Carrier Aggregation
Carrier Aggregation is a technology that aggregates multiple component carriers (CC), which can be jointly used for transmission to/from a single device. It combines two or more carriers into one data channel to enhance the data capacity of a network. Using existing spectrum, Carrier Aggregation helps mobile network operators (MNOs) in providing increased UL and DL data rates. When Carrier Aggregation is deployed, frame timing and SFN are aligned across cells that can be aggregated. 5G NR utilizes CA in both FR1 and FR2, supporting up to 16 component carriers. For Release 15, the maximum number of configured Component Carriers for a UE is 16 for DL and 16 for UL.
- Up to 16 carriers (contiguous and non-contiguous) can be aggregated
- Carriers can use different numerologies
- Transport block mapping is per carrier
- Cross carrier scheduling and joint feedback are also supported
- Flexibility for network operators to deploy their licensed spectrum by using any of the CA types (such as intra-band contiguous, intra-band noncontiguous or inter-band noncontiguous)
History
LTE release 10 introduced enhanced LTE spectrum flexibility through carrier aggregation which was required to support higher bandwidths and fragmented spectra. Up to 5 component carriers, possibly each of different bandwidth, can be aggregated in this release, allowing for transmission bandwidths of up to 100MHz. All component carriers need to have the same duplex scheme and in the case of TDD, same uplink downlink configuration.
In LTE release 10, Backwards compatibility was ensured as each component carrier uses the release-8 structure. Hence, to a release-8/9 device each component carrier will appear as an LTE release-8 carrier, while a carrier-aggregation capable device can exploit the total aggregated bandwidth, enabling higher data rates. In the general case, a different number of component carriers can be aggregated for the downlink and uplink. This was an important property from a device complexity point of view where aggregation can be supported in the downlink where very high data rates are needed without increasing the uplink complexity.
Release 13 marked the start of LTE Advanced Pro, included various enhancements in Carrier Aggregation. The number of component carriers possible to aggregate was increased to 32, resulting in a total bandwidth of 640MHz and a theoretical peak data rate around 25 Gbit/s in the DL considering 8 layers spatial multiplexing and 256 QAM. The main motivation for increasing the number of subcarriers was to allow for very large bandwidths in unlicensed spectra.
LTE release 13 also introduced license-assisted access, where the carrier aggregation framework is used to aggregate downlink carriers in unlicensed frequency bands, primarily in the 5 GHz range, with carriers in licensed frequency bands. Mobility, critical control signaling and services demanding high quality-of-service rely on carriers in the licensed spectra while (parts of) less demanding traffic can be handled by the carriers using unlicensed spectra.
In LTE release 14, license-assisted access was enhanced to address uplink transmissions also.
Carrier aggregation was one of the most successful enhancements of LTE till now with new combinations of frequency band added in every release.
Carrier Aggregation in NR
Like LTE, multiple NR carriers can be aggregated and transmitted in parallel to/from the same device, thereby allowing for an overall wider bandwidth and correspondingly higher per-link data rates. The carriers do not have to be contiguous in the frequency domain but can be dispersed, both in the same frequency band as well as in different frequency bands, resulting in three difference scenarios:
• Intraband aggregation with frequency-contiguous component carriers;
• Intraband aggregation with non-contiguous component carriers;
• Interband aggregation with non-contiguous component carriers.
Below figure depicts these 3 scenarios:
Carrier Aggregation Types
Although the overall structure is the same for all three cases, the RF complexity can be vastly different.
Up to 16 carriers, having different bandwidths and different duplex schemes, can be aggregated allowing for overall transmission bandwidths of up to 6,400 MHz (16 x 400 MHz) = 6.4 GHz, which is more than typical spectrum allocations.
A device capable of CA may receive or transmit simultaneously on multiple component carriers while a device not capable of CA can access one of the component carriers. It is worth noting that in the case of Inter-band carrier aggregation of multiple half-duplex (TDD) carriers, the transmission direction on different carriers does not necessarily have to be the same. This implies that a carrier-aggregation-capable TDD device may need a duplex filter, unlike the typical scenario for a noncarrier-aggregation-capable device.
In the specifications, carrier aggregation is described using the term cell, that is, a carrier-aggregation-capable device can receive and transmit from/to multiple cells. One of these cells is referred to as the primary cell (PCell). This is the cell which the device initially finds and connects to, after which one or more secondary cells (SCells) can be configured, once the device is in connected mode. The secondary cells can be rapidly activated or deceived to meet the variations in the traffic pattern. Different devices may have different cells as their primary cell—that is, the configuration of the primary cell is device-specific. Furthermore, the number of carriers (or cells) does not have to be the same in UL and DL. In fact, a typical case is to have more carriers aggregated in the DL than in the UL. Reasons being:
- There is typically more traffic in the DL that in the UL.
- The RF complexity from multiple simultaneously active uplink carriers is typically larger than the corresponding complexity in the downlink.
Carrier aggregation uses L1/L2 control signaling for the same reason as when operating with a single carrier. As baseline, all the feedback is transmitted on the primary cell, motivated by the need to support asymmetric carrier aggregation with the number of downlink carriers supported by a device different than the number of uplink carriers. For many downlink component carriers, a single uplink carrier may carry a large number of acknowledgments. To avoid overloading a single carrier, it is possible to configure two PUCCH groups where feedback relating to the first group is transmitted in the uplink of the PCell and feedback relating to the other group of carriers is transmitted on the primary second cell (PSCell).
Multiple PUCCH Groups
If carrier aggregation is used, the device may receive and transmit on multiple carriers, but reception on multiple carriers is typically only needed for the highest data rates. It is therefore beneficial to inactivate reception of carriers not used while keeping the configuration intact. Activation and inactivation of component carriers can be done through MAC signaling containing a bitmap where each bit indicates whether a configured SCell should be activated or deactivated.
Difference between self-scheduling and cross-carrier scheduling
Scheduling grants and scheduling assignments can be transmitted on either the same cell as the corresponding data, known as self-scheduling, or on a different cell than the corresponding data, known as cross-carrier scheduling.
Self-scheduling vs Cross-scheduling
Let’s discuss in detail – the scheduling decisions are taken per carrier and the scheduling assignments are transmitted separately for each carrier, that is, a device scheduled to receive data from multiple carriers simultaneously receives multiple PDCCHs. A PDCCH received can either point to the same carrier, known as self-scheduling, or to another carrier, commonly referred to as cross-carrier scheduling or cross-scheduling. In case of cross-carrier scheduling of a carrier with a different numerology than the one upon which the PDCCH was transmitted, timing offsets in the scheduling assignment, for example, which slot the assignment relates to, are interpreted in the PDSCH numerology (and not the PDCCH numerology).
Carrier Aggregation support in MAC Layer
MAC Layer is responsible for multiplexing/demultiplexing data across multiple component carriers when carrier aggregation is used. In case of CA, it is responsible for distributing data from each flow across the different component carriers, or cells.
The basic principle for carrier aggregation is independent processing of the component carriers in the physical layer, including control signaling, scheduling and HARQ retransmissions, while carrier aggregation is invisible above the MAC layer. Carrier aggregation is therefore mainly seen in the MAC layer, where logical channels, including any MAC control elements, are multiplexed to form transport blocks per component carrier with each component carrier having its own HARQ entity.
Carrier Aggregation in MAC
Note: In the case of carrier aggregation, there is one DL-SCH (or UL-SCH) per component carrier seen by the device
Relation with Dual Connectivity
Dual connectivity implies that a device is simultaneously connected to two cells. User-plane aggregation, where the device is receiving data transmission from multiple sites, separation of control and user planes, and uplink-downlink separation where downlink transmissions originate from a different node than the uplink reception node are some examples of the benefits with dual connectivity. To some extent it can be seen as carrier aggregation extended to the case of non-ideal backhaul. It is also essential for NR when operating in non-standalone mode with LTE providing mobility and initial access.
Example of Dual Connectivity
In dual connectivity, a device is connected to two cells, or in general, two cell groups, the Master Cell Group (MCG) and the Secondary Cell Group (SCG). The reason for the term cell group is to cover also the case of carrier aggregation where there are multiple cells, one per aggregated carriers, in each cell group. The two cell groups can be handled by different gNBs.
Dual Connectivity Details
A radio bearer is typically handled by one of the cell groups, but there is also the possibility for split bearers, in which case one radio bearer is handled by both cell groups. In this case, PDCP is in charge of distributing the data between the MCG and the SCG and thus PDCP plays an important role for Dual connectivity support.
Differences between Dual Connectivity and Carrier Aggregation
Both carrier aggregation and dual connectivity result in the device being connected to more than one cell. Despite this similarity, there are fundamental differences, primarily related to how tightly the different cells are coordinated and whether they reside in the same or in different gNBs.
Carrier aggregation implies very tight coordination, with all the cells belonging to the same gNB. Scheduling decisions are taken jointly for all the cells the device is connected to by one joint scheduler. Dual connectivity, on the other hand, allows for a much looser coordination between the cells. The cells can belong to different gNBs, and they may even belong to different radio-access technologies as is the case for NR-LTE dual connectivity in case of non-standalone operation.
Carrier aggregation and dual connectivity can also be combined. This is the reason for the terms master cell group and secondary cell group. Within each of the cell groups, carrier aggregation can be used.
Multi Connectivity includes Dual Connectivity (PDCP UP Split) and Carrier Aggregation (MAC UP Split) as shown in the figure below:
Carrier Aggregation with Dual Connectivity
Dual Connectivity should be preferred when latency is not neglectable between paths i.e. > 5-10ms or when there is a different RAT to be connected and TN of the master side is congested, whereas Carrier Aggregation has better and faster utilization of radio resources than Dual Connectivity but is used to connect same RATs. It requires low inter site latency (<5ms).
- In the case of carrier aggregation or dual connectivity, multiple power headroom reports can be contained in a single message (MAC control element).
- NR does not support carrier aggregation with LTE and thus dual connectivity is needed to support aggregation of the LTE and NR throughput.
- NR specifications supports carrier aggregation, where multiple carriers are present within a band, or in multiple bands, can be combined to create larger transmission bandwidths.
Relation with Supplementary Uplink
Both these techniques allow the uplink transmission to be switched between the FDD-band and the 3.5 GHz band. The use of these mechanisms effectively utilizes idle sub-3 GHz band resources, improve the uplink coverage of C-band, and enable the provisioning of 5G services in a wider area. Both solutions, NR Carrier Aggregation and Supplementary Uplink, offer transport of UL user data using sub-3GHz band NR radio resources. NR CA provides the added benefit of also providing sub-3GHz DL user data support on the FDD-band downlink, using 3GPP specified LTE-NR spectrum sharing, if needed. This provides opportunity to aggregate NR bandwidth as well as better operation of the NR uplink.
Difference between Carrier Aggregation (CA) and supplementary uplink (SUL)
Supplementary uplink differs from the aggregated uplink in that the UE may be scheduled to transmit either on the supplementary uplink or on the uplink of the carrier being supplemented, but not on both at the same time.
Описание Carrier Aggregation для LTE-Advanced
Одним из требований IMT-Advanced является требование к пропускной способности (до 1 Гбит/с) канала связи между базовой станцией и мобильной станцией. Для того, чтобы обеспечить требуемые значения пропускной способности в LTE-A предусмотрена поддержка до 5-ти частотных каналов по 20 МГц шириной. Таким образом общая ширина канала может достигать 100 МГц. Скорости передачи в этом случае могут достигать 3 Гбит/с в нисходящем канале.
Для того, чтобы обеспечить обратную совместимость с LTE Rel.8 предусмотрена возможность конфигурации каждого канала (carrier) как будто это обычный канал LTE Rel.8. Однако, необязательно, чтобы одновременно все каналы были сконфигурены в этом ключе. Используемые каналы могут занимать соседние частотные диапазоны (continuous), а могут находится и в различных частотных областях (non-continuous). Это позволяет обеспечить дополнительную гибкость при использовании имеющихся у оператора частотных диапазонах. Возможные комбинации частотных диапазонов для объединения специфицируются 3GPP (эти комбинации приводятся ниже).
В случае использования нескольких каналов, которые занимают соседние частотные диапазоны, требуется защитный интервал минимум в 300 КГц. Отметим, что с точки зрения реализации, вариант использования частотных каналов одинакового размера и занимающих соседние частотные диапазоны является наименее трудоемким. В то время как, реализация поддержки частотных каналов разного размера и из различных частотных диапазонов является наиболее трудоемкой.
Как правило, предполагается, что каждый частотный канал обслуживается базовой станцией независимо (распределение ресурсов, HARQ процедуры и т.д.). Однако, возможны варианты совместного обслуживания частотных каналов (cross-carrier). Такой вариант может быть использован, например, в гетерогенных сетях. Для снижения энергозатрат мобильной станции возможно использование только одного частотного канала для передачи данных (primary carrier) с динамическим подключением дополнительных каналов (если мобильная станция поддерживает данную опцию) в случаях, когда необходимо передать большие объемы данных.
Первым релизом LTE, где добавляется поддержка объединения каналов, является Release 10. Однако, определенных комбинаций для объединения каналов было всего 3 (см. таблицу ниже). В следующем релизе (Release 11) происходит существенное расширение разрешенных комбинаций. В Release 12 добавляются комбинации для объединения трех каналов в нисходящем направлении (downlink) и двух каналов в восходящем. Ниже приводятся определенные 3GPP комбинации для объединения каналов.
| Название | Частотные диапазоны | 3GPP релиз | Кем запрошены |
|---|---|---|---|
| CA_C_1 | 1 | Rel.10 | — |
| CA_C_40 | 40 | Rel.10 | — |
| CA_1-5 | 1+5 | Rel.10 | — |
| CA_1-19 | 1+19 | Rel.11 | NTT DOCOMO |
| CA_3-7 | 3+7 | Rel.11 | TeliaSonera |
| CA_4-13 | 4+13 | Rel.11 | Verizon |
| CA_4-17 | 4+17 | Rel.11 | AT&T |
| CA_7-20 | 7+20 | Rel.11 | Orange, . |
| CA_5-12 | 5+12 | Rel.11 | US Cellular |
| CA_4-12 | 4+12 | Rel.11 | Cox Communication |
| CA_2-17 | 2+17 | Rel.11 | AT&T |
| CA_4-5 | 4+5 | Rel.11 | AT&T |
| CA_5-17 | 5+17 | Rel.11 | AT&T |
| CA_3-5 | 3+5 | Rel.11 | SKT |
| CA_4-7 | 4+7 | Rel.11 | Rogers Wireless |
| CA_3-20 | 3+20 | Rel.11 | Vodafone |
| CA_8-20 | 8+20 | Rel.11 | Vodafone |
| CA_1-18 | 1+18 | Rel.11 | KDDI |
| CA_1-21 | 1+21 | Rel.11 | NTT DOCOMO |
| CA_11-18 | 11+18 | Rel.11 | KDDI |
| CA_3-8 | 3+8 | Rel.11 | KT |
| CA_2-29 | 2+29 | Rel.11 | AT&T |
| CA_4-29 | 4+29 | Rel.11 | AT&T |
| CA_C_41 | 41 (2DL/2UL) | Rel.11 | Clearwire, CMCC, . |
| CA_C_38 | 38 (2DL/2UL) | Rel.11 | CMCC |
| CA_C_7 | 7 (2DL/2UL) | Rel.11 | CUC, CT, Telenor, . |
| CA_NC_B25 | 25 (2DL/1UL) | Rel.11 | Sprint |
| CA_NC_B41 | 41 (2DL/1UL) | Rel.11 | CMCC |
| CA_1-3 | 1+3 | Rel.12 | China Unicom, China Telecom |
| CA_1-7 | 1+7 | Rel.12 | LG U+ |
| CA_1-8 | 1+8 | Rel.12 | Softbank |
| CA_1-11 | 1+11 | Rel.12 | Softbank |
| CA_1-18 | 1+18 | Rel.12 | KDDI |
| CA_1-26 | 1+26 | Rel.12 | KDDI |
| CA_2-4 | 1+4 | Rel.12 | TMO-US |
| CA_2-5 | 2+5 | Rel.12 | AT&T |
| CA_2-12 | 2+12 | Rel.12 | US Cellular |
| CA_2-13 | 2+13 | Rel.12 | Verizon |
| CA_3-19 | 3+19 | Rel.12 | NTT DOCOMO |
| CA_3-20 | 3+20 | Rel.12 | Telekom Austria |
| CA_3-26 | 3+26 | Rel.12 | KT |
| CA_3-27 | 3+27 | Rel.12 | KT |
| CA_3-28 | 3+28 | Rel.12 | eAccess |
| CA_4-12 | 4+12 | Rel.12 | TMO-US |
| CA_4-27 | 4+27 | Rel.12 | NII Holdings |
| CA_5-7 | 5+7 | Rel.12 | LG U+ |
| CA_5-25 | 5+25 | Rel.12 | US Cellular |
| CA_7-20 | 7+20 | Rel.12 | Telekom Austria |
| CA_7-28 | 7+28 | Rel.12 | Telefonica |
| CA_8-11 | 8+11 | Rel.12 | Softbank |
| CA_8-20 | 8+20 | Rel.12 | Vodafone |
| CA_12-25 | 12+25 | Rel.12 | US Cellular |
| CA_19-21 | 19+21 | Rel.12 | NTT DOCOMO |
| CA_20-32 | 20+32 | Rel.12 | Orange |
| CA_23-29 | 23+29 | Rel.12 | Dish |
| CA_39-41 | 39+41 | Rel.12 | CMCC |
| CA_41-42 | 41+42 | Rel.12 | China Unicom, China Telecom |
| CA_C_B3 | 3 (2DL/2UL) | Rel.12 | China Unicom |
| CA_C_B7 | 7 (2DL/2UL) | Rel.12 | Orange |
| CA_C_B23 | 23 (2DL/1UL) | Rel.12 | Dish |
| CA_C_B27 | 27 (2DL/1UL) | Rel.12 | NII Holdings |
| CA_C_B39 | 39 (2DL/2UL) | Rel.12 | CMCC |
| CA_C_B40 | 40 (3DL/1UL) | Rel.12 | CMCC |
| CA_C_B42 | 42 (2DL/2UL) | Rel.12 | CMCC, NII, Bollore |
| CA_NC_B2 | 2 (2DL/1UL) | Rel.12 | Verizon |
| CA_NC_B3 | 3 (2DL/1UL) | Rel.12 | SKT |
| CA_NC_B4 | 4 (2DL/1UL) | Rel.12 | TMO-US |
| CA_NC_7 | 7 (2DL/1UL) | Rel.12 | Telecom Italia |
| CA_NC_23 | 23 (2DL/1UL) | Rel.12 | Dish |
| CA_NC_25 | 25 (2DL/1UL) | Rel.12 | Telus |
| CA_NC_42 | 42 (2DL/1UL) | Rel.12 | CMCC, NII, Bollore |
| CA_8-40 | 8+40 | Rel.12 | KT |
| CA_1-42 | 1+42 | Rel.12 | NTT DOCOMO |
| CA_19-42 | 19+42 | Rel.12 | NTT DOCOMO |
| CA_1-3-5 | 1+3+5 | Rel.12 | SKT |
| CA_1-3-8 | 1+3+8 | Rel.12 | KT |
| CA_1-3-19 | 1+3+19 | Rel.12 | NTT DOCOMO |
| CA_1-3-20 | 1+3+20 | Rel.12 | Vodafone |
| CA_1-5-7 | 1+5+7 | Rel.12 | LG U+ |
| CA_1-7-20 | 1+7+20 | Rel.12 | Vodafone |
| CA_1-19-21 | 1+19+21 | Rel.12 | NTT DOCOMO |
| CA_1-42-42 | 1+42+42 | Rel.12 | NTT DOCOMO |
| CA_2-2-13 | 2+2+13 | Rel.12 | Verizon |
| CA_2-4-4 | 2+4+4 | Rel.12 | TMO-US |
| CA_2-4-5 | 2+4+5 | Rel.12 | US Cellular |
| CA_2-4-13 | 2+4+13 | Rel.12 | Verizon |
| CA_2-5-12 | 2+5+12 | Rel.12 | US Cellular |
| CA_2-5-30 | 2+5+30 | Rel.12 | AT&T |
| CA_2-12-12 | 2+12+12 | Rel.12 | AT&T |
| CA_2-12-30 | 2+12+30 | Rel.12 | AT&T |
| CA_2-29-30 | 2+29+30 | Rel.12 | AT&T |
| CA_3-3-7 | 3+3+7 | Rel.12 | TeliaSonera |
| CA_3-7-7 | 3+7+7 | Rel.12 | Orange, Deutsche Telekom |
| CA_3-7-20 | 3+7+20 | Rel.12 | Vodafone |
| CA_4-4-12 | 4+4+12 | Rel.12 | TMO-US |
| CA_4-4-13 | 4+4+13 | Rel.12 | Verizon |
| CA_4-5-12 | 4+5+12 | Rel.12 | US Cellular |
| CA_4-5-30 | 4+5+30 | Rel.12 | AT&T |
| CA_4-12-12 | 4+12+12 | Rel.12 | AT&T |
| CA_4-12-30 | 4+12+30 | Rel.12 | AT&T |
| CA_4-29-30 | 4+29+30 | Rel.12 | AT&T |
| CA_19-42-42 | 19+42+42 | Rel.12 | NTT DOCOMO |
- Увеличение скорости передачи. Увеличение используемого частотного диапазона приводит к возрастанию скоростей передачи данных в секторе.
- Повышение эффективности использования радиоресурсов. Объединение частотных каналов (диапазонов) позволяет добиться не только увеличения спектра, но и другие преимущества от динамического распределения ресурсов для передачи данных в рамках всего объединенного диапазона. Что ведет к увеличению ёмкости сектора и улучшению пользовательского опыта. Например, если пользователь попал в перегруженный сектор на одном частотном диапазоне, то он может быть тут же (распределение радиоресурсов осуществляется динамически каждый TTI, 1 мс) обслужен в другом частотном диапазоне, что позволяет поддерживать уровень пользовательского опыта (Quality of Experience).
- Оптимальное использование частотного ресурса, которым обладает оператор. Подавляющие большинство операторов имеет фрагментированный частотный ресурс, который, к тому же, может быть различного размера и в разных частотных диапазонах. Carrier Aggregation позволяет объединить этот частотный ресурс и использовать его одним блоком для обслуживания абонентов. Кроме этого, стандарт LTE Rel.8 имеет ограничение на максимальную ширину канала в 20 МГц, использование Carrier Aggregation позволяет уйти от этого ограничения и использовать канал с большей шириной (если, конечно, у оператора есть такой ресурс).
Для использования функциональности Carrier Aggregation в сети она должна поддерживаться как базовыми станциями, так и мобильными станциями (категории мобильных устройств).
Carrier Aggregation
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Discussion
- Intra-Band CA : The carriers belong to the same band. Carriers can be contiguous (next to each other) or non-contiguous. CA with contiguous carriers is easier to implement. Operators most likely don’t have large contiguous spectrum. Hence, non-contiguous CA is a useful feature.
- Inter-Band CA : The carriers belong to different bands. This is more complex to implement than the intra-band contiguous type. Because cellular operators have licenses to different bands, this has led to the standardization of many inter-band CA combinations to cater to industry needs.
In LTE-Advanced, up to five carriers can be aggregated for a maximum bandwidth of 100 MHz. Each carrier can use a different channel bandwidth. In LTE-Advanced Pro (Rel-13), up to 32 carriers can be aggregated for a maximum bandwidth of 640 MHz. Carriers from unlicensed bands could be aggregated.
- Scenario 1: F1 and F2 are in the same band and have similar coverage with co-located cells. This scenario provides higher capacity and more bandwidth to the UE .
- Scenario 2: F2 is in a higher band and hence has smaller coverage. F1 provides coverage while F2 improves the throughput.
- Scenario 3: Cells are co-located but F2 is directed to cover the holes in F1. F1 provides coverage and mobility while F2 improves the throughput.
- Scenario 4: F1 provides macro cell coverage while F2 Remote Radio Heads (RRH s) improve throughput at hot spots. F1 and F2 can be non-contiguous carriers in the same band or inter-band carriers.
- Scenario 5: Similar to scenario 2, but frequency-selective repeaters are used to improve F2 coverage.
- Intra-band Contiguous in FR1: CA_n78B (20 + 50)
- Intra-band Non-Contiguous in FR1: CA_n77(3A) (3 CC s, 2 BCS s, 1 combination per BCS )
- Inter-band in FR1: CA_n1A-n77A, CA_n1A-n77(3A) (2 non-contiguous CC s in n77)
- Inter-band in FR1 and FR2: CA_n66-n77-n260 (3 bands), CA_n1-n3-n8-n77-n257 (5 bands)
Band combinations can be browsed online: LTE CA , NR FR1, NR FR2 and NR FR1-FR2
LTE Carrier Aggregation
Carrier Aggregation (CA) is a technique used in LTE-Advanced to increase the peak data rate (i.e., maximum available speed) of a 4G LTE network. By aggregating multiple channels together a mobile network operator can increase the total available bandwidth of a single transmission, and thereby increase the bitrate and capacity of the network.
Before LTE-A, a mobile network operator could only use additional LTE bands to increase capacity (i.e., total number of users), by distributing traffic across multiple bands. While this is an effective way to provide more airtime to any one particular user and thereby improving available data rates during busy periods, it does not increase the peak data rate. Carrier Aggregation was introduced in 3GPP Rel. 10 (2011).
With radio spectrum a rare commodity, CA has also helped to utilise smaller spectrum allotments which only support smaller channel widths and where traditional LTE would lead to very low peak data rates.
Carrier aggregation is supported in both FDD and TDD duplex modes, with mixed duplex FDD+TDD aggregation possible. Special Supplemental Downlink (SDL) and Supplemental Uplink (SUL) bands have also been introduced to improve peak data rates in one direction only, often to utilise isolated pockets of radio spectrum unsuitable for duplex.
Top 10 Carrier Aggregation Band Combinations
The following chart depicts the popularity of CA Band Combinations amongst global LTE networks. Note: these are live data subject to change. We are continuously updating the network database as new information is made available.
LTE-A Carrier Aggregation Bands
The below table lists 631 recorded CA band combinations and has been compiled per 3GPP 36.101 Rel. 14 [September 2017].
To search multiple frequencies within FDD/TDD search boxes, please use a comma to delimit search terms.