If there are any sure bet about the future of mobile, They are that data usage will continue skyrocketing.
By 2020 the number of subscriptions which includes Mobile broadband, Mobile PCs, Tablets,
Routers and IOT Devices is expected to grow to more than 9 Billion.
Needless to say, New applications and services will require even higher data rates.
This cannot be achieved out of the blue right?
Certain means will be required.
MIMO and OFDM are two base technologies that will be enablers.
Along with these there are a number of other techniques and technologies such as
Carrieraggregation, Coardinate multipoint, LTE Relaying etc..
Which will be employed to improve the Throughput and Coverage.
Hello Everyone, Welcome back to the fundamentals of 4G.
Today we will be discussing about Carrier Aggregation.
Imagine a road is connecting two places.
Now, As the number of people travelling increases, what do we do to serve the increased traffic?
We add more lanes or construct flyovers.
Similarly in LTE, Carrier aggregation is used to serve increasing bit rate demand.
Here bandwidth is increased by aggregating separate spectrum, thus increasing the bitrate
and network performance.
Here Each aggregated carrier is referred to as a component carrier or CC.
The component carrier can have a bandwidth of 1.4, 3, 5, 10, 15 or 20MHz and as per 3GPP
a maximum of Five component carrier can be aggregated.
Hence the maximum aggregated Bandwidth is 20 X 5 = 100Mhz.
Now Carrier aggregation can be used for Both FDD and TDD, In FDD the number of aggregated
carriers in Downlink is always greater than or equal to the number of carriers in Uplink.
While in TDD the number will normally be same for both Downlink and Uplink.
Now, In LTE Advanced CA, Each component Carrier used for data transmission is also referred
to as a serving cell.
In CA we have multiple serving cell.
But RRC connection will always be handled by Primary Serving Cell.
In Idle Mode, the UE listens to, system information block broadcast message, through primary serving
cell and sends the uplink control information through the, Uplink Control Channel of it.
Basically all signalling messages are Handled by PCC.
The other component carriers are all referred to, as Secondary component Carriers or SCC.
Unlike PCC there can be multiple SCC.
The SCCs are added and removed as required, while the PCC is only changed at Handover.
Introduction of Carrier aggregation introduces, new messages in the protocol layers.
Here, some new RRC messages are introduced, to handle the SCC.
MAC, must be able, to handle scheduling on a number of CCs.
Regarding scheduling there are two main alternatives for Carrier Aggregation, Either resources are scheduled
on the same carrier as the grant is received, or so called cross carrier scheduling may be used.
In Physical Layer the signaling information about scheduling on CCs must be provided in
Downlink and HARQ ACK/NACK per component carrier must be delivered in Uplink and Downlink,
Now, The aggregated carriers can be Intra‐band contiguous, This simplest CA deployment scenario
aggregates multiple adjacent Component Carrier in a single operating band.
However in most countries the spectrum allocation is more fragmented and contiguous aggregation
within the same frequency band may not be possible.
For such scenarios non-contigious CA is deployed.
The main advantage of LTE is it can be deployed in various frequency bands and to serve huge
customer base, Operators have licnese to operate in multiple bands.
To aggregate CCs from different frequency band, the operators deploy Inter band CA.
Inter‐band CA is more complex than intra‐band CA because the multi‐carrier signal cannot
be treated as a single signal and therefore requires a more advanced transceiver in the User Equipment.
To specify different CA combinations we need to understand some new definitions:
1. Aggregated Transmission Bandwidth Configuration (ATBC) : It is the total number of aggregated
physical resource blocks (PRB).
2. CA bandwidth class : indicates a combination of maximum ATBC and maximum number of Component Carriers.
In R10 and R11, 3 classes are defined:
Class A : ATBC <= 100, maximum number of CC= 1
Class B : ATBC <= 100, maximum number of CC = 2
Class C : 100 < ATBC<=200, maximum number of CC = 2
3. eUTRA operating Band : It Refers to the chunks of frequency allocated by ITU to deploy LTE
in FDD or TDD mode in different parts of the world.
For example Band 40 refers to TDD operation in 2300-2400MHz range.
Now CA configuration, Indicates a combination of E-UTRA operating bands and CA bandwidth
classes, to exemplify, The configuration CA_40C indicates intra-band contiguous CA on E-UTRA
operating band 40 i.e 2300Mhz and CA bandwidth class C, CA_3A_3A indicates intra-band non-contiguous
CA on band 3 i.e 1800Mhz and CA Bandwidth class A, finally CA_3A-5B indicates inter-band
CA, on operating band 3 i.e 1800Mhz with bandwidth class A and operating band 5 i.e 850Mhz with
bandwidth class B.
To support CA, mobile device manufacturers must deploy capable CA products.
In LTE, User equipment categories define the capabilities of a mobile device.
After the network has identified, What category a mobile device supports, it knows the device
capabilities and can scale the data link accordingly.
In 2011, Intra Band Contiguous CA was introduced in 3Gpp release 10.
It was limited to two CCs and Maximum aggregated bandwidth of 40MHz.
In, 2013, the 3GPP release11 expanded the deployment options and capabilities of CA.
It introduced intra-band non contiguous aggregaion and support for multiple time advances i.e
cells belonging to two different sites.
In 2014, 3gpp release 12 was completed.
Uplink Inter-band CA was defined in this release.
requirement for 3 Component carrier in Downlink and 2 Component carrier in uplink was also
defined with a maximum aggregated Bandwidth of 50MHz.
In future releases LAA (Lincensed Assisted Access) and 4DL CA has been planned.
In 2013, the first commercial implementation of CA was deployed in South Korea, Followed
by UK.
Australian mobile operator Optus was the first to deploy CA on a TD-LTE network.
CA technologies has since been deployed on LTE Networks in regions throughout the world,
Notably in the North America, Japan, China and India.
From device point of view The main advantages of CA are -
It can be used to provide a bandwidth of upto 100MHz.
Which means user can get more Data rate.
However CA operation requires more receiver activity and more processing.
So the power consumption is higher.
From Network Operator's point of view, CA can be used to club fragmented Bandwidths
thus ensuring greater Bandwidth Utilization.
It supports cross component carrier scheduling, where the control channel at one carrier can
be used to allocate resources at another carrier.
Thus it is a powerful technology for effective utilization of radio resources.
From Release 11 it is possible to handle CA with Component carriers from different Sites.
So Macro Base station with full coverage could provide system information and RRC control
signalling and small cells and pico cells would serve high data requirements.
So friends, We have seen how network capacity is enhanced using Carrier Aggregation.
In our next video we will discuss how coverage is improved using Heterogeneous Network.
You can post your doubts in the comment section.
Happy learning.