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LTE Advanced - Carrier aggregation: Air interface changes

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Those who are going to read this article i want to inform them that first part of this article is written here. I suggest you to read that first, because I am going to continue from there as i left.
In my previous article I ended up with types of carrier aggregation ( ) Continuing that..

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Figure: These are different types of carrier aggregation.

and will elaborate the same thing further:

Radio Interface Aspects for Carrier aggregation:

Intra-band: This form of carrier aggregation uses a single band. There are two main formats for this type of carrier aggregation:

a. Contiguous: The Intra-band contiguous carrier aggregation is the easiest form of LTE carrier aggregation to implement. Here the carriers are adjacent to each other.
The aggregated channel can be considered by the terminal as a single enlarged channel from the RF viewpoint. In this instance, only one transceiver is required within the terminal or UE, whereas more are required where the channels are not adjacent. However as the RF bandwidth increases it is necessary to ensure that the UE in particular is able to operate over such a wide bandwidth without a reduction in performance. Although the performance requirements are the same for the base station, the space, power consumption, and cost requirements are considerably less stringent, allowing greater flexibility in the design. Additionally for the base station, multi-carrier operation, even if non-aggregated, is already a requirement in many instances, requiring little or no change to the RF elements of the design. Software upgrades would naturally be required to cater for the additional capability.

b. Non-contiguous: Non-contiguous intra-band carrier aggregation is somewhat more complicated than the instance where adjacent carriers are used. No longer can the multi-carrier signal be treated as a single signal and therefore two transceivers are required. This adds significant complexity, particularly to the UE where space, power and cost are prime considerations.

The most simple way for an operator to arrange aggregation would be to use contiguous component carriers within the same operating frequency band (as defined for LTE Rel-8/9), so called intra-band contiguous. A contiguous bandwidth wider than 20 MHz is not a likely scenario given frequency allocations today, however it can be common when new spectrum bands like 3.5 GHz are allocated in the future in various parts of the world. The spacing between center frequencies of contiguously aggregated CCs is a multiple of 300 kHz to be compatible with the 100 kHz frequency raster of Release-8/9 and preserving orthogonally of the subcarriers with 15 kHz spacing.

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c. Inter-band non-continuous:
Most operators in North America or Europe are currently facing the problem of a fragmented spectrum. The non-contiguous allocation has been specified to fit those scenarios, the allocation could either be intra-band, i.e. the component carriers belong to the same operating frequency band, but have a gap or gaps in between, or it could be inter-band, in which case the component carriers belong to different operating frequency bands.

This form of carrier aggregation uses different bands. It will be of particular use because of the fragmentation of bands - some of which are only 10 MHz wide. For the UE it requires the use of multiple transceivers within the single item, with the usual impact on cost, performance and power. In addition to this there are also additional complexities resulting from the requirements to reduce intermodulation and cross modulation from the two transceivers

The current standards allow for up to five 20 MHz carriers to be aggregated, although in practice two or three is likely to be the practical limit. These aggregated carriers can be transmitted in parallel to or from the same terminal, thereby enabling a much higher throughput to be obtained.

posted Mar 27, 2014 by anonymous

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This functionality – known as Carrier Aggregation (CA) – is a core capability of LTE-Advanced.
CA permits LTE to achieve the goals mandated by IMT-Advanced while maintaining backward
compatibility with Release-8 and 9 LTE. Release-10 CA permits the LTE radio interface to be
configured with any number (up to five) carriers, of any bandwidth, including differing
bandwidths, in any frequency band. Carrier aggregation can be used for both FDD and TDD.
In the following chapter Release-10 principle is presented as well as the extension provided in
see the below figure for an example where FDD is used.

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*Figure: Carrier Aggregation (FDD); The LTE-Advanced UE can be allocated DL and UL resources on the aggregated resource consisting of two or more Component Carriers (CC), the R8/R9 UEs can be allocated resources on any ONE of the CCs. The CCs can be of different bandwidths.*

LTE carrier aggregation basics

The target figures for data throughput in the downlink is 1 Gbps for 4G LTE Advanced. Even with the improvements in spectral efficiency it is not possible to provide the required headline data throughput rates within the maximum 20 MHz channel. The only way to achieve the higher data rates is to increase the overall bandwidth used. IMT Advanced sets the upper limit at 100 MHz, but with an expectation of 40 MHz being used for minimum performance. For the future it is possible the top limit of 100 MHz could be extended.
It is well understood that spectrum is a valuable commodity, and it takes time to re-assign it from one use to another in view - the cost of forcing users to move is huge as new equipment needs to be bought. Accordingly as sections of the spectrum fall out of use, they can be re-assigned. This leads to significant levels of fragmentation.
To an LTE terminal, each component carrier appears as an LTE carrier, while an LTE-Advanced terminal can exploit the total aggregated bandwidth.

Type of carrier aggregation:

The downlink and uplink can be configured completely independently, with only the limitation
that the number of uplink carriers cannot exceed the number of downlink carriers. Each
aggregated carrier is referred to as a component carrier, CC. The component carrier can have
a bandwidth of 1.4, 3, 5, 10, 15 or 20 MHz. With a maximum of five component carriers, the
maximum aggregated bandwidth is 100 MHz. 3 types of allocation have been defined in 3GPP
to meet different operator’s spectrum scenario.

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