New Spectrum for LTE-Advanced Carrier Aggregation

Inter-technology Carrier Aggregation

Another one from the 4G Americas whitepaper of Mobile Broadband explosion:

Carrier aggregation will play an important role in providing operators maximum flexibility for using all of their available spectrum. By combining spectrum blocks, LTE-Advanced will be able to deliver much higher throughputs than otherwise possible. Asymmetric aggregation (i.e., different amounts of spectrum used on the downlink versus the uplink) provides further flexibility and addresses the fact that currently there is greater demand on downlink traffic than uplink traffic. Specific types of aggregation include:

• Intra-band on adjacent channels.
• Intra-band on non-adjacent channels.
• Inter-band (e.g., 700 MHz, 1.9 GHz).
• Inter-technology (e.g., LTE on one channel, HSPA+ on another). This is currently a study item for Release 11. While theoretically promising, a considerable number of technical issues will have to be addressed.

Benefit of 1.4GHz for Mobile Downlink

Significant benefits could flow from use of 1.4 GHz band for a supplemental mobile downlink for enhanced multi-media and broadband services, according to a study by Plum Consulting conducted for Ericsson and Qualcomm.

The study by Plum Consulting shows that using the 1.4 GHz band (i.e. 1452-1492 MHz also called 1.5 GHz by the European Parliament or the L-band by the CEPT) for terrestrial supplemental mobile downlink could generate a net present value for Europe of as much as EUR54 billion over a 10 year period.

The band is currently allocated for use by digital audio broadcasting (DAB) services in most European countries -- part of the band is allocated to terrestrial networks and part is allocated to satellite networks. None of these services have developed in the band. Rather in all countries in Europe the satellite part of the band is unused and this is also the case in the terrestrial component in most countries.

There could be up to eight times as much data being downloaded than is being uploaded in mobile networks. This imbalance is expected to grow, as rich mobile content is increasingly made available and as consumer demand continues to soar. The study found that the use of the 1.4 GHz band as a supplemental downlink band for mobile applications is shown to drastically ease capacity, to enable considerably higher user data rates, to substantially enhance the user experience and to provide significant economic benefits.

The value of releasing the 1.4 GHz band depends on whether other substitute spectrum may become available in the next 5 to 10 years. Starting from today, all countries in Europe have planned or are planning to release the 800 MHz and 2.6 GHz bands in the next two years. There is equipment available for use in both bands and services are already deployed in some countries.

Which other bands might be released over the next 10-15 years? Table 3-2 gives a number of candidate bands, ordered by the likely timing for release, including the 1.4 GHz band for completeness. In each case, we summarise the current status of the band, initiatives that suggest it might be a candidate for future release and our views on the possible timing of deployment based on the difficulty of clearing the band and the harmonisation/standardisation initiatives that would need to be undertaken before equipment would be mass produced for the band.

The white paper is embedded below for reference:

Economic study of the benefits from use of 1.4 GHz for a supplemental mobile downlink

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Carrier Aggregation with a difference

Click on picture to enlarge

Another one from the LTE World Summit. This is from a presentation by Ariela Zeira of Interdigital.

What is being proposed is that Carrier Aggregation can use both the licensed as well as unlicensed bands but the signalling should only happen in the licensed band to keep the operator in control.

Note that this is only proposed for Small Cells / Femtocells.

The only concern that I have with this approach is that this may cause interference with the other devices using the same band (especially ISM band). So the WiFi may not work while the LTE device is aggregating this ISM band and the same goes for bluetooth.

Comments welcome!

LTE-Advanced (Rel-10) UE Categories

I blogged about the 1200Mbps of DL with LTE Advanced earlier and quite a few people asked me about the bandwidth, etc. I found another UE categories table in Agilent lterature on LTE-Advanced here.

The existing UE categories 1-5 for Release 8 and Release 9 are shown in Table 4. In order to accommodate LTE-Advanced capabilities, three new UE categories 6-8 have been defined.

Note that category 8 exceeds the requirements of IMT-Advanced by a considerable

margin.

Given the many possible combinations of layers and carrier aggregation, many configurations could be used to meet the data rates in Table 4. Tables 5 and 6 define the most probable cases for which performance requirements will be developed.

HSPA and LTE carrier aggregation

Last week there were press releases about the Long Term HSPA Evolution. The only thing that got reported mostly is the 650Mbps peak rates. There are other interesting features in Release-11 that is covered in Nokia Siemens Networks presentation. Here is one of them:

The idea of aggregating multiple carriers to increase performance is included in both LTE and HSPA. A logical step to fully leverage existing HSPA deployments and future LTE deployments is to aggregate the capacity of both systems and tie them together into a single mobile system. The concept is illustrated in Figure 3.

The aggregation of LTE and HSPA systems enables the peak data rates of the two systems to be added together. It also allows for optimal dynamic load balancing between the two radios. A small number of active LTE and HSPA aggregation-capable devices is sufficient to exploit this load balancing gain, since the network can schedule these devices to carry more data on the radio that has lower instantaneous loading and less data on the radio with the higher load at any given moment.

Carrier aggregation is expected to have no impact on the core network.

Multicarrier and multiband HSPA aggregation

From NSN Whitepaper on HSPA Evolution:

HSPA Release 10 with 4-carrier HSDPA provides a peak downlink data rate of 168 Mbps using 2x2 MIMO (Multiple Input Multiple Output) over the 20 MHz bandwidth. This matches the LTE Release 8 data rates obtained using comparable antenna and bandwidth configurations. A natural next step for the HSPA Release 10 downlink is to further extend the supportable bandwidths to 40 MHz with 8-carrier HSDPA, doubling the Release 10 peak rate to 336 Mbps.

8-carrier HSDPA coupled with 4x4 MIMO doubles the peak rate again to reach 672 Mbps, see Figure 1. The evolution of HSPA beyond Release 10 will push the peak data rates to rival those provided by LTE Advanced.

In addition to increased peak rates, the aggregation of a larger number of carriers improves spectrum utilization and system capacity owing to inherent load balancing between carriers. Additional capacity gains from trunking and frequency domain scheduling will also be seen.

Typical spectrum allocations do not provide 40 MHz of contiguous spectrum. To overcome spectrum fragmentation, HSDPA carrier aggregation allows carriers from more than one frequency band to be combined. 3GPP Release 9 already makes it possible to achieve 10 MHz allocation by combining two 5 MHz carriers from different frequency bands, such as one carrier on 2100 MHz and another on 900 MHz.

The 4-carrier HSDPA of Release 10 extends this further, allowing the aggregation of up to four carriers from two separate frequency bands. Long Term HSPA Evolution allows eight carriers. Typical cases of HSDPA multiband aggregation are shown in Figure 2.

Carrier aggregation deployment scenarios for Release-10 LTE-A

One of the important aspects to consider is that carrier aggregation should allow aggregation of not only the existing bands, but also bands that are introduced in future, e.g., 3.5 GHz band, etc. While existing bands already have certain deployments, new deployments can be considered for new bands that are introduced. Since introduction of new bands is done in a release independent fashion, considerations for such future bands are essential already in Rel-10. When higher frequencies such as 3.5 GHz are considered, path loss can be significant (e.g., 4-10 dB difference in link budget) when compared to 2 GHz. Hence, the most efficient deployment may not be to stick with the traditional macro-overlaying approach. Carrier aggregation should allow more flexible use of such new bands, since coverage and mobility can be ascertained by the existing band deployments, e.g., 2 GHz.

Picture below shows some of the potential deployment scenarios for carrier aggregation. Note that the scenarios listed are non-exhaustive. For example, other scenarios using repeaters and femto cells may be considered. Also note that F2 > F1.

Scenario 1

* F1 and F2 cells are co-located and overlaid, providing nearly the same coverage

* Both layers provide sufficient coverage and mobility can be supported on both layers.

* Likely scenario when F1 and F2 are of the same band, e.g., 2 GHz, 800 MHz, etc.

* It is expected that aggregation is possible between overlaid F1 and F2 cells.

Scenario 2

* F1 and F2 cells are co-located and overlaid, but F2 has smaller coverage due to larger path loss

* Only F1 provides sufficient coverage and F2 is used to provide throughput. Mobility is performed based on F1 coverage.

* Likely scenario when F1 and F2 are of different bands, e.g., F1 = {800 MHz, 2 GHz} and F2 = {3.5 GHz}, etc.

* It is expected that aggregation is possible between overlaid F1 and F2 cells.

Scenario 3

* F1 and F2 cells are co-located but F2 antennas are directed to the cell boundaries of F1 so that cell edge throughput is increased

* F1 provides sufficient coverage but F2 potentially has holes, e.g., due to larger path loss. Mobility is based on F1 coverage.

* Likely scenario when F1 and F2 are of different bands, e.g., F1 = {800 MHz, 2 GHz} and F2 = {3.5 GHz}, etc.

* It is expected that F1 and F2 cells of the same eNB can be aggregated where coverage overlap.

Scenario 4

* F1 provides macro coverage and on F2 Remote Radio Heads (RRHs) are used to provide throughput at hot spots

* Mobility is performed based on F1 coverage.

* Likely scenario when F1 and F2 are of different bands, e.g., F1 = {800 MHz, 2 GHz} and F2 = {3.5 GHz}, etc.

* It is expected that F2 RRE cells can be aggregated with the underlying F1 macro cells.

Scenario 5

* Similar to scenario #2, but frequency selective repeaters are deployed so that coverage is extended for one of the carrier frequencies

Scenarios supported in Rel-10 time frame

* For DL, all scenarios are supported in Rel-10

* For UL, scenario 4 and 5 are not supported in Rel-10

Source: R2-100531 CA deployment scenario NTT DOCOMO

Carrier Aggregation Concepts for LTE Rel-10

Carrier Aggregation Concepts for LTE Rel-10

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CA (Carrier Aggregation) Scenarios in LTE-Advanced

CA (Carrier Aggregation) may be used in three different spectrum scenarios as follows.

Intraband Contiguous CA — This is where a contiguous bandwidth wider than 20 MHz is used for CA. Although this may be a less likely scenario given frequency allocations today, 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 (Component Carriers) is a multiple of 300 kHz to be compatible with the 100 kHz frequency raster of Release 8/9 and preserving orthogonality of the subcarriers with 15 kHz spacing.

Intraband Non-Contiguous CA — This is where multiple CCs belonging to the same band are used in a non-contiguous manner. This scenario can be expected in countries where spectrum allocation is non-contiguous within a single band, when the middle carriers are loaded with other users, or when network sharing is considered.

Interband Non-Contiguous CA — This is where multiple CCs belonging to different bands (e.g., 2 GHz and 800 MHz are aggregated). With this type of aggregation, mobility robustness can potentially be improved by exploiting different radio propagation characteristics of different bands. This form of CA may also require additional complexity in the radio frequency (RF) front-end of UE. In LTE Release 10, for the UL the focus is on intraband CA, due to difficulties in defining RF requirements for simultaneous transmission on multiple CCs with large frequency separation, considering realistic device linearity. For the DL, however, both intra and interband cases are considered in Release 10, while specific RF requirements are being developed.

Text Source: Carrier Aggregation Framework in 3GPP LTE-Advanced - Mikio Iwamura et al. in IEEE Communications Magazine August 2010

Picture Source: http://www.catr.cn/tecm/dxwjs/201006/t20100610_1143968.htm

Dual-Cell HSPA in Release 8 and beyond

Some interesting developments are ongoing in the 3GPP standardisation from Release-8 onwards. You must be aware that the current bandwidth in UMTS/HSPA is 5 MHz. Since most of the operators generally won bigger chunk of spectrum of contiguous 5MHz band, they can actually combine these chunks to create a larger spectrum and hence increase data rates.

In Release 8 in downlink, it is possible to increase data rates using either a combination of MIMO and 64QAM or dual-cell HSDPA for operation on two 5MHz carriers with 64QAM, data rates reach up to 42Mbps.

In deployments where multiple downlink carriers are available, the new multicarrier operation offers an attractive way of increasing coverage for high bit rates. Rel-8 introduces dual-carrier operation in the downlink on adjacent carriers. This technique doubles the peak rate from 21Mbps to 42Mbps without the use of MIMO – it doubles the rate for users with typical bursty traffic; therefore, it also doubles the average user throughput, which translates into a substantial increase in cell capacity.

You may remember that I mentioned earlier that the operators are not too keen on going for MIMO for non-LTE technology. This is because they will have to upgrade their hardware and the antennas which could increase their cost significantly for a technology that is not going to be around for long.

Another thing to note before it becomes too confusing is that there are two terms for 'DC' being used right now. One of them is 'Dual Carrier' and other is 'Dual Cell'. In Release 8, the term being used is Dual-Cell for HSDPA which is also known as DC-HSDPA. The Technical specification to follow is 3GPP, TR 25.825 “Dual-Cell HSDPA operation” V1.0.0, May 2008.

The Dual-Cell assumes that both the 5MHz bands are contiguous. If they are not then the better term to refer for DC is Dual-Carrier.

A dual-carrier user can be scheduled in the primary serving cell as well as in a secondary serving cell over two parallel HS-DSCH transport channels. All non-HSDPA-related channels reside in the primary serving cell, and all physical layer procedures are essentially based on the primary serving cell. Either carrier can be configured to function as the primary serving cell for a particular user. As a consequence, the dual-carrier feature also facilitates an efficient load balancing between carriers in one sector. As with MIMO, the two transport channels perform hybrid automatic repeat request (HARQ) retransmissions, coding and modulation independently. A difference compared to MIMO is that the two transport blocks can be transmitted on their respective carriers using a different number of channelization codes. In terms of complexity, adding a dual-carrier receiver to UEs is roughly comparable to adding a MIMO receiver. Because the two 5MHz carriers are adjacent, they can be received using a single 10MHz radio receiver, which is already be available if the UE is LTE-capable.

Following the introduction in Release 8 of dual-carrier operation in the downlink, 3GPP is now discussing operation on multiple 5MHz carriers. Multiband operation of multiple carriers allows a single user to simultaneously aggregate and use the spectrum distributed over different bands. This gives operators greater fl exibility when using available spectrum. Increasing the number of carriers that UEs receive from two to four doubles the peak rate and achievable user throughput. For bursty traffic, this translates into substantially greater capacity, either as a larger number of users at a given data rate, or as a higher data rate for a given number of users. To substantially boost spectral effi ciency, 3GPP is studying the combination of dual-carrier operation and MIMO with 64QAM in the downlink, thereby doubling the peak data rate to 84Mbps. Similarly, they are studying the combination of MIMO, 64QAM and up to four downlink carriers to support peak data rates of more than 100Mbps. The support for UE reception on two frequency bands is an enabler to DC-HSDPA for operators who do not have adjacent 5MHz carriers available in one band, and is therefore of key importance for the further evolution of multi carrier HSPA.

As a consequence of increased data rates in downlink, the uplink data rates need to be improved too. From the aggregation of multiple FDD downlink carriers, the paired FDD uplink carriers can be utilized for improved uplink transmissions. 3GPP studies the usage of two adjacent 5MHz carriers for dual carrier uplink transmissions (DC-HSUPA) supporting data rates of up to 23Mbps. A further benefit of utilizing two uplink carriers is the possibility to support more efficient load balancing in the uplink direction.

In summary, uplink multicarrier operation increases availability as well as coverage of high data rates in the uplink.

In Conclusion, Rel-8 defines improvements in HSPA to achieve higher rates through dual carrier or combined 64QAM+MIMO operation. With the Rel-8 specification nearing completion (targeted for March 2009), planning is already under way in 3GPP for Rel-9 and Rel-10. Further multi-carrier and MIMO options are being explored for HSPA in Rel-9 and Rel-10

If you want to explore this topic further see:

• Nomor research White Paper – Dual Cell HSDPA and its Future Evolution.
• WirelessMoves - Dual Carrier HSDPA - The Push Beyond 5 MHz
• Ericsson - Continued HSPA Evolution of mobile broadband