HSPA - Network Optimization & Trouble Shooting

Part I: HSDPA Optimization & Trouble Shooting

HSDPA in Practice

Course Description

Logical Channel, Transport Channel and Physical Channel Details
- Practical Exercise: Name all the physical channels involved in HSDPA
  - Rel. 5 operation
Channel Type Switching (possible RRC State changes with and w/o HSDPA)
- Practical Exercise: Determine the RRC State(s) where HS-DSCH transmission is allowed!
Gross Throughput Calculations
- HSDPA category table and IR performance
- Stop & Wait scheme with minimum HARQ RTT of 12 ms
- Possible throughput rates considering various practical code rates R
- Practical Exercise: Determine the physical throughput rate of Cat 8 UE with 10 HS-PDSCH’s; 16-QAM and R = 2/3
CQI Reporting
- Purpose of CQI: Equal distribution of 30 CQI values over SNR range
  - CQI change by 1 corresponds to app. 1 dB power variation on HS-DSCH
- Practical Exercise: Work out the min. time between the radio conditions leading to an extreme good CQI report and the time instance the UE receives the actual related HS-DSCH block?
  - What is the min. CQI necessary to tempt the NodeB to go for a code rate 2/3 & 16-QAM?
Compressed Mode & HSDPA
- Reasons for CM: AMR 12.2 kbit/s and HSDPA, Inter Frequency HO, Cell Change Order 3G => 2G
- Option 1: A-DCH in CM and HS-XXXCH applying higher layer scheduling
- Option 2: Reconfiguration to Rel. 99 DCH/DCH only
  - 384kbit/s DL & 64 kbit/s UL, Start and stop of Radio Bearer during Inter Frequency HO
- Practical Exercise: Determine the CM method, parameter and pattern(s) for Inter Frequency HO and Inter RAT HO from a live trace
HSDPA Downlink Channel Power
- Method 1: Assign HS-PDSCH’s and HS-SCCH’s a fix max. power value
- Method 2: Allow HS-PDSCH’s and HS-SCCH’s to use always the left over on available power in the cell
- Impact of HSDPA transmit power on UE’s camping in idle mode
  - Ec/No deterioration at cell edge, ping pong 3G <=> 2G cell reselections, study case: MPO reduction of 2 dB and CPICH power increase of 2 dB => reduced IRAT cell reselections
- Impact of HSDPA transmit power on Rel. 99 in CELL_DCH and CELL_FACH on the same carrier
  - Bearers over A-DCH (SRB) and Rel. DCH drop more often in case of high load / weak Ec/No
- Practical Exercise: Determine the HS-PDSCH reference power for CQI reporting based on P-CPICH TX Power (e.g. 1 W), Measurement Power Offset Gamma (value: 18 to be converted in dB) and path-loss of 110 dB!
HS-SCCH Power Control
- Possibility 1: Fix power offset for HS-SCCH TTI relative to A-DCH
- Possibility 2: Closed loop power control with CQI and ACK/NACK/DTX decoding performance
- Practical Exercise: What is the impact on HS-SCCH Power Control when the A-DPCH power benefits from SHO gain (typically 3 dB)?
HS-DPCCH Decoding Success
- Improve Gain settings of ß(hs) for ACK, NACK and CQI
- Problem: SHO enforces lower power on uplink DPCCH
  - Problem mitigation in case of HS-DPCCH softer handover in NodeB
- Practical Exercise: Determine the power offset for HS-DPCCH relative to DPCCH using a quantized amplitude ratio of 24/15!
HS-PDSCH’s and Rel. 99 Code Shortage
- Alternative 1: Introduce 2nd Frequency F2 beside F1
  - F1 is for Idle mode & Rel. 99 traffic, F2 is the HSDPA preferred layer
- Alternative 2: Allow Secondary Scrambling Code on F1
  - HS-PDSCH’s and HS-SCCH’s on Secondary Scrambling Code, Impact on Admission and Congestion Control, Transmitted Carrier Power Utilization
- Alternative 3: Flexible code tree management
  - Dynamic code tree handling instead of static HS-PDSCH’s and HS-SCCH’s
- Practical Exercise: Try to assign 15 HS-PDSCH’s to an OVSF-tree under the primary scrambling code on F1 and another time on F2.
  - Please consider:
    - 3 x SF256 should be used for A-DCH’s as 3 users should be in CELL_DCH,
    - allocate the common channels P-CPICH and P-CCPCH to their mandatory fix channelization codes,
    - allocate AICH and PICH on the next possible channelization codes,
    - use separate S-CCPCH for PCH and FACH (assign FACH1 for SRB0 and FACH 2 for 32 kbit/s PS)
    - how is the code shortage improved / fixed with F-DPCH in Rel. 7?
RLC Single Sided Re-establishment
- Reasons behind 336 bits and 656 bits RLC-AM PDU size
- Practical Exercise: Determine the RLC-PDU sizes in a live trace!
  - Work out the potential data loss when RLC-AM PDU size gets reconfigured from size “656” to “336” one time with single sided RLC reestablishment and another time without that feature (<=> Rel. 99)!
SIB-5 Enhancement: Indication of HS capable Cell
- Flag: HS-DSCH capable cell, Flag: E-DCH capable Cell

Hands-on Exercises

HSDPA Protocol Stack
- Rel. 5: DTCH’s only mapped on HS-DSCH
- Rel. 6: DCCH’s can be alternatively mapped on HS-DSCH
- Practical Exercise: How long would it take to transmit a Radio Bearer Reconfiguration via HS-DSCH?
  - Considerations: RB Reconfiguration message consists of 4 segments each one with a RLC-AM PDU size of 144 bits and on HS-DCH a SRB speed of 28.8 kbit/s is employed?
- MAC-d Flow replacing Rate Matching Attribute and TrCH Multiplexing
- Practical Exercise: Determine the MAC-d flow parameters one time for the UE and another time for the NodeB based on live traces! What parameters are needed to support Streaming QoS?
MAC-hs Protocol PDU
- MAC-hs header parameter details
  - Questions to be answered:
  - Can several MAC-d flows (e.g. DCCH and DTCH be multiplexed into the same TTI?
  - Can there be MAC-d flows with more than one RLC-AM PDU size configured?
  - How is RRC Signaling transmitted in a separate MAC-d flow and how is the treatment of the control plane in HS-Scheduler?
Practical Exercises: Exhaustive Throughput Calculations
- Application Layer throughput of Cat 8 UE
  - Max possible rates on Physical Layer Throughput, MAC-hs Throughput, RLC-AM throughput, TCP/IP, Throughput with and w/o PDCP, RTP/UDP/IP, Throughput with and without PDCP
- Required minimum uplink RLC bearer capacity for a Cat 8 UE
  - Consideration of max TCP/IP throughput, Delayed TCP ACK (e.g. every 2nd TCP/IP frame gets acknowledged), TCP/IP SDU size = 40 bytes (no special options), RLC-AM PDU size in uplink is 336 bits
Scheduler Performance
- Scheduling Types
  - Max-C/I, Proportional Fair Resource/Throughput; Opportunistic Scheduling with the help of CQI (~ 6ms between CQI reporting and earliest possible HS-DSCH reception)
- Inaccurate CQI Reporting
  - Correction of wrong CQI taking the ACK/NACK ratio into account, Weighting the deviation of actual ACK/NACK ratio relative to desired BLER of 10%

Drivetest Analysis

RRC messages and parameter
- Radio Bearer Details
  - Setting of parameter values for MaxDAT, TimerPoll, TimerPollProhibit, TX/RX Window Size, Missing PDU Indicator, In-Sequence Delivery, TimerStatus, TimerStatusProhibit, etc.
- Uplink Bearer Transport Format Combination
  - Purpose of CTFC (TFCI), flexible uplink bearer throughput rates from
  - 0k, 16k, 32k, …384k
- MAC-hs Configuration in UE and NodeB
  - Number of HARQ processes and memory partioning, MAC-hs Window Size and Reorder Release Timer, Size Index, Priority Queue
- MAC-hs Configuration in UE and NodeB
  - Number of HARQ processes and memory partioning, MAC-hs Window Size and Reorder Release Timer, Size Index, Priority Queue
- Meaning of Minimum E-TFCI (HSUPA)
  - NodeB lets the UE starve without SG, what is the SG needed for 3 Mbit/s HS-DSCH download and what is recommended for uplink TCP-ACK transmission?
- Uplink HS-DPCCH Power
  - ß(hs) for ACK and NACK, Pro and Con of ACK/NACK repetitions
- CQI Configuration
  - ß(hs) for CQI, Pro and Con of CQI repetitions, feedback cycle and measurement power offset ?
HARQ Process Analysis
- HS-SCCH Decoding
  - Code Group Indicator and Code Offset Indicator (number of HS-PDSCH’s), TBS, modulation type, HARQ process ID, new/retransmission, redundancy & constellation version
    Practical Exercise: Determine why certain processes hang in retransmissions
- ACK/NACK mis-detection by NodeB
- Practical Exercise: How to distinguish retransmission types Full IR, Partial IR and Chase Combining?
MAC-hs Decoding and Stall Avoidance
- MAC-hs window size and reorder release timer verification
  - Practical Exercise: Find out the various conditions for T1 to expire or terminate
Determine optimum RLC parameter settings
- Considering HARQ retransmissions, MAC-hs window size & T1, uplink DCH bearer
Release 6 HSDPA Improvements
- Preamble and Postamble for better ACK/NACK from DTX distinction in NodeB
  - Lower gain settings for ACK/NACK
- Active Set Update message capable of HS-DSCH cell change
- DCCH on HS-DSCH
- F-DPCH
  - Fully supported / not fully supported
Etheral/Wireshark Trace
- Practical Exercise: Determine TCP parameters
  - MSS, SACK, RX/TX Window Size, RTT

Iub Protocol and KPI Analysis

NBAP Physical Shared Channel Reconfiguration message
- Max TX Power to be allowed for HS-PDSCH & HS-SCCH in dBm
- Scrambling code on which HS-PDSCH and HS-SCCH is transmitted
- HS-PDSCH & HS-SCCH channelization code information
Purpose of NBAP Radio Link Parameter Update message
- Possibility for NodeB to change CQI feedback cycle; ACK, NACK, CQI power offset and repetition factor
Iub Flow Control Management for HS-DSCH
- NodeB’s Capacity Allocation
  - CmCh-PI, Number of Credits, MAC-d SDU Length of 336 bits (656 bits), Interval, Repetition Period
- SRNC’s Capacity Request
  - User Buffer Size
- HS-DSCH Data Frame
  - CmCh-PI, MAC-d PDU Length, Flush, Number of MAC PDU, User Buffer Size
- Practical Exercise: Judge good from bad HS-DSCH flow control based on ‘Credits allocated’ versus ‘Credits utilized’ versus ‘User Buffer Size’ graph
Performance Measurements
- HARQ NACK ratio, number of concurrent users per cell
- HS-PDSCH's utilization, Transmitted Carrier Power (non HSDPA)
- Cell throughput over HS-DSCH (i.e. per scheduling priority)

HSDPA Mobility Performance

MAC-hs Reset Impact on Throughput
- MAC-hs preservation feature for Intra NodeB cell change
  - HARQ and MAC-hs details can be forwarded within NodeB channel cards
- Data loss or RLC-AM retransmissions
  - RLC-UM has to live with data loss, RLC-AM retransmissions are invoked from SRNC
HSDPA Performance in Pilot polluted Areas
- A-DCH in SHO with e.g. 3 Cells and Ec/NO < - 14 dB
  - Enhanced performance requirements type 1 (receiver diversity), Enhanced performance requirements type 2 (chip equalizer)
- Possible Fallback to Rel. 99 DCH/DCH?
HSDPA Cell Changes
- Inter Iub cell change
  - Possible Trigger: Event 1D, Event 1A, Event 1C
- Inter RNC with and w/o Iur
  - Reconfiguration to DCH/DCH (no HS-DSCH support on Iur), Outward and Inward Mobility
SRNS Relocation
- Iur not supported or not in use for HS
  - RRC Connection Release with Cause directed signalling connection re-establishment
- UE involved or not involved SRNS Relocation
  - Routing Area Update, UTRAN Mobility Information Confirm

Part II: HSUPA Optimziation & Troubleshooting

HSUPA Refresher

Logical Channel, Transport Channel and Physical Channel Details
- Practical Exercise: Name all the physical channels involved in HSUPA
- Rel. 6 operation
Channel Type Switching and Bit Rate Adaptation
- Practical Exercise: Determine the possible TrCH combinations in CELL_DCH for uplink and downlink with HS-DSCH, E-DCH and A-DCH.
HARQ with 2 ms or 10 ms TTI
- HARQ_RTT values
- Configuration of Full IR, Partial or Chase considering the code rate R
  - Deterministic retransmissions depending on code rate R and RV-table
- Practical Exercise: Determine the retransmission scheme applied by UE for the 4th retransmission of process X considering a TTI of 2 ms and an initial code rate R of 2/3! (refer to the parameters from the live trace)
Throughput and E-TFCI Calculations
- HSUPA category table
  - Purpose of Puncturing Limit PL for SF-Selection, PLnon-max and PLmax
- E-TFCI comparison of various vendors
  - Analysis of the best E-TFCI Scaling taking the downlink pathloss, UE TXPower and ul DPCCH SIR into account
- Expected Noise Rise due to E-DCH
  - RTWP rise due to E-DCH transmission in conjunction with mixed traffic (R99 CS and PS)
- Non-Scheduled transmission – Guaranteed Throughput
  - Delay critical CS services and control plane obtain NodeB scheduler independent guaranteed throughput rates
- ß(ed,j,harq)/ßc Amplitude Ratio
  - Reference E-TFCI list and reference power offset
- Possible throughput rates as a function of the Serving Grant and Reference E-TFCI(s)
  - HARQ Power Offset purpose is to decrease the initial BLER
- Practical Exercise: Determine the critical TBS where the HSUPA switches to lower SF or to multi-code operation!
- Practical Exercise: 10ms TTI E-DCH E-TFC Restriction
Compressed Mode of HSUPA
- Scaling down of SG in case of 10 ms TTI
  - Sort of “Higher Layer Signaling” in case of 2 ms TTI
Message Flow for a PDP Context Activation and HSPA Serving Cell Change
- Practical Exercise: Complete the prepared message flows of PDP Context Activation and HSPA Serving Cell Change.
  - Fill in the correct RRC message names, RRC states and vital IE’s based on the description provided.

HSUPA in Practice

Relative versus Absolute Grant
- Serving Grant Update
  - Relative Grant DOWN from non-serving cell, Relative Grant UP from serving cell, Secondary or Primary Absolute Grants, 3-index and 2-index threshold
- Practical Exercise: Determine the new SG for new and retransmissions after a Relative Grant DOWN!
  - What happens to retransmissions if continues DOWN’s are received?
Primary versus Secondary E-RNTI
- Monitoring of one or two E-RNTI’s
  - Group Scheduling, Individual Scheduling, Time Rate Scheduling
HSUPA Protocol Stack
- Difference between scheduled and non-scheduled MAC-d flows
  - Minimum Set E-TFCI, MAC-d Flow Multiplexing, SRB on E-DCH
- MAC-e/es PDU header
  - Data Descriptor Indicator
- Practical Exercise: Calculate the application layer throughput for a Cat 6 UE taking UTRAN and TCP/IP overhead into account!
  - RLC-AM PDU size = 336 bits, no MAC-d flow multiplexing ? only a single DDI is used, no PDCP header compression, MTU size = 1460 Bytes, no special options for TCP and IP frames

Drivetest Analysis

Parameter Analysis of a HSPA Radio Bearer Setup
- E-DCH and E-DCH MAC-d flow parameter
  - Max Number of Retransmissions, Power Offset, E-DCH TTI, RLC PDU Size List, Scheduling Info etc.
- E-DPDCH and E-DPCCH parameter
  - E-DPCCH PO, Happy Bit Delay Condition, E-TFCI Table Index, Reference E-TFCI and E-TFCI PO, PLnon-max, Periodicity for SI
- Radio Link related Parameter
  - Serving E-DCH Radio Link Indicator, E-AGCH Info, E-HICH Info (channelization code and signature sequence), E-RGCH Info (RG Combination Index, signature sequence), TPC Combination Index
- Practical Exercise: Which RRC messages can start, stop and/or reconfigure HSUPA?
  - Selection: {RRC Connection Setup, Radio Bearer Setup, Radio Bearer Release, Radio Bearer Reconfiguration, Transport Channel Reconfiguration, Physical Channel Reconfiguration, Cell Update Confirm, Active Set Update, RRC Connection Release}
Throughput Analysis
- SG versus E-TFCI
  - Happy Bit rate, Scheduling Info with UPH and buffer load
Active Set Update
- E-DCH soft and softer Handover – Serving E-DCH RLS
  - TPC Combination Index and RG Combination Index
- Practical Exercise: How many channelization codes must a UE receive in downlink considering a max Active Set Size of 6 for Rel. 99 and a max Active Set Size of 4 for E-DCH related RL’s.
HARQ Process Analysis
- Verification of SG, TBS, ACK/NACK, RSN
Etheral/Wireshark Trace Analysis
- FTP Upload

Iub Protocol and KPI Analysis

NBAP Physical Shared Channel Reconfiguration
- E-AGCH, E-RGCH and E-HICH code reservation
- Maximum transmission power to be allowed for HS-PDSCH, HS-SCCH; E-AGCH, E-RGCH and E-HICH codes over cell portion
- Uplink RTWP and E-DCH total power
  - Maximum target RTWP, Reference RTWP, Target non-serving E-DCH to total E-DCH power ratio
- Practical Exercise: What are the criteria’s which have to be fulfilled so that an E-DCH non serving cell is allowed to send RG DOWN? (two items)
E-DCH Frame Protocol Analysis
- HARQ failure indication
  - Setting of CFN and Subframe Number, Number of MAC-es PDUs, Number of HARQ Retransmissions
- SIR target update for uplink DPCCH <=> Outer Loop Power Control
  - Influence of HARQ retransmissions, HARQ failure indications
RLC-AM Performance
- Optimum parameter settings for user RAB and SRB’s
  - TimerPoll, TimerPollProhibit, MaxDAT, MaxRST, In-SequenceDelivery, TimerStatusProhibit, PollWindow, PollPDU, PollSDU etc.
Performance Measurements
- Total RTWP
- Provided bit rate per LCH priority per cell

HSUPA Mobility Performance

MAC-e/es Reset Impact on Throughput
- E-DCH TTI Change (2 ms <=> 10 ms)
- E-DCH Cell Change
  - Event 1D, Soft and Softer Handover, Inward and Outward Mobility
E-DCH Synchronized Cell Change Procedures
- Intra-Node B synchronized serving E-DCH cell change
- Inter-Node B (intra RNC) synchronized serving E-DCH cell change
- RNSAP support for E-DCH
  - Fallback to Rel. 99 DCH

v1.200

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