Proposals for LTE-Advanced Technologies 3GPP TSG RAN WG1 Meeting #53bis 　　　　　　　R1-082575 Warsaw, Poland, June 30 – July 4, 2008 Proposals for LTE-Advanced Technologies NTT DoCoMo, Inc. Agenda item: 12 Document for: Discussion and Decision

Proposed Techniques for LTE-Advanced Proposed radio access techniques for LTE-Advanced Support of wider bandwidth Advanced radio access scheme Advanced multi-cell transmission/reception techniques Enhanced multi-antenna transmission techniques Enhanced techniques to extend coverage area

Support of Wider Bandwidth

Support of Wider Bandwidth (1) Need wider bandwidth such as approximately 100 MHz to reduce bit cost per Hertz and to achieve peak data rate higher than 1 Gbps Continuous spectrum allocation should be prioritized, although both continuous and discontinuous usages are to be investigated Continuous spectrum usage Can simplify eNB and UE configuration Possible frequency allocation in new band, e.g., 3.4 – 3.8 GHz band Discontinuous spectrum usage  Requires spectrum aggregation UE capability for supportable spectrum aggregation should be specified so that increases in UE size, cost, and power consumption are suppressed to low level Frequency LTE bandwidth Frequency Aggregated bandwidth

Support of Wider Bandwidth (2) Continuous spectrum usage UE should have one RF receiver and one FFT  Common sub-carrier separation should be maintained over the entire system bandwidth Discontinuous spectrum usage UE structure supporting different spectrum usage Difficult to support different spectrum using one RF receiver and one FFT Hence, UE has multiple RF receivers and multiple FFTs e.g., 15 – 20 MHz Frequency Basic frequency block #1 Basic frequency block #2 Basic frequency block #3 Sub-carrier Df Df Df Df Df Df NDf NDf

Proposed Wider Bandwidth Structure Proposed wider bandwidth structure in LTE-Advanced Entire system bandwidth comprising multiple basic frequency blocks Bandwidth of basic frequency block is, e.g., 15 – 20 MHz Whether or not center frequency of every frequency block should be located on 100-kHz channel raster is FFS TS36.101 states that “The channel raster is 100 kHz for all bands, which means that the carrier center frequency must be an integer multiple of 100 kHz” However, it is unclear that it is necessary to place center frequency of every frequency block on 100-kHz channel raster for Rel-8 LTE terminals to camp at any frequency block Two options are considered Option 1: Center frequency of every frequency block does not need to be on 100-kHz channel raster  Simple contiguous sub-carrier usage is possible Option 2: Center frequency of every frequency block should be located on 100-kHz channel raster

Options for Wider Bandwidth Structure (1) Option 1: Contiguous sub-carrier usage based on bandwidths defined in Rel-8 LTE For example, 100 RBs (= 18.015 MHz including DC sub-carrier) are used for bandwidth of each basic frequency block This option is the most straightforward way, however, center frequency of each basic frequency block except for center one is not on 100-kHz channel raster defined in Rel-8 LTE Hence, Rel-8 LTE terminals may be supported using only center basic frequency block (Example) System bandwidth = 60 MHz 18.015 MHz 18.015 MHz 18.015 MHz Frequency Guard band = 2.9775 MHz 18.015 MHz 18.015 MHz 100-kHz channel raster

Options for Wider Bandwidth Structure (2) Option 2(a): Sub-carrier usage based on bandwidths defined in Rel-8 LTE with insertion of additional (dummy or useful) sub-carriers between basic frequency blocks At least additional 19 sub-carriers are required between basic frequency blocks to adjust the center frequency of each basic frequency block on 100-kHz channel raster In this case, however, bandwidth of guard bands at both ends of system bandwidth is reduced (Example) System bandwidth = 60 MHz 19 sub-carriers (285 kHz) 19 sub-carriers (285 kHz) 18.015 MHz 18.015 MHz 18.015 MHz Frequency Guard band = 2.6925 MHz 18.3 MHz 18.3 MHz 100-kHz channel raster

Options for Wider Bandwidth Structure (3) Option 2(b): Contiguous sub-carrier usage with new bandwidth that is slightly reduced for wider bandwidth structure Possible to increase guard band compared to Option 2(a) In this case, however, specification of new bandwidth may be necessary in future releases Hence, increase in testing complexity and backward compatibility to Rel-8 LTE terminals may be an issue (Example 1) System bandwidth = 60 MHz 18.0 MHz (one-sub-carrier reduction) 18.0 MHz 18.0 MHz Frequency Guard band = 3.0 MHz 18.0 MHz 18.0 MHz 100-kHz raster (Example 2) 17.7 MHz (21-sub-carrier reduction) 17.7 MHz 17.7 MHz Frequency Guard band = 3.45 MHz 17.7 MHz 17.7 MHz

Asymmetric Transmission Bandwidth Transmitted from different UEs Required bandwidth in uplink will be much narrower than that in downlink considering current and future traffic demands in cellular networks In FDD, asymmetric transmission bandwidth eases pair band assignment In TDD, narrower transmission bandwidth is beneficial in uplink, since an excessively wider transmission bandwidth degrades channel estimation and CQI estimation  Propose asymmetric transmission bandwidth both in FDD and TDD Freq. Transmitted from different UEs UL bandwidth DL bandwidth UL bandwidth TTI TTI Time DL bandwidth FDD TDD

Advanced Radio Access Scheme

Layered OFDMA Requirements for multi-access scheme Coexist with Rel-8 LTE in the same system bandwidth for LTE-Advanced Optimize tradeoff relation between achievable performance and control signaling overhead Sufficient frequency diversity gain is obtained when transmission bandwidth is approximately 20 MHz Control signaling overhead increases according to increase in transmission bandwidth Support of transmission bandwidth wider than 20 MHz, i.e., near 100 MHz, to achieve peak data rate requirements, e.g., higher than 1 Gbps Efficient support of scalable bandwidth to accommodate various spectrum allocations Propose Layered OFDMA radio access scheme in LTE-Advanced Layered transmission bandwidth Support of layered environments Layered control signal formats

Layered Transmission Bandwidth (1) Layered transmission bandwidths Layered structure comprising multiple basic frequency blocks Entire system bandwidth comprises multiple basic frequency blocks Bandwidth of basic frequency block is, e.g., 15 – 20 MHz SCH and PBCH transmissions At minimum, SCH and PBCH must be transmitted from the central basic frequency block SCH and PBCH belonging to the central basic frequency block are located on UMTS raster Transmission of SCH and PBCH from other basic frequency blocks is FFS Principle of UE access method Both LTE-A-UE with different capability and LTE-UE can camp at any basic frequency block(s) including narrow frequency block at both ends

Layered Transmission Bandwidth (2) Example when continuous wider bandwidth, e.g., 100 MHz, is allocated System bandwidth, e.g., 100 MHz Basic bandwidth, e.g., 20 MHz Center frequency on UMTS raster (on DC sub-carrier, SCH, and PBCH) UE capabilities Frequency 100-MHz case 40-MHz case 20-MHz case (LTE) Example when continuous wider bandwidth, e.g., 70 MHz, is allocated Basic bandwidth, e.g., 20 MHz Center frequency on UMTS raster System bandwidth, e.g., 70 MHz Frequency UE capabilities 100-MHz case 40-MHz case 20-MHz case (LTE-A) Narrow frequency block 20-MHz case (LTE)

Support of Layered Environments Achieves the highest data rate (user throughput) or widest coverage according to radio environment such as macro, micro, indoor, and hotspot cells and required QoS Adaptive radio access control according to radio environment MIMO channel transmission with high gain should be used particularly in local areas Indoor/hotspot layer Adaptive radio access control Micro layer Macro layer

Proposals for Uplink Radio Access Purpose: Achieve high gain in SU-MIMO as well as MU-MIMO by mitigating the influence of multipaths Propose SC/MC hybrid radio access Purpose: Achieve SC based transmission with low PAPR for UE with wider bandwidth capability when PUCCH is transmitted from the middle of the transmission bandwidth Support application of clustered DFT-Spread OFDM transmission [1][2] [1] NEC, REV-080022, [2] NSN and Nokia, R1-081842 Frequency Basic bandwidth, e.g., 20 MHz L1/L2 control channel region UE with wider bandwidth capability

OFDM Benefits for MIMO Transmission In LTE-Advanced UL, much higher user throughput and capacity than those for LTE are necessary particularly in local areas  UL radio access with high affinity to MIMO transmission should be adopted MLD based signal detection is more advantageous than LTE working assumptions such as LMMSE or SIC for reducing the required received SNR  Propose supporting the radio access scheme so that the MLD based signal detection as well as LMMSE and SIC are applicable Reasons why OFDM has high affinity to MIMO using MLD In OFDM, only symbol replica at each sub-carrier is required in order to perform MLD because multipaths are mitigated due to long symbol duration and insertion of cyclic prefix Meanwhile, in SC-FDMA, symbol replicas for respective resolved paths at each sub-carrier are required, bringing about significant increase in complexity

SC/MC Hybrid Radio Access Adaptive radio access using MC/SC hybrid to support layered environments Universal switching of MC/SC based access using frequency domain multiplexing/de-multiplexing Optimization of PAPR (coverage) and achievable peak data rate according to inter-site distance, cell structure, and QoS requirements High affinity with UL MIMO transmission SC generation DFT Mapping Pulse-shaping filter Switch IFFT CP insertion Coded data symbols S/P MC generation

Transport Blocks for LTE-Advanced (1) Wider transmission bandwidth than 20 MHz for LTE-Advanced Single stream case One transport block (TB) for the entire transmission bandwidth similar to that in Rel-8 LTE: Very long code block size  Inefficient HARQ Multiple TBs correspond to the number of basic frequency blocks, i.e., one TB in one basic frequency block  Reduces coding gain and increases control signaling overhead Number of TBs should be optimized independently of the number of basic frequency blocks Multi-stream case Basically, different TBs are allocated to different streams Similar to single stream case, number of TBs should be optimized independently of the number of basic frequency blocks and that of streams

Transport Blocks for LTE-Advanced (2) Downlink Number of TBs should be optimized based on Channel coding gain Gain of per-layer rate control Downlink / Uplink signaling overhead Uplink One or two TBs for SIMO (and MU-MIMO) Two TBs or more for SU-MIMO Transport blocks Transport blocks Channel coding Channel coding Channel coding Channel coding HARQ functionality HARQ functionality HARQ functionality HARQ functionality Data modulation Data modulation Data modulation Data modulation Frequency Frequency block mapping (including RB mapping) Frequency block mapping (including RB mapping) Frequency block Layer Time

Downlink Layered Control Signal Formats (1) Layered L1/L2 control signal formats Achieve high commonality with control signal formats in Rel-8 LTE Use layered L1/L2 control signal formats according to assigned transmission bandwidth to achieve efficient control signal transmission Examples of layered multiplexing of L1/L2 control signals Basic bandwidth, e.g., 20 MHz Frequency L1/L2 control channel region Subframe UE (LTE-A) UE (LTE) UE (LTE-A)

Downlink Layered Control Signal Formats (2) Layered L1/L2 control signal formats Following options are considered Option 1: Transmitted on all basic frequency blocks Obtains larger frequency diversity effect Requires CCE mapping for multiple frequency blocks Requires new PDCCH format Option 2: Transmitted on one of the basic frequency blocks Same frequency diversity effect and CCE mapping as that in LTE Option 3: Transmitted on each of the basic frequency blocks Requires no change from LTE Not suitable for one transport block to multiple frequency blocks  Our preference is Option 1 or 2 Option 1 Option 2 Option 3 Frequency block Freq. Freq. Freq. Assignment info.

Advanced Multi-cell Transmission/Reception Techniques

Advanced Multi-cell Transmission/Reception Techniques Use advanced multi-cell transmission/reception techniques Advanced multi-cell transmission/reception, i.e., coordinated multipoint transmission/reception, is to be used to increase frequency efficiency and cell edge user throughput Supported techniques – Inter-cell orthogonalization based on inter-cell interference coordination (ICIC) Efficient handover with multi-cell transmission/reception Use cell structure employing remote radio equipments (RREs) more actively in addition to that employing independent eNB Note that signaling format in optical fiber is not a standardization matter for the 3GPP, but control signaling for ICIC and handover that takes advantage of RREs are to be specified by 3GPP Optical fiber RREs eNB

Inter-cell Orthogonalization (1) (Partially) orthogonal One-cell frequency reuse Baseline is one-cell frequency reuse to achieve high system capacity Intra-cell orthogonalization Achieves intra-cell orthogonal multi-access (multiplexing) in both links as well as in LTE Inter-cell orthogonalization Although ICIC is adopted in LTE, it only introduces fractional frequency reuse at cell edge with slow control speed using control signals via backhaul Thus, inter-cell orthogonality will be established in LTE-Advanced to achieve high frequency efficiency and high data rate at cell edge W-CDMA LTE (Rel-8) LTE-Advanced Intra-cell DL (Partially) orthogonal Orthogonal UL Non-orthogonal Inter-cell (Quasi)-orthogonal

Inter-cell Orthogonalization (2) Achieve inter-cell orthogonality through fast inter-cell interference (ICI) management Centralized control: ICI management among cells of RREs using scheduling at central eNB  Achieves complete inter-cell orthogonality Autonomous control (similar to LTE method): ICIC among independent eNBs using control signals via backhaul and/or air  Achieves inter-cell quasi-orthogonality through faster control than that for LTE to achieve fractional frequency reuse at the cell edge RREs Optical fiber Autonomous ICI control Centralized ICI control

Macro Diversity with Multipoint Transmission/Reception Using RREs Downlink Fast cell selection (FCS) in L1 using bicast in L2/L3 Considered transmission methods associated with RS [3] Use common RS Explicit signaling for transmit RRE (or eNB) information Blind detection of transmit RRE (or eNB) Use DRS Uplink MRC reception at the central eNB Central eNB combines uplink data channel of the target UE without measurement report [3] [3] Ericsson, R1-082024 eNB RRE Optical fiber UE RRE

Macro Diversity with Multipoint Transmission/Reception Using Independent eNBs Downlink Faster cell selection than that for Rel-8 LTE, i.e., as fast as possible, in L1 using bicast/forwarding in L2/L3 Uplink Simultaneous reception at multiple cells or faster cell selection than that of LTE eNB eNB UE eNB

Enhanced Multi-antenna Transmission Techniques

Benefits of Higher-Order MIMO Necessity of higher-order MIMO channel transmissions Traffic demand in the era of LTE-Advanced Higher peak frequency efficiency than that for LTE is needed to satisfy the increased traffic demand in the era of LTE-Advanced  Increased number of antennas directly contributes to achieving higher peak spectrum efficiency Local area optimization Since LTE-Advanced will focus on local area, higher peak frequency efficiency also contributes to increasing average frequency efficiency More practical for higher-order MIMO in local areas

Number of Antennas Considered for LTE-Advanced User throughput is significantly improved according to the increase in the number of transmitter and receiver antennas, i.e., more effective than increasing modulation level Proposals for the number of supported antennas Antenna deployment Considering a variety of UE terminals, e.g., laptop PC with built-in antennas, more than 4, e.g., 8 antennas can be spatially implemented with antenna separation of longer than a half carrier wavelength assuming the C-band LTE (Rel-8) LTE-Advanced DL Baseline: 2-by-2 MIMO Max: 4-by-4 MIMO Baseline: 2-by-2, 4-by-2, and 4-by-4 according to UE categories and eNB types (optimization condition is FFS) Max: 8-by-8 MIMO UL Baseline: 1-by-2 SIMO Baseline: 2-by-2 and 2-by-4 according to eNB types Max: 4-by-4(8) MIMO

Enhanced MIMO Channel Techniques (1) Enhanced MIMO channel techniques to be considered SU-MIMO in UL Radio access with affinity to UL SU-MIMO multiplexing, i.e., OFDMA (SC/MC hybrid access) SU-MIMO schemes, e.g., precoding, block coding (STBC or SFBC) Orthogonal RSs and control signals to support UL SU-MIMO transmission schemes MIMO multiplexing / diversity using more antennas than four in DL Precoding codebook in MU-MIMO and SU-MIMO Orthogonal RSs and control signal to support more antennas than four in MU-MIMO and SU-MIMO

Enhanced MIMO Channel Techniques (2) Enhanced MIMO channel techniques to be considered Collaborative MIMO using RREs at different cell sites Collaborative MIMO can provide gain for cells with RREs at the central eNB Application of collaborative MIMO for independent eNBs is FFS Application of MIMO multiplexing to multicast (FFS)  Must investigate throughput gain considering the increase in RS overhead

Enhanced Techniques to Extend Coverage Area

Enhanced Techniques to Extend Coverage RREs using optical fiber (“sector” belonging to the same eNB) Should be used in LTE-Advanced as effective technique to extend cell coverage Relays using radio L1 relays with non-regenerative transmission, i.e., repeaters Since delay is shorter than cyclic prefix duration, no additional change to radio interface is necessary Repeaters are effective in improving coverage in existing cells Should be used as well as in 2G/3G networks L1 relays with regenerative transmission, L2 relays, and L3 relays Must improve coverage without reducing capacity Our concerns are efficient radio resource assignment to signals to/from relay station, delay due to relay, etc. L2 and L3 relays achieve more efficient radio resource assignment than L1 regenerative relays

Conclusion Proposed radio access techniques for LTE-Advanced Support of wider bandwidth to reduce network cost per bit and to achieve required peak data rate Layered OFDMA using layered physical channel structure with adaptive multi-access control to support layered environments and to achieve high commonality with LTE Advanced multi-cell transmission/reception techniques with inter-cell orthogonalization and efficient handover Enhanced multi-antenna transmission techniques including high-order MIMO channel transmission using larger number of antennas Enhanced techniques to extend coverage area such as RREs and relays using radio including repeaters