LTE-Advanced - 4.5G Evolution
LTE-Advanced is the evolution of LTE that meets IMT-Advanced requirements (true 4G). It was standardized in Rel-10 (2011), Rel-11 (2012), and Rel-12 (2014).
Key Features
LTE-Advanced introduced major enhancements:
- Carrier Aggregation - combining multiple carriers for higher bandwidth
- Enhanced MIMO - up to 8×8 DL, 4×4 UL
- CoMP - Coordinated Multi-Point transmission
- Relay Nodes - extending coverage
- HetNets - Heterogeneous Networks with small cells
IMT-Advanced Requirements
| Requirement | IMT-Advanced | LTE-A Capability |
|---|---|---|
| Peak DL | 1 Gbps | 3 Gbps (Rel-10) |
| Peak UL | 500 Mbps | 1.5 Gbps (Rel-10) |
| Bandwidth | Up to 100 MHz | Up to 100 MHz (5×20) |
| Spectral Eff. | 15 bps/Hz DL | 30 bps/Hz DL |
📋 Specifications: TS 36.300 (E-UTRAN Overall), TR 36.913 (Requirements)
Carrier Aggregation
Carrier Aggregation (CA) is the flagship feature of LTE-Advanced - combining multiple component carriers (CCs). See the detailed glossary entry for evolution across releases.
Basic Concepts
| Term | Description |
|---|---|
| Component Carrier (CC) | Individual LTE carrier (up to 20 MHz) |
| Primary Cell (PCell) | Main serving cell, handles RRC/NAS |
| Secondary Cell (SCell) | Additional capacity cells |
| Primary SCell (PSCell) | Primary of Secondary Cell Group (Rel-12) |
Aggregation Types
| Type | Description | Example |
|---|---|---|
| Intra-band contiguous | Adjacent CCs in same band | B7: 20+20 MHz |
| Intra-band non-contiguous | Same band, gap between CCs | B7: 20+gap+20 MHz |
| Inter-band | Different frequency bands | B3 + B7 |
CA Combinations (Examples)
| Combination | Bands | Max Bandwidth | Max DL |
|---|---|---|---|
| CA_3A-7A | B3 + B7 | 40 MHz | 300 Mbps |
| CA_3A-3A-7A | B3 + B3 + B7 | 60 MHz | 450 Mbps |
| CA_1A-3A-7A-20A | B1+B3+B7+B20 | 80 MHz | 600 Mbps |
| CA_1A-3A-7A-7A-20A | 5CC | 100 MHz | 750 Mbps |
Evolution by Release
| Release | Max CCs | Max Bandwidth | Notes |
|---|---|---|---|
| Rel-10 | 5 CC | 100 MHz | Basic CA |
| Rel-11 | 5 CC | 100 MHz | Multiple timing advance |
| Rel-12 | 5 CC | 100 MHz | Dual Connectivity |
| Rel-13 | 32 CC | 640 MHz | License Assisted Access |
📋 Specifications: TS 36.300 §5.5 (CA), TS 36.101 (UE RF)
Enhanced MIMO
LTE-Advanced extended MIMO capabilities significantly.
MIMO Configurations
| Release | Downlink | Uplink | Features |
|---|---|---|---|
| Rel-8 | 4×4 | 1×1 | Basic MIMO |
| Rel-10 | 8×8 | 4×4 | Enhanced MIMO |
| Rel-11 | 8×8 | 4×4 | 3D beamforming prep |
| Rel-12 | 8×8 | 4×4 | FD-MIMO study |
Transmission Modes (TM)
| TM | Name | MIMO | Use Case |
|---|---|---|---|
| TM1 | Single antenna | 1×1 | Basic |
| TM2 | Transmit diversity | 2×1/4×1 | Coverage |
| TM3 | Open-loop SM | 2×2/4×4 | High mobility |
| TM4 | Closed-loop SM | 2×2/4×4 | Low mobility, high throughput |
| TM7 | Single-layer BF | 1×1 | Beamforming |
| TM8 | Dual-layer BF | 2×2 | Rel-9, MU-MIMO |
| TM9 | Up to 8-layer | 8×8 | Rel-10, full MIMO |
| TM10 | Up to 8-layer | 8×8 | Rel-11, CoMP |
MU-MIMO (Multi-User MIMO)
Serving multiple UEs on same time-frequency resources:
- SU-MIMO: All layers to single UE
- MU-MIMO: Layers split between UEs
- Up to 4 UEs in Rel-10+
📋 Specifications: TS 36.213 (Physical Layer Procedures)
CoMP
Coordinated Multi-Point (CoMP) - coordinating transmission/reception across multiple cells. See the detailed glossary entry for evolution across releases.
CoMP Scenarios
| Scenario | Description |
|---|---|
| Scenario 1 | Homogeneous, intra-site |
| Scenario 2 | Homogeneous, high Tx power RRH |
| Scenario 3 | Heterogeneous, macro + low power |
| Scenario 4 | Heterogeneous, same cell ID |
CoMP Techniques
Downlink CoMP
| Technique | Description | Benefit |
|---|---|---|
| DPS | Dynamic Point Selection | Interference reduction |
| DPB | Dynamic Point Blanking | Interference avoidance |
| JT | Joint Transmission | Increased signal strength |
| CS/CB | Coordinated Scheduling/Beamforming | Interference coordination |
Uplink CoMP
| Technique | Description |
|---|---|
| JR | Joint Reception - multiple points receive |
| CS/CB | Coordinated Scheduling |
Backhaul Requirements
| CoMP Type | Latency Requirement | Information Shared |
|---|---|---|
| CS/CB | ~10ms | Scheduling info |
| DPS | ~10ms | Scheduling + CSI |
| JT | <1ms | User data + CSI |
📋 Specifications: TS 36.819 (CoMP Study), TS 36.300 §15 (CoMP)
Relay Nodes
Rel-10 introduced Layer 3 relays for coverage extension.
Relay Types
| Type | Backhaul | Cell ID | Transparent |
|---|---|---|---|
| Type 1 | Wireless | Own | No (visible to UE) |
| Type 1a | Wireless | Own | No, out-of-band BH |
| Type 1b | Wireless | Own | No, antenna isolation |
| Type 2 | Wireless | Donor's | Yes (invisible) |
Type 1 Relay Architecture
UE ←→ Relay Node ←→ Donor eNodeB ←→ EPC
(RN) (DeNB)
- Un interface: RN ↔ DeNB (wireless backhaul)
- Uu interface: UE ↔ RN (access link)
Use Cases
- Coverage holes
- Cell edge performance
- Temporary coverage (events)
- Cost-effective deployment
📋 Specifications: TS 36.300 §4.7 (Relay), TS 36.806 (Relay Study)
HetNets
Heterogeneous Networks - mixing macro cells with small cells.
Node Types
| Type | Power | Coverage | Use Case |
|---|---|---|---|
| Macro | 43-46 dBm | 1-30 km | Wide area |
| Micro | 30-37 dBm | 300m-2 km | Urban hotspots |
| Pico | 23-30 dBm | 100-300m | Indoor/outdoor capacity |
| Femto | <23 dBm | 10-50m | Home/enterprise |
Interference Management
eICIC (Enhanced ICIC) - Rel-10
Time-domain interference coordination:
- ABS (Almost Blank Subframes) - macro reduces power
- Protected subframes - small cell serves UEs
FeICIC (Further Enhanced) - Rel-11
- CRS interference cancellation
- Non-zero power ABS
- Improved performance
Range Extension
Small cells can extend their range using:
- Cell Range Expansion (CRE): +6 to +9 dB bias
- Combined with eICIC/FeICIC for protection
📋 Specifications: TS 36.300 §16 (HetNets), TR 36.839 (HetNet Mobility)
Dual Connectivity
Rel-12 introduced Dual Connectivity - UE connects to two eNodeBs simultaneously. See the detailed glossary entry for evolution to EN-DC and 5G.
Architecture
┌─────────┐
│ EPC │
└────┬────┘
│ S1
┌──────┴──────┐
│ │
┌────┴────┐ ┌────┴────┐
│ MeNB │───│ SeNB │ X2
└────┬────┘ └────┬────┘
│ │
└──────┬──────┘
│
┌──┴──┐
│ UE │
└─────┘
Key Concepts
| Term | Description |
|---|---|
| MeNB | Master eNodeB - RRC anchor |
| SeNB | Secondary eNodeB - additional capacity |
| MCG | Master Cell Group |
| SCG | Secondary Cell Group |
| Split Bearer | Bearer split between MeNB/SeNB |
Bearer Options
| Option | Description | Data Path |
|---|---|---|
| MCG Bearer | Only through MeNB | S1 → MeNB → UE |
| SCG Bearer | Only through SeNB | S1 → SeNB → UE |
| Split Bearer | Through both | S1 → MeNB → MeNB/SeNB → UE |
Benefits
- Throughput: Aggregate from both nodes
- Mobility: Reduced handover interruption
- Offloading: Traffic steering flexibility
📋 Specifications: TS 36.300 §21 (Dual Connectivity)
D2D / ProSe
Device-to-Device communication, also called ProSe (Proximity Services) - Rel-12.
Use Cases
| Category | Application |
|---|---|
| Public Safety | Emergency communication |
| Commercial | Social discovery, gaming |
| Network Offload | Direct UE-UE traffic |
Operating Modes
| Mode | Coverage | Description |
|---|---|---|
| In-coverage | Both UEs | Network coordinated |
| Partial | One UE | Relay through covered UE |
| Out-of-coverage | None | Autonomous (public safety) |
D2D Channels
| Channel | Direction | Purpose |
|---|---|---|
| PSDCH | Sidelink | Discovery messages |
| PSCCH | Sidelink | Control (scheduling) |
| PSSCH | Sidelink | Shared channel (data) |
Resource Allocation
| Mode | Description |
|---|---|
| Mode 1 | eNodeB scheduled |
| Mode 2 | UE autonomous selection |
📋 Specifications: TS 23.303 (ProSe Architecture), TS 36.300 §23 (Sidelink)
UE Categories
LTE-Advanced UE categories with Carrier Aggregation.
Rel-10 Categories
| Category | Max DL | Max UL | DL MIMO | CA |
|---|---|---|---|---|
| Cat 6 | 300 Mbps | 50 Mbps | 2×2 or 4×4 | 2 CC |
| Cat 7 | 300 Mbps | 100 Mbps | 2×2 or 4×4 | 2 CC |
| Cat 8 | 3 Gbps | 1.5 Gbps | 8×8 | 5 CC |
Rel-11/12 Categories
| Category | Max DL | Max UL | Features |
|---|---|---|---|
| Cat 9 | 450 Mbps | 50 Mbps | 3 CC CA |
| Cat 10 | 450 Mbps | 100 Mbps | 3 CC CA |
| Cat 11 | 600 Mbps | 50 Mbps | 4 CC CA |
| Cat 12 | 600 Mbps | 100 Mbps | 4 CC CA |
| Cat 13 | 390 Mbps | 150 Mbps | 64QAM UL |
| Cat 14 | 3.9 Gbps | 1.5 Gbps | 8×8 MIMO |
📋 Specifications: TS 36.306 (UE Capabilities)
Frequency Bands
LTE-Advanced added new bands and CA combinations.
New Bands in Rel-10+
| Band | Frequency | Mode | Region | Notes |
|---|---|---|---|---|
| B23 | 2000/2180 MHz | FDD | USA | S-band |
| B30 | 2305/2350 MHz | FDD | USA | WCS |
| B40 | 2300-2400 MHz | TDD | Global | Expanded |
| B41 | 2496-2690 MHz | TDD | USA/China | Large bandwidth |
| B42 | 3400-3600 MHz | TDD | Europe | C-band |
| B43 | 3600-3800 MHz | TDD | Europe | C-band |
Popular CA Combinations
| Region | Combination | Bands | Typical Use |
|---|---|---|---|
| Europe | CA_3A-7A | 1800+2600 | Common |
| Europe | CA_3A-7A-20A | +800 | +coverage |
| USA | CA_2A-4A | PCS+AWS | T-Mobile |
| USA | CA_2A-4A-12A | +700 | +coverage |
| APAC | CA_1A-3A | 2100+1800 | Common |
📋 Specifications: TS 36.101 (UE RF Requirements)
Timeline
- 2008 - LTE-Advanced study started (TR 36.913)
- 2010 - Rel-10 frozen (first LTE-A)
- 2010 - ITU recognizes LTE-A as IMT-Advanced
- 2012 - Rel-11 frozen (CoMP, FeICIC)
- 2013 - First commercial LTE-A (Korea, 150 Mbps CA)
- 2014 - Rel-12 frozen (Dual Connectivity, D2D)
- 2015 - 3CA deployments worldwide