hspa fundamentals for technicals

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HSPA Fundamentalfor TechnicalPersonnel

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3 Nokia Siemens Networks 2009TM5112EN01GLA00

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Courseoverview

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This workbook consistsof 7 chapters and 246pages total.

HSPA System Overview in UMTSNetwork

34 pages

1

HSDPA and HSUPA Features

49 pages

2

HSDPA and HSUPA Physical Channel

51 pages

3

HSPA Protocols

23 pages

4

HSPA Mobility Management andHandover control

25 pages

5

HSPA Throughput and CongestionControl

15 pages

6

NSN Products

49 pages

7

HSPA Fundamentalfor TechnicalPersonnel

TM5112EN01GLA00

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HSPA System Overview in UMTS Network

Nokia Siemens Networks 2009TM5112EN01GLA00

nazilute.en.lmm/dizagilo.en.slo

HSPA System Overview inUMTS Network

Contents1 Module Objectives.....................................................................................32 HSPA...........................................................................................................43 UMTS Release 99 Environment............................................................... 63.1 UMTS Network - Network components...................................................... 63.2 UMTS - The Air Interface............................................................................84 HSDPA......................................................................................................184.1 Higher Data Rate.......................................................................................194.2 Reduced Latency...................................................................................... 194.3 Increased Spectral Efficiency....................................................................245 HSUPA......................................................................................................265.1 Higher Data Rate.......................................................................................275.2 Reduced Latency...................................................................................... 275.3 Increased Cell Coverage and Throughput................................................ 276 Exercises..................................................................................................286.1 Solutions....................................................................................................32

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1 Module ObjectivesThe aim of this module is to give theparticipant overview ofUMTS system and itsnetwork. Air interface background is also provided. Issues in UMTS that aresolved in HSDPA and HSUPA are described.After completing this module, the participant should be able to:

Describe UMTS network and Radio Access Network.Explain aspects of UMTS Release 99 air interface.Briefly introduce HSPA system andkey elements of HSPA.

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2 HSPAHSPA or HSxPA (High Speed Packet Access) is a generic term to refer toimprovements in the UMTS Radio Interface in the Releases 5 and 6 of the 3rdGeneration Partnership Project (3GPP) standards. HSPA comprises both theimprovements made in the UMTS downlink and uplink:

High Speed Downlink Packet Access - HSDPAHigh Speed Uplink Packet Access - HSUPA

Both technologies offer distinctly increased data rates compared to UMTS Rel99:

HSDPA offers data rates up to 14.4 Mbps in the downlink direction.HSUPA offers data rates up to 5.76 Mbps in the uplink direction.

Additionally spectral efficiency is increased and latency is decreased. HSDPA andHSUPA can be implemented in the standard 5 MHz carrier of UMTS networksand can co-exist with the first generation of UMTS networks based on the 3GPPRel99 standard. HSPA affects mainly Radio Access Network (RAN) , thereforeno major changes in the Core Network (CN) are required.The following Releases are issued by 3GPP (3rd Generation Partnership Project):UMTS Release 99In UMTS Release 99 broad bandwidths of 5 MHz were reserved for UMTS.Therefore high data rates are possible, particularly while having few participantsin a cell. Additionally a new multiplex method was introduced (Code DivisionMultiple Access CDMA) which offers an increased flexibility in the exploitation ofthe spectral resources.UMTS Release 4Release 4 aims to transmit all applications over a common core network -independent whether they are real time or not. Therefore VoIP is introduced,because the future core network will be IP-based.UMTS Release 5In the core network the main alteration is the implementation of IMS (IPMultimedia Subsystem). The IMS represents and registers a user not only in themobile network but also in the Internet. Also the HLRis integrated in the IMS. Inthe radio access network, HSDPA and QoS are introduced.UMTS Release 6Release 6 was completed in March 2005 introducing further enhancements toUMTS including HSUPA (or E-DCH), MBMS (Multimedia Broadcast MulticastService) and Advanced Receivers.

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Fig. 1 UMTS releases and added features

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3 UMTS Release 99Environment

The evolution of UMTS affected mainly the air interface: WCDMA was introducedas new multiplex method in Release 99. The core network is basically unchangedfrom GSM. The followingsection deals with the changes in the network and onthe air interface made with UMTS.

3.1 UMTS Network - Network componentsThe core network in UMTS is based on the GSM cre network. However newcomponents are added in the Radio Access Network (RAN):User Equipment UEThe UE replaces the MS and the SIM is replaced by the USIM, that means newmobiles are required. By now all UEs are downward compatible to GSM.Node BInstead of the BTS a Node B is implemented. The Node B supports CDMA (CodeDivision Multiple Access) on the UMTS frequency bands.Radio Network Controller RNCSimilar to the BSC, an RNC is implemented as controller. In contrast to GSM adirect Interface between RNCs exists to support handovers (Iur).The RNC decides, like the BSC in the GPRS network, if the connection is circuitor packet switched and transfers it to the MSC or to the SGSN.

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Fig. 2 UMTS network components and interfaces

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3.2 UMTS - The Air InterfaceWith UMTS a new multiplex method was introduced:WCDMA - Wideband CodeDivision Multiple Access . Wideband refers to the used 5 MHz carrier of UMTSwhereas Code Division Multiple Access describes the used multiplexmethod.UMTS covers several different air interface modes. Only FDD mode isdescribed here since it isthe de facto choice of UMTS implemented worldwide.

3.2.1 FDD ModeIn FDD mode, all participants are assigned a frequencycarrier of5 MHz in eachdirection. The users are distinguished via codes. Theycantransmit and receivesimultaneously. The gap between the two frequency bands for UL and DL isknown as the duplex distance.

3.2.2 CDMAIn CDMA several signals are sent in the same frequency band and the same timeslot. Each signal is created by spreading a narrowband signal through the use ofa unique user code to a multiple of the original bandwidth. This process is calledspreading . The receiver correlates the sum of the received signal with the usercode and thereby reobtains the original narrowband signal,the process known asdespreading.

Fig. 3 Multiplex Methods

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3.2.3 SpreadingThe signal in UMTS is spread using codes. The binary, digital subscriber data(1,0) is converted on the transmission side to bipolar data (-1, +1) before thespreading process takes place. The spreading code also consists of bipolar data.The value of a chip can be +1 or -1. The subscriber data is then multiplied by thehigh chip rate spreading code. The result is the coded data, which is thentransmitted over the radio interface.The receiver multiplies the received, code data sequence with the bipolarspreading code to obtain a bipolar data sequence. The original subscriber data isrecovered by converting this data sequence to binary, digital data.

Fig. 4 Spreading

The smallest unit of digital information is generally called a bit (an abbreviationderived form binary digit). To distinguish the smallest units in the originalsubscriber information from the smallest units in the coded data, the smallest unitin the coded data after spreading is called chip .The smallest unit transmitted over the radio interface is called symbol . Themodulation methods differ in their ability to map a number of chips to symbols.The simplest method can just map one bit per symbol.

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Fig. 5 WCDMA: Transmission / Reception

To use the bandwidth of 5 MHz the user signal is spread to 3.84 Mchip/s. Toobtain a bandwidth being independent of theutilized bit rates in the cell, the chiprate in the cell must be kept constant. Therefore the user signal is spread usingspreading codes. That means the length of the spreading code has to differdependent on the user data rate. The overall degree of spreading varies toenable the final signal to fill the required channel bandwidth. As the input datarate may vary from one application to the next, the degree of spreading needs tobe varied accordingly.The spreading factor indicates the number of chips that spread a symbol eachtime. The number of chips per data symbol is called the Spreading Factor (SF) .The spreading factor therefore states the relationship between the chip rate andthe data rate of the subscriber. The higher the bit rate of a signal, the less it isspread and the less the processing gain. Processing Gain is the ratio of thetransmitted bandwidth to information bandwidth. One could say processing gain isthe amount of jamming or interference power that is reduced going through thedespreading process. Processing gain is the improvement in the signal-to-noiseratio of a spread spectrum system. Higher spreading factors are more easilycorrelated by the receiver and therefore a lower transmit power can be used forthe same symbol error rate.The codes required to spread the signal must be orthogonalif they are toenable multiple users and channels to operate without mutual interference. Codesare orthogonal of each other if they are independent of each other that meansthere is zero correlation between the different codes. In this way only the desired

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recipient is able to correlate and decode the signal, all other signals appearing asnoise. This allows the physical radio frequency channel to be used by severalusers simultaneously.The codes used in W-CDMA are Orthogonal Variable Spreading Factor(OVSF) codes. They are constructed from a tree, the OVSF code tree . Thecreation of this OVSF code tree is rather simple: Out of one mother code evolvestwo children codes. One of the children codes doubles the mother code. Theother children code takes the mother code and adds the inverted mother code.

Fig. 6 OVSF Code Tree

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Every user gets a unique channelization code assigned depending on therequested service. A code can be used in a channel if and only if no other codeon the path from the specific code to the root of the tree is used in the samechannel.The different users and their applications can be distinguished by their uniquechannelization code in the downlink direction per cell. Channelization codes areused to separate channels from the same source.

Fig. 7 Channelization and Scrambling Codes

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3.2.4 ScramblingIn addition to spreading, part of the process in the transmitter is the scramblingoperation. This is needed to separate terminals or base stations from each other.Scrambling is used on top of spreading, so it does not change the signalbandwidth but only makes the signal from different sources separable from eachother. In FDD so-called Gold codes are used to form scrambling codes (10msin length = 38400 chips).

Fig. 8 Usage of Channelization and Scrambling Code

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In the uplink direction another feature of scrambling code is used to address aproblem:

Fig. 9 Scrambling Codes for FDD in the uplink direction

As it is not possible to retain exact synchronization in the uplink direction,scrambling codes are used to ensure orthogonally of the signals in the uplink.

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3.2.5 Usage of OVSF code treeDepending on the current load situation every user is assigned the appropriatespreading factor and unique channelization code within the cell according to therequested service. The assigned channelization code determines the possibledata rate. As already mentioned a code can be used in a channel if and only if noother code on the path from the specific code to the root of the tree is used in thesame channel. That means channelization codes are a limited resource within acell.For example a 384 kbps Radio Bearer in the downlink is mapped to spreadingfactor 8, but only 8 channelization codes with spreading factor 8 exist per cell.Besides several channelization codes are needed for signaling purposes (e.g.CPICH on 256,0 etc.). That means a maximum of 7 user data connections having384 kbps in downlink direction are possible per cell.

Fig. 10 Utilization of OVSF code tree in the downlink direction

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3.2.6 Timing StructureIn FDD, the air interface timing structure is as follows:a timeslotis defined asthe length of 2560 chips: this corresponds to a duration of 2/3 ms. A timeslot isthe shortest repetitive period.A frame is defined by the duration of 10 ms andtherefore contains 15 timeslots.In the FDD mode, a frame is the shortest possible transmission duration. Shortdata packets for setting up a connection or packet-switched data packets are atleast one frame in duration. A frame is likewise the shortest period of time forchanging the transmission rate.

Fig. 11 Timing structure and usage in FDD mode

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4 HSDPATechnologically HSDPA is an upgrade to UMTS. Therefore HSDPA is alreadycalled 3.5G in parallel to 2.5G, which meant a technological add on for GSMnetworks in form of HSCSD or GPRS.HSDPA is the abbreviation for "High Speed Downlink Packet Access". The namedescribes an essential aspect of this new technology: the significantly increaseddata throughput per user - up to 14.4 Mbps. HSDPA is applicable topacket-switched data traffic.The increased data throughput is not the only argument in favor of HSDPA,further arguments will be introduced in the following sections.HSDPA was introduced in Release 5. However it is not mandatory to implementHSDPA in an UMTS network. HSDPA cells can coexist with non-HSPDA cells.Interworking between HSDPA cells and non-HSDPA cells is possible.Furthermore, HSDPA-capable mobiles can coexist with older mobiles in the sameHSDPA cell.Why HSDPA? The three prevailing arguments for HSDPA are:

increased data ratereduced latencyincreased spectral efficiency

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4.1 Higher Data RateHSDPA offers increased data rate per user compared to Rel 99. In the firstrelease 1.8 Mbps per user will be possible. Higher data rates up to 10.8 Mbps arepossible in newer releases. The maximumdata rate 14.4 Mbpsis only possibleunder certain conditions, for example good channel conditions and sufficientresources in the Node B which is rarely acheived.

4.2 Reduced LatencyHSDPA offers reduced latency compared to packet data connections via Rel99.

4.2.1 TCP Transmission Control ProtocolMost packet switched services use TCP for flow control. The protocol guaranteesreliable and in-order delivery of data from sender to receiver. TCP alsodistinguishes data for multiple, concurrent applications (e.g. web server ande-mail server) running on the same host. TCP supports many of the Internet'smost popular application protocols and resulting applications, including the WorldWide Web, e-mail and Secure Shell.TCP combined with IP is the standard which is used in the Internet. In theInternet protocol suite, TCP is the intermediate layer between the InternetProtocol (IP) below it, and an application above it. Applications often need reliablepipe-like connections to each other, whereas the Internet Protocol does notprovide such streams, but rather only unreliable packets. Therefore TCP is usedto provide a connection-oriented, reliable service between hosts.TCP was mainly developed for wireline networks. Wireline networks usually offerreliable, non-fluctuating quality. Therefore TCP works under the assumption, thatthe channel quality remains constant and discontinuities in the data rate iscaused by congestion. Packet loss is dealt with as congestion. To avoid furthercongestion and resulting retransmissions and drops in the data rate, TCPregulates the data transport rate down to adapt to the conditions until betterconditions are assumed. Then TCP increases the data transport rate slowly up tothe maximum data rate.

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4.2.2 TCP Slow Start and Congestion AvoidanceMechanism

The transmission performance in the beginning of a data transmission and after acongestion situation is characterized by the so called slow start phase.During slow start, the initial size of the so called congestion window, used by thesender for flow control, is usually one segment only.After eachacknowledgementreceived by the sender, the size of the congestion window is doubled during slowstart phase, i.e., the amount of transmitted data starts exponentially. At a certainpoint, when the congestion window becomes too large, congestion occurs anddata packets are discarded.The initial slow start threshold, which is set to 65535 bytes, is reset to one half ofthe receiver's window size. If now the congestion window is less or equal to thisreset slow start threshold, then TCP restarts with slow start.If the congestion window size reaches the slow start threshold again, TCPchanges from the slow start to the so called congestion avoidance phase. Inthis phase, the congestion window is not increased exponentially but linearly:Each time an acknowledgement is received, the congestion window is increasedby 1 step. But it cannot be increased more than the value suggested by thereceiver.In case of congestion, the slow start threshold is reset to half of its actual valueand the congestion window is reset to 1 segment.

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Fig. 12 TCP Slow start and congestion avoidance

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In mobile networks the air interface is characterized by fast-changing conditions,for example, fast fading effects. Therefore drops in the data rate are rathercommon. Because of the slow start/congestion avoidance characteristics in TCP,drops caused by Fast Fading Effects induce time-consuming adjustmentmechanisms. The impact of the slow start/congestion avoidance on mobile dataconnections is rather high and usually prevents the user from using thetheoretical possible data rate.Latency delays in mobile networks are rather high. In UMTS the common latencydelay amounts between 200ms and 300ms, in GPRS even up to 700ms. HSDPAoffers distinct decreased latency delay times, the latency delay is approximately100ms.With HSDPA, thanks to HARQ (Hybrid Automatic Repeat Request) in theUMTSNode Bat the MAC-hs level, a NACK requires less than 10 ms forretransmission, which enables the recovery of erroneous frames before the TCPtimer expires and leaves the TCP throughput unaffected.

Fig. 13 Retransmission cycle in Rel99 and HSDPA

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In wired networks error detection followed by retransmissions is usually used incase of error. This method is typically implemented as an ARQ(AutomaticRepeat Request) system.In mobile networks increased error rates are caused by fast changing conditionson the air interface. A simple ARQ system would require a high number ofretransmissions resulting in a low data rate. Therefore as a preventive measurethe sender duplicates the user data. The receiver can use the redundant data toreconstruct the original data. The need of retransmissions is consequentlyreduced. This method is called Forward Error Correction (FEC) .Hybrid ARQ (HARQ) is defined as any combined ARQ and FEC method thatsaves failed decoding attempts for future joint decoding. HARQ is not one methodbut encompasses many named variants.

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4.3 Increased Spectral EfficiencyIn Release 99 every user is assigned a dedicated channel, partly independent ofthe actual data rate. Resources are reserved for the user, but not completelyused. Therefore blocked but unused resources exist in a cell, the capacity of acell is not efficiently used.HSDPA introduces shared channels. Resources are not assigned/reserved forone user, but used among the users dependent on their demands. Node Bschedules the sharedchannels everyTransmission Time Interval (TTI) which is2ms in HSDPA.A set of input parameters are considered by the Node B forresource allocation. Input parameters are

feedback of the UEs about the channel quality (Channel Quality Indicator)UE capabilitiespriority classstatus of bufferavailable resourcesoutstanding retransmissions

Fig. 14 Increased spectral efficiency with HSDPA

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5 HSUPASimilarly to HSDPA in the downlink, HSUPA defines a new radio interface for theuplink communication. HSUPA was introduced in Release 6. The first standardwas improved in December 2004, and the 3GPP Release 6 core specificationsdefining the enhanced uplink were completed in May 2005. HSUPA is also knownas FDD Enhanced Uplinkor E-DCH.As with HSDPA, the aim with HSUPA has been to increase capacity andthroughput for packet switched traffic while reducing delay. HSDPA is aprerequisite for HSUPA support.With HSDPA only providing improvements in downlink, HSUPA achieves thefollowing advantages compare to Release 99 in the uplink:

increased data ratereduced latencyincreased cell coverage and throughput

Fig. 15 HSUPA advantages

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5.1 Higher Data RateHSUPA achieves higher uplink data rates by allowing spreading factor as low as2 while using up to 4 channelization codes per user giving the maximum datarate of 5.76 Mbps. In initial deployments of HSUPA, only up to1.44 Mbps ispossible.

5.2 Reduced LatencyWith help of the new MAC-e and MAC-es introducedfor HSUPA, the schedulerschedules radio resource and perform HARQ in the Node B in the uplinkdirection.Thus thedelay and round trip timein HSUPA is greatly reduced just likeHSDPA.

5.3 Increased Cell Coverage and ThroughputEven though HSUPA allocates dedicated channels for every user, the spreadingfactor is not fixed and can be switched between high data rate and minimal datarate in each Transmission Time Interval (TTI) . The resulting user is called"granted user" and "non-granted user", respectively.It is possible to base thescheduler on radiocondition so thatthe scarce uplink radio resource is directedtoward users with higher throughput. Thus the overall cell throughput isincreased. In HSUPA, TTI can be either 2msor 10ms.With fast retransmission, the required block error rate (BLER) required by the UEis reduced. This demands less power control headroom and results in larger cellcoverage.

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6 ExercisesExercise 1

What is the base station and controller in UMTS?

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Exercise 2

Explain the purpose of channelization code and scrambling code in DL.

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Exercise 3

Why latency is reduced in HSDPA and HSUPA?

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6.1 Solutions

Exercise 1 (Solution)

What is the base station and controller in UMTS?Node B andRNC, respectively

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Explain the purpose of channelization code and scrambling code in DL.Channelization code is used to spread narrowband user information tolarge bandwand. Differentchannels in the same cell are distinguishedby different channelization code.Scrambling code is used to distinguish signals coming from differentcells.

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Why latency is reduced in HSDPA and HSUPA?Because acknowledgement and retransmission is between UE andNodeB which is faster.Shorter TTI means thereceiver does not have to wait long for acomplete data block to send acknowledge response. Smaller datablock because of small TTI also reduce the amount retransmit data.

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HSDPA and HSUPAFeatures

Contents1 Module Objectives.....................................................................................32 Basic Principles of HSDPA...................................................................... 42.1 Introduction of new high speed channels................................................... 42.2 Short TTI ..................................................................................................... 82.3 Usage of OVSF Code Tree with HSDPA..................................................102.4 UE Capabilities..........................................................................................122.5 Summary Rel 99 - HSDPA.......................................................................143 HSDPA Features Summary.................................................................... 163.1 HSDPA RelatedFeatures in RAS06.........................................................163.2 HSDPA Related Features in UMR6.5.......................................................184 AssociatedDCH.......................................................................................205 HS-PDSCH Codes................................................................................... 226 Code Multiplexing................................................................................... 247 Dynamic HS-PDSCH Resource Allocation........................................... 258 UE Scheduling.........................................................................................269 Number of HSDPA Users....................................................................... 2910 Frequency Layer......................................................................................3011 HSDPA with AMR.................................................................................... 3212 Basic Principles of HSUPA.................................................................... 3412.1 New HSUPA Channels and OVSF Code Usage...................................... 3412.2 HSUPA terminal categories.......................................................................3712.3 Summary Rel' 99, HSDPA and HSUPA................................................... 3813 HSUPA Features Summary.................................................................... 40

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13.1 HSUPA Related Features in RAS06.........................................................4013.2 HSUPA Related Features in UMR6.5.......................................................4114 E-DCHCodes and Spreading Factors...................................................4215 HSUPA with AMR.................................................................................... 4216 HSPA+...................................................................................................... 4417 Exercises..................................................................................................4617.1 Solutions....................................................................................................48

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1 Module ObjectivesAt the end of the module the participant will be able to:

Explain the basic principles of HSDPA and HSUPA.Describe features contained in RAS06/UMR6.5 release.Explain HSDPA codes, codemultiplexing, and dynamic resource allocation.Explain different UE scheduling technique.Describe HSPA with simultaneous AMR voice call.

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2 Basic Principles of HSDPAThe followingsection illustrates the basic principles of HSDPA including newchannels, TTI (Transmission Time Interval), code usage, and UE capabilities.

2.1 Introduction of new high speed channelsWith HSDPAone new transport channel and three new physical channels wereintroduced in UMTS.Transport Channels:

HS-DSCH (Transport Channel)

Physical Channels: HS-PDSCH (High Speed Physical Downlink Shared Channel)HS-SCCH (High Speed Shared Control Channel)HS-DPCCH (High Speed Dedicated Physical Control Channel)

Fig. 1 HSDPA channels

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2.1.1 HS-DSCH and HS-PDSCHHSDPA introduces a new shared transport channel. The transport channelcarrying the user data with HSDPA operation is denoted as High Speed DownlinkShared Channel (HS-DSCH). HS-DSCH enables user data rates up to 14.4Mbps.The High Speed Physical Downlink Shared Channel (HS-PDSCH) is a downlinkphysical channel that carrying the HS-DSCH user data. The HS-DSCH can beallocated to a maximum of 15 HS-PDSCH. In HSDPA a fixed spreading factor of16 is specified for the HS-PDSCHs. The maximum number of HS-PDSCHs thatcan be allocated per cell is 15.

Fig. 2 HSDPA: shared channels and multi code transmission

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In HSDPA the newly introduced HS-DSCH is not only time multiplexed betweenthe users, but also code multiplexed. A code and time domain is introduced.The individual HS-PDSCH channels are characterized by their channelizationcode. Each Transmission Time Interval (TTI) , which consists of 3 timeslots inHSDPA, the assignment of the channelization codes to the different users can bechanged.

Fig. 3 User in code and time domain

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2.1.2 HS-SCCHThe High-Speed Shared Control Channel (HS-SCCH) is a downlink controlchannel that informs mobile devices when HSDPA data is scheduled for them,and how they can receive and decode it. It has a fixed spreading factor of 128.For each HS-DSCH TTI, each HS-SCCH carries HS-DSCH related downlinksignaling for one UE.

Fig. 4 HS-SCCH and HS-DPCH

A UE can monitor up to 4 HS-SCCHs simultaneously.A HS-SCCH set is a set of HS-SCCH which is used for HS-PDSCH allocation.There is a maximum of four HS-SCCHs in a given HS-SCCH set. The HS-SCCHset the UE is supposed to monitor is signaled by higher layers to the UE. SeveralHS-SCCH sets can be configured in a cell.Note: The number of HS-SCCHs per cells determines the maximum number ofsimultaneous users per TTI.

2.1.3 HS-DPCCHThe High Speed Dedicated Physical Control Channel (HS-DPCCH) is an uplinkcontrol channel used by the mobile to report the downlink channel quality, calledChannel Quality Index (CQI), and request for retransmissions. It uses fixedspreading factor 256.

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2.2 Short TTIThe introduction of a short Transmission Time Interval of 2ms in HSDPA is animportant contribution to reduce latency delays. TTI is defined as the inter-arrivaltime of the transport block set, and is equal to the periodicity at which a transportblock set is transferred by the physical layer on the radio interface. In Rel 9910ms, 20ms, 40ms and 80ms is possible as TTI time interval.In HSDPA the TTI is shortened to 2ms corresponding to 3 timeslots of 2/3 ms.Therefore every 2ms, the system can:

change the allocation of resources to the userreact to incorrect received datareact to changes concerning quality demands

Fig. 5 Quality cycle in HSDPA

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Allocation of resourcesEvery TTI it is determined, what users are being served, and which HS-PDSCHsthey get allocated.RetransmissionsIn case of failure with HSDPA just the data of 2ms has to be retransmitted,compared to 10ms/20ms/40ms/80ms in Rel99. Therefore the effective data rateis increased.Reaction to channel qualityThe congestion avoidance algorithm in TCP is less affected by slow fading effectsdue to faster adjustments to the channel quality on the air interface.

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2.3 Usage of OVSF Code Tree with HSDPAAs already mentioned, channelization codes are a limited resource within a cell.In one cell between 1 and 15 channelization codes can be reserved forHS-PDSCHs. The used spreading factor is always 16. The reserved codes forHSDPA can not be used for Rel 99 traffic, therefore the code usage has to beclosely monitored in HSDPA cells in order to avoid congestions within the OVSFcode tree.In the downlink direction several signaling channels have to be consideredregarding the code tree usage:

1 - n HS-SCCHs - fixed spreading factor of 128, allocated in sequence1 CPICH on 256,01 CCPCH on 256,1 (used by BCH/BCCH)1 AICH spreading factor 2561 PICH spreading factor 2561 - n FACH spreading factor 256 - 4 (depending on implementation)1 PCH spreading factor 256 - 4 (depending on implementation)

The PCH and one of the FACH may be multiplexed using the samechannelization code. In the following picture an example for an OVSF code treeusage is shown:

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Fig. 6 Usage of OVSF code tree with HSDPA (UMR example)

In the above example, four Rel 99 data connections with 384kbps in the directionare still possible. Here C SF, ndenotes channelization code n of spreading factorSF.

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2.4 UE CapabilitiesIn Release 5, twelve new UE categories have been specified, which differ in thenumber of channelization codes, the minimum inter-TTI interval, and the supportof the 16 QAM modulation:CodesThis is the maximum number of HS-DSCH multicodes that the UE cansimultaneously receive. It could be5, 10 or 15.Minimum Inter TTI IntervalMinimum inter-TTI time defines the minimum time between the beginning of twoconsecutive transmissions to this UE. If the inter-TTI time is one, this means thatthe UE can receive HS-DSCH packets during consecutive TTIs, i.e. every 2 ms. Ifthe inter-TTI time is two, the scheduler would need to skip one TTI betweenconsecutive transmissions to this UE.Transport Block SizeTransport block size is the maximum number of HS-DSCH transport block bitsthat can be received within an HS-DSCH TTI.Soft Buffer SizeSoft buffer size is the maximum number of soft channel bits over all the HARQprocesses. That means the buffer capacity for HARQ. This can impact the UEreceiver performance particularly in poor quality locations where the number ofretransmissions can be high.ModulationSupported modulations of UE can beQPSK only or both QPSK and 16QAM.

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Fig. 7 UE Categories

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2.5 Summary Rel 99 - HSDPAThe following table illustrates the main differences between HSDPA and Rel 99:

Fig. 8 Basic Principles of HSDPA in comparison to Rel 99

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3 HSDPA Features SummaryThis section gives the summary of the HSDPA support in Nokia SiemensNetworks products.Information up till RAS06 and UMR6.5 versions are providedin this courses. Many of the features are covered in subsequent sections.

3.1 HSDPA RelatedFeatures in RAS06HSDPA has been supported by Nokia Siemens Networks RNC 196/450 andrelated Node B's sinceversion RAS05. The following tables list the featuresrelated to HSDPA up toversion RAS06.

Fig. 9 RASHSDPA Feature (Part 1)

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3.2 HSDPA Related Features in UMR6.5HSDPA has been supported by Nokia Siemens Networks RNC RN750 andrelated Node B's since version UMR5.0. The following tables list the featuresrelated to HSDPA up to version UMR6.5.

Fig. 12 UMRHSDPA Feature (Part 1)

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Fig. 13 UMRHSDPA Feature (Part 2)

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4 AssociatedDCHHSDPA only covers downlink data direction. Release 99 dedicated channel(DCH) is still required for signaling and UL data. The maximum bit rate forsignaling is typically 3.4kbps in both UL and DL. Since DL DCH only containssignaling, fixed spreading factor 256 is used in DL direction.On the otherhand,UL DCH contains both signaling and UL data.Typical UL data rates are64kbps, 128kbps and 384kbps. Bit rate adaptation is possible by adjusting ULspreading factor accordingto the actualutilization by the UE.The feature 16 kbit/s Return Channel DCH Data Rate Support for HSDPA(RAS06) further expand the range to include 16kbps as an option. So thepossible data rate becomes 16, 64, 128 or 384kbps.The feature HSDPA RAB Handling Enhancements(UMR6.0) adds 32kbps ULdata rate. So thedata rates of 32, 64, 128 and 384kbps are possible in UL.The advantage of allowed lower data rate is two folded:

Many HSDPAusers do not use muchbandwidth in the uplink. The uplinkdata rate can be reduced. This frees upchannel element (CE) resource inthe Node B.The data rate can be reduced further in case of network overload orcongestion situation.The moredata rate reduction, the more interferencedecrease.

Higher UL data rate via DCH is not foreseen because 384kbps already requiresspreading factor 4. HSUPA is a more viable option for higher uplink throughput.

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Fig. 14 16kbpsuplink DCH in RAS06

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5 HS-PDSCH CodesHS-PDSCH uses spreading factor 16 for spreading HSDPA traffic. So amaximum 15 codes for HS-PDSCH are available.On RAS, 5 codes are supported with basic HSDPA feature. The feature HSDPA15 Codes further increase this number to 10 and 15.With more codes:

Average cell throughput increased by between 30-50%.With HSDPA 10 Mbps per User feature, user peak rates go up to 7.2 Mbpswith UEs supporting at least 10 codes (UE category 7-10) and up to10.8Mbps with UEs supporting 15 codes (UE category 9-10).There is significant resource gain if used with Shared HSDPA Schedulerand HSDPA Dynamic Resource Allocation featuresWhen terminals support less codes than a cell, HSDPA Code Multiplexingfeature is needed to use the remaining capacity (i.e., 10 codes and two 5code UEs each at 3.6 Mbps = 7.2Mbps).

On UMR, UMR5.0 can handle 15 codes and code multiplexing. Up to maximumof 4 HS-SCCHmay be configured. However, only 5 codes can be assigned to aUE. So UE incategory 7-10 only attains maximum 3.6 Mbps data rate. Fullsupport of UE category 7-10 is in UMR6.0.

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Fig. 15 Higher number of HS-PDSCH codes

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6 Code MultiplexingCode multiplexing means multiple UE can receive HSDPA simultaneously. Withup to 15 HS-PDSCH codes possible, if UE only supports 5 codes and there is nocode multiplexing, 10 codes become idle when the network sends data to thisUE. So this feature is suggested when more than 5 codes are activated in a cell.Since one HS-SCCH channel can signal data transmission for one UE, themaximum number of UE involved incode multiplexing during one TTI from singlecell equals the number of HS-SCCH channels configured (max 3 in RAS06, max4 in UMR).The available HS-PDSCH codes and HS-PDSCH power of the cell are dividedbetween the UEs. The number of HS-PDSCH codes used depends on thechannel conditions experienced by UEs.If a cell supports more codes than theUEs do, then more than one UE can be served during one TTI.

Fig. 16 Code multiplexing example with 3 HS-SCCH channelsand 15 HS-PDSCH channels

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7 Dynamic HS-PDSCHResource Allocation

Because both Release 99 and HSDPA services share the same resource,varyingthe amount ofresource assigned for HSDPA depending on the current Rel '99traffic situation is highly preferred. HSDPA DynamicResource Allocationfeature in RAS covers:Dynamic Power AllocationThe DL power used for HSDPA is controlled by Node B. All the power left afterDCH traffic, HSUPA control channels, and common channels is used for HSDPA.This means that as long as there is HSDPA traffic in the cell, all theavailablepower amplifierpower in the Node B can be efficiently utilized.Dynamic NRT DCH SchedulingThe RNC schedules the NRT DCH bit rates so that the DL power per user ofNRT DCH and HSDPA are equal.For example,if in a 20 W cell there happens tobe 8 W of RTand common channel load, then about 12 W is available for NRTtraffic. This 12 W is then divided so that in case of 2 NRT DCH users and 10HSDPA users, about 2 W would be given to DCH side and 10 W to HSDPA side.On operator's choice, the NRT DCH and HSDPAuser atdifferentTraffic HandlingPriority (THP) can be weighted differently toadjust the power resource allocatedfor each user type.Dynamic Allocation of HS-PDSCH CodesThe code allocation is dynamically following the power allocation. In practice thismeans that once the NRT DCH bit rates have been decided, based on equalpower criterion, the code requirements for the DCH side have been fixed. Allother codes are then given to the HSDPA (operator may leave some margin toallow fast voice call allocation). In case of new DCH connections (for which thebit rate is again determined based on power criteria), the required amount ofHSDPA codes are given back to the DCH.Direct Switch Between HS-DSCH and DCHThis feature also includes the direct switch from HS-DSCH to DCH other thanzero kbit/s and vice versa.

In UMR, the feature HSDPA Resource and Power Managementworks basedon the power availablefor HSDPA, HSDPA power utilization,and available datarate for HSDPA. NRT DCH power are adjusted so that the HSDPA could achievethe power and data rate target. The feature Dynamic Code Allocation forHSDPA adjusts the number of HSDPA codes according to DCH traffic.Remaining two items are in basic HSDPA supported.

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8 UE SchedulingThe packet scheduler has got a central function in HSDPA and is located in theNode B in MAC-hs. The scheduler's main task is the assignment of resources tothe individual UEs on the HS-DSCH. The way of the implementation of thescheduler is not specified in the 3GPP standard. Therefore the algorithms of thescheduler are vendor specific.Mainly three methods are distinguished:Fair Scheduler or Round Robin Scheduler The Round Robin Scheduler assigns the resources to the UEs sequentially.Channel conditions are not taken into account. Therefore a high degree offairness is reached, whereas the capacity of the cell is not efficiently used. UEshaving bad channel conditions decrease the data rate of the system.SNR-based Scheduler or Max-CIR SchedulerSNR-based Scheduler assigns the resources to the UE having the best channelconditions or CQI. The system capacity is optimally used. The exploitation of thefast fading channels produce an effect known as multi-user diversity, whichsignificantly contributes to the spectral efficiency of HSDPA. However UEs havingbad channel conditions may not get served at all.Proportional Fair SchedulerThe Proportional Fair Scheduler is a compromise between the completeexploitation of the system capacity and the fairness between the users. The userhaving the best Relative Channel Quality gets served: The Relative ChannelQuality is the ratio between the users instantaneously supported data rate to theusers average served throughput. When two UEs are in a cell having the sameCQI the UE which had been assigned less data in the previous period getsserved.

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Fig. 17 Different types of schedulers

Fig. 18 SNR Scheduling

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Fig. 19 Input for user ranking

The network operator has to evaluate the pro and cons of the different methods,particularly the exploitation of the maximal system capacity in contrast to evenlydistributed resources between the users. The basic HSDPA support in RAS isRound Robin while the one in UMR is Max-CIR. Proportional Fair Scheduler issupported as optional on both systems.

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9 Number of HSDPA UsersThe number of HSDPA users that can be handled on RAS depends on thefeatures activated as below:

Fig. 20 Type of scheduler and number of usersprovided byRAS feature

With scheduler working at WBTS level, only one scheduler works for all cells. Thenumber of concurrent users that are scheduled in the same TTI is limited. SharedHSDPA Scheduler for Baseband Efficiencyhandles maximum 3 UE's per TTIfor the whole WBTS. However, the hardware required for shared scheduler isonly 1/3 of cell based scheduler.UMRuses cellscheduler. The number of user depends on uplink DCH data rateand the number of HSDPA cells handled by one CHC card. See NSN Productschapter for more information.

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10 Frequency LayerWhen there are large amount of HSPA traffic, separating Rel '99 DCH and HSPAtraffic to different carrier frequencies (layers)of the same sector can be done.Upon connection the network will check:

UE capabilityThe service UE is requesting

and redirect the UE to the correct layer. The feature is named Directed RRCConnection Setup for HSDPA Layer on RAS and UE Differentiationon UMR.The same principle also applies to HSUPA with three different types of layer:

Non-HSDPAHSDPA onlyHSDPA and HSUPA

On RAS there is an additional HSPA Layering for UEs in Common Channelsthat redirect the UE when the UE makes transition from Cell_FACH to Cell_DCHstate.

Fig. 21 Directing UE to the correct frequency layer.

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Separating into layers allows high HSPA cell capacity. 15 HS-PDSCH codes canbe used without sacrifice Rel '99 support such as voice or video calls.With several carriers or layers belonging to the same type, load balancingbetween carriers can be done. Also load overflow from one layer type to anothertype might be possible. For example, if a DCH service is requested andnon-HSDPA layer is already congest, UE may setup in HSDPA layer and moveUE to HSDPA and move back to non-HSDPA when the situation of non-HSDPAlayer improves. In UMR, HSDPA Mobility Enhancementsis required for morethan one HSDPA-capable carriers.

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11 HSDPA with AMRSimultanous HS-DSCH and DCH is already in used in HSDPA. DCH is requiredfor signaling and UL traffic. It is possible that this DCH also handles AMR voicecall. It is enabled with HSDPA with Simultaneous AMR Voice Call (RAS) orHSDPA RAB Handling Enhancements(UMR). Without this feature, the systemcould revert back to Rel '99 CS+PS multi-call. UL data rate of packet switched isfixed to 64kbps in this case for stable voice connection.

Fig. 22 Simultaneous HSDPA and AMR services

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12 Basic Principles of HSUPAThe followingsection illustrates the basic principles of HSUPA including newchannels,code usage, and UE capabilities.

12.1 New HSUPA Channels and OVSF CodeUsage

HSUPA introduces a new transport channel:E-DCH (Enhanced Dedicated Channel).

For physical channels, there are two new channels in the uplink direction:

E-DPDCH (E-DCH Dedicated Physical Data Channel), SF=256 - 2E-DPCCH (E-DCH Dedicated Physical Control Channel), SF=256

The above channels are dedicatedto each HSUPA UE. For E-DPDCH, amaximum of 4 E-DPDCH channels is possible in one UE although the actualnumber of channels UE can handle depends on theE-DCH category of UE.In the downlink direction, the following physical channels are introduced:

E-AGCH (E-DCH Absolute Grant Channel), SF=256E-RGCH (E-DCH Relative Grant Channel), SF=128E-HICH (E-DCH HARQ Acknowledgement Indicator Channel), SF=128

The E-AGCH is time multiplexed and shared among HSUPA UE's. E-RNTI(E-DCH Radio Network Temporary Identifier) is encoded into the E-AGCH toidentify the intended UE. For E-RGCH and E-HICH,one channelizationcodeprovides 40 orthogonalsignatures. An HSUPA UE is addresseed using theassigned channelization code and signature. E-RGCH and E-HICH of one UEmustuse the same channelization code. Thus the 40 signatures is enough tosupport 20 different UE's. It is possible for the network to manage several UE'stogether by assigning the same signature.

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Fig. 23 Channels used by HSUPA UE

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The addition of HSUPA support consumes channelization code resource of thecell. The below picture is an example of OVSF code tree utilization:

Fig. 24 Usage of OVSF code tree with HSUPA in UMR

Release 99 associated DCHcan be used in HSUPA for UL and DL signaling.Alternatively, signaling may be carried in the same E-DPDCH and HS-PDSCH astraffic. In this case E-DPDCH is used for UL signaling while HS-PDSCH is for DLsignaling.

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12.2 HSUPA terminal categoriesAs in HSDPA, the UEs differ in their capabilities to use HSUPA and are classifiedin six UE categories. The UEs varies in their support of:

Maximum number of E-DCH codes transmitted.Minimum spreading factor.2 ms TTI.Maximum transport block size.

Fig. 25 E-DCH UE Category

Note that a UE supporting HSUPA must support HSDPA. Also the UL DCH isrestricted to 64 kbpsfor simultaneous DCH and E-DCH configuration.

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12.3 Summary Rel' 99, HSDPA and HSUPAThe following table gives the main differences between HSDPA, HSUPA, and Rel99:

Fig. 26 Feature comparison

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Fig. 27 Feature comparison

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13 HSUPA Features SummaryBelow are the summary of HSUPA featuressupported in Nokia SiemensNetworks products. Many of the functionalities in HSDPA, such as transportnetwork features, also apply to HSUPA. Only features previously not covered arelisted here.

13.1 HSUPA Related Features in RAS06

Fig. 28 RAS HSUPA Feature

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13.2 HSUPA Related Features in UMR6.5

Fig. 29 UMRHSUPAFeature

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14 E-DCHCodes andSpreading Factors

The basic HSUPA support provides 2x SF4. The feature HSUPA 2.0 Mbpsenables 2x SF2 to be used. So the data rate increases from 1.44 Mbps to 2Mbps. 2x SF2 is not supported in UMR6.5.The TTI is always 10 ms in RAS06/UMR6.5.

15 HSUPA with AMRIn analogous to simultaneous HSDPA and AMR, the same applies to HSUPA andAMR. The feature HSUPA With Simultaneous AMR Voice Call is required onRAS.HSUPA with AMRis included in basic HSUPA support in UMR.

Fig. 30 Simultaneous HSDPA, HSUPAand AMR services

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16 HSPA+With HSDPA introducedin Release 5 and HSUPA in Release 6, there are furtherimprovements to HSPA in later releases. The resulting HSPA with thoseimprovements in Release 7 and 8is called HSPA+ , Evolved HSPA or HSPAEvolution. Among additional features introduced are:

New modulation 64QAM for HSDPA. 64QAM modulates 6 bitsinto onesymbol, 50% increase of data rate comparing to 16QAM which modulates4bits into eachsymbol.New modulation16QAM for HSUPA. The modulation is also called 4PAM(Pulse Amplitude Modulation) since each UL physical channel only occupieseither I or Q part of 16QAM constellation.This doubles uplink data rate.Support of Multiple Input Multiple Output (MIMO) . The MIMO in HSPA+uses two antenna to send and receive, with different data stream being sentin each pair.Optional all-IP access network where Node B and RNC are connectedviaethernet.Flat architecture where user packet switched data is transferred directlybetween RNC and GGSN, bypassing SGSN.

HSPA+ will support the data rate up to 42Mbps in downlink and 22Mbps in uplink.

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Fig. 31 HSPA+ Improvements

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17 ExercisesExercise 1

List three HSDPA features on RAS and/or UMR that are useful when a carrier isshared between Rel 99 and HSDPA.

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Exercise 2

List three HSDPA features on RAS and/or UMR that are useful when the HSDPAtraffic is so large that Rel 99 and HSDPA are handled in different carriers.

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17.1 Solutions


List three HSDPA features on RAS and/or UMR that are useful when a carrier isshared between Rel 99 and HSDPA.

On RAS:HSDPA Dynamic Resource Allocation - to vary the number ofcode and power depending on Rel 99 load.16 kbit/s Return Channel DCH Data Rate Support for HSDPA -more UL resource for Rel 99.HSDPA with Simultaneous AMR Voice Call - No need to switchthe packet switched traffic Rel 99 so HSDPA benefit of efficientresource usage is preserved.

On UMR:HSDPA Resource and Power Management - to manage powerbetween Rel 99 and HSDPA.Dynamic Code Allocation for HSDPA - to vary the number of codeand power depending on Rel 99 load.HSDPA RAB Handling Enhancements - to support HSDPAPS+AMR multi call.

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List three HSDPA features on RAS and/or UMR that are useful when the HSDPAtraffic is so large that Rel 99 and HSDPA are handled in different carriers.

On RAS:Directed RRC Connection Setup for HSDPA Layer - tomove UE incorrect carrier during call setup.HSDPA 15 Codes - for larger HSDPA traffic.HSDPA Code Multiplexing - sharing 15 codes to several HSDPAUE.

On UMR:UE Differentiation - to move UE in correct carrier.HSDPA RAB Handling Enhancements -so thatPS+AMR multi callis retained in HSDPA layer.HSDPA Mobility Enhancements -support various types ofhandoverbetween layers.

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HSDPA and HSUPAPhysical Channel

Contents1 Module Objectives.....................................................................................32 New HSDPA Channels..............................................................................42.1 HS-PDSCH..................................................................................................52.2 HS-SCCH....................................................................................................62.3 HS-DPCCH..................................................................................................83 Adaptive Modulation and Coding..........................................................103.1 Adaptive Modulation..................................................................................113.2 Adaptive Coding........................................................................................133.3 Channel Quality Identifier CQI.................................................................. 144 Hybrid Automatic Repeat Request........................................................164.1 HARQ Methods and Processes................................................................ 174.2 16QAM Constellation Rearrangement...................................................... 194.3 Redundancy Version Parameter............................................................... 204.4 Stop and Wait HARQ................................................................................204.5 Soft Memory..............................................................................................224.6 Retransmissions in HSDPA...................................................................... 235 HSDPA Process on Layer 1 and 2.........................................................246 New HSUPA Channels............................................................................ 266.1 E-DPDCH Channelization Code Allocation and Modulation..................... 287 Fast Node B Scheduling.........................................................................327.1 Introduction of a Short TTI ........................................................................337.2 Introduction of HARQ................................................................................338 Support of Macro Diversity....................................................................369 HSUPA Scheduling Mechanism.............................................................389.1 Node B Scheduling................................................................................... 39

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9.2 Scheduling in UE.......................................................................................4310 Exercises..................................................................................................4410.1 Solutions....................................................................................................48

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1 Module ObjectivesAt the end of the module the participant will be able to:

List new channels used in HSDPA and HSUPA.Explain the function of new physical channels.Describe the procedures running within the physical channels.

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2 New HSDPA ChannelsThe newly introduced channels in HSDPA fit into the lower layers: transportchannels and physical channels. The logical channels are not affected.

Fig. 1 New Physical Channels introduced forHSDPA

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Fig. 2 Enhancement of channels in HSDPA, divided into transport channels and physical channels

To transmit user data the transport channel HS-DSCH(High Speed DownlinkShared Channel) was introduced in HSDPA, which is mapped onto the physicalchannel HS-PDSCH(High Speed Physical Downlink Shared Channel).HARQ functionality and scheduling requires the introduction of two additionalphysical channels for signaling purposes:In uplink a signaling channel is required to provide feedback about received datablocks, either ACK or NACK, for HARQ-processing: HS-DPCCH(High SpeedDedicated Physical Control Channel).Additionally a signaling channel is necessary in the downlink direction to informthe UE about impending data transmissions in the upcoming TTI and theirtransport block format: the so-called HS-SCCH(High Speed Shared ControlChannel).

2.1 HS-PDSCHHS-PDSCH is the downlink physical channel carrying data. It requires a separatededicated channel for uplink data and signaling. Spreading factor of 16 is usedand multi code is possible. Up to 15 codes may be used. HS-PDSCH is sharedamong all HSDPA users.

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2.2 HS-SCCHThe downlink signaling consists of a downlink DPCH (Dedicated PhysicalChannel) and a number of HS-SCCHs. A fixed spreading factor of 128 isassigned. For each HS-DSCH TTI, each HS-SCCH carries HS-DSCH-relateddownlink signaling for one UE.The HS-SCCHs carries information regarding HARQ processes and usedtransport format:Transport Format and Resource related Information (TFRI)

Channelization Code-Set: information to the UE, which UE is assigned for thesucceeding TTI,and channelization codes of HS-PDSCHthe UEis supposedto receive and decode.Modulation Scheme: information to the UE, whether 16QAM or QPSK isused.Transport Block Size.

HARQ related InformationHARQ Process Identifier: identifythe data belongs to.Redundancy and Constellation Version. The field contains the RedundancyVersion. parameter for incremental redundancy and the Constellation Versionparameter for 16QAM constellation.New Data Indicator: information whether new data or a retransmission istransmitted.UE Identity: The H-RNTI of the UEis implicitly encoded.

Between the notification via HS-SCCH and the start of the correspondingHS-DSCH TTI a fixed timing offset of 2*Tslot = 5120 chips is specified.

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Fig. 3 HS-SCCH structure

Fig. 4 Timing relation between HS-SCCH and HS-PDSCH

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2.3 HS-DPCCHThe High Speed Dedicated Physical Control Channel is configured in the uplinkdirection and contains the following information:

HARQ Acknowledgement including the result of the Cyclic RedundancyCheck (CRC): ACK or NACK. HARQ acknowledgement field is DTXed whenthere is no ACK/NACK information being sent.Channel Quality Indicator (CQI): The transmission cycle and timing for theChannel Quality Indicator is determined by UTRAN and signaled by higherlayer.

HS-DPCCH uses spreading factor SF=256.

Fig. 5 HS-DPCCH

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Transmission of ACK/NACK commences 7.5 slots following the end of thereceived HS-DSCH. This results in the following timing relations between theHSDPA signaling channels and the HS-DSCH:

Fig. 6 Timing relations between the HSDPA channels

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3 Adaptive Modulation andCoding

In HSDPA link adaption is used to adapt the signal to a certain UE to the radiochannel conditions. Link adaption therefore increases the spectral efficiency andcell capacity. Italso enables higher data rates of the individual user.In Rel 99 an adaption to the radio channel conditions was realized by the usageof power control. Depending on the channel conditions and the requested Qualityof Service the power was regulated. Capacity in an UMTS cell is limited byinterference. To exploit the capacity of the system, it is necessary to keep theused power of each transmitter as low as possible.However the used power control algorithm in Rel 99 is rather slow. Additionallylarge parts of the power spectrum are not used for transmission of user data.HSDPA uses the unused power of the Rel 99 system. In order to do so, adifferent approach to deal with changing channel conditions had to be found.

Fig. 7 Power in Rel 99 und HSDPA

In HSDPA the transmit power within a TTI is kept constant. Adaption to changingradio conditions is realized by the selection of an appropriate modulation andcoding scheme. This principle is called Adaptive Modulation and Coding (AMC).It constitutes one of the main principles of HSDPA.

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Adaptive modulation and coding (AMC) matches the modulation and codingscheme to the instantaneous channel conditions for each user transmission. Thepower of the transmitted signal is held constant over a subframe interval, and themodulation and coding format is changed to match the quality of the receivedsignal or the channel conditions. In this scenario, users close to the base stationare typically assigned higher-order modulation schemes with higher code rates.The modulation order and code rate will decrease as the distance from the basestation increases.

3.1 Adaptive ModulationIn Rel99 only QPSK (Quadrature Phase Shift Keying) is intended as modulationmethod. HSDPA introduces 16QAM (16 Quadrature Amplitude Modulation) as anadditional modulation method.Both methods use phase modulation wherethe phase of a carrier wave is variedin order to transmit the information contained in the signal. Having 2^n differentsymbols, n bits per symbol can be coded. QPSK realizes a distinction of 4symbols and can therefore transmit 2 bits per symbol (00,01,10,11). 16QAMadditionally uses amplitude modulation and enables therefore 16 symbols, bywhich 4 bits can be transmitted simultaneously. Therefore the physicaltransmission rate is doubled compared to QPSK while having the same symbolrate.

Fig. 8 QPSK and 16QAM in comparison

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HSDPA takes the different characteristics of 16QAM and QPSK into account anduses the modulation suitable to the current channel conditions: 16QAM when theyare good and QPSK when they are bad.However 16QAM requires distinct better channel conditions than QPSK. Becauseof the fine mapping of the symbols the signal can be easily disrupted. Particularlythe amplitude of an electromagnetical wave experiences higher fluctuation thanthe phase. The amplitude easily gets diminished by attenuation and can only becorrectly interpreted in good channel conditions. Therefore 16QAM is onlysuitable in case of good channel conditions. 16QAM is also more complex toimplement as the process of modulation and demodulation is much more complexthan in QPSK. Therefore 16QAM is not implemented in all UEs, UEs belonging tothe category 11 and 12 will not be able to use 16QAM.

Fig. 9 Adaptive Modulation

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3.2 Adaptive CodingCoding SchemesRel 99 uses two different channel coding schemes:

Convolutional coding with rate 1/3 and 1/2.Turbo coding with rate 1/3.

HSDPA only uses the 1/3 turbo encoder, which triples the original data in order totransmit sufficient redundant information. However the effective coding rate inHSDPA is the result of a combination of turbo coding and rate matching. Ratematching means that bits on a Transport Channel are repeated or punctured.First Rate Matching StateAfter channel codingusing the turbo code with rate 1/3 the number of transmittedbits is matched to the available UE soft-buffering capability during the first ratematching process. In the first rate matching process only Parity1 and Parity2 bitsare removed.Second Rate Matching StateIn the next step the number of bits is fitted to the number of physical channel bitsavailable in the HS-DSCH TTI. The number of available physical channel bits isdetermined by the scheduler which assigns a Transport Format ResourceCombination (TFRC).

Fig. 10 Rate Matching in HSDPA

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3.3 Channel Quality Identifier CQIThe Channel Quality Identifier (CQI) is a indicator notifying the quality of the usedradio link by the UE to the serving Node B. The CQI value can be 0 to 30. EachCQI value corresponds to a certain transport block size, number of HS-PDSCHs,and modulation format for a certain UE category, a so-called Transport FormatResource Combination (TFRC)The CQI is determined by the UE based on the P-CPICH. The CQI is a proposalof the UE for a Transport Format Resource Combination (TFRC) for the followingTTI. The proposal is made under the assumption that the transport block errorprobability (BLER) shall not exceed 10%. The TFRC includes:

ModulationTransport block sizeNumber of channelization codesTX power offset

The Scheduler in the Node B determines the actual transport format based on theproposal from the UE in form of the received CQI.Alternative methods are allowed by the 3GPP specification to determine thetransport format apart from evaluating the P-CPICH, e.g. selecting the transportformat based on the power of the associated DPCH.The scheduler has to consider the UE capabilities when assigning a transportformat. Therefore the CQI tables are UE specific. In the following the CQI tablesfor UE category 10 (having the highest possible data rate) and UE category 11and 12 (which were already available in 2006) are shown.

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Fig. 11 CQI Mapping Table UE category 10

Fig. 12 CQI Mapping Table UE category 11&12

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4 Hybrid Automatic RepeatRequest

Automatic Repeat Request (ARQ) protocols are protocols which are used forerror control. Basically the receiver checks the received data unit for possibleerrors (usually the Cyclic Redundancy Check or CRC is used) and returns anacknowledgment message, either to acknowledge a correct receipt of the data(Acknowledgement or ACK) or to request a retransmission (NegativeAcknowledgement or NACK) in case of an erroneous received data unit. ARQ isan error control method for data transmission in which the receiver detectstransmission errors in a message and automatically requests a retransmissionfrom the transmitter. Therefore ARQ ensures reliable transmission of dataForward Error Correction(FEC), also called channel coding , is a type ofdigital signal processing that improves data reliability by introducing a knownstructure into a data sequence prior to transmission or storage. FEC works byadding check bits to the outgoing data stream. Adding more check bits reducesthe amount of available bandwidth, but also enables the receiver to correct formore errors. The structure enables a receiving system to detect and possiblycorrect errors caused by corruption from the channel and the receiver. Thiscoding technique enables the decoder to correct errors without requestingretransmission of the original information. The probability of a successful datatransmission is increased, but because of the redundant data the data rate isdecreased.HSDPA introduces Hybrid AQR (HARQ) . HARQ is defined as any combinedARQ and FEC method that saves failed decoding attempts from previoustransmissions for future joint decoding with retransmissions.

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Fig. 13 Redundancy versions in HARQ

4.1 HARQ Methods and ProcessesHARQ encompasses a variety of methods. HSDPA implements two differentmethods:

Chase combiningIncremental redundancy

4.1.1 Chase CombiningChase combining is one of the simplest forms of HARQ. Chase combiningtransmits in case of a retransmission exact the same data once again. Thedecoder combines multiple received copies of the coded packet weighted by theSNR prior to decoding. Always the same information and parity bits are sent tobe combined and every version of packet is self decodable. The set of parity bitsis always obtained by using the same puncturing scheme. This method providestime diversity gain and is very simple to implement.

4.1.2 Incremental RedundancyIn Chase combining, always the same information and parity bits are sent.Incremental redundancy (IR) may use different sets of parity bits (obtained bydifferent puncturing schemes) in consecutive packet transmissions. All thesegroups of bits obtained from different transmissions have to be stored in the soft

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buffer for combining. Hence, incremental redundancy provides more effectivetransmission at the expense of increased soft buffer memory requirements.The following picture demonstrates the main principle:

Fig. 14 Example for Incremental Redundancy

For simplicity, an IR buffer size of 10 bits/process and a single process areassumed in this example:

The original data block containing 4 bits is turbo encoded at the 1/3 rate andtherefore tripled to 12 bits.In the First Rate Matching the data block gets punctured to match to the IRbuffer size of 10 bits. We obtain 10 bits.The Second rate-matching stage punctures the data again. The puncturingpattern is determined by the redundancy version (RV) parameters set bythe scheduler (five grey bits in the above figure).The five grey bits are transmitted.The data arrives at the UE, is demodulated, padded with dummy bits, andstuffed into the IR buffer. The data then is decoded. This block is checkedagainst the CRC (Cyclic Redundancy Check), and if found to be in error, isstored, and a NACK requests retransmission.The Node B sends the retransmission. It uses a different puncturing patternor redundancy version than on the first transmission (five white bits with a \inside in the figure).

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At the UE these bits are recombined with the original transmitted five bits.Now for every data bit here are 2.5 bits available for decoding, whichincreases the likelihood for success. If the block is after the CRC check stillin error, a NACK is sent to the Node B to request a retransmission.To obtain the data for retransmission, yet another puncturing pattern ortedundancy version is used (five white bits with a / inside in the figure).The data is recombined with the previous transmissions and decoded. Whenthe data is correctly decoded, an ACK is sent and the transmission of thenext data unit can start.

Incremental redundancy is called HARQ Type II . If each transmission has to beself-decodable, it is called is partial incremental redundancy or HARQ Type III. In HSDPA both versions are employed.Incremental redundancy reduces the effective coding rate in case of goodchannel conditions, whereas in bad channel conditions more retransmissions arenecessary which induces a decreased data rate. Therefore under bad channelconditions Chase combining is used, thus obtaining a diversity (time) gain.In Rel 99 error protection was provided by the RLC layer in the RNC. Erroneousdata was dumped and not used for combining with retransmissions.The HARQ functionality in HSDPA is located in the MAC-hs layer in the Node Band UE and uses previously sent data for decoding. Therefore in HSDPA HARQprovides a fast and effective error protection scheme.

4.2 16QAM Constellation RearrangementIf 16QAM is used as modulation scheme, 16QAM constellation rearrangement isdeployed.QPSK is much less prone to error than 16QAM. When using QPSK only a phaseestimate is necessary for the demodulation process. With 16QAM constellation,the different bits mapped to the 16QAM symbols have different reliability, as amore precise phase estimate is required and also the amplitude has to beinterpreted, and which may be easily affected by attenuation. Therefore two of thefour bits in a symbol have a higher probability of error than the other two bits.This is compensated for with a method called constellation rearrangement. Withconstellation rearrangement, the different retransmissions use slightly differentmapping of the bits to 16QAM symbols to improve the performance. Therearrangement occurs during re-transmission and disperses the error probabilityequally among all the bits in the average, after the re-transmission combining.16QAM constellation rearrangement consists in the variation of thebits-to-symbols-mapping, bits can be rearranged before retransmission in such amanner that some less protected bits become more protected.

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