HSDPA, sometimes known as "3.5G" makes downloads faster on UMTS networks, by opening up multiple channels, applying prioritisation and other means. It stands for High Speed Download Packet Access, and was shown at the 3GSM show in Cannes this year.
But how does it work?
Follow this link below for Nokia's explanation of how HSDPA works. This white paper also includes an explanation of the obvious follow-up High Speed Upload Packet Access (HSUPA)
White PaperNokia High Speed Packet Access SolutionUntitled Document2White PaperContentsExecutive summary 2High Speed Packet Access, major evolutionary step 3HSDPA improvements 3HSUPA Improvements 5Nokia High Speed Packet Access implementation 6Key benefits of Nokia High Speed Packet Access evolution 7HSDPA and HSUPA will optimize the network to enable lower production cost per bit 7HSDPA and HSUPA will improve the perceived value of user services 7Glossary 7Executive summaryThe volume of IP (Internet Protocol) traf c has already exceeded that for circuit-switched traf c in most xed networks. The same change will happen in mobile networks as new IP-based mobile services, such as video news bulletins, downloading music or checking bus arrivals, become available and are used by more people in their daily communications.Delivery of digital content over mobile networks, as well as IP-based person-to-person communication that combines different media and services into a single session, will generate additional traf c and revenue. The volume of data bits used in communications will grow faster than revenue, driving operators to optimize their networks to support the dominant traf c type. While downlink optimization is enough for content-to-person services, real interactive and person-to-person IP-based services require uplink optimization as well.In the Nokia High Speed Packet Access Solution two key technologies, HSDPA (High Speed Downlink Packet Access) and HSUPA (High Speed Uplink Packet Access), offer breakthrough data speeds theoretically up to 14.4 Mbps in downlink and up to 5.8 Mbps in uplink respectively using HSDPA will be able to support considerably higher numbers of high data rate users on a single radio carrier than is possible with any existing 3G technology. Moving scheduling from RNC to BTS also improves the ef cency of the Iub (connection between Radio Network Controller and Base Station). The improvement is 50 70% for typical web browsing with 128 384 kbps user data rates.Standardized WCDMA uplink evolution, HSUPA, is ongoing in 3GPP completion planned for the beginning of 2005. The target is to improve usability of higher bit rates in the uplink, resulting in greater capacity, higher peak rates and lower end-user delay.HSDPA will be introduced into operator networks in stages. The rst implementations will address business connectivity. The leading operators are expected to start commercial HSDPA trials in 2005. The second phase will be the introduction of HSDPA to all user segments in a multi-service environment with a wider terminal product range. This solution is expected to be on the market in 2006. HSUPA introduction is then part of the following stage after the HSDPA market has been established. clearly higher than the most advanced 3G networks. For users this means shorter service response times and less delay.Meanwhile, operators will be able to offer advanced services at lower costs and with increased pro tability. As the Nokia HSPA Solution is fully backwards compatible with current Nokia WCDMA networks, it is a cost-effective way to upgrade existing infrastructure. By providing higher quality and capacity it will help to drive up the consumption of data-intensive services, bringing operators more revenue in mobile communication. HSDPA and HSUPA technologies offer by far the highest performance at the lowest cost, enabling real mass-market mobile IP multimedia. WCDMA downlink evolution, HSDPA, is part of 3GPP/UTRAN-FDD Release 5 WCDMA speci cations. The new modulation method greatly improves the peak data rate and throughput, which enhances spectral ef ciency. In addition to these bene ts, users will perceive faster connections to services through shorter round trip times. As a result of these enhancements, operators Untitled Document3White PaperHSDPANew adaptivemodulation andcodingFastretransmissionin BTSEfficientschedulingin BTSFigure 1. HSDPA.High Speed Packet Access, major evolutionary stepThe WCDMA air interface has been standardized by the 3rd Generation Partnership Project (3GPP) as a radio transport medium for global mobile communications. Consequently, the rst versions of the 3GPP air interface speci cations enabled superior user data rates and system throughput capacities compared to any 2nd generation mobile communication standard.The channel types speci ed in Release 99 can carry IP traf c and can be used for delay sensitive applications as VoIP. With HSDPA and HSUPA, users will experience better Internet and intranet access with laptops, large le downloads and high quality streaming applications.The WCDMA system s adaptability enables a new and signi cant evolutionary step in packet data access. The Nokia High Speed Packet Access Solution comprises two key evolutionary steps: HSDPA and HSUPA, which can coexist in the network together with traditional WCDMA users.HSDPA and HSUPA improve system capacity and increase user data rates. HSDPA improves the downlink direction, that is transmission from the radio access network to the mobile terminal. HSUPA improves the uplink for transmitting data from mobile terminals to the radio access network.HSDPA can provide cell throughput gains of up to two to three-fold compared to normal Release 99 WCDMA. With HSUPA, the cell throughput is expected to be 20 50% greater than in Release 99 WCDMA.HSDPA improvementsImproved performance of HSDPA is based on:" New adaptive modulation and codingAdditional improvements are achieved by moving most of the control of the air interface from the Radio Network Controller to the Base Station (close to the air interface) resulting in:" Ef cient scheduling function" Fast retransmissionsNew adaptive Modulation and CodingNew adaptive modulation and coding in HSDPA is the ability to select a coding rate between 1/4 and 4/4 and a modulation method between 16QAM and QPSK. Of these two standardized methods, the former provides higher data rates. The link adaptation is based on fast channel quality feedback received from the mobile. The HSDPA speci cation supports the use of 5, 10 or 15 multicodes. The multicodes together with time multiplexing can be used to increase the number of users.Link adaptation ensures the highest possible data rate is achieved both for users with good signal quality (higher coding rate), typically close to the base station, and for more distant users at the cell edge (lower coding rate). In the future, advanced mobile terminal features such as dual antenna reception and equalized receivers can be used directly because new mobiles will simply report better channel conditions and the BTS will allocate higher data rates to those mobiles.Ef cient schedulingScheduling of the transmission of data packets over the air interface is moved from the RNC to the BTS. The packet scheduling in the BTS is based on information on the channel quality, terminal capability, and QoS class and power/code availability. These parameters are taken into account in the packet scheduler algorithm. Scheduling is ef cient because it is performed as close to the air interface as possible, using the physical layer feedback information on the channel quality and because a short frame length is used.Fast retransmissionsShould link errors occur, caused for example by interference, the mobile terminal rapidly requests physical layer retransmission of the data packets. In current WCDMA networks, these requests are processed by the RNC. In HSDPA, the request is processed in the Base Station providing the fastest possible response. This mechanism is called hybrid ARQ, or HARQ. The retransmission can be received in 10 ms with HSDPA. In addition to fast retransmissions, incremental redundancy can also be used. This technique selects correctly transmitted bits from the original transmission and retransmission to minimize the need for further repeat requests when multiple errors occur in transmitted signals. Untitled Document4White PaperMultiplexedHS-DSCHDCH3DCH2DCH1Figure 2. Channel sharing.Macro cellKbps per cell60000Small cellWCDMA Release 99HSDPA simple schedulerHSDPA advanced scheduler50004000300020001000HSDPA advanced mobilesFigure 3. HSDPA capacity increase with two different fast packet scheduling algorithms and with advanced mobile terminals.Time Multiplexed Channel for ef cient radio resource utilisationThe WCDMA system normally carries user data over dedicated transport channels, DCHs, which are code multiplexed onto one RF carrier. In the future, user applications are likely to involve the transport of large volumes of data that will be bursty in nature and require high peak bit rates. HSDPA introduces a new transport channel type, High Speed Downlink Shared Channel (HS-DSCH) that makes ef cient use of valuable radio frequency resources and takes into account bursty packet data.This new transport channel shares multiple access codes, transmission power and use of infrastructure hardware between several users. The radio network resources can be used ef ciently to serve a large number of users accessing bursty data. To illustrate this, when one user has sent a data packet over the network, another user then gains access to the resources and so forth. In other words, several users can be time multiplexed so that during silent periods, the resources are available to other users. This improves not only air interface resource usage, but also improves Iub ef cency.Figure 2 shows a simpli ed explanation of the principle of sharing a common transport channel. New signalling channels are needed in downlink and uplink. In the downlink the HS-SCCH (High Speed Shared Control Channel) facilitates signalling related to HS-DSCH reception while in the uplink direction, the channel quality feedback and feedback on the packet decoding errors are carried on the HS-DPCCH (High Speed Dedicated Physical Control Channel).HSDPA PerformanceHSDPA offers maximum peak rates of up to 14.4 Mbps (with 15 spreading codes and with no channel coding) in a 5 MHz channel. However, more important than the peak rate is the packet data throughput capacity, which is improved signi cantly. This increases the number of users that can be supported at higher data rates on a single radio carrier. Performance with two different fast scheduling algorithms is shown in Figure 3. Fairness between users and the total cell capacity are a trade-off because scheduling data equally to all users doesn t take into account momentary changes in the radio channel quality and cannot maximize the cell throughput. On the other hand, maximizing cell throughput by scheduling users with best radio channel quality cannot quarantee Quality Of Service (QoS) for all users in the cell. Advanced scheduling algorithm gives the best balance of QoS and cell capacity. Advanced mobile terminals with features like dual antenna reception and equalized receivers can bene t directly from HSDPA.Another important characteristic of HSDPA is the reduced downlink transmission delay and reduced variance in delay. A short delay time is important for many applications such as interactive games. In general, HSDPA s enhancements can be used to implement ef ciently the interactive and background QoS classes standardized by 3GPP. HSDPA s high data rates also improve the use of streaming applications on shared packet channels, while the shortened roundtrip time will bene t web-browsing.Untitled Document5White PaperHSDPA data ratesHSDPA data rates are dynamically adjusted during the call according to radio link quality. This ensures the highest possible data rate for the user. HSUPA ImprovementsThe main technological improvements with HSUPA are:" Ef cient uplink scheduling function based in the BTS" Fast retransmission with control in the BTSThe additional technique of new adaptive modulation and coding used in HSDPA is not useful in HSUPA due to the fundamental difference in the management of the total transmission power for the uplink.Ef cient uplink schedulingSimilar to HSDPA, HSUPA control for uplink scheduling is moved to the BTS. The BTS can do the scheduling based on the information readily available in the BTS or based on terminal feedback which can include, for example, information about whether a terminal would like to increase the transmission rate.Fast uplink retransmissionsAs with the downlink without HSDPA, the uplink currently relies on retransmission control by the RNC. By moving the retransmission handling to the BTS, faster response times and less roundtrip delay can be achieved. HSUPA performanceEf cient scheduling in the uplink can react rapidly to changes in the traf c load and offered data rate from applications. This reduces noise rise variations in the uplink and gives an opportunity to reduce the head-room reserved in the uplink for overload protection. Higher user data rates and cell capacity are achieved by using this capacity that was reserved in Release 99 solutions.In addition to ef cient scheduling, fast retransmissions and incremental redundancy contribute to enhanced uplink performance. Fast retransmissions allow the uplink to operate with a higher block error ratio (BLER) and this ModulationInter TTIThroughput (UE Category) with 5 codesThroughput (UE Category) with 10 codesThroughput (UE Category) with 15 codesQPSK11.8 Mbps(Cat. 12)20.9 Mbps(Cat. 11)QPSK/16QAM13.6 Mbps(Cat. 5 and 6)7.2 Mbps(Cat. 7 and 8)14.4 Mbps(Cat. 9 and 10)21.8 Mbps(Cat. 3 and 4)31.2 Mbps(Cat. 1 and 2)Table 1. Peakuser data rates for HSDPA terminal categories de ned by 3GPP.Noise rise (dB)ProbabilityRNC schedulingNode B schedulingFigure 4. Fast scheduling reduces noise rise variance.Release 99Kbps per cell25000Fast proportionalschedulingFast retransmitNode Bscheduling+45%+10%+25%200015001000500Figure 5. Example of user throughput gain in a loaded cell. Average user throughput with 21 users per cell can be 50% higher than in Release 99.Untitled Document6White PaperNokia WCDMA base stations can accommodate HSDPA by adding the HSDPA software application. The HSDPA traf c can be allocated to a dedicated carrier or share the same carrier with Release 99 based traf c. Nokia baseband contains powerful processors that can handle both uplink and downlink in the same unit. This eliminates communication between separate uplink and downlink baseband units, which results in ef cient scheduling and fast reaction to uplink HSDPA control signalling.enables initial transmission with a lower power level for a given data rate. With a xed data rate, the cell range is also improved since lower energy per bit is needed.HSUPA data ratesThe wide bandwidth of WCDMA gives high user data rates with one code transmission, which provides ef cient Mobile terminal RF performance.Furthermore, the use of powerful integrated baseband simpli es system evolution and makes it easier to adapt to asymmetric traf c. When introducing new features in the network, processing power can be allocated between the downlink and the uplink based on traf c needs, with no onsite HW upgrades needed.Nokia HSDPA is also fully backwards compatible with 3GPP Release 99 WCDMA. This enables HSDPA to be introduced into networks gradually. Both Release 99 and HSDPA capable terminals can share the same radio carriers.The versatile Nokia BTS platform can also accommodate the changes expected to arise from HSUPA improvements, such as BTS-based scheduling or retransmission handling. The powerful baseband processors can handle traf c in either direction depending on the software.Table 2. Example of teoretical HSUPA peak data rates with spreading factor 4.Coding rateUser data rate with 1 codeUser data rate with 2 codesUser data rate with 4 codesUser data rate with 6 codes2/3640 kbps1.28 Mbps2.56 Mbps3.84 Mbps3/4720 kbps1.44 Mbps2.88 Mbps4.32 Mbps4/4960 kbps1.92 Mbps3.84 Mbps5.76 MbpsNokia High Speed Packet Access implementationA key attribute of Nokia s WCDMA infrastructure is its exibility for future upgrades. Even features in the earliest stages of standardization have been taken into account in the Radio Access Network architecture and in system design and speci cation. This approach enables Nokia to implement HSDPA into its current RAN platforms through simple additional software applications.Being able to integrate HSDPA and non-HSDPA (WCDMA Release 99) traf c into the same carrier is essential. With the Nokia solution, this is achieved without changing the base station s radio elements. Consequently, HSDPA can boost user and system performance using the initial (5 MHz) frequency layer.Figure 6 shows an example of power resource sharing between non-HSDPA users (for example speech traf c) and HSDPA users on the same carrier. The power allocated to HSDPA is dynamically adjusted by the RNC according to the instantaneous traf c requirements. HSDPA uses fast link adaptation and does not need head-room for fast power control.Furthermore, with HSDPA the DCH is typically used to carry time critical signalling information and conversational type services, such as speech in parallel with HSDPA operation. Thus the user can bene t from a simultaneous speech connection on the DCH in parallel with, for example, a high speed data download on the HS-DSCH.BTS Transmit powerHSDPA powerCommon channelsDCHHSDPANon-HSDPA powerTarget powerMaximum powerPower controlhead-room for DCHFigure 6. Carrier power sharing between HSDPA and DCH traf c.Untitled Document7White PaperServed MB per user per month (MB/User/Month)100GPRSEDGE1000700400WCDMAHSPA900600300800500200Network infrastructure cost per subscriber per month (OPEX, CAPEX, IMPEX)Key bene ts of Nokia High Speed Packet Access evolutionHSDPA and HSUPA will optimize the network to enable lower production cost per bitThe Nokia High Speed Packet Access solution will bene t network operators by: " Improving the WCDMA network s packet data capacity" Enhancing spectral ef ciency" Increasing BTS baseband and Iub ef ciency" Enabling cost-effective network implementation Consequently, network operators that implement HSDPA and HSUPA will achieve a lower delivery cost per bit.The contents of this document are copyright 2005 Nokia. All rights reserved. A license is hereby granted to download and print a copy of this document for personal use only. No other license to any other intellectual property rights is granted herein. Unless expressly permitted herein, reproduction, transfer, distribution or storage of part or all of the contents in any form without the prior written permission of Nokia is prohibited.The content of this document is provided as is , without warranties of any kind with regards its accuracy or reliability, and speci cally excluding all implied warranties, for example of merchantability, tness for purpose, title and non-infringement. In no event shall Nokia be liable for any special, indirect or consequential damages, or any damages whatsoever resulting form loss of use, data or pro ts, arising out of or in connection with the use of the document. Nokia reserves the right to revise the document or withdraw it at any time without prior notice.Nokia and Nokia Connecting People are registered trademarks of Nokia Corporation. Nokia product names are either trademarks or registered trademarks of Nokia. Other product and company names mentioned herein may be trademarks or trade names of their respective owners.Glossary 16QAM 16 Quadrature Amplitude Modulation3GPP Third Generation Partnership ProjectBLER Block error ratioBTS Base StationDCH Dedicated Channel (transport channel)HS-DSCH High Speed Downlink Shared ChannelHS-DPCCH High Speed Dedicated Physical Control ChannelHS-SCCH High Speed Shared Control ChannelHSDPA High Speed Downlink Packet AccessHSPA High Speed Packet AccessHSUPA High Speed Uplink Packet AccessHW HardwareIP Internet ProtocolIub Connection between Radio Network Controller and Base StationMS Mobile StationPS Packet SwitchedQoS Quality of ServiceQPSK Quadrature Phase Shift KeyingRAN Radio Access NetworkRLC Radio Link ControlRNC Radio Network ControllerSW SoftwareTTI Transmission Time IntervalWCDMA Wideband Code Division Multiple AccessHSDPA and HSUPA will improve the perceived value of user servicesThe Nokia High Speed Packet Access solution will bene t users by providing:" Higher data rates " Shorter service response time" Better availability of servicesConsequently, users will experience better quality of service.Figure 7. WCDMA/HSPA is the most cost-effective technology for transmitting combined voice and data.Untitled DocumentNOKIA CORPORATIONNetworksP.O. Box 300FIN-00045 NOKIA GROUP, FinlandPhone: +358 (0) 7180 08000www.nokia.com