How Advanced is LTE Advanced.pdf

8/10/2019 How Advanced is LTE Advanced.pdf

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MobileCommProfessionals Inc.

How Advanced is LTE Advanced? RF Aspects Challenges

Jasminder Sahni, BE (E&C)

LTE became a commercial reality in 2010 following the launch of many LTE networks using 3G/LTEmultimode devices. LTE Advanced is the next major milestone in the evolution path, encompassing3GPP Rel. 10, 11 and beyond.

In order to achieve higher data rates while preserving compatibility with older LTE standards, thedesigners of LTE-Advanced had to use some relatively advanced techniques. Larger amounts ofradio frequency spectrum may be utilized in addition to new techniques for more efficient use oflimited spectrum. Devices compatible with the new technology are likely to feature a number ofantenna arrays, and a process called beam-forming can turn would-be interference into a tool to

boost signal.

Worldwide functionality & roaming

Compatibility of services

Interworking with other radio access systems


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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 astream of data and transmit it through multiple radio frequencies to a users 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


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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). Thisscheme is similar to SC-FDMA but has the advantage that it allows noncontiguous(clustered) groups of subcarriers to be allocated for transmission by a single UE, thusenabling uplink frequency-selective scheduling and better link performance. Clustered SC-FDMA was chosen in preference to pure OFDM to avoid a significant increase in PAPR. Itwill help satisfy the requirement for increased uplink spectral efficiency while maintainingbackward-compatibility with LTE.

Enhanced multiple antenna transmissionTo 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 therequisite eight receivers in the UE, allows the possibility in the downlink of 8x8 spatial


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multiplexing. The UE will be specified to support up to four transmitters allowing thepossibility of up to 4x4 transmission in the uplink when combined with four eNB receivers.

Coordinated multipoint transmission and reception (CoMP)Another technique known as coordinated multipoint transmission/reception employsmultiple base stations to simultaneously send and receive data to a single device. This canbe especially beneficial to customers who are on the edge of a particular base stationscoverage area; by combining two base stations, a faster and more reliable connection canbe achieved. Multiple LTE-Advanced base stations can even be used in a relay, with eachbase station transmitting information 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 havebeen defined.


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Downlink Configurations Uplink Configurations

LTE-Advanced BS transmissions and receptions

- Transmitter aspects:Base Station output powerTransmitted signal quality

Unwanted emissions

Transmitter spurious emissions

- Receiveraspects:Reference sensitivity level

Adjacent Channel Selectivity (ACS)Narrow-band blocking, BlockingReceiver intermodulationDemodulation Performance requirements


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As already in LTE Rel-8 and also in LTE-Advanced robust general minimum RRMrequirements ensure good mobility performance across the cellular network for variousmobile speeds and different 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 toensure that good mobility performance in all cases while still minimizing UE batteryconsumption especially with long DRX cycles.

Different network controlled parameter values for cell reselection in idle mode and forhandover in active mode can be utilized for optimizing mobility performance in differentscenarios, which also include low mobility and high mobility scenarios.

Challenges of LTE-Advanced3GPP'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 suchas a 1Gbps peak data rate, LTE-Advanced will meet International TelecommunicationUnion (ITU) requirements for the International Mobile Telecommunications (IMT)-

Advanced 4G radio-communication standard.

The current release of LTE already meets most IMT-Advanced requirements. Exceptionsare peak data rate and uplink spectral efficiency, which LTE-Advanced addresses via widerbandwidths, enabled by carrier aggregation, and higher efficiency, enabled by enhanceduplink 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 MHzformed by aggregating up to five 20MHz component carriers. Contiguous and non-contiguous carriers may be aggregated. Carrier aggregation will undoubtedly pose majordifficulties for user equipment (such as smart phones and other wireless devices), whichmust handle multiple simultaneous transceivers. The use of simultaneous, non-contiguoustransmitters creates a highly challenging radio environment in terms of spur managementand 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-selectivescheduling of component carriers for better link performance. The Physical Uplink SharedChannel (PUSCH) and the Physical Uplink Control Channel (PUCCH) can be scheduledtogether to reduce latency. However, clustered SC-FDMA increases peak-to-average powerratio, leading to transmitter linearity issues. And the presence of multi-carrier signalsincreases opportunities for in-channel and adjacent-channel spur generation.


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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 in the UE or user equipment), enabling 8x8 spatial multiplexing in the downlink.The UE supports up to four transmitters, allowing up to 4x4 transmission in the uplinkwhen combined with four receivers in the base station.

MIMO increases the number of system antennas. A major challenge will be designingmultiband MIMO antennas with good de-correlation to operate in the small space of anLTE-Advanced UE. New methods are required for predicting actual radiated performanceof an advanced MIMO terminal in an operational network, so 3GPP is considering ways toextend 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 workftp://ftp.3gpp.org/Specs/html-info/36912.htm

Study item final status report RP-100080

ftp://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 layerftp://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

www.agilent.com
ftp://ftp.3gpp.org/tsg_ran/TSG_RAN/TSGR_41/Docs/RP-080599.zipftp://ftp.3gpp.org/Specs/html-info/36913.htmftp://ftp.3gpp.org/Specs/html-info/36912.htmftp://ftp.3gpp.org/tsg_ran/TSG_RAN/TSGR_47/Docs/RP-100080.zipftp://ftp.3gpp.org/Specs/html-info/36814.htmftp://ftp.3gpp.org/Specs/html-info/36807.htmhttp://www.agilent.com/http://www.agilent.com/ftp://ftp.3gpp.org/Specs/html-info/36807.htmftp://ftp.3gpp.org/Specs/html-info/36814.htmftp://ftp.3gpp.org/tsg_ran/TSG_RAN/TSGR_47/Docs/RP-100080.zipftp://ftp.3gpp.org/Specs/html-info/36912.htmftp://ftp.3gpp.org/Specs/html-info/36913.htmftp://ftp.3gpp.org/tsg_ran/TSG_RAN/TSGR_41/Docs/RP-080599.zip

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How Advanced is LTE Advanced.pdf