05 tm51175en02gla01 radio channel types

LTE FDD and TDD Mode: Radio Channel Types


Contents 1 Radio Channel Types 3 1.1 Logical Channel Types 4 1.2 Transport Channel Types 6 1.3 Physical Channel Types 8 1.4 Multiplexing of Channels 10

TM5117 LTE AIR INTERFACE 2010 Nokia Siemens Networks

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TM5117EN02GLA01 2010 Nokia Siemens Networks

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1 Radio Channel Types


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1.1 Logical Channel Types Logical channels are in a one-to-one fashion associated with radio bearers. Logical channel types are used to distinguish the type of information transmitted within the attached radio bearer. The two major groups of logical channel types are therefore control channels for signaling and traffic channels for IP user data. Currently the following logical channel types are defined for EUTRAN signaling:

BCCH (Broadcast Control Channel): The BCCH is used to transmit system information regarding access and non-access stratum. It allows the UE to retrieve cell and network configuration parameters (e.g. PLMN code, cell identity, cell re-selection parameters, etc.) required for normal operation within EUTRAN.

PCCH (Paging Control Channel): The PCCH is used to transmit the paging messages from RRC. Hence it is a downlink point-to-multipoint channel a UE is using when it is in LTE_IDLE mode.

CCCH (Common Control Channel): The CCCH is an uplink (NOTE: DL is under investigation.) RRC signaling channel used by UEs to do the initial access signaling when it is in RRC_IDLE state and wants to enter RRC_CONNECTED state. The UE will send only one message (RRC CONNECTION REQUEST) and the rest of the communication takes place on DCCH. CH (Dedicated Control Channel): The DCCH is a bidirectional RRC signaling channel used for point-to-point (dedicated) RRC and NAS signaling proce

DCdures.

MC It ut the associated

DTe bidirectional, uplink only or downlink only. DTCH

MTarries IP traffic for broadcast or multicast services driven

by the MBMS feature.

It is the main signaling channel to be used by RRC_CONNECTED UEs. CH (Multicast Control Channel): The MCCH is associated with MBMS.

allows the eNB to inform UEs that want to listen to broadcast or multicast service traffic about availability of such services and aboMBMS radio bearer (point-to-multipoint) radio bearers.

On the traffic channel side we have currently only two types defined: CH (Dedicated Traffic Channel): The DTCH is used for user radio bearers carrying IP traffic. The eNB connects DTCHs with their associated S1-U tunnel to the SAE GW. DTCH can bare of course point-to-point. CH (Multicast Traffic Channel): The MTCH is a point-to-multipoint traffic channel for MBMS. It c


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Logical ChannelLogical Channel type of information; MAC priority; UE identification;

type of information; MAC priority; UE identification;

Control ChannelControl Channel

signaling info (RRC); signaling info (RRC);

Traffic ChannelTraffic Channel

user plane data (IP) user plane data (IP)

BCCHBCCH broadcast control ch.; system information; downlink only;

broadcast control ch.; system information; downlink only;

PCCHPCCH paging control ch.; paging message for LTE_IDLE UE; downlink only;

paging control ch.; paging message for LTE_IDLE UE; downlink only;

CCCHCCCH

common control ch.; initial access signaling for RRC_IDLE UE;

common control ch.; initial access signaling for RRC_IDLE UE;

MCCHMCCH multicast control ch.; MBMS control information for MTCH; downlink only;

multicast control ch.; MBMS control information for MTCH; downlink only;

DCCHDCCH dedicated control ch.; dedicated RRC signaling with one UE; bi-directional;

dedicated control ch.; dedicated RRC signaling with one UE; bi-directional;

DTCHDTCH dedicated traffic channel; IP user plane data; bi- or uni-directional;

dedicated traffic channel; IP user plane data; bi- or uni-directional;

MTCHMTCH multicast traffic ch.; MBMS traffic for broadcast or multicast MBMS services; downlink only;

multicast traffic ch.; MBMS traffic for broadcast or multicast MBMS services; downlink only;

Fig. 1 Logical channel types.

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1.2 Transport Channel Types Transport channels are used as the basic transmission service offered by layer 1 to MAC. MAC will use transport channels to multiplex and demultiplex logical channels onto and from them. In contrast to logical channel types, referring to the type of information transmitted, transport channel types are used to indicate the transport characteristics. This means that certain transport channel type is associated with certain bit rates (transport block sizes, number of blocks), a transmission time interval (the time it takes to send one transport block set), delay, support for HARQ, support for beam-forming, support for DRX/DTX, and so on.

Transport channels are always unidirectional, in the downlink we have the following: BCH (Broadcast Channel): The BCH is a transport channel with fixed transport

format. It is used to transmit the BCCH in the entire cell. It will only support QPSK modulation and no HARQ or beam-forming is allowed.

PCH (Paging Channel): The PCH is used to carry the PCCH. In contrast to BCH there might be beam-forming applied to PCH, but still no HARQ is available. Also the channel supports at least QPSK and 16QAM as modulation scheme and DRX.

DL-SCH (DL Shared Channel): This is the major transport channel in the downlink direction. It is used to carry mainly DCCH and DTCH. But also BCCH, MCCH and if required MTCH can be sent on it. The channel supports HARQ, beam-forming and all modulation schemes QPSK, 16QAM and 64QAM. The DL-SCH will support DRX and DTX on UE side to reduce power consumption of end terminals. H (Multicast Channel): The MCH is used for broadcast and multicast MB

services. It thus carries MTCH and MCCH. It will allow at least QPSK and 16QAM as modulation scheme, 64QAM is under investigation. Obviously HARcannot be supported as MTCH/MCCH are point-to-multipoint channels. Thchannel has a unique special property, as UEs are able to combine MCH signals from different cells using the same frequency (MBSFN= Multicast Broadcast Single Frequency Networks). In this case all MBSFN cells must

MC MS Q

is

onized with each other.

RA rather

tigation whether the RACH should be able to

ULCCH run over this

channel. It supports HARQ and at least QPKS and 16QAM.

use the same MCH configuration and must be synchrIn the uplink there are only two transport channel defined:

CH (Random Access Channel): The RACH is used as initial access request by the UE to the network. Currently it does not contain logical information,the RACH is formed by a special layer 1 preamble that acts as a channel request message. It is under invescarry logical channel information. -SCH (UL Shared Channel): The UL-SCH is the only uplink transport channel able to carry logical channel data. Thus CCCH, DTCH and D


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Transport Channel (TrCH)Transport Channel (TrCH)

transfer characteristics: delay, collision risk; supported block sizes and number of blocks; support for HARQ; support for beam-forming; support for DRX/DTX; coding (reliability); static | dynamic resource allocation; support for QPSK, 16QAM, 64QAM;

transfer characteristics: delay, collision risk; supported block sizes and number of blocks; support for HARQ; support for beam-forming; support for DRX/DTX; coding (reliability); static | dynamic resource allocation; support for QPSK, 16QAM, 64QAM;Downlink TrCHDownlink TrCH Uplink TrCHUplink TrCH

BCHBCH

broadcast channel; carries BCCH; broadcast channel; carries BCCH;

PCHPCH

paging channel; carries PCCH; paging channel; carries PCCH;

MCHMCH

multicast channel; carries MTCH, MCCH; multicast channel; carries MTCH, MCCH;

DL-SCHDL-SCH downlink shared channel; carries DCCH, DTCH, BCCH, MTCH, MCCH; supports HARQ;

downlink shared channel; carries DCCH, DTCH, BCCH, MTCH, MCCH; supports HARQ;

RACHRACH random access channel; carries no logical channel; only for initial L1 access request;

random access channel; carries no logical channel; only for initial L1 access request;

UL-SCHUL-SCH uplink shared channel; carries CCCH, DCCH, DTCH; supports HARQ;

uplink shared channel; carries CCCH, DCCH, DTCH; supports HARQ;

Fig. 2 Transport channel types.

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1.3 Physical Channel Types The physical layer uses resource blocks (e.g. 12 subcarriers with 6 or 7 OFDM symbols) to transmit binary coded information in QPKS, 16QAM or 64QAM or OOK modulation form. Physical channels determine how data is processed and then mapped via dynamical scheduling onto resource blocks. Thus physical channels also in EUTRAN represent the available physical resources. Like transport channels, also physical channels are unidirectional. There is usually a fixed linkage between transport channel types and physical channel type used to transmit the transport blocks. Next to the physical channels that are used to carry transport channels, there are also physical channels that carry physical layer control data and physical signals that are mainly used for synchronization and measurement purposes.

On the downlink side we have the following: PBCH (Physical Broadcast Channel): The PBCH is the physical channel used to

carry BCH (BCCH), in other words on this channel the system information can be found. It will use a fixed mapping onto resource blocks. There will be one PBCH per cell.

PDSCH (Physical Downlink Shared Channel): The PDSCH can carry DL-SCH or PCH. Thus this channel type will allocate most of the capacity in a cell. It is still under investigation how many PDSCHs a cell can have and how many PCH and DL-SCH a single PDSCH can carry.

PMCH (Physical Multicast Channel): This channel type is used to carry MCH. It implements the option of MBSFN where a UE receives the PMCH from several cells operating in the same area on the same frequency band. All the PMCH will be jointly decoded by the UE. This would allow a UE to do cell re-selection without interrupting MBMS services. CCH (Physical Downlink Control Channel): This is a pure physical layer control channel. It contains the scheduler signaling to inform the UEs aboucoming downlink (and maybe also uplink) resource block assignments to PDSCH

PDt the

. The PDCCH will be sent in each subframe shortly before PDSCH

PC e UE is

e UE. DL

be

l

can be used as some form of cell color code to distinguish direct neighbors.

starts. FICH (Physical Control Format Indicator Channel): The PCFICH is like thPDCCH a pure physical layer control channel. It indicates how many OFDM symbols are used to encode the PDCCH. So the order of decoding for ato read first the PCFICH to get the PDCCH format. Then the PDCCH is decoded to find out which resource blocks to the PDSCH of interest for th Synchronization Signal: There are two DL synchronization signals - a primary and a secondary one. Both consist of predefined code sequence to used for cell detection and initial time and frequency synchronization. Both synchronization sequences are transmitted within slot 0 and slot 10 of each radio frame (frame type 1). The synchronization signals always use 2 subcarrier centered around the DC subcarrier. For the primary synchronization signal therewill be three distinct code sequences defined, which one is applicable for a celis determined by the cell identity. This


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Physical Channels / SignalsPhysical Channels / Signals

set of OFDM/SC-FDMA resource elements; carry higher layer data (physical channel PhyCH) or used internally by L1 (physical channel/signal);

set of OFDM/SC-FDMA resource elements; carry higher layer data (physical channel PhyCH) or used internally by L1 (physical channel/signal);

Downlink PhyCHDownlink PhyCH Uplink PhyCHUplink PhyCH

PBCHPBCH

physical broadcast ch.; carries BCH (BCCH); physical broadcast ch.; carries BCH (BCCH);

PDSCHPDSCH

phys. DL shared channel; carries PCH and DL-SCH; phys. DL shared channel; carries PCH and DL-SCH;

PMCHPMCH

phys. multicast channel; carries MCH; phys. multicast channel; carries MCH;

PDCCHPDCCH

phys. DL control channel; L1 control information (scheduling assignments);

phys. DL control channel; L1 control information (scheduling assignments);

PUSCHPUSCH

phys. UL shared channel; carries UL-SCH; phys. UL shared channel; carries UL-SCH;

PRACHPRACH phys. random access (channel); carries RACH (access request preamble); [in TS 36.211 referenced as signal, not as channel]

phys. random access (channel); carries RACH (access request preamble); [in TS 36.211 referenced as signal, not as channel]

PCFICHPCFICH phys. control format indicator channel L1 control information (no. of ODFM symbols used for PDCCH);

phys. control format indicator channel L1 control information (no. of ODFM symbols used for PDCCH);

Downlink SignalDownlink Signal

DL reference signalDL reference signal

pre-defined 2-dimensional orthogonal/pseudo-noise sequence; used for DL channel estimation, demodulation;

pre-defined 2-dimensional orthogonal/pseudo-noise sequence; used for DL channel estimation, demodulation;

DL synch. signalDL synch. signal

1 of 3 pre-defined sequences (Zadoff-Chu); associated with cell-id; used for cell detection and initial time/phase synch.;

1 of 3 pre-defined sequences (Zadoff-Chu); associated with cell-id; used for cell detection and initial time/phase synch.;

PUCCHPUCCH

phys. UL control channel; L1 information phys. UL control channel; L1 information

Uplink SignalsUplink Signals

Demodulation ref. signalDemodulation ref. signal

pre-defined sequence sent along with PUSCH/PUCCH used for uplink channel estimation, demodulation;

pre-defined sequence sent along with PUSCH/PUCCH used for uplink channel estimation, demodulation;

Sounding ref. signalSounding ref. signal

pre-defined (long) sequence sent alone; used by NW to optimize channel dependent scheduling;

pre-defined (long) sequence sent alone; used by NW to optimize channel dependent scheduling;

Fig. 3 Physical channel types.

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DL Reference Signal: Reference signals allow coherent decoding and

permanently repeated channel estimation. Therefore in each slot (and each resource block) some OFDM symbols are reserved for reference signals and cannot be used for data transmission. The reference signals itself are created from an orthogonal and a pseudo-noise sequence. This allows efficient channel and phase detection at the receiver side.

In the uplink there some less physical channels defined: PUSCH (Physical Uplink Shared Channel): The PUSCH is the major uplink

channel, because on it we will find the transport blocks of UL-SCH on which all radio bearers uplink occur. Like PDSCH also the PUSCH is dynamically assigned to uplink resource blocks. This happens via so called UL Assignments which are not completely specified yet. The PUSCH supports DTX, HARQ and at least QPSK and 16QAM. 64QAM is under investigation for this channel.

PUCCH (Physical Uplink Control Channel): This is a pure physical layer control channel. One idea is to use this channel for UL capacity requests and HARQ ACK/NACK indications by the UE as well as CQI (Carrier Quality Indication) feedback information to optimize CDS and MIMO. ACH (Physical Random Access Channel): The PRACH carries the RACH. Currently this means, that the PRACH simply transmits preamble sequencethat act as in

PRs

itial access request for UL and DL resources when the UE is

Del.

e ase and frequency correction, channel estimation and

So

r efficient decoding, but also for efficient channel dependent scheduling (CDS).

1.4 Multiplexing of Channels

eir multiplexing. The multiplexing arrows are shown from point of iew of the UE.

RRC_IDLE. modulation Reference Signal: Some OFDM symbols of the resource block assigned to PUCCH/PUSCH are reserved for the demodulation reference signaLike in downlink also here the reference signal is a predefined code sequence that allows the eNB coherent decoding of the transmitted SC-FDMA signal. TheNB derives from it phtime synchronization. unding Reference Signal: The sounding reference signal is a very long reference sequence that is transmitted by the UE only on explicit request by the network. It is used for a very detailed channel estimation especially when MIMO is in use. This information is required fo

The following figure summarizes the logical, transport and physical channels of EUTRAN and thv


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PBCHPBCH

PMCHPMCH

PDSCHPDSCH

PDCCHPDCCH

PCFICHPCFICH

DL referenceDL reference

DL synch.DL synch.

PUSCHPUSCH

PUCCHPUCCH

PRACHPRACH

Demod. Ref.Demod. Ref.

Sounding Ref.Sounding Ref.

BCHBCH

PCHPCH

MCHMCH

DL-SCHDL-SCH

RACHRACH

UL-SCHUL-SCH

BCCHBCCH

PCCHPCCH

CCCHCCCH

MCCHMCCH

DCCHDCCH

DTCHDTCH

MTCHMTCH

DL TrCH

UL TrCH

TrCH PhysicalLogCH

Fig. 4 Multiplexing of channels.


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05 tm51175en02gla01 radio channel types

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