication (URLLC) is a key feature of 5G networks that offers low latency, high reliability, and high availability for mission-critical applications such as autonomous driving, remote surgery, and industrial automation. The 3rd Generation Partnership Project (3GPP) has defined a set of technical specifications to support URLLC, including enhanced Physical Downlink Control Channel (ePDCCH), Short TTI (Transmission Time Interval), adaptive beamforming, and carrier aggregation.

In this article, we will provide a technical explanation of these key features of URLLC services and their importance in meeting the stringent requirements of mission-critical applications.

Ultra-Reliable Low-Latency Communication (URLLC):

URLLC is a key feature of 5G networks that is designed to meet the stringent requirements of mission-critical applications such as autonomous driving, remote surgery, and industrial automation. URLLC offers ultra-reliable and low-latency communication, which is achieved by minimizing the delay between the transmission of data and its reception. This is crucial for applications that require real-time responsiveness and high reliability.

To support URLLC services, 3GPP has defined a set of technical specifications, including ePDCCH, Short TTI, adaptive beamforming, and carrier aggregation.

Enhanced Physical Downlink Control Channel (ePDCCH):

The Physical Downlink Control Channel (PDCCH) is a key component of the 5G control plane that is used to deliver control information to the user equipment (UE). The ePDCCH is an enhanced version of the PDCCH that offers higher reliability and lower latency by reducing the complexity of control signaling and increasing the efficiency of channel utilization.

ePDCCH is achieved by introducing a new aggregation level, which allows multiple PDCCH candidates to be mapped to a single ePDCCH resource. This reduces the overhead of control signaling, which in turn reduces the delay and increases the reliability of communication. Additionally, ePDCCH can operate in both the normal and the extended CP (Cyclic Prefix) formats, which allows for greater flexibility in the deployment of ePDCCH resources.

Short TTI (Transmission Time Interval):

Transmission Time Interval (TTI) is the time duration between two consecutive transmissions in a wireless communication system. Short TTI is a feature that reduces the duration of TTI from 1ms to 0.5ms or even lower. This feature is particularly important for URLLC services because it reduces the delay in transmission and reception, which improves the responsiveness of the system.

Short TTI is achieved by reducing the size of the time-frequency resource blocks used for data transmission. This increases the granularity of the scheduling, which in turn allows for more efficient use of the available resources. Additionally, short TTI allows for more frequent feedback from the UE, which improves the accuracy of the control signaling.

Adaptive Beamforming:

Beamforming is a technique that is used to focus the transmission and reception of radio waves in a particular direction. Adaptive beamforming is a variant of beamforming that adjusts the direction of the beam in response to changes in the wireless channel. This is particularly important for URLLC services because it improves the reliability of communication by reducing the interference and the effects of fading.

Adaptive beamforming is achieved by using an array of antennas to steer the beam in a particular direction. The direction of the beam is adjusted based on the feedback from the UE, which provides information about the quality of the wireless channel. This allows for more efficient use of the available resources and reduces the interference and the effects of fading.

Carrier Aggregation:

Carrier Aggregation (CA) is a feature of 5G New Radio (NR) that allows mobile devices to combine multiple frequency bands to increase their data transfer rates and improve network capacity. In essence, Carrier Aggregation combines the bandwidth of multiple frequency bands to create a wider channel and increase the maximum achievable data rate.

With Carrier Aggregation, the mobile device can simultaneously communicate with multiple base stations, each using a different frequency band. The device can then combine the data streams from each base station to create a single, faster data stream. For example, a device can combine two 20 MHz bands to create a 40 MHz channel, which doubles the data transfer rate.

Carrier Aggregation can be implemented in two ways: contiguous and non-contiguous. Contiguous Carrier Aggregation combines adjacent frequency bands to create a wider channel, while non-contiguous Carrier Aggregation combines non-adjacent frequency bands.

In NR, there are several Carrier Aggregation configurations, each with different bandwidth combinations and maximum data rates. The maximum data rate that can be achieved with Carrier Aggregation depends on the number of bands being aggregated and their individual bandwidths, as well as other factors such as modulation scheme, coding rate, and antenna configuration.

Overall, Carrier Aggregation is an important feature of 5G NR that enables higher data transfer rates and improved network capacity, which are essential for supporting the increasing demand for high-speed mobile data services.

URLLC (Ultra-Reliable Low-Latency Communication) is one of the three key usage scenarios defined for 5G networks, alongside enhanced mobile broadband (eMBB) and massive machine-type communication (mMTC). URLLC is targeted at applications that require extremely low latency and high reliability, such as industrial automation, autonomous vehicles, and critical infrastructure monitoring. In this response, we will discuss the technical aspects of URLLC in NR (New Radio), the 5G air interface.

URLLC Requirements:

The requirements of URLLC can be broadly classified into two categories: latency and reliability. In terms of latency, URLLC requires an end-to-end latency of less than 1 ms. This means that the time it takes for a packet to be transmitted from the device to the base station and back should be less than 1 ms. In terms of reliability, URLLC requires a packet error rate (PER) of less than 10^-5. This means that less than one packet in 100,000 should be lost or corrupted during transmission.

Radio Interface Design:

To meet the URLLC requirements, NR has introduced several new features and enhancements to the radio interface design. Some of the key features are:

a. Numerology: NR introduces a flexible numerology design that allows for different subcarrier spacing and slot durations. The smaller subcarrier spacing and slot durations allow for higher transmission rates and lower latency.

b. Channel Coding: NR introduces a new channel coding scheme called Polar coding that provides higher coding gain and lower latency than the previous convolutional coding scheme used in LTE.

c. HARQ (Hybrid Automatic Repeat Request): NR introduces a new HARQ scheme called HARQ-ACK bundling that allows for the transmission of multiple HARQ acknowledgments in a single subframe. This reduces the latency for HARQ retransmissions.

d. Scheduling: NR introduces a new scheduling mechanism called dynamic TDD (Time Division Duplexing) that allows for more flexible scheduling of uplink and downlink transmissions. This enables faster turnaround times for URLLC packets.

e. Beamforming: NR introduces advanced beamforming techniques such as massive MIMO (Multiple-Input Multiple-Output) and beam tracking that improve the reliability and coverage of the radio interface.

RAN Architecture:

The RAN (Radio Access Network) architecture for URLLC is designed to minimize latency and improve reliability. Some of the key features of the RAN architecture are:

a. Control User Plane Separation (CUPS): CUPS separates the control and user planes in the RAN, allowing for more efficient and flexible handling of URLLC traffic.

b. Multi-connectivity: Multi-connectivity allows for simultaneous connections to multiple base stations, reducing the latency and improving the reliability of URLLC traffic.

c. Edge Computing: Edge computing moves the computation and storage closer to the devices, reducing the latency for URLLC applications that require real-time data processing.

Network Slicing:

Network slicing is a key feature of 5G networks that allows for the creation of dedicated virtual networks for specific use cases. For URLLC, network slicing allows for the creation of dedicated slices with guaranteed resources and low latency, ensuring that the URLLC traffic is not affected by other traffic on the network.

Security:

Security is a critical aspect of URLLC, particularly for applications that require critical infrastructure monitoring and control. NR introduces several new security features such as device authentication, network authentication, and secure key exchange to ensure the integrity and confidentiality of URLLC traffic.