3g overview - part6 dedicated physical channels
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Part VI
Dedicated Physical
Channels
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Downlink Dedicated Physical Channel (DPCH)
The downlink DPCH is used to transmit the DCH data. Control information and user
data are time multiplexed. The control data is associated with the Dedicated
Physical Control Channel (DPCCH), while the user data is associated with theDedicated Physical Data Channel (DPDCH).
The transmission is organised in 10 ms radio frames, which are divided into 15
timeslots. The timeslot length is 2560 chips. Within each timeslot, following fields
can be found: Data field 1 and data field 2, which carry DPDCH information
Transmission Power Control (TPC) bit field
Transport Format Combination Indicator (TFCI) field, which is optional
Pilot bits
The exact length of the fields depends on the slot format, which is determined byhigher layers. The TFCI is optional, because it is not required for services with fixed
data rates. Slot format are also defined for the compressed mode; hereby different
slot formats are in used, when compression is archived by a changed spreading
factor or a changed puncturing scheme.The pilot sequence is used for channel estimation as well as for the SIR ratio
determination within the inner loop power control. The number of the pilot bits can
be 2, 4, 8 and 16 it is adjusted with the spreading factor. A similar adjustment is
done for the TPC value; its bit numbers range between 2, 4 and 8.
The spreading factor for a DPCH can range between 4 and 512. The spreading factor
can be changed every TTI period.
Superframes last 720 ms and were introduced for GSM-UMTS handover support.
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Downlink Dedicated Physical Channel (DPCH)
Superframe = 720 ms
Radio Frame
0
Radio Frame
1
Radio Frame
2
Radio Frame
71
10 ms Frame
Slot 0 Slot 1 Slot 2 Slot 14
TPC
bits
Pilot bitsTFCI
bits
(optional)
Data 2 bitsData 1 bits
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DPDCHDPDCH DPCCH DPCCH
17 different slot formats
Compressed mode slotformat for changed SF
& changed puncturing
2,4,8,16 bits (SIR estimation)2,4,8 bits
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Downlink Dedicated Physical Channel (DPCH)
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Following features are supported in the downlink:
Blind rate detection, and Discontinuous transmission.
Rate matching is done to the maximum bit rate of the connection. Lower bit rates are
possible, including the option of discontinuous transmission. Please note, that
audible interference imposes no problem in the downlink, since Common Channelshave continuous transmission.
Multicode usage:Several physical channels can be allocated in the downlink to one UE. This can
occur, when several DPCH are combined in one CCTrCH in the PHY layer, and the
data rate of the CCTrCH exceeds the maximum data rates allowed for the physical
channels. Then, on all downlink DPCHs, the same spreading factor is used. Also
the downlink transmission of the DPCHs takes place synchronous. One DPCH
carries DPDCH and DPCCH information, while on the remaining DPCHs, noDPCCH information is transmitted.
But also in the case, when several DPCHs with different spreading factors are in use,
the first DPCH carries the DPCCH information, while in the remaining DPCHs, this
information is omitted (discontinuous transmission).
Multicode usage is not implemented in RAN1.
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Physical Layer Bit Rates (Downlink)
Spreading
factor
Channel
symbol
rate(ksps)
Channel
bit rate
(kbps)
DPDCH
channel bit
rate range(kbps)
Maximum user
data rate with -
rate coding(approx.)
512 7.5 15 36 13 kbps256 15 30 1224 612 kbps
128 30 60 4251 2024 kbps
64 60 120 90 45 kbps
32 120 240 210 105 kbps16 240 480 432 215 kbps
8 480 960 912 456 kbps
4 960 1920 1872 936 kbps
4, with 3
parallelcodes
2880 5760 5616 2.8 Mbps
The number of orthogonal channelization codes = Spreading factor
Half rate speech
Full rate speech
128 kbps
384 kbps
2 Mbps
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Downlink Dedicated Physical Channel (DPCH)
TS TS
maximum bit rate
TS TS TS
discontinuous transmission with lower bit rate
Multicode usage:
TS TS TS
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TS TS TS
DPCH 1
DPCH 2
DPCH 3
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Power Offsets for the DPCH
Node B RNC
DCH Data Frame
Iub
UE
Uu
PO1
NBAP: RADIO LINK SETUP REQUEST
TPC
bitsPilot bits
TFCI
bits(optional) Data 2 bitsData 1 bits
PO3PO2
Power offsets
TFCS
DL DPCH slot
format
FDD DL TPCstep size
P0x: 0..6 dB
step size: 0.25dB
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Nokia Parameters Related to DPCHs
RNC: PowerOffsetDLdpcchPilot
The parameter defines the power offset for the pilot symbols in relative tothe data symbols in dedicated downlink physical channel[0 6 dB]; step size 0.25 dB; default: 3 dB for 12.2 kbps
RNC: PowerOffsetDLdpcchTpc,The parameter defines the power offset for the TPC symbols relative to thedata symbols in dedicated downlink physical channel[0 6 dB]; step size 0.25 dB; default: 3 dB for 12.2 kbps
RNC: PowerOffsetDLdpcchTfci,The parameter defines the power offset for the TFCI symbols relative to thedata symbols in dedicated downlink physical channel.[0 6 dB], step size 0.25 dB; default: 3 dB for 12.2 kbps
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Superframe = 720 ms
Slot 0 Slot 1 Slot 2 Slot 14
10 ms Frame
TPC
bits
Pilot bitsTFCI bits(optional)
Data 1 bits
Radio Frame
0
Radio Frame
1
Radio Frame
2
Radio Frame
71
DPDCH
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DPCCH FBI bits
7
differentslot
formats
6 different slotformats
Compressed mode
slot format for
changed SF &
changed puncturing
Feedback Indicator for
Closed loop mode transmit
diversity, & Site selection diversity
transmission (SSDT)
Uplink Dedicated Physical Channels
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Discontinuous Transmission and Power OffsetsDiscontinuous transmission (DTX) is supported for the DCH both uplink and
downlink. If DTX is applied in the downlink as it is done with speech then 3000
bursts are generated in one second. (1500 times the pilot sequence, 1500 times the
TPC bits) This causes two problems:
Inter-frequency interference, caused by the burst generation. At the Node B, the
problem can be overcome with exquisite filter equipment. This filter equipment is
expensive and heavy. Therefore it cannot be applied in the UE. The UEs solution isI/Q code multiplexing, with a continuous transmission for the DPCCH. DPDCH
changes can still occur, but they are limited to the TTI period. The minimum TTI
period is 10 ms. The same effects can be observed, then the DPDCH data rate and
with it its output power is changing. 3000 bursts causes audible interference with other equipment just see for
example GSM. By reducing the changes to the TTI period, the audible interference
is reduced, too.
Determination of the power difference between the DPCCH and DPDCHI/Q code multiplexing is done in the uplink, i.e. the DPCCH and DPDCH are transmitted with
different codes (and possible with different spreading factors). Gain factors are specified: c is
the gain factor for the DPCCH, while d is the gain factor for the DPDCH. The gain factors
may vary for each TFC. There are two ways, how the UE may learn about the gain factors:
The gain factors are signalled for each TFC.
If so, the nominal power relationAj between the DPDCH and DPCCH is d/c. The gain factor is calculated based on reference TFCs.
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DPCCH
DPDCH
DPCCH
DPDCH
DPCCH
DPDCH
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TTI TTI TTI
UL DPDCH/DPCH Power Difference:
DPCCH
DPDCH
=dc
=Nominal Power RelationAj
two methods to determine the gain factors:
signalled for each TFCs
calculation based on reference TFCs
Discontinuous Transmission and Power Offsets
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Initial Uplink DCH Transmission
When we look to the PRACH, we can see, that a preambles were used to avoid UEs
to access UTRAN with a too high initial transmission power. The same principle isapplied for the DPCH.After PRACH procedure the UE transmits between 0 to 7
radio frames only the DPCCH uplink (the period is called DPCCH power control
Preamble), before the DPDCH is code multiplexed. The number of radio frames is
set by the higher layers (RRC resp. the operator).Also for this period of time, onlyDPCCH can be found in the downlink.
The UE can be also informed about a delay regarding RRC signalling this is
called SRB delay, which can also last 0 to 7 radio frames. The SRB delay follows
after the DPCCH preamble.
How to set the the transmission power of the first UL DPCCH preamble? Its powerlevel is
DPCCH_Initial_power = CPICH_RSCP + DPCCH_Power_offset
The DPCCH Power Offset is retrieved from RRC messages. Its value ranges
between 164 and 6 dB (step size 2 dB). CPICH_RSCP is the received signalcode power on the P-CPICH, measured by the UE.
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Initial Uplink DCH Transmission
T0
DPCCH only DPCCH & DPDCH
reception
at UE
trans-
mission
at UE
0 to 7 frames for
power control preamble
DPCCH only,
always based on PCA1
DPCCH & DPDCH
PCA based on RRC
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DPCCH_Init ial_power = CPICH_RSCP + DPCCH_Power_offset
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Radio frame timing and access slot timing of downlink physical channels
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k:th S-CCPCH
AICH accessslots
SecondarySCH
PrimarySCH
S-CCPCH,k
10 ms
PICH
#0 #1 #2 #3 #14#13#12#11#10#9#8#7#6#5#4
Radio framewith (SFN modulo 2) = 0 Radio framewith (SFN modulo 2) = 1
DPCH,n
P-CCPCH
Any CPICH
PICH for k:thS-CCPCH
Any PDSCH
n:th DPCH
10 ms
Subframe#0
HS-SCCHSubframes
Subframe#1
Subframe#2
Subframe#3
Subframe#4