Interference Sensitivity of Digital Receivers in Fiber-Radio Distribution Networks

Proceedings of the

Ist International Summer School

Inters.ctiorts \etueen Minrowoues snf Optics

l-

Autrons fronce

24 ^{28 August 1998}

ORGANIZAUON

in

collaboration

with

^:

/J nroMsoN-csF

Laboratoire Central de Recherches

Edited

by I.

Schanen,

B.

Cabon,

A. Vilcot

156 Proceedings of the l" internationol Summer School OMW Posters sessions

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A.HILT, T.BERCELI, A.VILCoT, B.cABoN, A.z6LoMY

LEMO-ENSERG-INPG, 23 rue des Martyrs, BP 257, F-38016 Grenoble, France BME-MHT, Technical University of Budapest,

H-I I I I Goldmann Gydrg tdr 3. V2 dpiilet, Hungary

Lmail: hilLo'enserg.fr

Abstract :

Fiber-radio distribution networks have been investigated by several authors recently

[],

^{2]. In}

such networks wideband access ofseveral subscribers is provided with the advantage ofeasy installation and reduced maintenance costs (Fig.l). Due to the wireless connection in the last few hundred meters some mobility of the users is also tolerated. Much effort has been carried out

to

reduce the complexity

of

the base stations. Various solutions are proposed

for

the optical generation and distribution

of the

microwave

or

millimeter-wave

(MWIvIMW)

carriers in the network

ll,

^{2, 31. These solutions} are compared to each other in term of phase noise usually. Phase noise

of

the

MWIVIMW

carrier results

in a bit

error rate (BER) degradation

in

the digital channel. System trials are usually performed on individual fiber- radio links [3]. However, ^a real network incorporates multiple picocells, which introduce new sources

ofBER

degradation. In the radio channels RF interference (RFI) among neighboring transmitters should be considered as one main reason of BER degradation.

directional fixed

pti fibe

Figure

I.

Fiber-radio distribution network. Figure

2.

Measurement setup

for

^RFI

immunity tests.

ln

this paper the necessity of channel separation as well as the importance of good receiver

RFI

immunity

is

shown.

An

effrcient method

is

presented

for the

characterization

of

interference properties of the MW or MMW digital radio receivers employed in the fiber-radio network [a]. ^The measurement setup is depicted in Fig.2. Measured signal-to-interferer (S/[) contours

of

38 GHz digital receivers are plotted

in

Fig.3. The curves are drawn for the S/I ratios degrading the error free channel

to

a BER level

of

10-6 due

to

the presence

of

the sinusoidal CW interferer. The points are normalized to the midband signal-to-interferer ratio SiI(fRx). The normalizing factor and the shape of the curves are depending on the capacity

of

the

digital

cha4nel and on the quality

of

the receiver, on the receiver

RF

and

IF

filter bandwidths as well as on the spectral efficiency of the transmitter. In the demonstrated cases

In*ference sensit*aity of digital receivers infiber-radio distribution networks 157

4FSK modulation was used without any error correction algorithm. Applyrng higher interferer levels inside the RX channel, the reception becomes faulty. However, outside the reception band the tested receivers tolerate interferer levels

of

50 dB higher than the wanted sienal.

Applyrng the presanted test method, we performed sensitivity measurements of radio receivers operating in the communication bands

of

1.5, 15,

18,23,26

and 38 GHz. Digital FSK and PSK receivers from different manufacturers (TKI, Alcatel, Ericsson, NEC and Siemens) have been characterized. The advantage

of

the method

is its

simplicity, meanwhile the radio receiver can be treated as a "black box". ^Besides co-channel and adjacent channel RFI tests, image rejection and spurious reception properties ofthe receivers can be haced as well.

0 -10

-14-70714

frequency offset: Af = ^fir,IT - fnx _[MHzl

References :

[l]

R.P.Braun, G.Grosskopf et al. : "Optical Microwave Generation and Transmission Experiments in the 12- and 60-GHz Region for Wireless Communications", IEEE Trans. on MTT, Vol.46, No.4, pp.320-330, April 1998.

[2] A.Hilt, A.Vilcot, T.Berceli et

al. :

"New Carrier Generation Approach

for

Fiber-Radio Systems to Overcome Chromatic Dispersion Problems", IEEE MTT- S Digest, pp.l525-1528, Baltimore, USA, June 1998.

[3] G.H.Smith and D.Nowak : "Broadband millimetenilave fiber-radio network incorporating remote up/down- conversion", IEEE MTT-S Digest, pp. I 509- I 5 I 2, Baltimore, USA, June 1998.

-60 -70

Figure 3. Normalized signal-to-interferer _{_} _

ratio resulting in

nnn : lO'6 t1].:.:"ltl

l't'nasv0lryi, J'Gv0r6si' I'csonka : "Micro- wave Digital Radio Measurements in the 23 ald26 GHz Frequency Bands", Journal on Communicatiow, vol- XLIIT, pp.37-39, Budapest, Hungary, August 1993.

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