SS

7

(RN

SA

P)

Us

er P

lan

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RNCUE

WBTS

DNBAP

AAL2SIG

CNBAPPRACH

FACH-c&u

DCH

AIR Interface IuB Interface

User Plane

Iur Interface

IuCS Interface

User Plane

SS7 (RANAP)

IuPS Interface

User Plane

User Plane

SS7 (RANAP)

PCH

WSPResource

CodeCapacity

Throughput

Connectivity

Unit Load

DSP Usage

HS-DSCH

#Cells per scheduler

SS

7

(RN

SA

P)

SS

7

(RN

SA

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Us

er P

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RNCUE

WBTS

DNBAP

AAL2SIG

CNBAPPRACH

FACH-c&u

DCH

AIR Interface IuB Interface

User Plane

Iur Interface

IuCS Interface

User Plane

SS7 (RANAP)

IuPS Interface

User Plane

User Plane

SS7 (RANAP)

PCH

WSPResource

CodeCapacity

Throughput

Connectivity

Unit Load

DSP Usage

HS-DSCH

#Cells per scheduler

3G RAN resources in different interface

• Radio Interface – BTS controls the amount of HSDPA DL transmission power, after the power for

DCH, HSUPA control channels and common channels have been set up. The BTS can measure the total power, NonHSDPA power and HSDPA power.

– The blocking in Radio Interface gives information about the lack of radio resources. This could mean that Node B is using all the DL power what is available in order to maintain the connection for the users. Therefore admission control is denying the additional users to have the wanted service. Related to HSDPA in RAS06, all available power is allocated for HSDPA, but in RU10 HSDPA use only power it needs (due to Spectral efficient link adaption).

– Another reason could be the increased UL interference situation meaning that there is no room for more Ues to be connected into that particular cell.

– Additionally, the available (free) codes in the Channelisation Code Tree can become a key resource, especially when HSDPA and HSUPA are enabled in that cell.

• Iub interface– The key Iub resource is the available Iub bandwidth at WBTS level, measured

in Cps or Kbps. In particular, the Iub User Plane VCC is to be monitored. The blocking in Iub interface gives information about the capacity shortage between Node B and Transport layer. Blocking is related to the load of ATM and especially AAL2 layer user plane resources. In transport layer the Connection Admission Control (CAC) in RNC could also deny the service if there is no room in AAL2 layer.

– As the Iub CAC resource allocation system is an input for the Radio Admission Control functionality, blocking on Iub will result in a degradation of Call Setup Success Rate.

3G RAN RESOURCES & BLOCKING

3G RAN RESOURCES & BLOCKING

• BTS HW– The key resource in terms of WBTS Hardware is the amount of free

Channel Elements (CE) at WBTS level. Channel Elements are DSP located of the WSP card of the Ultra BTS and in the system module of the FlexiBTS. The blocking in Node B HW interface gives information about the lack of Node B HW resources. As we know each RAB type needs different number of channel elements based on the used bit rate. Normally HSDPA needs more CEs. Thus if there is not enough HW channels for connection this could mean BTS HW blocking.

3G RAN RESOURCES & BLOCKING

• Iu-CS– Iu-CS interface represents the connection between RNC and Circuit

Switch network element. All traffic is carried over AAL2 connection. Traffic counters could be used for IU-CS traffic calculations.

– Iu-PS interface represents the connection between RNC and Packet Switch network element. All traffic is carried over AAL5 connection. Activity Factor (AF) should be taken into account in the calculation (with traffic counters) due to the bursty nature of PS data. The activity factor of the source traffic indicates how much of the time during the active connection a traffic source is active (i.e. is sending data), compared to the total time of a connection. AF is dependent on the packet size, which is different based on the applications.

– The interface between RNCs is needed when mobile station transmit and receive the same signal via two different BTS belonging to two different RNCs and for signalling between the individual RNCs (e.g. for handover, RNSAP signalling). The Iur traffic has the same traffic structure as Iu-CS.

Channelisation code utilization

• A single downlink scrambling code supports an OVSF code tree containing 1020 codes (based upon spreading factors from 4 to 512). The Channelisation Code Occupancy provides an indication of the percentage of codes which are either used or blocked. Channelisation codes assigned to both the common and dedicated downlink channels are included by the KPI. Furthermore there are also counter to monitor the average, maximum and minimum code occupancy. This can be used to detect the busy hour and non busy hour of the cells respectively. Enabled HSDPA will reserve 5 x SF16 codes which cannot be used for other traffic regardless if there is active Mac-d flow or not (~ 36% from code tree together with HSDPA and CCH )

PI Name Unit Object Description

RNC_113a Average Code Occupancy % WCEL Average code tree occupancy

RNC_519b Min Code Occupancy % WCEL Minimum code tree occupancy

RNC_520b Max Code Occupancy % WCEL Maximum code tree occupancy

M1000C83 NBR_SUCC_CODE_TREE_ALLO # WCEL The number of successful code tree allocations, this counter is updated when code is allocated from the code tree.

Code tree monitoring

3G RAN RESOURCES & BLOCKING

• High code blocking does not necessary mean that call setups are failing. Dynamic resource allocation will downgrade codes allocated for HSDPA based on R99 traffic need. (RT has always priority, NRT priority over HSDPA can be decided with the parameter).

• RNC_520b KPI can be used as triggering point to upgrade upgrade (second carrier). The max code tree occupancy ranges from 35% up to 100% (35% stands for the 5 codes HSDPA + CCCH). It has been seen that when max code occupancy is less than 80% the code allocation failure rate still remains close to 0% and roughly <90% max code occupancy means that code allocation failure rate is <1%. So 85-90 % limit could be used

• RAS06 introduces a possibility to increase the number of used HS-PDSCH code up to 10 or 15. The usage of more than 5 codes requires the activation of the HSDPA 15 Codes and Dynamic Resource Allocation features. The latter enables the dynamic code allocation functionality, which is required to adapt the allocated number of HS-PDSCH codes according to DCH traffic code consumption. Dynamic Code Allocation and Code Multiplexing are applied when higher number of codes than 5 is used. The efficiency of code usage can be further improved with the HSDPA Code Multiplexing feature. The feature requires 2-3 HS-SCCH codes (2-3 UEs). Dynamic Code Allocation will free the HS-PDSCH codes if required by the RT/NRT DCH allocation

3G RAN RESOURCES & BLOCKING

RRC, RAB or PS, Setup Failure % due AC exceed the set

target per Cell

Max Code Occupancy > limit where code

allocation failure rate is acceptable

High Code tree usage and low

share for HSDPA codes > 5

Possibility to reduce the

usage

Upgrade to 2nd carrier

Reduce the Usage

Predict when the code usage > limits

Yes

No

No

No

No

Yes

Yes

Yes

BTS hardware analysis•The possible reasons for BTS blocking could be lack of hardware capacity. This is also known as the channel elements in the WBTS. The new service setup would be blocked if the current traffic mix does not leave enough free hardware channels to support these new services. Below show the summaries of CE requirement in common channel, R99, HSDPA and HSUPA

BTS hardware analysis• HSDPA BTS CE resource reservation is always fixed, and cannot be used to other services. The

HSDPA Baseband resource reservation is symmetric for uplink and downlink and depends on used features. However, resources are not reserved for HSDPA UL return channel

– Enough free UL CE capacity is required for HSDPA return channel or HSDPA setup will fail– In RAS51 and RAS06 basic, the bit rate combination for HSDPA UL return channel is 64, 128 and 384.

Maximum bit rate cannot be limited with the parameter. 64 kbps and 128 kbps requires 4 CE and 384 kbps require 16 CE

– 16 kbit/s Return Channel DCH Data Rate Support for HSDPA is RAS06 optional feature. When16 kbps is activated, the throughput based optimisation and flexible upgrade features can be activated for HSDPA return channel with parameter DynUsageHSDPAReturnChannel

– HSDPA SETUP FAILURE counters due the BTS (for interactive and background) are updated when HSDPA setup fail due the lack of CE resources for UL return channel

• HSUPA consumes both UL and DL baseband processing within the WBTS, so it's necessary to ensure that there is sufficient baseband processing resource prior to enabling HSUPA. The HSUPA baseband processing requirements are symmetric across the UL and DL directions. Additionally, DPCCH for HSPA needs one extra CE.

– The minimum static allocation of 8 CE (for both UL and DL) is reserved as soon as HSUPA is enabled at a WBTS

– With the exception of the first 8 CE’s, the CE allocation for HSUPA is dynamic. Depending upon both the number of HSUPA connections and load generated by the DCH traffic.

– In the CE allocation, DCH has a higher priority than HSUPA => DCH capacity requests are able to pre-empt the set of CE allocated to HSUPA (with the exception of the minimum static allocation of 8 CE).

• In RU10 there is a change in CE consumption with Flexi Rel 2 BTS: with 384 kbits/s there is only 12 CE needed instead of 16 with 384 kbits/s. The other bitrates remains having same CE consumption compared to RAS06. The different scheduler types are shown in Table 4 Below is list of CE needs for common channels in Flexi BTS.

BTS hardware analysis

BTS hardware analysis• The following gives a summary of proactive and reactive measurements that can be used to

monitor the WBTS hardware blocking.– Proactive monitoring

• Continues monitoring of Channel element utilisation can give good indication when CE capacity upgrade is required • Prior to activation of new features (e.g. HSDPA & HSUPA) it is necessary to ensure that there is sufficient baseband

processing resources– Reactive monitoring

• Setup Failures can be used to monitor congestion level in more details, i.e. RRC and RAB Setup Failures due to BTS, or HS-DSCH Setup Failures due to BTS.

• It has been noticed that the Average CE Usage (max(UL,DL)) vs. RRC & RAB (voice) Setup failure rates due BTS and Frozen BTS of ~80% means that certain BTSs start to have RRC Setup failures due to BTS (in general these are the BTSs with less CE capacity) and due to Frozen BTS. However typically the average CE usage of ~85% means ~1% RRC/RAB (Voice) setup failures due to lack of CE.

• It is also possible to derive the max usage limits before the blocking starts to limit the usage. This can be evaluated by checking how the peak to average usage (Max usage - average usage) is at different average usage values in UL and DL. It has been noticed that the in UL the average usage can be up to 85% after which the 10% peak to average usage cannot be maintained in DL.

• CE usage can cause bottleneck for HSDPA users (UL return channel being rejected) or in terms of limiting the DL throughput (i.e. UL not supporting even the TCP akcs). 64kbps UL return channel (4 CE) seems to be enough up to ~2mbps and 16kbps is enough up to ~600kbps. Also it has bee noticed that the UL return channel allocation share is:

– ~30% UL 16kbps (1 CE needed)– ~50% UL 64kbps (4 CE)– ~10% UL 128kbps (4 CE)– ~10% UL 384kbps (16 CE)

KPI Counter to monitor CE ShortagePI Name Unit Object Description

M5001C0 MAX_AVAIL_CE # LCG Maximum number of available Channel Elements. I.e. maximum amount of working baseband resources (HW capacity).

M5001C1 MIN_AVAIL_CE # LCG Minimum number of available Channel Elements. I.e. maximum amount of working baseband resources (HW capacity).

M5001C2 AVE_AVAIL_CE # LCG The average number of available Channel Elements. I.e. maximum amount of working baseband resources (HW capacity).

M5001C3 MAX_USED_CE_DL # LCG Maximum number of used Channel Elements in Downlink direction.

M5001C4 MAX_USED_CE_UL # LCG Maximum number of used Channel Elements in Uplink direction.

M5001C5 MIN_USED_CE_DL # LCG Minimum number of used Channel Elements in Downlink direction.

M5001C6 MIN_USED_CE_UL # LCG Minimum number of used Channel Elements in Uplink direction.

M5001C7 AVG_USED_CE_DL # LCG Average number of used Channel Elements in Downlink direction.

M5001C8 AVG_USED_CE_UL # LCG Average number of used Channel Elements in Uplink direction.

RNC_730a Average ratio of utilized CE for DL in BTS

% WBTS Average ratio of utilized CE for DL in BTS [%] This KPI is based on the WBTS HW Resource Measurement

RNC_731a Average ratio of utilized CE for UL in BTS

% WBTS Maximum number of used Channel Elements in the uplink.

KPI Counter to monitor CE Shortage

PI Name Unit Object Description

M5001C9 MAX_HSUPA_CE_UL # LCG Maximum number of used Channel Elements for HSUPA in Uplink direction.

M5001C12 MAX_HSUPA_CE_DL # LCG Maximum number of used Channel Elements for HSUPA in Downlink direction.

M5001C10 MIN_HSUPA_CE_UL # LCG Minimum number of used Channel Elements for HSUPA in Uplink direction.

M5001C13 MIN_HSUPA_CE_DL # LCG Minimum number of used Channel Elements for HSUPA in Downlink direction.

RNC_947a Average ratio of utilised CE for DL for HSUPA in BTS

% LCG Average ratio of utilized CE for HSUPA in DL in BTS This KPI is based on the WBTS HW Resource Measurement

RNC_948a Average ratio of utilised CE for UL for HSUPA in BTS

% LCG Average ratio of utilized CE for HSUPA in UL in BTS This KPI is based on the WBTS HW Resource Measurement

KPI Counter to monitor CE ShortagePI Name Unit Object Description

RNC_924a RRC Setup failure due to BTS % WCEL This calculates the RRC Setup failure that is due to the BTS hardware channel elements limitations

RNC_925a RAB Setup failure due to BTS, RT % WCEL This calculates the Real time RAB Setup failure that is due to the BTS hardware channel elements limitations

RNC_955a PS Call Setup FR due to BTS % WCEL The percentage of packet call setup failures due to BTS for interactive and background traffic classes.

RNC_958a RL Setup Failure due the MISC % WCEL Level of blocked RL Setup

RNC_674a HSDPA Access FR due the BTS % WCEL Share of BTS originated failures from all failures (real failures and special reasons to release HS-DSCH channel)

RNC_956a E-DCH Setup FR due the BTS % WCEL The percentage of E-DCH setup failures due to BTS for interactive and background class connections.

RNC_957a E-DCH Not Selected due the BTS HW % WCEL

The percentage of times when E-DCH uplink transport channel cannot be selected in this cell for an interactive or background class connection because BTS has reported to have no capacity available for E-DCH.

M1000C268 BTS_HSUPA_HW_NOT_LIMITED_DUR s LCG

This counter indicates the amount of time that the BTS local cell group HW pool (where this cell belongs to) is in the HSUPA HW not-limited state during the measurement period. In this state, the BTS HW does not limit the HSUPA throughput. The same counter value is updated for all HSUPA enabled cells in the local cell group.

M1000C269 BTS_HSUPA_HW_LIMITED_DUR s LCG

This counter indicates the amount of time the BTS local cell group HW pool (where this cell belongs to) is in the HSUPA HW limited state during the measurement period. In this state, the RNC sets up the E-DCH but the BTS HW shortage may cause the throughput to be lower than expected. The same counter value is updated for all HSUPA enabled cells in the local cell group.

M1000C270 BTS_HSUPA_NO_HW_CAPA_DUR s LCG

This counter indicates the amount of time the BTS local cell group HW pool (where this cell belongs to) is in the HSUPA HW limited state during the measurement period. In this state, the RNC does not set up the E-DCH. The same counter value is updated for all HSUPA enabled cells in the local cell group.