OWA200003 WCDMA Radio Interface_Physical Layer (With Comment) ISSUE 1.0(Fr)

8/12/2019 OWA200003 WCDMA Radio Interface_Physical Layer (With Comment) ISSUE 1.0(Fr)

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UTRAN:UMTS Terrestrial Radio Access Network.

The UTRAN consists of a set of Radio Network Subsystems connectedto 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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The radio interface (Uu) is layered into three protocol layers:

the physical layer (L1)

the data link layer (L2)

the network layer (L3).

The layer 1 supports all functions required for the transmission of bit streams on the physicalmedium. It is also in charge of measurements function consisting in indicating to higherlayers, for example, Frame Error Rate (FER), Signal to Interference Ratio (SIR), interference power, transmit power, It is basically composed of a layer 1 managemententity, 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 sublayers: MAC(Medium AccessControl), RLC(Radio Link Control), PDCP(Packet Data Convergence Protocol) and BMC(Broadcast/Multicast Control).

The layer 3 is split into 2 parts: the access stratumand the non access stratum. The accessstratum part is made of RRC(Radio Resource Control) entity and duplication avoidanceentity. The non access stratum part is made of CC, MMparts.

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 node B or the RNC.


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Spreading is applied to the physical channels. It consists of two operations.

The first is the channelization operation, which transforms every data symbolinto a number of chips, thus increasing the bandwidth of the signal. The

number of chips per data symbol is called the Spreading Factor (SF). The

second operation is the scrambling operation, where a scrambling code is

applied to the spread signal.


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The channelization codes are Orthogonal Variable Spreading Factor(OVSF)codes. Theyare used to preserve orthogonality between different physical channels. They also increase

the clock rate to 3.84 Mcps. The OVSF codes are defined using a code tree.In the code tree, the channelization codes are individually described by C ch,SF,k, where SF isthe Spreading Factor of the code and k the code number, 0 k SF-1.

A channelization sequence modulates one users bit. Because the chip rate is constant, thedifferent lengths of codes enable to have different user data rates. Low SFs are reserved forhigh rate services while high SFs are for low rate services.

The length of an OVSF code is an even number of chips and the number of codes (for one SF)is equal to the number of chips and to the SF value.

The generated codes within the same layer constitute a set of orthogonal codes. Furthermore,any two codes of different layers are orthogonal except when one of the two codes is amother code of the other. For example C4,3is not orthogonal with C1,0and C2,1, but is

orthogonal with C2,0.Each Sector of each Base Station transmits W-CDMA Downlink Traffic Channels with up to512 code channels.

Code tree repacking may be used to optimize the number of available codes in downlink.

Exercise: Find code Cch,8,3and code Cch,16,15

OVSF shortage

Scrambling enables neighboring cells to use the same channelization codes. This allows thesystem to use a maximum of 512 OVSF codes in each cell. Notice that the use of an OVSFcode forbids the use of the other codes in its branch. This reduces considerably the number ofavailable codes especially for high rate services. This may lead to an OVSF shortage. In sucha case, secondary scrambling codes may be allocated to the cells and enable the reuse of thesame OVSF in the same cell.


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Uplink scrambling code

All the physical channels in the uplink are scrambled. In uplink, the

scrambling code can be described as either long or short, depending on the

way it was constructed. The scrambling code is always applied to one 10 ms

frame. Different scrambling codes will be allocated to different mobiles.

In UMTS, Gold codeswere chosen for their very low peak cross-correlation.


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Downlink link scrambling code

The scrambling codes used in downlink are constructed like the long uplink

scrambling codes. They are created with two 18-cell shift registers.

218-1 = 262,143different scrambling codes can be formed using this method.

However, not all of them are used. The downlink scrambling codes are

divided into 512sets, of one primaryscrambling code and 15 secondary

scrambling codes each.

The primary scrambling codes are scrambling codes n=16*iwhere i=0511.The 15 secondary scrambling codes associated to one primary scrambling

code are n=16*i + k, where k=115. For now 8192scrambling codes have

been defined.


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There is a total of 512 primary codes. They are further divided into 64

primary scrambling code groupsof 8 primary scrambling codes each. Eachcell is allocated one and only one primary scrambling code. The group of the

primary scrambling code is found by the mobiles of the cell using the SCH,

while the specific primary scrambling code used is given by the CPICH. The

primary CCPCHand theprimary CPICHchannels are always scrambled with

the primary scrambling code of the cell, while other channels can be

scrambled by either the primary or the secondary scrambling code.


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In UMTS, there are 3 types of channels:

Logical channels: each logical channel type is defined by is transferred.

Transport channels: each transport channel is described by and with data is transmitted over the radio interface.

Physical channels: provide the real transmission resource, being in charge of theassociation between bits and physical symbols (electrical signals). It corresponds, inUMTS, to a frequency , a specific set of codes and phase.

As a conclusion:

Physical Channel= information container

Transport Channel= characteristics of transmission

Logical Channel= specification of the information global content


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As in GSM, UMTS uses the concept of logical channels.

A logical channel is characterized by the type of informationthat is transferred.

For example, some channels are used to transfer dedicated information, some for transfer of general control

information, etc..

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-directionalchannel, 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 sublayer will also add a header to the RLC PDU.

Common Traffic CHannel (CTCH):a point-to-multipoint downlinkchannel for transfer of dedicated

user information for all or a group of specified UEs. This channel is used tobroadcast 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.

The control channels are:

Broadcast Control CHannel (BCCH):a downlinkchannel that broadcasts all system informationtypes (except type 14 that is only used in TDD). For example, system information type 3 gives the cellidentity. UEs decode system information on the BCH except when in Cell_DCH mode. In that case, theycan decode system information type 10 on the FACH and other important signaling is sent on a DCCH.

Paging Control CHannel (PCCH):a downlinkchannel that transfers paging information. It is used toreach a UE (or several UEs) in idle modeor in connected mode(Cell_PCH or URA_PCH state). Thepaging 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-directionalchannel that transmits dedicatedcontrol information between a UE and the network. This channel is used for dedicated signaling after aRRC connection has been done. For example, it is used for inter-frequency handover procedure, fordedicated paging, for the active set update procedure and for the control and report of measurements.

Common Control CHannel (CCCH):a bi-directionalchannel for transmitting control informationbetween network and UEs. It is used to send messages related to RRC connection, cell update and URAupdate. This channel is a bit like the DCCH, but will be used when the UE has not yet been identified bythe 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 thesame channel, and will send him its temporary identities (cell and UTRAN identities). After these initialmessages, the DCCH will be used.


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In order to carry logical channels, several transport channels are defined.

They are:

Broadcast CHannel (BCH):a downlinkchannel used for broadcast of system

information into the entire cell.

Paging CHannel (PCH):a downlinkchannel used for broadcast of control

information into the entire cell, such as paging.

Random Access CHannel (RACH):a contention based uplinkchannel 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 downlinkchannel 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.


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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 carrier frequency, code and relative phase. In

CDMA system, the different code (scrambling code or spreading code)

can distinguish the channel. 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. Lets look at the uplink

physical channel first.


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The different physical channels are:

Synchronization CHannel (SCH):used for cell search procedure. There is the

primary and the secondary SCHs. Downlink.

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). Downlink.

Common Pilot CHannels (P-CPICH and S-CPICH):used for coherent detection

of common channels. They indicate the phase reference. Downlink.

Dedicated Physical Data CHannel (DPDCH):used to carry dedicated data coming

from layer 2 and above (coming from DCH). Uplink and Downlink.

Dedicated Physical Control CHannel (DPCCH):used to carry dedicated control

information generated in layer 1 (such as pilot, TPC and TFCI bits). Uplink and

Downlink.

Page Indicator CHannel (PICH):carries indication to inform the UE that paging

information is available on the S-CCPCH. Downlink.

Acquisition Indicator CHannel (AICH):it is used to inform a UE that the network

has received its access request. Downlink.

High Speed Packet Downlink Shared

CHannel (HS-PDSCH):it is used to carrysubscribers BE service data (mapping on HSDPA) coming from layer 2. Downlink.

High Speed Shared Control Channel (HS-SCCH):it is used to carry control

message to HS-PDSCH such as modulation scheme, UE ID etc. Downlink.


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The different physical channels are:

Dedicated Physical Data CHannel (DPDCH):used to carry dedicateddata coming from layer 2 and above (coming from DCH). Uplink and

Downlink.

Dedicated Physical Control CHannel (DPCCH):used to carry dedicated

control information generated in layer 1 (such as pilot, TPC and TFCI bits).

Uplink and Downlink.

Physical Random Access CHannel (PRACH):used to carry random

access information when a UE wants to access the network. Uplink.

High Speed Dedicated Physical Control CHannel (HS-DPCCH):it is

used to carry feedback message to HS-PDSCH such CQI,ACK/NACK.

Uplink.


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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.

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.

The P-SCH, which 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.

Each cell of a node B has its own SCH timing, so that there is no overlapping.


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The S-SCH also consists of a code, the Secondary Synchronization Code (SSC) that

indicates which of the 64 scrambling code groups the cells 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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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 CPICH 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.

There are two types of common pilot channels, the primary and secondary CPICH. The use

of the S-CPICH is optional.

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.

If it is used, the S-CPICH provides the phase reference for the secondary CCPCH and the

downlink DPCH. It is transmitted over the entire cell or only over a part of the cell. It is

spread by an arbitrary channelization code of SF=256, and scrambled with the primary or

with a secondary scrambling code.


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The Primary Common Control Physical Channel(P-CCPCH) is a fixed

rate (SF=256) downlink physical channel used to carry the BCHtransportchannel. 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 transmittedduring 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. Also,

it is always scrambled by the primary scrambling code of the cell.


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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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The Secondary Common Control Physical Channel(S-CCPCH) is used to carry the

FACH and PCHtransport 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 sublayer. 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 softhandover. The advantage is that it is a

fast access channel.


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The Physical Random Access Channel (PRACH)is used by the UE to access the network andto carry small data packets. It carries the RACH transport channel. The PRACH is an open looppower 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 andthe message part that carries the RACH message. The preamble is anidentifier which consists of 256 repetitions of a 16 chip long signature(total of 4096 chips). There are 16 possible signatures which correspondto the 16 OVSF codes of SF=16. Basically, the UE randomly selectsone of the 16 possible preambles and transmits it at increasing poweruntil it gets a response from the network (on the AICH). That preambleis scrambled before being sent. That is a sign that the power level ishigh enough and that the UE is authorized to transmit, which it will doafter acknowledgment from the network. If the UE doesnt get aresponse 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) andis made of the RACH data and the layer 1 control information.


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The PRACH transmission is based on the access framestructure. Theaccess 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 waitat least 3 or 4 access slots between two consecutive preambles.

The PRACH resources (access slots and preamble signatures) can bedivided between different Access Service Classes (ASC) in order to

provide different priorities of RACH usage. The ASC number rangesfrom 0 (highest priority) to 7 (lowest priority).


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The data and control bits of the message part are processed in parallel. TheSF 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 estimationand 2 TFCI bits to indicate the transport format of the RACH (transportchannel), for a total of 10 bits per slot.

The OVSF codes to use (one for RACH data and one for control) depend onthe signature that was used fo the preamble (for signatures s=0 to s=15:OVSFcontrol= Cch,256,m, where m=16s + 15; OVSFdata= Cch,SF,m, wherem=SF*s/16.


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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 node B receives the random access from a

mobile, it sends back the signature of the mobile to grant its access. If the node B 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 node B 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 is given by a predefined table. There are 16 sequences

, 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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Now look at the feature of uplink dedicated physical channel.

Pilot is used to help demodulate

TFCI: transport format combination indicator

FBI:used for the FBTD. (feedback TX diversity)

TPC: used to transport power control command.

Dedicated channels are established between one UE and the network to carry user

dedicated data and control.

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 sublayer control bits.

There can be up to 6 uplink DPDCHs, but only one DPCCH is associated to these

DPDCHs on each radio link. More than one DPDCH is used for data rates above

960 ksps (maximum capacity of one DPDCH). Thus, the maximum channel bit rate

for one UE is 960 * 6 = 5.76 Msps in uplink, which can correspond to a user bit rate

of 2.048 Mbps.


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One 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

The different slot formats of the DPDCH and the DPCCH are given in

TS 25.211.

The SF of the DPDCH is determined by higher layers.


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Downlink physical channels are used to carry user specific information like

speech, data or signaling, as well as layer 1 control bits. Like it wasmentioned 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.


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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

chips of one slot is also 2560. Because the SF of downlink DPCH can be 512, so the k

can be 7.

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.

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 whenthe TFC doesnt change.

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.


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HS-PDSCH is a downlink physical channel that carries user data and layer2

overhead bits mapped from the transport channel: HS-DSCH.

The user data and layer2 overhead bits from HS-DSCH is mapped onto one or

several HS-PDSCH and transferred in 2 ms subframe using one or several

channelization code with fixed SF=16


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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 theHS-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)

1.Modulation scheme(1bit) QPSK or 16QAM

2.Channelization Code Set (7bits)

3.Transport Size ( 6bits)

4.HARQ process number (3bits)

5.Redundancy version (3bits)

6.New Data Indicator (1bit)

7.UE identity (16 bits)

In each 2 ms interval corresponding to one HS-DSCH TTI , one HS-SCCH carries physical-layer signalling to asingle 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 asseen from a UE point of view .i.e. UE must be able to decode four HS-SCCH.

1. The HS-SCCH is a fixed rate (60 kbps, SF=128) downlink physical channel used to carry downlink signallingrelated to HS-DSCH transmission

2. XueUE IDHS-SCCHUE

XccsHS-PDSCH

XmsQPSK16QAM

Xrv16QAM

Xtbs

XhapHARQXnd


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The uplink HS-DSCH related physical layer signalling consists of:

1.Acknowledgements for HARQ

2.Channel Quality Indicator (CQI)

As the HS-SCCH 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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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 sublayer.

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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The purpose of the Cell Search Procedureis 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 SCHs 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 boundariesand 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.

CPICH(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 CPICH with all the codeswithin 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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This page shows the transmission timing of the various downlink channels. The 256

chips gap in the beginning of each of the PCCPCH slots is to accommodate the

transmission of the SCH. The SCH is always transmitted from the base station and is

transmitted at the same timing reference as the CPICH. The SCCPCH is only

transmitted when there is data available. Therefore ,it has its own transmission

timing. The timing offset is a multiple of 256 chips. The PICH has a fixed time

offset time offset with respect to the SCCPCH to be able to tell UE that there is

paging coming on the PCH mapped onto the SCCPCH


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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 nor1)

corresponding to the selected signature is detected in the downlink accessslot 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


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Transmitter-antenna diversity can be used to generate multipath diversity in

places where it would not otherwise exist. Multipath diversity is a usefulphenomenon, 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 Node B 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 Node B 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 Node Bcannot 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

em lo closed loo ower control, as the are allocated for onl one user at a


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The TX diversity methods in the open-loop mode are

(1) space time-block coding-based transmit-antenna diversity (STTD)

(2) 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 symbol sequence for the second pilot is given in

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 UEs receiver.


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Time-switched transmit diversity (TSTD) can be applied to the SCH. Just as

with STTD, the support of TSTD is optional in the UTRAN, but mandatory inthe 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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The closed-loop-mode transmit diversity can only be applied to the

downlink channel if there is an associated uplink channel. Thus this

mode canonly 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. This is depicted in next slide .The UE uses

the base stations 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 UEs 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


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OWA200003 WCDMA Radio Interface_Physical Layer (With Comment) ISSUE 1.0(Fr)

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