5G KPIs Part IV

General 5G KPIs

The general KPIs given in this part are based on a collection taken from SDOs, regulatory bodies and forums like 5G PPP and NGMN.

Area traffic capacity

(based on 3GPP/ITU-R; aka traffic volume density by 5G PPP)

The total traffic throughput served per geographic area (in bps/m2). This metric can be evaluated by two different traffic models: Full buffer model and non-full buffer model.

·       By full buffer model: The computation of the total traffic throughput served per geographic area is based on full buffer traffic.

·       By non-full buffer model: Again, the total traffic throughput served per geographic area is computed, but in addition to the area traffic capacity also the user experienced data rate need to be evaluated at the same time using the same traffic model.

The area traffic capacity is a measure of how much traffic a network can carry per unit area. It depends on site density, bandwidth, and spectrum efficiency. In the case of full buffer traffic and a single layer single band system, it may be expressed as:

Area traffic capacity (bps/m2) = site density (site/m2) × bandwidth (Hz) × spectrum efficiency (bps/Hz/site)

Site here refers to a single transmission and reception point (TRxP). It is proposed to perform full buffer evaluation, using the spectrum efficiency results together with assumptions on available bandwidth and site density in order to derive a quantitative area traffic capacity KPI for information.

Area traffic capacity is typically evaluated through system level simulations. Note that D2D traffic should be evaluated independently from the cellular one. Besides, the link between source and destination may cover multiple hops especially when non-ideal backhaul is taken into consideration.

Availability

(based on 3GPP/5G PPP/NGMN/ETSI)

Percentage value (%) of the amount of time a system is in condition to deliver services divided by the amount of time it is expected to deliver services in a specific area.

The availability may be specific for a communication service. In that case, it refers to the percentage value of the amount of time the end-to-end communication service is delivered according to an agreed QoS, divided by the amount of time the system is expected to deliver the end-to-end service according to the specification in a specific area.

Note 1: The end point in "end-to-end" is assumed to be the communication service interface.

Note 2: The communication service is considered unavailable if it does not meet the pertinent QoS requirements. If availability is one of these requirements, the following rule applies: the system is

considered unavailable in case an expected message is not received within a specified time, which, at minimum, is the sum of end-to-end latency, jitter, and survival time.

The RAN availability is characterised by its availability rate [x], defined as follows: a TRxP is available for the targeted communication [x]% of the time. Unavailable communication for shorter period than [y] ms shall not be counted. The 5G specification’s ability to provide URLLC services shall not be compromised by the functions defined to improve the network or UE energy efficiency, or by system reconfigurations and software upgrades. The availability may be targeted for the whole coverage area of a TRxP or for [z]% of the locations within the area.

Considering NFV-based implementations of a system the service availability may be also defined as the total service available time divided by the sum of total service available time and total restoration time required to set up the service again [ETSI-REL003]. In that case, typically only the communication path in the network infrastructure is considered, i.e., without involvement of UE and radio link.

In the classical resilience theory, the availability of a system/component is defined as the relative uptime, or more precisely as the mean time between failures (MTBF) divided by the sum of MTBF and mean time to repair (MTTR) (e.g., [ETSI-REL003] w.r.t. availability considerations for systems consisting of NFV-based components).

Bandwidth

(based on 3GPP)

Bandwidth means the maximal aggregated total system bandwidth. It may be supported by single or multiple RF carriers. It is a quantitative KPI.

Cell-edge user throughput

(based on 3GPP)

The cell edge user throughput is defined as the fifth percentile point of the CDF of user’s average packet call throughput

Connection density

(based on 3GPP/ITU-R)

The total number of connected and/or accessible devices per unit area (per km2). Connectivity or accessibility refers to devices fulfilling a target QoS, where the target QoS is to ensure a system packet drop rate less than [x]% under given packet arrival rate [l] and packet size [S]. The packet drop rate is equal to the number of packets in outage divided by the number of generated packets, where a packet is in outage if this packet failed to be successfully received by destination receiver beyond a packet dropping timer.

Analytical, link level, and system level evaluations can be performed to derive the connection density in a certain deployment scenario (note: 3GPP proposes to use an Urban environment for mMTC related evaluations).

Control plane latency

(based on 3GPP/5G PPP)

Time to move from a battery efficient state (e.g., IDLE) to the start of continuous data transfer (e.g., ACTIVE).

Analytical evaluation is typically used as the evaluation methodology.

Coverage

(based on 3GPP)

Maximum coupling loss (MaxCL) in UL and DL between UE and TRxP (antenna connector(s)) for a data rate of [x] bps, where the data rate is observed at the egress/ingress point of the radio protocol stack in each direction.

Link budget and/or link level analysis are typically used as evaluation methodology.

CL is defined as the total long-term channel loss over the link between UE antenna ports and the TRxP antenna ports, and includes in practice antenna gains, path loss, shadowing, body loss, etc. The MaxCL is the limit value of CL at which the service can be delivered, and therefore defines the coverage of the service. The MaxCL is independent of the carrier frequency. It is defined in the UL and DL as:

UL MaxCL = UL Max Tx power - TRxP Sensitivity DL MaxCL = DL Max Tx power - UE Sensitivity

Note: 3GPP proposed a target for coverage of 164 dB for an mMTC service assuming 160 bps. For a basic MBB service characterised by a DL/UL data rates of 2(1) Mbps/60(30) kbps for stationary users, 3GPP proposed a target MaxCL of 140(143) dB. For mobile users 3GPP assumes a DL data rate of 384 kbps as acceptable. At a coupling loss of 143 dB relevant DL/UL control channels should also perform adequately.

Coverage area probability

(based on 5G PPP)

The coverage area probability is defined as the percentage of the area under consideration, in which a service is provided by the mobile radio network to the end user in a quality (i.e., data rate, latency, packet loss rate) that is sufficient for the intended application (QoS/QoE level). The RAN may consist of a single radio cell or of a multi-cell deployment. For services of different types and QoS/QoE levels the coverage area probability will be also typically different. For radio network planning purposes or coverage measurements the area under consideration will be usually divided into 2-dimensional pixels or segments (e.g., along roads) with the same size.

End-to-end latency

(based on 3GPP/5G PPP)

The time that takes to transfer a given piece of information from a source to a destination, measured at the communication interface, from the moment it is transmitted by the source to the moment it is successfully received at the destination. It is also referred to as one trip time (OTT) latency.

Another latency measure is the round-trip time (RTT) latency which refers to the time from when a data packet is sent from the transmitting end until acknowledgements are received from the receiving entity.

Energy efficiency

(based on 3GPP/ITU-R)

Energy efficiency means to sustain a certain data rate while minimising the energy consumption. It has two aspects:

·       On the network side, energy efficiency refers to the quantity of information bits transmitted to/received from UEs, per unit of energy consumption of the RAN (in bit/Joule).

·       On the UE side, energy efficiency refers to quantity of information bits per unit of energy consumption of the communication module (in bit/Joule).

It is a qualitative KPI. The evaluation methodology should be based on inspection, but more detailed quantitative assessment can be performed.

Latency for infrequent small packets

(based on 3GPP)

For infrequent application layer small packet/message transfer, the time it takes to successfully deliver an application layer packet/message from the radio protocol layer 2/3 SDU ingress point at the UE to the radio protocol layer 2/3 SDU egress point in the RAN, when the UE starts from its most "battery efficient" state.

Analytical evaluation is the baseline evaluation methodology and system level evaluation can be considered if needed.

Mean time between failures (MTBF)

(by ETSI)

The MTBF is the statistic mean uptime of a system/component before it fails.

Note: The MTBF is a property of the system/component and hardly can be influenced by the operator (except by ensuring that it is kept within its specified operational limits).

Mean time to repair (MTTR)

(by ETSI)

The MTTR is the statistic mean downtime before the system/component is in operations again.

Note 1: In contrast to the MTBF the MTTR is determined solely by procedural aspects, namely how long will it take to organise a spare part and to get the repair work done.

Note 2 (extension by 5G-MoNArch): In contrast to former telco network generations, where systems are primarily characterised by exchange of HW boxes in the repair case, for more SW-oriented systems using NFV approaches the time for SW fault localisation, remediation, and recovery without the need to exchange the underlying HW will be considered which may drastically reduce the resulting MTTR and therefore the reliability

Mobility

(based on 3GPP/ITU-R)

Maximum speed at which a defined QoS and seamless transfer between TRxPs which may belong to different deployment layers and/or radio access technologies (multi-layer/-RAT) can be achieved (in km/h).

The evaluation methodology should be link level evaluation with deployment scenario specific operating point.

Mobility interruption time

(based on 3GPP/5G PPP)

The shortest time duration supported by the system during which a UE cannot exchange UP packets with any TRxP during transitions. This KPI is for both intra- and inter-frequency mobility as well as for intra- and inter-AIV mobility.

Analytical evaluation is typically used as the evaluation methodology.

Ideally, the mobility interruption time should be 0 ms, which may be achievable by multi-connectivity and CP/UP decoupling.

Peak data rate

(based on 3GPP/ITU-R/5G PPP)

Highest theoretical single user data rate (in bps), i.e., assuming ideal, error-free transmission conditions, when all available radio resources for the corresponding link direction are utilised (i.e., excluding radio resources that are used for physical layer synchronisation, reference signals or pilots, guard bands and guard times).

Analytical evaluation is typically used as the evaluation methodology.

Peak spectral efficiency

(based on 3GPP)

The peak data rate normalised by the bandwidth applied. Higher frequency bands could have higher bandwidth but lower spectral efficiency and lower frequency bands could have lower bandwidth but higher spectral efficiency. Thus, peak data rate cannot be directly derived from peak spectral efficiency and bandwidth multiplication.

Analytical evaluation is typically used as the evaluation methodology.

Reliability

(based on 3GPP/ITU-R/5G PPP/NGMN)

Percentage (%) of the amount of sent network layer packets successfully delivered to a given system node (incl. the UE) within the time constraint required by the targeted service, divided by the total number of sent network layer packets.

Note 1: The reliability is evaluated only when the network is available.

Note 2: Dependent on the targeted service the RTT latency instead of the E2E (OTT) latency may be applied.

The RAN reliability can be evaluated by the success probability of transmitting X bytes within a certain delay of [t] ms, which is the time it takes to deliver a data packet from the radio protocol layer 2/3 SDU ingress point to the radio protocol layer 2/3 SDU egress point of the radio interface. The target communication range and reliability requirement is dependent of the selected deployment and operation scenario, i.e., by taking into account a certain channel quality (e.g., at the coverage edge).

Link level evaluation with deployment scenario specific operating point and system level simulations are to be performed (e.g., Indoor Hotspot and Urban Macro for eMBB; Highway and Urban grid for connected cars/URLLC).

In the classical resilience theory, the reliability of a system/component over time is directly related to its MTBF. In the simplified case that the MTBF will not change over the system’s/component’s lifetime, it can be calculated as follows:

R (t) = exp(-t/MTBF).

It should be noted, however, that the MTBF of most systems/components (respectively their failure rate

= 1/MTBF) will change significantly over time (e.g., [ETSI-REL003] w.r.t. reliability considerations for systems consisting of NFV-based components).

Resilience

(based on ITU-R)

Resilience is the ability of the network to continue operating correctly during and after a natural or man- made disturbance, such as the loss of mains power.

Service continuity

(based on 3GPP)

The uninterrupted user experience of a service that is using an active communication when a UE undergoes an access change without, as far as possible, the user noticing the change.

Note 1: In particular service continuity encompasses the possibility that after a change the user experience is maintained by a different telecommunication service (e.g., tele- or bearer service) than before the change.

Note 2: Examples of access changes include the following. For EPS: CS/PS domain change. For EPS and 5G: radio access change, switching between a direct network connection and an indirect network connection. Indirect in that sense means using a relay node (TRxP or another device) in the connection to the end customer device (e.g., via D2D/slide link mode).

Spectral efficiency per cell/transmission and reception point (TRxP)

(based on 3GPP/ITU-R)

TRxP spectral efficiency is defined as the aggregate throughput of all users (the number of correctly received bits, i.e., the number of bits contained in the service data units (SDUs) delivered to Layer 3, over a certain period of time) within a radio coverage area (site) divided by the channel bandwidth divided by the number of TRxPs. A 3-sector site consists of 3 TRxPs.

In case of multiple discontinuous "carriers" (one carrier refers to a continuous block of spectrum), this KPI should be calculated per carrier. In this case, the aggregate throughput, channel bandwidth, and the number of TRxPs on the specific carrier are employed. It is a quantitative KPI.

Spectrum and bandwidth flexibility

(based on ITU-R)

Spectrum and bandwidth flexibility refers to the flexibility of the 5G system design to handle different scenarios, and in particular to the capability to operate at different frequency ranges, including higher frequencies and wider channel bandwidths than today.

UE battery life

(based on 3GPP)

Life time of the UE battery to be evaluated without recharge. Analytical evaluation is typically used as the evaluation methodology.

Note: For mMTC, 3GPP proposed that UE battery life in extreme coverage shall be based on the activity of mobile originated data transfer consisting of 200 bytes UL per day followed by 20 bytes DL from MaxCL of 164 dB, assuming a stored energy capacity of 5 Wh.

User experienced data rate

(based on 3GPP/ITU-R; aka experienced user throughput by 5G PPP)

The achievable data rate that is available ubiquitously across the coverage area to a mobile user/device (in bps). It is usually related to the minimum data rate required to achieve a sufficient quality experience (dependent on the selected service type).

The user experienced data rate can be evaluated for non-full buffer traffic and for full buffer traffic, but non-full buffer system level simulations are preferred for the evaluation of this KPI taking care of respective deployment scenarios and using bursty traffic models.

For non-full buffer traffic, the user experienced data rate is the 5%-percentile (5%) of the user throughput. User throughput (during active time) is defined as the size of a data burst divided by the time between the arrival of the first packet of a burst and the reception of the last packet of the burst.

For full buffer traffic, user experienced data rate is calculated as:

User experienced data rate = 5% user spectrum efficiency × bandwidth

Here it should be noted that the 5% user spectrum efficiency depends on the number of active users sharing the channel (e.g., 10 in the evaluations in ITU-R Report M.2135), and that the 5% user spectrum efficiency for a fixed transmit power may vary with bandwidth. To keep a high 5% user spectrum efficiency and a few users sharing the channel, a dense network is beneficial, i.e., 5% user spectrum efficiency may vary also with site density (site here refers to single TRxP).

5% user spectrum efficiency means the 5% point of the cumulative distribution function (CDF) of the normalised user throughput. The (normalised) user throughput is defined as the average user throughput (the number of correctly received bits by users, i.e., the number of bits contained in the SDU delivered to Layer 3, over a certain period of time), divided by the channel bandwidth and is measured in bps/Hz. The channel bandwidth for this purpose is defined as the effective bandwidth times the frequency reuse factor, where the effective bandwidth is the operating bandwidth normalised appropriately considering the uplink/downlink ratio. In case of multiple discontinuous “carriers” (one carrier refers to a continuous block of spectrum), this KPI should be calculated per carrier. In this case, the user throughput and channel bandwidth on the specific carrier are employed.

The user experienced data rate is calculated separately for DL (transmission from TRxP(s) to UE), UL (transmission from UE to TRxP(s) and (potentially) for D2D (transmission directly between involved UEs).

User plane latency

(based on 3GPP/5G PPP)

The time it takes to successfully deliver an application layer packet/message from the radio protocol layer 2/3 SDU ingress point to the radio protocol layer 2/3 SDU egress point via the radio interface in both UL and DL directions, where neither UE nor TRxP reception is restricted by DRX.

Analytical evaluation is typically used as the evaluation methodology. The evaluation needs to consider all typical delays associated with the transfer of the data packets in an efficient way (e.g., applicable procedural delay when resources are not pre-allocated, averaged HARQ retransmission delay, impacts of network architecture).

Note: that the reliability KPI also provides a latency value with an associated reliability requirement.

Source: 5G-MoNArch