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I N V I T E D PA P E R

LTE-ADVANCED: NEXT-GENERATION WIRELESS BROADBAND TECHNOLOGY
AMITAVA GHOSH, RAPEEPAT RATASUK, BISHWARUP MONDAL, NITIN MANGALVEDHE, AND TIM THOMAS, MOTOROLA INC.

ABSTRACT
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LTE-Advanced (also known as LTE Release 10) significantly enhances the existing LTE Release 8 and supports much higher peak rates, higher throughput and coverage and lowerlatencies resulting in a better user experience.

LTE Release 8 is one of the primary broadband technologies based on OFDM, which is currently being commercialized. LTE Release 8, which is mainly deployed in a macro/microcell layout, provides improved system capacity and coverage, high peak data rates, low latency, reduced operating costs, multi-antenna support, flexible bandwidth operation andseamless integration with existing systems. LTE-Advanced (also known as LTE Release 10) significantly enhances the existing LTE Release 8 and supports much higher peak rates, higher throughput and coverage, and lower latencies, resulting in a better user experience. Additionally, LTE Release 10 will support heterogeneous deployments where low-power nodes comprising picocells, femtocells, relays, remoteradio heads, and so on are placed in a macrocell layout. The LTE-Advanced features enable one to meet or exceed IMT-Advanced requirements. It may also be noted that LTE Release 9 provides some minor enhancement to LTE Release 8 with respect to the air interface, and includes features like dual-layer beamforming and time-difference-of-arrival-based location techniques. In this article an overviewof the techniques being considered for LTE Release 10 (aka LTEAdvanced) is discussed. This includes bandwidth extension via carrier aggregation to support deployment bandwidths up to 100 MHz, downlink spatial multiplexing including single-cell multi-user multiple-input multiple-output transmission and coordinated multi point transmission, uplink spatial multiplexing including extension tofour-layer MIMO, and heterogeneous networks with emphasis on Type 1 and Type 2 relays. Finally, the performance of LTEAdvanced using IMT-A scenarios is presented and compared against IMT-A targets for full buffer and bursty traffic model.

operation of up to 20 MHz. Currently, enhancements are being studied to provide substantial improvements to LTE Release 8, allowing it to meet or exceed InternationalMobile Telecommunications-Advanced (IMT-A) requirements [1]. These enhancements are being considered as part of LTE-Advanced (LTE-A, also known as LTE Release 10), which includes carrier aggregation, advanced uplink (UL) and downlink (DL) spatial multiplexing, DL coordinated multipoint (CoMP) transmission, and heterogeneous networks with special emphasis on Type 1 and Type 2 relays. This articleprovides an overview of the technologies being considered for LTE-A. This article is organized as follows. In the next section an overview of the LTE Release 8 physical layer (PHY) is provided. This is followed by an overview of evolved UMTS terrestrial radio access (E-UTRA) LTE-A requirements. In the following section a discussion on carrier aggregation is provided. We then provide an overview ofDL and UL spatial multiplexing and fundamentals of DL CoMP design. We introduce the concept of heterogeneous networks, withy an emphasis on LTE relays. We compare the performance of LTE Release 8 and LTE-A in the context of IMT-A requirements. Finally, conclusions are drawn in the last section.

LTE RELEASE 8 PHY OVERVIEW
In LTE Release 8, orthogonal frequency-division multiplexing (OFDM) isthe DL multiple access scheme, while single-carrier frequency-division multiple access (SC-FDMA) is the UL multiple access scheme. LTE Release 8 also supports scalable bandwidth up to 20 MHz, and uses DL/UL frequency selective and DL frequency diverse scheduling, respectively. The DL subframe structure is common to both time-division duplex (TDD) and frequencydivision duplex (FDD), and is shown...
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