Friday, 19 November 2010

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:

Monday, 15 November 2010

HTML5 for Mobile Devices

I had been recently talking to some developers about the programming and App development on mobiles and quite a few people are of the opinion that HTML5 may help the mobile Apps go to the next level.

The biggest problem HTML5 is supposed to solve is write once run anywhere applicatons. Most of the programs will have the same look and feel if they are run on a PC or mobile and between different devices.

Ofcourse not everything is perfect. There are yet many API's that need to be implemented in for HTML5 like the 3D and Mic API's, etc. Another problem is that a lot of phones are not yet supporting HTML5 and some of them that are supporting, not supporting it completely. This will have to be solved asap.

The following is a recent presentation from Ericsson on HTML5 that gives a good idea on why it is a good idea.
Another interesting place to look for some HTML5 stuff is Patrick Chanezon's html5 Bookmarks

Thursday, 11 November 2010

UEInformationRequest/UEInformationResponse - New RRC messages in Release-9

As is obvious from the title, The UE information procedure is used by E-UTRAN to request the UE to report information [1].

There are two different scenarios for the Network to send the UEInformationRequest message to the UE. One is to find out the number of RACH preambles it needed for the random access procedure and the other is to get the measurement information when a Radio Link Failure (RLF) occurred.

[2] also provides the following detail:

The network may poll for the UE report after a successful random access procedure (UEInformationRequest) and the UE responds with the number of preambles sent by MAC for the last successfully completed random access procedure and whether contention is detected by MAC for at least one of the transmitted preambles for the last successfully completed random access procedure (UEInformationResponse).


[1] 3GPP TS 36.331 V9.3.0: Radio Resource Control (RRC); Protocol specification - Section 5.6.5

[2] 3GPP TR 36.902 V9.2.0: Self-configuring and self-optimizing network (SON) use cases and solutions

Wednesday, 10 November 2010

Proximity Indication - New RRC Uplink Message in Rel-9

The inbound handover from a Macro eNB to an HeNB (a.k.a. Femtocell) is not supported in Release 8. Before making a handover decision to a HeNB, the Macro eNB needs to acquire UE measurement information related to the so-called target CSG cell. Nevertheless, UEs cannot continuously make measurements and read the system information of lots of CSG cells in cases of large scale HeNB deployments.

In order to allow the UE to make those measurements efficiently, a newly defined proximity report can be configured within the RRC Reconfiguration message. This proximity report will allow the UE to send a so-called “proximity indication” to the source eNB in the uplink whenever it is entering or leaving the proximity of one or more cells with CSG IDs that the UEs has in its CSG Whitelist.

A UE that is able to determine that it is near its CSG cell can thus inform the network to take the necessary actions for handover preparation. The detection of proximity is based on an autonomous search function.

The source eNB, upon receiving the proximity indication, might ask the UE to perform measurements of the CSG cell, to read the System Information (SI) or, in case it already has all required information, it might already start the handover procedure. PCI (Physical Cell Identification) confusion is resolved in Release 9. The eNB will ask the UE to report the global cell identity. As usual the UE reporting is using the RRC measurement procedures. The ovell procedure is illustrated in Figure below.

In summary five basic steps can be identified:
1. Proximity configuration/reporting
2. HO measurement configuration/reporting
3. Resolution of PCI confusion by requesting and reporting System Information
4. Access Control in the network
5. HO execution

Since the CSG search can be very slow there are no strict requirements on the inbound handover performance, which can range from one to several 10’s of seconds.

Since the proximity information is based on UE signaling, the network might be receiving a lot of proximity indications, increasing the network load. Therefore, it was agreed to limit proximity indications a UE can send within a certain time frame. A timer, called the prohibit proximity timer, was introduced.


Monday, 8 November 2010

Single Radio Voice Call Continuity (SR‐VCC)

From a 3GPP presentation by Hannu Hietalahti

1. SR-VCC use case
1a. IMS call initiated in LTE can continue in CS domain after moving outside of LTE coverage area
1b. SR-VCC is invoked if no other VoIP capable PS system (e.g., HSPA/eHRPD) is available for VoIP PS-PS HO (Handovers)
1c. Only HO of a single voice bearer from PS to CS is specified
1d. Requires overlapping with 1xRTT/GSM/WCDMA coverage

2. SR-VCC allows a voice calls are anchored in IMS
2a. One-way HO from PS to CS systems (LTE to GSM/UMTS or LTE to 1xRTT)
2b. No simultaneous operation of different radio transceivers needed

3. Rel-9 SR-VCC improvements
3a. IMS support of mid call services (e.g., HOLD, MPTY)
3b. SR-VCC support for emergency calls

4. Video calls, reverse direction from CS call to IMS and optimisations are being studied in Rel-10

Saturday, 6 November 2010

LTE CS Fallback Procedure

From a 3GPP presentation by Hannu Hietalahti:

1. CS FallBack from EPS to CS domain
2. CSFB reuses voice and other CS-domain services provided by legacy CS infrastructure
3. EPS redirects the UE to CS Domain for CS services
3a. SMS can be delivered to the UE without redirecting to CS Domain
3b. After CS service the UE returns to LTE, depending on coverage and policy
4. User can decide, based on CLI, whether to accept CSFB request
5. Application of CSFB:
5a. CS capable device camping on LTE cell can establish/receive CS services
5b. Reuse of existing CS infrastructure for voice service until IMS VoIP is deployed
5c. Provide voice roaming support with LTE
5d. Support E911 using existing CS infrastructure
5e. Rel-9 IMS provides full emergency call support
5f. Requires overlapping CS domain coverage

Note: CSFB applies between LTE and GSM, WCDMA and 1xRTT