How Advanced is LTE Advanced

7/27/2019 How Advanced is LTE Advanced

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How Advanced is LTE Advanced? – RF Aspects & Challenges

LTE became a commercial reality in 2010 following the launch of many LTE networks using3G/LTE multimode devices. LTE Advanced is the next major milestone in the evolution path,encompassing 3GPP Rel. 10, 11 and beyond.

In order to achieve higher data rates while preserving compatibility with older LTE standards,the designers of LTE-Advanced had to use some relatively advanced techniques. Largeramounts of radio frequency spectrum may be utilized in addition to new techniques for moreefficient use of limited spectrum. Devices compatible with the new technology are likely tofeature a number of antenna arrays, and a process called beam-forming can turn would-beinterference into a tool to boost signal.

Worldwide functionality & roaming

Compatibility of services

Interworking with other radio access systems

Enhanced peak data rates to support advanced services and applications (100 Mbit/s for high

and 1 Gbit/s for low mobility)

We here are evaluating the radio parameters and performance from the RF aspects.



Radio Parameters

Carrier Aggregation

Using a scheme known as carrier aggregation, a cellular base station can break apart a stream

of data and transmit it through multiple radio frequencies to a user’s device, which then

reassembles these multiple pieces into the original data stream.

Support wider transmission bandwidths up to 100MHz

Two or more component carriers (CC) are aggregated

A terminal may simultaneously receive one or multiple component carriers depending on its

capabilities

Possible to aggregate a different number of component carriers of possibly different

bandwidths in the UL and the DL In typical TDD deployments, the number of component

carriers and the bandwidth of each component carrier in UL and DL will be the same.

Both Intra and Inter band carrier aggregation are considered as potential Tx RF scenarios and

parameters and cover both of; Contiguous Component Carrier and non-contiguous Component

Carrier aggregation



Enhanced uplink multiple access

LTE-Advanced enhances the uplink multiple access scheme by adopting clustered SC-FDMA,also known as discrete Fourier transform spread OFDM (DFT-S-OFDM). This scheme is similar toSC-FDMA but has the advantage that it allows noncontiguous (clustered) groups of subcarriersto be allocated for transmission by a single UE, thus enabling uplink frequency-selectivescheduling and better link performance. Clustered SC-FDMA was chosen in preference to pureOFDM to avoid a significant increase in PAPR. It will help satisfy the requirement for increaseduplink spectral efficiency while maintaining backward-compatibility with LTE.

Enhanced multiple antenna transmission



To improve single user peak data rates and to meet the ITU-R requirement for spectrumefficiency, LTE-Advanced specifies up to eight layers in the downlink which, with the requisiteeight receivers in the UE, allows the possibility in the downlink of 8x8 spatial multiplexing. TheUE will be specified to support up to four transmitters allowing the possibility of up to 4x4transmission in the uplink when combined with four eNB receivers.

Coordinated multipoint transmission and reception (CoMP)

Another technique known as coordinated multipoint transmission/reception employs multiple

base stations to simultaneously send and receive data to a single device. This can be especially

beneficial to customers who are on the edge of a particular base station’s coverage area; by

combining two base stations, a faster and more reliable connection can be achieved. Multiple

LTE-Advanced base stations can even be used in a relay, with each base station transmittinginformation to the next.

LTE Advanced UE Receivers and Categories

The following aspects to be defined considering the CA scenarios, bandwidth of the Tx/Rxsignals as well as multiple antenna effects:

Receiver Sensitivity

Selectivity

Blocking performance

Spurious response

Intermodulation performance

Spurious emission

The existing UE categories 1-5 for Release 8 and Release 9 are shown in below table.



In order to accommodate LTE-Advanced capabilities, three new UE categories 6-8 have beendefined.

Downlink Configurations Uplink Configurations

LTE-Advanced BS transmissions and receptions

- Transmitter aspects:

Base Station output powerTransmitted signal qualityUnwanted emissionsTransmitter spurious emissions

- Receiver aspects:Reference sensitivity level

Adjacent Channel Selectivity (ACS)Narrow-band blocking, Blocking



Receiver intermodulationDemodulation Performance requirements

As already in LTE Rel-8 and also in LTE-Advanced robust general minimum RRM requirementsensure good mobility performance across the cellular network for various mobile speeds anddifferent network deployments.

The minimum RRM requirements are defined both in idle mode and in active mode.

In Active mode the requirements are defined both without DRX and with DRX in order to ensurethat good mobility performance in all cases while still minimizing UE battery consumptionespecially with long DRX cycles.

Different network controlled parameter values for cell reselection in idle mode and for handoverin active mode can be utilized for optimizing mobility performance in different scenarios, whichalso include low mobility and high mobility scenarios.

Challenges of LTE-Advanced

3GPP's Long Term Evolution (LTE) is the leading technology standard for 4G wirelesscommunications. Although it is just now being launched commercially, development of thestandard continues, with the latest version being LTE-Advanced. With enhancements such as a1Gbps peak data rate, LTE-Advanced will meet International Telecommunication Union (ITU)requirements for the International Mobile Telecommunications (IMT)-Advanced 4G radio-communication standard.

The current release of LTE already meets most IMT-Advanced requirements. Exceptions arepeak data rate and uplink spectral efficiency, which LTE-Advanced addresses via widerbandwidths, enabled by carrier aggregation, and higher efficiency, enabled by enhanced uplink multiple access and enhanced multiple antenna transmission (advanced MIMO).

Carrier Aggregation

To achieve a 1Gbps peak data rate, LTE-Advanced supports bandwidths up to 100 MHz formedby aggregating up to five 20MHz component carriers. Contiguous and non-contiguous carriersmay be aggregated. Carrier aggregation will undoubtedly pose major difficulties for userequipment (such as smart phones and other wireless devices), which must handle multiplesimultaneous transceivers. The use of simultaneous, non-contiguous transmitters creates ahighly challenging radio environment in terms of spur management and self-blocking.

Enhanced Uplink Multiple Access

LTE's uplink is based on single-carrier frequency division multiplexing (SC-FDMA), whichallocates carriers across a contiguous block of spectrum, thus limiting scheduling flexibility. LTE-

Advanced introduces clustered SC-FDMA in the uplink, allowing frequency-selective schedulingof component carriers for better link performance. The Physical Uplink Shared Channel (PUSCH)and the Physical Uplink Control Channel (PUCCH) can be scheduled together to reduce latency.



However, clustered SC-FDMA increases peak-to-average power ratio, leading to transmitterlinearity issues. And the presence of multi-carrier signals increases opportunities for in-channeland adjacent-channel spur generation.

Advanced MIMO

To improve single-user peak data rates and meet spectral efficiency requirements, LTE- Advanced specifies up to eight transmitters in the downlink (with the requisite eight receivers inthe UE or user equipment), enabling 8x8 spatial multiplexing in the downlink. The UE supportsup to four transmitters, allowing up to 4x4 transmission in the uplink when combined with fourreceivers in the base station.

MIMO increases the number of system antennas. A major challenge will be designing multibandMIMO antennas with good de-correlation to operate in the small space of an LTE-Advanced UE.New methods are required for predicting actual radiated performance of an advanced MIMOterminal in an operational network, so 3GPP is considering ways to extend MIMO over the air(OTA) testing for LTE-Advance

References

Study Item RP-080599Outlines the overall goals of LTE-Advancedftp://ftp.3gpp.org/tsg_ran/TSG_RAN/TSGR_41/Docs/RP-080599.zip

Requirements TR 36.913 v9.0.0 (2009-12)Defines requirements based on the ITU requirements for 4G systemsftp://ftp.3gpp.org/Specs/html-info/36913.htm

Study Phase Technical Report TR 36.912 v9.3.0 (2010-06)Summarizes the stage 1 development work

ftp://ftp.3gpp.org/Specs/html-info/36912.htm

Study item final status report RP-100080ftp://ftp.3gpp.org/tsg_ran/TSG_RAN/TSGR_47/Docs/RP-100080.zip

Physical Layer Aspects TR 36.814 v9.0.0 (2010-03)Summarizes the stage 2 development for the physical layer ftp://ftp.3gpp.org/Specs/html-info/36814.htm

Study phase Technical Report on E-UTRA UE Radio Transmission and Reception TR 36.807Summarizes study of CA, enhanced multiple antenna transmission and CPEftp.3gpp.org/Specs/html-info/36807.htm

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