Session 02/09 : 5G Mini Slots & Preemptive Scheduling : For Ultra-Low Latency Use-Cases

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In this video, we dive deep into how 5G achieves ultra-low latency, making it a game-changer for real-time applications like autonomous vehicles, industrial IoT, and mission-critical communications. The introduction of mini-slots, preemptive scheduling, and self-contained slots brings unparalleled flexibility to 5G networks.   We’ll explore: * Mini-Slots: A shortened version of traditional slots that reduces wait times, allowing data transmission without waiting for slot boundaries. Mini-slots can start at any symbol boundary, making data scheduling more dynamic. * Preemptive Scheduling: Learn how 5G schedules high-priority traffic (like URLLC) by "stealing" resources from ongoing lower-priority traffic. This ensures that latency-sensitive data gets through without delay. * Self-Contained Slots: Understand how self-contained slots in 5G allow complete downlink transmission, acknowledgment, and uplink response within a single slot, reducing latency to as low as 500 microseconds. * Subcarrier Spacing: Discover how the flexible subcarrier spacing in 5G allows different slot durations depending on the use case, helping optimize for both latency and throughput. * Trade-Offs: We’ll also discuss the trade-off between latency and power efficiency. With 5G’s mini-slots and preemptive scheduling, low-latency devices often need to stay active, consuming more power.   Whether you're working in telecom or simply interested in how 5G technology supports low-latency applications, this video is for you. Understand how these advanced features pave the way for future technologies like smart cities, remote surgery, industrial automation, and real-time communication.    Subscribe to "Learn And Grow Community"  YouTube : https://www.youtube.com/@LearnAndGrowCommunity LinkedIn Group : https://linkedin.com/company/LearnAndGrowCommunity Follow #learnandgrowcommunity      #5g #5gsa #5gnsa #5gran #5gcore #5gnr #5gnetwork #5gnetworks #newradio #telecommunications #telecom #oran #openran #4gvs5g #5gvs4g #5gtechnology #MiniSlots #PreemptiveScheduling #lowlatency  #WirelessInnovation #telecominsights  #urllc  #mobilebroadband  #RealTime5G #smartcities  #autonomousdriving #telecominsights

Transcript

00:00Hi, in the last session, we learned

00:02that how the flexible subcarrier spacing in 5G

00:05can lead to different slot lengths

00:07and how it can improve the network latency, which

00:10is crucial for time-sensitive applications.

00:13We learned that how the higher subcarrier spacings

00:15reduce the slot durations.

00:18We also learned that why we actually

00:20needed flexible numerology in 5G to cater millimeter bands.

00:25Now, in this session, we will explore two additional features

00:28in 5G NR that further contribute

00:30to achieving lower latencies.

00:33In LTE, the transmission time interval, or TTIE,

00:37is the duration of a transmission slot,

00:39and it is fixed at 1 millisecond.

00:42As shown in picture, the shortest delay

00:45in the LTE between a downlink data transmission

00:47and the corresponding ACK or NACK notification in the uplink

00:51is 4 milliseconds.

00:54Although this 4 millisecond delay

00:55is acceptable for the mobile broadband applications,

00:59but it is too long for the ultra-reliable low latency

01:02communication, or URLLC use cases.

01:06In 5G NR, this delay can be significantly

01:09reduced, which make it more suitable for low latency

01:12applications.

01:14So 5G NR introduced the concept of self-contained slots.

01:19This self-contained slot allows more efficient data

01:22transmission, especially in TDD systems or time division

01:26duplex systems.

01:28This means that within a TDD band,

01:30the downlink data, guard period, and the corresponding ACK

01:34or NACK notification can all be accommodated

01:37within a 500 millisecond slot.

01:39Now, depending on the numerology,

01:41this entire process can be completed

01:43within a single slot.

01:45Apart of the self-contained slot and flexible subcarrier

01:48spacing, 5G NR also introduced another concept

01:52of mini-slot, which provides even more flexibility

01:55in the data transmission.

01:57A mini-slot is just a shortened version of a regular slot.

02:01This is introduced to further reduce the latency

02:04by allowing quicker data transmissions.

02:07In NR, a mini-slot can start at any symbol boundary.

02:11So there is no need to wait for the next slot boundary

02:14to schedule any data.

02:16That is why it reduces the delay.

02:18Additionally, a mini-slot is not fixed in length.

02:22It can contain either two or four or seven symbols.

02:25However, a standard slot is fixed at 14 symbols.

02:30So mini-slots can offer flexibility in slot duration

02:34based on the specific needs of the transmission.

02:37And this is especially beneficial for the low latency

02:40applications.

02:41This flexibility in the duration and start time

02:45allows low latency devices to transmit data

02:48without waiting for the next slot boundary

02:50or being constrained by a long slot.

02:52And this has effectively minimized the latency.

02:56Now let's talk about preemptive scheduling

02:59and understand how it works in practice.

03:02So in this scenario, the Mac scheduler

03:05initially allocates some resources

03:07to a mobile broadband UE, which you can see here

03:09with the gray color.

03:11But then we steal some resources from this pre-scheduled mobile

03:14broadband transmissions and reallocate that resource

03:17to transmit URLLC data, which is in red color.

03:22This happens to ensure that the URLLC low latency

03:26data gets the priority.

03:28This approach is known as preemptive scheduling,

03:31where URLLC data can override the pre-scheduled transmissions

03:36to meet its strict latency requirement.

03:39Now, if you are doing this, then we

03:41need to inform the UE as well that some of the scheduled

03:44slots are now used for other services.

03:46And for this purpose, a preemption indicator is sent.

03:50And you will get notified that some of its resources

03:53have been reallocated for URLLC data transmissions.

03:57These different levels of flexibility

03:59are helping 5G NR to achieve lower latency,

04:02as URLLC data can be scheduled with a lot of flexibility

04:07in slot duration and slot time.

04:09Typically, the UE monitors the downlink control information

04:13channel, or DCI channel, to know when it needs to receive data.

04:19The UE monitors the channel at the beginning of each slot

04:22and then goes into the sleep mode

04:24for the rest of the slot duration

04:26to save the battery power.

04:28However, for the low latency devices that uses many slots

04:32and the data can be scheduled at any time and at any slot,

04:36so we have a trade-off here.

04:38Because low latency devices has to constantly monitor

04:41the DCI channel.

04:42And hence, they cannot sleep between the slot boundaries.

04:46And this increases the power consumption.

04:49Therefore, it's essential to understand

04:52the trade-off between achieving a low latency

04:54and maintaining the power efficiency.

04:57In summary, many slots and preemptive scheduling

05:00are the important design innovations in 5G NR

05:04to serve the ultra-reliable and low latency use cases.

05:07And they significantly contribute

05:09in achieving these low latency requirements

05:11for the next generation applications.

05:14So that's it for today.

05:15In the next session, we'll be talking

05:16about scheduling in 5G NR.

05:19So stay tuned for the updates.

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05:22then please do subscribe to learn and grow

05:24community for regular updates.

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