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IJMOT-2009-8-462 © 2010 ISRAMT

INTERNATIONAL JOURNAL OF MICROWAVE AND OPTICAL TECHNOLOGY,

VOL.5, NO.2, MARCH 2010

A Modular Wireless-over-Fibre (WoF) System using

Photonic Active Integrated Antennas (PhAIAs)

V.Sittakul and M.J.Cryan

Department of Electrical and Electronic Engineering University of Bristol, BS8 1UB, UK.

Tel: 44-117-954-5176; Fax: 44-117-331-5106; E-mail: [email protected] and [email protected]

Abstract- This paper demonstrates a low cost,

wireless-over-fibre system using Photonic Active

Integrated Antennas implemented with packaged

optical devices. The packaged devices are

characterized in terms of input impedance and link

gain is measured in a simple wireless-over-fibre

link. The design of both local and remote modules

for use in a WLAN distributed antenna system is

then described. Finally, the system is tested using a

live access point and 317m of installed fibre and a

system link budget is calculated. Results show that

a maximum range of 10.5m can be obtained at

2.5Mbps data rate.

Index Terms- Radio-over-fibre, VCSELs, WLAN.

I. INTRODUCTION

The success of Wireless Local Area Networks (WLANs) using the IEEE 802.11 standard in the last decades has led to many studies of Distributed Antenna Systems (DASs) using the Wireless-over-Fibre (WoF) concept [1-9]. Using WoF, the coverage of WLANs can be increased by distributing wireless signals from the central station (CS) over optical fibres which have low loss and large bandwidth. In such systems all expensive equipment can placed at the CS, resulting in low cost, easily managed systems. However, most WoF links suffer from low electrical-to-optical and optical-to-electrical conversion efficiency and impedance mismatches which result in high link loss [10] and thus high gain RF amplifiers have to be included to overcome these losses. Recently, the Photonic Active Integrated Antenna (PhAIA) concept has been introduced [1,2,11], where photonic devices (lasers and photodiodes) are directly matched to

any point along the edge of an antenna. This is a very useful technique since the input impedance of a basic rectangular antenna varies from 0 Ω at

the centre to ~100 Ω at the non-radiating edge. This technique allows direct matching of both low impedance lasers and high impedance photodiodes and hence the mismatch loss can be minimised. For further improvement, lossless matching circuits can be applied to achieve conjugate matching [2]. The use of PhAIAs also significantly reduces the packaging and fabrication costs since it removes the need for components such as RF cables, connectors and amplifiers and allows all components to be integrated in one module. In [1,2], the PhAIA concept has been developed using VCSEL and photodiode (PD) chips integrated with antennas using X-Y-Z stages for alignment to fibres. In reality, this procedure is not a commercially viable one, however, chip devices can be replaced by connectorised and packaged ones where no alignment is required. Thus in this work, for the first time, connectorised and packaged VCSELs and PDs are integrated with antennas both with and without low cost monolithic amplifier chips (ERA-1+). The block diagram of the WoF system for WLAN applications can be seen in Fig.1.

Fig. 1. Block diagram of a WoF system for WLAN

applications

VCSEL2

Fibre

d PhAIAs

Built-in Wireless card

Access point

Laptop

To the internet

LAN

Server

VCSEL1

PD1

Amp1

PD2

Splitter

Fibre

Amp2

Amp3

Amp4

Local module Remote module Uplink

Downlink

105

mailto:[email protected]

mailto:[email protected]



It can be seen that for the downlink the RF signal is tapped off from the accesspoint and transmitted over the WoF link. A laptop communicates back to the access point for the uplink and bi-directional communication can be achieved. The local and remote devices can be grouped into local and remote modules. The local module was designed to combine the splitter, VCSEL1, PD1, amplifiers 1 and 2 together. Similarly, the remote module contains PhAIAs with VCSEL2 and PD2 and amplifiers3 and 4. The paper is organised as follows. In section II, the individual devices have been characterised. Section III studies a basic WoF link. In section IV, the design of the splitter, bias tees and the integration of the local components is shown. Section V shows the PhAIAs used and their frequency responses before integrating them with the amplifiers. Finally, in section VI, the WoF system using PhAIAs with and without amplifiers is demonstrated over 317m in-building fibre including a power link budget calculation.

II. INDIVIDUAL DEVICE CHARACTERIZATION

A. VCSELs

VCSELs 1 and 2 (TTR-1A43-117) are manufactured by Truelight (www.truelight.com.tw). These VCSELs are packaged and connectorised with ST adapters – fibre can be directly connected without alignment. Since packaged VCSELs can have different performance due to internal misalignment, it is necessary to measure the slope efficiency, an important parameter of the laser. To measure their slope efficiencies, VCSEL1 and 2 optical output powers were measured against their input currents. This measurement has been done using a 1m Multimode Fibre (MMF) linking the VCSELs and an optical power meter (Agilent 8613A). The results can be seen in Fig.2. Fig. 2 shows the slope efficiencies of the VCSEL1 and 2 to be 0.36 and 0.5 W/A respectively.

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

0 1 2 3 4 5 6 7 8 9 10 11 12 13

VCSEL curret (mA)

VC

SE

L p

ow

er

(mW

)

VCSEL1

VCSEL2

Slope1 =0.36 W/A

Slope2 =0.5 W/A

Fig. 2. L-I curve of the VCSELs

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

0 1 2 3 4 5 6 7 8 9 10 11 12

VCSEL current (mA)

Op

tic

al

po

we

r (m

W)

80degree Slope = 0.44




Fig. 3. L-I curves of VCSELs at different temperatures The variation in slope efficiency is probably due to the misalignment in each VCSEL package. This parameter is used to predict the link gain in the next section. In reality, the VCSELs may operate at different temperatures. Thus, it is important to understand the effect of the temperature on the VCSEL. Here, the slope efficiency of VCSEL2 was measured at different temperatures from 25 to 80 ºC. The results are shown in Fig.3. It can be seen that the slope efficiency of VCSEL2 is not very sensitive to temperature with only 0.001 W/A/ºC variation. Also, the threshold current increases exponentially with temperature. The relationship between the threshold current (Ith) and Temperature (T) is given by [12],

00

TT

th eII (1)

Where, T0 is the characteristic temperature in Kelvin, I0 is the threshold current at T = T0. Extracting the threshold data in Fig.3, the threshold current can be predicted and plotted

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against the measurement as shown in Fig.4. The result from the prediction agrees well with the measurement data.

0

0.5

1

1.5

2

2.5

3

290 300 310 320 330 340 350 360

Temperature (Kelvin)

Th

resh

old

cu

rren

t (m

A)

Measurement

Prediction

Fig. 4. Threshold current of VCSEL2 at different

temperatures. (I0 = 1.13mA and T0 = 150K) As mentioned earlier, one of the issues with WoF links is high loss caused by impedance mismatches [13]. The mismatch loss (LM) can be written by

)log()(2

110 dBLM (2)

Where , the return loss of the device, given by

0

0

ZZ

ZZ

(3)

Where Z is the VCSEL or PD impedance and Z0 is the source or load impedance. Practically most source and load impedances are standardised to 50 Ω. As a result, the return loss

of the VCSEL can be measured using the 50Ω

network analyser. By soldering VCSEL1 on a 50 Ω microstrip line, the return loss was measured

using a Vector network analyser (Agilent E8364A) and the result is shown in Fig.5. The figure shows the return loss of VCSEL1 is below -10dB in the frequency band between 1.8 and 3.2GHz at different VCSEL1 bias currents. Since our system operates at 2.4GHz, it is useful to calculate the mismatch loss at 2.4GHz here. Taking a value of -15dB return loss at 2.4GHz and source impedance 50 Ω, the mismatch loss

was found from equation (2) to be 0.14 dB. This implies that very low loss can be obtained if the 50 Ω point along the non radiating edge of a

patch antenna was used to match to the VCSEL.

S11 (Measurement)

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-35

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-20

-15

-10

-5

0

0 1 2 3 4 5 6 7 8 9 10

Frequency (GHz)

Retu

rn L

oss (

dB

)

4mA

6mA

8mA

10mA

Fig. 5. Return loss of VCSEL1 at different VCSEL1

bias currents

B. Photodiodes

Packaged PDs were obtained from Truelight (TRR-8A33-001). For a PD, the most important parameter is its responsivity. The responsivity of PD can be found from the slope of PD current against incident optical power.

0

0.5

1

1.5

2

2.5

0 0.5 1 1.5 2 2.5 3 3.5 4

Input power (mW)

PD

cu

rren

t (m

A)

PD1

PD2

Responsivity = 0.6 A

Fig. 6. PD current vs input optical power

Fig.6 shows the responsivities of PD1 and PD2 which are 0.6 A/W. As expected, the PD aperture (~100μm) is relatively large compared to

fibre core and thus, small misalignment does not affect its responsivity. As with VCSEL2, the effect of temperature on PD2 has been studied. At different temperatures, the PD2 current was plotted against its input power as shown in Fig.7. It can be seen that the responsivity of the PD2 has a very small variation with temperature. In addition, the mismatch loss between the PD and load was calculated here. To measure the mismatch loss between a PD and a 50 Ω load, the return loss of the PD2 was measured.

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0

0.5

1

1.5

2

2.5

0 0.5 1 1.5 2 2.5 3 3.5 4

Input power (mW)

PD

cu

rren

t (m

A)

80degree

60degree

40degree

25degree

Responsivity = 0.6 A/W

Fig. 7. PD 2 current vs optical input power at different

temperatures This measurement has been taken in the same way as for VCSEL2 and the result can be seen in Fig.8. In Fig.8, the return loss of PD1 at 2.4GHz is about -5dB. This implies that the input impedance of PD is not close to 50 Ω, compared

to VCSEL2. Using the equation (2), this gives a mismatch loss of 1.65dB, ~1.5dB greater than VCSEL2.

-30

-25

-20

-15

-10

-5

0

0 1 2 3 4 5 6 7 8 9 10

Frequency (GHz)

Retu

rn L

oss (

dB

)

Fig. 8. Return loss of PD1

III. BASIC LINK

The basic link comprises a VCSEL and a PD with a short length of fibre. This helps to understand the behaviour of the devices alone with negligible fibre effects. Here VCSEL1 and PD1 were used to form a link over 1m of MMF. The setup is shown in Fig.9. The RF signal from port 1 of the network analyser modulates VCSEL1 through bias tee1. The modulated light was transmitted over the fibre and demodulated by PD1. The recovered RF signal was then fed back to the port 2 and the link gain (S21), as

shown in Fig.10, was measured at different VCSEL1 bias currents. At low frequency, the link gain, gi, of a matched system is given by [1,2,14]

22222dfdflfli STSg (4)

Where Sl is the slope efficiency of the laser, Sd is the responsivity of the PD, lf and fd are the coupling efficiencies from laser and PD to MMF respectively and Tf is the loss in the fibre.

Fig. 9. Basic link gain setup

As shown in section II, our slope efficiency and responsivity measurements already included the coupling loss from the fibre and the fibre loss can be assumed to be negligible. Substituting a slope efficiency of 0.36W/A and a responsivity of 0.6 A/W into the equation (4), the matched link gain at low frequency can be predicted to be -12.4 dB which is 1.6 dB better than the measurement in Fig.10 (~14 dB). The discrepancy here can be explained by the insertion losses of connector and microstrip line and the mismatch loss. At higher frequency, the link gain starts rolling off and limits the bandwidth of the link. The dip around 1.5GHz can be explained by the high return loss of VCSEL1 around 1.5 GHz. At 2.4GHz, the link gain is approximately -16 to -18 dB depending on the VCSEL1 current. Taking the mismatch losses at 2.4GHz of 0.14 dB from VCSEL1 and 1.65 dB from PD1 calculated in section II, the link gain of the matched system at 2.4GHz is predicted to be -14.21 to -16.21 dB. This implies the link gain can be further improved by 1.79dB if a lossless matching circuit is used. However, the lossless matching circuit

Network analyzer (Agilent E8364A)

Power supply

Am-meter 1

VCSEL1 PD1 1m MMF

Bias Tee1

Am-meter 2

Bias Tee2

Port1 Port2

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will increase complexity of the system and also introduce its own insertion loss which reduces the obtained gain (1.79dB) or even increases the system loss. Therefore, in this work, the resistive matching technique will be used rather than lossless matching technique. S21 (Measurement)

-80

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-60

-50

-40

-30

-20

-10

0

0 1 2 3 4 5 6 7 8 9 10

Frequency (GHz)

S21 (

dB

)

4mA

6m

8mA

10mA

Fig. 10. Basic link gain at different VCSEL1 bias

currents

IV. LOCAL DEVICE INTEGRATION

This section integrates all the local devices shown in Fig.1 into a single module which is portable, low loss and easy to install. To achieve this, a printed circuit board (PCB) was designed and fabricated on FR4 substrate (εr = 4.5 and thickness = 1.6mm). The layout of all the local components on the PCB can be seen in Fig.11. A Wilkinson divider and bias circuits were also included in the design. The geometry of the Wilkinson divider was designed in order to match to 50 Ω according to [15] using Agilent Advanced Design System (ADS). The insertion loss of the splitter was measured to be 3.5 dB at 2.4GHz. The bias tees were also designed on ADS using microstrip lines and microstrip radial stubs [16]. Moreover, to compensate the loss of the WoF system, amplifiers 1 and 2 with gain of ~ 8.3 dB at 2.4GHz have been integrated on the same PCB. The 100nF capacitors (C1- C4) with 0.5dB insertion loss at 2.4GHz were used here to block the DC component and enable the power supply to power up VCSEL1 and amplifiers 1 and 2. It is noted here that PD1 operates in a short circuit condition to reduce power consumption and power supply requirements. As can be seen later, this local integrated module will be tested together with the remote integrated

module to perform a bi-directional links in a real system.

Fig. 11. Integration of the local components

V. PHOTONIC ACTIVE INTEGRATED ANTENNAS (PHAIAS)

This section shows how the PhAIAs in this work were designed. Fig. 12 illustrates PhAIAs containing VCSEL2 and PD2. To operate in the 2.4GHz frequency band, rectangular patch antennas with dimensions of 38x28.5 mm were designed and implemented on the same substrate as described in section IV. VCSEL2 and PD2 were placed at the back of the antennas and via hole connected to 50 Ω microstrip lines and the

microstrip lines were fed to 50Ω positions along

the non radiating edge of antennas. It has to be pointed out that the 50Ω positions are used here

to match to 50 Ω amplifiers as shown in the next

section. The bias circuits were the same as those shown in Fig.11. The bias circuit in Fig.12 (a) functions to bias VCSEL2 whereas the bias circuit in Fig.12 (b) allows the current of PD2 to flow in the short circuit condition.

Amp2

λ/4 C4

PD1

Bias Tee4

C3

RFin/out

C2

Amp1 VCSEL1

Bias Tee1 Bias Tee2

C1

100 Ω

Wilkinson divider

80mm

87.5mm

5mm

50 Ω SMA

connector

Bias Tee3

50 Ω line

Power supply

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(a)

(b) Fig. 12. Front view of PhAIAs with (a) VCSEL2, (b)

PD2

A. Frequency Response of PhAIA –VCSEL

Although the microstrip patch antennas were designed to operate at 2.4GHz, the frequency response of both antennas may change after the VCSEL2 and PD2 are integrated due to the impedance loading effect. To validate this, the setup in Fig.13 was performed.

Fig. 13. PhAIA -VCSEL frequency response setup

diagram This setup is similar to the basic link gain measurement in section II but now a wireless link is placed in the setup. Compared to the microstrip patch antenna, the dipole designed at

2.4GHz has larger bandwidth and it can be assumed that the frequency response is flat over 2.4GHz frequency band.The distance of 10cm was used here since this can be treated as being in the far field [15]. Thus, the measured link gain (S21), as shown in Fig.14, can be assumed to be the frequency response of the PhAIA-VCSEL2 over 2.4GHz frequency band.

-80

-70

-60

-50

-40

-30

-20

-10

0

1 2 3 4

Frequency (GHz)

S21 (

dB

)

4mA

6mA

8mA

10mA

40000000

00

Fig. 14. Frequency response of PhAIA-VCSEL2 at

different VCSEL2 bias currents Results show the resonant frequency occurs at 2.4 GHz with link gain of -28 to -32 dB. This confirms that the antenna still operates at 2.4GHz frequency. Compared to the basic link gain at 2.4GHz in Fig.10, this is about 12-14 dB lower, caused by the path loss introduced by the wireless link. The path loss here can be calculated from the well-known path loss equation from the Keenan-Motley propagation model defined in equation (5) [2,3]

ndc

fGGdBPL 2

214

10 )log()(

(5)

Where f is the frequency, c is the velocity of light, n is the path loss exponent and G1 and G2 are the gains of transmitter and receiver antennas. Substituting f = 2.4GHz, d = 0.1m, c = 3x108 m/s and n = 2, and gain values for G1=+2.15 dBi (dipole) and G2=+7dBi (patch antenna), the path loss at 1m can be calculated to be 10.85dB. This number is close to the measurement (12-14dB) with ~3dB difference resulting from the antenna insertion losses and polarization mismatch between both antennas.

Power supply

PhAIA-VCSEL2 1m MMF

Bias Tee1


PD1

Short

circuit

10cm

Am-meter 1

50 Ω Microstrip Carrier

2.4 GHz Microstrip Patch Antenna

Antenna

100 mm

PD

Via hole 50 Ω point

80 mm

Bias Circuit6

100 mm


2.4GHz Microstrip Patch Antenna

VCSEL

Bias Circuit5

Via hole

50 Ω point 80 mm

10 mm

38 mm

28.5 mm

2.4 GHz dipole

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B. Frequency Response of PhAIA – PD

This section observes the frequency response of PhAIA-PD2. A similar setup to Fig.13 has been performed but now the wireless link is placed at the receiver side as shown in Fig.15.

Fig. 15. PhAIA –PD2 frequency response setup diagram

The same dipole was used here and place at the same distance 10cm away from the patch antenna of PhAIA-PD2. The link gain (S21) which contains frequency response of PhAIA-PD2 was plotted against VCSEL1 bias current as shown in Fig.16.

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-60

-50

-40

-30

-20

-10

0

1 2 3 4

Frequency (GHz)

S2

1 (

dB

)

4mA

6mA

8mA

10mA

Fig. 16. Frequency response of PhAIA-PD2 at

different VCSEL1 bias current

The link gain in Fig. 16 at 2.4GHz is 2 dB lower than that in Fig. 14. This can be explained by the lower VCSEL1 slope efficiency. These results show that the WoF link loss at the distance 10cm away from the antenna for 1m MMF is approximately 30 dB. In practice, this may not be sufficient for some applications. Thus, the same amplifier chips used in section IV were assembled into PhAIAs to increase the gain. The final design can be seen in Fig.17.

Fig. 17. Integration of the remote components

The bias circuits 6 and 7 were used to bias the amplifiers 3 and 4. The capacitors C5 and C6 as in section IV were used to block the DC component. Bias circuit 5 is included to bias the VCSEL2 and bias circuit 8 creates a short circuit condition allowing the PD2 current to flow.

VI. BI-DIRECTIONAL WOF LINKS FOR WLAN

This section brings together all components from the previous sections to create a bi-directional link. The WoF links were tested for the WLAN application shown in Fig.1. The local and the remote modules as shown in Figs. 11and 17 were used here. The optical fibre is 317m of installed MMF (OM1). The access point (Aironet 1200) from Cisco operates at 2.4GHz band in 802.11g mode. The sensitivity of the access point was found from the datasheet [17] to be -94dBm at 1Mbps. For the downlink link, the wireless signal was tapped off from the access point and coaxially fed to a RF spectrum analyser (Anritsu MS2668) using the peak hold option which

20 mm

100 mm


2.4 GHz Microstrip Patch Antenna

Antenna

Bias Circuit8

PD C5

Amp3

Via hole

50 Ω point

Lightin

Bias Circuit6


2.4GHz Microstrip Patch Antenna

Bias Circuit

VCSEL C6

Amp4

Bias Circuit5

Via hole

50 Ω point

Lightout

180 mm

Bias Circuit7

2.4 GHz dipole

Power supply

Am- meter 1

VCSEL1 1m MMF

Bias Tee1


PhAIA -PD2

10 cm

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allows the capture of the full spectrum of the signal. A peak power of 0 dBm was measured from the RF spectrum analyser. This signal level seems to be low due to the configuration set by network administrators. This signal was fed to the Wilkinson divider of the local module and amplified by the amplifier1 before modulating VCSEL1. The modulated light from VCSEL1 was transmitted over the in-building fibre. Both VCSEL1 and 2 were operated at 10mA bias current. The wireless signal from the access point then was recovered by PD2 and amplified by amplifier3 and the recovered signal was transmitted to the laptop of a distance (d). Similarly, for the uplink, the transmitted signal from the laptop was received by the PhAIA-VCSEL2. Then, this wireless signal modulated VCSEL2 and the modulated light was transmitted back over the fibre. The signal was recovered by PD1 and transmitted back to the access point – creating two way communication. In order to measure the link performance, a laptop was used to measure the signal strength and the throughput of the wireless signal. The sensitivity of the built-in laptop wireless adapter (Intel PRO Wireless 3945ABG) was found from the datasheet to be -95dBm at 1Mbps. Commercial software netstumbler (www.netstumbler.com) was used to measure the signal strength, however, since this software does not support throughput measurement, real-time software provided by Provision Communications was used here to measure the throughput. The measurement results with and without the use of amplification in the PhAIAs can be seen in Figs 18 and 19. Results show that the signal strength and the throughput decrease as a function of distance (d) as expected. It can be seen that the signal strength of the link with amplifiers included in the PhAIAs is approximately 8-9 dB better than without amplifiers. This agrees well with the gain of the amplifiers measured to be 8.3 dB at 2.4GHz. Without amplifiers, the maximum range was measured to be 4.5 m whereas the maximum range was improved to 10.5m with the use of amplifiers.

-100

-95

-90

-85

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-65

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-50

0 1 2 3 4 5 6 7 8 9 10 11

Distance (m)

Sig

na

l S

tre

ng

th (

dB

m)

PhAIAs with Amps

PhAIAs without Amps

Fig. 18. Signal strength vs Distance with and without

amplifiers

0

5000

10000

15000

20000

25000

0 1 2 3 4 5 6 7 8 9 10 11

Distance (m)

Th

rou

gh

pu

t (k

bp

s)

PhAIAs with Amps

PhAIAs without Amps

Fig. 19. Throughput vs distance with and without

amplifiers The measured throughput in Fig.19 is also consistent with the signal strength in Fig.18 ; the throughput is decreased in proportion to signal strength. In order to clearly understand whether uplink or downlink limits the system performance, the power link budget of the WoF links was calculated as shown in Tables 1 and 2. It is noted here that the 317m in-building fibre loss was approximated by the RF loss of the 300m MMF reel with the same fibre type (OM1). To measure the RF loss of a 300m MMF, the same setup in Fig.9 was used. Extracting the link gain at 2.4GHz of 1m MMF from 300m MMF, the RF loss can be approximated to be 22 dB. The path loss here was calculated from the equation (5). Taking f = 2.4GHz, d = 1m, c = 3x108 m/s and n = 3, and typical gain values for the antennas of G1=+7dBi and G2=0dBi (isotropic), the path loss at 1m can be calculated as shown in Tables 1 and 2. Table 1 shows the downlink budget. It can be

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seen that the received power at the laptop at 1m was calculated to be -64.9 dBm close to the measurement (-65.5dBm) from Fig.18. For the uplink, it is impossible to directly coaxially measure the RF signal from the wireless card. Therefore, an RF spectrum analyzer (Anritsu MS2668) and the same patch antenna as shown in Fig.12 was used to measure the output power from the laptop at a distance of 1m. The received power here is approximately the same as the input power after the patch antenna. As shown in Table 2, the received power at the access point was calculated to be -68.9 dBm. Taking the sensitivities of the access point to be -94 dBm and the laptop to be -95 dBm at 1Mbps, the downlink and uplink received power level above the sensitivities are 30.1 and 25.1 dB respectively and thus the uplink limits the system performance. Table1: RF downlink budget at 1m

Unit Loss (dB)

Gain (dB)

Remaining Power (dBm)

Output power from the access point

0

Cable&connector loss 3 -3 Splitter loss 3.5 -6.5

Capacitor loss (DC Block) 2 -8.5 Amplifier gain 16.6 8.1 Link loss (1m) 18 -9.9

317m Fibre loss 22 -31.9 1m Path Loss 33 -64.9

Received power at the laptop -64.9

Table2: RF uplink budget at 1m

Unit Loss (dB)

Gain (dB)

Remaining Power (dBm)

Received power after patch antenna

-37

317m Fibre loss 22 -59 Capacitor loss (DC Block) 2 -61

Amplifier gain 16.6 -44.4 Link loss(1m) 18 -62.4 Splitter loss 3.5 -65.9

Cable&connector losses 3 -68.9 Received power at the access

point -68.9

This implies that increasing power of the access point is not a solution to improve the maximum range. In order to increase the maximum range, either the output power from the wireless card of

the laptop or the gain in the uplink link would need to be increased.

VII. CONCLUSION

The concept of PhAIAs has been demonstrated using packaged VCSELs and PDs. All local and remote components including the amplifiers can be grouped into portable local and remote modules to minimise the system loss. The WoF for WLAN application over 317m In-building fibre using the PhAIAs with and without low-cost amplifier chips was successfully demonstrated. Results show that the maximum ranges of 10.5m and 4.5m were achieved for the links with and without the use of amplification in the PhAIAs. Power budgets for both uplink and downlink at 1m were calculated and the results show that the uplink limits the system performance.

ACKNOWLEDGMENT

The authors would like to thank Prof. Dave Bull of Provision Communications and Pierre Ferre for providing the throughput measurement codes, Sam Shahin for help with the in-building fibre connections and James Hooper and Henryk Glogowski for granting access UoB WiFi access point and network.

REFERENCES

[1] V.Sittakul and M.J.Cryan, “A fully bidirectional

2.4GHz wireless-over fibre system using photonic active integrated antenna (PhAIAs)”, IEEE Journal of Lightwave Technology, vol.25, no. 11, pp. 3358 – 3365, Nov. 2007.

[2] V.Sittakul and M.J.Cryan, “A 2.4GHz Wireless-over-Fibre system using Photonic Active Integrated Antennas (PhAIAs) and Lossless Matching circuits”, IEEE Journal of Lightwave Technology, in Press, Feb 2009.

[3] A. Das, A. Nkansah, N.J. Gomes, J.C. Batchelor, D. Wake, “Design of low- cost multimode fiber-fed indoor wireless networks”, IEEE Microwave Theory and Techniques, vol. 54, Issue8, pp.3426 – 3432, Aug. 2006.

[4] A. Das, M. Mjeku, A. Nkansah, and N. J. Gomes,”

Effects on IEEE 802.11 MAC throughput in

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