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`LTE -THE UMTS LONG TERM EVOLUTION
`
`Table 9.6 RBG size for Type 0 resource allocation.
`
`
`
`
`Downlink bandwidth Nfit RBG size
`(P)
`0:::10
`J
`1 l-26
`2
`27-63
`3
`4
`64-110
`
`RBS12 RBG13
`RBG11
`RSG11 RBGS RBG10
`RBG7
`RBG6
`R5Cl5
`RBG3 RllG-4
`RBG2
`RBGI
`PR8 PRGIPRB PRB PRB l'RB PRB l'RB ?RB PRB PRB PRB PRS PRll PRll PRB PRB!PRB PR8 PRB PR8 PRB PRB PRB PRBI
`
`
`
`
`
`'t 2 3 4 5 6 7 8 9 10 11 ,2 13 '\4 15 16 1J J 18 19 2Q 21 22 23 24 25 �
`
`frequonc.y
`
`
`
`
`
`
`
`
`
`
`
`Figure 9.1 0 PRB addressed by a bitmap Type 0, each bit addressing a complete RBG.
`
`smaller than for Type 0, since some bits are used to indicate the subset of the RBG which is
`
`
`
`
`
`
`
`
`
`
`
`addressed, and a shift in the position of the bitmap. The total number of bits (including these
`case of N[?} = 25, N1rno
`
`
`additional flags) is the same as for Type 0. An ex.ample for the
`= 11
`
`
`
`bit io and P = 2 is shown in Figure 9.11. One bit is used for subset selection and another
`
`indicate the shift.
`The motivation for providing this method ofresource allocation is flexibility in spreading
`
`
`
`
`
`
`
`
`the resources across the frequency domain to exploit frequency diversity.
`
`• a distributed allocation comprising multiple non-consecutive PRBs (see Section
`
`Resource allocation Type 2. In resource allocations of Type 2, the resource allocation
`
`
`
`
`
`
`information indicates to a scheduled UE either:
`
`• a set of contiguously allocated PRBs, or
`
`
`9.2.2.1).
`The distinction between the two allocation methods is made by a 1-bit Hag in the resource
`
`
`
`
`
`
`
`
`
`allocation message. PRB allocations may vary from a single PRB up to a maximum number
`
`
`
`
`
`
`of PRBs spanning the system bandwidth. A Type 2 resource allocation field consists of a
`
`Resource Indication Value (RIV) corresponding to a starting resource block (RBsTART) and
`
`
`
`
`
`
`a length in terms of contiguously-al located resource blocks (LcRBs), The resource indication
`
`value is defined by
`then RIV = N[l,/;(Lrn.ss
`if (LcRBs - I) S LN/?k /2J
`-I) + RBsTART
`else
`RIV= Nf/;(N{l/;
`-LcRBs + I)+ (N{?/;-1 - RBSTART)
`
`
`
`
`
`An example of a method for reversing the mapping to derive the resource allocation from the
`
`RIV can be found in [2].
`
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`203
`
`RBG1
`
`S\JBSE'f SELECTION = 0, SHIFT= 0
`
`R8G2 RSG:l ABG4 RBG5 RBG6 RBG7 RBGII
`RBG9 RBG10 RBG11
`lPRB; PAil PAB PRB
`f'l<B1 /�81 PRB PRB PRB
`PRB lPRai
`17
`19
`11 13 I
`3 j i 5 l 7
`
`1
`
`9
`
`21
`
`SUBSET SEl.ECTJON = 1, SHIFT= 0
`RBGI RBG2 RBG3 RBG4 RllG5
`RBG6 R6G7 RBG8 RBG9 R8G10 RBGH
`"f28
`PRB PRB
`PRB
`I f� B
`18
`
`16
`
`20
`
`"
`
`PRB! PRB PR8
`6
`
`2 ' 4
`
`PR8
`6
`
`PRB
`
`rn
`
`SUBSET SELE<:TION = O. SHIFT= 1
`RBG1 RBG2 RBG3 RBG4 !lBG5 RBG6 RIIG7
`PRB
`PRB PRB
`PRB PRB
`9 11 13
`
`7
`
`PRB
`
`PRB
`17
`
`15
`
`SUBSET SELECTmN-=: l. SHIFT::;; 1
`RSG4 RBG5
`RBGS
`RBG7 RSG8
`mm, RBG2 RBG3
`PRB PRB PRB
`6
`
`4
`
`8
`
`IPRB PRB PRB PRB, PRB PRB
`10
`12
`16
`14 16 l
`
`PREI PRB
`2C
`22 24
`
`RBG8
`RBG9 RBGiO RBG11
`PRB PRB
`19
`
`PRB PRB
`25
`
`21 23
`
`RBG9 RBG10 RBGH
`
`rrequeney
`
`Figure 9.1 I
`
`
`
`
`
`depending on a subset selection and shift value.
`
`
`
`PRBs addres.sed by a bitmap Type 1, each bit addressing a subset of a RBG,
`
`
`
`9.3.3.2 PDCCH Transmission and Blind Decoding
`
`The previous discussion has covered the structure and possible contents of an indi.vidual
`
`
`
`
`
`
`
`
`PDCCH message, and transmission by an eNodeB of multiple PDCCHs in a subframe.
`
`
`
`
`
`This section addresses the question of how these transmissions are organized so that a UE
`
`
`
`
`
`can locate the PDCCHs intended for it. while at the same time making efficient use of the
`
`resources allocated for PDCCH transmission.
`
`
`A simple approach, at least for the eNodeB, would be to allow the eNodeB to place any
`
`
`
`PDCCH anywhere in the PDCCH resources (or CCEs) indicated by the PCFICH. In this
`
`
`
`
`case the UE would need to check all possible PDCCH locations, PDCCH formats and DCI
`
`
`
`
`formats, and act on those messages with con-eel CRCs (taking into account that the CRC
`
`
`
`
`is scrambled with a UE identity). Carrying out such a 'blind decoding' of all the possible
`
`
`
`
`
`combinations would require Che UE to make many PDCCH decoding attempts in every
`
`
`
`
`subframe. For small system bandwidths the computational load would be reasonable, but
`
`
`
`for large system bandwidths, with a large number of possible PDCCH locations, it would
`
`
`
`become a significant burden, leading to excessive power consumption in the UE receiver.
`
`
`
`
`For example, blind decoding of 100 possible CCE locations for PDCCH Format O would be
`
`
`
`equivalent to continuously receiving a data rate of around 4 Mbps.
`The alternative approach adopted for LTE is to define for each UE a limited sel of CCE
`
`
`
`
`
`
`
`
`locations where a PDCCH may be placed. Such a constraint may lead to some limitations as
`
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`204
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`LTE -THE UMTS LONG TERM EVOLUTION
`
`to which UEs can be sent PDCCHs within the same subframe, which would thus restlict the
`
`
`
`
`
`
`
`
`
`
`
`
`UEs to which the eNodeB could grant resources. Therefore it is important for good system
`
`
`
`
`
`performance that the set of possible PDCCH locations available for each UE is not too small.
`
`
`The set of CCE locations in which the UE may find its PDCCHs can be considered as a
`
`
`
`
`
`'search space•. In LTE the search space is a different size for each PDCCH format. Moreover,
`
`
`
`
`
`is where a dedicated search space spaces are defined, dedicated separate and common search
`
`
`
`
`
`
`configured for each UE individually, while all UEs are informed of the extent of the common
`
`
`
`
`
`
`search space. Note that the dedicated and common search spaces may overlap for a given UE.
`
`
`
`
`The sizes of the common and dedicated search spaces are listed in Table 9. 7.
`
`Table 9.7 Search spaces for PDCCH formats.
`
`Number of CCEs Number of candidates
`
`Number of candidates
`
`
`
`in common search space in dedicated search space
`PDCCH fOl"mat (n)
`
`0
`
`2
`
`3
`
`2
`4
`8
`
`4
`
`2
`
`6
`
`6
`
`2
`
`2
`
`With such small search spaces it is quite possible in a given subframe that theeNodeB can­
`
`
`
`
`
`
`
`
`
`
`not find CCE resources to send PDCCHs to all the UEs that it would like to, because having
`
`
`
`
`
`assigned some CCE locations the remaining ones are not in the search space of a particular
`
`
`
`
`UE. To minimize the possibility of such blocking persisting into the next subframe, a UE­
`
`
`
`
`
`
`specific hopping sequence is applied to the starting positions of the dedicated search spaces.
`
`
`
`
`
`In order to keep under control the computational load arising from the total number of
`
`
`
`blind decoding attempts, the UE is not required to search for all the defined DCI formats
`
`
`simuhaneously. Typically, in the dedicated search space, the UE will always search for
`
`
`
`
`Formats O and l A, which are both the same size and are distinguished by a flag in the
`
`
`
`
`
`message. In addition, a UE may be required to receive a further format (i.e. 1, I B or 2,
`
`
`
`
`depending on the PDSCH transmission mode configured by the eNodeB).
`In the common search space the UE will search for Formats lA and 1 C. In addition the
`
`
`
`
`
`
`
`
`UE may be configured to search for Format 3 or 3A, which have the same size as formats 0
`
`
`
`
`and IA, and may be distinguished by having the CRC scrambled by a different (common)
`
`
`
`identity, rather than a UE-specific one.
`Considering the above, the UE would be required io carry out a maximum of 44 blind
`
`
`
`
`
`
`
`decodings in any subframe. This does not include checking the same message with different
`
`
`
`
`CRC values, which requires only a small additional computational complexity.
`
`
`
`It is also worth noting thal the PDCCH structure is adapted to avoid situations where
`
`
`
`
`a PDCCH CRC 'pass' might occur for multiple positions in the configured search-spaces
`
`
`
`
`
`due to repetition in the channel coding (for example, if a PDCCH was mapped to a high
`
`
`number of CCEs with a low code rate, then the CRC could pass for an overlapping smaller
`
`
`
`set of CCEs as well if the channel coding repetition was aligned). Such situations are avoided
`
`
`
`
`
`by adding a padding bit to any PDCCH messages having a size which could result in this
`problem occurring.
`
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`
`
`
`PHYSICAL DATA AND CONTROL CHANNELS
`
`205
`
`
`
`
`
`
`
`9.3.4 Scheduling Process from a Control Channel Viewpoint
`
`To summarize the operation of the downlink control channels, a typical sequence of steps
`
`
`
`
`
`
`
`
`
`
`carried out by the eNodeB could be envisaged as follows:
`
`I.Determine which UEs should be granted resources in the uplink, based on information
`
`
`
`
`
`
`
`
`such as channel quality measurements, scheduling requests and buffer status reports.
`
`
`Also decide on which resources should be granted.
`
`2.Determine which UEs should be scheduled for packet transmission in the downlink,
`
`
`
`
`
`
`
`
`based on information such as channel quality indicator reports. and in the case of
`
`
`
`MIMO, rank indication and preferred precoding matrix.
`
`3.Identify any common control channel messages which are required (e.g. power control
`
`
`
`
`
`
`
`
`commands using DCI Format 3 ).
`
`4.For each message decide on the PDCCH format (i.e. I, 2, 4 or 8 CCEs), and any power
`
`
`
`
`
`
`
`
`
`offset to be applied, in order to reach the intended UE(s) with sufficient reliability,
`
`while minimizing PDCCH overhead.
`
`5.Determine how much PDCCH resource (in terms of CCEs) will be required, how many
`
`
`
`
`
`
`OFDM symbols would be needed for these PDCCHs and therefore what should be
`
`signalled on PCFICH.
`
`
`
`
`
`
`
`
`
`6.Map each PDCCH to a CCE location within the appropriate search space.
`
`7. If any PDCCHs cannot be mapped to a CCE location because all locations in the
`
`
`
`
`
`
`
`
`
`relevant search space have already been assigned, either:
`
`•continue to next step (step 8) accepting that one or more PDCCHs will not be
`
`
`
`
`
`
`
`transmitted, and not all DL-SCH and/or UL-SCH resources will be used, with a
`
`likely loss in throughput, or:
`
`•allocate one more OFDM symbol to support the required PDCCHs and possibly
`
`
`
`
`
`
`
`
`
`revisit step 1 and/or 2 and change UE selection and resource allocation (e.g. to
`
`
`fully use uplink and downlink resources).
`
`
`
`8. Allocate the necessary resources to PCFICH and PHICH.
`
`
`
`
`
`
`
`
`
`9.Allocate resources to PDCCHs.
`
`I 0. Check that total power level per OFDM symbol does not exceed maximum allowed,
`
`
`
`
`and adjust if necessary.
`
`
`
`
`
`11.Transmit downlink control channels.
`
`Whatever approach the eNodeB implementer follows, the potentially high complexity of
`
`
`
`
`
`
`
`
`
`
`the scheduling process is clear, particularly bearing in mind that a cell may easily contain
`
`
`many hundreds of active UEs.
`
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`206
`
`EVOLUTION
`LTE -THE U!vITS LONG TERM
`
`5
`References
`
`8)',
`Channel Coding (FDD) (Release
`36.32L 'Multiplexing and
`[I] 3GPP Technical Specification
`www.3gpp.org.
`Signalling', www.3gpp.org, 3GPP
`TSO RAN
`Allocation
`Resource
`l 9: DL Unicast
`[2] NEC, 'Rl-0721
`WGI, meeting 49, Kobe, Japan, May
`2007.
`
`th
`5 All web sites confirmed I 8
`December 2008.
`
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`

`17
`
`Uplink Physical Channel
`
`Structure
`
`
`
`Robert Love and Vijay Nangia
`
`17.1 Introduction
`
`The LTE Single-Carrier Frequency Division Multiple Access (SC-FDMA) uplink provides
`
`
`
`
`
`
`
`
`
`
`
`separate physical channels for the transmission of data and control signalling, the latter being
`
`
`
`
`
`
`predominantly to support the downlink data transmissions. The detailed structure of these
`
`
`
`
`channels, as explained in this chapter, is designed to make efficient use of the available
`
`
`
`
`frequency-domain resources, and to support effective multiplexing between data and control
`signalling.
`LTE also introduces multiple antenna techniques to the uplink, including closed•loop
`
`
`
`
`
`
`
`
`
`
`antenna selection and Spatial Division Multiple Access (SDMA) or Multi-User Multiple­
`
`
`Input Multiple-Output (MU-MIMO). The physical layer transmissions of the LTE uplink are
`
`
`
`comprised of three physical channels and two signals:
`
`
`
`
`
`• PRACH -Physical Random Access CHannel (see Chapter 19);
`
`
`
`•PUSCH - Physical Uplink Shared CHanncl (see Section 17 .2);
`
`
`
`•PUCCH -Physical Uplink Control CHannel (see Section 17.3);
`
`
`
`
`
`
`
`
`
`•DM RS -DeModuiation Reference Signal (see Section 16.5);
`
`
`
`
`
`
`
`
`
`•SRS -Sounding Reference Signal (see Section J 6.6).
`
`
`
`The uplink physical channels, and their relationship to the higher-layer channels, are
`
`
`
`
`
`
`
`summarized in Figure 17.L
`
`
`
`LTE The UMTS L<mf{ Term Evolution: from Themy Jo Practice Stefani;. Sesia, lssam Toufik and Matthew Baker
`
`
`
`
`
`© 2009 John Wiley & Sons, Ltd
`
`-
`
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`
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`
`1
`i
`f !!
`
`-
`Logical Channels- - - - - - - -
`-\-
`
`Uplink
`
`CCCH DCCH DTCH
`
`MAC LAYER
`
`Transporl Channels-- - - - - - - RACH UL-SCH
`
`Uplink
`
`PrlY LAYER
`
`Uplink __ -c::>----
`
`Physical Channels PUCCH
`
`____ _
`
`PRACH
`
`PUSCH
`
`
`
`
`
`Figure 17. I Summary of uplink physical channels and mapping to higher layers.
`
`
`
`
`
`
`
`
`
`17.2 Uplink Shared Data Channel Structure
`
`The Physical Uplink Shared CHannel (PUSCH), which carries data from the Uplink
`
`
`
`
`
`
`
`Shared Channel (UL-SCH) transport channel, uses DFI'-Spread OFDM (DFI'-S-OFDM),
`
`
`
`
`as described in Chapter 15. The transmit processing chain is shown in Figure 17.2. As
`
`
`
`
`explained in Chapter 10, the information bits are first channel-coded with a turbo code of
`
`
`rate-matching mother code rate r = I /3, which is adapted to a suitable final code rate by a
`
`
`process. This is followed by symbol-level channel interleaving which follows a simple 'time­
`
`
`
`
`first' mapping [ I] -in other words, adjacent data symbols end up being mapped first to
`
`
`
`
`adjacent SC-FDMA symbols in the time domain, and then across the subcarriers (see f2],
`
`
`
`
`
`Section 5.2.2.8). The coded and interleaved bits are then scrambled by a length-31 Gold code
`
`
`(as in Section 6.3) prior to modulation mapping, OFT-spreading, subcarrier mapping1 and
`
`
`
`
`
`
`
`
`
`OFDM modulation. The signal is frequency-shifted by half a subcarrier prior to transmission,
`
`
`
`to avoid the distortion caused by the d.c. subcarrier being concentrated in one RB, as
`
`
`
`
`
`
`described in Section 15.3.3. The modulations supported are QPSK, 16QAM and 64QAM
`
`
`
`
`(the latter being only for the highest category of User Equipment (UE)).
`
`
`
`
`The baseband SC-FDMA transmit signal for SC-FDMA symbol e is thus of the form
`
`(see [3], Section 5.6),
`
`k=-fN,VkN:f'i21-1
`se(t)
`
`
`k=-tNfkN_!},ll/2J
`
`= L ak- .c ex.p[j2.1r(k - NcP.eT.�)] + l/2)n./(t
`
`
`(17.I)
`
`for O:::: t < (NcP.t + N)T.,-, where Ncp,e is the number of samples of the Cyclic Prefix
`
`
`
`
`
`
`
`
`
`(CP) in SC-FDMA symboi e. (see Section 15.3), 2048 is the Inverse Fast Fourier
`N =
`
`
`
`1 Only localized mapping (i.e. to contiguous blocks of subcarriers) is suppmtcd for PUSCH and PUCCH
`
`
`transmissions in LTE.
`
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`UPLfNK PHYSICAL CHANJ\i'EL STRUCTURE
`
`379
`
`PUSCH
`Turbo Cllllnrn!I
`Symbo!-!evei
`informatlon--_.,_1 codinG end Raie
`Channel
`lnter.eavtng
`bits
`Malchinl)
`
`8ft Scrambling
`
`Subearrter
`Mapping
`
`OFlJM
`PUSCH
`Moooiaoon With
`½$Ubcetrle,
`besel'.land
`srn�
`Transmit Sign�I
`
`
`
`
`
`
`
`Figure 17.2 Uplink physical data channel processing.
`
`Transform (IFFT) size, 6.f = 15 kHz is the subcarrier spacing. T.., = l/(N • �f) is the
`
`
`
`
`
`
`sampling interval, N�k is !'he uplink system bandwidth iri RBs, Ns�B = 12 is the number of
`
`
`
`
`subcarricrs per resource block, k(-) = k + LN�k N:8 /2J and Ok.f. is the content of subcaJTier
`
`
`k on symbol £. For PUSCH data SC-FDMA symbols, ak,i is obtained by DFT-spreading
`
`
`the data QAM symbols, [do,e, d1,e, ... , dMf�s<:H_uJ lO be lransmiued on data SC-FDMA
`
`symbol.(; (see [3], Section 5.3.3),
`
`SC
`
`. II
`
`(l7.2)
`ak,C = J "f PUSCH
`2, ... , M{cUSCH - I, where Ms1::USCH = M��SCH · Ns�B and M��SCH is the
`for k = 0, ! ,
`
`
`allocated PUSCH bandwidth in RBs.
`
`
`
`
`
`
`As explained in Sec£ion 4.4.1, a Hybrid Automntic Repeal reQuesl (HARQ) scheme
`
`
`is used, which in the uplink is synchronous, using N-channel stop and wait. This
`means
`
`
`that retransmissions occur in specific periodically-occurring subfr.tmes (HARQ channels).
`
`Further details of the HARQ operation are given in Section J0.3. 2.5.
`
`17.2.l Scheduling Supported in LTE SC-FDMA Uplink
`
`
`
`
`In the LTE uplink, both frequency-selective scheduling and non-freq uency-selective schedul­
`
`ing are supported. The fo!ll1er is based on the eNodeB exploiting available channel
`
`
`knowledge to schedule a UE to trn11smil using specific Resource Blocks (RBs) in the
`
`
`frequency domain where the channel response is good. The latter does not make use of
`
`
`
`
`
`frequency-specific channel knowledge, but rather aims to benefit from frequency diversity
`
`during the transmission of each transport block. The possible techniques supported in LTE
`
`are discussed in more detail be[ow. Intermediate approaches are also possible.
`
`
`17.2.1.l Frequency-Selective Sclieduling
`
`With frequency-seleclivescheduling, the same localized2 allocation of transmission resources
`
`is typically used in both slots of a subframe -there is no frequency hopping during a
`
`
`subframe. The frequency-domain RB ailocation and the Modula.lion and Coding Scheme
`
`
`(MCS) are chosen based on the location and quality ol' an above-average gain in the uplink
`
`
`2Localirect means that aflocatcd RBs are consecutive in the frequency domain.
`
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`
`
`channel response [4J. In order to enable frequency-selective scheduling, timely channel
`
`
`
`
`
`quality information is needed at the eNodeB. One method for obtaining such information in
`
`
`
`
`
`
`
`LTE is by uplink channel sounding using the SRS described in Section 16.6. The performance
`
`
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`
`of frequency-selective scheduling using the SRS depends on the sounding bandwidth and the
`
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`
`quality of the channel estimate, the latter being a function of the transmission power spectral
`
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`density used for the SRS. With a large sounding bandwidth, link quality can be evaluated
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`
`on a larger number of RBs. However, this is likely to lead to the SRS being transmitted
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`at a lower power density, due to the limited total UE transmit power, and this reduces the
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`accuracy of lhe estimate for each RB within the sounding bandwidth. Conversely, sounding a
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`smaller bandwidth can improve channel estimation on the sounded RBs but results in missing
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`channel information for certain parLs of the channel bandwidth, thus risking exclusion of
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`the best quality RBs. As an ,;xample, experiments performed in reference [5] sho\v that at
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`least for a bandwidth of 5 MHz, frequency-selective scheduling based on full-band sounding
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`outperforms narrower bandwidth sounding.
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`
`17.2.1.2
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`
`
`Frequency-Diverse or Non-Selective Scheduling
`
`There are cases when no, or limited, frequency-specific channel quality information is
`
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`available, for example because of SRS overhead constraints or high Doppler conditions. In
`
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`such cases, it is preferable to exploit Lhe frequency diversity ofLTE's wideband channel.
`
`
`
`In LTE, frequency hopping of a localized transmission is used to provide frequency­
`
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`
`diversity. Two hopping modes are supported - hopping only between subframes (inter­
`
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`subframe hopping), or hopping both between and within subframes (inter-and intra-subframe
`
`
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`
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`hopping), These modes are illustrated in Figure 17 .3, Cell-specific broadcast signalling is
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`
`
`used to configure the hopping mode (see [6], Section 8.4).
`In case of intra-subframe hopping, a frequency hop occurs at the slot boundary in the
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`middle of a subframe; this provides frequency diversity within a codeword (i.e. within a
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`single transmission of transport block). On the other hand, inter-subframe hopping provides
`frequency diversity
`
`
`between HARQ retransmissions of a transport block, as the
`frequency
`
`
`allocation hops every allocated subframe.
`Two methods are defined for the frequency hopping allocation (see [6], Section 8.4):
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`either a pre-determined pseudo-random frequency hopping pattern (see reference [3],
`
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`Section 5.3.4), or an explicit hopping offset signalled in the UL resource grant on the
`
`PDCCH. For uplink system bandwidths less than 50 RBs, the size of the hopping offset
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`{modulo the system bandwidth) is approximately half the number of RBs available for
`
`
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`PUSCH transmissions (i.e. LN{�SCH j2J), while for uplink system bandwidths of 50 RBs
`
`
`or more, the possible hopping offsets are LNl:;�SCH/2J,
`and ±LNf�SCH/4J (see [6],
`
`Section 8.4).
`Signalling the frequency hop via the uplink resource grant can be used for frequency semi­
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`selective scheduling [7], in which the frequency resource is assigned selectively for the first
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`slot of a subframe and frequency diversity is also achieved by hopping to a different frequency
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`in the second slot. In some scenarios this may yield intermediate performance between that
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`of fully frequency-selective and ful1y non-selective scheduling; this may be seen as one way
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`to reduce the sounding overhead typically needed for fully frequency-selective scheduling.
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`!
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`UPLlf\lK PHYSICAL CHANNEL STRUCTURE
`
`381
`
`Ill.. SUBFRAME k
`1 ms
`I
`I
`Nfi -l ._:;;;_,,:,�;..PUCCH·•���-� --...puccH---t
`
`UL SUBF�E �+8
`
`1ms
`1
`,
`f:J'UCCH�.,:=.�·.:..� ::c;,.�i PlJCCH��
`
`N� -J !.�.;�·�:-
`f.;l�Jr:!:,1.��
`
`;;!:l:Ji'Ft;.iit �.j;l�,;i•�:• ·m . .--!;.a<1-..,;11
`
`·%,FJ.'t?�t:il f.�l[��H;;: -1�-nn�:·l� �=::tt.�:
`
`c:::J
`
`PUSGH RS
`
`C:=]
`
`-
`.
`
`.
`
`. �
`
`1ntrn-subframe
`hc;ppi,,g
`N!-;1:4!��-l=llnle-r-.sc.n,rrame
`h�ppoig
`j.-: :· ... ··_:�.-fNo hoppi r..g
`(FSSorFNS)
`
`---
`
`'.-,\'..._'�·-··:,= :.... :,:,·.'-·'· ·:..
`
`·.-. ··,',,:-.·-::'} •• ;._._,,;:·-.... .-,.·
`
`I ·l · -�I�-�-".,,., .-.. ··.> .. : .. >\ ... _.· .. · : . .... . ·-..
`
`RB7
`R97
`RB6 -:�N l:ru,; �1:�F';'itt ;i��:lt-t; 1!.'0;�\:�Vt,�
`
`RB8
`
`RBS iJ!i�j rm.·:.;-:, WKt::ri�:� ,:1t7�_t:m� lf-.�tt�-� �J
`
`R84
`:: -----+-------1
`RB3 1-- -- - - +- -- -- --1
`!<B2
`RB2 t---- - - +-- - -- --1
`:•
`RB1
`Rln
`.j,
`
`ABO - PUCCH__,,..._ ·.::.,,fi;f,�FUCCHt?::f.:.C:.� 12 �ttsP.1$ RBO �P UCCH= -��� PUCC.Ht)-)':1,; 12 sab:.arriei:$
`)• sio: 1 -, f
`!o.t
`sl�t 1 -i t
`,'4· slot a
`•
`+----S
`
`RB3
`
`
`
`Figure 17 3 Uplink physical data channel processing,
`
`
`
`17.3 Uplink Control Channel Design
`
`In general, uplink control signalling in mobile communications systems can be divided into
`
`
`
`
`
`
`
`two categories:
`
`•Data-associated control signalling. Conlrol signalling which is always transmitted
`
`
`
`
`
`together with uplink data, and is used in the processing of that data. Examples include
`
`
`transport format indications, 'new data' indicators, and MIMO parameters.
`
`•Data non-associated control signalling. Control signalling not associated with
`
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`
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`uplink data, transmitted independently of any uplink data packet. Examples include
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`
`
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`HARQ Acknowledgments (ACK/NACK) for downlink datn packets, Channel Quality
`
`
`Indicators (CQis), and MilVIO feedback (such as Rank Indicator (RI) or Precoding
`
`
`Matrix: Indicator (PMI)) for downlink transmissions. Scheduling Requests (SRs) for
`
`
`
`uplink transmissions also fall into this category,
`
`In LTE, the low signalling latency afforded by the shon subframe duration of l ms,
`
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`
`together with the orthogonal nature of the uplink multiple access scheme which necessitates
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`centralized resource allocation, make it approprime for the eNodeB to be in full control of
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`
`
`the uplink transmission parameters. Consequently uplink data-associated control signalling is
`
`
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`
`
`not necessary in LTE, as the relevant information is already known to tbe eNodeB. Therefore
`
`
`
`
`
`only data non-associated conLrol signalling is supported in the LTE uplink.
`
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`382
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`LTE -THE UMTS LONG TERM'. EVOLUTION
`
`When simultaneous uplink PUSCH data and control signalling is scheduled for a UE, the
`
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`control signalling is multiplexed together with the data prior to !he DFT spreading, in order to
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`
`preserve lhe single-carrier low-Cubic Meuic (CM) property of the uplink transmission. The
`channel,
`
`control signaHing
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`
`
`uplink control PUCCH, is used by a UE to transmit any necessary
`
`
`only in subframes in which the UE has not been allocated any RBs for PUSCH transmission.
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`
`
`In the design of the PUCCH, special consideration wac;; given to maintaining a low CM [8J.
`
`
`
`17.3.1 Physical Uplink Control Channel (PUCCH) Structure
`
`
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`
`
`The control signalling on the PUCCH is transmitted in a freque11cy region on the edges of
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`
`
`the system bandwidth.
`In order to minimize the resources needed for transmission of control signalling, the
`
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`
`
`PUCCH in LTE is designed to exploit frequency diversily: each PUCCH transmission in one
`
`
`
`subframe is comprised of a single (0.5 ms) RB at or near one edge of the system bandwidth,
`followed {in the second slot of the subframe) by a second RB at or near the opposite
`edge
`
`
`
`of the system bandwidlh, as shown in Figure 17.5; together, the two RBs are referred to as a
`
`
`
`
`
`This design can achieve a frequency diversity benefit of approximately 2 dB­
`PUCCH region.
`
`
`
`compared to transmission in the same RB throughout !he subframe.
`
`Al the same time, the narrow bandwidth of the PUCCH in each slot (only a single
`
`
`
`
`resource block) maxjmizes the power per subcarrier for a given total transmission power
`
`
`
`coverage requirements. (see Figure 17 A), and therefore helps to fulfil stringent
`
`j+1 �subcarrier
`subcarrief j
`
`
`�
`
`I symbol 1+1 symbol
`I
`!es >; >·!i�s;_;:,_
`j
`
`K
`"'E !K
`.( I
`�
`
`!=L_ ...... , < E .. --.
`
`Figure 17.4 The link budget of a two-slot narrowband transmission exceeds that of a one-slot
`
`
`
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`
`
`wider-band transmission, given equal coding gain.
`
`Positioning the control regions at the edges of the system bandwidth has a number of
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`
`
`advantages, including the following:
`
`maximized by allowing hopping is •The frequency diversity achieved through frequency
`
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`
`
`hopping from one edge of the band to the of.her.
`
`•Out-Of-Band (OOB) emissions are smaller if a UE is only transmitting on a single
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`
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`RB per slot compared to multiple RBs. The PUCCH regions can therefore serve as a
`
`
`
`kind of guard band between the wider-bandwidth PUSCH t�imsmissions of adjacent
`
`
`
`
`carriers, and therefore can improve coexistence [9].
`
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`

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`�---.. --
`
`TJPLINK PHYSICAL CHANNEL STRUCTURE
`
`383
`
`
`
`Table 17 .1 Typical numbers of PUCCH regions.
`
`Number of PUCCH regions
`0.5 ms RBs subframe Bandwidth (MHz) Number of
`
`
`2
`IA
`4
`3
`8
`5
`16
`JO
`32
`20
`
`2
`4
`8
`16
`
`• Using control regions on the band edges maximizes the achievable PUSCH data rate,
`
`
`
`
`
`
`
`as the entire central portion of the band can be allocated to a single UE. If the control
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`
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`regions were in the central portion of a carrier, a UE bandwidth allocation would be
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`
`
`limited to one side of the control region in order to maintain the single-carrier nature
`
`
`
`of the signal, thus limiting the maximum data achievable rate.
`
`dataregions on the band edges impose fewer constraints on the uplink
`
`
`
`•Control
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`
`
`scheduling, both with and without inter-/intra-subframe frequency hopping.
`
`The number of resource blocks (in each slot) that can be used for PUCCH transmission
`
`
`
`
`
`within the cell is N�}ICCH (parameter
`
`
`'pusch-HoppingOffset'). This is indicated to the UEs
`
`
`
`
`in the cell through broadcast signalling. Note Lhat the number or PUCCH RBs per slot is the
`
`
`
`
`
`
`same as the number of PUCCH regions per subframe. Some typical expected numbers of
`
`
`
`
`
`PUCCH regions for different LTE bandwidths are shown in Table 17. I.
`
`
`
`
`Figures 17.5 and 17.6 show respectively examples of even and odd numbers of PUCCH
`
`
`
`regions being configured in a cell. In the case of an even number of PUCCH regions
`
`
`
`(Figure 17.5), both RBs of each RB-pair (e.g. RB-pair 2 and RB-pair Ni/.k - 3) are used
`
`
`for PUCCH transmission. However, for the case of an odd number of PUCCH regions
`
`
`
`
`(Figure 17.6), one RB of an RB-pair in each slot is not used for PUCCH (e.g. one RB of
`
`
`
`RB-pair 2 and RB-pair Nit/; 3 is unused). In order to exploit rhe unused RBs in each slot in
`
`
`
`
`the case of an odd number of PUCCH regions, the eNodeB may schedule a UE with an intra­
`
`
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`
`
`
`subframe frequency hopping (i.e. mirror hopping) PUSCH allocation in the unused RBs.
`
`
`
`
`
`Alternatively, a UE can be assigned a localized allocation which includes the unused RB­
`
`
`UE will transmit PUSCH data on pair, (e.g. RB-pair 2 or RB-pair N�k -3). In this case, the
`
`
`
`both RBs of the RB-pair, assuming that neither of the RBs are used for PUCCH by any UE in
`
`
`
`
`the subframe. Thus, the eNodeB scheduler can appropriately schedule PUSCH transmission
`
`
`
`
`
`(miITor hopping or localized) on the PUCCH RBs when they are under-utilized. The eNodeB
`
`
`
`may also choose to schedule low-power PUSCH transmission (e.g. from UEs close to the
`
`
`eNodeB) in the outer RBs of the configured PUCCH region, while the inner PUCCH region
`
`
`
`
`is used for PUCCH signalling. This can provide further reduction in OOB emissions which
`
`
`
`
`is necessary in some frequency bands, by moving higher-power PUCCH transmission (e.g.
`
`
`
`those from cell-edge UEs) slightly away from the edge of the band.
`
`-
`
`
`
`17.3.1.1 Multiplexing ofUEs within a PUCCH Region
`
`
`
`Control signalling from multiple UEs can be multiplexed into a single PUCCH region using
`
`
`
`
`
`
`
`
`orthogonal Code Division Multiplexing (CDM). In some scenarios this can have benefits
`
`IPR2022-00648
`Apple EX1017 Page 71
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`

`

`384
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`LTE -THE UIVITS LONG TERM EVOLUTION
`
`N){i -I
`N};fj - 2 r-'---:�:-::: :';--;-�---=- ��
`N�fi -3
`N;i; -4 1----- --"'c- c-- ----+ - -- ----, ..:,.,-,------1
`Nf� -5
`
`□PUSCH
`@j PUSCH RS
`
`RB4
`RB3
`RB2
`RB1
`RBO
`
`Figure 17 .5 PUCCH uplink control su11cture with an even number of 'PUCCH Control
`
`
`Regions' (Nf�CCH = 6). Reproduced
`
`by permission of© 3GPP.
`
`N j{f; -1 C;��-t.RUC_e1:1r rii::;1 !J.��
`
`NI{� - 2 · PUCCH m� -
`N�}-3
`, -·
`N'if; - 41-----, --- -- �;-- -_.;.i-------1
`N'i{fi -5
`
`□PUSCH
`EJ PUSCH RS
`
`RB4
`RB3
`R82
`RB1
`RBO
`
`
`
`
`
`
`
`Figure 17 .6 Example of odd number of PUCCH conlrol RBs or regions (Nk}FCH = 5).
`
`over a pure FDM approach, as it reduces the need to limit the power differentials between
`
`
`
`
`
`
`
`lhe PUCCH transmissions of different UEs. One technique to provide orthogonality bet ween
`
`
`
`
`
`UEs is by using cyclic time shifts of a sequence with suitable propenies, as explained in
`
`
`
`
`Section 16.2.2. In a given SC-FDMA symbol, different cyclic time shifts of a wavefom1 (e.g.
`
`
`
`
`a Zadoff-Chu (ZC) sequence as explained in Section 7.2.J) are modulated with a UE-specific
`
`
`
`QAM symbol carrying the necessary control signalling information, with the supported
`
`
`
`
`number of cyclic time-shifts determining the number of UEs which can be multiplexed per
`
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`UPLINK PHYSICAL CHANIVEL STRUCTURE
`
`385
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`SC-POMA symbol. As the PUCCH RB spans 12 subcarriers, and assuming the channel is
`
`
`
`
`
`
`
`
`
`
`approximately constant over the RB (i.e. a single-tap channel), the LTE PUCCH supports up
`
`to 12 cyclic shifts per PUCCH RB.
`For conu·ol information transmissions wich a small number of control signalling bits, such
`
`
`
`
`as 1-or 2-bit positive/negative acknowledgments (ACK/NACK), orthogonality is achieved
`
`
`
`
`belween UEs by a combination of cyclic time shifts within an SC-FOMA symbol and SC­
`
`
`
`
`
`
`POMA symbol time-domain spreading with orthogonal spreading codes, i.e. modulating the
`
`
`
`
`SC-FDMA symbols by elements of an orthogonal spreading code {10]. COM of multiple
`
`
`
`
`UEs is used rather than Time Domain Multiplexing (TOM) because COM enables the time
`
`
`
`
`
`
`duration of the transmission to be longer, which increases the total transmitted energy per
`
`
`signalling message in the case of a power-limited UE.
`
`
`Thus, the LTE PUCCH control structure uses frequency-domain code multiplexing
`
`
`
`
`(different cyclic time shifts of a base sequence) and/or time-domain code multiplexing
`
`
`
`
`
`
`
`(different orthogonal block spreading codes), thereby providing an efficient, orthogonal
`
`
`
`cornrol channel which supports small payloads (up to 22 coded bits) from multiple UEs
`
`
`
`
`simultaneously, together with and good operational capability at low SNR.
`
`
`
`17.3.1.2
`
`
`
`Control Signalling Information Carried on PUCCH
`
`
`
`The control signalling information carried on the PUCCH can consist of:
`
`
`
`o Scheduling Requests (SRs) (see Section 4A.2.2).
`
`
`
`•HARQ ACK/NACK in response to downlink data packets on (PDSCH). One ACK/
`
`
`
`
`NACK bit is transmitted in case of single codeword d