Page 18 - ITU Journal Future and evolving technologies Volume 2 (2021), Issue 6 – Wireless communication systems in beyond 5G era

ITU Journal on Future and Evolving Technologies, Volume 2 (2021), Issue 6

sometimes conflict with each other. In detail, the targeted
classi use values of the KPI for 5G networks have been proposed by
cases, which is depicted in Fig. 4. This also implied a the industry [19], [20] to be:
preliminary and general inition of system’s Key Per‐ −1
• throughput/data rate up to 1 −10 Gbit s ,
formance Indicators (KPI) including a user’s experienced
data rate, end‐to‐end latency, mobility, connection den‐ • end‐to‐end latency down to 1 −10 ms,
sity, ic density, spectrum iciency, coverage, re‐
• 1000 times increase in bandwidth per unit of area,
source and signalling iciency. However, the authors
of [18] had already mentioned some potential technolo‐
• 99.999% perceived availability and 100% geograph‐
gies, which could have been exploited to host the several
ical coverage,
potential‐upcoming verticals. First, they envisioned the
1
employment of massive Multiple‐Input Multiple‐Output • frame error rate equal to 1 − 10 −5 [21],
(MIMO) and mmWave frequencies in the new RAN to
• 90% reduction in network energy usage,
boost the data rate. Next, they looked at the existing
research, standardization, and implementation of cloud
• signi icantly‐increased battery life for various kinds
computing and network virtualisation (see Section 2.2)
of end‐users’ devices.
and suggested the pivotal role that softwarization and
computing could have had in 5G. This is not only impor‐ • localisation precision equal to 10 cm in two dimen‐
tant for the core network but also for the evolution of sions [21],
the RAN towards a Cloud Radio Access Network (C‐RAN)
paradigm. • spectrum ef iciency three‐ ive times greater than the
one of 4G [22],
Afterwards, several verticals were inally organised into
6
three main categories [19] according to their common • density of connected devices 10 km −2 [22],
KPI. First, enhanced Mobile Broadband (eMBB) includ‐
• receiver sensitivity about −120 dBm [22].
ing mobile broadband and mobile video streaming, with
throughput and availability as main requirements. Next, Those proposals have then been provided to the IMT‐
ultra‐reliable Machine‐Type Communications (uMTC), process, leading to the technical performance require‐
or Ultra‐Reliable Low‐Latency Communication (URLLC), ments Report ITU‐R M.2410 produced by ITU‐R Work‐
refers to communications whose requirements are con‐ ing Party 5D (WP 5D), which is responsible for the over‐
currently and mainly focused on bandwidth, latency and all radio system aspects of International Mobile Telecom‐
reliability. Finally, massive Machine‐Type Communi‐ munications (IMT) systems, comprising IMT‐2000, IMT‐
cation (mMTC) will support massive communications
Advanced, IMT‐2020 and IMT for 2030 and beyond.
within IoT, eHealth sensors/wearables, smart grids and
surveillance; its requirements are focused on bandwidth Even if it was important in previous generation networks,
supply for a large number of devices and reliability. the frame error rate becomes critical in 5G since URLLC
groups very sensitive services like remote surgery. In par‐
Another major breakthrough in 5G, compared to previous ticular, the concept of frame error rate links with reliabil‑
generations, is the change of the communication network ity, which is characterised by its reliability rate, that is “[...]
paradigm [1]. Until 4G and in parallel within the Inter‐ de ined as [...] the amount of sent packets successfully de‐
net, information routed from the source(s) to the sink(s) livered to the destination within the time constraint re‐
was merely stored and queued, waiting for the availability quired by the targeted service, divided by the total num‐
of link resources to be transmitted. This paradigm is nor‐ ber of sent packets. Note that the reliability rate is eval‐
mally called store‑and‑forward. The softwarized architec‐ uated only when the network is available. [...]” [17]. It is
ture of 5G with the key role of network functions, run‐ possible to see from this de inition and from the previous
ning within softwarized environments (e.g. virtual ma‐ list that network availability (i.e. a high availability rate)
chines, containers, etc.), has moved the focus on comput‐ becomes subsequently critical and so, the related concept
ing. In this sense, 5G represents the irst communication of resilience. In detail, resilience is de ined as “[...] the ca‐
network based on compute‑and‑forward. pability of the network to recover from failures [...]” [17].
Additionally, the request is also that the network should
3.1 Performance and metrics
be capable to somehow remotely self‐heal.
We have seen that 5G is user‐centred, so that the perfor‐ An important consideration on the KPI also concerns la‐
mance and design requirements are driven by the verti‐
tency, which highlights another big difference between
cals. By looking at KPI, what marked an important change
5G and the previous generations. While until LTE latency
in 5G (in respect of previous generations) was not merely
issues were mainly concerning the links within the RAN
the de inition of more stringent goals. The turning point
was represented by their concurrent satisfaction, from 1 The frame is the data unit at Layer 2 of the International Organization
which rose critical technological trade‐offs. Various new for Standardization (ISO)‐Open Systems Interconnection (OSI) proto‐
col stack.
services that 5G is planning to host require KPI which

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