UMTS: Alive and Well - 4G Americas

C.2.2E-UTRAN AIR-INTERFACEThis section outlines UTRAN Long Term Evolution (LTE) air interface, the LTE physical layers, radiointerface protocols and architecture as defined by 3GPP. LTE is a new packet-only wideband radio withflat architecture, as part of the 3GPP radio technology family evolution beyond GSM, GPRS, EDGE andWCDMA-HSPA. In addition, 3GPP has defined both FDD and TDD options for LTE, but this sectionmainly focuses on the specifics of the FDD system. For information about TDD systems please refer tosection C.3 of this white paper.3GPP initiated its investigation of LTE in 2004 and in March 2005, began a feasibility study; the keyissues were to agree on the multiple access method and the network architecture in terms of thefunctional split between the radio access and the core network. The feasibility study on the E-UTRANtechnology alternatives was concluded by September 2006 when 3GPP finalized selection of the multipleaccess and basic radio access network architecture. 3GPP concluded that Orthogonal FrequencyDivision Multiple Access (OFDMA) is to be used in downlink direction and Single Carrier FrequencyDivision Multiple Access (SC-FDMA) is to be used in the uplink direction. These techniques are discussedin detail in the following downlink and uplink sections.The Multiple Antenna Systems section discusses current considerations of multi-antenna technologies forthe LTE standard. In all next-generation cellular standards, including LTE, the target is to increasecapacity and/or to provide spatial diversity. The technologies being considered in this section are Multiple-MIMO, SM, Space-Time Coding and Beamforming. Finally, Interference Mitigation aspects areconsidered as identified in the LTE study item. Presented techniques for inter-cell interference mitigationare interference randomization, interference cancellation and interference coordination/avoidance.The 3GPP LTE Rel-8 specification was officially completed in March 2009 (functionally frozen inDecember 2008), with the RAN1 specifications stable since September 2008. The RAN1 specificationshave the biggest impact on long term lead development items. The later specification completion in Marchfulfilled needs for data rates and performance beyond HSDPA and HSUPA evolution. LTE is designed tofacilitate the integration with existing GSM and WCDMA deployments for seamless coverage offering.The chosen uplink technology ensures a power efficient transmitter for the device transmission andmaximizes the uplink coverage. LTE performance, together with flat architecture, ensures low cost per bitfor a competitive service offering for end-users.C.2.2.1DOWNLINKThis section provides details about the downlink LTE structure defined in 3GPP as well as a briefintroduction on mapping between the transport and physical channel. An examination of LTE downlinkstructure and numerology is also provided followed by a discussion on downlink Reference Signal (RS)structure. Details of DL control channels are then provided, along with DL and UL scheduling grantsdesign and Ack/Nack channel. An overview of the synchronization channel and a description of thePrimary broadcast control and MCH channels are discussed. Finally, the DSCH performance for theSingle Input Multiple Output (SIMO) case and for MBMS transmission is reviewed.In the downlink, Orthogonal Frequency Division Multiplexing (OFDM) is selected as the air interface forLTE. OFDM is a particular form of multi-carrier modulation (MCM). Generally, MCM is a parallel183 3GPP TS 23.402, Architecture Enhancements for Non-3GPP Accesses.www.3GAmericas.org February 2010 Page 158