ΑΣΥΡΜΑΤΕΣ-ΔΟΡΥΦΟΡΙΚΕΣ_διάλεξη 8η

ΑΣΥΡΜΑΤΕΣ-ΔΟΡΥΦΟΡΙΚΕΣΕΠΙΚΟΙΝΩΝΙΕΣ

Διδάσκων

Λούβρος Σπυρίδων

Επίκουρος Καθηγητής - ΤΕΣΥΔ

ΔΙΑΛΕΞΗ 8

ΕΠΙΓΕΙΑ ΜΙΚΡΟΚΥΜΑΤΙΚΗ ΖΕΥΞΗ (MW LINK) – ΣΧΕΔΙΑΣΜΟΣ 2ο Μέρος

Σχεδιασμός κοντινής Μικροκυματικής Ζεύξης

Short-haul microwave radio design

Ποιότητα & Διαθεσιμότητα Ζεύξης Quality and Availability

The prediction cycle (1)

• Free-space loss• Gas attenuation

Link budget

• Rain attenuation• Diffraction – Refraction loss

• Multipath propagation

Quality and Availability

• Interference

”Slow”

”Fast”+

• Obstacle loss• Reflection loss

•BBER •ESR •SESR •UATR

Frequency planningLoss & attenuation Fading prediction

Fade marginObjectivesfulfilled?

No

Yes

Thresholddegradation

Fading probabilityPath loss

The prediction cycle (2)

• Free-space loss• Gas attenuation

Link budget

• Rain attenuation• Diffraction – Refraction loss

• Multipath propagation

• Interference

”Slow”

”Fast”+

• Obstacle loss• Reflection loss

Frequency planningLoss & attenuation Fading prediction

Fade margin

Thresholddegradation

Fading probabilityPath loss

Quality and Availability

Diversity improvmentObjectives

Ποιότητα & Διαθεσιμότητα Ζεύξης

• Introduction to applicable ITU-T and -R recommendations• Definition of Quality and Availability (Q&A) parameters• Digital transmission network models• Q&A objective allocations• Q&A parameters versus fading mechanisms

Agenda:

To provide a knowledge about Quality and Availability targets for transmission networks in accordance with ITU-T and ITU-R recommendations

ΣΚΟΠΟΣ ΔΙΑΦΑΝΕΙΩΝ

Planning:

• Dimensioning of the transmission connection is based on the required Quality and Availability

• ITU recommendations are developed in order to obtain internationally accepted standardsfor allocation of Q&A objectives

Ποιότητα & Διαθεσιμότητα Ζεύξης

Applicable ITU recommendations

G.826• 1993 • PDH at or above

primary rate• Quality

G.828• 2002• SDH• Quality

F.696Medium grade

F.1668 F.1668F.1703

F.697Local grade

ITU-T Recommendations Independent of physical network

ITU-R Recommendations Adaptation of the ITU-T recommendations to real radio links

G.821• 1980• PDH below

primary rate • Quality

Bit Error Ratio Block Error

G.827• 2000• PDH at or above

primary rate• SDH• Availability

F.695High grade

Primary rate= ETSI: 2Mbit/s, ANSI: 1.5Mbit/s

Error eventsWhat happens

• Errored Second, ES A one-second period in which one or more bits are in error.

• Severely Errored Second, SES A one-second period with a BER 10-3.

“A block is a set of consecutive bits associated with the path andeach bit belongs to only one block”.

• Errored Block, EBA block in which one or more bits are in error.

• Errored Second, ES A one-second period in which one or more blocks are in error.

• Severely Errored Second, SES A one-second period which contains 30% errored blocks.

• Background Block Error, BBEAn errored block not occurring as part of an SES

G.821 G.826, 827, 828


Block sizes as specified by the ITU-T G.826:

Traffic ------Radio equip----- Rec. G.826 Number of Number of Mbit/s Blocks/s Bits/block Bits/block blocks/4 ms bits/4 ms2* 500 4096 800-5000 2 8192 2x2 1000 4096 800-5000 4 163844x2 / 8 2000 4224 2000-8000 8 337928x2 / 2x8 3000 5632 4000-20000 12 6758417x2 / 34+2 4000 9104 4000-20000 16____ 145664_


In G.828 the block size is equal to the VC-4 18792bits.

BBE: Gives a value of how “bad” ES are. Fills the gap between the definition of ES (one or more block(s) in error) and SES (30% blocks in error).

For some rates in some recommendations the SES definition is not 30% EB.

Studies have shown that SES defined according to G.826 corresponds to a BER of 1.7 x10E-5

In G.828 there is an other Error event defined, Severely Errored Period, SEP, and the ratio of it Severely Errored Period Intensity, SEPI. SEP is defined as a period of 3 to 9 consecutive SES events. ITU leaves up to the individual administration to implement this in their own network. No objectives are currently stated.

Availability parameters• Available Time, AT

Starts with the first second in a period of ten consecutive non-SES events in both directions.

• Unavailable Time, UATStarts with the first second in a period of ten consecutive SES eventsin any direction

• AT + UAT = Total Time

•Availability Ratio, AR Ratio (or percent) of AT out of total time (usually expressed per year)

•Unavailability Ratio, URRatio (or percent) of UAT out of total time (usually expressed per year)•AR + UAR = 1

Availability parameters

Severely Errored SecondErrored SecondError-free Second

Time(s)SESES ESSESESESSES

Available period

< 10 s

Unavailable period

10 sAvailability detected

10 s

Unavailability detected

The number of Error events during Available period will be the path Quality





F.696Medium grade

F.1668 F.1668F.1703

F.697Local grade








F.695High grade


ITU-T Rec. G.821

• Errored Second, ES A one-second period in which one or more bits are in error

• Severely Errored Second, SES A one-second period which has a BER 10-3

• Errored Second Ratio, ESR The ratio of Errored Seconds during Available time

• Severely Errored Second Ratio, SESR The ratio of Severely Errored Seconds during Available time

Quality parameters (how often it happens):

Error events (what happens):

ITU-T Rec. G.821Hypothetical Reference Connection, HRX

(longest possible connection on Earth)

Highgrade

Mediumgrade

Mediumgrade

Localgrade

Localgrade

LE ISC LEISC

1250 km 25,000 km 1250 km

27,500 km

T=Terminal Point, LE= Local Exchange ISC=International Switching Centre

TT

Mediumgrade

Mediumgrade

15%15%

Objective Allocation

(SESR objective = 0.002, ESR = 0.08)

ITU-T Rec. G.821Hypothetical Reference Digital Section, HRDS

1250 km

PORTION OF HRXMedium grade

50 km and 280 kmclass1-4

X kbit/s

One or more repeaters may occur.

HRDS X kbit/s

ITU-R Rec. F.696-2HRDS classes

ClassHRDS length

(km)

Quality and Availability Planning Objectives:SESR Circuit

classification

3 50 Medium grade

1 280 High grade0.00006

2 280 Medium grade0.000075

4 50 Medium grade

ESR

0.00002

0.00005

0.00036

0.0016

0.0016

0.004

UAT(%)

0.033

0.05

0.05

0.1

The objectives shall be fulfilled per: any month, year

Possible allocation strategyITU-T G.821/ITU-R F.696-2

5km 20km10km10km 15km

15km

7km

Q&A1 Q&A2 Q&A3 Q&A4 Q&A5

Q&A6

Q&A7

BC

DE

F

A

G

H A – E: Path length 45kmE – F: Path length 15kmA – H: Path length 32km

Q&A = ESR, SESR, UAT





F.696Medium grade

F.1668 F.1668F.1703

F.697Local grade








F.695High grade


quality availability

ITU-T Rec. G.826/827/828Block

“A block is a set of consecutive bits associated with the path andeach bit belongs to only one block”.

800-5000 2000-8000 4000-200006000-2000015000-30000

1.5 to 5 >5 to 15 >15 to 55 >55 to 160 >160 to 3500Rate [Mbit/s]

Bits per block

G.826 (PDH)

1120 18792

VC-12 VC-4Rate

Bits per block

G.828 (SDH) Examples of block sizes

ITU-T Rec. G.826/827/828

• Errored Second Ratio,ESR The ratio of ES during available time

• Severely Errored Second Ratio, SESRThe ratio of SES during available time.

• Background Block Error Ratio, BBERThe ratio of BBE during available time, excluding SES events.

Quality parameters (how often it happens):

• Errored Block, EBA block in which one or more bits are in error.

• Errored Second, ES A one-second period in which one or more blocks are in error.

• Severely Errored Second, SES A one-second period which contains 30% errored blocks.

• Background Block Error, BBEAn errored block not occurring as part of a SES

Error events (what happens):

ITU-T Rec. G.826/827/828Hypothetical Reference Path, HRP, 27.500km

Intermediate countriesTerminating

country

Nationalportion

Internationalportion

IG

Terminatingcountry

IG

Nationalportion

PEP PEP

Access Shorthaul

Longhaul

LE PC

SCTC

IG: International GatewayPEP: Path End PointPC: Primary CenterSC: Secondary CenterTC: Tertiary CenterLE: Local Exchange

SESR objective= 0.002

SESR objective= 17.5% of 0.002+ a length dependant part for the

Long haul section

Quality planning objectiveNational portion, ITU-R Rec. F.1668

A = (A1+0.01dR

500) x dLink

dR

A1= 1-2%, dLink= real link length [km]dR= link length rounded up to nearest 500km

Short haulAccess Long haulTo be fulfilled during any month

ESR 0.075 x A0.075 x B0.075 x C

0.002 x A0.002 x BSESR 0.002 x C

0.0002 x A0.0002 x BBBER 0.0002 x C

B = 7.5 - 8.5% C = 7.5 - 8.5%For further studies refer to: ITU-R Rec F.1668

Access Shorthaul

Longhaul

LEPEP IGPC

SCTC

Traffic rate>15 - 55Mbit/s

Availability planning objectiveNational portion, ITU-R Rec. F.1703

UR = B x dlink2500+ CAccepted Unavailability Ratio per year: dlink = Real link length [km]

Access Shorthaul

Longhaul

LEPEP IGPC

SCTC

Short haulAccessLong haul

B 0

C0

5.0 x 10-4 4.0 x 10-4

50<dlink<250km 250<dlink<2500km

1.9 x 10-3 1.1 x 10-4

1.1 x 10-4 0

For further studies refer to: ITU-R Rec F.1703

MSC

Possible allocation strategyITU-T G.826, 827, 828/ITU-R F.1668, 1703

For each transmission direction and for each of the different bit-rates

SESR objective = 7.5 – 8.5% of 0.002To the last site of each path

BSCRNC

Short haul section

Access section

Q&A parameters vs fading

• UAT <=> Rain and hardware unavailability• ES <=> Rain and multipath propagation• SES <=> Multipath propagation,

and a percentage (5%) of rain

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