control channel dimensioning
TRANSCRIPT
Control Channel Dimensioning
RECOMMENDATION
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Copyright
© Ericsson AB 2009-2014. All rights reserved. No part of this document may bereproduced in any form without the written permission of the copyright owner.
Disclaimer
The contents of this document are subject to revision without notice due tocontinued progress in methodology, design and manufacturing. Ericsson shallhave no liability for any error or damage of any kind resulting from the useof this document.
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Contents
Contents
1 Introduction 1
1.1 Limitations 1
1.2 Concepts 1
2 Resource Structure 3
2.1 Time Domain Structure 3
2.2 Frequency Domain Structure 5
2.3 Resource Element 5
2.4 Resource Element Group 6
2.5 Control Channel Elements 6
2.6 Resource Block 6
2.7 Scheduling Block 7
2.8 Resource Grid 7
3 Downlink Common Control Channels and Signals 9
3.1 Channels and Signals 9
3.2 Cell-Specific Reference Signals 9
3.3 UE-Specific Reference Signals 11
3.4 Positioning Reference Signals 13
3.5 Physical Broadcast Channel 13
3.6 Primary and Secondary Synchronization Signal 14
3.7 Physical Control Format Indicator Channel 15
3.8 Physical HARQ Indicator Channel 16
3.9 Physical Downlink Control Channel 17
4 Dimensioning Downlink Control Channels 23
4.1 Resource map 23
4.2 Resource Use 23
5 Uplink Common Control Channel Configuration 25
5.1 Channels and Signals 25
5.2 Demodulation Reference Signal 25
5.3 Sounding Reference Signal 25
5.4 Physical Uplink Control Channel 26
5.5 Physical Random Access Channel 34
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Control Channel Dimensioning
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Introduction
1 Introduction
This document describes control channel dimensioning recommendations forthe Long Term Evolution (LTE) Radio Access Network (RAN).
The document provides guidelines for dimensioning the common controlchannels in LTE, including an estimate of spectral and power use of thecontrol channels. Channel configuration parameters are also recommended.In addition, the document describes how the common control channels aremapped to the resource elements and resource blocks in the resource grid.
1.1 Limitations
This guideline is valid for the current release of LTE.
1.2 Concepts
The following concept is used in control channel dimensioning.
Antenna ports An antenna port is defined by its associated referencesignal. The set of antenna ports supported depends onthe reference signal configuration in the cell:
• Cell-specific reference signals support aconfiguration of one, two, or four antenna portsnumbered 0, 1, 2, and 3
• UE-specific reference signals are transmitted onantenna port 5 or antenna port 7 and 8
• Positioning reference signals are transmitted onantenna port 6
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Resource Structure
2 Resource Structure
This chapter describes the resource structure for LTE control channels.
2.1 Time Domain Structure
In the time domain, the signal is structured in the following parts:
Table 1 Time Domain Signal Structure
Structure Element Description
Radio Frames 10 ms length
Subframes 1 ms length. One frame consists of 10subframes.
Slot 0.5 ms length. One subframe consists of twoslots.
OFDM symbol Approximately 71.4 µs length. One slot consistsof 7 OFDM symbols.
The following figure illustrates the time domain structure:
One radio frame (10 ms) = 10 subframes = 20 slots Subframe Subframe 1 Subframe 9
One subframe (1 ms) = 2 slots
One slot (0.5 ms) = 7 OFDM symbols
OFDM symbol 1–6
Tcp = 4.7 µs Tu = 66.7 µs
Cyclic prefixUser data
OFDM symbol 0
Tcp= 5.2 µs Tu = 66.7 µs
L0000222B
Figure 1 Time Domain Structure
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Control Channel Dimensioning
Downlink and uplink are transmitted on the same frequency. The resources aredivided in time on subframe level between uplink and downlink. Also in everyframe one or two subframes are configured as special subframes. A specialsubframe is used to switch from downlink to uplink. It is divided in three partsDwPTS, a guard period and UpPTS. The symbols in DwPTS are allocated fordownlink transmission and those in UpPTS for uplink transmission. Figure 2illustrates the radio frame structure with special subframes:
Subframe 7
Subframe 4
Subframe2
Subframe 3
Subframe 0
Dw
PTS
GP
UpP
TS
Dw
PTS
GP
UpP
TS
Subframe 1ms
One half frame 5 ms
One radio frame 10 ms
Subframe 8
Subframe 5
Specialsubframe
Specialsubframe
Subframe 9
L0000467B
Figure 2 Radio Frame Structure with 2 Special Subframes
Two of the uplink-downlink configurations specified by 3GPP are supported.These two uplink-downlink configurations are shown in Table 2. "DL", "UL"and "SS" denotes subframes used as downlink, uplink and special subframesrespectively.
Table 2 Supported TDD Uplink-downlink Configurations
Subframe NumberUplink-Downlink
Configuration
SpecialSubframePeriodicity 0 1 2 3 4 5 6 7 8 9
1 5 ms DL SS UL UL DL DL SS UL UL DL
2 5 ms DL SS UL DL DL DL SS UL DL DL
Subframe 0 and 5 are always reserved for downlink transmission. A specialsubframe is always followed by uplink transmission in the next subframe.
Table 3 shows the supported special subframe configurations.
Table 3 Supported Special Subframe Configuration
Special SubframeConfiguration
DwPTS[symbols]
GuardPeriod[symbols]
UpPTS[symbols]
5 3 9 2
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Resource Structure
Special SubframeConfiguration
DwPTS[symbols]
GuardPeriod[symbols]
UpPTS[symbols]
6 9 3 2
7 10 2 2
The length of the guard period will put an upper limit for the cell range sinceround trip time needs to be shorter than the guard period.
2.2 Frequency Domain Structure
Orthogonal Frequency-Division Multiplexing (OFDM) utilize a large number ofsubcarriers. Each subcarrier is orthogonal to all other subcarriers. Subcarrierspacing is equal to the subcarrier bandwidth, which is 15 kHz, see Figure 3.
L0000212A
One resource block(12 subcarriers)
DC-subcarrier
∆f = 15 kHz
NRB resource blocks(12 NRB + 1 subcarriers)
Figure 3 Frequency Domain Structure
2.3 Resource Element
The smallest resource unit handled in LTE consists of the combination of:
• The smallest time domain unit, one OFDM symbol
• The smallest frequency domain unit, one subcarrier
This unit is called Resource Element (RE). An RE that is not used fortransmission is referred to as a hole.
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2.4 Resource Element Group
A Resource Element Group (REG) consists of four REs. In a REG, all REs arelocated on the same OFDM symbol within 12 consecutive subcarriers, andgrouped together with at most one RE (or hole) intervening.
2.5 Control Channel Elements
The mapping of Physical Downlink Control Channel (PDCCH) to REs is subjectto a certain structure. The structure is based on Control Channel Elements(CCE). Nine REGs are grouped in one CCE, as shown in the following figure:
L0000211A
4 RE
9 REG
1 CCE = 9 × 4 = 36 RE
1 CCE
REG
REG
Figure 4 CCE Configuration
2.6 Resource Block
A number of REs are grouped into a physical Resource Block (RB). An RBis defined as follows:
• In the time domain: 7 OFDM symbol times (one slot)
• In the frequency domain: 12 consecutive subcarriers
One RB consists of 84 REs. It covers 0.5 ms in the time domain and 180 kHz inthe frequency domain, see Figure 5.
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Resource Structure
L0000221A
∆f= 15 kHzOne resource block(12×7 = 84 resource elements)
One resource element
One slot,7 OFDM symbols
Figure 5 Resource Block
2.7 Scheduling Block
A scheduling block consists of two RBs adjacent in time and with the samesubcarriers. A scheduling block is the smallest downlink unit that can bescheduled to UE.
2.8 Resource Grid
The mapping of channels and signals in each subframe is described by aresource grid. The resource grid size is:
• One radio frame in the time domain
• The system bandwidth in the frequency domain
The system bandwidth expressed as total number of RBs in the frequencydomain, ���, is given in Table 4.
Table 4 System Bandwidth to Resource Blocks Relation
Bandwidth [MHz] Number of Resource Blocks,���10 50
15 75
20 100
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Control Channel Dimensioning
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Downlink Common Control Channels and Signals
3 Downlink Common Control Channels andSignals
This chapter describes how downlink Layer 1 and Layer 2 common controlchannels and signals are mapped to REs.
3.1 Channels and Signals
Four physical channels are specified to carry Layer 1 and Layer 2 controlinformation for LTE.
• Physical Downlink Control Channel (PDCCH)
• Physical Control Format Indicator Channel (PCFICH)
• Physical Hybrid Automatic Repeat Request (HARQ) Indicator Channel(PHICH)
• Physical Broadcast Channel (PBCH)
In addition to the control channels there are also physical signals. The downlinkphysical signals are:
• Cell-Specific Reference Signals (CRS)
• Positioning Reference Signal (PRS)
• Primary Synchronization Signals (PSS) and Secondary SynchronizationSignals (SSS)
3.2 Cell-Specific Reference Signals
To demodulate different downlink physical channels coherently, the UE requirescomplex valued channel estimates for each subcarrier. Known cell-specificreference symbols are inserted into the resource grid. The CRS is mapped toREs spread evenly in the resource grid, in an identical pattern in every RB.
When transmitting with several antennas, each antenna must transmit a uniquereference signal. When one antenna transmits its reference signal, the otherantenna must be silent. The mapping of the CRS on the resource grid thereforedepends on the antenna configuration, see Figure 6. The pattern of CRS canbe shifted in frequency compared to figure below. Which one of the six possiblefrequency shifts to use depends on the Physical Cell Identity (PCI) sent onPSS and SSS.
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Control Channel Dimensioning
x
x
x
x
xx
x x
x
x
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x
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x x
x x
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Transmission of CRS
Transmission of CRSNo transmission
Transmission of CRSx
Antenna port 1
time
Antenna port 0
Antenna port 0
frequ
ency
One antenna port
Two antenna ports
No transmission x
L0000213C
time
frequ
ency
time
frequ
ency
Transmission of CRSNo transmission
Transmission of CRSx
Antenna port 1
time
Antenna port 0
frequ
ency
Four antenna ports
No transmission x
time
frequ
ency
Transmission of CRSNo transmission
Transmission of CRSx
Antenna port 3
time
Antenna port 2
frequ
ency
No transmission x
time
frequ
ency
Figure 6 Example of Mapping CRS and Holes to One Scheduling Block
With one antenna port, the number of REs in one scheduling block occupied bythe CRS is 8. With two antenna ports the number is 16 and for four antennaports 24.
The following table shows the total number of REs occupied by the CRS,������� , assuming special subframe configuration 6 or 7 for the bandwidthsavailable:
Table 5 REs Occupied by CRS in One Radio Frame for Each Antenna Port
Uplink-Downlinkconfiguration
Bandwidth
[MHz]
��� �������
(one antenna port)�������
(two antenna ports)�������
(four antenna ports)
1 10 50 2200 4400 6800
1 15 75 3300 6600 10200
1 20 100 4400 8800 13600
2 10 50 3000 6000 9200
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Table 5 REs Occupied by CRS in One Radio Frame for Each Antenna Port
Uplink-Downlinkconfiguration
Bandwidth
[MHz]
��� �������
(one antenna port)�������
(two antenna ports)�������
(four antenna ports)
2 15 75 4500 9000 13800
2 20 100 6000 12000 18400
3.3 UE-Specific Reference Signals
For transmission modes based on beamforming, additional referencesignals called UE-specific reference signals are used for channel estimation.UE-specific reference signals are transmitted on either antenna port 5 iftransmission mode 7 (TM7) is used or antenna ports 7 and 8 if transmissionmode 8 (TM8) is used. UE-specific reference signals are only transmitted inRBs allocated to UEs using either TM7 or TM8. The mapping of UE-specificreference signals on the resource grid can be seen in Figure 7 and Figure 8.
L0000590A
frequ
ency
time
Transmission of UE-specific RS on Antenna port 5
Figure 7 Example of Mapping UE-Specific RS Transmitted on Antenna Port 5to One Scheduling Block
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L0000589A
frequ
ency
time
Transmission of UE-specific RS on Antenna port 7 and 8
frequ
ency
time
All other subframes Special subframes, configuration 6 and 7
Figure 8 Example of Mapping UE-Specific RS Transmitted on Antenna Port 7and 8 to One Scheduling Block
To avoid that UE-specific RS are mapped to the same REs as other controlchannels antenna port 5 is not allowed in scheduling blocks containing PBCHand antenna port 7 and 8 are not allowed in scheduling blocks containing PSSand SSS.
The total number of REs occupied by UE-specific RS �������� in RBs whichare used for TM7:
Table 6 REs Occupied by UE-specific RS on Antenna Port 5 when using TM7
Subframe type ��������
RBs in Downlink Subframes 12
RBs in Special SubframesConfiguration 6
6
RBs in Special SubframesConfiguration 7
9
The total number of REs occupied by UE-specific RS �������� in RBs whichare used for TM8:
Table 7 REs Occupied by UE-specific RS on Antenna Port 7 and 8 whenusing TM8
Subframe type ��������
RBs in All Subframes 12
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3.4 Positioning Reference Signals
Positioning reference signals are used for OTDOA User Plane Location Support.Positioning reference signals are transmitted with a periodicity ���� [ms],as specified by prsPeriod. At each transmission occasion the positionreference signals are sent in ������� consecutive DL subframes. The numberof consecutive DL subframes can be specified by nConsecutiveSubframes.In the figure below an example of the transmission scheme for PRS subframesis shown.
L0000485A
PRS subframe
D: Downlink subframe
Radio frame #0 Radio frame #1 Radio frame #16 Radio frame #17
U: Uplink subframe
S: Special subframe
D S U U D D S U U D D S U U D D S U U D
D S U D D D S U D D D S U D D D S U D D
D S U U D D S U U D D S U U D D S U U D
D S U D D D S U D D D S U D D D S U D D
nsubf,con=4
nsubf,con=4TPRS=160 ms
TPRS=160 ms
Figure 9 Example of Transmission of PRS Subframes with Four ConsecutiveDL Subframes and a Periodicity of 160 ms. Uplink-Downlinkconfiguration 1 (top), configuration 2 (bottom).
To minimize the interference in the PRS subframes, PDSCH is not scheduled inany RB in those subframes. Also note that PBCH, PSS and SSS have higherpriority than PRS. For a configuration with two antennas, PRS is transmittedfrom one antenna at the time. The same antenna is used the entire PRSoccasion. For more information, refer to OTDOA User Plane Location Support.
The more PRS subframes, the more accurate will the OTDOA positioning be.This comes at the expense of resources available for PDSCH. The fraction ofsubframes used for PRS can be calculated by the following formula:
��������� ��������
����
Equation 1 Fraction of Subframes Used for PRS
3.5 Physical Broadcast Channel
The PBCH carries part of the system information required by the UE to accessthe network. In the frequency domain, PBCH occupies 72 subcarriers in themiddle of the band independent of deployed bandwidth. In the time domain,
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Control Channel Dimensioning
PBCH is mapped in the first subframe, second slot on OFDM symbol 0, 1, 2and 3 of every radio frame.
The information sent on the PBCH channel in one subframe is retransmitted inthe subsequent three radio frames. New data is transmitted only every fourthradio frame, every 40 ms.
Within the area for PBCH mapping described above, some REs overlap REsalready booked for CRS, as described in Section 3.2 on page 9. CRS havepriority over PBCH, so these REs have to be excluded when mapping PBCHto REs. In this process, REs are excluded as if four antenna ports wouldhave been configured, regardless of the actual number of configured antennaports, see Figure 10.
RE allocated for CRS in case of4 Antenna ports
frequ
ency
time
Slot 0 Slot 1
PBCH Channel
Radio frame,10 ms
72 subcarriersin the middleof the bandwidth
L0000215B
Figure 10 PBCH Mapping
The number of REs used by PBCH in one radio frame is always 240,independent of bandwidth and number of configured antenna ports:
�������� � ���
3.6 Primary and Secondary Synchronization Signal
The PSS and SSS are used for cell-search procedures and cell identification.Together they carry the PCI , PSS sending one of three orthogonal sequencesand SSS sending one of 168 binary sequences.
As with PBCH, PSS and SSS are mapped on 72 subcarriers in the middle ofthe band. PSS is mapped on OFDM symbol 2 in the first slot of subframes 1
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Downlink Common Control Channels and Signals
and 6 and SSS is mapped on last symbol in the second slot of subframes 0and 5, see Figure 11.
Five subcarriers at each end of the 72 subcarriers designated for PSS and SSSare reserved for future use. Nothing is transmitted there, so they are regardedas holes. Reference signals (or holes related to reference signals) are nevermapped in the region designated for PSS and SSS.
PSS
Subframe 0 Subframe 1 SubFrame 2 SubFrame 4 SubFrame 3 SubFrame 5
72 subcarriers in the middle of the bandwidth
SSS
SubFrame 6
frequ
ency
time
L0000468A
Figure 11 PSS and SSS Mapping for TDD
The number of REs used by PSS and SSS per radio frame is independent ofbandwidth and the number of antenna ports:
������� � ���
������� � ���
3.7 Physical Control Format Indicator Channel
The Physical Control Format Indicator Channel (PCFICH) carries ControlFormat Indicator (CFI), which informs about the number of OFDM symbolsused for PDCCHs in a subframe. PCFICH occupies four REGs (16 REs),independent of system bandwidth. It is mapped on OFDM symbol 0 of the firstslot in all downlink subframes. The PCFICH is mapped to REGs to leave roomfor the reference signals and holes as if two antenna ports were configured,even when only one port is configured, see Figure 12.
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Control Channel Dimensioning
frequ
ency
timeL0000216B
PCFICH
CRS antenna port 0
CRS antenna port 1
1st slot 2nd slot
Figure 12 Example of PCFICH Mapping
The number of REs used by PCFICH in one radio frame is independent ofbandwidth and the number of antenna ports:
Table 8 Number of Resource Elements Used by PCFICH per Radio Frame
Uplink-downlink Configuration ����������
1 96
2 128
3.8 Physical HARQ Indicator Channel
The Physical Hybrid ARQ Indicator Channel (PHICH) carries the hybrid ARQAcknowledgement (ACK) and Negative Acknowledgement (NACK) messagesfor the uplink transmission. UE has an individual PHICH assigned. MultiplePHICHs mapped to the same set of REs constitute a PHICH group, where theindividual PHICHs within the same PHICH group are separated by differentorthogonal sequences. Like PCFICH, PHICH is distributed in REGs acrossthe whole bandwidth. It is mapped on OFDM symbol 0 of the first slot in alldownlink subframes.
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Downlink Common Control Channels and Signals
frequ
ency
timeL0000217B
PHICH
CRS antenna port 0
CRS antenna port 1
1st slot 2nd slot
Figure 13 Example of PHICH Mapping
PHICH is only mapped to subframes in downlink where HARQ signaling can beexpected. Therefore the number of downlink subframes that carry PHICH isequal to the number of configured uplink subframes.
Table 9 Presence of PHICH in Downlink Subframes
SubframeUplink-downlinkConfiguration 0 1 2 3 4 5 6 7 8 9
1 no yes - - yes no yes - - yes
2 no no - yes no no no - yes no
The total number of REs that carry PHICH in TDD will not only depend on thebandwidth but also the chosen uplink-downlink configuration, see Table 10.
Table 10 Number of Resource Elements Used by PHICH in One Radio Frame
��������� Uplink-downlink Configuration
Bandwidth [MHz] 1 2
10 336 168
15 480 240
20 624 312
3.9 Physical Downlink Control Channel
The Physical Downlink Control Channel (PDCCH) is used for:
• Downlink scheduling assignments, including� Physical Downlink Shared Channel (PDSCH) resource indication
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Control Channel Dimensioning
� Transport format indication� Hybrid-ARQ information and transport block size� Control information related to Multiple Input Multiple Output (MIMO)� PUCCH power control commands if applicable
• Uplink scheduling grants, including� Physical Uplink Shared Channel (PUSCH) resource indication� Transport format indication� Hybrid-ARQ information� PUSCH power control commands
PDCCH is transmitted in the beginning of each downlink subframe in REsnot used for reference signals, PHICH or PCFICH. Mapping the PDCCHs toREs is based on CCEs, see Section 2.5 on page 6. The number of CCEsrequired for a certain PDCCH depends on the PDCCH message size and onthe channel coding rate. It is restricted to four different aggregation levels, 1,2, 4 or 8 CCEs per PDCCH.
The number of OFDM symbols available for PDCCHs in a subframe is equalto CFI, see Section 3.7 on page 15. The number of OFDM symbols is limitedby the parameter pdcchCfiMode. pdcchCfiMode has four static and twodynamic options. In the static options, CFI is fixed to the same value for all TTIsand subframes. In the dynamic options, CFI can vary between subframes tomatch the estimated demand of PDCCH in that subframe.
Table 11 Parameter Values of pdcchCfiMode
pdcchCfiMode Description
CFI_STATIC_BY_BW CFI=1 for system bandwidth 10 MHz and greater, CFI=2 otherwise,which corresponds to the hard coded setting in previous releases.
CFI_STATIC_1 CFI=1 statically
CFI_STATIC_2 PDCCH uses only CFI=2 statically
CFI_STATIC_3 PDCCH uses only CFI=3 statically
CFI_AUTO_MAXIMUM_2 Dynamic adaptation up to CFI=2
CFI_AUTO_MAXIMUM_3 Dynamic adaptation up to CFI=3
For Uplink-downlink configuration 1 it is recommended to set pdcchCfiModeto CFI_AUTO_MAXIMUM_2. To secure a sufficient amount of PUCCH resourcesit is recommended for Uplink-downlink configuration 2 to set pdcchCfiMode toCFI_STATIC_BY_BW, see Section 5.4.3 on page 30.
The number of CCEs available for PDCCH depends on CFI, bandwidth, and theamount of resources occupied by PHICH and PCFICH. In many cases someCCEs are left unused by the PDCCH. Unused CCEs are part of the interleavingand mapping process in the same way as any other CCE.
The following figure shows an example of how five PDCCH (and a few unusedCCEs) are aggregated and multiplexed with different formats:
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Downlink Common Control Channels and Signals
8 16
12 16 20
10 12 14 16
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
18 20 220 2 4 6 8
4 80
8-CCEaggregations
4-CCEaggregations
2-CCEaggregations
1-CCEaggregations
CCE transmitted in thecontrol region
PDCCH 3 PDCCH 2 PDCCH 1
Unused CCEs
0
PDCCH 0
PDCCH 4
L0000210B
Figure 14 CCE Aggregation and PDCCH Multiplexing
The following table shows the maximum number of REs, ��������� , used byPDCCH in one frame, including holes associated with unused CCEs for eachsetting of pdcchCfiMode:
Table 12 Maximum Number of REs Available for PDCCH in One Radio FrameUplink-downlink Configuration 1 for One or Two Antenna Ports
��������� Bandwidth [MHz]
10 15 20
CFI_STATIC_BY_BW 1872 2880 3960
CFI_STATIC_1 1872 2880 3960
CFI_STATIC_2CFI_AUTO_MAXIMUM_2
5544 8280 11160
CFI_STATIC_3CFI_AUTO_MAXIMUM_3
7920 11880 15984
Table 13 Maximum Number of REs Available for PDCCH in One RadioFrame Uplink-downlink Configuration 1 for Four Antenna Ports
��������� Bandwidth [MHz]
10 15 20
CFI_STATIC_BY_BW 1872 2880 3960
CFI_STATIC_1 1872 2880 3960
CFI_STATIC_2CFI_AUTO_MAXIMUM_2
4248 6480 8784
CFI_STATIC_3CFI_AUTO_MAXIMUM_3
6696 10080 13608
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Table 14 Maximum Number of REs Available for PDCCH in One Radio FrameUplink-downlink Configuration 2 for One or Two Antenna Ports
��������� Bandwidth [MHz]
10 15 20
CFI_STATIC_BY_BW 2736 4320 5760
CFI_STATIC_1 2736 4320 5760
CFI_STATIC_2CFI_AUTO_MAXIMUM_2
7632 11520 15480
CFI_STATIC_3CFI_AUTO_MAXIMUM_3
11232 16920 22680
Table 15 Maximum Number of REs Available for PDCCH in One RadioFrame Uplink-downlink Configuration 2 for Four Antenna Ports
��������� Bandwidth [MHz]
10 15 20
CFI_STATIC_BY_BW 2736 4320 5760
CFI_STATIC_1 2736 4320 5760
CFI_STATIC_2CFI_AUTO_MAXIMUM_2
5904 9000 12312
CFI_STATIC_3CFI_AUTO_MAXIMUM_3
9576 14400 19512
The number of CCEs in a radio frame can be calculated by dividing the numberof REs in the table above by 36, note that the number of CCEs is higher insubframes without PHICH compared to subframes mapped with PHICH.
Normally, some REGs per subframe are left unused. This is because theunused REGs are too few to form a complete CCE. The unused REGs areinterleaved and mapped in the same way as the REGs grouped in a CCE.The following table shows the total number of REs ������ in unused REGsfor different bandwidth:
Table 16 Number of REs Not Used by PDCCH in One Radio FrameUplink-downlink Configuration 1 for One or Two Antenna Ports
������ Bandwidth [MHz]
CFI 10 15 20
1 96 144 120
2 24 144 120
3 48 144 96
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Table 17 Number of REs Not Used by PDCCH in One Radio FrameUplink-downlink Configuration 1 for Four Antenna Ports
������ Bandwidth [MHz]
CFI 10 15 20
1 96 144 120
2 120 144 96
3 72 144 72
Table 18 Number of REs Not Used by PDCCH in One Radio FrameUplink-downlink Configuration 2 for One or Two Antenna Ports
������ Bandwidth [MHz]
CFI 10 15 20
1 168 112 200
2 72 112 80
3 72 112 80
Table 19 Number of REs Not Used by PDCCH in One Radio FrameUplink-downlink Configuration 2 for Four Antenna Ports
������ Bandwidth [MHz]
CFI 10 15 20
1 168 112 200
2 72 112 80
3 72 112 80
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Control Channel Dimensioning
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Dimensioning Downlink Control Channels
4 Dimensioning Downlink Control Channels
This section gives methods to estimate the amount of air interface resourceused by control channels.
4.1 Resource map
The following figure provides an example of the mapping of common controlchannels in the downlink, assuming a bandwidth of 5 MHz, CFI=2, two antennaports and uplink-downlink configuration 1 with special subframe 6.
L0000469A
Details of colors PDSCH PDCCH PHICH PCFICH PBCH SSS PSS CRS Not Used
Subframe 0 Subframe 1, 6 Subframe 4, 9 Subframe 5
Freq
uenc
y
Time
288
168
108
180
0
Sub
carr
ier
inde
x
Figure 15 Example of Mapping Downlink Channels
4.2 Resource Use
The percentage of resources used, relative to the total amount availableis calculated based on the numbers of REs ��� for the control channelspresented in Section 3 on page 9.
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Control Channel Dimensioning
Table 20 gives the resource use for one and two antenna ports, 20 MHz, CFI=1and Uplink-downlink Configuration 1 with special subframe 7:
Table 20 Resource Use Percentage, 20 MHz Bandwidth
Notused
CRS PSS SSS PBCH PCFICH PHICH PDCCH TotalControlChannel
PDSCH
OneAntennaPort
1.5 4,8 0.1 0.1 0.3 0.1 0.7 4.3 10.5 88.0
TwoAntennaPorts
5.0 4,8 0.1 0.1 0.3 0.1 0.7 4.3 10.5 84.5
The figures above assume that PRS transmission is not activated in thecell. If PRS transmission is activated the available resources for PDSCH isapproximately reduced by a factor � ,���
���������
�������
�
Equation 2 PDSCH usage reduction due to PRS
where ��������� is defined in sectionSection 3.4 on page 13and ������� is thefraction of subframes used for DL transmission..
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Uplink Common Control Channel Configuration
5 Uplink Common Control ChannelConfiguration
This chapter describes how the uplink common control channels and signalsare mapped to the REs.
5.1 Channels and Signals
The following control channels for uplink are specified to carry the Layer 1 andLayer 2 control information for LTE:
• Physical Uplink Control Channel (PUCCH)
• Physical Random Access Channel (PRACH)
The uplink physical signals are the Demodulation Reference Signal (DMRS)and the Sounding Reference Signal (SRS).
5.2 Demodulation Reference Signal
Similar to the downlink, reference signals for channel estimation are requiredfor the LTE uplink to enable coherent demodulation of the uplink physicalchannels PUSCH and PUCCH on the receiver side. This reference signal ismore specifically referred to as the uplink Demodulation Reference Signal(DMRS). The DMRS is time multiplexed with both PUCCH and PUSCH.
When DMRS is multiplexed with PUSCH, the middle symbol in each slot is usedfor DMRS, see Figure 16. This means that in each RB 12 REs (approximately14%) are used for transmission of DMRS.
PRACH
PUCCH
PUSCH
Subframe 0 Subframe 1 Subframe 9Subframe 2 Subframe 4 Subframe 5 Subframe 6 Subframe 7 Subframe 8Subframe 3
DMRS in PUSCH
L0000470A
Figure 16 Example of mapping of Uplink Channels with Uplink-downlinkConfiguration 1
5.3 Sounding Reference Signal
Sounding is a prerequisite for UL Frequency Selective Scheduling (FSS), seeUplink Frequency-Selective Scheduling. When sounding is activated a UE can
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Control Channel Dimensioning
transmit a Sounding Reference Signal (SRS) over the uplink system bandwidth.With the help of SRS the eNB can estimate the UL frequency dependent pathloss between the UE and the eNB.
As indicated in Figure 17, REs for SRS are allocated on 2 UpPTS symbols inevery special subframe (subframe 1 and 6). Since these symbols are not usedfor anything else, no capacity loss occurs due to sounding. Several UE cantransmit SRS simultaneously in the same UpPTS and RB combination usingdifferent transmission combs and cyclic shifts. Which SRS resource to use issignaled to the UE by RRC signalling. A UE keeps its SRS resource as longas it is uplink synchronized.
Subframe 7
Subframe 4
Subframe2
Subframe 3
Subframe 0
Dw
PTS
GP
UpP
TS
Dw
PTS
GP
UpP
TS
Subframe 8
Subframe 5
2 symbolsfor SRS
2 symbolsfor SRS
Subframe 9
L0000535A
Figure 17 Mapping of SRS
The number of RBs over which the SRS is transmitted is given by the followingtable:
Table 21 Number of RBs over which SRS are Transmitted (SRS Bandwidth)
Bandwidth [MHz] RBs
10 48
15 72
20 96
A UE which is allocated sounding resources transmits SRS in one UpPTS every5th ms. At each transmission occasion the UE sends SRS over 24 consecutiveRBs. To cover the entire SRS bandwidth (96 RBs), 4 SRS transmissionoccasions are required.
5.4 Physical Uplink Control Channel
5.4.1 General
The Physical Uplink Control Channel (PUCCH) carries uplink controlinformation from UE for which no PUSCH resource is granted in the samesubframe. For a UE already granted a PUSCH, control signalling is multiplexedwith data onto PUSCH.
PUCCH is used for transmitting:
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Uplink Common Control Channel Configuration
• Hybrid Automatic Repeat Request (HARQ) Acknowledgement/NegativeAcknowledgement (ACK/NACK)
• Scheduling Request (SR)• Channel status reports, Channel Quality Indicator (CQI), Precoding Matrix
Indicator (PMI) and Rank Indicator (RI)
The RBs allocated for PUCCH are placed at the band edges. The informationsent on PUCCH uses one RB in each of the two consecutive slots in asubframe. The two RB used for PUCCH is here after called resource block pair(RB-pair). RB-pairs (m in Figure 18) are allocated in the lower frequency bandedge in the first slot and in the upper band edge in the last slot or vice versa.
m=2
m=1m=0
m=3
m=1
m=2m=3
m=0
One Subframe
12 Subcarriers
L0000220A
Figure 18 Mapping PUCCH Resources
To be able to share PUCCH in the time domain, each PUCCH is assigned toa UE with a periodicity specifying in which subframes the UE can access thePUCCH. The default periodicity of CQI is 80 ms and for SR 20 ms.
PUCCH is not only specified by an RB-pair and a periodicity. To allow anRB-pair to be shared by several UE, a resource on PUCCH is specified by acyclic shift, and for SR and HARQ resources also one of a series of orthogonalcover sequences.
Depending on the information to be carried on PUCCH, one of two formatsis used:
• PUCCH Format 1 for SR and HARQ ACK/NACK
• PUCCH Format 2 for CQI, PMI and RI
The parameters noOfPucchCqiUsers and noOfPucchSrUsers determinethe number of resources for CQI and SR per cell. To avoid PUSCH frominterfering with PUCCH, it is recommended to use the same number of
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Control Channel Dimensioning
PUCCH RBs in all cells. This can be achieved by the same setting ofnoOfPucchCqiUsers and noOfPucchSrUsers in all cells.
To maximize PUSCH throughput, the number of RB-pairs should not beover-dimensioned. An even number of RB-pairs is preferable, as an oddnumber will leave one RB-pair unused by both PUCCH and PUSCH.
A UE is allowed to connect to a cell only if there are free SR resources. Ifmore CQI resources than SR resources are allocated some CQI resource willbe unused. CQI and SR resources are allocated for a UE as long as the UE isuplink synchronized. UE already in connected mode will stay connected evenwhen uplink synchronization is timed out and PUCCH resources are released.
If one or more cells in an eNodeB are experiencing CQI and SR congestioneven with the largest possible CQI and SR allocations, it is recommended toactivate the feature Random Access Re-sync and PDCCH ordered re-sync.With this feature the UE will lose the uplink synchronization after a time ofinactivity and the CQI and SR resources are released and can be allocated toanother UE.
5.4.2 Parameter Limitations
When performing the calculations in Section 5.4.3 on page 30 or Section 5.4.4on page 32, two limitations for the two parameters noOfPucchCqiUsers andnoOfPucchSrUsers need to be considered. These limitations are:
• Maximum allowed value of noOfPucchCqiUsers and noOfPucchSrUsers per cell.
• Maximum number of RB pair used for PUCCH per DU.
Maximum allowed value of noOfPucchCqiUsers and noOfPucchSrUsers
Table 22 shows the maximum allowed values of noOfPucchCqiUsers andnoOfPucchSrUsers:
Table 22 Maximum Allowed of SR and CQI Resources per Cell
DU Type Uplink/Downlink
Configuration
Numberof Rx
Antennas
Maximum noOfPucchSrUsers
MaximumnoOfPucchCqiUsers
1 2,4 1328 704DUS31
2 2,4 664 352
2 1472 800
4 1504 8001
8 864 480
2,4 768 400
DUS41
28 416 240
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Uplink Common Control Channel Configuration
The value of maximum noOfPucchSrUsers assumes default setting ofcommonSrPeriodicity.
In case commonSrPeriodicity is changed or if a cell is considered as aprimary cell in carrier aggregation, maximum noOfPucchSrUsers must beadjusted by using Equation 3. From PUCCH dimensioning perspective, a cell isconsidered as a primary cell in CA if the following is true:
• noOfChannelSelectionSets >0 and
• dlChannelBandwidth >= 5000 and
• Carrier Aggregation featureState = ON on the eNodeB and
• the cell has one sCellCandidate set to ALLOWED
�������� �
�������������
���
������ � �� ����
��
����
Equation 3 Adjustment of Maximum Allowed Value of SR Resources per Cell
where
������������ is the maximum number of SR resources in Table 22.
��� is the periodicity for SR in milliseconds, specified byoperator parameter commonSrPeriodicity. Defaultvalue is 20 ms.
�� ���� number of subframes with PUCCH, equal to 4 and 2 foruplink-downlink configuration 1 and 2, respectively.
������ is the number of HARQ resources reserved for 2CC DLCarrier Aggregation in primary cell. It is calculated as 2� noOfChannelSelectionSets and is 12 when defaultvalue for noOfChannelSelectionSets is used.
Maximum number of RB pair used for PUCCH per DU
Table 23 shows the maximum allowed number of RB pair used for PUCCHper DU:
Table 23 Maximum Number of RB Pair Used for PUCCH per DU
DU Type Number of Rx Antennas Maximum Number of RB Pairper DU
DUS31 2, 4 27
2, 4 48DUS41
8 36
For some configurations special considerations must be taken then calculatingresource consumption:
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Control Channel Dimensioning
CombinedCell
In case of combined cell, noOfPucchSrUsers andnoOfPucchCqiUsers are set on cell level, that is the PUCCHconfiguration will be the same for all sector carriers in a combinedcell. As each sector carrier will require its own PUCCH RB pairs,a combined cell with n sector carriers will use n times more PUCHRB pairs than a single sector carrier cell, if sets same valuesfor noOfPucchSrUsers,noOfPucchCqiUsers and otherparameters. Therefore, a DU configured with three combinedcells each with two sector carriers and a DU configured with sixsingle sector carrier cells will use the same amount of RB pairsassuming the same parameter setting and bandwidth.
Differentnumberof RXantennas
If cells with different number of RX antennas are configured in aDU, the highest number of RX antennas used in a cell should bechosen for the maximum number of RB pairs inTable 23.
5.4.3 Calculation of the Number of PUCCH RB-pairs
The number of RB-pairs for PUCCH can be calculated for a given a setting ofnoOfPucchSrUsers and noOfPucchCqiUsers.
The number of RB-pairs for format 1 is shared between SR and HARQresources. In the current release of LTE, up to 36 scheduling requests andHARQ resources can be used per RB-pair. The number of RB-pairs for theseresources must be calculated together by:
����������� �
������ � � ��������� � ����������
��
�
Equation 4 RB-pairs for SR and HARQ Resources
where
����� � is the number of resources for SR per subframe.
��������� is the number of HARQ resources per subframe.
���������� is the number of HARQ resources reserved for 2CC DLCarrier Aggregation in primary cell. It is calculated as 2� noOfChannelSelectionSets and is 12 when defaultvalue for noOfChannelSelectionSets is used. Fornon-primary cells the value is 0.
� � indicates round up to next higher integer.
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Uplink Common Control Channel Configuration
The number of SR resources per subframe, ���������, are calculated by:
��������� �
�������
���
��
��������
�
Equation 5 Scheduling Request Resources
where
������ is the desired number of SR resources on thePUCCH channel, specified by operator parameternoOfPucchSrUsers.
��� is the periodicity for SR in milliseconds, specified by theoperator parameter commonSrPeriodicity. Defaultvalue is 20 ms.
�������� number of subframes with PUCCH, equal to 4 and 2 foruplink-downlink configuration 1 and 2, respectively.
By decreasing the SR periodicity, latency will be decreased at the cost of anincreased number of PUCCH RB-pairs or lower SR capacity.
The amount of HARQ resources required per subframe, �����������, islinked to the amount of CCEs that can be allocated for PDCCH in the downlinksee Section 3.9 on page 17. The maximum number of CCEs ��� ���� dependson the bandwidth and is given in Table 24:
Table 24 Maximum Number of CCEs
�������� pdcchCfiMode
Bandwidth [MHz] CFI_STATIC_BY_BW
CFI_STATIC_1 CFI_AUTO_MAXIMUM_2CFI_STATIC_2
CFI_AUTO_MAXIMUM_3CFI_STATIC_3
10 11 11 27 44
15 16 16 41 66
20 22 22 55 88
����������� is also affected by the chosen uplink-downlink configuration.If more downlink than uplink subframes are allocated, an uplink subframeneeds to cater for ACK/NACKs associated to more than one DL subframe.The maximum number of downlink subframes that can be ACK/NACKed inone uplink subframe, that is, the maximum ACK/NACK bundling window sizeis shown in Table 25:
Table 25 Maximum Bundling Window Size
Uplink-downlink Configuration �����������
1 2
2 4
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Control Channel Dimensioning
The number of resources needed for HARQ-ACK����������� is nowdetermined by:
����������� � ���������� ������
Equation 6 HARQ Resources with Bundling
The number of RB-pairs allocated for format 2 is calculated by:
��������� �
���������
��� �����
��
���������
�
Equation 7 RB-pairs for CQI Resources
where
�������� is the desired number of CQI resources on the PUCCH,specified by the operator parameter noOfPucchCqiUsers.
��� is the number of CQI resources per RB-pair, equal to 4.
���� is the periodicity for CQI reporting in milliseconds. All UEare allocated the same periodicity of 80 ms.
The total capacity allocated for PUCCH in terms of RB-pairs or RBs per slot,��������� is given by:
��������� � ����� ���� � ����� ����
Equation 8 RB-pairs for PUCCH
It must be verified that the total number of RB-pairs per DU does not exceedthe number in Table 23.
5.4.4 Calculation of Parameter Settings
Given a desired number of RB-pairs for format 1 and format 2, the setting ofnoOfPucchSrUsers and noOfPucchCqiUsers is calculated as:
������� � ������������ � ����������� � �����������������������
��
Equation 9 Calculation of SR Resources from a Desired Number of RB-pairsfor Format 1
�������� � ��������� ��� �������������
��
Equation 10 Calculation of CQI Resources from a Desired Number ofRB-pairs for Format 2
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Uplink Common Control Channel Configuration
It must be verified that the number of SR resources and CQI resources doesnot exceed the number in Table 22.
5.4.5 Example Calculation of Parameter Settings
Assume that the following configuration is used:
• Three cells
• DUS41
• 2 RX diversity
• Uplink-downlink Configuration 2
• pdcchCfiMode=CFI_AUTO_MAXIMUM_2
• Network bandwidth of 20 MHz
What is the highest setting for noOfPucchSrUsers and noOfPucchCqiUsers?
Table 23 shows that DUS41 can support 48 RB-pairs. Each cell can thereforeuse 16 RB-pairs. As a first attempt 8 RB-pairs are allocated to both Format1 and Format 2.
By using Equation 9 noOfPucchSrUsers is calculated to:
������� � ��� � �� �� � �� � �� � �
�� ��
By using Equation 10 noOfPucchCqiUsers is calculated to:
�������� � � � � �� � �
�� ���
������� is not limited according to Table 22.
�������� is limited to 400 according to Table 22.
Since �������� is limited by Table 22 one less RB-pair is allocated for Format2 and one more RB-pair is allocated for Format 1:
By using Equation 9 noOfPucchSrUsers is calculated to:
������� ��� � �� �� � �� � �� � �
�� ���
By using Equation 10 noOfPucchCqiUsers is calculated to:
�������� � � � �� � �
�� ���
�������� still exceeds the limit 400 resources in Table 22.
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Control Channel Dimensioning
The second attempt gives the best solution as it allows most SR resources.Therefore noOfPucchSrUsers is set to 416 and noOfPucchCqiUsers is setto 400 due to limitation in Table 22.
5.5 Physical Random Access Channel
The Physical Random Access Channel (PRACH) is used for random access. Itallows the RBS to estimate the delay between the RBS and UE.
The PRACH has a bandwidth of 72 subcarriers and in the time domain thelength is 1 ms, which is equivalent to one subframe. In cells with cell rangeexceeding 15 kilometers the length in the time domain is doubled to 2 ms or twoconsecutive subframes. Cell ranges exceeding 15 kilometers are only allowedwith the feature Maximum Cell Range.
The PRACH resource is allocated once every radio frame and placed adjacentto the PUCCH lower frequency band allocation, see Figure 16.
The number of RBs used by PRACH per radio frame, ��������� isindependent of bandwidth and given in the table below:
Table 26 Number of Resource Blocks Used by PRACH per Radio Frame
Cell Range ���������
Cell range ≤ 15 km 12
Cell range >15 km 24
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