High-Speed Downlink Packet Access(HSDPA) is an enhanced3G(third-generation)mobile telephonycommunications protocolin theHigh-Speed Packet Access(HSPA) family, also dubbed 3.5G, 3G+, or Turbo 3G, which allows networks based onUniversal Mobile Telecommunications System(UMTS) to have higher data-transfer speeds and capacity. As of 2013HSDPA deployments can support down-link speeds of up to 42.3Mbit/s.HSPA+offers further speed increases, providing speeds of up to 337.5Mbit/s with Release 11 of the3GPPstandards

CapacityIt is the maximum throughput that the RBS can deliver to one cell. The capacity is shared by all HSDPA users.

System CapacityIt is the average capacity per cell for a cluster of cells. For system capacity calculation it is assumed that the load is homogenously distributed and HSDPA is deployed in all cells.

Dedicated Channel TrafficDCH traffic is defined as the traffic carried by dedicated transport channels such as speech, PS or CS radio bearers i.e. on channels other than HSDPA.

RBS LoadIt is the percentage of the maximum available RBS power that is used in the downlink.

Power MarginPower margin saves a part of the RBS power to cater for power variations, due to the dynamic UE behavior when users move and experience varying channels conditions.For HSDPA it is assumed that no power margin is needed and RBS may use 100% of the available power in a system with HSDPA.

Shared Channel TransmissionShared channel transmission means that a set of radio resources are dynamically shared among multiple users.The sharing is done in time and code domain

Fast Radio Dependent SchedulingScheduling is the function that determines which UE to transmit to at a given time instant.Three scheduling algorithms are implemented.1. Proportional Fair Scheduling2. Round Robin Scheduling3. Maximum Channel Quality IndicatorProportional Fair SchedulingThe algorithm uses information about fading peaks to prioritize users with good radio conditionsIt also takes delay into account promoting users that have not been given any data for a long timeRound Robin SchedulingThe algorithm gives every user same amount of radio resources (TTI).The algorithm is fair for all users from a resource point of view but bit rate varies.

Max CQI(Channel Quality Indicator)UE sends CQI in the UL to aid rate adaptation and schedulingThe algorithm maximizes system throughput by prioritizing users with good radio channelsThe CQI report estimates the number of bits that can be transmitted to the UE using a certain assumed power with a block error rate of 10%

High-order ModulationHS-DSCH uses 16 QAM if the UE category permit.This allows twice as high data rates to be transmitted as compared to QPSK2 ms TTITransmission Time Interval for HSDPA is short when compared to R99It is 2 ms for HS-DSCH for R99 it is 10-40 ms

Fast Link AdaptationAs opposed to R99 RBs, HS-DSCH is transmitted with constant power within the TTI.Transmission rate is controlled by adaptive channel coding.Data rate depends on radio conditions (CQI)Fast Hybrid ARQ with soft combiningIn hybrid automatic repeat request scheme, the received blocks that cannot be decoded are buffered and soft combined with later received transmissions of same information bits. Hybrid ARQ protocol terminates in Node B which means short RTT (typically 12 ms

HSDPA PowerThe RBS power available for HSDPA is determined dynamically, depending on R99 power usageAt least 25% of the average power can be used for HSDPA

HSDPA Channel Structure

New Physical and Transport channels are introduced in HSDPA:

Transport ChannelHigh Speed Downlink Shared Channel (HS-DSCH)

Physical ChannelsHigh Speed Physical Downlink Shared Channel (HS-PDSCH)High Speed Shared Control Channels (HS-SCCH)High Speed Dedicated Physical Control Channel (HS-DPCH)Associated Dedicated Channel (A-DCH)

HSDPA accessibility rate degraded. Hi experts,What's the possible reasons of HSDPA accessibility rate degraded (NSN Technologie). The PS384 is used 20% in the infected NodeB,then i suspect that the basic proble m is the CE congestion in the uplink .In fact,the PS384 uplink bearer uses about 12 to 16 CE according to the system module used. I'll change the parameter HSDPAMaxBitrateUL from 6 (384kbps) to 4 (128kbps). This parameter defines the maximum user bit rate allowed in a cell for HSDPA UL DCH return channel. It is applicable to the PS domain NRT RAB.

For the HSDPA Accessibility please first check the RSRAN 073 Report for the infe cted NodeB and see where you are having the maximum failures which is contributi ng max to HSDPA Accessibiility degradation. Then Below are the reasons you have to look into. 1) For Setup Fail BTS--Check CEs at BH 2) For setup fail UL Return Channel--check UL power congestion and reduce the UL bit rate accordingly. 3) For Setup Fail Iub Transport-- check Iub Resource Congestion 4) For Setup Fail UE-- Check RAB Reconfiguration failure Rate 5) For Setup Fail RNC-- Check RNC Unit Load and Alarms on units 6) For Setup Fail too many Users-- Check simultaneous HSDPA Users So first thing to do is to find actually which out of these 6 reasons is contrib uting for your accessibility degradation so that you can work on that. Hope will be helpful. the HSDPA =downlink and PS384 should be R99! the HSUPA=uplink and should be not use 384k, so what you saying is DCH/HS, so if you have high RTWP (UL RSSI) than try to lower the DCH rate to 128 or 64 Actually if the RAB used is DL=HS/UL=DCH you will need HSDPAMaxBitrateUL =384 ot herwise don't expect to have high bit rates on HSDPA DL (like 14 Mbpsec or more when you have MIMO or DC-HSDPA)). That is because whatever application is used b y your mobile(TCP/IP usually) on your test laptop it will need an acknowledgemen t sent in uplink( to UTRAN network). That acknowledgement is using a DCH channel ( R99) that needs to have a specific bandwidth. You can try a new value of HSDPAMaxBitrateUL =384 Kbpsec but have a look at your HSDPA throughput and see if it is not limited by this change. After implementing the HSDPAMaxBitrateUl=128Kbpsec,I found that HSDPA throughput has deteriorated even more.Then I'll return to the first configuration and try an alternative. Usually synchronization affects RRC accessibility and you need to maintain a cer tain number of consecutive sync burst to establish/keep your connection. You nee d to check your sync timers, sometimes if it is set to high value you lose your connection more frequently otherwise you should have a look on the sync server/s olution. It is also a good idea to check Sync alarms on node-B/RNC level. In cas e you have server issue, then you are supposed to see more alarms at node-b/RNC level. Moreover, you are supposed to see RAB drop due to abnormal release/sync i ssue.

As Dan mention RRC failure will not effect HS accessibility or HS/EUL Throughput , it will shows poor PS or CS accessibility, and again if the failure due to syn ch it most be problem in Air interface DL or UL. it could be UE accessing the ce ll from too far, cell has high UL RSSI, or there is pilot population in DL. IF y ou sure that cell s footprint is controlled and UL RSSI is good you need to modify some timers as Dan suggest, I can t recommend values as I m not NSN expert

While CE congestion is one of the common causes of accessibility problems in mos t countries and vendors we should not conclude until we see the actual CE utiliz ation...i suggest pulling CE util stats first on a per hour basis to really veri fy if CE util is reaching capacity/license limit....also there are counters indi cating if accessibility issues are due to HW limitation...