Carrier Aggregation Part-1



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Hello readers today we are going to learn about carrier aggregation. To make the topic more interesting and easier to learn I have written this article in the question answer format. So first thing first,

When was CA introduced?

It has been defined for the first time in 3GPP release 10(it’s also called LTE Advance features).

What is Carrier Aggregation and why it is needed?

CA is a technology to combine two or more carriers into one data channel to enhance the data capacity. It is also possible to combine same or different frequency bands.



CA is used in LTE-Advanced in order to increase the bandwidth, and thereby increase the bit rate. Since it is important to keep backward compatibility with R8 and R9 UEs the aggregation is based on R8/R9 carriers. CA can be used for both Time division duplex (TDD) as well as Frequency division duplex (FDD).

OR

What is goal of CA?

The goal of carrier aggregation is to enhance network performance and ensure a high-quality user experience by enabling operators to provide higher uplink and downlink data rates using their existing spectrum.


How CA can increase user throughput?
Carrier Aggregation (CA) was introduced in 3GPP to allow a UE to simultaneous transmit and receive data on multiple component carriers from a single eNB scheduler. Carrier Aggregation (CA) can increase user throughput as the aggregated bandwidth is increased for example after CA enable for particular UE, now UE can used 10 MHz of PCC and 10 MHz of SCC instead of 10 MHz for serving cell bandwidth without CA enable .   

What are the Benefits of CA?


Following are the benefits of CA:
  • Increasing bandwidth and enhancing data rates for users hence reduce file download delay.
  • It is also support for non-contiguous carrier aggregation to more efficiently utilize fragmented frequency resources.
  • More options for spectrum re-farming.
  • It also multiplexes gain by dynamically distributing traffic over multiple carriers (we can say that the utilization of frequency resource and obtain load balance effects).
  • LTE advance also allows CA of TDD and FDD carriers, inter-band TDD CA with different UL-DL configurations, and CA with multiple uplink timing advance values.


Does CA works in ENDC?


Yes CA works in ENDC case we can configure CA in master cell group and secondary cell group also.

What are the types of CA? Or
What are intra-band contiguous / intra-band non-contiguous / inter-band non-contiguous?

Depending on the configurations of the component carriers there are following three different carrier aggregation scenarios:

Intra-band (Contiguous and Non-contiguous): 

This type of carrier aggregation uses a single band. For this type of carrier aggregation there are two main formats:

Contiguous:   
The Intra-band contiguous carrier aggregation is the easiest form of LTE carrier aggregation to implement. In this form the carriers are adjacent to each other. 



Here the aggregated channel can be considered as a single enlarged channel by the terminal from RF point of view. In this case only one transceiver is require within the UE or terminal whereas more than one are require where the channels are not adjacent. 

As the RF BW increases it is necessary to ensure that the UE in particular is able to operate over such wide BW without a reduction in performance. 

Although the performance requirement is same for base station, the power consumption, the space and cost requirements are lenient so this allows greater flexibility in the design.  

In addition to this for the base station multi carrier operation, even if non-aggregated is already a requirement in many cases, requires little or no change to the RF elements of the design. Therefore software upgrades would be required to feed additional capability.



Note: PCC BW Size and SCC BW size can be same or can be different.

For 2 CC: 

1) PCC = 10MHz and SCC-1 =20MHz,

2) PCC = 20MHz and SCC-1 =10MHz, 

3) PCC = 5MHz and SCC-1 =20MHz,

For 3 CC: 

1) PCC = 10MHz, SCC-1 =10MHz and SCC-2 =10MHz, 

2) PCC = 5MHz SCC-1 =10MHz and SCC-1 =20MHz,

 

Non-contiguous:   
This CA is somewhat more complicated than the cases where adjacent carriers are used. In this type of carrier aggregation, no longer can the multi carrier signal be treated as a single signal and thus two transceiver are required. 



This leads to significant complexity. Particularly to the UE where space, power and cost are vital considerations.

Inter-band non-contiguous:   
This carrier aggregation uses different bands. Because of the fragmentation bands it is of particular use. Some of which are only 10 MHz wide or 15 MHz wide or 20MHz. 



It requires the use of multiple transceivers within the single item for the UE with the usual impact on performance, power and cost. 

Along with this there are also additional complexities resulting from the requirements to reduce cross modulation and inter modulation from the transceivers.


In Upcoming Part we will learn more about CA and CA interview question and its answer. And for more learning please go through our 5G and LTE page.

Stay tune for more Update…………………

Pinal Dobariya…




References:
- 3GPP TS 36.101(User Equipment radio transmission and reception)
- 3GPP TS 36.300(Overall description; Stage 2)
- 3GPP TS 36.331(Radio Resource Control (RRC)

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