5G Mobile Networks: Requirements, Enabling Technologies, and Research Activities 35
Another fundamental requirement is latency, which is typically expressed as end‐to‐
end latency perceived by the end user. With the advent of newly defined services such
as Tactile Internet, self‐driving car, and automatic traffic control, which require real‐
time responses and interactions, minimizing the latency is becoming more crucial.
More specifically, the 5G system is expected to reduce the latency ten times in the user
plane, down to 1 millisecond, and half in the control plane, down to 50 milliseconds,
compared to the 4G system [9].
2.2.2 Massive Connectivity and Seamless Mobility
Massive connectivity refers to the requirement of supporting a large number of connected devices and consequently a large or massive number of connections in an area
unit (e.g. connection per square kilometer). In the 5G era, the increased number of
devices in the network is not only coming from the emergence of new types of services
and new types of devices such as sensors, meters, wearable devices, and vehicles, but it
also from the exponential increase in the number of existing device types such as smart
phones and tablets. Due to the proliferation of these smart things, the 5G system is
expected to support a connection density of up to 1 billion connected devices per square
kilometer, or put differently, 100 times more devices compared to the 4G system. In
addition to the number of connected devices, the network densification can also be
reflected by the traffic density, which is measured by the total amount of traffic
exchanged by all devices over the considered area [2]. The expected value for this metric
in the 5G era is tens of Gbps per square kilometer.
Besides the requirement to support a massive number of connected devices, the 5G
system is also expected to provide seamless service experience to mobile users. However,
not all devices and users in the 5G era are mobile, thus seamless mobility is not necessary. Therefore, on‐demand mobility solutions should be supported, depending on the
types of devices and services [2]. For example, it is expected to enable an acceptable
service experience for mobile devices moving at speeds up to 500 km/h.
2.2.3 Reliability and High Availability
Reliability and high availability are two other important requirements that need to be
guaranteed in the 5G system. In general, the reliability of a system refers to its capability of
guaranteeing the success rate of data transmission under stated conditions (e.g. a latency
budget) over a certain period of time. Depending on different use cases and services, the
reliability rate will vary. As described previously, there are a number of services and applications in the third usage scenario (i.e., ultra‐reliable and low latency communications),
such as public safety, eHealth, automatic traffic control, and mission critical services,
which require extremely high reliability for the communication. In order to support these
kinds of services, the 5G system is expected to guarantee a reliability rate of up to 99.999%.
In order to provide services to end users anywhere, at any time, the 5G system must
ensure its availability, which refers to the ability to endure against possible outage scenarios. The availability is usually expressed as a percentage of uptime in a given period
of time (e.g. a year) and assessed based on the number of nines in the digits (e.g. 99.99%).
The 5G system should guarantee the availability rate with as many nines as possible, for
example, five nines or 99.999%.
Another fundamental requirement is latency, which is typically expressed as end‐to‐
end latency perceived by the end user. With the advent of newly defined services such
as Tactile Internet, self‐driving car, and automatic traffic control, which require real‐
time responses and interactions, minimizing the latency is becoming more crucial.
More specifically, the 5G system is expected to reduce the latency ten times in the user
plane, down to 1 millisecond, and half in the control plane, down to 50 milliseconds,
compared to the 4G system [9].
2.2.2 Massive Connectivity and Seamless Mobility
Massive connectivity refers to the requirement of supporting a large number of connected devices and consequently a large or massive number of connections in an area
unit (e.g. connection per square kilometer). In the 5G era, the increased number of
devices in the network is not only coming from the emergence of new types of services
and new types of devices such as sensors, meters, wearable devices, and vehicles, but it
also from the exponential increase in the number of existing device types such as smart
phones and tablets. Due to the proliferation of these smart things, the 5G system is
expected to support a connection density of up to 1 billion connected devices per square
kilometer, or put differently, 100 times more devices compared to the 4G system. In
addition to the number of connected devices, the network densification can also be
reflected by the traffic density, which is measured by the total amount of traffic
exchanged by all devices over the considered area [2]. The expected value for this metric
in the 5G era is tens of Gbps per square kilometer.
Besides the requirement to support a massive number of connected devices, the 5G
system is also expected to provide seamless service experience to mobile users. However,
not all devices and users in the 5G era are mobile, thus seamless mobility is not necessary. Therefore, on‐demand mobility solutions should be supported, depending on the
types of devices and services [2]. For example, it is expected to enable an acceptable
service experience for mobile devices moving at speeds up to 500 km/h.
2.2.3 Reliability and High Availability
Reliability and high availability are two other important requirements that need to be
guaranteed in the 5G system. In general, the reliability of a system refers to its capability of
guaranteeing the success rate of data transmission under stated conditions (e.g. a latency
budget) over a certain period of time. Depending on different use cases and services, the
reliability rate will vary. As described previously, there are a number of services and applications in the third usage scenario (i.e., ultra‐reliable and low latency communications),
such as public safety, eHealth, automatic traffic control, and mission critical services,
which require extremely high reliability for the communication. In order to support these
kinds of services, the 5G system is expected to guarantee a reliability rate of up to 99.999%.
In order to provide services to end users anywhere, at any time, the 5G system must
ensure its availability, which refers to the ability to endure against possible outage scenarios. The availability is usually expressed as a percentage of uptime in a given period
of time (e.g. a year) and assessed based on the number of nines in the digits (e.g. 99.99%).
The 5G system should guarantee the availability rate with as many nines as possible, for
example, five nines or 99.999%.