In this chapter we shall have a look at the important concepts that are required to understand 5G air interface.
5G will operate on 2 different frequencies.
Frequency Range 1 (FR1): 450 MHz to 7.125 GHz
Frequency Range 2 (FR2): 24.25 GHz to 52.6 GHz
Low Band Spectrum:
It will support widespread coverage for urban, rural areas.
Good for in-building coverage.
Peak Data Rage is 100 Mbps
Mid Band Spectrum:
It is a good mixture of coverage and capacity.
Peak Data Rage is 400 Mbps
High Band Spectrum:
It is also called as millimeter wave.
It has limited availability
Peak Data Rage is 10Gbps.
It has a low coverage and poor building penetration.
According to TS 3GPP TS 38.101-1 version 15.3.0 Release 15, provides the list of bands
Available 5G NR operating Band in FR 1:
Available 5G NR operating Band in FR 2 [3GPP TS 38.104]:
From the above image we can see that there are 4 different ways of communication.
FDD: Frequency Division Duplex
TDD: Time Division Duplex
SUL: Supplimentary Uplink
SDL: Supplimentary Downlink
First we will understand what is FDD and TDD.
From the image below, it is clear that:
In FDD mode, uplink and downlink can transmit at the same time by using 2 different spectrum.
In TDD mode, both uplink and downlink use the same frequency but at different time intervals.
SUL: Supplementary Uplink:
It refers to an RF that is only used for uplink transmission.
Need for SUL:
The cell coverage for the UE in UL direction is limited because of UE Tx power.
So when the UE approaches the cell edge (end of cell coverage) area, there will be a performance degradation.
So to avoid this problem, is to use a low frequency than the original UL frequency as the cell coverage gets larger as frequency gets lower.
NR bands dedicated for SUL n80, n81, n82, n83, n84, n86
SDL: Supplemental Downlink:
It refers to an RF carrier which is only used for downlink transmissions.
This helps in case of streaming video content, as in today scenario there is an increase of downlink traffic of 10x. This will put lots of pressure on the network. Hence to achieve this network can make use of SDL.
Transmission Scheme in 5G:
5G uses CP-OFDM in DL, CP-OFDM or SC-FDMA in UL.
Cyclic Prefix Orthogonal Frequency Division Multiplexing. Orthogonal means, when there is a peak of one sub carrier, then all other sub carrier will point to zero. Hence there will be no interference.
Sub carrier Spacing: The space between 2 sub carrier is called as sub carrier spacing.
Modulation:
In 5G NR supports QPSK and QAM modulation.
In QAM it uses 16 QAM, 64 QAM, 256 QAM.
QPSK stands for Quadrature Phase-Shift Keying
QAM stands for Quadrature Amplitude Modulation
QAM is used to provide more benefits for data transmission. As the QAM order increases higher data rate can be achieved.
A symbol in simple terms is one wave as shown below. In the same time, we will be able to transmit more data:
For example, if we consider 16QAM, it is able to transmit 4 bits per symbol
As the QAM order increases the distance between the different points in constellation will decrease and hence there is a higher chances of data errors being introduced.
Guard Band: guard band is an unused part of the radio spectrum between radio bands, for the purpose of preventing interference.
Channel Bandwidth: Channel Bandwidth in communication refers to the data throughput capacity. A simple way to understand is to consider water pipe, larger the pipe, larger the flow rate. Similarly larger the channel bandwidth, larger is the throughput capacity.
So in the next chapter, depending upon the Sub Carrier Spacing (SBS), channel bandwidth and Modulation technique used, the actual data transmission capacity will vary.
Below are the Channel BW supported by FR1 and FR2.