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Introduction to the challengesof current GSM and GPRS planning

Technical PresentationTechnical Presentation

Slide 2Prof. Dr. Volker Amelung / Dr. Karim Rizk Wavecall SA

Wavecall SA

Prof. Dr. Fred Wagen

Senior Consultant

Wavecall SA

Lausanne, Switzerland

[email protected]

Prof. in telecommunication at the Univ. of Applied Sciences (HES-SO)

in Fribourg, Switzerland (www.eif.ch/telecom)


Outline

• GSM-vs-GPRS = circuit-vs-packet:so what ?

• GSM & GPRS planning: similarities and differences

• The crucial role of radio propagation prediction:

accurate model is a must• The challenges ahead:

prepare to react quickly


The challenges of GSM and GPRS planning







GSM-vs-GPRS

GSM-vs-GPRS : so what ?

same TDMA-FDMA air interface …

BCCH

coul

d al

so b

e tra

ffic

slots

frequency

time


GSM and GPRS

BCCH


… but flexible multi-slots allocation for GPRS

GSMVoice

GPRS3 up

1 down

GPRS1 up

2 downthen 3 down

GPRS1 up

2 downthen 3 down

=> fewer empty slots



GSM

Voice: a few errors can be tolerated but no delay

(< 200 ms)

SMS: store & forward

WAP: connecting …

data: 9.6 kbps CS or HSCSD on the move but not moving



GPRS

Voice: ??? … may be for voice mail services

SMS: cheaper for operator and … users

WAP: … learn from i-mode

data: Packet Data, “always on” (claim or reality?)

Needs a new phone and a PC (laptop, palmtop), or

a PDA (Palm, EPOC, PocketPC,…), or a smart phone

(terminals withvoice recording)


GSM-vs-GPRS : Voice-vs-Data bearers

GSM voice GSM data13 kbps (Full Rate) 9.6 kbps

20 ms12.2 kbps (EFR)

20 ms 20 ms

260 bits (FR) 260 bits (FR) 192 bits+padding

Interleaving on 8 ½ bursts

R=1/2456 bits

R=1/2 R=1/2456 bits 456 bits

Interleaving on 4 bursts

2x57 bits2x57 bitsAverage 22.8 kbps per slot

270 kbps bursts on air interfaceAverage 22.8 kbps per slot

270 kbps bursts on air interface


GSM-vs-GPRS : GPRS Data

GPRS

9.05 kbps or 13.4 or 15.6 or 21.4 kbps

20 ms

181 bits or 268 or 312 or 428 bits

R=1/2 or 2/3 or 3/4 or no coding

CS1 or CS2 or CS3 or CS4456 bits

Similar to GSM data but

4 Coding Schemes

=> 4 data rates

Interleaving on 4 bursts

Average 22.8 kbps per slot270 kbps bursts on air interface

2x57 bits


GSM-vs-GPRS : coverage

GSM voice

Voice Quality(e.g.,MOS)

Analog voiceSufficient quality

Transmission quality

GSM

C/I

Goodenough

bad

9 to 12 dB


GSM-vs-GPRS : quality coverage

Quality is a subjective opinionGood

Threshold

Bad

Must be set by operator to quantify qualityand simplify the identification of problems.


GSM-vs-GPRS : coverage

GPRS : even more difficult

Voice Quality(e.g.,MOS)

Analog voiceSufficient quality

Transmission quality

GSM

C/I

Goodenough

bad

9 to 12 dB

Data ‘‘Quality’’(here bit rate)

CS1

CS2CS3

CS4GSM voice

C/I9 13 17 25 dB


GSM-vs-GPRS : coverage - urban

GPRSGSM voice

No coverage orother cell

coverageCS4

CS3CS1 CS2

2

3

3.5

4

9 kbps13 kbps

16 kbps

21 kbps

Urban environment


GSM-vs-GPRS : coverage - LOS

GSM voice GPRS

CS4

CS3

CS1

CS2

Free space

4

8

12

16

13 kbps

16 kbps

21 kbps

9 kbps

No coverage orother cell

coverage



GSM-vs-GPRSRequirements for planning


GSM-vs-GPRS : Voice-vs-Data

GSM voice

13 kbps (Full Rate)

1 slot up / 1 slot down(total of 2)

Support ~1% FER

Plan coverage for voice service

GSM data

CS: 9.6 kbps (or 14.4 kbps)

HSCSD n*9.6 (or 14.4) kbps

1,2 or 3 slots up / 3, 2 or 1 slots down

(total of 4)

Error must be handled with ARQ

For users on the moveaccepting best effort service

and/or non-moving



GSM voice

13 kbps (Full Rate)

1 slot up / 1 slot down(total of 2)

Support ~1% FER

Plan coverage for voice service

GPRS

Packet data

n*9 or *13 or *16 or *21 kbps

n = 1,2 or 3 slots up / 3, 2 or 1 slots down

(total of 4)

Errors must be handled with ARQ

Plan multi-coverage for new services



GSM voiceTraffic characteristics are “well known”

Quality is in fact a best effort service

butgood planning

lead to acceptable quality

GPRSTraffic characteristics are unknown

Quality depends on service profile:•Precedence class: indicates the importanceof the packet with regard to discarding it in case of problems and degradation of QoS when necessary.•Reliability class: specifies the mode of operation for various error detection and recovery protocols & how securely the datashould be delivered. •Delay class: specifies the transfer delay including the uplink radio channel access ordownlink radio channel scheduling delay, theradio channel transit delay, and GPRS network transit delay.•Peak throughput class: defines themaximum transfer rate.•Mean throughput class: defines the long term average transfer rate.









GSM & GPRS planning: similarities & diff.

GPRS Number of subscribers ???

Traffic statistics ???+

??? simulation+

Reserve channels for GPRSif needed

combined planningWith GSM

Very difficult to planOffer best effort servicethen plan to be flexibleand follow the demand

GSM voiceNumber of subscribers

Traffic statistics+

Erlang B+

Add control channel if SMS traffic increases

Conventional planningStill not easy to plan when

exponential growth



GSM voice GPRS

“no drop” regions(e.g., indoor)

Blue = with indoor coverageRed = enhanced capacityGreen = GPRS capacityBrown = GPRS high throughput

handy coveragemust “work”



GSM voice GPRS

Coverage Traffic data

InterferenceMatrix

Tools Experience

FP (Frequency Plan)

C/I

OK

Yes, load FP in network

No

C/I

= propagationprediction

Coverage Traffic data

Interference

Matrix

Tools Experience

FP (Frequency Plan)

C/I

OK


No

C/I

Combine • GSM planning and • GPRS-CS1 to 4 analysis

Many more and fasteriterations are required



GSM voice and GPRS

• Cannot be planned separately (… or consider full load).• Introduce GPRS “slowly” but be prepared for rapid take-off

(… “i-mode scenario”…):1. If easy user interfaces are developed (e.g., a mobile

internet button on every terminals),2. If appropriate charging is used (e.g., set-up time is either

short or not billed, flat rate combination),3. If the market can decide (open to innovative services).

• New Key Performance Indicators (KPI) must be developed and used.

• Tools must be as accurate and as easy to use as possible to concentrate on difficult tasks.









Radio propagation prediction

CoverageTraffic data

InterferenceMatrix

Tools Experience

FP

C/I

OK


No

C/I

Since GPRS traffic is unknown, only various scenarios can be investigated.Starting with a best-effort GPRS add-on to an existing GSM network, various growth scenarios must be taken into account orways to deploy rapidly the required level of “GPRS quality” must be found.In both cases, tools allowing to quickly and accurately assess the quality of a possible deployment are then critical.Proper coverage is key:=> accurate and fast radio propagation prediction model is a must in an integrated planning tool.


Radio propagation prediction

Conventional models.

•The smaller the cell the worse the inaccuracy.

•Need tuning => measurements => time.

•Need experience to mitigate the drawbacks.

•OK with GSM: took 10 years to be fully deployed.

Fast and accurate WaveSight.•Accuracy independent of cell size.

•No need for tuning.

•Need measurements to convince first time users.

•Allows to test various GSM-GPRS scenarios before field tests and deployment.









The challenges ahead: react quickly

! ! ! !

? Plan all possibilities ?

Or prepare to react quickly ?


The challenges ahead: react quickly

Everything may not work as expected :

⇒Suppress the guess work wherever you can⇒ accurate propagation predictions will help


Conclusion

GSM and GPRS have the same FDMA-TDMA air-interface.

But different coverage characteristics depending on data rate (Coding Scheme), on unused voice slots, and on expected or required user services.

Challenges are coming from the many unknowns.

Number of unknowns can be reduced by using more accurate planning tools wherever possible. Gather the proper tools, databases and methodology now !

WaveSight TM - see your net work!

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