Network Slicing in 5G

Today, we’ll discuss about the network slicing in 5G core. So, slicing is not a new concept in 5G, it was there in 4G as well but with limited potentials such as APN, MORAN and GWCN as it doesn’t support the full End-to-End solution as in 5G. To make it easier, imagine that the operator network is a big cake and we’ll divide it into slices. Each slice will contain a part of the whole network including radio network, transport network and core network. Also, each slice is isolated from the others and they use different network resources (can be shared as well). So, each slice can support a separate use case such as different slice for each 5G use case. Also, each slice can be dedicated to a specific service such as automotive, health care or media. Then, each slice can be shared with different companies using the same service but with different SLA for each company, so for example the automotive slice can be shared between BMW, Mercedes and Audi, which we call horizontal and vertical slicing.

self-contained slot in 5G

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

Me: Please, go ahead.

My friend: I am wondering what is meant by self-contained slot in 5G?

Me: Actually, it is a new concept in 5G to allow for lower latency as you know that URLLC is one of the basic use cases in 5G and so self-contained slot is used to enhance this concept for TDD frames.

My friend: But, how does it work?

Me: It is done by allowing both the DL transmission and UL feedback to be in the same slot which will reduce the delay and this is implemented by allowing the HARQ ACK sent from the UE in the last one or two symbols of a slot (using short PUCCH) to be in the same slot where the UE will receive its DL packets, so the symbols of the slot will contain both the DL data and also the UL feedback which is the HARQ ACK (check the attached photo). 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.

My friend: Thanks a lot. You make it very simple.

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Mini-slot in 5G

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

Me: Please, go ahead.

My friend: While reading about the min. scheduling unit in 5G which is the slot, then …

Me (Interrupting him): Excuse me, what is the min scheduling unit in 5G?

My friend: It is the slot, right?

Me: No, the min. scheduling unit in 5G is called the mini-slot which is a new concept in 5G which was not available for 4G?

My Friend: So, what is mini-slot?

Me: It is the minimum scheduling unit used in 5G NR, it occupies 2, 4 or 7 OFDM symbols (regardless of numerology), so a user can be allocated a mini-slot which is less than the slot (14 symbols) and it is suitable for low latency communication. It enables what is called non-slot based scheduling that will have higher priority than normal eMBB user, so it can pre-empt other eMBB transmissions as it has requirements for lower latency.

My friend: Thanks a lot. You make it very simple.

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Reflective QoS in 5G

1 month ago

What is Reflective QoS in 5G?

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

Me: Please, go ahead.

My friend: While checking our last discussion about QoS in 5G (see below link), I found one term we didn’t discuss named Reflective QoS, what is it exactly?

Me: Actually, this is one of the most intelligent new concepts introduced in 5G which I really like and it is a simple method to perform QoS in UL with less signaling between the UE and the core.

My friend: Great, but how does it work?

Me: First, the UE will indicate that it supports Reflective QoS during PDU session establishment or modification, then when the UPF receives from SMF an indication to use Reflective QoS for a certain QoS flow, so UPF will include in the encapsulation header of the packets sent to gNB via N3 interface a new field named RQI (Reflective QoS Indicator). When the gNB receives the RQI and QFI from UPF, it’ll indicate it to the UE, so the UE will just monitor the header and once RQI is set, so it’ll apply same QoS in DL to all UL data packets transmission with no specific signaling to tell the UE which QoS will be used in UL.

My friend: Thanks a lot. You make it very simple.

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Numerologies in 5G

Why do we have multiple numerologies in 5G?

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

Me: Please, go ahead.

My friend: In 4G, we have one SCS which is 15KHz, while in 5G, there are multiple SCSs such as 15, 30, 60, 120 and 240KHz, so why do we have all these SCSs?

Me: Actually, the support of multiple numerologies is considered one of the most outstanding 5G features when compared to LTE.

My friend: Really, why?

Me: The 5G freq band is huge (unlike the 4G freq band) from around 400MHz till 52.6GHz (according to Rel-15), so at different frequency bands we can use different numerologies to achieve different purposes. For example, at low freq bands, pathloss is lower and so coverage is better, so we can use lower SCS as it’ll have large cell radius due to large CP (cyclic prefix) and high CP is achieved as we have long symbol duration (CP is a ratio of symbol duration). While at high freq bands, phase noise is increasing and so we use higher numerology to overcome it as it is more robust than lower numerology in combating phase noise. This is just one example as also for low latency requirements, short symbol duration is needed which means higher SCS.

My friend: Thanks a lot.

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Are EN-DC and Split bearer the same concept in 5G?

My friend: Hi Soumya, we found a problem during last drive test done for one 5G site as 5G DL PDCP throughput was less than previous drive although EN-DC was active in both cases?

Me: I think you mean split bearer not EN-DC, right?

My friend: Are they different?

Me: Yes, as EN-DC is a feature to allow 5G users to have dual connectivity for both 4G and 5G networks. Without it, 5G users will be kept on 4G network and won’t be connected to 5G network. It is activated at the eNB side.

My friend: So, what is split bearer?

Me: It is a feature that is activated at the gNB side to control the DL data coming from the EPC to be transmitted either at the 5G air interface only or 4G air interface only or both 4G and 5G air interfaces simultaneously. Of course, last option will have the highest possible throughput. So, I think you checked EN-DC parameters and not the split bearer, so please check it.

My friend: Yes, you are right, I checked it and split bearer was set to 5G only at the last DT, while it was previously set to both 4G+5G. Thanks a lot.

Me: Take care about it as this is very important and many engineers are mixing them.

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Is System Information Handling different in 5G?

My friend: Hi Soumya, I have a question from one of my friends who is working in 5G network with SA mode.

Me: Go ahead, please.

My friend: He told me about a strange problem as when he was checking the SIB messages from DT logs, he can’t see some SIBs.

Me: He can’t see SIB2 till SIB9, right?

My friend (staring at me): How did you know? I didn’t tell you yet.

Me: It is logic as in 5G, system information is divided into three parts:
Minimum System Information (MSI) which is called MIB: always present and sent periodically.
Remaining Minimum System Information (RMSI) which is called SIB1: always present and sent periodically.
Other System Information (OSI) which contains all the remaining SIBs from SIB2 till SIB9: which is optionally present and broadcast periodically or sent on demand based on request from UE or triggered by the network.
So, I guessed that OSI is configured to be on demand and so your friend didn’t notice as maybe neither the UE nor the network triggered it. Please ask him to check the network configuration.

My friend: I informed him and he told me that it was already set to be on demand. Thanks a lot.

Me: You are most welcomed.

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SA vs NSA Deployment in 5G?

SA vs NSA Deployment in 5G?

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

Me: Go ahead, please.

My friend: Which is better SA or NSA for 5G deployment?

Me: You can’t judge it like that, every model has its own merits and shortages, so it depends on the business case of the MNOs, which mode is suitable to their requirements, current network architecture and of course, the financial state.

My friend: But, what are the advantages of NSA that aren’t available in SA?

Me: It has many adv. such as faster deployment as EPC is already in use, also existing LTE idle mode used, so coverage gaps due to low no. of 5G sites at initial phase will be enhanced by the 4G network, also dual connectivity with LTE which can enhance the throughput instead of 5G alone and I think you already saw it in our DT results where split bearer was enabled.

My friend: That means MNOs usually will go for NSA first?

ME: Not necessarily as if MNO is covering a small area, or it is a new one, also if there is a need to deploy all the 5G use cases, so MNO can go directly for SA and I know some MNOs who followed this approach and already some 5G networks started with SA.

My friend: Thanks a lot.

Me: You are most welcomed.

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