Why latency in 5G is less than 4G?

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Why latency in 5G is less than 4G?

My friend: Hi Ibrahim, I have a question for you.

Me: Please, go ahead.

My friend: I know that 5G latency should be lower than 4G as per IMT-2020 requirements, but how can this be achieved?

Me: 5G is designed with URLLC as one of the main use cases, so there are a lot of methods that can be used to reduce latency in 5G, such as using multiple numerologies than 4G, as using different Subcarrier Spacing (SCS) allows for lower slot duration. So, in 5G, we can use 15, 30, 60, or 120 KHz as SCS while only 15KHz is used in 4G. So, 5G slot duration can be short as 0.125 ms (using 120 KHz) compared to 1 ms in case of 4G. Also, Mini-Slot can be used to reduce latency as here, user can occupy 2, 4 or 7 OFDM symbols only compared to normal slot which is 14 symbols and mini-slot is having higher priority and can pre-empt a normal eMBB user, so latency is reduced too much.

My friend: That’s good, are there any other techniques to reduce latency in 5G?

Me: Yes, MEC (Multi-Access Edge Computing) brings technology resources closer to the end user. So, data is processed and stored at the network’s edge, not at some distant data center, which significantly will reduce latency. Also, Self-Contained slot can be used to lower latency as it allows both the DL transmission and UL feedback (which is the HARQ ACK) to be in the same slot, this will reduce the delay from the end of the DL transmission until the reception of the ACK from the UE to be in the order of an OFDM symbol, corresponding to a few tens of microseconds depending on the numerology used. This can be compared to almost 3ms in LTE. Also, network slicing can be used to reduce latency.

My friend: But how can network slicing reduce latency in 5G?

Me: By assigning a specific slice for the services that require low latency, then this slice will be prioritized more than the remaining slices, thus we can have much lower latency that can be utilized for specific applications that require such a low latency.

My friend: Thank you very much. You made it very clear.

Me: You are most welcome.

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Techniques being used to reduce latency in 5G

Summary:

  • Front-loaded control signals in very first OFDM symbol or first two OFDM symbols of a slot to inform Rxr of DL data.

  • No T-domain interlacing across OFDM symbols.

  • Mini-slot Txn: can be useful in various other scenarios, including transmissions in unlicensed spectrum and transmissions in the millimeter wave spectrum (mmWave band). URLLC and LBT based transmission in unlicensed spectrum via mini-slots.

  • HARQ ACK within 1 Slot-Quick.

  • 1 slot time b/w receiving an UL grant on DL and UL Txn.

  • Changes in MAC and RLC: can schedule Txns w/o knowing the data volume unlike LTE.

  • Shorter transmission time interval (sTTI) operation reduces processing times and hence radio latency at the Physical Layer.

  • Grant-Free transmission mode.

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5G vs LTE: How Does 5G Deliver Faster Speeds and Lower Latency?

We all know 5G provides faster speeds and lower latency than LTE, but the real question is: how does 5G do that?

In this article, I’ll take you step-by-step through simple call flow and highlight key differences between 5G and LTE in a clear and easy way.

How Does 5G Deliver Faster Speeds and Lower Latency
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