1. LTE 개요 및 주요특징 작성일 : 2015. 3. 2. 소속 : ETRI/ 무선전송연구1실 작성자 : 고영조 연락처 :
소속 :
ETRI/ 무선전송연구1실
작성자 :
고영조
연락처 :

2. Outline LTE radio access
Basic transmission and multiple access schemes
OFDM and OFDMA
SC-FDMA (DFT-S-OFDM)
Physical layer (PHY)
Uplink
Uplink physical resources
Uplink reference signals
Uplink L1/L2 control signaling
Downlink
Downlink physical resources
Downlink reference signals
Downlink L1/L2 control signaling
Medium Access Control layer (MAC)
Downlink scheduling
Uplink scheduling

3. OFDM
Characteristics of OFDM (Orthogonal Frequency Division Multiplexing)
Parallel transmission of data over multiple carriers
A high data rate stream is divided into multiple streams with lower data rates and carried by multiple sub-carriers.
The subcarriers are orthogonal to each other
Different subcarriers modulated with different amplitudes and phases are orthogonal over the time period of symbol duration
The OFDM signals can be generated by applying IFFT operation
Guard time and cyclic extension is used to remove inter-symbol interference (ISI) and inter-carrier interference (ICI)

4. OFDM OFDM signal T T: Symbol duration fc: Carrier frequency,
OFDM signal
T: Symbol duration
fc: Carrier frequency
Ns: Number of subcarriers
di: QAM symbol T
Baseband OFDMA signal

5. OFDM Characteristics of OFDM
The subcarriers are orthogonal to each other
Different subcarriers modulated with different amplitudes and phases are orthogonal over the time period of symbol duration
time
frequency

6. OFDM Characteristics of OFDM
OFDM signals can be generated by applying IFFT operation
Equivalent baseband signal
In discrete time,
OFDM transmitter
OFDM receiver

7. OFDM Characteristics of OFDM Transmission on multiple frequencies
A high data rate stream is divided into multiple streams with lower data rates and carried by multiple sub-carriers.
The subcarriers are orthogonal to each other
Different subcarriers modulated with different amplitudes and phases are orthogonal over the time period of symbol duration
OFDM signals can be generated by applying IFFT operation
Guard time and cyclic extension is used to remove inter-symbol interference (ISI) and inter-carrier interference (ICI)

8. OFDM Characteristics of OFDM
Guard time and cyclic extension are used to remove inter-symbol interference (ISI) and inter-carrier interference (ICI)
ISI/ICI: Interference between an original signal and a delayed version of it
Multipath Channel Tx Rx
ISI & ICI without guard time f
Tsub
CP Insertion

9. OFDM Characteristics of OFDM Simple frequency-domain equalization
Long OFDM symbol time with a cyclic prefix  Fading caused by multipath propagation can be considered as constant (flat) over an OFDM sub-carrier if the sub-carrier is sufficiently narrow-banded
In OFDM, the equalizer only has to multiply each detected sub-carrier (each Fourier coefficient) in each OFDM symbol by a constant complex number.
Disadvantages
Sensitive to frequency-offset
Cause of frequency offset  Mismatch between Tx and Rx oscillator frequencies, and Doppler shift
Frequency-offset causes inter-carrier interference
Potentially high PAPR (Peak-to-Average Power Ratio)
High PAPR reduces power utilization efficiency

10. OFDMA Application of OFDM to multiple access
OFDMA: Orthogonal Frequency Division Multiple Access
Different UE are served with different resources: orthogonal separation in the time-frequency domain

11. SC-FDMA (Single-Carrier FDMA)
Serial transmission of data over single carrier.
Cf. OFDM: Parallel transmission of data over multiple carriers
DFT precoding applies before the sub-carrier mapping
In comparison with OFDM, SC-FDMA is also called DFT-Spread OFDM.
Low PAPR because of the single carrier transmitter structure.
Attractive alternative to OFDMA, especially in the uplink, where UE can be benefited from low PAPR in terms of transmit power efficiency
SC-FDMA transmitter

12. SC-FDMA (Single-Carrier FDMA)
Localized transmission
Distributed transmission
SC-FDMA subcarrier mapping

13. SC-FDMA (Single-Carrier FDMA)
SC-FDMA vs. OFDM
OFDMA: Subcarrier-by-subcarrier detection
SC-FDMA: Detection after IDFT  SINR of a modulation symbol is averaged over the whole transmission band
OFDM
SC-FDMA
FFT

14. SC-FDMA vs. OFDM PAPR/CM (Cubic Metric)
x[n]: time domain signal after IFT
SC-FDMA has a lower PAPR than OFDM
OFDM
SC-FDMA vs. OFDM

15. LTE radio access

16. References
“3G Evolution: HSPA and LTE for Mobile Broadband”, E. Dahlman, S. Parkvall, J. Skold, and P. Beming, Academic Press (2nd Ed, 2008).
“LTE-The UMTS Long Term Evolution: from theory to practice”, S. Sesia, I. Toufik, and M. Baker, Jonh Wiley & Sons Ltd (2009)
Physical layer specifications
3GPP TS : "Evolved Universal Terrestrial Radio Access (E-UTRA); Physical Layer – General Description".
3GPP TS : "Evolved Universal Terrestrial Radio Access (E-UTRA); Physical channels and modulation".
3GPP TS : "Evolved Universal Terrestrial Radio Access (E-UTRA); Multiplexing and channel coding".
3GPP TS : "Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer procedures".
3GPP TS : "Evolved Universal Terrestrial Radio Access (E-UTRA); Physical layer – Measurements“
3GPP TS : “Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN); Overall description; Stage 2”
MAC layer specification
3GPP TR , “Evolved Universal Terrestrial Radio Access (E-UTRA); Medium Access Control (MAC) protocol specification”

17. Overview of LTE radio access
Long Term Evolution (LTE)
Evolution of 3G WCDMA
Significantly improved performance in a wide range of spectrum allocations
Data rates up to ~ 300 Mbps in 20 MHz bandwidth
First step toward 4G (IMT-Advanced)
LTE standardization activity started since RAN long term evolution workshop, Nov. 2~3, 2004, Toronto.
First release of technical specifications: Release 8 (2008)

18. Basic transmission schemes
Downlink OFDM
Robust against multi-path channels
Long OFDM symbol time with a cyclic prefix
Simple frequency-domain equalization
Frequency-domain scheduling: additional degree of freedom
cf. HSPA: only time-domain scheduling
Flexible transmission bandwidth
Spectrum allocation with different sizes
Broadcast/multicast transmission
Uplink DFT-spread OFDM (DFT-S-OFDM, SC-FDMA)
Single-carrier transmission
Motivated by low PAPR (peak-to-average power ratio)
Allows for higher average transmission power
(Note) Obsession with the single-carrier property -> Leading to very complicated spec!!

19. Key features of LTE Rate control
Channel-dependent scheduling in the time-frequency domain
Scheduler can take into account channel variation in both time and frequency domains
Downlink scheduling
Based on channel-status report by UE (FDD)
Uplink scheduling
Based on UE sounding
Inter-cell interference coordination
Restricting the transmission power of certain parts of the spectrum in a cell
Fractional frequency reuse
Rate control
Adaptive modulation and coding (rather than power control)
Hybrid ARQ with soft-combining
Multiple parallel H-ARQ processes
Soft-combining
Retransmission with incremental redundancy
Multiple antennas
1, 2 and 4 Tx antennas in downlink (extended to include 8 Tx in LTE-A)
1 Tx antenna in uplink (extended to include 2 and 4 Tx in LTE-A)
Multicast/broadcast support
MBSFN

20. Key features of LTE
Channel-dependent scheduling

21. Key features of LTE Rate control
Rate control is more efficient than power control
Full power transmission -> relatively efficient power utilization
Link adaptation through AMC (Adaptive Modulation and Coding)
High order modulation (16, 64 QAM) and high code rate for high SINR
Low order modulation (QPSK) and low code rate for low SINR

22. Key features of LTE
Hybrid ARQ with soft-combining

23. Key features of LTE Spectrum flexibility
Flexibility in duplex arrangement
Support FDD (paired spectrum) and TDD (unpaired spectrum)
Commonality between FDD and TDD
Support half-duplex FDD
No simultaneous reception and transmission
(Reception and transmission separated in frequency and time)
Scalable transmission bandwidths
1 ~ 20 MHz
Transmission bandwidths
1.4, 3, 5, 10, 15, 20 MHz

24. LTE-Advanced LTE-Advanced 3GPP RAT for IMT-Advanced (4G)
LTE (3.9G) + alpha
Including new features such as carrier aggregation, relaying, coordinated multipoint transmission, uplink MIMO etc.
3GPP standardization schedule

25. 30bps/Hz in DL 15bps/Hz in UL
LTE-Advanced
Requirements
ITU Requirement
3GPP Requirement
Peak data rates
1Gbps
1Gbps in DL, 500Mbps in UL
Bandwidth
40MHz (max. scalable BW)
Multi-carrier allowed
Up to 100MHz
User plane latency
10ms
Improved compared to LTE
Control plane latency
100ms
Active  Active dormant(<10ms) Camped  Active (<50ms)
Peak spectrum efficiency
15bps/Hz in DL 6.75bps/Hz in UL
30bps/Hz in DL 15bps/Hz in UL
Average spectrum efficiency
Set for four scenarios and several antenna configurations
Cell edge spectrum efficiency
VoIP capacity
Up to 200 UEs per 5MHz

26. LTE-Advanced Requirements ITU system performance requirement
Environment
Indoor
Micro-cell
Base coverage Urban
Rural/High speed
Spectrum Efficiency
DL (4x2 MIMO) 3
2.6
2.2
1.1
UL (2x4 MIMO)
2.25
1.8
1.4
0.7
Cell Edge Spectrum Efficiency
0.1
0.075
0.06
0.04
0.07
0.05
0.03
0.015
Case-1 Config
LTE Cell Avg. SE [bps/Hz/cell]
LTE-A Cell Avg. SE [bps/Hz/cell]
LTE Cell Edge SE [bps/Hz/user]
LTE-A Cell Edge SE [bps/Hz/user] UL
1x2
0.735
1.2
0.024
0.04
2x4 -
2.0
0.07 DL
2x2
1.69
2.4
0.05
4x2
1.87
2.6
0.06
0.09
4x4
2.67
3.7
0.08
0.12

27. Frame structure [TS36.211 Sec4]
Basic time unit, Ts = 1/(15000 x 2048) second
Frame structure type 1
FDD
Slot = 0.5 ms, subframe = 1 ms (TTI)
One radio frame consists of 10 subframes
Supports full-and half-duplex operations at the terminal
Full duplex: simultaneous transmission/reception
Half duplex: only transmission or reception at a time

28. Frame structure [TS36.211 Sec4]
Frame structure type 2
TDD
Special subframe to provide guard time for downlink-to-uplink switching
DwPTS: downlink part
UpPTS: uplink part
GP: No transmissions to avoid interference between uplink and downlink transmissions

29. Frame structure [TS36.211 Sec4]
Frame structure type 2 (continued)
Seven configurations with different UL/DL ratios

30. LTE - Uplink

31. Uplink transmission scheme [TS36.211 Sec5.3]
Basic transmission scheme
For both FDD and TDD, the uplink transmission scheme is based on single-carrier FDMA, more specifically DFT S-OFDM
Low PAPR (Peak-to-Average Power Ratio)
Sub-carrier spacing f = 15 kHz.
Two cyclic-prefix lengths
Normal cyclic prefix and extended cyclic prefix corresponding to seven and six SC-FDMA symbol per slot, respectively.
Normal cyclic prefix: TCP = 160Ts (SC-FDMA symbol #0) , TCP = 144Ts (SC-FDMA symbol #1 to #6)
Extended cyclic prefix: TCP-e = 512Ts (SC-FDMA symbol #0 to SC-FDMA symbol #5)

32. Uplink physical resources [TS36.211 Sec5.2]
Resource element (RE)
Basic resource unit
Resource block (RB)
Basic allocation unit
Normal CP:
12 subcarriers x 7 SC-FDMA symbols
Extended CP:
12 subcarriers x 6 SC-FDMA symbols
# of resource blocks can range from NRB-min = 6 to NRB-max = 110.
(LTE) Always consecutive allocation
A set of frequency consecutive RBs
To maintain low PAPR

33. Overview of UL Physical Channel Processing
LTE Rel-8/9 UL physical channel processing
PAPR (Peak-to-Average Power Ratio), CM (Cubic Metric)
LTE-A UL physical channel processing

34. Uplink reference signals
Uplink reference signals [TS Sec 5.5 ]
Two types of reference signals
Demodulation reference signals (DMRS)
Transmitted within data transmission RBs
Used for channel estimation -> coherent demodulation of uplink transmissions
Sounding reference signals (SRS)
Transmitted over a range of frequency bands
Used for estimation of uplink channel quality -> frequency-domain scheduling
Structure of DMRS
Time-division multiplexed with
other uplink transmissions

35. Uplink reference signals
SRS symbol structure [TS Sec 5.5.3]

36. Uplink L1/L2 control signaling
Uplink L1/L2 control signaling [TS Sec 5.4]
Signaling to support downlink and uplink transport channels
H-ARQ acknowledgement in response to downlink data
Downlink channel quality feedback
Scheduling request for uplink resource allocation
Two different transmission methods
If no simultaneous transmission of UL-SCH
L1/L2 control signaling on PUCCH
If simultaneous transmission of UL-SCH
L1/L2 control signaling on PUSCH

37. Uplink L1/L2 control signaling
L1/L2 control signaling on PUCCH [TS Sec 5.4]
PUCCH structure
Frequency hopping for frequency diversity
Positioned at the edge of the band to avoid fragmentation of PDSCH transmission, making it possible to allocate a wide spectrum without breaking the single-carrier property
FDM/CDM (Code Division Multiplexing)

38. Uplink L1/L2 control signaling
Physical uplink control channel (PUCCH) [TS Sec 5.4]
PUCCH formats
Cyclic shift of a sequence in each symbol
Format 1: Scheduling Request (SR)
Information is carried by the presence/absence of transmission
Format 1a and 1b: HARQ-ACK 1 and 2 bits, respectively
Format 2: CQI
Format 2a and 2b: CQI + HARQ-ACK

39. Uplink L1/L2 control signaling
PUCCH formats 1, 1a, and 1b [TS Sec 5.4.1]
SR, ACK/NAK
Two-dimensional CDM
Spreading along the frequency axis
Block-wise spreading along the time axis
Resources
Resource index -> (Orthogonal sequence index, Cyclic shift)

40. Uplink L1/L2 control signaling
PUCCH formats 1, 1a, and 1b (continued) [TS Sec 5.4.1]
Normal PUCCH formats 1 and 1a/1b -> Length-4 Walsh sequences
Shortened PUCCH formats 1 and 1a/1b ->Length-3 DFT sequences

41. Uplink L1/L2 control signaling
PUCCH formats 2, 2a, 2b [TS Sec 5.4.2]
CQI or CQI + ACK/NAK
One-dimensional CDM
Resources
Resource index -> Cyclic shift
Symbol-level cell-specific CS hopping
Slot-level CS remapping
d(10) for format 2a/2b

42. Uplink L1/L2 control signaling
L1/L2 control signaling on PUSCH [TS Sec , ]
If control signaling is simultaneous with UL-SCH, control signaling is multiplexed with data on PUSCH
Simultaneous transmission of PUCCH and PUSCH is not allowed to keep the single-carrier property
H-ARQ ACK/NAK
Placed right next to RS
Channel quality status report
Rank Indicator (RI)
(3, 2) block code, encoded separately from CQI/PMI
Placed right next to ACK/NAK
Channel Quality Indicator (CQI), Precoding Matrix Indicator (PMI)
Tail-biting convolution code or block code
Mapped across the full subframe duration

43. Uplink L1/L2 control signaling
Multiplexing of control and data on PUSCH [TS Sec , ]
HARQ ACK, RI, CQI
A/N resources puncture into data, placed next to RS
RI bits placed next to the A/N bits in PUSCH, irrespective whether or not A/N is present
CQI resources placed at the beginning of the data resources with time-first mapping

44. Uplink transmission
PUSCH frequency hopping [TS Sec 5.3.7] [TS Sec 8.4.1]
Cell-specific hopping/mirroring
Slot level hopping according to predefined hopping/mirroring patterns
Different cells have different patterns
Period is one frame
Hopping according to explicit information
The uplink scheduling grant indicates the offset of the resource to use for the second slot.
Dynamic selection between the two modes
Indication bits in the scheduling grant

45. LTE - Downlink

46. Downlink transmission
Basic transmission scheme
OFDM numerology

47. Downlink physical resources [TS36.211 Sec 6.2]
Resource element
Basic resource unit
Resource block (RB)
Basic allocation unit
Normal CP:
12 subcarriers x 7 SC-FDMA symbols
Extended CP:
12 subcarriers x 6 SC-FDMA symbols
Non-consecutive allocation allowed

48. Downlink physical channels and signals [TS36.211 Sec 6.2]
Physical downlink shared channel (PDSCH)
carries the downlink shared channel (DL-SCH) and paging channel (PCH)
Physical downlink control channel (PDCCH)
informs the UE about the resource allocation of PCH and DL-SCH, and Hybrid ARQ information related to DL-SCH
carries the uplink scheduling grant
Physical control format indicator channel (PCFICH)
informs the UE about the number of OFDM symbols used for the PDCCHs;
transmitted in every subframe.
Physical broadcast channel (PBCH)
The coded broadcast channel (BCH) transport block is mapped to four subframes within a 40 ms interval
Each subframe is self-decodable
Physical Hybrid ARQ Indicator Channel (PHICH)
carries Hybrid ARQ ACK/NAKsin response to uplink transmissions.
Physical multicast channel (PMCH)
carries the multicast channel (MCH) transport channel
Physical signals
Reference signal
Synchronization signal

49. Downlink physical resources
Downlink frame structure [frame type 1 (FDD)]

50. Synchronization and cell search
Two cell search procedures [TS Sec 6.11]
Initial synchronization
Synchronization -> PBCH decoding -> SI acquisition
New cell identification
Synchronization -> RS detection -> RSRP/RSRQ measurement

51. Downlink Physical Channel
Overview of downlink physical channel processing
Note
(number of codewords)  2
(number of layers)  (channel rank)
Resource element mapper
Time-frequency resource
OFDM signal generation
IFFT

52. DL L1/L2 control signaling [TS36.211 Sec 6.7, 6.8, 6.9]
Downlink L1/L2 control signaling
Transmitted in the control region, which is the first part of the subframe
Control region size
Variable, 1 ~ 3 (4) OFDM symbols
Three types of physical channels
PCFICH
Informs the UE about the size of the control region
PDCCH/E-PDCCH
Carries downlink scheduling assignment, uplink scheduling grants
Each (E-)PDCCH carries a signal for a single UE
PHICH
Carries H-ARQ ACK/NAK in response to uplink UL-SCH transmission
Multiple PHICHs in each cell

53. Downlink reference signal
Cell-specific reference signal (CRS)
Introduced in Rel-8 for channel estimation and demodulation
Cell-specific RS sequences and frequency shifts
High overheads
Tx antennas 0 and 1: twice in the slot
Tx antennas 2 and 3: once in the slot

54. Downlink reference signal
Channel State Information Reference Signal (CSI RS)
Introduced in Rel-10 for CSI report
Sparse in frequency and time
Low overhead: around 1/(10*14*6) = 1/840 = 0.12% per antenna port (8 antenna ports = 0.96%)
Periodicity of CSI RS is configurable as an integer multiple of subframe

55. Downlink reference signal
Demodulation RS (DM RS)
Introduced in Rel-10 for data demodulation
UE-specific
PDSCH and the DM RS are subject to the same precoding operation
Present only in resource blocks and layers scheduled for transmission
Lower overhead compared to CRS

56. Downlink MIMO LTE LTE-Advanced 1, 2, 4 Tx antennas
Spatial multiplexing up to 4 layers
Closed-loop codebook based precoding
Open-loop
Multi codewords
Spectral efficiency up to 15 bps/Hz
Tx diversity
SFBC for 2 Tx antennas
SFBC + FSTD for 4 Tx antennas
Semi-static SU- and MU MIMO switching
LTE-Advanced
1, 2, 4, 8 Tx antennas
Spatial multiplexing up to 8 layers
Closed-loop precoding
Spectral efficienty up to 30 bps/Hz
Dynamic SU- and MU-MIMO switching

57. LTE – Scheduling

58. Downlink assignment eNB UE
Scheduling decision, DCI (Downlink control information) and Data preparation
(E-)PDCCH /PDSCH transmission UE
(E-)PDCCH monitoring
If downlink assignment, DCI acquisition and PDSCH detection/decoding
PUCCH (ACK/NACK) transmission

59. Uplink grant
eNB
Scheduling decision, DCI (Downlink control information) preparation
(E-)PDCCH transmission UE
(E-)PDCCH monitoring and/or PHICH detection
If uplink grant, DCI acquisition and PUSCH preparation
PUSCH transmission
PUSCH detection/decoding

60. HARQ process Hybrid ARQ New transmission Retransmission
If NDI (New Data Indicator) is toggled, it indicates a new transmission
Scheduled through (E)PDCCH
Retransmission
Non-adaptive retransmissions (uplink): triggered by a NACK on PHICH
Adaptive retransmissions are scheduled through PDCCH
Downlink HARQ
Uplink HARQ
Mode
Adaptive
Non-adaptive/Adaptive
Sync
Asynchronous
Synchronous (HARQ RTT = 8 ms)
ACK/NACK
Using PUCCH/PUSCH
PHICH (+ PDCCH) 사용
Process No
Indicated in PDCCH
Fixed (determined by the subframe)
Note
Retransmissions are always scheduled through PDCCH
If non-adaptive, retransmissions on the same uplink resource as previously used by the same HARQ process

61. HARQ process
Downlink and uplink Hybrid ARQ

62. Downlink scheduling DL Scheduling
eNB receives CSI from UE: Rank/PMI, CQI, HARQ ACK/NAK
Rank/PMI  the number of layers to transmit
CQI  MCS for each codeword
eNB performs scheduling for every subframe
UE selection, resource allocation, MCS selection etc

63. Uplink scheduling UL Scheduling
eNB receives SRS (Sounding Reference Signal) from UE
eNB estimates Rank/PMI and CQI from the SRS
eNB performs scheduling for every subframe
UE selection, power control, resource allocation, MCS selection etc

64. Semi-persistent scheduling
Assignment/grant recurs with a configured interval between the assignments/grants
SPS interval: 10, 20, 32, 40, 64, 80, 128, 160, 320, 640 ms
SPS configuration by RRC signaling
Activation/Re-activation and Release by PDCCH
In DL configuration only
Number of configured HARQ processes
In UL configuration only
Implicit release after a number of empty transmissions

65. Scheduling request Scheduling Request
If a regular BSR triggered but no UL resources
An SR is triggered
If an SR is pending
If no valid PUCCH resource for SR configured in any TTI
Initiate a random access procedure
Else if valid PUCCH resource for SR
Transmit SR on PUCCH

66. Buffer status reporting
BSR on a logical-channel group basis
A BSR Indicates the amount of data across all logical channels in a logical channel group or all four logical channel groups
Regular BSR
Triggered if
Arrival of UL data with higher priority than the one currently being transmitted
Arrival of UL data with no already existing data
retxBSR-Timer expires and the UE has data available for transmission
retxBSR-Timer restarts upon the indication of an uplink grant for new transmission
If there are UL resources for new transmission, transmitted on the allocated resources
If no UL resources, triggers a Scheduling Request

67. Buffer status reporting
Periodic BSR
Timer controlled periodic reporting
Triggered if periodicBSR-Timer expires (can be disabled)
Transmitted on UL resources allocated for new transmission
Padding BSR
Transmitted, instead of padding, on UL resources allocated for new transmission if there are enough padding bits
At most one Regular/Periodic BSR is reported in a TTI

68. Buffer status reporting
BSR
New Data
New Data
No Data
retxBSR -
Timer
Regular BSR
Regular BSR
Periodic BSR
Periodic BSR
Periodic BSR
periodicBSR -
Timer
UL Transmission
UL Transmission
Scheduling Request
Scheduling Request
Regular BSR
Periodic BSR
New Transmission
Timer starts
Timer restarts
Timer expires

69. UL scheduling logical channel prioritization
Applies to a new transmission
RRC controls scheduling by signaling for each logical channel
Priority: 1, 2, ..16
Prioritized Bit Rate (PBR): 0, 8, …, 2048 kbps
Bucket Size Duration (BSD): 50, 100, …., 1000 ms
UE maintains Bj for each logical channel j
Bj = 0 when the logical channel is established
Incremented by PBR X TTI duration for each TTI
Not exceeding the bucket size of the logical channel j
Bj <= Bucket size = PBR x BSD
Scheduling prioritization
Step 1: All the logical channels with Bj > 0 are allocated resources in a decreasing priority order until meeting their Bj
Step 2: Bj is decremented by the total size of MAC SDUs served to the logical channel j
Step 3: if any resources remain, all the logical channels are served in a strict decreasing priority order

70. Logical channel prioritization
UL scheduling prioritization of logical channels