HSPA scheduling principles

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HSPA Scheduling

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contents
 UMTS evolution path .
 HSDPA scheduling algorithm and functions .
 Dynamic code allocation in HSDPA .
 Code multiplexing in HSDPA .
 “CQI adjustment on feature” in HSDPA .
 Maximum throughput calculation –HSDPA .
 EUL scheduling and function .
 Maximum throughput calculation –EUL .
 Capacity parameters –HSDPA & EUL .

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UMTS Mobile evolution path
 Shown is the roadmap of 3GPP
 Peck rate up to 14.4 mbps/384 kbps is achieved with Rel 5.
 Peck rate up to 14.4 mbps/5.76 mbps and 42 mbps/11.5 mbps can be achieved with Rel 6
and Rel 7 .

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HSDPA THROUGHPUT ENHANCEMENT
The following are the enhancement made in HSDPA compared to R99 .
 Adaptive Modulation Coding
 Fast feedback of channel condition .
 QPSK or 16-QAM .
 Coding from R=1/3 to 1 .
 Multiple code allocation
 Multiple code allocated per user .
 Fixed spreading factor
 Node B scheduling
 Physical layer HARQ

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Additional channels in HSDPA
 High speed downlink physical shared channel( HS-PDSCH) : A downlink shared channel shared
by several UE’s.
 High speed shared control channel (HS-SCCH) :This channel will information like code details,
Modulation sheame,transport block size ect .
 High speed dedicated physical control channel (HS-DPCCH) : Carries the information for
channel dependent scheduling such as CQI, HARQ parameters .

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HSDPA-scheduling algorithms
 6 different Non-GBR scheduling algorithms are available in HSDPA , they are .
 Maximum CQI.
 Proportional fair – Low fairness .
 Proportional fair - Medium fairness .
 Proportional fair - High fairness .
 Round robin .
 Equal rate .
 We can choose the scheduling algorithm by setting parameter “queue select algorithm”.
 Round robin , Equal rate are fixed algorithm's and Maximum CQI , Proportional fair are
channel dependent algorithms based on the channel quality reported by UE .
 “Proportional fair - Medium fairness” is the commonly used algorithm .
 High fairness can be made by scaling down the CQI and low fairness by scaling up the
CQI .

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Scheduling in HSDPA-Proportional fair
 The HSDPA scheduler algorithm determines the priority queue that will be allocated the
HS-DSCH resource in the upcoming 2ms TTI.
 With code multiplexing , HSDPA scheduler can allocate the resources up to 4 different
users in one TTI .
.
1) Resource Estimation.
2) Queue validation.
3) Resource sharing.
4) Queue selection.
5) Remaining resource
check.

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Channel Quality Indicator-CQI
 The UE measures the channel quality of the downlink channel and measures the channel
quality index.
 The value is index in to a table , corresponds to maximum data rate the UE can decode
with an error rate of less than 10%.
 The index table for the UE depends on the category of the mobile. Means each UE
category have different CQI table.
 From the channel quality, CQI mapping is the preparatory algorithm by UE vendor.
 The number of times CQI repetition depends on parameter “ CQI-Repetition factor “
 The period of CQI reporting depends on parameter “CQI feedback cycle”
 “hsmeasurementpoweroffseton” is the offset relative to P-CPICH that the UE must use
when calculating the HS-PDSCH power in the CQI calculation.

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 The resource estimation procedure estimate the available HS-PDSCH codes and HS-PDSCH
power available in the upcoming TTI.
Resource scheduling at node B

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Dynamic code allocation
 HSDPA dynamic code allocation is done per cell.
 The algorithm will periodically check whether there are available codes free in the code
tree , if so add it to the HSDPA allocation .
 The Addition of HS-PDSCH codes is done periodically ( Once per second) .
 The codes that are added by dynamic code allocation will be immediately deallocated from
HS-DSCH if the request from RNC for DCH channel.
 “FeaturestateHSDPAdynamiccodeallocation” this parameter is used to activate dynamic
code allocation .
 “NumHSpdschcodes” Fixed number of codes allocated for HS-DSCH .
 The maximum number of codes can be added decides by License and parameter “
maxNumHSpdschcodes “ .

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Dynamic code allocation

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HSDPA scheduling and HS-scch
 Number of HS-SCCH channel will decide how many users allocate data in one 2ms TTI .
 Maximum 4 HS-SCCH channel can configure in one cell.
 Cell having one HS-SCCH channel can only schedule only one user in one 2ms TTI .
 “Hsscchmaxcode “ parameter will decide the power of HS-SCCH channel and by setting
“numscchcodes” we can configure number of HS-SCCH channel.
Scheduling with one HS-SCCH channel
Scheduling with more than one HS-SCCH channel

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HSDPA feature-CQI adjustment on
 CQI adjustment algoritham is an optional feature and can be enable through parameter
“cqiAdjustmenton”.
 By enabling this feature UE must report CQI so that the NACK ratio does not exceed
10%.
 This feature will help to reduce BLER rate and to improve the user throughput in most of
the case.
Disadvantage – CQI adjustment on
 This adversely effect in very good RF condition .
 In good RF condition the actual NACK ratio is better than its target value , but by enabling
CQI adjustment feature on the NACK ratio will be steered up to 10%, consequenly
throughput got decreases in some cases .

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Theoretical maximum throughput-hsdpa
 Throughput = (Chip rate /Spreading factor) *Number of HS-PDSCH codes
* TTI interval *Number of bits per symbol*Coding rate .
Maximum throughput with different modulation:
Here assume coding rate = 1 and TTI intervel =1
1) QPSK
Maximum Tput (DL) = 240 kbps * 15* 2*1*1 = 7.2 Mbps
2) 16-QAM
Maximum Tput (DL) = 240 kbps * 15* 4*1*1 = 14.4 Mbps
3) 64-QAM Maximum Tput (DL) = 240 kbps * 15* 6*1*1 = 21.6 Mbps
 “featureState16Qam” , “featureState64Qam” have to enble for
16QAM and 64 QAM modulation .

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Additional channels in EUL
 E-HICH (DL) :Hybrid indicator channel for channel depend scheduling.
 E-AGCH (DL) : Carries the scheduler grant information from E-DCH serving cell.
 E-RGCH (DL) :Carries the scheduler grant information from E-DCH non-serving cell in AS.
 E-DPDCH (UL): Enhanced uplink physical channel carrying payload
 E-DPCCH (UL): Enhanced uplink physical channel carrying control information.

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ThE enhancement in EUL
 2 ms TTI :2ms TTI added to previous TTI of 10 ms .
 Fast resource control : Allocation done in the node B scheduler instead of RNC .
 HARQ : Improve physical layer performance compared to ARQ .
 Spreading factor from 2 to 256 available in EUL .Multicodes up to 4 channels are available in
EUL .
 With 4 channels (2*SF2+2*SF4) : Maximum peak rate up to 5.72 Mbps with Rel 6.

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EUL-scheduling algorithms
 Several UE want to transmit at higher data rate all the item, the task of EUL scheduler is to
allocate available uplink resource not allocated by DCH users to E-DCH users .
 Node B scheduler ,works to satisfy all the requested grants while preventing overloading and
maximizing resource utilization.
 Scheduling consist of 4 steps a) Transmission request b) Grant assignment c) Data
transmission 4) Data acknowledgment

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EUL-Transmission request
 The UE request data transmission by means of scheduling information (SI).
 Scheduling information is determined according to the UE power and buffer data availability .

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EUL-grant assignment
 The Node B determines the UE grant by monitoring following .
1) Uplink interference ( Rise over thermal at receiver).
2) By considering UE transmission request (SI) .
3) Level of satisfaction ,the RBS hardware,lub transport capacity .
4) Max and min rate configuration at RNC , E-TFCI table .
 The node B provide the grant through E-AGCH channel .E-AGCH contains E-DPDCH/E-
DPCCH power ratio, UE convert the same in to transport format (E-TFC) .

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EUL-Data transmission
 The UE uses the received grant and based on its power and data availability, selects the E-
DCH transport format.
 The data transmitted by the UE along with control information.
 The transport format information is signaled to node B through E-DPCCH channel.

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EUL-Data ACKnowledgement
 The node B attempt to decode the received data and indicated to the UE with ACK/NAK
successful.
 If no ACK received by the UE , the data will retransmitted.
 The node B send the ACK/NAK through E-HICH channel .

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Theoretical maximum throughput-EUL
Here assume coding rate = 1 and TTI interval =1
1) With 10ms TTI and Offset-QPSK modulation .
 Offset –QPSK having one bit per symbol .
 Maximum Throughput put = 2*SF4 =2*960 kbps =1.96 Mbps ( SF2 was not
implemented with 10 ms TTI in P5) .
2) With 2ms TTI and Offset-QPSK modulation
 With multicode , up to 4 channels can be used .
 Maximum Throughput put =2*SF2+2*SF4 = 2*1.96 +2*0.960=5.76 mbps .
3) With 2ms TTI and 4PAM modulation
 4PAM modulation provide 2 bits per symbol .
 Maximum Throughput put =2*SF2+2*SF4 = 2*2*1.96 +2*2*0.960=11.52mbps .

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EUL scheduling parameters
 “eultargetrate” : if the scheduled grant is below “eultargetrate” , the EUL scheduler
always try to increase the grant to at least “eultargetrate”
 “eulNoReschUsers” at rescheduling, a maximum of eulNoReschUsers EUL users per
cell can be involved
 “eulMaxNoSchEdch:” this parameter decide how may users can use zero throughput .
 “eulMaxShoRate “ decide the maximum rate in soft handover , maximum rate in soft
handover cannot exceed this parameter .

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Capacity parameters-HSDPA and EUL
 The following are the parameters restricting capacity in HSDPA and EUL.
 “hsdpausersadm” is the cell parameter that defines the admission limit for number of users
assigned to the HS-DSCH ( Range 0-1000 ; Default value :10 ; Unit :# of radio link) .
 “MaxNumHSDPAUsers” the parameter that limits maximum allowed number of
simultaneous HSDPA users per cell that can be served ( Range 0-96 ; Default value :16 ; Unit
Number of users) .
 “maxNumAdchReservation” this parameter limit the number of ADCH resources .
 “eulServingCellUsersAdm” Admission control reject the request for EUL if the total number
of serving EUL users is above eulServingCellUsersAdm ( Range 0-100,default:32,unit:1 EUL
user) .
 “eulNonServingCellUsersAdm” Is the EUL limit for 10ms TTI non serving cell ( Range 0-
100,default:100,unit:1 EUL user) .
 “eulServingCellUsersAdmTti2” Is the EUL limit for 2ms TTI non serving cell ( Range 0-
100,default:4,unit:1 EUL user) .

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