simulation of 1.25 gbs downstream transmission performance of gpon-fttx

8/22/2019 Simulation of 1.25 Gbs Downstream Transmission Performance of GPON-FTTx

1/5

Abstract In this paper, 1.25 Gb/s GPON downstream link is

presented. All the optical distribution network (ODN) classes are

implemented, using Optisystem, to investigate the transmission

capability and performance of the proposed downstream physical

media (PM) GPON model. Some of the design constraints

involved in an optical network design such as fiber span analysis,

power budget and margin calculations are taken into

consideration with worst case. The quality or performance of a

digital communication system is specified by its BER or Q value

with respect to other parameters such as receiver sensitivity. The

simulated model can support 18, 50 and 128 number of users for

classes A, B, and C respectively.

Index Terms Bit error rate, fiber to the home, GPON,

passive optical network

I. INTRODUCTIONHE passive optical network (PON) technology is based on

passive star fiber network and offers a cost effective

optical access solution with point-to-multipoint (P2MP)

nature. With rapidly growing customer bandwidth

requirements and proliferation of bandwidth in metro

networks, broadband passive optical networks (BPONs) [1],

[2] and the emerging gigabit-capable passive optical networks(GPONs) are expected to prevail as the leading optical access

technology eliminating the bandwidth bottleneck in the last

mile. The full-services access networks (FSAN) GPON can

provide high bandwidth services to customers following

different fiber-to-the premises/ cabinet/building/home/user

(FTTx) scenarios [3].

Recently, the FSAN initiated GPON network

standardization via recommendations for the GPON physical-

media-dependent (PMD) layer and the transmission

convergence (TC) layer [4], [5]. Figure 1 illustrates a

symmetric 1.25 Gb/s GPON access system.

A continuous downlink in the wavelength band of 1480

1500 nm carries 1.25 Gb/s time-division-multiplexed (TDM)

Hesham A. Bakarman is with the Photonics Technology Laboratory (PTL),

Institute of Micro Engineering and Nanoelectronics (IMEN) UniversitiKebangsaan Malaysia, Bangi, 43600 UKM Bangi Malaysia (phone: 03-8736-

0705; e-mail: hesham@ vlsi.eng.ukm.my).

Sahbudin Shaari , was with Photonics Technology Laboratory (PTL),

Institute of Micro Engineering and Nanoelectronics (IMEN) Universiti

Kebangsaan Malaysia, Bangi, 43600 UKM Bangi Malaysia (e-mail:

[email protected]).Mahamod Ismail is with the Electrical, Electronics and Systems

Engineering Department, Universiti Kebangsaan Malaysia, Bangi, 43600

UKM Bangi Malaysia (e-mail: [email protected]).

data from a single optical line termination (OLT) toward

multiple optical network units (ONUs) or optical network

terminations (ONTs). A burst-mode link in the 1310-nm

window collects all ONU/ONT upstream traffic toward the

OLT as variable-length packets at a 1.25-Gb/s aggregate rate,

in a P2MP time-division multiple-access (TDMA) scheme.

This paper focuses on the downlink part only. It presents

transmission performance of downstream link GPON network

with 1.25 Gb/s bit rate.

Fig. 1. GPON network architecture for FTTx scenarios.

II. GPONACCESSNETWORKDue to the limitation of the ADSL (asymmetric digital

subscriber line) service, which suffers from limited

transmission speed and distance, because it uses conventional

metallic cables, optical access is expected to become the

default broadband access system in the future. For this reason,

ITU-T (International Telecommunication UnionTelecommunication Standardization Sector) has discussed a

standard for optical access systems called G-PON (Gigabit

passive optical network), which is an optical access system

with gigabit per second-class transmission capability; it is

suitable as the next-generation optical access system.

A. Previous Optical Access System StandardsITU-T has created several standards for optical access

systems. One of the most important is the BPON (Broadband

PON) standard. PON is a network topology that shares a

Simulation of 1.25 Gb/s Downstream

Transmission Performance of GPON-FTTx

Hesham A. Bakarman, Sahbudin Shaari,Member, IEEE, and Mahamod Ismail,Member, IEEE

T

ICP2010-98

978-1-4244-7187-4/10/$26.00 2010 IEEE


2/5

single optical fiber among two or more customers. Figure 2

shows its basic structure. The main feature is that network

equipment, called OLT placed in a central office, is connected

to the optical network terminal equipment, called ONU

installed in a customers premises, via an optical splitter. Since

several customers share the optical fiber and OLT, PON can

offer economical services by reducing subscriber (or

customer) cost. For these reasons, a PON system is considered

to be eminently suitable for the future optical access system.

Fig. 2. Basic composition of PON

B-PON was developed as a PON system that uses ATM

cells for transmission and has a maximum access speed of 155

Mbit/s upstream and 622 Mbit/s downstream. By using ATM

cells, B-PON can accommodate various services, such as

Internet or CATV services.

B. Network Architecture of the GPONThe PON access technology is a passive tree network in

which one OLT serves up to 128 customers [6]. Figure 3

depicts the reference points and the optical interfaces of the

generic physical configuration of the ODN (G.983.2). The two

directions for optical transmission in the ODN (Optical

Distribution Network) are identified for the symmetric GPON

as follows:

(1) Downstream direction for signals traveling from the

OLT to the ONU(s):

Wavelength: 1480-1500 nm (basic band)

Physical link rate: 1.24416 Gbit/s, TDM

(2) Upstream direction for signals traveling from the

ONU(s) to the OLT: Wavelength: 1260-1360 nm bands

Physical link rate: 1.24416 Gbit/s, TDMA

C. Physical Media Building BlocksFigure 4 show the purely optical layer includes the optical

fiber, splitters, WDM multiplexers/demultiplexers, connectors,

attenuators, optical filters and optical amplifiers (not used in

this simulation).

Fig. 3. GPON generic physical configuration of the optical distribution

network

Fig. 4. Reference physical medium model

Just above the purely optical layer there is a layer for

electrical-to-optical and optical-to-electrical conversion; the

electrical-to-optical conversion function is performed by a

semiconductor laser diode, turning an electrical current signal

into an optical power signal. At the other side of the link, the

optical-to-electrical conversion is performed by an optical

receiver comprising a semiconductor photodiode and an

electrical (pre) amplifier. A further layer is then added above

the analogue electrical layer for the conversion from/to the

electrical digital layer. Digital-to-analogue conversion is

performed by the laser driver (including an electrical filter) in

one direction and by the decision stage in the opposite

direction. The digital layer is very useful for the link

performance evaluation since it allows the BER evaluation.

This model can be used for every fiber optics digital

transmission system [3].

D. 1.25 Gb/s Downstream PMD Layer SpecificationsThe optical parameters defined in [5] refer to values

measured at S/R and R/S points, as shown in Figure 3. In this

paper, all the ODN classes are considered, therefore Class A,

Class B, and Class C parameters are reported.

III. NETWORKDESIGNANDMODELINGA network planner needs to optimize the various electrical

and optical parameters to ensure smooth operations of an

optical network. Whether the network topology is that of a

point-to-point link, a ring, or a mesh, system design inherently

can be considered to be of two separate parts: optical system

design and electrical or higher-layer system design. This

section explores some of the design constraints involved in an

ICP2010-98


3/5

optical network design such as power budget and margin

calculations.

To ensure that the fiber system has sufficient power for

correct operation, network designer needs to calculate the

spans power budget, which is the maximum amount of power

it can transmit [7]. From a design perspective, worst-case

analysis calls for assuming minimum transmitter power and

minimum receiver sensitivity. This provides for a margin that

compensates for variations of transmitter power and receiversensitivity levels

)(

)()(

min

minPRysensitivitreceiverMinimum

PTpowerrtransmitteMinimumbudgetPower bP= (1)

The span losses can be calculated by adding the various

linear and nonlinear losses. Factors that can cause span or link

loss include fiber attenuation, splice attenuation, connector

attenuation, chromatic dispersion, and other linear and

nonlinear losses

)arg()()(

)*()

*()*()(

inmSafetylossesNonlinearlossesdevicelineIn

connectorsofnumbernattenuatioConnectorsplices

ofnumbernattenuatioSpliceKmnattenuatioFiberPlossSpans

++

++

+=

(2)

The next calculation involves the power margin ( mP ),

which represents the amount of power available after

subtracting linear and nonlinear span losses ( sP ) from the

power budget ( bP ). A mP greater than zero indicates that the

power budget is sufficient to operate the receiver. The formula

for power margin ( mP ) is as follows:

)()()(arg sbm PlossSpanPbudgetPowerPinmPower = (3)

To prevent receiver saturation, the input power received by

the receiver, after the signal has undergone span loss, must not

exceed the maximum receiver sensitivity specification

( maxPR ). This signal level is denoted as ( IinP ). The

maximum transmitter power ( maxPR ) must be considered as

the launch power for this calculation. The span loss ( sP )

remains constant.

lossSpanPTpowrertransmitteMaximumPpowerInputin

= )()(max

(4)

The design equation:

Input power ( IinP )


4/5

1E-50

1E-46

1E-42

1E-38

1E-34

1E-30

1E-26

1E-22

1E-18

1E-14

1E-10

1E-06

0.01

-30 -29 -28 -27 -26 -25 -24 -23 -22 -21 -20

Reveived input optical powe r

BER

Fig. 6. BER as a function of the received input optical power for a directdetection system

Q

eQerfcBER

Q

2

2

2

1)]

2(1[

2

1

=

(7)

Based on this Q value of 6.1 corresponds to 910 , and a Q

value of 7.2 to BER = 1210

.

IV. RESULTSANDDISCUSSIONThe specified optical levels at the optical interface Old /

Ord as shown in figure 3, for each class are listed in Table 1.

The values take into account the worst case, for application in

a single or dual fiber ODN (with or without coarse WDM).

A. Minimum BER and Receiver ResistivityAn optical link is designed by taking into account a figure

of merit, which is generally the bit error rate (BER) of the

system. The signal entering the decision circuit fluctuates due

to the various noise mechanisms. It is the probability of

incorrect bit identification by the decision circuit. For most

practical optical networks, this requirement of BER is 1210

(~ 910 to 1210 ), which means that a maximum one out of

every 1210 bits can be corrupted during transmission.

Figure 7 shows the minimum BER for class A, B and C

with transmitted power of 4, 1 and 5 dBm respectively.

Typical requirements for optical receivers used in this

simulation are optimized to be BER < 1010 (less than one

error in 1010 bits).

The receiver sensitivity is the minimum averaged received

optical power required to achieve BER = 1010 . From this

explanation, it becomes evident why optical system design

considers power budget and power margins (safety margins

for good design) so important.

Fig. 7. Minimum BER obtained from BER analyzer

Figure 8 shows the relation between receiver sensitivity and

BER. It is obvious; to achieve the required BER a

photodetector should have sensitivity power of -26.5 dBm for

class A and B and -27.5 dBm for class C. In this range, even a

very small rise in optical signal power improves BER by some

order of magnitudes.

1E-50

1E-46

1E-42

1E-38

1E-34

1E-30

1E-26

1E-22

1E-18

1E-14

1E-10

1E-060.01

-32 -31 -30 -29 -28 -27 -26 -25 -24 -23 -22

Receiver sens itivity (dBm)

BE

Class A

Class B

Class C

Fig. 8. BER as a function of attenuation for PIN sensitivity measurement

Figure 9 shows the BER behavior as a function of the span

loss, keeping the fiber length constant 20 Km and the

transmitter power constant (minimum values) for each class.

BER of 1010 is obtained with over all span losses of 22.5 dB,

27.5 dB and 32.5 dB for class A, B and C respectively. Figure

9 can be expressed in terms of number of users (ONTs). It is

clear from figure 10 that GPON with 1.25 Gbit/s can provide

communication service from at least 18 up to 128 ONTs users

with BER = 1010 .

ICP2010-98


5/5

1E-50

1E-46

1E-42

1E-38

1E-34

1E-30

1E-26

1E-22

1E-18

1E-14

1E-10

1E-06

0.01

17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35

Losses (dB)

BER

Class A

Class B

Class C

Fig. 9. BER as a function of loss for 1244 Mbit/s downstream GPON

1E-50

1E-481E-46

1E-44

1E-42

1E-401E-38

1E-361E-341E-32

1E-30

1E-281E-26

1E-24

1E-22

1E-20

1E-18

1E-161E-14

1E-12

1E-101E-08

1E-06

0.0001

0.01

8 16 24 32 40 48 56 64 72 80 88 96 104 112 120 128 136 144

Number of ONTs users

BER

Class A

Class B

Class C

Fig. 10. BER as a function of number of ONTs users

V. CONCLUSIONSDue to its unprecedented offered bandwidth, GPON is the

ideal technology for large-scale FTTH applications where

multiple end-users are requiring an ever-growing bandwidth.Moreover, in areas populated by both business and residential

customers, GPON is the most cost-effective solution.

This paper presented the downstream transmission

performance of 1.25 Gb/s GPON bit rate. All the ODN classes

are simulated separately. A bit error rate BER 1010 with Q

values between 6 and 7 are obtained, which are convenient to

sustain a good communication.

Multiple customers who are connected to the PON share the

OLT costs. While EPON allows only 16 ONTs per PONs,

GPON standard allows the OLT PON card to support up to

128 ONTs. This makes the GPON solution 4 to 8 times more

cost effective. In this simulation, number of users (ONTs) of

18, 50 and 128 are obtained for classes A, B and C.

REFERENCES

[1] X. Z. Qiu, J. Vandewege, F. Fredricx, and P. Vetter, Burst ModeTransmission in PON Access Systems, in Proc. 7th Eur. Conf.

networks Optical Communication, 2002, pp.127132.[2] P. Vetter et al. Study and Demonstration of Extensions to the Standard

FSAN BPON, inProc. Int. Symp. Services Local Access, 2002, p.119

128.[3] Xing-Zhi Qiu. Development of GPON Upstream Physical-Media-

Dependent Prototypes, Journal of Lightwave Technology, 2004, Vol.

22.[4] ITU-T Recommendation G.984.1, General characteristics for Gigabit-

capable Passive Optical Networks 2003.

[5] ITU-T Recommendation G.984.2, Gigabit-Capable Passive OpticalNetworks (GPON): Physical Media Dependent (PMD) Layer

Specification ITU-T Recommendation G.984.3 Transmission

Convergence Layer for Gigabit Passive Optical Networks, 2004.[6] F. J. Effenberger and E. Shraga. Status of GPON and B-PON

standards, Flexlight-networks, (2004).

[7] V. Alwayn, Optical Network Design and Implementation: Cisco Press,(2004).

[8] J. H. Franze and V. K. Jain , Optical Communications: Components andSystems, Narosa Publishing House, (2000).

[9] T. Antony and A. Gumaste, WDM Network Design, Cisco Press, ch. 4,(2003).

ICP2010-98

simulation of 1.25 gbs downstream transmission performance of gpon-fttx

Documents