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WCDMA Air Interface Physical Layer
Confidential Information of Huawei. No Spreading Without Permission
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www.huawei.com
Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
WCDMA Radio Interface
Physical Layer
WCDMA Air Interface Physical Layer
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Page1Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Foreword
� The physical layer offers data transport services to higher layers.
� The physical layer is expected to perform the following functions in
order to provide the data transport service, for example: spreading,
modulation and demodulation, despreading, Inner-loop power
control and etc.
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Page2Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Objectives
� Upon completion of this course, you will be able to:
� Outline radio interface protocol Architecture
� Describe structure and functions of different physical channels
� Describe UMTS physical layer procedures
WCDMA Air Interface Physical Layer
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Page3Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Contents
1. Physical Layer Overview
2. Physical Channels
3. Physical Layer Procedure
WCDMA Air Interface Physical Layer
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Page4Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Contents
1. Physical Layer Overview
2. Physical Channels
3. Physical Layer Procedure
WCDMA Air Interface Physical Layer
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Page5Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
UTRAN Network Structure
RNS
RNC
RNS
RNC
Core Network
NodeB NodeB NodeB NodeB
Iu-CS Iu-PS
Iur
Iub IubIub Iub
CN
UTRAN
UEUu
CS PS
Iu-CSIu-PS
CSPS
� UTRAN: UMTS Terrestrial Radio Access Network.
� The UTRAN consists of a set of Radio Network Subsystems connected to the Core Network
through the Iu interface.
� A RNS consists of a Radio Network Controller and one or more NodeBs. A NodeB is
connected to the RNC through the Iub interface.
� Inside the UTRAN, the RNCs of the RNS can be interconnected together through the Iur.
Iu(s) and Iur are logical interfaces. Iur can be conveyed over direct physical connection
between RNCs or virtual networks using any suitable transport network.
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Page6Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Uu Interface Protocol Structure
L3
control
control
control
control
C-plane signaling U-plane information
PHY
L2/MAC
L1
RLC
DCNtGC
L2/RLC
MAC
RLCRLC
RLC
Duplication avoidance
UuS boundary
L2/BMC
control
PDCPPDCP L2/PDCP
DCNtGC
RRC
RLCRLC
RLCRLC
BMC
radio bearer
logical channel
transport channel
� The layer 1 supports all functions required for the transmission of bit streams on the
physical medium. It is also in charge of measurements function consisting in indicating to
higher layers, for example, Frame Error Rate (FER), Signal to Interference Ratio (SIR),
interference power, transmit power, … It is basically composed of a “layer 1 management”
entity, a “transport channel” entity, and a “physical channel” entity.
� The layer 2 protocol is responsible for providing functions such as mapping, ciphering,
retransmission and segmentation. It is made of four sub-layers: MAC (Medium Access
Control), RLC (Radio Link Control), PDCP (Packet Data Convergence Protocol) and BMC
(Broadcast/Multicast Control).
� The layer 3 is split into 2 parts: the access stratum and the non access stratum. The access
stratum part is made of “RRC (Radio Resource Control)” entity and “duplication avoidance”
entity. “duplication avoidance” terminates in the CN but is part of the Access Stratum. The
higher layer signalling such as Mobility Management (MM) and Call Control (CC) is
assumed to belong to the non-access stratum, and therefore not in the scope of 3GPP TSG
RAN. In the C-plane, the interface between 'Duplication avoidance' and higher L3 sub-
layers (CC, MM) is defined by the General Control (GC), Notification (Nt) and Dedicated
Control (DC) SAPs.
� Not shown on the figure are connections between RRC and all the other protocol layers
(RLC, MAC, PDCP, BMC and L1), which provide local inter-layer control services.
� The protocol layers are located in the UE and the peer entities are in the NodeB or the RNC.
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� Many functions are managed by the RRC layer. Here is the list of the most important:
� Establishment, re-establishment, maintenance and release of an RRC
connection between the UE and UTRAN: it includes an optional cell re-selection,
an admission control, and a layer 2 signaling link establishment. When a RNC is in
charge of a specific connection towards a UE, it acts as the Serving RNC.
� Establishment, reconfiguration and release of Radio Bearers: a number of
Radio Bearers can be established for a UE at the same time. These bearers are
configured depending on the requested QoS. The RNC is also in charge of ensuring
that the requested QoS can be met.
� Assignment, reconfiguration and release of radio resources for the RRC
connection: it handles the assignment of radio resources (e.g. codes, shared
channels). RRC communicates with the UE to indicate new resources allocation
when handovers are managed.
� Paging/Notification: it broadcasts paging information from network to UEs.
� Broadcasting of information provided by the non-access stratum (Core Network)
or access Stratum. This corresponds to “system information” regularly repeated.
� UE measurement reporting and control of the reporting: RRC indicates what
to measure, when and how to report.
� Outer loop power control: controls setting of the target values.
� Control of ciphering: provides procedures for setting of ciphering.
� The RRC layer is defined in the 25.331 specification from 3GPP.
WCDMA Air Interface Physical Layer
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� The RLC’s main function is the transfer of data from either the user or the control plane
over the Radio interface. Two different transfer modes are used: transparent and non-
transparent. In non-transparent mode, 2 sub-modes are used: acknowledged or
unacknowledged.
� RLC provides services to upper layers:
� data transfer (transparent, acknowledged and unacknowledged modes).
� QoS setting: the retransmission protocol (for AM only) shall be configurable by
layer 3 to provide different QoS.
� notification of unrecoverable errors: RLC notifies the upper layers of errors that
cannot be resolved by RLC.
� The RLC functions are:
� mapping between higher layer PDUs and logical channels.
� ciphering: prevents unauthorized acquisition of data; performed in RLC layer for
non-transparent RLC mode.
� segmentation/reassembly: this function performs segmentation/reassembly of
variable-length higher layer PDUs into/from smaller RLC Payload Units. The RLC size
is adjustable to the actual set of transport formats (decided when service is
established). Concatenation and padding may also be used.
� error correction: done by retransmission (acknowledged data transfer mode only).
� flow control: allows the RLC receiver to control the rate at which the peer RLC
transmitting entity may send information.
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� MAC services include:
� Data transfer: service providing unacknowledged transfer of MAC SDUs between
peer MAC entities.
� Reallocation of radio resources and MAC parameters: reconfiguration of MAC
functions such as change of identity of UE. Requested by the RRC layer.
� Reporting of measurements: local measurements such as traffic volume and
quality indication are reported to the RRC layer.
� The functions accomplished by the MAC sub-layer are listed above. Here’s a quick
explanation for some of them:
� Priority handling between the data flows of one UE: since UMTS is multimedia,
a user may activate several services at the same time, having possibly different
profiles (priority, QoS parameters...). Priority handling consists in setting the right
transport format for a high bit rate service and for a low bit rate service.
� Priority handling between UEs: use for efficient spectrum resources utilization for
bursty transfers on common and shared channels.
� Ciphering: to prevent unauthorized acquisition of data. Performed in the MAC
layer for transparent RLC mode.
� Access Service Class (ACS) selection for RACH transmission: the RACH
resources are divided between different ACSs in order to provide different priorities
on a random access procedure.
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� PDCP
� UMTS supports several network layer protocols providing protocol transparency for
the users of the service.
� Using these protocols (and new ones) shall be possible without any changes to
UTRAN protocols. In order to perform this requirement, the PDCP layer has been
introduced. Then, functions related to transfer of packets from higher layers shall be
carried out in a transparent way by the UTRAN network entities.
� PDCP shall also be responsible for implementing different kinds of optimization
methods. The currently known methods are standardized IETF (Internet Engineering
Task Force) header compression algorithms.
� Algorithm types and their parameters are negotiated by RRC and indicated to PDCP.
� Header compression and decompression are specific for each network layer protocol
type.
� In order to know which compression method is used, an identifier (PID: Packet
Identifier) is inserted. Compression algorithms exist for TCP/IP, RTP/UDP/IP, …
� Another function of PDCP is to provide numbering of PDUs. This is done if lossless
SRNS relocation is required.
� To accomplish this function, each PDCP-SDUs (UL and DL) is buffered and numbered.
Numbering is done after header compression. SDUs are kept until information of
successful transmission of PDCP-PDU has been received from RLC. PDCP sequence
number ranges from 0 to 65,535.
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� BMC (broadcast/multicast control protocol)
� The main function of BMC protocol are:
� Storage of cell broadcast message. the BMC in RNC stores the cell broadcast
message received over the CBC-RNC interface for scheduled transmission.
� Traffic volume monitoring and radio resource request for CBS. On the UTRAN
side, the BMC calculates the required transmission rate for the cell broadcast service
based on the messages received over the CBC-RNC interface, and requests
appropriate .CTCH/FACH resources from from RRC
� Scheduling of BMC message. The BMC receives scheduling information together
with each cell broadcast message over the CBC-RNC interface. Based on this
scheduling information, on the UTRAN side the BMC generates schedule message
and schedules BMC message sequences accordingly. On the UE side ,the BMC
evaluates the schedule messages and indicates scheduling parameters to RRC, which
are used by RRC to configure the lower layers for CBS discontinuous reception.
� Transmission of BMC message to UE. The function transmits the BMC messages
according to the schedule
� Delivery of cell broadcast messages to the upper layer. This UE function
delivers the received non-corrupted cell broadcast messages to the upper layer
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� The layer 1 (physical layer) is used to transmit information under the form of electrical
signals corresponding to bits, between the network and the mobile user. This information
can be voice, circuit or packet data, and network signaling.
� The UMTS layer 1 offers data transport services to higher layers. The access to these
services is through the use of transport channels via the MAC sub-layer.
� These services are provided by radio links which are established by signaling procedures.
These links are managed by the layer 1 management entity. One radio link is made of
one or several transport channels, and one physical channel.
� The UMTS layer 1 is divided into two sub-layers: the transport and the physical sub-layers.
All the processing (channel coding, interleaving, etc.) is done by the transport sub-layer in
order to provide different services and their associated QoS. The physical sub-layer is
responsible for the modulation, which corresponds to the association of bits (coming from
the transport sub-layer) to electrical signals that can be carried over the air interface. The
spreading operation is also done by the physical sub-layer.
� These two parts of layer 1 are controlled by the layer 1 management (L1M) entity. It is
made of several units located in each equipment, which exchange information through the
use of control channels.
WCDMA Air Interface Physical Layer
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Page13Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
RAB, RB and RL
RAB
RB
RLNodeB
RNC CNUE
UTRAN
� RAB: The service that the access stratum provides to the non-access stratum for transfer of
user data between User Equipment and CN.
� RB: The service provided by the layer 2 for transfer of user data between User Equipment
and Serving RNC.
� RL: A "radio link" is a logical association between single User Equipment and a single
UTRAN access point. Its physical realization comprises one or more radio bearer
transmissions.
WCDMA Air Interface Physical Layer
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Page14Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Contents
1. Physical Layer Overview
2. Physical Channels
3. Physical Layer Procedure
WCDMA Air Interface Physical Layer
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Page15Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Contents
2. Physical Channels
2.1 Physical Channel Structure and Functions
2.2 Channel Mapping
WCDMA Air Interface Physical Layer
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Page16Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
WCDMA Radio Interface Channel Definition
� Logical Channel = information container
� Defined by <What type of information> is transferred
� Transport Channel = characteristics of transmission
� Described by <How> and with <What characteristics> data is
transmitted over the radio interface
� Physical Channel = specification of the information global
content
� providing the real transmission resource, maybe a specific set of
codes and phase
� In terms of protocol layer, the WCDMA radio interface has three types of channels: physical
channel, transport channel and logical channel.
� Logical channel: Carrying user services directly. According to the types of the carried
services, it is divided into two types: control channel and service channel.
� Transport channel: It is the interface between radio interface layer 2 and layer 1, and it is
the service provided for MAC layer by the physical layer. According to whether the
information transported is dedicated information for a user or common information for all
users, it is divided into dedicated channel and common channel.
� Physical channel: It is the ultimate embodiment of all kinds of information when they are
transmitted on radio interface. Each channel which uses dedicated code (spreading code
and scramble) and carrier phase (I or Q) can be regarded as a physical channel.
WCDMA Air Interface Physical Layer
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Page17Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Logical Channel
Control channel
Traffic channel
Dedicated traffic channel (DTCH)
Common traffic channel (CTCH)
Broadcast control channel (BCCH)
Paging control channel (PCCH)
Dedicate control channel (DCCH)
Common control channel (CCCH)
� As in GSM, UMTS uses the concept of logical channels.
� A logical channel is characterized by the type of information that is transferred.
� As in GSM, logical channels can be divided into two groups: control channels for control
plane information and traffic channel for user plane information.
� The traffic channels are:
� Dedicated Traffic Channel (DTCH): a point-to-point bi-directional channel, that
transmits dedicated user information between a UE and the network. That
information can be speech, circuit switched data or packet switched data. The
payload bits on this channel come from a higher layer application (the AMR codec
for example). Control bits can be added by the RLC (protocol information) in case of
a non transparent transfer. The MAC sub-layer will also add a header to the RLC
PDU.
� Common Traffic Channel (CTCH): a point-to-multipoint downlink channel for
transfer of dedicated user information for all or a group of specified UEs. This
channel is used to broadcast BMC messages. These messages can either be cell
broadcast data from higher layers or schedule messages for support of
Discontinuous Reception (DRX) of cell broadcast data at the UE. Cell broadcast
messages are services offered by the operator, like indication of weather, traffic,
location or rate information.
WCDMA Air Interface Physical Layer
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Page18Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Logical Channel
Control channel
Traffic channel
Dedicated traffic channel (DTCH)
Common traffic channel (CTCH)
Broadcast control channel (BCCH)
Paging control channel (PCCH)
Dedicate control channel (DCCH)
Common control channel (CCCH)
� The control channels are:
� Broadcast Control Channel (BCCH): a downlink channel that broadcasts all system
information types (except type 14 that is only used in TDD). For example, system information
type 3 gives the cell identity. UEs decode system information on the BCH except when in
Cell_DCH mode. In that case, they can decode system information type 10 on the FACH and
other important signaling is sent on a DCCH.
� Paging Control Channel (PCCH): a downlink channel that transfers paging information. It
is used to reach a UE (or several UEs) in idle mode or in connected mode (Cell_PCH or
URA_PCH state). The paging type 1 message is sent on the PCCH. When a UE receives a
page on the PCCH in connected mode, it shall enter Cell_FACH state and make a cell update
procedure.
� Dedicated Control Channel (DCCH): a point-to-point bi-directional channel that
transmits dedicated control information between a UE and the network. This channel is used
for dedicated signaling after a RRC connection has been done. For example, it is used for
inter-frequency handover procedure, for dedicated paging, for the active set update
procedure and for the control and report of measurements.
� Common Control Channel (CCCH): a bi-directional channel for transmitting control
information between network and UEs. It is used to send messages related to RRC
connection, cell update and URA update. This channel is a bit like the DCCH, but will be
used when the UE has not yet been identified by the network (or by the new cell). For
example, it is used to send the RRC connection request message, which is the first message
sent by the UE to get into connected mode. The network will respond on the same channel,
and will send him its temporary identities (cell and UTRAN identities). After these initial
messages, the DCCH will be used.
WCDMA Air Interface Physical Layer
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Page19Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Transport Channel
Dedicated Channel (DCH)
Broadcast channel (BCH)
Forward access channel (FACH)
Paging channel (PCH)
Random access channel (RACH)
High-speed downlink shared channel
(HS-DSCH)
Common transport channel
Dedicated transport channel
� In order to carry logical channels, several transport channels are defined. They are:
� Broadcast Channel (BCH): a downlink channel used for broadcast of system
information into the entire cell.
� Paging Channel (PCH): a downlink channel used for broadcast of control
information into the entire cell, such as paging.
� Random Access Channel (RACH): a contention based uplink channel used for
initial access or for transmission of relatively small amounts of data (non real-time
dedicated control or traffic data).
� Forward Access Channel (FACH): a common downlink channel used for
dedicated signaling (answer to a RACH typically), or for transmission of relatively
small amounts of data.
� Dedicated Channel (DCH): a channel dedicated to one UE used in uplink or
downlink.
WCDMA Air Interface Physical Layer
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Page20Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Physical Channel
� A physical channel is defined by a code (scrambling code, spreading
code) and relative phase.
� In UMTS system, the different code (scrambling code or spreading
code) can distinguish the channels.
� Most channels consist of radio frames and time slots, and each radio
frame consists of 15 time slots.
� Two types of physical channel: UL and DL
Physical Channel
Code, Phase
� Now we will begin to discuss the physical channel. Physical channel is the most important
and complex channel, and a physical channel is defined by a specific code and relative
phase. In CDMA system, the different code (scrambling code or spreading code) can
distinguish the channels. Most channels consist of radio frames and time slots, and each
radio frame consists of 15 time slots. There are two types of physical channel: UL and DL.
WCDMA Air Interface Physical Layer
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Page21Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Downlink Physical Channel
� Downlink Dedicated Physical Channel (DL DPCH)
� Downlink Common Physical Channel
� Primary Common Control Physical Channel (P-CCPCH)
� Secondary Common Control Physical Channel (S-CCPCH)
� Synchronization Channel (SCH)
� Paging Indicator Channel (PICH)
� Acquisition Indicator Channel (AICH)
� Common Pilot Channel (CPICH)
� High-Speed Physical Downlink Shared Channel (HS-PDSCH)
� High-Speed Shared Control Channel (HS-SCCH)
� The different physical channels are:
� Synchronization Channel (SCH): used for cell search procedure. There is the primary and the secondary SCHs.
� Common Control Physical Channel (CCPCH): used to carry common control
information such as the scrambling code used in DL (there is a primary CCPCH and
additional secondary CCPCH).
� Common Pilot Channels (P-CPICH and S-CPICH): used for coherent detection of
common channels. They indicate the phase reference.
� Dedicated Physical Data Channel (DPDCH): used to carry dedicated data coming
from layer 2 and above (coming from DCH).
� Dedicated Physical Control Channel (DPCCH): used to carry dedicated control
information generated in layer 1 (such as pilot, TPC and TFCI bits).
� Page Indicator Channel (PICH): carries indication to inform the UE that paging information is available on the S-CCPCH.
� Acquisition Indicator Channel (AICH): it is used to inform a UE that the network
has received its access request.
� High Speed Physical Downlink Shared Channel (HS-PDSCH): it is used to carry
subscribers BE service data (mapping on HSDPA) coming from layer 2.
� High Speed Shared Control Channel (HS-SCCH): it is used to carry control
message to HS-PDSCH such as modulation scheme, UE ID etc.
WCDMA Air Interface Physical Layer
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Page22Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Uplink Physical Channel
� Uplink Dedicated Physical Channel
� Uplink Dedicated Physical Data Channel (Uplink DPDCH)
� Uplink Dedicated Physical Control Channel (Uplink DPCCH)
� High-Speed Dedicated Physical Channel (HS-DPCCH)
� Uplink Common Physical Channel
� Physical Random Access Channel (PRACH)
� The different physical channels are:
� Dedicated Physical Data Channel (DPDCH): used to carry dedicated data coming
from layer 2 and above (coming from DCH).
� Dedicated Physical Control Channel (DPCCH): used to carry dedicated control
information generated in layer 1 (such as pilot, TPC and TFCI bits).
� Physical Random Access Channel (PRACH): used to carry random access
information when a UE wants to access the network.
� High Speed Dedicated Physical Control Channel (HS-DPCCH): it is used to
carry feedback message to HS-PDSCH such CQI,ACK/NACK.
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Page23Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Function of Physical Channel
NodeB UE
P-CCPCH-Primary Common Control Physical Channel
P-CPICH--Primary Common Pilot Channel
SCH--Synchronisation Channel
Cell Search Channels
DPDCH--Dedicated Physical Data Channel
DPCCH--Dedicated Physical Control Channel
Dedicated Channels
Paging Channels
PICH--Paging Indicator Channel
SCCPCH--Secondary Common Control Physical Channel
PRACH--Physical Random Access Channel
AICH--Acquisition Indicator Channel
Random Access Channels
HS-DPCCH--High Speed Dedicated Physical Control Channel
HS-SCCH--High Speed Share Control Channel
HS-PDSCH--High Speed Physical Downlink Share Channel
High Speed Downlink Share Channels
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Page24Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Synchronization Channels (P-SCH & S-SCH)
� Used for cell search
� Two sub channels: P-SCH and S-SCH
� SCH is transmitted at the first 256 chips
of every time slot
� Primary synchronization code is
transmitted repeatedly in each time slot
� Secondary synchronization code specifies
the scrambling code groups of the cell
Primary
SCH
Secondary
SCH
Slot #0 Slot #1 Slot #14
ac si,0
pac pac pac
ac si,1 acs
i,14
256 chips
2560 chips
One 10 ms SCH radio frame
� When a UE is turned on, the first thing it does is to scan the UMTS spectrum and find a
UMTS cell. After that, it has to find the primary scrambling code used by that cell in order
to be able to decode the BCCH (for system information). This is done with the help of the
Synchronization Channel.
� Each cell of a NodeB has its own SCH timing, so that there is no overlapping.
� The SCH is a pure downlink physical channel broadcasted over the entire cell. It is
transmitted unscrambled during the first 256 chips of each time slot, in time multiplex with
the P-CCPCH. It is the only channel that is not spread over the entire radio frame. The
SCH provides the primary scrambling code group (one out of 64 groups), as well as the
radio frame and time slot synchronization.
� The SCH consists of two sub-channels, the primary and secondary SCH. These sub-
channels are sent in parallel using code division during the first 256 chips of each time slot.
P-SCH always transmits primary synchronization code. S-SCH transmits secondary
synchronization codes.
� The primary synchronization code is repeated at the beginning of each time slot. The same
code is used by all the cells and enables the mobiles to detect the existence of the UMTS
cell and to synchronize itself on the time slot boundaries. This is normally done with a
single matched filter or any similar device. The slot timing of the cell is obtained by
detecting peaks in the matched filter output.
� This is the first step of the cell search procedure. The second step is done using the
secondary synchronization channel.
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Page25Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Secondary Synchronization Channel (S-SCH)
slot number Scrambling Code Group #0 #1 #2 #3 #4 #5 #6 #7 #8 #9 #10 #11 #12 #13 #14
Group 0 1 1 2 8 9 10 15 8 10 16 2 7 15 7 16
Group 1 1 1 5 16 7 3 14 16 3 10 5 12 14 12 10
Group 2 1 2 1 15 5 5 12 16 6 11 2 16 11 15 12
Group 3 1 2 3 1 8 6 5 2 5 8 4 4 6 3 7
Group 4 1 2 16 6 6 11 15 5 12 1 15 12 16 11 2
…
Group 61 9 10 13 10 11 15 15 9 16 12 14 13 16 14 11
Group 62 9 11 12 15 12 9 13 13 11 14 10 16 15 14 16
Group 63 9 12 10 15 13 14 9 14 15 11 11 13 12 16 10
�……..acp
Slot # ?
P-SCH acp
Slot #?
16 6S-SCH
acp
Slot #?
11Group 2
Slot 7, 8, 9256 chips
� The S-SCH also consists of a code, the Secondary Synchronization Code (SSC) that
indicates which of the 64 scrambling code groups the cell’s downlink scrambling code
belongs to. 16 different SSCs are defined. Each SSC is a 256 chip long sequence.
� There is one specific SSC transmitted in each time slot, giving us a sequence of 15 SSCs.
There is a total of 64 different sequences of 15 SSCs, corresponding to the 64 primary
scrambling code groups. These 64 sequences are constructed so that one sequence is
different from any other one, and different from any rotated version of any sequence. The
UE correlates the received signal with the 16 SSCs and identifies the maximum correlation
value.
� The S-SCH provides the information required to find the frame boundaries and the
downlink scrambling code group (one out of 64 groups). The scrambling code (one out of
8) can be determined afterwards by decoding the P-CPICH. The mobile will then be able to
decode the BCH.
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Page26Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Primary Common Pilot Channel (PCPICH)
� Primary PCPICH
� Carrying pre-defined sequence
� Fixed channel code: Cch, 256, 0, Fixed rate 30Kbps
� Scrambled by the primary scrambling code
� Broadcast over the entire cell
� A phase reference for SCH, Primary CCPCH, AICH, PICH and downlink
DPCH, Only one PCPICH per cell
Pre-defined symbol sequence
Slot #0 Slot #1 Slot # i Slot #14
Tslot = 2560 chips , 20 bits
1 radio frame: Tr = 10 ms
� The Common Pilot Channel (CPICH) is a pure physical control channel broadcasted over
the entire cell. It is not linked to any transport channel. It consists of a sequence of known
bits that are transmitted in parallel with the primary and secondary CCPCH.
� The PCPICH is used by the mobile to determine which of the 8 possible primary scrambling
codes is used by the cell, and to provide the phase reference for common channels.
� Finding the primary scrambling code is done during the cell search procedure through a
symbol-by-symbol correlation with all the codes within the code group. After the primary
scrambling code has been identified, the UE can decode system information on the P-
CCPCH.
� The P-CPICH is the phase reference for the SCH, P-CCPCH, AICH and PICH. It is
broadcasted over the entire cell. The channelization code used to spread the P-CPICH is
always Cch,256,0 (all ones). Thus, the P-CPICH is a fixed rate channel. Also, it is always
scrambled with the primary scrambling code of the cell.
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Primary Common Control Physical Channel
(PCCPCH)
� Carrying BCH transport channel
� Fixed rate, fixed OVSF code (30kbps,Cch, 256, 1)
� The PCCPCH is not transmitted during the first 256 chips of each time
slot
PCCPCH Data
18 bits
Slot #0
1 radio frame: Tf= 10 ms
Slot #1 Slot #i
256 chips
Slot #14
Tslot
= 2560 chips,20 bits
SCH
� The Primary Common Control Physical Channel (P-CCPCH) is a fixed rate (SF=256)
downlink physical channel used to carry the BCH transport channel. It is broadcasted
continuously over the entire cell like the P-CPICH.
� The figure above shows the frame structure of the P-CCPCH. The frame structure is special
because it does not contain any layer 1 control bits. The P-CCPCH only has one fix
predefined transport format combination, and the only bits transmitted are data bits from
the BCH transport channel. It is important to note that the P-CCPCH is not transmitted
during the first 256 chips of the slot. In fact, another physical channel (SCH) is transmitted
during that period of time. Thus, the SCH and the P-CCPCH are time multiplexed on every
time slot.
� Channelization code Cch,256,1 is always used to spread the P-CCPCH.
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Paging Indicator Channel (PICH)
� Carrying Paging Indicators (PI)
� Fixed rate (30kbps), SF = 256
� N paging indicators {PI0, …, PIN-1} in each PICH frame, N=18, 36, 72,
or 144
One radio frame (10 ms)
b1b0
288 bits for paging indication 12 bits (undefined)
b287 b288 b299
� The Page Indicator Channel (PICH) is a fixed rate (30kbps, SF=256) physical channel
used by the NodeB to inform a UE (or a group of UEs) that a paging information will soon
be transmitted on the PCH. Thus, the mobile only decodes the S-CCPCH when it is
informed to do so by the PICH. This enables to do other processing and to save the
mobiles’ battery.
� The PICH carries Paging Indicators (PI), which are user specific and calculated by higher
layers. It is always associated with the S-CCPCH to which the PCH is mapped.
� The frame structure of the PICH is illustrated above. It is 10 ms long, and always contains
300 bits (SF=256). 288 of these bits are used to carry paging indicators, while the
remaining 12 are not formally part of the PICH and shall not be transmitted. That part of
the frame (last 12 bits) is reserved for possible future use.
� In order not to waste radio resources, several PIs are multiplexed in time on the PICH.
Depending on the configuration of the cell, 18, 36, 72 or 144 paging indicators can be
multiplexed on one PICH radio frame. Thus, the number of bits reserved for each PI
depends of the number of PIs per radio frame. For example, if there is 72 PIs in one radio
frame, there will be 4 (288/72) consecutive bits for each PI. These bits are all identical. If
the PI in a certain frame is “1”, it is an indication that the UE associated with that PI should
read the corresponding frame of the S-CCPCH.
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Secondary Common Control Physical Channel
(SCCPCH)
� Carrying FACH and PCH, SF = 256 - 4
� Pilot: used for demodulation
� TFCI: Transport Format Control Indication, used for describe data format
Data
N bits
Slot #0 Slot #1 Slot #i Slot #14
1 radio frame: T f = 10 ms
T slot = 2560 chips,
Data
PilotN bitsPilotN bits
TFCI
TFCI
20*2 kbits (k=0..6)
� The Secondary Common Control Physical Channel (S-CCPCH) is used to carry the
FACH and PCH transport channels. Unlike the P-CCPCH, it is not broadcasted
continuously. It is only transmitted when there is a PCH or FACH information to transmit.
At the mobile side, the mobile only decodes the S-CCPCH when it expects a useful message
on the PCH or FACH.
� A UE will expect a message on the PCH after indication from the PICH (page indicator
channel), and it will expect a message on the FACH after it has transmitted something on
the RACH.
� The FACH and the PCH can be mapped on the same or on separate S-CCPCHs. If they are
mapped on the same S-CCPCH, TFCI bits have to be sent to support multiple transport
formats
� The figure above shows the frame structure of the S-CCPCH. There are 18 different slot
formats determining the exact number of data, pilot and TFCI bits. The data bits
correspond to the PCH and/or FACH bits coming from the transport sub-layer. Pilot bit are
typically used when beamforming techniques are used.
� The SF ranges from 4 to 256. The channelization code is assigned by the RRC layer as is
the scrambling code, and they are fixed during the communication. They are sent on the
BCCH so that every UE can decode the channel.
� As said before, FACH can be used to carry user data. The difference with the dedicated
channel is that it cannot use fast power control, nor soft handover. The advantage is that it
is a fast access channel.
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Physical Random Access Channel (PRACH)
� Carrying uplink signaling and data, consist of two parts:
� One or several preambles: 16 kinds of available preambles
� 10 or 20ms message part
Message partPreamble
4096 chips10 ms (one radio frame)
Preamble Preamble
Message partPreamble
4096 chips 20 ms (two radio frames)
Preamble Preamble
� The Physical Random Access Channel (PRACH) is used by the UE to access the network
and to carry small data packets. It carries the RACH transport channel. The PRACH is an
open loop power control channel, with contention resolution mechanisms (ALOHA
approach) to enable a random access from several users.
� The PRACH is composed of two different parts: the preamble part and the message part
that carries the RACH message. The preamble is an identifier which consists of 256
repetitions of a 16 chip long signature (total of 4096 chips). There are 16 possible
signatures, basically, the UE randomly selects one of the 16 possible preambles and
transmits it at increasing power until it gets a response from the network (on the AICH).
That preamble is scrambled before being sent. That is a sign that the power level is high
enough and that the UE is authorized to transmit, which it will do after acknowledgment
from the network. If the UE doesn’t get a response from the network, it has to select a
new signature to transmit.
� The message part is 10 or 20 ms long (split into 15 or 30 time slots) and is made of the
RACH data and the layer 1 control information.
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PRACH Message Structure
Pilot
N bits
Slot # 0 Slot # 1 Slot # i Slot # 14
Message part radio frame T = 10 ms
Tslot = 2560 chips, 10*2
Pilot
TFCI
N bitsTFCI
Data
Ndata
bitsData
Control
kbits (k=0..3)
� The data and control bits of the message part are processed in parallel. The SF of the data
part can be 32, 64, 128 or 256 while the SF of the control part is always 256. The control
part consists of 8 pilot bits for channel estimation and 2 TFCI bits to indicate the transport
format of the RACH (transport channel), for a total of 10 bits per slot.
� The OVSF codes to use (one for RACH data and one for control) depend on the signature
that was used for the preamble (for signatures s=0 to s=15: OVSFcontrol= Cch,256,m, where
m=16s + 15; OVSFdata= Cch,SF,m, where m=SF*s/16.
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PRACH Access Timeslot Structure
#1 #2 #3 #4 #5 #6 #7 #8 #9 #10 #11 #12 #13 #14
5120 chips
radio frame: 10 ms radio frame: 10 ms
Access slot #0 Random Access Transmission
Access slot #1
Access slot #7
Access slot #14
Random Access Transmission
Random Access Transmission
Random Access TransmissionAccess slot #8
� The PRACH transmission is based on the access frame structure. The access frame is access of 15 access slots and lasts 20 ms (2 radio frames).
� To avoid too many collisions and to limit interference, a UE must wait at least 3 or 4 access slots between two consecutive preambles.
� The PRACH resources (access slots and preamble signatures) can be divided between different Access Service Classes (ASC) in order to provide different priorities of RACH usage. The ASC number ranges from 0 (highest priority) to 7 (lowest priority).
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Acquisition Indicator Channel (AICH)
� Carrying the Acquisition Indicators (AI), SF = 256
� There are 16 kinds of Signature to generate AI
AS #14 AS #0 AS #1 AS #i AS #14 AS #0
a1 a2a0 a31 a32a30 a33 a38 a39
AI part Unused part
20 ms
� The Acquisition Indicator Channel (AICH) is a common downlink channel used to control
the uplink random accesses. It carries the Acquisition Indicators (AI), each corresponding
to a signature on the PRACH (uplink). When the NodeB receives the random access from a
mobile, it sends back the signature of the mobile to grant its access. If the NodeB receives
multiple signatures, it can sent all these signatures back by adding the together. At
reception, the UE can apply its signature to check if the NodeB sent an acknowledgement
(taking advantage of the orthogonality of the signatures).
� The AICH consists of a burst of data transmitted regularly every access slot frame. One
access slot frame is formed of 15 access slots, and lasts 2 radio frames (20 ms). Each
access slot consists of two parts, an acquisition indicator part of 32 real-valued symbols
and a long part during which nothing is transmitted to avoid overlapping due to
propagation delays.
� s (with values 0, +1 and -1, corresponding to the answer from the network to a specific
user) and the 32 chip long sequence <bs,j> is given by a predefined table. There are 16
sequences <bs,j>, each corresponding to one PRACH signatures. A maximum of 16 AIs
can be sent in each access slot. The user can multiply the received multi-level signal by the
signature it used to know if its access was granted.
� The SF used is always 256 and the OVSF code used by the cell is indicated in system
information type 5.
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Page34Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Uplink Dedicated Physical Channel
(DPDCH&DPCCH)
� Uplink DPDCH and DPCCH are I/Q code division multiplexed
(CDM) within each radio frame
� DPDCH carries data generated at Layer 2 and higher layer, the
OVSF code is Cch,SF,SF/4, where SF is from 256 to 4
� DPCCH carries control information generated at Layer 1, the
OVSF code is Cch,256,0
� There are two kinds of uplink dedicated physical channels, the Dedicated Physical Data
Channel (DPDCH) and the Dedicated Physical Control Channel (DPCCH). The DPDCH
is used to carry the DCH transport channel. The DPCCH is used to carry the physical sub-
layer control bits.
� Each DPCCH time slot consists of Pilot, TFCI,FBI,TPC
� Pilot is used to help demodulation
� TFCI: transport format control indicator
� FBI:used for the FBTD. (feedback TX diversity)
� TPC: used to transport power control command.
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Uplink Dedicated Physical Channel
(DPDCH&DPCCH)
� Frame Structure of Uplink DPDCH/DPCCH
PilotNpilot bits
TPCNTPC bits
DataNdata bits
Slot #0 Slot #1 Slot #i Slot #14
Tslot = 2560 chips, 10*2k bits (k=0..6)
1 radio frame: Tf = 10 ms
DPDCH
DPCCHFBI
NFBI bitsTFCI
NTFCI bits
� On the figure above, we can see the DPDCH and DPCCH time slot constitution. The
parameter k determines the number of symbols per slot. It is related to the spreading
factor (SF) of the DPDCH by this simple equation: SF=256/2k. The DPDCH SF ranges from 4
to 256. The SF for the uplink DPCCH is always 256, which gives us 10 bits per slot. The
exact number of pilot, TFCI, TPC and FBI bits is configured by higher layers. This
configuration is chosen from 12 possible slot formats. It is important to note that symbols
are transmitted during all slots for the DPDCH
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Downlink Dedicated Physical Channel
(DPDCH+DPCCH)
� Downlink DPDCH and DPCCH is time division multiplexing
(TDM).
� DPDCH carries data generated at Layer 2 and higher layer
� DPCCH carries control information generated at Layer 1
� SF of downlink DPCH is from 512 to 4
� The uplink DPDCH and DPCCH are I/Q code multiplexed. But the downlink DPDCH and
DPCCH is time multiplexed. This is main difference.
� Basically, there are two types of downlink DPCH. They are distinguished by the use or non
use of the TFCI field. TFCI bits are not used for fixed rate services or when the TFC doesn’t
change.
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Downlink Dedicated Physical Channel
(DPDCH+DPCCH)
� Frame Structure of Downlink DPCH (DPDCH+DPCCH)
One radio frame, Tf = 10 ms
Slot #0 Slot #1 Slot #i Slot #14
Tslot = 2560 chips, 20*2k bits (k=-1..6)
Data2
Ndata2 bits
DPDCH
TFCI
NTFCI bits
Pilot
Npilot bits
Data1
Ndata1 bits
DPDCH DPCCH DPCCH
TPC
NTPC bits
� We have known that the uplink DPDCH and DPCCH are I/Q code multiplexed. But the
downlink DPDCH and DPCCH is time multiplexed. This is main difference. The parameter k
in the figure above determines the total number of bits per time slot. It is related to the SF,
which ranges from 4 to 512. The chips of one slot is also 2560.
� Downlink physical channels are used to carry user specific information like speech, data or
signaling, as well as layer 1 control bits. Like it was mentioned before, the payload from
the DPDCH and the control bits from the DPCCH are time multiplexed on every time slot.
The figure above shows how these two channels are multiplexed. There is only one
DPCCH in downlink for one user.
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High-Speed Physical Downlink Shared Channel
(HS-PDSCH)
� Bearing service data and layer 2 overhead bits mapped from the
transport channel
� SF=16, can be configured several channels to increase data service
Slot #0 Slot#1 Slot #2
Tslot = 2560 chips, M*10*2k bits (k=4)
DataNdata1 bits
1 subframe: Tf = 2 ms
� HS-PDSCH is a downlink physical channel that carries user data and layer 2 overhead bits
mapped from the transport channel: HS-DSCH.
� The user data and layer 2 overhead bits from HS-DSCH is mapped onto one or several HS-
PDSCH and transferred in 2ms subframe using one or several channelization code with
fixed SF=16.
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High-Speed Shared Control Channel (HS-SCCH)
� Carries physical layer signalling to a single UE ,such as modulation scheme (1
bit) ,channelization code set (7 bit), transport block size (6bit),HARQ process
number (3bit), redundancy version (3bit), new data indicator (1bit), UE
identity (16bit)
� HS-SCCH is a fixed rate (60 kbps, SF=128) downlink physical channel used to
carry downlink signalling related to HS-DSCH transmission
Slot #0 Slot#1 Slot #2
Tslot = 2560 chips, 40 bits
DataNdata1 bits
1 subframe: Tf = 2 ms
� HS-SCCH uses a SF=128 and has q time structure based on a sub-frame of length 2 ms, i.e.
the same length as the HS-DSCH TTI. The timing of HS-SCCH starts two slot prior to the
start of the HS-PDSCH subframe.
� The following information is carried on the HS-SCCH (7 items)
� Modulation scheme(1bit) QPSK or 16QAM
� Channelization code set (7bits)
� Transport block size ( 6bits)
� HARQ process number (3bits)
� Redundancy version (3bits)
� New Data Indicator (1bit)
� UE identity (16 bits)
� In each 2 ms interval corresponding to one HS-DSCH TTI , one HS-SCCH carries physical-
layer signalling to a single UE. As there should be a possibility for HS-DSCH transmission to
multiple users in parallel (code multiplex), multiplex HS-SCCH may be needed in a cell. The
specification allows for up to four HS-SCCHs as seen from a UE point of view .i.e. UE must
be able to decode four HS-SCCH.
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High-Speed Dedicated Physical Control Channel
(HS-DPCCH )
� Carrying information to acknowledge downlink transport blocks and
feedback information to the system for scheduling and link
adaptation of transport block
� CQI and ACK/NACK
� Physical Channel, Uplink, SF=256
Subframe #0 Subframe #i Subframe #n
One HS-DPCCH subframe ( 2ms )
ACK/NACK
1 radio frame: Tf = 10 ms
CQI
Tslot = 2560 chips 2 ×××× Tslot = 5120 chips
� The uplink HS-DPCCH consists of:
� Acknowledgements for HARQ
� Channel Quality Indicator (CQI)
� As the HS-DPCCH uses SF=256, there are a total of 30 channel bits per 2 ms sub frame (3
time slot). The HS-DPCCH information is divided in such a way that the HARQ
acknowledgement is transmitted in the first slot of the subframe while the channel quality
indication is transmitted in the rest slot.
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Page41Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Contents
2. Physical Channels
2.1 Physical Channel Structure and Functions
2.2 Channel Mapping
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Mapping Between Channels
Logical channels Transport channels Physical channels
BCCH BCH P-CCPCH
FACH S-CCPCH
PCCH PCH S-CCPCH
CCCH RACH PRACH
FACH S-CCPCH
CTCH FACH S-CCPCH
DCCH, DTCH DCH DPDCH
HS-DSCH HS-PDSCH
RACH, FACH PRACH, S-CCPCH
� This page indicates how the mapping can be done between logical, transport and physical
channels. Not all physical channels are represented because not all physical channels
correspond to a transport channel.
� The mapping between logical channels and transport channels is done by the MAC sub-
layer.
� Different connections can be made between logical and transport channels:
� BCCH is connected to BCH and may also be connected to FACH;
� DTCH can be connected to either RACH and FACH, to RACH and DSCH, to DCH and
DSCH, to a DCH or a CPCH;
� CTCH is connected to FACH;
� DCCH can be connected to either RACH and FACH, to RACH and DSCH, to DCH and
DSCH, to a DCH or a CPCH;
� PCCH is connected to PCH;
� CCCH is connected to RACH and FACH.
� These connections depend on the type of information on the logical channels.
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Page43Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Contents
1. Physical Layer Overview
2. Physical Channels
3. Physical Layer Procedure
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Synchronization Procedure - Cell Search
Frame synchronization & Code Group Identification
Scrambling Code
Identification
UE uses SSC to find frame
synchronization and identify the code
group of the cell found in the first step
UE determines the primary scrambling
code through correlation over the PCPICH
with all codes within the identified group,
and then detects the P-CCPCH and reads BCH information。
Slot Synchronization
UE uses Primary Syn Code to
acquire slot synchronization to
a cell
� The purpose of the Cell Search Procedure is to give the UE the possibility of finding a cell
and of determining the downlink scrambling code and frame synchronization of that cell.
This is typically performed in 3 steps:
� PSCH (Slot synchronization): The UE uses the SCH’s primary synchronization code to
acquire slot synchronization to a cell. The primary synchronization code is used by
the UE to detect the existence of a cell and to synchronize the mobile on the TS
boundaries. This is typically done with a single filter (or any similar device) matched
to the primary synchronization code which is common to all cells. The slot
timing of the cell can be obtained by detecting peaks in the matched filter output.
� SSCH (Frame synchronization and code-group identification): The secondary
synchronization codes provide the information required to find the frame boundaries
and the group number. Each group number corresponds to a unique set of 8
primary scrambling codes. The frame boundary and the group number are provided
indirectly by selecting a suite of 15 secondary codes. 16 secondary codes have been
defined C1, C2, ….C16. 64 possible suites have been defined, each suite corresponds
to one of the 64 groups. Each suite of secondary codes is composed of 15
secondary codes (chosen in the set of 16), each of which will be transmitted in one
time slot. When the received codes matches one of the possible suites, the UE has
both determined the frame boundary and the group number.
� PCPICH (Scrambling-code identification): The UE determines the exact primary
scrambling code used by the found cell. The primary scrambling code is typically
identified through symbol-by-symbol correlation over the PCPICH with all the codes
within the code group identified in the second step. After the primary scrambling
code has been identified, the Primary CCPCH can be detected and the system- and
cell specific BCH information can be read.
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Random Access ProcedureSTART
Choose a RACH sub channel from
available ones
Get available signatures
Set Preamble Retrans Max
Set Preamble_Initial_Power
Send a preamble
Check the corresponding AI
Increase message part power by
p-m based on preamble power
Set physical status to be RACH
message transmittedSet physical status to be Nack
on AICH received
Choose a access slot again
Counter> 0 & Preamble power
< maximum allowed power
Choose a signature and increase preamble transmit power
Set physical status to be Nack
on AICH received
Get negative AI
No AI
Report the physical status to MAC
END
Get positive AI
The counter of preamble retransmit
Subtract 1, Commanded preamble power
increased by Power Ramp Step
N
Y
Send the corresponding message part
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� Physical random access procedure
� 1. Derive the available uplink access slots, in the next full access slot set, for the set
of available RACH sub-channels within the given ASC. Randomly select one access
slot among the ones previously determined. If there is no access slot available in the
selected set, randomly select one uplink access slot corresponding to the set of
available RACH sub-channels within the given ASC from the next access slot set. The
random function shall be such that each of the allowed selections is chosen with
equal probability;
� 2. Randomly select a signature from the set of available signatures within the given
ASC.;
� 3. Set the Preamble Retransmission Counter to Preamble_ Retrans_ Max
� 4. Set the parameter Commanded Preamble Power to Preamble_Initial_Power
� 5. Transmit a preamble using the selected uplink access slot, signature, and
preamble transmission power.
� 6. If no positive or negative acquisition indicator (AI ≠ +1 nor –1) corresponding to the selected signature is detected in the downlink access slot corresponding to the
selected uplink access slot:
� A: Select the next available access slot in the set of available RACH sub-channels within the given ASC;
� B: select a signature;
� C: Increase the Commanded Preamble Power;
� D: Decrease the Preamble Retransmission Counter by one. If the Preamble Retransmission Counter > 0 then repeat from step 6. Otherwise exit the physical random access procedure.
� 7. If a negative acquisition indicator corresponding to the selected signature is
detected in the downlink access slot corresponding to the selected uplink access slot,
exit the physical random access procedure Signature
� 8. If a positive acquisition indicator corresponding to the selected signature is
detected , Transmit the random access message three or four uplink access slots
after the uplink access slot of the last transmitted preamble
� 9. exit the physical random access procedure
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Page47Copyright © 2008 Huawei Technologies Co., Ltd. All rights reserved.
Transmit Diversity Mode
� Application of Tx diversity modes on downlink physical channel
––applied–AICH
––applied–HS-SCCH
–appliedapplied–HS-PDSCH
––applied–PICH
appliedappliedapplied–DPCH
––applied–S-CCPCH
–––appliedSCH
––applied–P-CCPCH
Mode 2Mode 1STTDTSTD
Closed loop modeOpen loop modePhysical channel type
� Transmitter-antenna diversity can be used to generate multi-path diversity in places where
it would not otherwise exist. Multi-path diversity is a useful phenomenon, especially if it
can be controlled. It can protect the UE against fading and shadowing. TX diversity is
designed for downlink usage. Transmitter diversity needs two antennas, which would be
an expensive solution for the UEs.
� The UTRA specifications divide the transmitter diversity modes into two categories: (1)
open-loop mode and (2) closed-loop mode. In the open-loop mode no feedback
information from the UE to the NodeB is available. Thus the UTRAN has to determine by
itself the appropriate parameters for the TX diversity. In the closed-loop mode the UE sends
feedback information up to the NodeB in order to optimize the transmissions from the
diversity antennas.
� Thus it is quite natural that the open-loop mode is used for the common channels, as they
typically do not provide an uplink return channel for the feedback information. Even if
there was a feedback channel, the NodeB cannot really optimize its common channel
transmissions according to measurements made by one particular UE. Common channels
are common for everyone; what is good for one UE may be bad for another. The closed-
loop mode is used for dedicated physical channels, as they have an existing uplink channel
for feedback information. Note that shared channels can also employ closed loop power
control, as they are allocated for only one user at a time, and they also have a return
channel in the uplink. There are two specified methods to achieve the transmission diversity
in the open-loop mode and two methods in closed-loop mode
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Transmit Diversity - STTD
� Space time block coding based transmit antenna diversity (STTD)
� 4 consecutive bits b0, b1, b2, b3 using STTD coding
b0 b1 b2 b3 Antenna 1
Antenna 2Channel bits
STTD encoded channel bits
for antenna 1 and antenna 2.
b0 b1 b2 b3
-b2 b3 b0 -b1
� The TX diversity methods in the open-loop mode are
� space time-block coding-based transmit-antenna diversity (STTD)
� time-switched transmit diversity (TSTD).
� In STTD the data to be transmitted is divided between two transmission antennas at the
base station site and transmitted simultaneously. The channel-coded data is processed in
blocks of four bits. The bits are time reversed and complex conjugated, as shown in above
slide. The STTD method, in fact, provides two brands of diversity. The physical separation
of the antennas provides the space diversity, and the time difference derived from the bit-
reversing process provides the time diversity.
� These features together make the decoding process in the receiver more reliable. In
addition to data signals, pilot signals are also transmitted via both antennas. The normal
pilot is sent via the first antenna and the diversity pilot via the second antenna.
� The two pilot sequences are orthogonal, which enables the receiving UE to extract the
phase information for both antennas.
� The STTD encoding is optional in the UTRAN, but its support is mandatory for the UE’s
receiver.
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Transmit Diversity - TSTD
� Time switching transmit diversity (TSTD) is used only on SCH
channel
Antenna 1
Antenna 2
i,0
i,1
acsi,14
Slot #0 Slot #1 Slot #14
i,2
acp
Slot #2
(Tx OFF)
(Tx OFF)
(Tx OFF)
(Tx OFF)
(Tx OFF)
(Tx OFF)
(Tx OFF)
acp acp
acsacs
acp
acs(Tx OFF)
� Time-switched transmit diversity (TSTD) can be applied to the SCH. Just like STTD, the
support of TSTD is optional in the UTRAN, but mandatory in the UE. The principle of TSTD
is to transmit the synchronization channels via the two base station antennas in turn. In
even-numbered time slots the SCHs are transmitted via antenna 1, and in odd-numbered
slots via antenna 2. This is depicted in above Figure. Note that SCH channels only use the
first 256 chips of each time slot (i.e., one-tenth of each slot).
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Closed Loop Mode
� Used in DPCH and HS-PDSCH
� The closed-loop-mode transmit diversity can only be applied to the downlink channel if
there is an associated uplink channel. Thus this mode can only be used with dedicated
channels. The chief operating principle of the closed loop mode is that the UE can control
the transmit diversity in the base station by sending adjustment commands in FBI bits on
the uplink DPCCH. The UE uses the base station’s common pilot channels to estimate the
channels separately. Based on this estimation, it generates the adjustment information and
sends it to the UTRAN to maximize the UE’s received power.
� There are actually two modes in the closed-loop method. In mode 1 only the phase can be
adjusted; in mode 2 the amplitude is adjustable as well as the phase. Each uplink time slot
has one FBI bit for closed-loop-diversity control. In mode 1 each bit forms a separate
adjustment command, but in mode 2 four bits are needed to compose a command.
� This functions can be configured by LMT command ADD CELLSETUP.
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References
� TS 25.104 UTRA (BS) FDD Radio Transmission and Reception
� TS 25.201 Physical layer-general description
� TS 25.211 Physical channels and mapping of transport channels onto physical
channels (FDD)
� TS 25.212 Multiplexing and channel coding (FDD)
� TS 25.213 Spreading and modulation (FDD)
� TS 25.214 Physical layer procedures (FDD)
� TS 25.308 UTRA High Speed Downlink Packet Access (HSDPA)
� TR 25.877 High Speed Downlink Packet Access (HSDPA) - Iub/Iur Protocol Aspects
� TR 25.858 Physical layer aspects of UTRA High Speed Downlink Packet Access
WCDMA Air Interface Physical Layer
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� This course mainly introduces the basic concept, key
technology and procedures of WCDMA physical layer.
� These knowledge is very important for understanding Uu
interface and further study.
Summary
WCDMA Air Interface Physical Layer
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