Hybrid (OCDMA/WDM) System with DPSK Modulation Using

INTERNATIONAL JOURNAL OF MICROWAVE AND OPTICAL TECHNOLOGY,

Hybrid (OCDMA/WDM) System with DPSK Modulation

Using Different Detection Technique at Bit Rate 2.5Gbps for

Optical Access Network

Monirul Islam*, N. Ahmed, Sharafat Ali, S. A. Aljunid, R. B. Ahmad, Md. Shawkat Ali

Center of Excellence, Advanced Communication Engineering Cluster,

School of Computer and Communication Engineering, University Malaysia Perlis,

Pauh Putra Campus, 02600 Arau, Perlis, Malaysia. *E-mail: [email protected]

Abstract- This paper introduces a differential phase

shift keying (DPSK) modulation using different

detection techniques to design a new hybrid

system. The implementation of DPSK modulation

technique is to find the optimal solution for optical

access network. Modified double weight (MDW)

code is proposed as a signature code. MDW code

has a better technique to decrease multiple access

interference (MAI). MAI is the main cause to

degradation the performance of optical CDMA for

large number of users. OptiSystem version 12 has

been proposed and stimulated fibre length as

single-mode fibre (SMF) wavelength of 1550 nm.

This system can support large number of users

with high bit rate 2.5Gbps where the targeted bit-

error-rate (BER) is ≤10-10

.

Index Terms- optical code division multiple access,

wavelength division multiplexing, bit error rate,

differential phase shift code, on-off keying.

I. INTRODUCTION

Over the last two decades, OCDMA

communication systems enhanced to meet the

increasing transmission capacity for the demand

of subscriber [1]. OCDMA has superior feature

that makes suitable action for achieve large

number of concurrent user’s demands like voice,

video and transfer data services [2]. Moreover,

WDM is a flourishing and popular scheme for

fiber optics communication systems which

provides immense bandwidth facility of the

optical fibers with multiple parallel channels consider to very low data rates [3, 4]. To operate

these systems have high security due to the low

power spectral density and internal interference

elimination competence which suppresses

narrowband interference [5]. Therefore, these

systems can have higher bandwidth efficiency

and flexibility [6]. Based on a user demands to

transmit data bit one and sent out a code-word

refereeing to the address signature of the receiver

[7]. This signature codes known as incoherent

and the bipolar code word is called coherent

system. Though the coherent system is phase

sensitive, use of this technique might be more

complicated than incoherent [8]. The hybrid

system techniques contain the capability for

higher connectivity and usages of flexible

bandwidth within optical networks [9].

In DPSK modulation, no absolute phase required

for references transmitted where signal is used as

a phase reference. The requirement of bandwidth

has been reduced significantly with the use of

DPSK modulation [10]. Advanced modulation

DPSK is a technique where phase modulation

technique contains information by shifting the

phase of carrier of the wave. In PSK have high

state for only one cycle but in DPSK modulation

add one and half cycle for transferring data [11].

The influence of DPSK modulation on hybrid

system transmission is considered as the bit error

rate (BER) and power density of the modulated

signal [12].

In this paper, we have proposed a new hybrid

(OCDMA/WDM) system which used DPSK

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mailto:[email protected]


modulation to obtain high bit rate and compare

the performance of two different detection

techniques. We have analysed 8km fibre length

where the channel spacing is 0.8 nm. The

proposed hybrid system is simple and the

resulted optical properties are also commendable

than other reported conventional system. So that,

this proposed (OCDMA/WDM) system is far and

foremost applicable for communication system as

well as optical access network.

II. MODIFIED DOUBLE WEIGHT CODE

(MDW) PROPERTIES

MDW code is the derivative form of Double

weight (DW) code family. MDW code properties

have a weight that can be any even number larger

than 2. Modified double weight code has ideal

cross-correlation where =1 and =0. As the

code weight is increases, OCDMA system also

increase where the performance refer to better

SNR. The basic matrix for MDW code can be

denoted by K × N matrix where k as the number

of user and N as the code length which can be

developed by the mapping technique [13]. The

MDW elements of every sector rely on the value

n, for W=4, n=2. This sequence is demonstrated

in Table 1.

Table 1. Represents the matrix of MDW code where

weight (w=4)

The basic MDW code referred by (9, 4, 1)

and the code possess following properties:

1. Maximum cross-correlation is equal to

1.

2. MDW code weight can be any even

number which is greater than 2.

3. The weight pair structure is

maintained, and the chips combination is

maintained 1, 2, and 1 for every three columns

for every consecutive pairs of codes [10].

III. DETECTION TECHNIQUES

Detection technique is one of the most important

Optical code division multiple access schemes.

These technique are becoming more popular

regarding their enormous benefits as example the

ability to operate asynchronously, enriched

privacy and improved capacity to the network

and the flexibility in the allocation of the network

channels [14]. Detection technique has

effectively concealed Multiple Access

Interference (MAI) but performance of the

system is not satisfactorily good enough.

However, this is considered a big limitation of

the existing detection technique [15]. Direct

detection uses, one single decoder and detector

required and it’s achievable for the simple

reason. The information can be adequately

recovered from any of the chip that does not

overlap with other chips from any other code

.The decoder will only need to filter the clean

chips and be deleted by photodiode, as in the

normal direct modulation [16].

AND subtraction technique, the cross-correlation

kYX

is substituted by YYX )( , where )( YX

denotes the AND operation between sequences X

and Y. For example, let X = 0110 and Y = 1100

and therefore (X AND Y) = 0100.

At the receiver,

0)()( )&( KKZ YYXXYAND (1)

Equation (1) shows that multiple access

interference or the interference from any other

channels can be cancelled by using AND

subtracted technique [17].

IV. PROPOSED SYSTEM ARCHITECTURE

In this research papers, we have to simulate the

proposed system using advanced modulation

DPSK. with different detection techniques to

C K

C9 C8 C7 C6 C5 C4 C3 C2 C1

K1 0 0 0 0 1 1 0 1 1

K2 0 1 1 0 0 0 1 1 0

K3 1 1 0 1 1 0 0 0 0

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investigate the exclusive findings. Design the

hybrid system, optisystem version 12 has been

involved for simulation to find out the results.

Figure 1 illustrates the flow chart of hybrid

DPSK system for optical Access network.

Figure 2 and Figure 3 depict, schematic block

diagram for direct detection technique and AND

subtraction detection technique. Block diagram

contains of four users which are 3 users belongs

to OCDMA and 1 user occupied by WDM. In

addition, transmitter and receiver section are

illustrated in both figures. In architectural design

shows that AND subtraction detection technique

block diagram have the significant difference

compared with direct detection technique.

Fig.1. Flow chart of the new Hybrid system

Fig.2. The block diagram hybrid system using

direct detection.

Fig.3. Block diagram hybrid system AND

subtraction detection.

OptiSystem version 12 deploy for the

simulation. Figure 2 and Figure 3 shows that we

have investigated the simulation on the system at

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1km to 8km. The single mode fiber (SMF)

configuration ITU-T G652 standard has been

used with NRZ modulation format at 2.5Gbps bit

rate. Specific channel spacing is 0.8nm. The

proposed system parameters are shown in Table

2.

Table 2. The proposed system parameters and value

Parameter Value

Wavelength 1550 nm

Bit Rate 2.5 Gbps

Targeted BER 10E-09

Advanced Modulation Technique

DPSK

Electrical DPSK Modulation 650 MHz

Channel spacing 0.08

Detection Technique Direct Detection, AND subtraction detection

V. RESULTS and DISCUSSION

We have investigated the simulation results based

on the parameter for DPSK modulation where

650MHz frequency for direct detection and AND

subtraction detection referred to the bit rate

2.5Gbps. Figure 4 and Table 3 depicts the effect

between the fiber distance against the BER for

both OCDMA and WDM. Here, the figure

illustrates that proposed system transmit signal

up to 8km fiber distance. According to the

investigation results, proposed system error free

transmission up to 8km fiber distance where the

BER for both OCDMA and WDM are 3.45×10-

09, 2.92 ×10

-14 respectively.

Table 3. BER versus length at 2.5Gbps bit rate

Length(Km) BER

OCDMA WDM

1 1.63E-22 6.04E-28

2 8.02E-18 2.28E-25

4 8.99E-14 1.39E-23

6 1.36E-11 3.64E-17

8 3.45E-09 2.92E-14

1 2 3 4 5 6 7 810

-30

10-25

10-20

10-15

10-10

10-5

Length (Km)

BE

R

OCDMA

WDM

Fig.4. BER versus Length at the Bit rate 2.5Gbps

with direct detection

-35 -31 -27 -23 -19 -15 -1110

-30

10-20

10-10

100

Receieved Power (dBm)

BE

R

Proposed

Conventional

Fig.5. Received power versus BER at the Bit rate

2.5Gbps with direct detection

The simulation results carried out the BER

performance with consider receiving power as

shown in Figure 5. The proposed system

minimum received power is -30.13 dBm,

whereas the conventional system minimum

power -26.07 dBm. According to the BER results

BER-OCDMA is 1.52×10-14

for proposed system

and BER-OCDMA 4.34×10-08

for conventional

system. BER results revealed that the

conventional system is not competent to transmit

signal at the same distance with same input

optical power. The performance of the OCDMA

system using MDW code can be improved by

increasing the input power.

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0 1 2 3 4 5 610

-25

10-20

10-15

10-10

10-5

Length (Km)

BE

R

OCDMA

WDM

Fig.6. BER versus length at the bit rate 2.5Gbps

with AND subtraction detection

Figure 6 shows that the effect of BER versus

fiber distance based on AND subtraction

detection technique. Moreover figure 6 illustrates

that the error rate increases exponentially with

fiber distance. Thus a result shows that the

distance up to 6 km. The satisfactory BER results

revealed up to 4km fiber distance, where the

BER-OCDMA and BER-WDM is 1.82×10-09

and

3.12×10-10

respectively. The BER performance

carried out the proposed system has ability to

transmit the signal up to 4km fiber distance with

error free transmission.

-25 -20 -15 -10 -510

-20

10-15

10-10

10-5

Receieved Power (dBm)

BE

R

Proposed

Conventional

Fig.7. Received power versus BER at the Bit rate

2.5Gbps in AND subtraction detection

The effect of BER versus measured received

power at bit rate 2.5Gbps based on the AND

subtraction detection technique is shown in

Figure 7. According to the received optical power, the minimum power for proposed system

is -20.43 dBm at 6km fiber distance, while the

conventional system minimum power is -17.10

dBm. Moreover, the BER results revealed that

BER-OCDMA is 7.12×10-09

for proposed system

and for the conventional system BER-OCDMA is

5.20×10-08

at the same fiber distance. The BER

results carried out that conventional system can

transmit signal up to 4km fiber distance. Whereas

the same input optical power for the proposed

system error free transmissions up to 8km fiber

distance. In conventional system, increasing the

input optical power, the BER gradually decreases

and thus the system performance have been

improves. In that case the conventional system

power consume rate is higher than proposed

system.

1 2 3 4 5 6 7 810

-25

10-20

10-15

10-10

10-5

100

Length (Km)

BE

R

BER-Direct

BER-AND Subtraction

9.12E-09

3.45E-09

4km

Fig.8. BER versus distance at 8km

Figure 8 shows the fiber distance against BER for

comparison between direct detection and AND

subtraction detection techniques at bit rate

2.5Gbps. The BER performance for direct

detection is 3.45E-09 at 8km fiber distance,

whereas the BER for AND subtraction 9.12E-09

at 4km. So, the BER results carried out that direct

detection technique can transmit signal 4km more

than AND subtraction detection technique.

Finally, the comparison results revealed, the

proposed system with direct detection technique

is more efficient and consume less optical power

than AND subtraction technique. The

performance of proposed system indicates that it

will be the most promising solution for optical

access network.

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a) OCDMA

b) WDM

Fig.9. Eye diagram for direct detection at 8Km

a) OCDMA

b) WDM

Fig.10. Eye diagram for AND detection at bit rate at

8km

Fig. 9 and Fig. 10 depicts that eye diagram for

direct detection technique is wider and clear than

AND subtraction detection technique.

Table 3: Comparison between previously published systems with proposed hybrid system

Hybrid system

Fiber length (Km)

Bit rate BER

Ref.[5] 10 1.25Gbps 1.8×10-09

Ref.[9] 20 622Mbps 7.71×10-09

Ref.[11] 30 622Mbps 4.35×10-16

Proposed hybrid system

8 2.5Gbps 3.45×10-09

Table 3 shows that comparison between the

conventional system and proposed hybrid

system. Moreover, Table 3 also illustrates

that the conventional system (previous work)

has been studied with low bit rate, whereas

the proposed hybrid system considered high

bit rate.

VI. CONCLUSION

In this research work, we have analyzed a

proposed hybrid system with DPSK modulation.

The comparison results revealed that proposed

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system has a better performance using direct

detection technique. We have found that the BER

performance for direct detection and AND

subtraction are 3.45×10-09

and 2.84×10-03

respectively at 8km fiber distance. The

simulation results carried out that proposed

system with direct detection technique has the

significant improvement which can transmit

signal is 4km more fiber distance than

conventional system. So that we can conclude,

consider high bit rate the proposed system is a

very good candidate for optical access network.

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Hybrid (OCDMA/WDM) System with DPSK Modulation Using