6.2 Slot structure and physical resource elements
36.2113GPPEvolved Universal Terrestrial Radio Access (E-UTRA)Physical channels and modulationRelease 17TS
6.2.1 Resource grid
The transmitted signal in each slot is described by one or several resource grids of 
subcarriers and 
OFDM symbols. The resource grid structure is illustrated in Figure 6.2.2-1. The quantity 
depends on the downlink transmission bandwidth configured in the cell and shall fulfil
where 
and 
are the smallest and largest downlink bandwidths, respectively, supported by the current version of this specification.
The set of allowed values for 
is given by TS 36.104 [6]. The number of OFDM symbols in a slot depends on the cyclic prefix length and subcarrier spacing configured and is given in Table 6.2.3-1.
An antenna port is defined such that the channel over which a symbol on the antenna port is conveyed can be inferred from the channel over which another symbol on the same antenna port is conveyed. For MBSFN reference signals, positioning reference signals, UE-specific reference signals associated with PDSCH, demodulation reference signals associated with SPDCCH, and demodulation reference signals associated with EPDCCH, there are limits given below within which the channel can be inferred from one symbol to another symbol on the same antenna port. There is one resource grid per antenna port. The set of antenna ports supported depends on the reference signal configuration in the cell:
– Cell-specific reference signals support a configuration of one, two, or four antenna ports and are transmitted on antenna ports 
,
, and 
, respectively.
– MBSFN reference signals are transmitted on antenna port
. The channel over which a symbol on antenna port
is conveyed can be inferred from the channel over which another symbol on the same antenna port is conveyed only if the two symbols correspond to subframes (slots in case of 0.37 kHz subcarrier spacing) of the same MBSFN area.
– UE-specific reference signals associated with PDSCH intended for non-BL/CE UE are transmitted on antenna port(s) 
, 
, 
, or one or several of 
. The channel over which a symbol on one of these antenna ports is conveyed can be inferred from the channel over which another symbol on the same antenna port is conveyed only if the two symbols are within the same subframe and in the same PRG when PRB bundling is used or in the same PRB pair when PRB bundling is not used.
– UE-specific reference signals associated with PDSCH intended for BL/CE UE are transmitted on one or several of antenna port(s) 
. The channel over which a symbol on one of these antenna ports is conveyed can be inferred from the channel over which another symbol on the same antenna port is conveyed only if the two symbols are in the same set of
consecutive subframes and have the same PRB index.
– Demodulation reference signals associated with EPDCCH are transmitted on one or several of 
. The channel over which a symbol on one of these antenna ports is conveyed can be inferred from the channel over which another symbol on the same antenna port is conveyed only if the two symbols are in the same PRB pair.
– Demodulation reference signals associated with MPDCCH are transmitted on one or several of 
. The channel over which a symbol on one of these antenna ports is conveyed can be inferred from the channel over which another symbol on the same antenna port is conveyed only if the two symbols are in the same set of
consecutive subframes and have the same PRB index.
– Demodulation reference signals associated with SPDCCH are transmitted on 
.
– Positioning reference signals are transmitted on antenna port
. The channel over which a symbol on antenna port
is conveyed can be inferred from the channel over which another symbol on the same antenna port is conveyed only within one positioning reference signal occasion consisting of 
consecutive downlink subframes, where 
is configured by higher layers.
– CSI reference signals support a configuration of 1, 2, 4, 8, 12, 16, 20, 24, 28, or 32 antenna ports and are transmitted on antenna ports 
, 
, 
, 
, 
, 
, 
, 
, 
and
, respectively.
Two antenna ports are said to be quasi co-located if the large-scale properties of the channel over which a symbol on one antenna port is conveyed can be inferred from the channel over which a symbol on the other antenna port is conveyed. The large-scale properties include one or more of delay spread, Doppler spread, Doppler shift, average gain, and average delay.
6.2.2 Resource elements
Each element in the resource grid for antenna port 
is called a resource element and is uniquely identified by the index pair 
in a slot where 
and 
are the indices in the frequency and time domains, respectively. Resource element 
on antenna port 
corresponds to the complex value
.
When there is no risk for confusion, or no particular antenna port is specified, the index 
may be dropped.
Figure 6.2.2-1: Downlink resource grid
6.2.3 Resource blocks
Resource blocks are used to describe the mapping of certain physical channels to resource elements. Physical and virtual resource blocks are defined.
A physical resource block is defined as 
consecutive OFDM symbols in the time domain and 
consecutive subcarriers in the frequency domain, where 
and 
are given by Table 6.2.3-1. A physical resource block thus consists of 
resource elements, corresponding to one slot in the time domain and 180 kHz in the frequency domain.
Physical resource blocks are numbered from 0 to 
in the frequency domain. The relation between the physical resource block number 
in the frequency domain and resource elements 
in a slot is given by
Table 6.2.3-1: Physical resource blocks parameters
|
Configuration |
|
|
|
|
Normal cyclic prefix |
|
12 |
7 |
|
Extended cyclic prefix |
|
6 |
|
|
|
24 |
3 |
|
|
72 |
1 |
||
|
|
144 |
1 |
|
|
486 |
1 |
||
Except for subcarrier spacing and , a physical resource-block pair is defined as the two physical resource blocks in one subframe having the same physical resource-block number 
.
A virtual resource block is of the same size as a physical resource block. Two types of virtual resource blocks are defined:
– Virtual resource blocks of localized type
– Virtual resource blocks of distributed type
For each type of virtual resource blocks, a pair of virtual resource blocks over two slots in a subframe is assigned together by a single virtual resource block number, 
.
6.2.3.1 Virtual resource blocks of localized type
Virtual resource blocks of localized type are mapped directly to physical resource blocks such that virtual resource block 
corresponds to physical resource block
. Virtual resource blocks are numbered from 0 to
, where 
.
6.2.3.2 Virtual resource blocks of distributed type
Virtual resource blocks of distributed type are mapped to physical resource blocks as described below.
Table 6.2.3.2-1: RB gap values
|
System BW ( |
Gap ( |
|
|
1st Gap ( |
2nd Gap ( |
|
|
6-10 |
|
N/A |
|
11 |
4 |
N/A |
|
12-19 |
8 |
N/A |
|
20-26 |
12 |
N/A |
|
27-44 |
18 |
N/A |
|
45-49 |
27 |
N/A |
|
50-63 |
27 |
9 |
|
64-79 |
32 |
16 |
|
80-110 |
48 |
16 |
)
)
)
)
The parameter 
is given by Table 6.2.3.2-1. For 
, only one gap value 
is defined and 
. For 
, two gap values 
and 
are defined. Whether 
or 
is signaled as part of the downlink scheduling assignment as described in TS 36.212 [3].
Virtual resource blocks of distributed type are numbered from 0 to
, where 
for 
and 
for 
.
Consecutive 
VRB numbers compose a unit of VRB number interleaving, where 
for 
and 
for 
. Interleaving of VRB numbers of each interleaving unit is performed with 4 columns and 
rows, where 
, and 
is RBG size as described in TS 36.213 [4]. VRB numbers are written row by row in the rectangular matrix, and read out column by column. 
nulls are inserted in the last 
rows of the 2nd and 4th column, where 
. Nulls are ignored when reading out. The VRB numbers mapping to PRB numbers including interleaving is derived as follows:
For even slot number 
;
,
where 
,
and 
,
where 
and 
is obtained from the downlink scheduling assignment as described in TS 36.213 [4].
For odd slot number 
;
Then, for all 
;
.
Virtual resource blocks of distributed type are not applicable to BL/CE UEs.
6.2.4 Resource-element groups (REGs)
Resource-element groups are used for defining the mapping of control channels to resource elements.
A resource-element group is represented by the index pair 
of the resource element with the lowest index 
in the group with all resource elements in the group having the same value of 
. The set of resource elements 
in a resource-element group depends on the number of cell-specific reference signals configured as described below with 
, 
.
– In the first OFDM symbol of the first slot in a subframe the two resource-element groups in physical resource block 
consist of resource elements 
with 
and 
, respectively.
– In the second OFDM symbol of the first slot in a subframe in case of one or two cell-specific reference signals configured, the three resource-element groups in physical resource block 
consist of resource elements 
with 
, 
and 
, respectively.
– In the second OFDM symbol of the first slot in a subframe in case of four cell-specific reference signals configured, the two resource-element groups in physical resource block 
consist of resource elements 
with 
and 
, respectively.
– In the third OFDM symbol of the first slot in a subframe, the three resource-element groups in physical resource block 
consist of resource elements 
with 
, 
and 
, respectively.
– In the fourth OFDM symbol of the first slot in a subframe in case of normal cyclic prefix, the three resource-element groups in physical resource block 
consist of resource elements 
with 
, 
and 
, respectively.
– In the fourth OFDM symbol of the first slot in a subframe in case of extended cyclic prefix, the two resource-element groups in physical resource block 
consist of resource elements 
with 
and 
, respectively.
Mapping of a symbol-quadruplet 
onto a resource-element group represented by resource-element 
is defined such that elements 
are mapped to resource elements 
of the resource-element group not used for cell-specific reference signals in increasing order of 
and 
. In case a single cell-specific reference signal is configured, cell-specific reference signals shall be assumed to be present on antenna ports 0 and 1 for the purpose of mapping a symbol-quadruplet to a resource-element group, otherwise the number of cell-specific reference signals shall be assumed equal to the actual number of antenna ports used for cell-specific reference signals. The UE shall not make any assumptions about resource elements assumed to be reserved for reference signals but not used for transmission of a reference signal.
For frame structure type 3, if the higher layer parameter subframeStartPosition indicates ‘s07’ and the downlink transmission starts in the second slot of a subframe, the above definition applies to the second slot of that subframe instead of the first slot.
6.2.4A Enhanced Resource-Element Groups (EREGs)
EREGs are used for defining the mapping of enhanced control channels to resource elements.
There are 16 EREGs, numbered from 0 to 15, per physical resource block pair. Number all resource elements, except resource elements carrying DM-RS for antenna ports 
for normal cyclic prefix or 
for extended cyclic prefix, in a physical resource-block pair cyclically from 0 to 15 in an increasing order of first frequency, then time. All resource elements with number 
in that physical resource-block pair constitutes EREG number 
.
For frame structure type 3, if the higher layer parameter subframeStartPosition indicates ‘s07’ and the downlink transmission starts in the second slot of a subframe, the above definition applies to the second slot of that subframe instead of the first slot.
6.2.4B Short Resource-Element Groups (SREGs)
Short resource-element groups (SREGs) are used for defining the mapping of short control channels to resource elements.
One SREG is composed of all resource elements in a physical resource block in a given OFDM symbol. The set of resource elements 
in an SREG in physical resource block 
consist of resource elements with 
with 
, 
, all having the same value of 
.
6.2.5 Guard period for half-duplex FDD operation
For type A half-duplex FDD operation, a guard period is created by the UE by
– not receiving the last part of a downlink subframe immediately preceding an uplink subframe from the same UE.
For type B half-duplex FDD operation, guard periods, each referred to as a half-duplex guard subframe, are created by the UE by
– not receiving a downlink subframe immediately preceding an uplink subframe from the same UE, and
– not receiving a downlink subframe immediately following an uplink subframe from the same UE.
6.2.6 Guard Period for TDD Operation
For frame structure type 2, the GP field in Figure 4.2-1 serves as a guard period.
6.2.7 Narrowbands and widebands
A narrowband is defined as six non-overlapping consecutive physical resource blocks in the frequency domain. The total number of downlink narrowbands in the downlink transmission bandwidth configured in the cell is given by
The narrowbands are numbered 
in order of increasing physical resource-block number where narrowband 
is composed of physical resource-block indices
where
and is according to Table 6.2.7-1 for the narrowbands used for PDSCH resource allocation in CEModeB if the higher-layer parameter ce-PDSCH-FlexibleStartPRB-AllocConfig is set, otherwise .
If 
, a wideband is defined as four non-overlapping narrowbands in the frequency domain. The total number of downlink widebands in the downlink transmission bandwidth configured in the cell is given by
and the widebands are numbered 
in order of increasing narrowband number where wideband 
is composed of narrowband indices 
where 
.
If 
, then 
and the single wideband is composed of the 
non-overlapping narrowband(s).
Table 6.2.7-1: Shift of narrowbands for PDSCH resource allocation in CEModeB when higher layer parameter ce-PDSCH-FlexibleStartPRB-AllocConfig is set.
|
System bandwidth |
Shift of narrowband |
|
6 |
0 |
|
15 |
-1 for narrowband #0; 0 for narrowband #1 |
|
25 |
0 for narrowbands 0, 1; – 1 for narrowband 2, 3 |
|
50 |
– 1 for all narrowbands |
|
75 |
-1 for narrowbands 0, 1, …, 5; 0 for narrowbands 6, 7, …, 11 |
|
100 |
-2 for all narrowbands. |
6.2.8 Guard period for narrowband and wideband retuning
For BL/CE UEs, a guard period of at most 
OFDM symbols is created for Rx-to-Rx and Tx-to-Rx frequency retuning between two consecutive subframes.
– If the higher layer parameter ce-RetuningSymbols is set, then 
equals ce-RetuningSymbols, otherwise 
.
– If the higher layer parameter ce-pdsch-maxBandwidth-config is set to 5 MHz, then the rules for guard period creation defined in the remainder of this clause apply not for retuning between narrowbands but for retuning between widebands and for transmissions involving multiple widebands.
– If the UE is configured with CEModeA and higher layer parameter ce-PDSCH-FlexibleStartPRB-AllocConfig, the rules for guard period creation defined in the remainder of this clause apply for retuning between tuning narrowbands defined for the allocation resources not fully within one narrowband defined in Clause 6.2.7 as the consecutive 6PRBs starting from if is aligned with RBG boundary, or the consecutive 6PRBs ending at if is aligned with RBG boundary, where and are defined in Table 7.1.6.3-2 [4].
– If the UE is configured with CEModeB and higher layer parameter ce-PDSCH-FlexibleStartPRB-AllocConfig, the rules for guard period creation defined in the remainder of this clause apply for retuning between the tuning narrowband defined as the narrowband shifted according to Table 6.2.7-1.
– If the UE retunes from a first downlink narrowband to a second downlink narrowband with a different center frequency, a guard period is created by the UE not receiving at most 
OFDM symbols in the second narrowband.
– If the UE retunes from a first uplink narrowband to a second downlink narrowband with a different center frequency for frame structure type 2, a guard period is created by the UE not receiving at most 
OFDM symbols in the second narrowband.
Furthermore, for BL/CE UEs configured with the higher layer parameter srs-UpPtsAdd, a guard period of at most OFDM or SC-FDMA symbols is created for Rx-to-Tx frequency retuning within a special subframe for frame structure type 2. Primarily, the TDD guard period (GP) specified in clause 4.2 serves as the guard period for narrowband retuning, and if GP is not sufficient then additional guard period is created by the UE according to:
– If SRS is configured to be transmitted in the first UpPTS symbol, the additional guard period is created by the UE not receiving at most 
DwPTS symbols in the first narrowband.
– If SRS is configured to be transmitted in the second UpPTS symbol but not in the first UpPTS symbol, the additional guard period is created by the UE primarily by not transmitting the first UpPTS symbol and (if 
) secondarily by not receiving the last DwPTS symbol.