What are the functions of your phone UE (user equipment) when it come to the technical aspects of LTE?
Usually the functional role of UE is explained as the end user device which is used to make RRC connection request as indicated in the picture.
If UE is leaving from RRC Connected Mode to RRC Idle Mode, then cell selection will take place like this. However that's not the only function of UE
There is more to the discussion than just UE getting connected to an LTE based station and getting registered. During this process and later on -- a whole lot depends upon UE Capabilities.
There are 8 UE categories as defined in 3GPP release 10.
Each UE category defines both Uplink and Downlink Capabilities. This is different from WCDMA which has separate UE categories for High Speed Downlink Packet Access (HSDPA) and different categories for High Speed Uplink Packet Access ( HSUPA).
Capabilities Associated with Each UE Category
- Category 1 to 5 were introduced with in Release 8 of 3GPP specifications.
- Category 6 to 8 were introduced within Release 10 version of 3GPP specifications.
Capabilities associated with each UE category. Credits: LTE in Bullets
- Release 8 or 9 UE can be implemented to support any UE category between 1 to 5.
- Release 10 UE can be implemented to support a UE category between 1 and 8 which means release 10 UEs are backward compatible.
- Maximum total bits per Transmission Time Interval (TTI) in the downlink defines the maximum downlink throughput. A single TTI corresponds to the 1 ms subframe duration.
- Max downlink throughput specified for release 8 and 9 versions of 3GPP specifications is 300 Mbps. It is applicable when transferring 2 transport blocks per subframe on a single RF carrier.
- Max downlink throughput specified for release 10 version of 3GPP specifications is 3 Gbps. It is applicable when transferring 10 transport blocks per subframe across 5 Component Carriers.
- Max total bits per TTI in the uplink define the max uplink throughput:
- Max uplink throughput specified for Release 8 and 9 versions of the 3GPP specifications is 75 Mbps. This is supported when transferring 1 transport blocks per subframe on a single RF carrier
- Max uplink throughput specified for release 10 version of the 3GPP specifications is 1.5 Gbps. This is supported when transferring 10 transport blocks per subframe across 5 Component Carriers
- Release 8 and 9 versions of the 3GPP specifications allow only a single transport block to be transferred in the Uplink direction during each TTI so the maximum total bits per TTI equals the maximum bit per transport block
- All UE categories support:
- the 20 MHz channel bandwidth
- 64 QAM in the downlink
- downlink transmit diversity with up to 4 transmit antenna elements
- UE performance requirements have been specified based upon the assumption that all UE support downlink receive diversity.
- UE categories 2,3 and 4 support 2x2 MIMO in the downlink.
- UE category 5 can also support 4x4 MIMO in the downlink.
- UE category 8 is required to support 8x8 MIMO in the downlink
- Question: When does UE signals its category? Answer: A UE signals its category (or categories) within UE Capability Information message.
- UEs which are category 6 or 7, also signal support for category 4. This allows the network to treat these UE as category 4 devices when the network does not support categories 6 or 7. Similarly, UEs which are category 8, also signal support for category 5.
other ue capabilities
As discussed above UEs inform about their optional capabilities within the UE Capability Information message.
The message is shown in the figure below.
UE Capability Information Message
UE Capability Information message include capability information relevant to each supported Radio Access Technology ( RAT).
This information relevant to LTE capabilities is signalled using ' UE EUTRA Capability ' information element.
What are the general UE capabilities included within the 'UE EUTRA Capability' information element?
The table above indicates general UE capabilities included within the 'UE EUTRA Capability' information element.
- Access Stratum Release specifies the version of 3GPP specification upon which UE implementation is based. For example is it 3GPP release 8, 9 or 10 etc.
- Device Type indicates whether or not the UE benefits from battery power consumption optimization. Handheld devices are likely to rely upon batters as a source of power, whereas data dongles are most likely to obtain their power from a laptop or similar devices which could be connected to main electric supply. Differentiating between these types of devices provide the eNodeB with the potential to apply different radio resource management to devices which would benefit from reduced power consumption. For example battery life could be prolonged or UEs which benefit from reduced power consumption could be allocated reduced inactivity timers so the Discontinuous Reception (DRX) mode of operation is entered sooner and more frequently.
Does UE Capability indicate PDCP related Information?
The table above presents the Packet Data Convergence Protocol (PDCP) UE capabilities include within the ' UE EUTRA Capability ' information element.
Robust Header Compression (ROHC) can be used to reduce protocol stack overheads when transmitting user plane data across the air-interface. This is very particularly importance for services where the payload is relatively small compared to the protocol stack headers. For example Voice over IP (VoIP) requires ROHC to ensure that protocol stack overheads are manageable.
How many Robust Header Compression (ROHC) profiles does UE support?
During UE Capability information message, UE can indicate support for the following ROHC profiles.
- RTP/UDP/IP header compression
- UDP/IP header compression
- ESP/IP header compression
- IP header compression
- TPC/IP header compression
- RTP/UDP/IP updated header compression
- UDP/IP updated header compression
- ESP/IP updated header compression
- IP updated header compression
VoIP services use RTP/UDP/IP protocol stack for the speech data and UDP/IP protocol stack for associated RTCP signalling.
UE also signals its capabilty in terms of maximum number of support ROHC context sessions. In other words the number of parallel streams of data being compressed / decompressed. UE can specify values between 2 an384.
How ue informs its physical layer capabilities in 'ue eutra capability' information element?
UE informs about its physical layer capabilities in 'UE EUTRA Capability' information element as shown in the table below.
Optional Physical Layer capabilities
UE sends a flag when the following capabilities are supported:
- UE Transmit Antenna Selection, i.e. the UE has the ability to switch between multiple antenna for its uplink transmissions. This can be useful if the end-user's hand is shielding one antenna.
- When UE specific reference signals are supported. Transmission mode 7 uses antenna port 5 to transmit a UE specific Reference Signal. Beamforming can be applied to the UE specific Reference Signal and to the set of allocated Resource Blocks.
- Enhanced Dual Layer (FDD) refers to support for downlink transmission mode 8. Transmission mode 8 allows 2 UEs to simultaneously benefit from dual layer beamforming, in other words a total of 4 layers can be transferred.
- Enhanced Dual Layer (TDD) refers to the equivalent support for TDD.
- Two (2) Antenna Ports for PUCCH Transmission refers to PUCCH transmit diversity
- Transmission Mode 9 with 8 Channel State Information (CSI) Reference Signal Antenna ports (FDD) refers to support for single user beamforming with up to 8x8 MIMO
- PMI Disabling indicates whether or not PMI reporting can be disabled for a UE using transmission mode 9. If PMI reporting is disabled, CQI reports are derived from the cell specific Reference Signals. Otherwise, CQI reports are derived from the CSI Reference Signals.
- Cross Carrier Scheduling is applicable to Carrier Aggregation. This capability allows the PDCCH on serving cell ' x' to allocate resources on serving cell 'y'. When Carrier Aggregation is supported in the uplink direction, this capability also allows the UE to use the primary serving cell as a path loss reference for secondary serving cell. This is applicable to uplink power control calculations.
- Simultaneous PUCCH and PUSCH Transmission refers to capability of the baseband processing within the UE. The eNodeB interprets this capability in combination with the RF capability of the UE. The baseband capability is independent of the operating band.
- if a UE indicates baseband support, and if the UE indicates that is supports non-continguos uplink resource allocation at the RF level for a specific RF carrier within a specific operating band, then the UE supports simultaneous PUCCH and PUSCH transmission for all RF carriers within that operating band
- if a UE indicates baseband support, and if the UE indicates that it supports uplink Carrier Aggregation, then the UE supports simultaneous PUCCH and PUSCH transmission for any uplink Component Carrier which the UE can aggregate.
- Multi-Cluster PUSCH within a Component Carrier refers to the capability of the baseband processing within the UE. Multi-cluster PUSCH transmission corresponds to non-contiguous Resource Block allocations provided by the PDCCH Downlink Control Information ( DCI ), i.e., PUSCH resource allocation type 1. This baseband capability is independent the operating band.
- if a UE indicates baseband support, and if the UE indicates that it supports non-contiguous uplink resource allocation at the RF level for a specific RF carrier within a specific operating band, then the UE supports multi-cluster PUSCH transmission for all RF carriers within that operating band
- if a UE indicates that it supports uplink Carrier Aggregation, then the UE supports multi-cluster PUSCH transmission for any uplink Component Carrier which the UE can aggregate.
- Non-Contiguous Uplink Reosurce Allocation within a Component Carrier refers to the RF capability of the UE. This information is interpreted in combination with the baseband capability of the UE. The RF capability for non-contiguous uplink resource allocation is specified for each supported operating band. The operating bands themselves are not listed explicitly as part of this capability information, but the list of indications are ordered using the same operating band sequence as used for the 'Supported E-UTRA band List' within the RF capabilities information.
- In 3GPP release 10, UE can signal their uplink MIMO capability using values of '2 layers' or '4 layers' corresponding to support for 2x2 MIMO or 4x4 MIMO. This capability information is signalled for each Carrier Aggregation bandwidth class that UE specifies for each operating band within the set of supported band combinations.
- Also in 3GPP release 10, UE can signal their downlink MIMO capability using values of '2 layers' , '4 layers' or '8 layers' corresponding to support for 2x2 MIMO, 4x4 MIMO or 8x8 MIMO. This capability information is signalled for each Carrier Aggregation bandwidth class that the UE specifies for each operating band within the set of supported band combinations.
There are a lot of more additional UE capabilities which are included in UE Capability Information message and Feature group indicators, which I will list out in a separate post.