HSDPA
High-Speed Downlink Packet Access (HSDPA)
Why HSDPA?
Gain more throughput per cell and higher bit rate per user.
HSDPA is based on the following features
•Higher-order modulation
•Shared channel transmission
•Short transmission time interval (TTI)
•Fast link adaptation
•Fast scheduling
•Fast hybrid automatic-repeat-request (ARQ)
•Dynamic Power Allocation
High-Speed Downlink Packet Access (Cont’d)
Fixed Spreading Factor =16
Multi Code Transmission
Two types of multiplexing TDM and CDM
HSDPA features
1- Short TTI (2 MS)
•One reason for a shorter TTI is to reduce the air-interface delay by reducing the RTT
•This will improve the end-user performance since shorter TTI improves the interaction with
TCP/IP.
Old releases
80 ms
40 ms
20 ms
10 ms
2 ms
HSDPA
2- Shared Channel Transmission
•Certain amount of radio resources of a cell (code space and power) is seen as a common are
dynamically shared between users in the time domain.
•The main benefit with DL shared channel transmission is to reduce the risk for code-limited
capacity and power limited capacity
HSDPA features (Cont’d)
Shared channel transmission(Cont’d)
SF
1
2
4
Channelization codes allocated
for HS-DSCH transmission
8 codes (example)
8
16
32
Shared
channelization
codes
TTI=2ms
TTI=2ms
TTI=2ms
TTI=2ms
TTI=2ms
time
HSDPA features (Cont’d)
3- Higher-Order Modulation
•R99 is based on QPSK modulation
•To support higher data rates, higher-order data modulation, such as 16QAM
•Higher-order modulation is more bandwidth efficient, i.e. can carry more bits per Hertz.
•Higher-order modulation is also less robust and typically requires higher energy per bit for a
given a given error rate
HSDPA features (Cont’d)
4-Fast Link Adaptation
•Radio-channel conditions will typically vary significantly, both in time and between different
positions
•Reasons for these variations in channel conditions:
Different positions within the cell, due to distance dependent path loss and locationdependent shadowing
Variations in the interference level.
The interference level will depend on:
The position within the cell, with typically higher interference level close to the
cell border.
The instantaneous transmission activity of neighbor cells.
Own-cell interference
Multi-path fading, The rate of these variations depends on the speed of the mobile
terminal.
HSDPA features (Cont’d)
Multi-path propagation
2
3
0
1
Time dispersion
h()
0
1 2
3

HSDPA features (Cont’d)
Combined Signal
Direct Signal
Reflected Signal
Combined Signal
HSDPA features (Cont’d)
Fast (Rayleigh) Fading due to Multipath relctions
Composite
Received
Signal
Strength
msec
Deep fade caused by destructive summation
of two or more multipath reflections
Deep fade caused by destructive summation
of two or more multipath reflections
time (mSec)
HSDPA features (Cont’d)
Fast link adaptation(Cont’d)
Fast adjustment of the data rate every TTI (2 ms).
E b C RC
 
No
I Rb
HSDPA features (Cont’d)
5- Fast Channel Dependent Scheduling
Scheduled User
User 1
User 2
TTI=2ms
TTI=2ms TTI=2ms
TTI=2ms TTI=2ms
TTI=2ms
TTI=2ms
HSDPA features (Cont’d)
Scheduling algorithms
Max C/I Ratio
oAssign the channel to the user with the best channel quality
oHigh system throughput but not fair(if user is on cell border)
Round Robin (RR)
oCyclically assign the channel to users without taking channel conditions into account
oSimple but poor performance
Proportional Fair (PF)
oSchedules all users in the cell but prioritize users with better channel quality
oBut ensure that all users receive a guaranteed minimum throughput. It gives rather
High throughput, fair
HSDPA features (Cont’d)
6- Fast hybrid automatic-repeat-request (ARQ)
P1
P2
P3
P2
P1
P3
HSDPA features (Cont’d)
7-Dynamic Power Allocation
Power
Max cell power
HSDPA power
DCH Power
CCH power
•HSDPA will take the power left after CCHs and DCHs have taken their parts
•Average power utilization will increase in the network with HSDPA
time
HSDPA Mobility
HSDPA Mobility
HSDPA introduction
•3GPP Release 5 extends the WCDMA specification with a new downlink transport channel for packet data,
the High-Speed Downlink Shared Channel (HS-DSCH).
•The HS-DSCH utilizes the remaining transmission power which is not used for the dedicated and common
channels.
•With shared channel transmission, a certain amount of the channelization codes and transmission power in
a cell are considered a common resource that is dynamically shared among the users.
Power
Max Cell Power
HSDPA power
DCH Power
CCH power
time
HSDPA Mobility (Cont’d)
HS-DSCH - High-Speed Downlink Shared Channel
Mapped on one or several (HS-PDSCHs) which are simultaneously received by the UE.
In the 3GPP standard, there are up to 15 HS-PDSCHs per cell with the spreading factor fixed 16. The number
of HS-PDSCHs per cell is configurable and depending on the license, each cell has up to 5, 10, or 15 HSPDSCHs.
High-Speed Shared Control Channel (HS-SCCH)
Carries control information to the scheduled UE.
The control information required for each 2-ms TTI
UE ID
Codes
Modulation
Coding%
High-Speed Dedicated Physical Control Channel (HS-DPCCH)
•The UE uses this channel to :
oRequest retransmission of the incorrectly received blocks on the HS-DSCH (ACK/NACK)
oReport CQI is used by the scheduling and link adaptation functions
HSDPA Mobility (Cont’d)
Transport Channel
Physical Channel
HS-DPCCH
RBS
CQI Request
HS-SCCH
HS-DSCH
User
User data
data
Control Information
UE ID, codes, Modulation ,Coding%
HS-DPCCH
ACK/NACK
HS-PDSCH
A-DCH
User data
User data +
Over head bits
HSDPA Mobility (Cont’d)
•The dedicated uplink and downlink channels use soft handover.
•HS-DSCH do not use soft handover as it is shared transport channel.
•Mobility for the HS-DSCH is called HS-DSCH cell change
•HS-SCCH carries control signaling for the HS-DSCH, and is never in soft handover.
•HS-DPCCH only capable of softer handovers since it is terminated in the RBS
RNC
IUR
IUB
RNC
IUB
Cell Change
Softer HO
RBS
Soft /Softer HO
RBS
HSDPA Mobility (Cont’d)
•Serving cell change is triggered when:
oChange of the best cell within the Active set (event 1d HS).
oCurrent serving cell should be removed or replaced from the Active set (event 1b or 1c).
•When HSDPA is started, an extra MEASUREMENT CONTROL related to the event 1d HS , is
sent to the UE having another MEASUREMENT ID
•The reason for having a separate event 1d HS is to be able to
oUse different hysteresis
oUse different time to trigger parameters to trigger serving HS-DSCH. It
oUse a different quality criteria
HS-DSCH mobility can be divided into the following parts:
oServing HS-DSCH Cell Change triggered by change of “Best Cell” within the Active Set.
oServing HS-DSCH Cell Change triggered by removal of the serving HS-DSCH cell from the Active Set.
oCoverage triggered IF or IRAT HO attempts,
oHS-DSCH Cell Selection.
HSDPA Mobility (Cont’d)
When a serving HS-DSCH Cell Change is triggered by change of best cell
Change of best cell
RNC will take no more
actions
blocked
OFF
event 1d HS
hsToDchTrigger
Transition
to
DCH is
allowed?
Serving HS-DSCH
Cell Change Evaluation
Admission
Control
HS to DCH
ON
hsCellChangeAllowed
Cell
Change
Allowed ?
No
RNC attempt to
reconfigure to DCH
False
TRUE
Yes
RNC selects the best of
the active set cells
Fail in Execution
No (No Suitable
HS cell is found)
No
Target. Cell
Support
HS
Yes
No
Target
Cell
DRNC
with IUR?
Yes
RNC Execution
Yes
IUR link
Support
HS?
HSDPA Mobility (Cont’d)
Serving HS-DSCH Cell Change triggered by removal of the serving HS-DSCH cell from the
Active Set.
Removal of the current serving cell
RNC shall release the
connection
blocked
OFF
event 1b
hsToDchTrigger
Transition
to
DCH is
allowed?
Serving HS-DSCH
Cell Change Evaluation
supports HS-DSCH
Admission
Control
HS to DCH
ON
hsCellChangeAllowed
Cell
Change
Allowed ?
No
RNC attempt to
reconfigure to DCH
False
TRUE
Yes
RNC selects the best of the
other remaining active set
cells
Fail in Execution
No (No Suitable
HS cell is found)
No
Target. Cell
Support
HS
Target
Cell
DRNC
with IUR?
Yes
Yes
No
Yes
RNC Execution
IUR link
Support
HS?
HSDPA Mobility (Cont’d)
Coverage Triggered IF or IRAT HO attempt
OFF
event 2d /6d
RNC will take no more
actions
blocked
hsToDchTrigger
No
IF/IRAT
Mobility
HSDPA
Active?
Transition
to
DCH is
allowed?
RNC attempt to
reconfigure to DCH
ON
Admission
Control
Yes
Compressed Mode
HS to DCH
IF or IRAT HO attempt
might start
GSM_PREFERRED
HoYType
Yes
IFHO_PREFERRED
no defined
GSM neighbors
IF
handover
can not be
done
IRAT
handover
can not be
done
NO
Yes
no defined
IF neighbors
NO
Execution
Yes
Support
HS
NO
CQI
HSDPA Mobility (Cont’d)
•CQI report
oUE sends a Channel Quality Indicator (CQI) on the uplink (HS-DPCCH)
oCQI
Estimates the number of bits that can be transmitted to the UE using a certain assumed HSPDSCH power with a block error rate of 10%
UE receiver performance
Good UE receiver can report that it can receive more bits than a Bad UE receiver
implementation for the same channel conditions.
PCPICH_RX
Г
∆
Received power of the P-CPICH
Measurement Power Offset MPO
Cell level parameter hsMeasurementPowerOffset
Reference power adjustment
Given by Table 7A, 7B, 7C, 7D, 7E, 7F or 7G depending on
the UE category.
HSDPA Mobility (Cont’d)
Physical layer procedures (FDD), 3GPP TS 25.214
•CQI algorithm indicates
•Transport block size
•Number of HS-PDSCH codes
•Modulation Type
•HS-PDSCH Power
•HSDPA Scheduler algorithm indicates
• Which UE to transmit to in the TTI,
•Available HS-PDSCH transmission power,
Available number of HS-PDSCH codes.
•It does not indicate how much data to
transmit.
CQI
Value
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
Transport Block Number
Size
of HSPDSCH
137
1
173
1
233
1
317
1
377
1
461
1
650
2
792
2
931
2
1262
3
1483
3
1742
3
2279
4
2583
4
3319
5
3565
5
4189
5
4664
5
5287
5
5887
5
6554
5
7168
5
7168
5
7168
5
7168
5
7168
5
7168
5
7168
5
7168
5
7168
5
CAT6
Modulation
QPSK
QPSK
QPSK
QPSK
QPSK
QPSK
QPSK
QPSK
QPSK
QPSK
QPSK
QPSK
QPSK
QPSK
QPSK
16-QAM
16-QAM
16-QAM
16-QAM
16-QAM
16-QAM
16-QAM
16-QAM
16-QAM
16-QAM
16-QAM
16-QAM
16-QAM
16-QAM
16-QAM
Reference Power
Adjustment
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
-1
-2
-3
-4
-5
-6
-7
-8
Why CQI !
Why CQI
Back to Developing Basics
Back to Developing Basics
PN 1
PN 2
PN 3
OC5, OC6, OC7
OC3, OC4
OC1, OC2
OC1, OC2
•PN codes (distinguish each Base Station)
Not orthogonal
High cross correlation properties
PN1 * PN2 ≠ 0 (mini. output)
•Channelization Codes (distinguish data channels Coming from each Base Station)
Orthogonal Codes
OC1 * OC2 = 0
Back to Developing Basics (Cont’d)
PN 1
PN 2
Ec/No=-11 dB
CQI=27
Ec/No=-11 dB
CQI=20
PN 1
PN 3
PN 4
Back to Developing Basics (Cont’d)
•Ec/No for most of us is quality measurement metric.
•It gives us how good or bad the link quality is.
•However by definition it is confusing
•RSCP
Received signal code power
Received power level of pilot channel of a one cell (dBm/mW)
Using RSCP we can compare different cells
Using RSCP handover and cell reselection decisions can be taken
•RSSI
Signal power over the complete 5MHZ carrier which include all components received
Signal from the current cell and neighboring cells on the same frequency
Theoretically in an isolated cell having only CPICH power with no other channels
RSSI ≈ CPICH power
RSSI will change if the carrier use the DCH or the common channels
Back to Developing Basics (Cont’d)
•CPICH Ec/No
Pilot channel quality ,energy per chip over total received power spectral density
Ec/No= RSCP/RSSI
The Better this value the better the signal can be distinguished from the over all nosie
Always negative
Using Ec/No we can compare different cells
Using Ec/No handover and cell reselection decisions can be taken
•No
Noise power spectral density
Interfering power
Non interfering power
Thermal noise
•Test bed being served by single cell
Ec/No of UE is
oMeasure of PCPICH =RSCP
oMeasure of total wide band power =RSSI
Back to Developing Basics (Cont’d)
•Assume that UE is in Test bed being served by single cell`
Cell MAXTXPOWER 20 watt (43 dBm)
Assuming that 10 % of the cell power is dedicated for CPICH 2 watt (33 dBm)
If you have no DCH or HS channels
Ec/No= 10 log (CPICH Power/Total transmitted power)
Ec/No=10 log (2w/2w)= 10 log 1 = 0
Power
2 watt
CPICH Power
Non consumed power
•Assume that you start HS session
Ec/No= 10 log (CPICH Power/Total transmitted power)
Ec/No=10 log (2w/20w)= -10 dB (Poor value)
Ec/No will always give a false value for an HSDPA user
HSDPA Power
20 watt
Why CQI
Why CQI
CQI Adjustment
1
18
19
20
21
22
23
24
25
26
27
28
29
30
Transport block Size increase
Number of codes increase
Higher order Modulation technique
More probability of Scheduling
•Deviating CQI reports lead to faulty decisions
•CQI accuracy will continue to vary depend on :
UE model
UE vendor
Deviating CQI
oUE that consistently overestimates the channel quality
Scheduled too often, at the price of other users.
Experience a block error rate that is higher than the target 10%, with more retransmissions and reduced
system throughput and increased service delay
oUE instead underestimates the channel quality
 Scheduled too seldom.
Experience a Block error rate will be lower than 10%, which will lead to lower transmitted data rates than
possible and hence reduced system throughput.
•In both cases, both system throughput and end-user experience of the service is negatively impacted.
Why CQI
•To avoid the negative system impact due to inaccurate CQI reports,
CQI adjustment algorithm
RBS works on the ACKs and NACKs received from the UE to determine if the UE is overestimating or
underestimating the channel quality.
The algorithm make every effort to achieve a block error rate of 10%
BLER =10%
Increase CQI
Decrease CQI
BLER
The output from the adjustment algorithm is CQIadjusted,
The CQI adjustment algorithm is an optional feature and can be enabled on cell level through
parameter cqiAdjustmentOn.
Thank you
Thanks