Carrier Aggregation in LTE Releases
3rd Generation Partnership Project (3GPP)
The 3GPP unites seven telecommunications standard development organizations (ARIB, ATIS, CCSA, ETSI, TSDSI, TTA, TTC), which is an umbrella for these standards organizations, that develop protocols for mobile telecommunication. The 3GPP organizes its work into three different streams: Radio Access Networks, Services and Systems Aspects, and Core Network and Terminals, which provide a complete system description for mobile telecommunications. It was established in December 1998 with the goal of developing a specification for a 3G mobile phone system based on the 2G GSM system, within the scope of the International Telecommunication Union’s.
LTE and LTE-A
The Long-Term Evolution (LTE) is an emerging technology, which is standardized by the 3GPP and evolving to meet the International Mobile Telecommunication Advanced (IMT-Advanced) requirements named as LTE-Advanced. The main goal of LTE is to provide a high data rate, low latency and packet optimized radio access technology supporting flexible bandwidth deployments. The network architecture of LTE has been designed with the goal to support packet-switched traffic with seamless mobility and great quality of service.
LTE is a standard for wireless broadband communication for mobile devices and data terminals. LTE is based on the GSM/EDGE and UMTS/HSPA technologies. LTE increases the capacity and speed of wireless mobile communication by using a different radio interface and other core network improvements. LTE uses different frequencies and bands in different countries. LTE is commonly marketed as 4G LTE & Advance 4G. LTE is also commonly known as 3.95G. LTE-Advanced or LTE-A is a major enhancement of the LTE standard. LTE-A uses several techniques and technologies (hardware and software) to meet higher network-performance standards. The technique of this standard which we are using in our work is following.
· Increased peak data rate for DL/UL
· Improved performance at cell edges.
· Carrier Aggregation (CA), the enhanced use of multi-antenna techniques.
· Support for Relay Nodes, LTE Femtocell and macro cell.
Based on the requirements and observations, the 3GPP has identified carrier aggregation (CA) as major feature for achieving improved data rate. It is a worth noting that BW aggregation basic concept has been used in 3G. Similarly, there are options in High Speed Packet Access (HSPA) evaluation to aggregate up to four carriers for downlinks, up to two carriers for uplink and have consider both the carriers contiguous. In release 8/9 of 3GPP LTE different carrier BW of 1.4, 3, 5, 10, 15 and 20 MHz being used that provide support for several deployment plus spectrum plans. Succeeding the desires of 100 MHz BW of system, Release 10 of 3GPP LTE has presented CA one of the foremost important structure of LTE-Advanced to balance the bandwidth a far 20 MHz. CA Release 10 described up to 100 MHz system bandwidth can be achieved by concurrently aggregating up to 5 CCs of 20 MHz, according to user equipment compatibility. To acknowledge better network advancements, it is important to guarantee backward compatibility for an LTE-Advanced design, thus LTE Release 10 UE and LTE Release 8/9 might be able to sustain in the consistent carrier deployed by Release 10 eNode Bs (eNBs). CA is very well-defined for Release 10 and establishes that every Component Carrier (CC) is companionable for LTE Release 8/9 and also one of BW expressed in Release 8/9. It has similarly permit reuse of RF in Release 8/9 schemes and implementation in UE and eNB. Frequency Division Duplex and Time Division Duplex carrier aggregation added in Release 12. In Release 13, the CC improved from count 5 to 32. It will be huge value for that, which expending huge block of unlicensed spectrum in 5 GHz band. Different releases of LTE with time are shown in Fig 2.1, our work is based on these following releases of LTE which explained in detail in upcoming sections.
Figure 2. 1 Different releases of LTE with time.
3GPP release 10 driving force to further develop LTE technology towards LTE–Advanced. LTE Release 10 was to provide higher bit rates in a cost-efficient way and, at the same time, completely fulfil the requirements set by ITU for IMT Advanced, also referred to as 4G. Its specifications freeze in 2011.
· Increased peak data rate, DL 3 Gbps, UL 1.5 Gbps
· Higher spectral efficiency, from a maximum of 16bps/Hz in Release 8 to 30 bps/Hz in Release 10
· Carrier aggregation (CA), allowing the combination of up to five separate carriers to enable bandwidths up to 100MHz
· MIMO antenna configurations up to 8×8 downlink and 4×4 uplink
· Increased number of simultaneously active subscribers
· Improved performance at cell edges, e.g. for DL 2×2 MIMO at least 2.40 bps/Hz/cell.
The main features that LTE Release 10 introduce are
· Carrier Aggregation
· Enhanced Downlink Multiple Antenna Transmission for LTE
· Uplink Multiple Antenna Transmission for LTE
· Relay for LTE
· New LTE Bands for US and ATC
· Self-Optimizing Networks (SON) Enhancements
· Enhancements to MBMS
Carrier Aggregation 3GPP release 10 needs to support wider transmission bandwidths than the currently supported 20 MHz specified in Rel.8/9 while maintaining the backwards compatibility with Rel-8/9. The preferred solution to this is carrier aggregation, where multiple component carriers are aggregated to form a larger overall transmission bandwidth. The carrier aggregation supposed to consider following scenarios.
· Release-8/9 backward compatible carriers are the basic building blocks and should be supported
· Release-10 signalling shall support aggregation of up to 5 DL CCs and 5 UL CCs, irrespective of intra- or inter-band CA.
· Release-10 shall be support both intra- and inter-band aggregation.
· Releasel-10 shall be support inter-band aggregation under deployments with RRH and repeaters, i.e., with different signal reception timings across CCs of different bands.
· UE-specific asymmetric number of component carriers in DL and UL shall be supported
· Component carriers can have any of the bandwidths supported in Rel-8
· The signalling and protocol specifications to support carrier aggregation shall be designed in a generic way
· Specification of carrier aggregation bands shall be done in Release independent manner.
· UL and DL control channel structure
· L1 procedures shall support CA
· L2/L3 protocols and procedures shall support CA
· UE and BS RF core requirements
3GPP standards development falls into three principal areas: radio interfaces, core networks and services. 3GPP Release 11 standards were frozen in December 2012 with the core network, protocols in December 2012 and radio access network (RAN) protocols in March 2013.For LTE, Rel-11 provides enhancements to the LTE-Advanced technologies introduced in 3GPP Release 10. Release 11 Features Lists
· Enhancements to Carrier Aggregation
· Coordinated Multi-Point (CoMP) transmission/reception
· Further enhancements to non-carrier aggregation based eICIC (FeICIC)
· Enhanced Physical Downlink Control Channel (EPDCCH)
· Enhancements to eMBMS
· Enhancements to Self-Organised Network
· Minimization of Drive Tests (MDT)
· Home eNodeB Enhancements
Carrier Aggregation was first introduced in LTE-Advanced 3GPP Release 10, which allows multiple Release 8 component carriers to be aggregated together to offer high peak data rates and throughput. Essentially, 3GPP Release 11 enhances the following carrier aggregation features aspects
· Provides better support for TDD configurations in which the TDD UL and DL can be configured differently on each of the component carriers and bands either in a full-duplex or in a half-duplex mode.
· Allows multiple timing advances in UE different for each component carriers to support the case where the transmission delays from the UE to the eNodeB are significantly different for each of the component carriers.
· Enhances Uplink signaling with the support of multi-cell periodic CSI multiplexing and multi-cell HARQ-ACK and periodic CSI. Also, transmit diversity is supported for PUCCH for the case of HARQ-ACK multiplexing with channel selection.
3 GPP Release 12 was largely completed on-time in March 2015, with a few exceptional features allowed an extension to later in the year. Release 12 builds on the innovations in Release 10 and Release 11 to further increase performance, efficiency and capabilities. All three releases are known as LTE-Advanced. Figure show evolution of LTE Advance.
A priority in this release was to use LTE technology for emergency and security services, with technical specifications for mission-critical application. Mission-Critical Press-to-Talk (MC-PTT) and other features, scheduled in Release 13.
3 GPP Release 12 defines following new features and improvements
· Downlink enhancements for MIMO
· Small cells (Femtocells)
· Machine to Machine (M2M)
· Proximity Services (ProSe)
· User Equipment (UE) enhancements
· Self-Organized Network (SON)
· Heterogeneous Network (HetNet) mobility
· Multimedia Broadcast/Multicast Services (MBMS)
· Local Internet Protocol Traffic Offload/Selected Internet Protocol Traffic Offload (LIPTO/SIPTO)
· Enhanced International Mobile Telecommunications Advanced (eIMTA)
· FDD-TDD Carrier Aggregation (CA)
FDD-TDD Carrier Aggregation (CA) Within Release 12, 3GPP has specified support for allowing UEs to operate TDD and FDD spectrum jointly. The main solution to be specified is CA between a number of TDD and FDD carriers. CA between the FDD and TDD spectrum would allow user throughputs to be boosted (at least for DL CA) and it would allow a better way to divide the load in the network between TDD and FDD spectrum. In addition to CA support operation of dual connectivity between TDD and FDD is further specified. Dual connectivity1 provides a tool to connect UEs to cells that are operating either TDD or FDD while the cells are connected with a backhaul of higher delay than that required for CA. The reason for operating in such a mode can, for example, be to enhance user throughputs, lower core network signalling or enhance the mobility performance.
3GPP Release 13 first release was frozen in March 2016. It was brought to reality with quite extensive set of new functionalities as compared to LTE-Advanced. They are summarized below.
· LTE in unlicensed spectrum
· Carrier Aggregation enhancements
· LTE enhancements for Machine-Type Communications (MTC)
· Enhancements for D2D
· Elevation Beamforming / Full-Dimension MIMO
· Indoor positioning
· Single-cell Point-to-Multipoint (SC-PTM)
LTE in unlicensed spectrum (LAA) feature goal is to enhance LTE to operate in unlicensed spectrum. While licensed spectrum remains 3GPP operators’ top priority to deliver advanced services and user experience, the opportunistic use of unlicensed spectrum is becoming an important complement to meet the capacity requirement. Licensed-Assisted Access will give operators the option to make use of unlicensed spectrum with a unified network, result in operational cost saving, improved spectral efficiency and a better user experience. The focus of the Release 13 is on the aggregation of a primary cell, operating in licensed spectrum to deliver critical information and guaranteed Quality of Service, with a secondary cell, operating in unlicensed spectrum to opportunistically boost data rate. A key objective of this feature is to ensure fair coexistence between LTE LAA and Wi-Fi.
Carrier Aggregation enhancement: The LTE CA basic framework was standardized in Release 10, with the protocol allowing aggregation of up to 5 Component Carriers (CCs) in downlink and uplink. As operators have planned for deployments with the aggregation of more and more carriers, it has become necessary to expand the LTE CA framework to be able to aggregate more than 5 CCs. The goal in Release 13 is to expand LTE CA up to 32 CCs and to achieve high data rates for LTE as well as in the flexibility to aggregate large numbers of carriers in different bands. This enhanced framework will also be useful for LAA operation in unlicensed spectrum where large blocks of spectrum are available.
The work is approved by the 3GPP in December 2019 will lead to the introduction of new features for the three main use case families: enhanced mobile broadband (eMBB), URLLC and massive machine type communications (mMTC). The purpose is to support the expected growth in mobile-data traffic, as well as customizing new radio for automotive, logistics, public safety, media and manufacturing use cases. The enhancements to existing features introduced in release 17 will be for functionality already deployed in live new radio networks (NR) or relate to specific new requirements that are emerging in the market. 3GPP Release-17 is up in the air (and is about to be started soon). It will mostly be about enhancing and “further” enhancing 5G features in different areas.
As of now, the items likely to be incorporated within Rel-17 from the RAN perspective include the following (examples).
· Small data transfer optimization
· Side link enhancements for NR
· NR for above 52.6GHz
· Coverage enhancements
· NB-IoT and eMTC enhancements
· NR for non-terrestrial networks
· Mobile Integrated Access Backhaul (IAB) enhancements
· RAN Data Collection Enhancements
· Power Saving Enhancements
· Positioning Enhancements
· Supporting of Railway Smart Station Services
· Proximity Services in 5GS
· Enhancement of support for Edge Computing in 5GC
· Enhancements for the Support of Integrated access and backhaul
· 5G enhancements for UAV
· Enablers for Network Automation for 5G
· Enhancement of Network Slicing
· Enhanced Support for Industrial IoT
· Support for Minimization of Service Interruption
Below, is short elaboration for each of the above items.
NR-Light and Small Data Transfer Optimization – NR optimization for MTC type of devices, mostly related to power saving aspects, inactive data transmission.
Side link enhancements for NR – should focus on areas relating to vehicle to everything services, commercial and critical communications, including Frequency Range 2 (“mmWave bands”), to achieve maximum commonality between those services in terms of usage of Side link.
NR for above 52.6GHz – will include discussions and decisions on waveforms for frequencies higher than currently standardized, and the discussion on switching point for different waveforms, as well as the inclusion of 60GHz unlicensed spectrum.
Coverage enhancements – should work on clarifications for all scenarios which are focusing on extreme coverage including both indoor and wide area.
NB-IoT, eMTC, Industrial IoT, URLLC enhancements – cover enhancements related to current commercial needs and deployments as well as some small leftovers from Rel-16, like header compression.
NR for Non-Terrestrial Networks and Integrated Access Backhaul (IAB) enhancements – should include mobile IAB.
RAN data collection enhancements – focuses on data collection related to enabling of Artificial Intelligence (AI) for SON and MDT, as well as including the enhancements for SON and MDT themselves.
Power Saving Enhancements – with a focus on power saving related to smartphones and network-related power saving aspects.
Positioning Enhancements – shall include further adjustments for more accurate positioning services (like 3D-positioning and cm-level accuracy, latency and reliability improvements) on specific areas, like: IoT, factory positioning.
a. 3GPP service and system content for Rel-17 under discussion
The following are example features from the 3GPP service and system perspective for Rel-17.
Supporting of Railway Smart Station Services – aims at studying use cases for railway station operation monitoring and control, passenger supporting services, and evolution of business and applications already included together with analysis of the gaps from the requirements and functionality already provided from previous studies.
Proximity Services (ProSe) in 5GS – aims at developing a common framework for supporting proximity-based services, by gap analysis between existing Rel-16 5GS architecture, functionalities, procedures and requirements of ProSe including roaming and non-roaming scenarios. The work should include two sets of objectives: public safety related ProSe, like support of one-to-many (and one-to-one) direct communications including out-of-coverage, and UE-to-UE relay; as well as commercial related ProSe, like system enhancements for Network Controlled Interactive Service (NICS)-related service requirements. Study should also include Mission Critical services over 5GS.
Enhancement of support for Edge Computing in 5GC – covers two objectives: study potential enhancements for edge computing support, including solutions to support forwarding of UE application traffic (like support for traffic steering in edge computing environment), impact on charging and policy control, ; study deployment guidelines for use cases like, URLLC, V2X, AR/VR/XR, 5GSAT, CDN.
Enhancements for the Support of Integrated Access and Backhaul (IAB) – item which aims at introducing architecture and system level enhancements to support IAB including, system level description of IAB architecture, and its integration within 5GS and earnings per share, support of capability indication of IAB nodes to the core network, and authorization of IAB nodes’ operation and signalling towards next generation radio access technology network or evolved universal terrestrial radio Access network.
5G enhancements for Unmanned Aerial Vehicles (UAV) – objective of this item is to document new KPIs and requirements to meet the industry applications and service needs to 3GPP subscription including: KPIs for command and control traffic, onboard radio access node, service restriction and network exposure for UAV.
Enhancement of Network Slicing (phase 2) – aims at identification of gaps in the current 5GS system procedures to support Generic Slice Template (GTS) parameters and to study solutions to address those identified gaps – with the main goal to allow for more specific “slice boundaries”. It will include at least those parameters: maximum number of UEs per slice.
Support for Minimization of Service Interruption (MINT) – should specify normative service requirements with regard to ensuring the behaviour of UEs supporting MINT taking into account existence of disaster condition, or enabling the system to prevent congestion due to incoming large number of roaming user equipment’s related to disaster situation as well as handling of restrictions related to disaster condition.