Hspa systems 002

HSPA systems

Kari AhoSenior Research Scientist

[email protected]

2 © 2008 Magister Solutions Ltd

Disclaimer

Effort has been put to make these slides as correct as possible, however it is still suggested that reader confirms the latest information from official sources like 3GPP specs (http://www.3gpp.org/Specification-Numbering)

Material represents the views and opinions of the author and not necessarily the views of their employers

Use/reproduction of this material is forbidden without a permission from the author

http://www.3gpp.org/Specification-Numbering


Readings related to the subject

General readings WCDMA for UMTS – H. Holma, A. Toskala HSDPA/HSUPA for UMTS – H. Holma, A. Toskala 3G Evolution - HSPA and LTE for Mobile Broadband - E.

Dahlman, S. Parkvall, J. Sköld and P. Beming, Network planning oriented

Radio Network Planning and Optimisation for UMTS – J. Laiho, A. Wacker, T. Novosad

UMTS Radio Network Planning, Optimization and QoS Management For Practical Engineering Tasks – J. Lempiäinen, M. Manninen


Contents

Introduction HSDPA HSUPA Continuous Packet Connectivity I-HSPA Conclusions

5 © 2008 Magister Solutions Ltd5 © 2008 Magister Solutions Ltd

Introduction


High Speed Packet Access (1/3)

There were number of pushing forces to improve the packet data capabilities of WCDMA even further, e.g. Growing interest towards rich calls, mobile-TV and music streaming in

the wireless domain Competitive technologies such as WIMAX

High Speed Packet Access (HSPA) evolution introduced first downlink counterpart of the evolution called High Speed Downlink Packet Access (HSDPA) in Release 5

Uplink evolution followed later in Release 6 by the name of High Speed Uplink Packet Access (HSUPA)

HSPA was originally designed for non-real time traffic with high transmission rate requirements



HSPA features/properties include e.g. Higher order modulation and coding

Higher throughput and peak data rates In theory up to 5,8 Mbps in the uplink and 14 Mbps in the downlink

without Multiple Inputs and Multiple Outputs (MIMO) Multiple Inputs and Multiple Outputs (MIMO)

Roughly speaking equals to additional transmitter and receiver antennas

Fast scheduling in the Node B Possibility to take advantage of channel conditions with lower latency



Link adaptation in downlink Possibility to adjust the used modulation and coding scheme according

to be appropriate for current radio channel conditions Improved retransmission capabilities

Newly introduced layer one retransmissions called as Hybrid Automatic Repeat Request (HARQ) => reduced delay

Radio Link Control (RLC) level retransmissions still possible Shorter frame sizes and thus Transmission Time Intervals (TTI)

With HSDPA 2ms and with HSUPA 10ms and 2ms


WCDMA Background and Evolution

2000 2002 2004 2006 2007200520032001

3GPP Rel -9912/99

3GPP Rel 403/01

3GPP Rel 5 (HSDPA)

03/02

3GPP Rel 6(HSUPA)

2H/04

3GPP Rel 7HSPA+06/07

Further Releases, (LTE)

JapanEurope

(pre-commercial)

Europe(commercial)

HSDPA (commercial)

HSUPA (commercial)


Questions

Why were the packet data capabilities of WCDMA improved even further?

For what kind of services was HSPA originally designed?


High Speed Downlink Packet Access(HSDPA)


Introduction to HSDPA (1/2)

In Release 99 there basically exists three different methods for downlink packet data operation DCH, Forward Access Channel (FACH) and Downlink Shared Channel (DSCH)

After the introduction of HSDPA in Release 5 some changes to downlink packet data operations occurred New High Speed DSCH (HS-DSCH) channel was introduced DSCH was removed due to lack of interest for implementing it

in practical networks


Introduction to HSDPA (2/2)

HSDPA Improvements for packet data performance both in terms of capacity and practical bit rates are based on The use of link adaptation, Higher order modulation, Fast scheduling, Shorter frame size (or transmission time interval), and Physical layer retransmission

HSDPA does not support DCH features like fast power control or soft handover


HSDPA channels (1/2)

The Release 99 based DCH is the key part of the system – despite the introduction of HSDPA Release 5 HSDPA is always operated with the DCH

DCH with HSDPA If the service is only for packet data, then at least the signaling

radio bearer (SRB) is carried on the DCH In case the service is circuit-switched then the service always

runs on the DCH With Release 6, signaling can also be carried without the DCH In Release 5, uplink user data always go on the DCH (when

HSDPA is active)


HSDPA channels (2/2)

in Release 6 an alternative is provided by the Enhanced DCH (E-DCH) with the introduction of high-speed uplink packet access (HSUPA)

User data is sent on High Speed Downlink Shared Channel (HS-DSCH)

Control information is sent on High Speed Common Control Channel (HS-SCCH)

HS-SCCH is sent two slot before HS-DSCH to inform the scheduled UE of the transport format of the incoming transmission on HS-DSCH


Questions

Mention at least purpose to which Rel’99 DCH is used with HSDPA

What kind of handovers are supported with HSDPA?


Link Adaptation (1/3)

UE informs the Node B regularly of its channel quality by CQI messages (Channel Quality Indicator)



Adaptive modulation and higher order modulation (16/64QAM) with HSDPA

0 2 0 4 0 6 0 8 0 1 00 1 20 1 40 1 60- 202468

10121416

Time [number of TTIs]

QPSK1/4

QPSK2/4

QPSK3/4

16QAM 2/4

16QAM 3/4

Inst

anta

neou

s Es

No

[dB]

Link adaptation adjusts the

mode within few ms based

on CQI



More complex modulation schemes require more energy per bit to be transmitted than simply going for transmission with multiple parallel code channels, thus HSUPA benefits more from using multiple codes as PC keeps the signal levels quite good anyway


Fast Retransmissions (1/3)

Radio Link Control (RLC) layer ACK/NACKs also possible with HSPA

Packet

RLC ACK/NACK

Retransmisson Packet

Layer 1 ACK/NACK

Retransmisson

Rel ‘99 HSPA

RNC

NodeB

UE



RNCNodeBUE

User data

RLC

MAC-d

Layer1

MAC-hs

HARQ (N)ACK

(Re)transmission

RLC (N)ACK

(Re)transmission



Layer 1 signaling indicates the need of retransmission which leads to much faster round trip time that with Rel ‘99

Retransmission procedure with layer 1 retransmissions (HARQ) is done so that decoder does not get rid of the received symbols if the transmission fails but combines them with new transmissions

Retransmissions can operate in two ways: Identical retransmissions (soft/chase combining) Non-identical retransmissions (incremental redundancy)


Questions

What is CQI? What does link adaptation do? Which entity initiates RLC re-transmissions? Which entity initiates HARQ re-transmissions?


Downlink scheduling (1/5)

NodeB has certain amount of users connected to it and it needs to schedule the different users for transmission in different fractions of time (Transmission Time Intervals) Certain fairness for scheduling time for each user should be

maintained Resources should be utilized in optimal manor

There exists different ways that users can be scheduled in downlink, e.g. Round Robin Proportional Fair



Round Robin (RR) Simplest scheduling algorithms Assigns users in order i.e. handling all users without priority Positive sides

Easy to implement Each user gets served equally

Negative sides No channel conditions are taken into account and thus resources

might be wasted



Proportional Fair (PF) Compromise-based scheduling algorithm Based upon maintaining a balance between two competing

interests Maximize network throughput i.e. users are served in good channel

conditions Allowing all users at least a minimal level of service



PF assigning each users a scheduling priority that is inversely proportional to its anticipated resource consumption

High resource consumption => low priority



In general priority metric for certain user can be defined as follows

,r

dpriority

where instantaneous data rate, d, is obtained by consulting the link adaptation algorithm and average throughput, r, of the user is defined and/or updated as follows

,otherwise ,*)1(

served isuser if ,**)1(

old

old

ra

darar

where is so called forgetting factor. Hence, equals the equivalent averaging period in a number of TTIs for the exponential smoothing filter

a 1a


Mobility with HSDPA (1/4)

Handovers are roughly tradeoff between two issues When channel conditions are getting worse, handover to better

cell should be made so that packets won’t get lost due to poor channel conditions

However, each time when the handover is made, transmission buffers in the Node B are flushed resulting to additional delays from RLC level retransmission or disruption of service

When regarding HSDPA, the user can be connected only to one serving HSDPA Node B at the time Leading to hard handover when the handover between HSDPA

Node Bs is required in contrary to DCH soft handover



Even though there is only one serving HS-DSCH cell, the associated DCH itself can be in soft(er) handover and maintain the active set as in Rel’99

DCH

Node B,Serving HSDPA

UE

Node B,Part of DCH active set

HS-SCCH

DCH/HSDPA

DCH

DCH



HSDPA handover procedure includes following steps Serving HS-DSCH cell change procedure is initiated when a link

in (DCH) active set becomes higher in strength and stays stronger for certain period of time, referred as time-to-trigger

If the condition mentioned above is met then the measurement report is sent from the UE to the Node B, which forwards it to the RNC

If e.g. the admission control requirements are met the RNC can then give the consent for the UE to make the handover by sending so called Signaling Radio Bearer (SRB) (re)configuration message



In the case of intra Node B handover, the HARQ processes (transmissions) and Node B buffers can be maintained and thus there is only minimal interruption in data flow

However, with inter Node B handover i.e. between Node Bs, the Node B packet buffers are flushed including all unfinished HARQ processes which are belonging to the UE that is handed off


Questions

How does Round Robin allocate resources for the users? How intra- and inter-Node B handovers differ from each

other?


High Speed Uplink Packet Access(HSUPA)


Introduction to HSUPA (1/2)

Roughly three years later when HSDPA was introduced uplink counterpart of the high speed packet access evolution was introduced in Release 6 In 3GPP original name was not HSUPA but Enhanced Dedicated

Channel (E-DCH) The obvious choices for uplink evolution was to investigate the

techniques used for HSDPA and, if possible, adopt them for the uplink as well

Improvements in HSUPA when compared to Rel’99 Layer 1 Hybrid ARQ (HARQ) i.e. fast retransmissions Node B based scheduling


Introduction to HSUPA (2/2)

Easier multicode transmissions Shorter frame size, 10ms mandatory for all HSUPA capable

devices and 2 ms as optional feature HSUPA is not a standalone feature, but requires many of

the basic features of the WCDMA Rel’99 Cell selection and synchronization, random access, basic power control loop functions, basic mobility procedures (soft handover), etc.


HSUPA channels (1/4)

New uplink transport channel - Enhanced Dedicated Channel (E-DCH) Supports key HSUPA features such as HARQ, fast scheduling

etc. Unlike HS-DSCH (HSDPA) E-DCH is not a shared channel, but a

dedicated channel (*) Similarly to DCH, E-DCH is also mapped to physical control and

data channels The user data is carried on the enhanced dedicated physical data

channel (E-DPDCH) while new control information is on the E-DPCCH

(*)Dedicated channel means that each UE has its own data path to the Node B that is continuous and independent from the DCHs and E-DCHs of other UEs



From the Release 99 DCH, the dedicated physical control channel (DPCCH) is unchanged and the need for the DPDCH depends on possible uplink services mapped to the DCH DPCCH is used e.g. for fast power control

New channels for scheduling control E-DCH absolute grant channel (E-AGCH) - absolute scheduling

value E-DCH relative grant channel (E-RGCH) - relative step up/down

scheduling commands



New channel for retransmission control, carries information in the downlink direction on whether a particular base station has received the uplink packet correctly or not E-DCH HARQ indicator channel (E-HICH)



NodeB

UEE-RGGH

E-AGCH

E-HICH

DPCCH

E-DPCCH

E-DPDCH


Questions

What new features on top of multicodes and shorter frame sizes do HSUPA offer?

Is DCH part of the HSUPA?


Uplink scheduling (1/5)

With HSDPA all the cell power can be directed to a single user for a short period of time Very high peak data rates achievable for certain UE and all the

others can be left with a zero data rate However, in the next time instant another UE can be served

and so on With HSUPA HSDPA type of scheduling is not possible

HSUPA is a many-to-one scheduling The uplink transmission power resources are divided to

separate devices (UEs) which can be used only for their purposes and not shared as with HSDPA



The shared resource of the uplink is the uplink noise rise(*), or the total received power seen in the Node B receiver

Typically, one UE is unable to consume that resource alone completely and it is very beneficial for the scheduler to know at each time instant how much of that resource each UE will consume and to try to maintain the interference level experienced close to the maximum

Thus, HSUPA scheduling could be referred as very fast DCH scheduling

(*)ratio between the total power received from all of the UEs at the base station and the thermal noise



Two different scheduling schemes are defined for HSUPA traffic Scheduled transmissions controlled by Node B which might not

guarantee high enough minimum bit rate. In addition each request requires time consuming signaling

Non-scheduled transmissions (NST) controlled by radio network controller (RNC) which defines a minimum data rate at which the UE can transmit without any previous request. This reduces signaling overhead and consequently processing delays



Scheduled transmissions The scheduler measures the noise level and decides whether

Additional traffic can be allocated Should some users have smaller data rates

The scheduler also monitors the uplink feedback Transmitted on E-DPCCH in every TTI Referred as happy bits Tells which users could transmit at a higher data rate both from the

buffer status and the transmission power availability point of view



Depending on possible user priorities given from the RNC, the scheduler chooses a particular user or users for data rate adjustment

The respective relative or absolute rate commands are then send on the E-RGCH or E-AGCH

UE in soft handover receives only relative hold/down commands from other than serving HSUPA Node B


Questions

What is the shared resource in the uplink if power is in the downlink?

What kind of scheduling possibilities HSUPA offer?


Multicodes with HSUPA (1/2)

Even though Rel’99 DCH supports in theory multicode transmissions in practice only E-DCH can support multicode transmissions and thus higher bitrates In theory DCH can use 6xSF4 leading to 5.4 Mbps E-DCH can in practice support 2xSF2 + 2xSF4 leading to 5.4

Mbps The reason why DCH does not support multicodes is that

the DCH is controlled by RNC and thus DCH is rather slowly controllable


Multicodes with HSUPA (2/2)

If the UE could send with fully utilizing multicodes in some time instant this might not be the case later and UE might end up in power outage and thus wouldn’t be able to use its allocation

With RNC control reallocation of resources is slow => resources wasted

Also, HSUPA with HARQ increases the possibility to operate with higher BLER target which leads to lower power requirement for corresponding data rate


Mobility with HSUPA (1/2)

HSUPA supports the soft(er) handover procedure similar to WCDMA Rel’99

The HARQ operation in HSUPA soft handover situation is done in following manor If any Node B part of the active set sends an ACK, then the

information given to the Medium Access Control (MAC) layer is that an ACK has been received and the MAC layer will consider the transmission successful


Mobility with HSUPA (2/2)

Data

Layer 1 ACK/NACK

RNC

NodeB

UE

NodeB

Layer 1 ACK/NACK

Correctly received packet

Packet reordering


Questions

Why does not DCH support multicodes in practice? If UE is in a two-way soft handover how does the HARQ

operate?


Continuous Packet Connectivity(CPC)


Continuous Packet Connectivity (1/5)

Continuous Packet Connectivity (CPC) was released in Release 7

Designed to improve the performance of delay critical small bit rate services like VoIP

Eliminates the need for continuous transmission and reception when data is not exchanged. Can be categorized into three feature UL discontinuous transmission DL discontinuous transmission HS-SCCH less for HSDPA VoIP



Benefits Connected inactive HSPA users need less resources and create

less interference => more users can be connected UE power savings => increased talk time (VoIP) UTRAN resources are saved



= DPDCH (DCH) / E-DPDCH (E-DCH)= DPCCH

E-DCH with 2-ms TTI(Rel-6, phase 2, VoIP)

E-DCH with 10-ms TTI(Rel’6, phase 1, VoIP)

R99 DCH with 20-ms TTI(Rel’99, CS voice)

12.2 kbps DCH

32 kbps E-DCH

160 kbps E-DCHPower offset

E-DCH with 2 ms TTIand UL DPCCH gating

(Rel-7, VoIP)

160 kbps E-DCH

PO



DL discontinuous transmission or Discontinuous Reception (DRx) cycles allow an idle UE to power off the radio receiver for a predefined period Period after the UE wakes up again is called as DRx cycle When UE wakes up it listens predefined time for incoming

transmissions and if it successfully decodes a new transmission during that time it starts timer for staying active certain period of time

UE shall monitor PDCCH

On Duration

DRX Cycle

DRX Period

No measurements done or data received



HS-SCCH-less HSDPA operation in downlink Initial transmission of small (VoIP) packets can be sent without

High Speed Secondary Control Channel (HS-SCCH) Eliminates the control channel overhead from small packets

sent over HSDPA Retransmissions are sent with HS-SCCH pointing to the initial

transmission


VoIP performance with and without CPC In general major performance enhancements visible if circuit switched

voice over WCDMA and VoIP over HSPA Rel 7 is compared With Rel 99 CS voice capacity 60-70 users/cell With Rel 7 VoIP capacity goes beyond 120 users/cell

H. Holma, M. Kuusela, E. Malkamäki, K. Ranta-aho, C. Tao: “VoIP over HSPA with 3GPP Release 7”, PIMRC, 2006.


Internet HSPA(I-HSPA)


I-HSPA (1/3)

Internet-HSPA (I-HSPA) aims to provide competitive mobile internet access with much more simpler network architecture than it is in normal WCDMA systems

Deployable with existing WCDMA base stations Utilizes standard 3GPP terminals Simplified architecture brings many benefits such as

Cost-efficient broadband wireless access Improves the delay performance Transmission savings Enables flat rating for the end user Works anywhere (compared to WLAN or WIMAX)


I-HSPA (2/3)

UE

NodeB /E-NodeB

RNC

SGSN

GGSN

Internet /Intranet

Internet /Intranet

I-HSPA


I-HSPA (3/3)

Round trip time of 32-Byte packet

0

20

40

60

80

100

120

140

160

180

200

Today HSDPA HSDPA+HSUPA

Release 99 ~200

ms

HSDPA <100 ms

HSUPA ~50 ms

InternetIu + coreRNCIubNode BAIUE

I-HSDPA+I-HSUPA

I-HSPA ~25 ms


Conclusions


Conclusions (1/2)

High Speed Packet Access evolution for WCDMA was introduced in Release 5 and 6 for downlink and uplink, respectively

HSPA offers much higher peak data rates, reaching in theory up to 14 Mbps in the downlink and 5,4 Mbps in the uplink, in addition to reduced delays

Key technologies with HSPA are Fast Layer 1 retransmissions i.e. HARQ Node B scheduling Shorter frame size (2ms in DL and 2/10ms UL) Higher order modulation and coding along with link adaptation

in downlink Real support for multicodes in the uplink


Conclusions (2/2)

HSPA improved also the performance of delay critical low bit rate services like VoIP even though it was not originally designed for it

Continuous Packet Connectivity (CPC) enhancements introduced in Release 7 improved VoIP performance even more

I-HSPA was introduced to provide competitive internet access solution High data rates with low delay Reduced costs => flat rate could be possible

Femtocells were introduced to improve the mobile convergence and performance in small offices or at home, for instance


HSPA vs DCH (basic WCDMA)

Feature

Variable spreading factor

Fast power control

Adaptive modulation

BTS based scheduling

DCH

Yes

Yes

No

No

HSUPA

Yes

Yes

No

Yes

Fast L1 HARQ No Yes

HSDPA

No

No

Yes

Yes

Yes

Multicode transmission Yes(No in practice)

Yes Yes

Soft handover Yes Yes No(associated DCH only)


5 codes QPSK

# of codesModulation

5 codes 16-QAM

10 codes 16-QAM

15 codes 16-QAM

15 codes 16-QAM

1.8 Mbps

Maxdata rate

3.6 Mbps

7.2 Mbps

10.1 Mbps

14.4 Mbps

2 x SF4 2 ms10 ms

# of codes TTI

2 x SF2 10 ms

2 x SF2 2 ms

2 x SF2 +2 x SF4 2 ms

1.46 Mbps

Maxdata rate

2.0 Mbps

2.9 Mbps

5.76 Mbps

Downlink HSDPA Theoretical up to 14.4 Mbps Initial capability 1.8 – 3.6 Mbps

Uplink HSUPA Theoretical up to 5.76 Mbps Initial capability 1.46 Mbps

HSPA Peak Data Rates


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Thank you!

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