5G channel modelling

1. Channel Modeling

2. Requirement of 5G Channel Modelling
There are two main factors determining
requirements on the propagation modelling
The first is the scenarios from the
environment and user perspective
Second is the technology components
predicted to provide the required end user
services.

3. Requirement of 5G Channel Modelling
 Spatial consistency and mobility
 Diffuse versus specular scattering
 Very large antenna arrays
 Frequency range
 Complexity vs. Accuracy

4. Is propagation on our side?
Can we attain the kind of system specs that we want
with technology and also compatible with the build
market?
Link budget for indoor links
Link budget for outdoor links (oxygen absorption)
CMOS power amps: sweet spot 0-10 dBm
SiGe power amps can go higher
Using antenna arrays, can we go far enough so it is
interesting?

5. Free space propagation
The simplest model for how transmit power translates to received power
Isotropic transmission  at range R, the power is distributed over
the surface of a sphere of radius R
Receiver antenna provides an aperture with an effective area for
catching a fraction of this power
If the transmitter uses a directional antenna:
Transmit antenna
gain
Receive
antenna
aperture

6. Relating gain to aperture
Aperture for an
“isotropic” antenna
Antenna gain = ratio of aperture to that of an isotropic antenna
Remarks
--For given aperture, gain decreases with wavelength
--Aperture roughly related to area  at lower carrier frequencies
(larger wavelengths) we need larger form factors to achieve
a given antenna gain

7. Friis’ formula for free space propagation
Given the antenna gains:
For fixed antenna gains, the larger the wavelength the better
Given the antenna apertures:
For fixed antenna apertures (roughly equivalent to fixed form factors),
the smaller the wavelength the better, provided we can point the
transmitter and receiver at each other

8. Applying Friis’ formula
Going to the dB domain:
More generally:
Plug in your
favorite model
for path loss
Free space path loss model gives us back the first formula:

9. Link budget
Given a desired receiver sensitivity (i.e., received power),
what is the required transmit power to attain a desired
range?
OR
What is the attainable range for a given transmit power?
Must account for transmit and receive directivities, path
loss, and add on a link margin

10. Link budget analysis
Receiver sensitivity: minimum received power required to attain
a desired error probability
(depends on the modulation scheme, bit rate, channel model,
receiver noise figure)
Link budget: Once we know the receiver sensitivity, we can work
backward and figure out the physical link parameters required
to deliver the essential received power
Basic comm theory maps modulation & coding scheme to Eb/N0
requirement; we then need to map to received power needed
We can now design the physical link parameters: transmit and receive
antennas, transmit power, link range

11. Receiver sensitivity
(noise power)
Receiver sensitivity (minimum receive power needed)

12. Receiver sensitivity in dBm
We therefore obtain
How should we design the system to attain the desired RX sensitivity?
Need to relate transmit power to received power
kTroom ´1 Hz = 4 ´10-21
W = 4 ´10-18
mW
Þ -174 dBm
At room temperature and for a bandwidth of 1 Hz, the noise power
equals -174 dBm
(for noise figure
of F dB)

13. Example 60 GHz indoor link budget
4x4 antenna array at each end, 2 dBi gain per element
 14 dBi gain at each end
10 m range  free-space path loss is about 88 dB
2.5 Gbps link using QPSK and rate 13/16 code operating 2 dB
from Shannon limit
Receiver sensitivity = -71.5 dBm
Noise figure 6 dB
Transmit power with 10 dB link margin is only about -1.5 dBm!
( can use less directive antennas)

14. Example 100 m outdoor 60 GHz link
(backhaul, base-to-mobile)
Free space propagation loss increases by 20 dB
Oxygen absorption (16 dB/km) leads to 1.6 dB additional loss
Rain margin (25 dB/km for 2 inches/hr): 2.5 dB
Required transmit power goes up to 22.6 dBm
EIRP = 22.6 dBm + 14 dBi = 36.6 dBm < FCC EIRP limit
of 40 dBm
Using 10 m indoor link budget as reference

15. What the link budgets tell us?
• 60 GHz is well matched to indoor networking and to
picocellular networks
• Oxygen absorption has limited impact at moderate ranges
• Heavy rain can be accommodated in link budget
• Moderate directivity suffices
• Electronically steerable links give flexibility in networking
• Low-cost silicon implementations are possible
• For truly long range, need to avoid oxygen absorption
• 64-71 (unlicensed), 71-76, 81-86 GHz (semi-unlicensed)
• Bands above 100 GHz
• Need very high directivity (can we steer effectively?)

16. Channel Characterization
Geometrically predictable channels
Very different from statistical models used at lower frequencies

17. Basics of channel modeling
• Sum of propagation paths
• Free space propagation (LOS)
• Specular reflection
• Propagation through dielectric obstacles
• Diffraction and scattering
All these components are strong in conventional lower frequency bands
(<6GHz)
But in mmwave..?

18. Reflection

19. Reflection
• Plane wave traveling in homogenous environment
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20. Reflection
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21. Reflection coefficients
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• Depend on magnetic permeability and electric permittivity
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22. Reflection coeffs have mild freq dependence
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25

23. Main freq dependence is from rough scattering
• Reflection from rough surfaces:
part of wave energy is scattered
Higher loss at higher frequencies (exponential)
(surfaces are rougher at shorter wavelengths)
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* 26

24. Roughness: 5 GHz vs 60 GHz
• Surface roughness std deviation varies from 0 (e.g. glass) to a
few mm
• At low frequencies (f < 6 GHz, λ > 5 cm) most surfaces are
smooth
• At 60 GHz a surface with 0.6 mm roughness causes 5 dB of
excess loss
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27

25. 5G System Architecture
28

26. Main Components
• The cellular network provides wireless connectivity to
the devices that are on the move
• These devices, which are known as User Equipment
(UE), have traditionally corresponded to smartphones
and tablets
• But, will increasingly include cars, drones, industrial
and agricultural machines, robots, home appliances,
medical devices, and so on.
• The cellular network consists of a Radio Access
Network (RAN) and Mobile Core (MC)
29

27. 30
Cellular Access Network

28. 31
RAN
• The RAN manages the radio spectrum, making sure it is
used efficiently and meets the quality-of-service
requirements of every user.
• It corresponds to a distributed collection of base stations.
• In 4G, these are (somewhat cryptically) named
eNodeB (or eNB), which is short for evolved Node B.
• In 5G, they are known as gNB. (The g stands for “next
Generation”.)

29. 32
MC
• The Mobile Core is a bundle of functionality that serves
several purposes
• Provides Internet (IP) connectivity for both data and
voice services
• Ensures this connectivity fulfils the promised QoS
requirements
• Tracks user mobility to ensure uninterrupted service
• Tracks subscriber usage for billing and charging
• In 4G, this is called the Evolved Packet Core (EPC) and in
5G it is called the Next Generation Core (NG-Core).

30. BN
• A Backhaul Network interconnects the base stations that
implement the RAN with the Mobile Core.
• This network is typically wired, and is often constructed
from commodity components found elsewhere in the
Internet
• For example, the Passive Optical Network (PON) that
implements Fiber-to-the-Home is a prime candidate for
implementing the RAN backhaul
• The backhaul network is obviously a necessary part of the
RAN

31. Two important distinctions from CAN
• The first is that a base station has an analog
component (depicted by an antenna) and a digital
component (depicted by a processor pair)
• The second is that the Mobile Core is partitioned
into a Control Plane and User Plane, which is similar
to the control/data plane split that someone
familiar with the Internet would recognize

32. Explanation of RAN
• First, each base station establishes the wireless
channel for a subscriber’s UE upon power-up or
upon handover when the UE is active.
• This channel is released when the UE remains idle
for a predetermined period of time.

33. • Second, each base station establishes connectivity
between the UE and the corresponding Mobile Core
Control Plane component, and forwards signalling
traffic between the two.
• This signalling traffic enables UE authentication,
registration, and mobility tracking.

34. • Third, for each active UE, the base station establishes
one or more tunnels between the corresponding
Mobile Core User Plane component.

35. • Fourth, the base station forwards both control and user plane
packets between the Mobile Core and the UE
• These packets are tunnelled over SCTP/IP and GTP/UDP/IP,
respectively. SCTP (Stream Control Transport Protocol) is an
alternative reliable transport to TCP, tailored to carry signalling
(control) information for telephony services
• GTP (a nested acronym corresponding to (General Packet Radio
Service) Tunnelling Protocol) is a tunnelling protocol designed
to run over UDP

36. • Fifth, each base station coordinates UE handovers
with neighbouring base stations, using direct station-
to-station links.
• Exactly like the station-to-core connectivity shown in
the previous figure, these links are used to transfer
both control plane (SCTP over IP) and user plane (GTP
over UDP/IP) packets.

37. • Sixth, the base stations coordinate wireless multi-
point transmission to a UE from multiple base
stations, which may or may not be part of a UE
handover from one base station to another.

38. • The main function of the Mobile Core is to provide
external packet data network (i.e., Internet)
connectivity to mobile subscribers, while ensuring that
they are authenticated and their observed service
qualities
• An important aspect of the Mobile Core is that it needs
to manage all subscribers’ mobility
• It’s the fact that the Mobile Core is keeping track of
individual subscribers
• The 5G Mobile Core, called as the NG-Core, adopts a
microservice-like architecture
• A set of functional blocks is very different from the
collection of engineering decisions that go into
designing a microservice-based system
5G Mobile Core

39. • The set of functional blocks are divided into three groups
• The first group runs in the Control Plane (CP)
• AMMF (Core Access and Mobility Management Function):
• Responsible for connection and reachability management,
mobility management, access authentication and authorization,
and location services
• SMF (Session Management Function):
• Manages each UE session, including IP address allocation,
selection of associated UP function, control aspects of QoS, and
control aspects of UP routing.
Functional Blocks

40. • PCF (Policy Control Function):
• Manages the policy rules that other CP functions then
enforce
• UDM (Unified Data Management):
• Manages user identity, including the generation of
authentication credentials.
• AUSF (Authentication Server Function):
• Essentially an authentication server.
Functional Blocks

41. • The second group also runs in the Control Plane (CP)
• SDSF (Structured Data Storage Network Function):
• A “helper” service used to store structured data. Could be
implemented by an “SQL Database” in a microservices-
based system
• UDSF (Unstructured Data Storage Network Function):
• A “helper” service used to store unstructured data. Could
be implemented by a “Key/Value Store” in a microservices-
based system
Functional Blocks

42. • NEF (Network Exposure Function):
• It means to expose select capabilities to third-party services,
including translation between internal and external
representations for data. Could be implemented by an “API
Server” in a microservices-based system
• NRF (NF Repository Function):
• It means to discover available services. Could be
implemented by a “Discovery Service” in a microservices-
based system
• NSSF (Network Slicing Selector Function):
• It means to select a Network Slice to serve a given UE.
Network slices are essentially a way to partition network
resources in order to differentiate service given to different
users
Functional Blocks

43. • The third group includes the one component that
runs in the User Plane (UP)
• UPF (User Plane Function):
• It Forwards traffic between RAN and the Internet
• In addition to packet forwarding, it is also responsible
for policy enforcement, traffic usage reporting, and
QoS policing.
Functional Blocks

44. 5G Mobile Core (NG-Core)

45. • The 4G Mobile Core, which officially refers to as
the Evolved Packet Core (EPC), consists of five
main components
• The first three of which run in the Control Plane
(CP)
• The second two of which run in the User Plane
(UP)
4G Mobile Core

46. • MME (Mobility Management Entity):
• Tracks and manages the movement of UEs throughout the
RAN. This includes recording when the UE is not active.
• HSS (Home Subscriber Server):
• A database that contains all subscriber-related information.
• PCRF (Policy & Charging Rules Function):
• Tracks and manages policy rules and records billing data on
subscriber traffic.
• SGW (Serving Gateway):
• Forwards IP packets to and from the RAN. Anchors the
Mobile Core end of the bearer service to a (potentially
mobile) UE, and so is involved in handovers from one base
station to another.
Functional Blocks

47. • PGW (Packet Gateway):
• Essentially an IP router, connecting the Mobile Core to the
external Internet. Supports additional access-related
functions, including policy enforcement, traffic shaping, and
charging.
• Although specified as distinct components, in practice
the SGW (RAN-facing) and PGW (Internet-facing) are
often combined in a single device, commonly referred
to as an S/PGW.
Functional Blocks

48. 4G Mobile Core (EPC)

49. Deployment Options
• With an already deployed 4G RAN/EPC in the field
and a new 5G RAN/NG-Core deployment underway,
we can’t ignore the issue of transitioning from 4G to
5G (an issue the IP-world has been grappling with for
20 years)
• There are three deployment options can be
summarized as follows.
• Stand-Alone 4G / Stand-Alone 5G
• Non-Stand-Alone (4G+5G RAN) over 4G’s EPC
• Non-Stand-Alone (4G+5G RAN) over 5G’s NG-Core

50. Deployment Options
• The second of the three options, which is generally referred to as
“NSA“, involves 5G base stations being deployed alongside the
existing 4G base stations in a given geography to provide a data-
rate and capacity boost
• In NSA, control plane traffic between the user equipment and the
4G Mobile Core utilizes (i.e., is forwarded through) 4G base
stations, and the 5G base stations are used only to carry user
traffic
• Eventually, it is expected that operators complete their migration
to 5G by deploying NG Core and connecting their 5G base
stations to it for Standalone (SA) operation

51. NSA and SA operations

52. (OTP)
(OWA)
5G Network Model

53.  OSI layer 1 & OSI layer 2 define the wireless
technology
 For these two layers the 5G mobile network is
likely to be based on Open Wireless
Architecture (OWA)
 Physical layer + Data link layer = OWA
Open Wireless Architecture (OWA)

54.  All mobile networks will use mobile IP
 Each mobile terminal will be FA (Foreign Agent)
 A mobile can be attached to several mobiles or
wireless networks at the same time
 The fixed IPv6 will be implemented in the mobile
phones
 Separation of network layer into two sub-layers:
(i) Lower network layer (for each interface)
(ii) Upper network layer (for the mobile terminal)
Network Layer (NL)

55.  Wireless network differs from wired network
regarding the transport layer
 In all TCP versions the assumption is that lost
segments are due to network congestion
 In wireless, the loss is due to higher bit error ratio
in the radio interface
 5G mobile terminals have transport layer that is
possible to be downloaded & installed – Open
Transport Protocol (OTP)
 Transport layer + Session layer = OTP
Open Transport Protocol (OTP)

56.  Provides intelligent QoS (Quality of Service)
management over variety of networks
 Provides possibility for service quality testing &
storage of measurement information in information
database in the mobile terminal
 Select the best wireless connection for given
services
 QoS parameters, such as, delay, losses, BW, reliability,
will be stored in DB of 5G mobile
 Presentation layer + Application layer =
Application
Application (Service) Layer

57. 5G Hardware:
• Uses UWB (Ultra Wide
Band) networks with
higher BW at low
energy levels
• BW is of 4000
Mbps, which is 400
times faster than
today’s wireless
networks
• Uses smart antenna
• Uses CDMA (Code
Division Multiple
Access)
5G Software:
• 5G will be single
unified standard of
different wireless
networks, including LAN
technologies, LAN/WAN,
WWWW- World Wide
Wireless Web, unified IP
& seamless combination
of broadband
• Software defined
radio, encryption, flexibil
ity, Anti-Virus
Hardware and Software of 5G