03_CT82353EN01GLA1_LTE FDD and TDD Mode - Radio Channel Types

CT82353EN01GLA1 ©2014 Nokia Solutions and Networks. All rights reserved.

LTE FDD and TDD Mode: Radio Channel Types

LTE Air Interface Course

2 CT82353EN01GLA1 ©2014 Nokia Solutions and Networks. All rights reserved.

Nokia Solutions and Networks Academy

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At the end of this module, you will be able to:

• Name the LTE radio channels (logical, transport and physical) and their

main features/functionalities

• Describe the multiplexing of LTE channels

Module Objectives



LTE Channel Architecture

Logical Channel Types

Transport Channel Types

Physical Channel Types

Multiplexing of channels


MAC Sublayer

Physical Layer

RRC Sublayer User Data Plane

PDCP Sublayer

RLC Sublayer

MAC Sublayer

Radio Bearers

E-RAB

Signaling Radio Bearers

Logical Channels

Transport Channels

Physical Channels



LTE Channel Architecture, cont.

The LTE Channel Architecture defines E-RAB channels, Radio Bearer (RB) channels, Signaling Radio Bearer (SRB) channels, Logical Channels, Transport Channels, and Physical Channels. In general, each category behaves as a service access point between adjacent protocol layers.

3GPP TS 36.211 Physical Channel and Modulation

3GPP TS 36.321 Medium Access Control (MAC) Protocol Specification

3GPP TS 36.322 Radio Link Control (RLC) Protocol Specification


MAC Sublayer

Physical Layer


PDCP Sublayer

RLC Sublayer

MAC Sublayer

Radio Bearers

E-RAB

Signaling Radio Bearers

Logical Channels

Transport Channels

Physical Channels



LTE Channel Architecture, cont. E-RAB - An E-RAB channel carries one or more service data flows between a UE and the EPC.

Radio Bearer - A Radio Bearer channel transports the data packets of an E-RAB from the eNodeB toward the UE. Each E-RAB has a one-to-one mapping with a radio bearer.

Signaling Radio Bearer - A Signaling Radio Bearer (SRB) channel transports signaling packets between the RRC Sublayer and the PDCP Sublayer.

Logical Channel - A Logical Channel transports control or data traffic between the RLC Sublayer and the MAC Sublayer. Logical control channels are mapped to signaling radio bearer channels, while logical traffic channels are mapped to radio bearer channels. Logical Channels describe transmission reliability (RLC Acknowledged Mode, etc.).

Transport Channel - A Transport Channel forwards control or data traffic between the MAC Sublayer and the Physical Layer. Each Logical Channel is mapped to a transport channel. Transport Channels describe how the information will be formatted before being transmitted (coding, transport block size, etc.).

Physical Channel - A Physical Channel provides the transmission media (resource elements) through which the information is actually transmitted. Each Transport Channel is mapped to a physical channel.


MAC Sublayer


PDCP Sublayer

RLC Sublayer

MAC Sublayer

Logi

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Radio

Bearers

Signaling

Radio Bearers

Control

Channels

Traffic

Channels

Logical Channels

Rad

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Logical Channels provide control and data transport between the RLC and MAC Sublayers. Signaling traffic is carried by control channels (xCCH), and data traffic is carried by traffic channels (xTCH). Control channels are mapped to SRB channels, and traffic channels are mapped to user plane radio bearer channels.









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RLC Sublayer

MAC Sublayer

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Logical Channel Types, cont. 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 and downlink channel. 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.

DCCH (Dedicated Control Channel): The DCCH is a bidirectional RRC signaling channel used for point-to-point

(dedicated) RRC and NAS signaling procedures. It is the main signaling channel to be used by RRC_CONNECTED

UEs.

MCCH (Multicast Control Channel): The MCCH is associated with MBMS. It allows the eNB to inform UEs that want

to listen to broadcast or multicast service traffic about availability of such services and about the associated MBMS

radio bearer (point-to-multipoint) radio bearers.

On the traffic channel side we have currently only two types defined:

DTCH (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 be bidirectional, uplink only or downlink only.

DTCH are of course point-to-point.

MTCH (Multicast Traffic Channel): The MTCH is a point-to-multipoint traffic channel for MBMS. It carries IP traffic for

broadcast or multicast services driven by the MBMS feature.


Logical Channel • type of information;

• MAC priority;

• UE identification;

Control Channel

• signaling info (RRC);

Traffic Channel

• user plane data (IP)

BCCH • broadcast control ch.;

• system information;

• downlink only;

PCCH • paging control ch.;

• paging message for

LTE_IDLE UE;

• downlink only;

CCCH

• common control ch.;

• initial access

signaling for

RRC_IDLE UE;

MCCH • multicast control ch.;

• MBMS control

information for MTCH;

• downlink only;

DCCH

• dedicated control ch.;

• dedicated RRC

signaling with one UE;

• bi-directional;

DTCH

• dedicated traffic

channel;

• IP user plane data;

• bi- or uni-directional;

MTCH

• multicast traffic ch.;

• MBMS traffic for

broadcast or multicast

MBMS services;

• downlink only;









MAC Sublayer

Physical Layer

MAC Sublayer

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Transport Channel Types, cont. 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.

MCH (Multicast Channel): The MCH is used for broadcast and multicast MBMS services. It thus carries MTCH

and MCCH. It will allow at least QPSK and 16QAM as modulation scheme, 64QAM is under investigation.

Obviously HARQ cannot be supported as MTCH/MCCH are point-to-multipoint channels. This channel 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 use the same MCH

configuration and must be synchronized with each other.


MAC Sublayer

Physical Layer

MAC Sublayer

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In the uplink there are only two transport channel defined:

RACH (Random Access Channel): The RACH is used as initial access request by the UE to the network.

Currently it does not contain logical information, rather the RACH is formed by a special layer 1 preamble that

acts as a channel request message. It is under investigation whether the RACH should be able to carry

logical channel information.

UL-SCH (UL Shared Channel): The UL-SCH is the only uplink transport channel able to carry logical channel

data. Thus CCCH, DTCH and DCCH run over this channel. It supports HARQ and at least QPKS and

16QAM.


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;

Downlink TrCH

Uplink TrCH

BCH

• broadcast channel;

• carries BCCH;

PCH

• paging channel;

• carries PCCH;

MCH

• multicast channel;

• carries MTCH, MCCH;

DL-SCH

• downlink shared

channel;

• carries DCCH, DTCH,

BCCH, MTCH, MCCH;

• supports HARQ;

RACH

• random access channel;

• carries no logical

channel;

• only for initial L1 access

request;

UL-SCH • uplink shared channel;

• carries CCCH, DCCH,

DTCH;

• supports HARQ;


Physical Layer

MAC Sublayer

RLC Sublayer

MAC Sublayer

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Logical to Transport Channel Mapping

The graphic shows the mapping between the LTE Logical Channels and Transport Channels.









Physical Layer

DL Physical Channels

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DL Physical Channels, cont.

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.

PDCCH (Physical Downlink Control Channel): This is a pure physical layer control channel. It contains the

scheduler signaling to inform the UEs about the coming downlink (and maybe also uplink) resource block

assignments to PDSCH. The PDCCH will be sent in each Subframe shortly before PDSCH starts.


Physical Layer

DL Physical Channels

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DL Physical Channels, cont.

PCFICH (Physical Control Format Indicator Channel): The PCFICH is like the PDCCH a pure

physical layer control channel. It indicates how many OFDM symbols are used to encode the

PDCCH. So the order of decoding for a UE is to 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 the UE.

DL Synchronization Signal: There are two DL synchronization signals - a primary and a

secondary one. Both consist of predefined code sequence to be 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 there will be three distinct code sequences defined, which one is applicable for a cell is

determined by the cell identity. This can be used as some form of cell color code to distinguish

direct neighbors.

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.


Physical Layer

UL Physical Channels

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UL Physical Channels, cont.

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.

PRACH (Physical Random Access Channel): The PRACH carries the RACH. Currently this means, that the

PRACH simply transmits preamble sequences that act as initial access request for UL and DL resources when

the UE is RRC_IDLE.

Demodulation Reference Signal: Some OFDM symbols of the resource block assigned to PUCCH/PUSCH are

reserved for the demodulation reference signal. Like in downlink also here the reference signal is a predefined

code sequence that allows the eNB coherent decoding of the transmitted SC-FDMA signal. The eNB derives

from it phase and frequency correction, channel estimation and time synchronization.

Sounding 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 for efficient decoding, but also for efficient

channel dependent scheduling (CDS).


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


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


• pre-defined sequence

sent along with

PUSCH/PUCCH

• used for uplink channel


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;


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Physical Layer

Transport to Physical Channel Mapping

MAC Sublayer

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The graphic shows the mapping between LTE Transport Channels and Physical Channels. The PDCCH, PCFICH, PHICH, and PUCCH Physical Channels are not mapped to Transport Channels.









Uu Interface Sublayers Overview – worksheet 01

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03_CT82353EN01GLA1_LTE FDD and TDD Mode - Radio Channel Types