Providing efficient and reliable multimedia telephony...

Providing efficient and reliable multimedia telephony over HSPA

2006-05-09

Ericsson AB 2006 1


Stefan Wänstedt, Mårten Ericsson

Ericsson Research

© Ericsson AB 2006 Ericsson Confidential Providing efficient and reliable multimedia telephony over HSPA 2006-05-092

Luleå


2006-05-09

Ericsson AB 2006 2


Outline

§ All-IP or convergence

§ Mobile IP services

§ HSPA basics

§ Some examples of results

§ Why do we get the results we get?




§ HSPA basics



Outline


2006-05-09

Ericsson AB 2006 3


Why All-IP and MM Telephony?

§ All-IP means fixed-mobile convergence; one network for all traffic.

All-IP and MMTel


IMS = IP Multimedia Subsystem

P-CSCF

I-CSCFMRF

MGW

MGCF

IMSIMS

S-CSCF

SIP Application

ServersSIP Application

Servers

HSS

RNCMSC(Server)

SGSNGGSN

CNCNMGW

BSC

UMTS/GPRSUMTS/GPRS

§ A common architecture for service control of IP based services

§ Main track for delivery of new IP based services

§ (VoIP essential for convergence)

All-IP and MMTel


2006-05-09

Ericsson AB 2006 4


MM Telephony in WCDMA evolution

§ HSDPA – improved downlinkpacket-data support

– Reduced delays

– 14 Mbit/s peak data rate

– Flexible bit rate

– Increased capacity

§ Enhanced Uplink – improved uplink packet-data support

– Reduced roundtrip delays 30-50 ms end-to-end RTT possible

– High bit rate availability –5.76 Mbit/s peak data rate

– Flexible bit rate

– Increased capacity

Enhanced

Uplink

Rel 4 Rel 6R99

Enhanced Downlink

(HSDPA)

Rel 5

WCDMA WCDMA EvolvedEvolvedWCDMAWCDMA

Rel 7

MM Tel.

All-IP and MMTel


Why IMS VoIP?

§Fixed and mobile service convergence

§Possible to run all IMS services on the same transport– Add services during “call”

– Presence

§VoIP is integral service

All-IP and MMTel


2006-05-09

Ericsson AB 2006 5




§ HSPA basics



Outline


Multimedia telephony

§ Telephony service with possibility of

– Flexible selection of media

– Add/drop of participants

§ Currently being standardized in 3GPP

§ Forms the foundation to create new rich services

– New applications created based on the MMTel

Mobile IP services


2006-05-09

Ericsson AB 2006 6


Presence/Active phone book

§ Active phone book shows contact list status

– Who is available

– For which service/media

§ Active phone book updated with the presence signaling

Mobile IP services


Changed way of communication

§ Start with contact list

§ See who is available

§ Select which service/media to use

§ Add another media

§ Add another session

Mobile IP services


2006-05-09

Ericsson AB 2006 7


RAN PS Domain IMS

Session control signaling SIP/SDP/UDP/IP

Media flow AMR/RTP/UDP/IP

Media control flow RTCP/UDP/IP

PS Domain RAN

Mobile IP services

VOIP data flow components

Presence flow not incuded in this figure


IP protocols are generous in size

§ More than half of a VoIP packet is IP header overhead

§ Call control using SIP/SDP is a chatty ASCII protocol

IP/UDP/RTP AMR

60 or 40 octets 32 octetsInvite till Ringing

Originating Terminating

NetworkUE

INVITE

183 PROGRESS

PRACK

200 OK (PRACK)

UPDATE

180 RINGING

PRACK

200 OK (PRACK)

200 OK (INVITE)

ACK

UE

200 OK (UPDATE)

Network …User A

initiates

se ssion

INVITE

Alerting

Accept

Conversation on

Alerting

Indication

Resource Allocation

Signalling Bearer

Resource Allocation

Signalling Bearer

Resource Allocation

Media Bearer

Resource AllocationMedia Bearer

Invite till RingingInvite till Ringing


NetworkUE

INVITE

183 PROGRESS

PRACK

200 OK (PRACK)

UPDATE

180 RINGING

PRACK

200 OK (PRACK)

200 OK (INVITE)

ACK

UE

200 OK (UPDATE)

Network …User A

initiates

se ssion

INVITE

Alerting

Accept

Conversation on

Alerting

Indication


NetworkUE

INVITE

183 PROGRESS

PRACK

200 OK (PRACK)

UPDATE

180 RINGING

PRACK

200 OK (PRACK)

200 OK (INVITE)

ACK

UE

200 OK (UPDATE)

Network …User A

initiates

se ssion

INVITE

Alerting

Accept

Conversation on

Alerting

Indication

NetworkUE

INVITE

183 PROGRESS

PRACK

200 OK (PRACK)

UPDATE

180 RINGING

PRACK

200 OK (PRACK)

200 OK (INVITE)

ACK

UE

200 OK (UPDATE)

Network …User A

initiates

se ssion

INVITE

Alerting

Accept

Conversation on

Alerting

Indication

Resource Allocation

Signalling Bearer

Resource Allocation

Signalling Bearer

Resource Allocation

Media Bearer

Resource AllocationMedia Bearer

INVITE sip:al@jaguar SIP/2.0From: SIP:bo@e005004b57366:5061To: sip:al@jaguarCall-ID: e53cdd755e5decf@e005004b57366CSeq: 1 INVITESubject: helloVia: SIP/2.0/UDP e005004b57366:5061Require: 100relContent-Type: application/sdpContent-Length: 208

Compression is needed

Mobile IP services


2006-05-09

Ericsson AB 2006 8


Robust Header Compression (ROHC)

40 or 60 14-32

3

Mobile IP services


VoIP bit rate example

12.2

Bit rate (DL) [kbps]

42

24

16 14

5

Time

VoIP Initial state with no header compression

Header compression active

DTX period

CS voice bit rate

Mobile IP services


2006-05-09

Ericsson AB 2006 9


The VoIP service - characteristics

§ AMR-NB and AMR-WB speech codecs

§ Low media bit rates– 4.75 to 12.2 kbps for AMR-NB– 6.60 to 15.85 (23.85) kbps for AMR-WB

§ Small payload sizes (BW efficient RTP payload format)– 14 to 32 bytes for AMR-NB– 18 to 41 (61) bytes for AMR-WB

§ Discontinuous transmission (DTX)– SID frames of 7 bytes sent in average every 160 ms during

silent periods

§ Speech frame length of 20 ms

§ Transport over RTP/UDP/IP protocols– Overhead of 40 or 60 bytes (IPv4 and IPv6, respectively)

Mobile IP services


The VoIP service - quality

§ Quality constraints set by CS services; PS flexible

§ Handles some packets losses

– For AMR 12.2, 2% packet loss is ”allowed”

§ End-to-end delay cannot be too large

– CS ~220ms

Mobile IP services

High Quality

CS equivalent Quality

Economy Quality

WB


2006-05-09

Ericsson AB 2006 10




§ HSPA basics



Outline


Bearer alternatives

§ DCH

– “Circuit switched”

– Low delay

– Low bit rate flexibility

§ HSPA

– HSDPA and EUL

– Packet switched

– Varying delay

– High bit rate flexibility

§ MMTel requirement

– Varying bit rate

– Easy to add or delete services on the fly

HSPA Basics


2006-05-09

Ericsson AB 2006 11


§ Fast Link Adaptation

– Data rate adapted to radio conditions

– 2 ms time basis

§ Fast Retransmissions

– Roundtrip time ~12 ms possible

– Soft combination of multiple attempts

§ Shared Channel Transmission

– Dynamically shared code resource

2 ms

§ Short TTI (2 ms)

– Reduced delays

HSDPA - Basic Principles

TTI = 2 ms

Shared Multi-code

transmission (15 codes)

Link

Adaptation

Features

Hybrid ARQ with

Soft Combining in RBS

HSPA Basics


Enhanced Uplink - important principles

§ Short TTI

– Reduced delays

– Both 2 and 10 ms supported

§ Hybrid ARQ

– Fast retransmissions

– Soft combination of multiple attempts

§ Multi-code transmission

– 1-4 codes for E-DPDCH of SF 2/4

2/10 ms

Hybrid ARQ with

Soft Combining in RBS

TTI = 2 / 10 ms

Features

Multi-codetransmission

HSPA Basics


2006-05-09

Ericsson AB 2006 12


Signaling RB in 3GPP Release 6

E-DPDCH :t

ransits

the a

ctual d

ata

DPCCHHS-DPCCH

HS-PDSCH: t

ransm

its th

e actual d

ata

HS-SCCH

F-DPCH

E-DPCCH

E-HIC

HE-AGCH

HSPA Basics


HS-DSCH Data transmissionCompressed voice packet of 280 bits

Additional RLC UM OH of 8 bits

Additional MAC OH of typically 0+21 = 21 bits for voice packets

L1 CRC of 3 bytes (24 bits)L1

RLC SDU

L2 MAC-d

L2 RLC

3 bytes

L2 MAC-hs

Mapped onto HS-PDSCH(s) (1 TTI = 3 slots)

Transport Block (MAC-hs PDU, HARQ data block)

voice packet

RLCheader

1 bytes

MAC-dheader

RLC PDU

MAC-d PDU = MAC-hs SDU

…

…0 bits

MAC-hsheader

MAC-hs payload

RLC SDU

voice packet

RLCheader

MAC-dheader

RLC PDU

Typically

21 bits

Transport Block CRC

(Segmentation/Concatenation)

MAC-d PDU should be optimized for codecs used for MM Telephony to increase capacity. The number of PDU

sizes is limited to 8 (by a 3 bit field in the MAC-hs header)

HSPA Basics


2006-05-09

Ericsson AB 2006 13


Scheduling – A key challenge!

§ Real-time media – Continuously send small packets, avoid fading dips

– Scheduler that takes delay into account seems favorable

§ A well-tuned scheduler should optimize MM Telephony voice capacity but also not starve TCP

Node B

Scheduler

CQIFlow

charact.

RNC

HSPA Basics


Scheduling in general

Node BBuffers

§ Best effort traffic create large packets and possibility to buffer (and delay) packets

HSPA Basics


2006-05-09

Ericsson AB 2006 14


§ Real-time VoIP traffic create small delay sensitive packets

Node BBuffers

Voice capacity requires code

multiplexing

Scheduling in generalHSPA Basics


HSDPA Schedulers

§ Max CIR

§ PF

§ Delay scheduler

§ Barrier function example

( )maxi

iR

max i

ii

R

r

delay threshold

delay of first packet in buffer

th

i

d

d

=

=

1

( )i

th i

Bd d

=−

instantaneous possible bitrate

average offered bitrate

i

i

R

r

=

=

max ii

i

RB

r

⋅

HSPA Basics


2006-05-09

Ericsson AB 2006 15


Example of a delay scheduler

§ Based on e.g Proportional fair or Max C/I scheduler

§ Packets with high delay are given high priority

§ Packets with delay above threshold are dropped

§ Retransmissions automatically get priority

HSPA Basics




§ HSPA basics



Outline


2006-05-09

Ericsson AB 2006 16


Assumptions and parameters

• Codec AMR 12.2 kbps

• Speech activity 50%

• ROHC yes

• Frames/packet 1

• Support small packets Code mux (4)

• Scheduler PF/Delay

• Hybrid ARQ yes

•Mobility yes (Poisson traffic)

• Channel HSDPA (DCH)

• Fading TU and Ped A

• Site to site distance 1500 m

• MS Antenna RX single

• Advanced receivers no

•

HSDPA


KPIs - User satisfaction & capacity

§ If packet loss ratio < 2 % user is satisfied– Ratio of packets delayed > max delay +

ratio of lost packets

§ 99% satisfied users in the system gives the maximum users per cell - the capacity


2006-05-09

Ericsson AB 2006 17


PF vs Delay scheduler

Capacity with delay scheduler is higher than for PF

Results


PF & RR vs Delay scheduler

Results

Re

lative

ca

pa

city


2006-05-09

Ericsson AB 2006 18


Delay threshold

Significant capacity reduction if delay budget decreases

Results


Channel

Capacity affected by radio channel

Results


2006-05-09

Ericsson AB 2006 19


Delay vs capacity

30

40

50

60

70

80

90

0 50 100 150 200 250

Delay [ms]

Nu

mb

er

of

users 1% loss

2% loss

Results

1.5

1

0.5

Re

lati

ve


Enables smooth migration from CS telephony to MM Telephony

§ Concurrent CS and PS voice users on the same carrier maintaining capacity

– MM Tel over HSPA use “remaining” power not used by CS

– No total voice capacity loss (rather the opposite!) when a part of the power budget is used by PS voice users

Ø Competitive advantage compared to CDMA 2000 EV-DO

0

0,2

0,4

0,6

0,8

1

1,2

1,4

20 18 16 14 12 10 8 6

VoIP

CS

CS + VoIP

Power reserved for CS traffic (W)

Rela

tive

Cap

acity

Results


2006-05-09

Ericsson AB 2006 20


VoIP over HSDPA CapacityResults

>10%


VoIP over EUL CapacityResults


2006-05-09

Ericsson AB 2006 21


Transport characteristics/qualitySummary of evaluations

§ IMS MMTel speech quality as good as CS speech

– Low jitter & fast RTT

– 220 ms or lower end-to-end latency

– No or low packet loss

End-to-end Application Layer Jitter Performance

-20

0

20

40

60

80

100

120

140

160

0 200 400 600 800 1000 1200 1400

Transmission Id Sorted according to PLR

De

lay

[m

se

c]

Delay min

Median

98 percentile

99 percentile

Results




§ HSPA basics



Outline


2006-05-09

Ericsson AB 2006 22


Channel impactTCP benefits from ped A

VoIP capacity decided by the “worst”users!

Theory etc


Base station equations

Base station b

Mobile m

All other base stations n

,

target to get good quality

m b

m

CIR

g gain

orthogonality

γ

α

−

−

−

Theory etc


2006-05-09

Ericsson AB 2006 23


Base station equations CS capacity

Theory etc



§ Solve for Ptot and simplify

§ Interference limited

§ Orthogonality and “F factor”or inverse of geometry factor

cP≈

Theory etc


2006-05-09

Ericsson AB 2006 24


Base station equations Channel variations

§ Orthogonality

§ Fast fading

Theory etc



§ Simplify

§ Where

§ Mcs gives the number of CS voice users for a given Ptot=Pmax


2006-05-09

Ericsson AB 2006 25


PS over HSDPA capacitymodify base station equations

§ Modify (6) to fit for HSDPA and PS voice instead

§ Add HSDPA channels HS-SCCH and A-DPCH

§ We get:

Power of the CS users if any

Theory etc


PS over HSDPA capacitymodify base station equations

§ Note! Only C users transmitting data per TTI (=2ms)!

What about CIR target for HSDPA?

Theory etc


2006-05-09

Ericsson AB 2006 26


PS over HSDPA capacitymore about the channel variations

,,

,

1 ( 1)

hs scch adpch common

tot hs C Bm n

total mm bm n

CP MP PP

g

gγ α

− + +≈

− + −∑ ∑,m b

m

CIR

g gain

orthogonality

m mobiles

n cells

γ

α

−

−

−

−

−

Channel variations. DCH case: 0.6+0.8=1.4

,

1

hs scch adpch common

tot hs C

total worst

m

CP MP PP

γ φ

− + +≈

−∑

HS case: use “worst” user approach, =~4.5 for Typical Urban (6.0 for ped A)

φ

Theory etc


PS over HSDPA capacitythe HSDPA scheduler buffer - MAC hs buffer

§ Number of packets n at the MAC hs buffer:

1/ 2 / 20 1/10ms msλ = =%

1

2

3

4

5

6

7

8

9

10

11

12

13

14

...Time [2ms TTI:s]

10 TTI:s = 20ms …….…….

10 TTI:s = 20ms …….

User 1

User 2…….

10 TTI:s = 20ms …….User 3…….

MAC hs buffer, user to be transmittedPacket

Theory etc


2006-05-09

Ericsson AB 2006 27


§ The required CIR γ is a function

of # packets to transmit each TTI

§ γ 320bits – required CIR to transmit

320 bits (~ AMR 12.2 kbps)

§ Rretx – number of transmissions

§ Round Robin assumed

320total total bits

total retx

n

Mn RC

γ γ

λ

= ⋅

= ⋅

RR – all users has the same number of packets in the buffer

PS over HSDPA capacity required CIR (1)

Theory etc


§ But what happens if there is not

enough power to transmit ntotal

packets?

§ Answer: Segmentation the ntotal

of into Rcoverage packets => extra

retransmissions!

§ Rcoverage – a model of the number

of possible (re)transmissions

with Dmax ms

§ The maximum delay at MAC-hs

buffer: Dmax ms

320

cov

320

max

2

320

max

total bitstotal

erage

total bits

total voip

total bits voip

n

R

n

D

n T

n T

D

γγ

γ

γ

⋅=

⋅=

⋅

⋅ ⋅=

PS over HSDPA capacity required CIR (2) – maximum delay

Theory etc


2006-05-09

Ericsson AB 2006 28


PS over HSDPA capacity add CIR to base station equation

( )

( ) ( )

( )

, max,

max,

2320 max,

max

max, max

1

1 /

1 /

1 /

hs scch commontot hs hs C

total worst

m

Chs scch common hs

totalworstm

Cbits voip hs scch common hs

retxworstm

hs scch common hs

wo

CP PP P

CP P P

T CP P PM RC D

CP P P C DM

γ φ

γφ

γλφ

φ

−

−

−

−

+= ≈

−

− +=

⋅ − +⋅ =

− + ⋅ =

∑

∑

∑

( )2

320rst retx bits voipMR Tλ γ ⋅

Theory etc


Theoretical VoIP capacitygives answer to the “why”?

§ Capacity is ~ sqrt(delay )

§ Activity (packet arrival) λ –

linear vs capacity

§ Required CIR is 1/sqrt(γ 320bits)

( )

( )max, max

2

320

1 /hs scch common hs

worst retx bits voip

CP P P C DM

MR Tφ λ γ

− − + ⋅ ≈⋅

Theory etc


2006-05-09

Ericsson AB 2006 29


Delay vs capacity

§Delay is sqrt(Dmax ) ~ capacity


Rx diversity vs capacity

§Required CIR is 1/sqrt(γ 320bits)


2006-05-09

Ericsson AB 2006 30


Technology challenges - summary

Some have been solved but work remains:– How to trade delay, capacity and coverage appropriately– Small payloads – low bit rate– Scheduling– Signaling channels– Efficient radio bearer– Reduction of IP related overhead – Low latency and round trip time– End-to-end service assurance– Service differentiation– Speech / conversational quality and handling of jitter– Session setup– Voice as part of a multimedia scenario as well as stand-alone– Coverage


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