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

2. 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

3. Support of Wider Bandwidth

4. 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

5. 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

6. 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
TS 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

7. Options for Wider Bandwidth Structure (1)
Option 1: Contiguous sub-carrier usage based on bandwidths defined in Rel-8 LTE
For example, 100 RBs (= 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
MHz
MHz
MHz
Frequency
Guard band
= MHz
MHz
MHz
100-kHz channel raster

8. 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)
MHz
MHz
MHz
Frequency
Guard band
= MHz
18.3 MHz
18.3 MHz
100-kHz channel raster

9. 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

10. 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

11. Advanced Radio Access Scheme

12. 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

13. 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

14. 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)

15. 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

16. 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 , [2] NSN and Nokia, R
Frequency
Basic bandwidth, e.g., 20 MHz
L1/L2 control channel region
UE with wider bandwidth capability

17. 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

18. 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

19. 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

20. 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

21. 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)

22. 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.

23. Advanced Multi-cell Transmission/Reception Techniques

24. 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

25. 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

26. 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

27. 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, R
eNB
RRE
Optical fiber UE
RRE

28. 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

29. Enhanced Multi-antenna Transmission Techniques

30. 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

31. 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

32. 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

33. 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

34. Enhanced Techniques to Extend Coverage Area

35. 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

36. 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