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LTE Radio Channel Type
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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
Legal notice
Intellectual Property Rights
All copyrights and intellectual property rights for Nokia Solutions and Networks training documentation, product documentation and slide presentation material, all of which are forthwith known as Nokia Solutions and Networks training material, are the exclusive property of Nokia Solutions and Networks. Nokia Solutions and Networks owns the rights to copying, modification, translation, adaptation or derivatives including any improvements or developments. Nokia Solutions and Networks has the sole right to copy, distribute, amend, modify, develop, license, sublicense, sell, transfer and assign the Nokia Solutions and Networks training material. Individuals can use the Nokia Solutions and Networks training material for their own personal self-development only, those same individuals cannot subsequently pass on that same Intellectual Property to others without the prior written agreement of Nokia Solutions and Networks. The Nokia Solutions and Networks training material cannot be used outside of an agreed Nokia Solutions and Networks training session for development of groups without the prior written agreement of Nokia Solutions and Networks.
4 CT82353EN01GLA1 ©2014 Nokia Solutions and Networks. All rights reserved.
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
5 CT82353EN01GLA1 ©2014 Nokia Solutions and Networks. All rights reserved.
LTE FDD and TDD Mode: Radio Channel Types
LTE Channel Architecture
Logical Channel Types
Transport Channel Types
Physical Channel Types
Multiplexing of channels
6 CT82353EN01GLA1 ©2014 Nokia Solutions and Networks. All rights reserved.
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
7 CT82353EN01GLA1 ©2014 Nokia Solutions and Networks. All rights reserved.
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
8 CT82353EN01GLA1 ©2014 Nokia Solutions and Networks. All rights reserved.
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
9 CT82353EN01GLA1 ©2014 Nokia Solutions and Networks. All rights reserved.
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.
10 CT82353EN01GLA1 ©2014 Nokia Solutions and Networks. All rights reserved.
MAC Sublayer
RRC Sublayer User Data Plane
PDCP Sublayer
RLC Sublayer
MAC Sublayer
Logi
cal
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ann
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Radio
Bearers
Signaling
Radio Bearers
Control
Channels
Traffic
Channels
Logical Channels
Rad
io
Be
are
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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.
11 CT82353EN01GLA1 ©2014 Nokia Solutions and Networks. All rights reserved.
LTE FDD and TDD Mode: Radio Channel Types
LTE Channel Architecture
Logical Channel Types
Transport Channel Types
Physical Channel Types
Multiplexing of channels
12 CT82353EN01GLA1 ©2014 Nokia Solutions and Networks. All rights reserved.
MAC Sublayer
RLC Sublayer
MAC Sublayer
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Logi
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Logical Channel Types
13 CT82353EN01GLA1 ©2014 Nokia Solutions and Networks. All rights reserved.
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.
14 CT82353EN01GLA1 ©2014 Nokia Solutions and Networks. All rights reserved.
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;
15 CT82353EN01GLA1 ©2014 Nokia Solutions and Networks. All rights reserved.
LTE FDD and TDD Mode: Radio Channel Types
LTE Channel Architecture
Logical Channel Types
Transport Channel Types
Physical Channel Types
Multiplexing of channels
16 CT82353EN01GLA1 ©2014 Nokia Solutions and Networks. All rights reserved.
MAC Sublayer
Physical Layer
MAC Sublayer
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Transport Channel Types
17 CT82353EN01GLA1 ©2014 Nokia Solutions and Networks. All rights reserved.
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.
18 CT82353EN01GLA1 ©2014 Nokia Solutions and Networks. All rights reserved.
MAC Sublayer
Physical Layer
MAC Sublayer
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Transport Channel Types
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.
19 CT82353EN01GLA1 ©2014 Nokia Solutions and Networks. All rights reserved.
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;
20 CT82353EN01GLA1 ©2014 Nokia Solutions and Networks. All rights reserved.
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.
21 CT82353EN01GLA1 ©2014 Nokia Solutions and Networks. All rights reserved.
LTE FDD and TDD Mode: Radio Channel Types
LTE Channel Architecture
Logical Channel Types
Transport Channel Types
Physical Channel Types
Multiplexing of channels
22 CT82353EN01GLA1 ©2014 Nokia Solutions and Networks. All rights reserved.
Physical Layer
DL Physical Channels
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23 CT82353EN01GLA1 ©2014 Nokia Solutions and Networks. All rights reserved.
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.
24 CT82353EN01GLA1 ©2014 Nokia Solutions and Networks. All rights reserved.
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.
26 CT82353EN01GLA1 ©2014 Nokia Solutions and Networks. All rights reserved.
Physical Layer
UL Physical Channels
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27 CT82353EN01GLA1 ©2014 Nokia Solutions and Networks. All rights reserved.
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).
28 CT82353EN01GLA1 ©2014 Nokia Solutions and Networks. All rights reserved.
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;
29 CT82353EN01GLA1 ©2014 Nokia Solutions and Networks. All rights reserved.
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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.
30 CT82353EN01GLA1 ©2014 Nokia Solutions and Networks. All rights reserved.
LTE FDD and TDD Mode: Radio Channel Types
LTE Channel Architecture
Logical Channel Types
Transport Channel Types
Physical Channel Types
Multiplexing of channels
31 CT82353EN01GLA1 ©2014 Nokia Solutions and Networks. All rights reserved.
Uu Interface Sublayers Overview – worksheet 01