Prerequisite Features
l (Optional) LAOFD-001001 LTE-A Introduction
This feature is required if at least two FDD carriers are involved in FDD+TDD CA and the total bandwidth of the FDD carriers does not exceed 20 MHz.
l (Optional) LAOFD-001002 Carrier Aggregation for Downlink 2CC in 40MHz
This feature is required if at least two FDD carriers are involved in FDD+TDD CA and the total bandwidth of the FDD carriers is greater than 20 MHz but not greater than 40 MHz.
l (Optional) LAOFD-080207 Carrier Aggregation for Downlink 3CC in 40MHz This feature is required if three FDD carriers are involved in FDD+TDD CA and the total bandwidth of the FDD carriers does not exceed 40 MHz.
l (Optional) LAOFD-080208 Carrier Aggregation for Downlink 3CC in 60MHz This feature is required if three FDD carriers are involved in FDD+TDD CA and the total bandwidth of the FDD carriers is greater than 40 MHz but not greater than 60 MHz. l (Optional) LAOFD-070201 Flexible CA from Multiple Carriers
This feature is required if the function of Flexible CA from Multiple Carriers is used for the FDD carriers involved in the CA.
l (Optional) TDLAOFD-001001 LTE-A Introduction
This feature is required if at least two TDD carriers are involved in FDD+TDD CA and the total bandwidth of the TDD carriers does not exceed 30 MHz.
This feature is required if at least two TDD carriers are involved in FDD+TDD CA and the total bandwidth of the TDD carriers is greater than 30 MHz but not greater than 40 MHz.
l (Optional) TDLAOFD-081405 Carrier Aggregation for Downlink 3CC This feature is required if three TDD carriers are involved in FDD+TDD CA. l (Optional) TDLAOFD-070201 Flexible CA from Multiple Carriers
This feature is required if the function of Flexible CA from Multiple Carriers is used for the TDD carriers involved in the CA.
Mutually Exclusive Features
l FDD+TDD CA is not compatible with the following FDD eRAN features:
– LOFD-003029 SFN, LOFD-070205 Adaptive SFN/SDMA, LOFD-081208 Inter- eNodeB SFN Based on Coordinated BBU, and LOFD-081209 Inter-eNodeB Adaptive SFN/SDMA Based on Coordinated BBU
The PCell and SCells of a CA UE cannot be SFN cells.
– LOFD-001007 High Speed Mobility and LOFD-001008 Ultra High Speed Mobility The PCell and SCells of a CA UE cannot be high-speed or ultra-high-speed cells. – LBFD-002017 DRX and LOFD-001105 Dynamic DRX
DRX does not work on UEs in the FDD+TDD CA state. – LAOFD-080202 Carrier Aggregation for Uplink 2CC [Trial]
Uplink 2CC aggregation does not work in FDD+TDD CA scenarios. l FDD+TDD CA is not compatible with the following TDD eRAN features:
– TDLOFD-001075 SFN, TDLOFD-002008 Adaptive SFN/SDMA,
TDLOFD-001098 Inter-BBP SFN, TDLOFD-001081 Inter-BBP Adaptive SFN/ SDMA, TDLOFD-001080 Inter-BBU SFN, TDLOFD-001082 Inter-BBU Adaptive SFN/SDMA, and TDLOFD-070227 PDCCH DCS in SFN
The PCell and SCells of a CA UE cannot be SFN cells.
– TDLOFD-001007 High Speed Mobility and TDLOFD-080205 Handover Enhancement at Speed Mobility
In high speed scenarios, RRC connection reconfiguration procedures may frequently take place because the eNodeB notifies UEs of SCell configuration or removal through RRC Connection Reconfiguration messages. This increases the network signaling load. To prevent the frequent RRC connection reconfiguration procedures, cells with the Cell.HighSpeedFlag parameter set to
HIGH_SPEED(High speed cell flag) cannot participate in CA currently.
– TDLBFD-002017 DRX and TDLOFD-001105 Dynamic DRX
DRX does not work on UEs in the FDD+TDD CA state. – TDLAOFD-081407 Carrier Aggregation for Uplink 2CC [Trial]
Uplink 2CC aggregation does not work in FDD+TDD CA scenarios.
Impacted Features
l The impacted FDD eRAN features are as follows:
– LBFD-070103 Multi-Band Compatibility Enhancement
Frequency-based CA and adaptive CA do not apply to multi-band cells. In either configuration mode, when an eNodeB compares its band combination capability
with that of a CA UE, the eNodeB calculates band indicators based on the downlink E-UTRA absolute radio frequency channel numbers (EARFCNs) of the PCC and SCCs in SccFreqCfg MOs. However, currently the eNodeB does not consider multi-band capabilities of cells. Therefore, the calculation produces only the primary-band indicator.
– LOFD-001016 VoIP Semi-persistent Scheduling
According to 3GPP TS 36.321, semi-persistent scheduling takes effect only on the PCCs for CA UEs.
– LOFD-001032 Intra-LTE Load Balancing and LOFD-070215 Intra-LTE User Number Load Balancing
When selecting UEs for either type of load balancing defined in the two features, the eNodeB filters out the CA UEs that treat the source cell as their PCells or SCells.
– LOFD-002001 Automatic Neighbour Relation (ANR) and LOFD-002002 Inter- RAT ANR
During ANR, the eNodeB determines whether to select CA UEs to perform measurements based on the ANR.CaUeChoseMode parameter setting. For details, see ANR Management.
– LOFD-070208 Coordinated Scheduling based Power Control (Cloud BB)
This feature requires a centralized controller, which is a process deployed on a BBP in the eNodeB. The centralized controller increases the average throughput of cells on the affected frequency and the cell edge UE throughput in the network.
However, it has a negative impact on the high-throughput UEs that cause co- channel interference to the cell edge UEs. If basic scheduling is used with CA, the data rate of a CA UE is the total data rate of the UE on all the aggregated carriers and therefore is typically higher than the data rate of a non-CA UE. As a result, CA UEs have a lower probability of being scheduled and therefore a lower data rate in CSPC scenarios.
– LOFD-070220 eMBMS Phase 1 based on Centralized MCE Architecture When this feature is enabled, CA UEs can receive MBSFN subframes in their PCells but not in their SCells. This feature works for CA UEs only in PCells. – LAOFD-002001 Static TDM eICIC and LAOFD-081233 Dynamic TDM eICIC
When one or both of these two features are enabled, the interference between macro and micro cells cannot be mitigated as expected, because of subframe
synchronization between the PCell and SCells of each CA UE. l The impacted TDD eRAN features are as follows:
– TDLBFD-00201806 Multi-Band Compatibility Enhancement
If Multi-Band Compatibility Enhancement is enabled for a cell, the primary and secondary operating bands of the cell are all compared with the CA band
combinations supported by CA UEs. The cell can be configured as an SCell for a CA UE as long as an operating band of the cell is included in the CA band combinations supported by the UE. If the CA UE can operate in the primary band and a secondary band and only the secondary band supports CA, the eNodeB transfers the UE to the secondary band through an intra-cell handover before configuring the cell as an SCell for the UE.
– TDLOFD-001016 VoIP Semi-persistent Scheduling
According to 3GPP TS 36.321, semi-persistent scheduling takes effect only on the PCCs for CA UEs.
– TDLOFD-001032 Intra-LTE Load Balancing and TDLOFD-070215 Intra-LTE User Number Load Balancing
When selecting UEs for either type of load balancing defined in the two features, the eNodeB filters out the CA UEs that treat the source cell as their PCells or SCells.
– TDLOFD-002001 Automatic Neighbour Relation (ANR) and TDLOFD-002002 Inter-RAT ANR
During ANR, the eNodeB determines whether to select CA UEs to perform measurements based on the ANR.CaUeChoseMode parameter setting. For details, see ANR Management Feature Parameter Description.
– TDLOFD-070220 eMBMS Phase 1 based on Centralized MCE Architecture When this feature is enabled, CA UEs can receive MBSFN subframes in their PCells but not in their SCells. This feature works for CA UEs only in PCells.
5
Network Impact
5.1 LAOFD-001001 LTE-A Introduction
System Capacity
l Number of RRC_CONNECTED UEs
A CA UE with SCells configured has only one RRC connection to the network and consumes one sales unit of the license for the number of RRC_CONNECTED UEs. However, the CA UE consumes a hardware resource unit in each of its serving cells. In an extreme case with 2CC aggregation for all UEs on the network, the maximum number of UEs that can access the network decreases by half. The maximum number decreases depending on the number of CCs aggregated. When all hardware resources are used, the eNodeB preferentially releases the CA UEs that treat a local cell as their SCell to maximize the number of UEs that can access the network.
l PUCCH and PUSCH overheads
Each CA UE sends the ACK/NACK and CSI related to its SCells in its PCell. When the PUSCH is not scheduled, the UE sends the information over the PUCCH. When the PUSCH is scheduled, the UE sends the information over the PUSCH. Therefore, PUCCH overhead or PUSCH associated signaling overhead increases.
l Overall throughput in the entire network
CA does not directly affect network capacity. However, when spare resources are available on a network, CA increases the resource usage and overall throughput in the network.
l Data rates of CA UEs
– When spare resources are available on a network, CA in the network increases the data rates of CA UEs.
– When no spare resources are available, the data rates of CA UEs are dependent on scheduling policies (described in 3.3.4 Scheduling Under CA) and UE locations. Activating an SCell may result in a decrease in the overall SCell throughput if the UE is located at the edge of the SCell. However, activating an SCell may cause an increase in the overall SCell throughput if the UE is located in the cell center or at a place of a medium distance to the center of the SCell.
Network Performance
l PRB usage
In commercial networks, most services on CA UEs are burst services, and there is little probability that PRBs in all CCs of a UE will be exhausted simultaneously. When CA is enabled, cell load can be rapidly balanced through carrier management and scheduling, utilizing idle resources and increasing the PRB usage of the network.
l Number of CQI reports
According to section 10.1.1 "PUCCH format information" in 3GPP TS 36.213 V10.10.0, CA UEs cannot send CSI reports together with ACK/NACK over the PUCCH with format 1b. Therefore, the UEs discard CSI reports according to 3GPP specifications. CSI reports include periodic CQI reports. As a result, the number of CQI reports from CA UEs decreases, as indicated by the values of the L.ChMeas.CQI.DL.0 to
L.ChMeas.CQI.DL.15 counters, after CA is enabled.
When the number of CQI reports from CA UEs decreases, the total number of CQI reports in the entire network may decrease, increase, or remain unchanged, depending on the radio conditions of the CA UEs and the ratio of CA UEs to all UEs. For example, if CA UEs are located in cell centers and account for a high proportion of total UEs, the total number of CQI reports may also decrease. If CA UEs are not located in cell centers or they account for a low proportion, the total number of CQI reports may increase or remain unchanged.
5.2 LAOFD-001002 Carrier Aggregation for Downlink 2CC
in 40MHz
This feature itself does not have any network impacts. For the impacts of its prerequisite features, see 5.1 LAOFD-001001 LTE-A Introduction.
5.3 LAOFD-070201 Flexible CA from Multiple Carriers
This feature itself does not have any network impacts. For the impacts of its prerequisite features, see 5.1 LAOFD-001001 LTE-A Introduction.
5.4 LAOFD-070202 Inter-eNodeB CA based on
Coordinated BBU
The prerequisite features have the impacts described in 5.1 LAOFD-001001 LTE-A Introduction.
In a centralized multi-BBU interconnection scenario, where there is inter-BBU transmission delay, the LAOFD-070202 feature has a slight negative impact on the peak data rate of a CA UE but does not affect user experience. The reason is that the data to be sent does not arrive at an SCell of the UE on the SCell's scheduling occasion and the UE cannot be scheduled at that moment.
In a distributed multi-BBU interconnection scenario, if the round trip time for inter-eNodeB transmission is between 32 μs (including 32 μs) and 260 μs, the LAOFD-070202 feature imposes the following impact on the UEs involved:
l CQI reports are delayed, causing slight deterioration in frequency-selective scheduling performance and an increase in IBLER.
l Reports of HARQ demodulation results are delayed, affecting the peak data rate of a single UE and resulting in an increase in RBLER.
l CQI and IBLER feedback is delayed, causing a fluctuation in the data rate of UEs located at places of medium or long distances to the center of their SCells.
l Due to the difference in RLC data arrival time between the aggregated carriers, a CA UE has to combine the received data and arrange the order of the data. The data combining and ordering consume UE CPU resources. If the CPU capacity is insufficient, the data rate of the UE fluctuates.
l Due to possible errors in the estimated scheduling priority of a CA UE, the PRBs in an SCell for the UE may not be fully utilized when the SCell serves a small number of non- CA UEs and the non-CA UE traffic is light.
l To minimize the impact of inter-eNodeB transmission delay, RLC retransmissions occur only in the PCell of each CA UE. If the Uu bandwidth of the PCell is used up by GBR services, RLC retransmissions for a CA UE are often blocked and the data rate of the UE fluctuates.
l If an eNodeB detects congestion in the transmission queues on an eX2 interface, it triggers backpressure on the inter-eNodeB CA UEs on the interface, and the data rates of the CA UEs decrease. When the eNodeB detects that the congestion is relieved, it stops the backpressure, and the data rates of the CA UEs return to the original levels.
5.5 LAOFD-080201 Inter-eNodeB CA based on Relaxed
backhaul
The prerequisite features have the impacts described in 5.1 LAOFD-001001 LTE-A Introduction. Due to inter-eNodeB transmission delay and limited bandwidth, the LAOFD-080201 feature itself has the following impacts on the UEs involved:
l CQI reports are delayed, causing slight deterioration in frequency-selective scheduling performance and an increase in IBLER.
l Reports of HARQ demodulation results are delayed, affecting the peak data rate of a single UE and resulting in an increase in RBLER.
l CQI and IBLER feedback is delayed, causing a fluctuation in the data rate of UEs located at places of medium or long distances to the center of their SCells.
l Due to the difference in RLC data arrival time between the aggregated carriers, a CA UE has to combine the received data and arrange the order of the data. The data combining and ordering consume UE CPU resources. If the CPU capacity is insufficient, the data rate of the UE fluctuates.
l Due to possible errors in the estimated scheduling priority of a CA UE, the PRBs in an SCell for the UE may not be fully utilized when the SCell serves a small number of non- CA UEs and the non-CA UE traffic is light.
l To minimize the impact of inter-eNodeB transmission delay, RLC retransmissions occur only in the PCell of each CA UE. If the Uu bandwidth of the PCell is used up by GBR services, RLC retransmissions for a CA UE are often blocked and the data rate of the UE fluctuates.
l If an eNodeB detects congestion in the transmission queues on an eX2 interface, it triggers backpressure on the inter-eNodeB CA UEs on the interface, and the data rates of
the CA UEs decrease. When the eNodeB detects that the congestion is relieved, it stops the backpressure, and the data rates of the CA UEs return to the original levels.
5.6 LAOFD-080202 Carrier Aggregation for Uplink 2CC
[Trial]
The prerequisite features have the impacts described in 5.1 LAOFD-001001 LTE-A Introduction. The LAOFD-080202 feature itself has the following impact:
If MTA is enabled, non-contention-based random access occurs in SCells. As a result, the counters related to random access to the SCells produce larger values.
5.7 LAOFD-080207 Carrier Aggregation for Downlink 3CC
in 40MHz
The prerequisite features have the impacts described in 5.1 LAOFD-001001 LTE-A Introduction. The LAOFD-080207 feature itself has the following impact on PUCCH overheads:
When downlink 3CC aggregation is enabled, one RB is used for PUCCH format-3 overhead. If PucchSwitch under the CellAlgoSwitch.PucchAlgoSwitch parameter is on, this RB is an additional RB for the PUCCH. It was originally allocated for the physical uplink shared channel (PUSCH). If PucchSwitch is off, this RB is an existing RB for the PUCCH. It was originally allocated for periodic CQI reporting. As a result, more UEs have to use aperiodic CQI reporting.
5.8 LAOFD-080208 Carrier Aggregation for Downlink 3CC
in 60MHz
This feature itself does not have any network impacts. For the impacts of its prerequisite features, see 5.7 LAOFD-080207 Carrier Aggregation for Downlink 3CC in 40MHz.
5.9 LAOFD-081237 Carrier Aggregation with DL 4x4
MIMO [Trial]
This feature itself does not have any network impacts. For the impacts of its prerequisite features, see 5.1 LAOFD-001001 LTE-A Introduction.
5.10 MRFD-101222 FDD+TDD Carrier Aggregation(LTE
FDD) [Trial]
The prerequisite features have the impacts described in 5.1 LAOFD-001001 LTE-A Introduction. The MRFD-101222 feature itself has the following impact:
When an FDD carrier works as the PCC and TDD carriers as SCCs for a CA UE, the downlink TDD spectral resources are fully utilized to increase downlink throughput. In
addition, the FDD PCC provides better uplink coverage for the CA UE than a TDD carrier does for a non-CA UE.