Figure 3 Return loss versus frequency for the antennas with slot radii of Ds 0 and 12 mm. Other antenna parameters are given in Figure 2
Figure 4 E-plane and H-plane radiation patterns at both operating frequencies for the antenna with Ds 12 mm. Other antenna
param-Ž . Ž .
eters are given in Figure 3: a E-plane, fs 1916 MHz; b H-plane,
Ž . Ž .
fs 1916 MHz; c E-plane, f s 2457 MHz; d H-plane, f s 2457 MHz
As for the radiation patterns at the two operating frequen-cies, which are of perpendicular polarization planes, no sig-nificant variations are found for the antennas with and with-out a circular slot. Figure 4 presents the radiation patterns for the case of Ds 12 mm. It is observed that, for both operating frequencies, the radiation patterns are at broadside radiation, and the cross polarizations in the H-plane are larger than that in the E-plane.
3. CONCLUSIONS
The design of a dual-frequency compact rectangular mi-crostrip antenna with a circular slot has been successfully demonstrated. Experimental results have been presented and discussed. Results indicate that, by cutting a circular slot of
Ž .
Ds 12 mm DrW s 0.47 , a 20% antenna size reduction can be achieved, as compared to that of a conventional
w x dual-frequency microstrip antenna 1 . REFERENCES
1. J. S. Chen and K. L. Wong, ‘‘A Single-Layer Dual-Frequency Rectangular Microstrip Patch Antenna Using a Single Probe
Feed,’’ Microwa¨e Opt. Technol. Lett., Vol. 11, Feb. 5, 1996, pp. 83]84.
2. Y. M. M. Antar, A. I. Ittipiboon, and A. K. Bhattacharyya, ‘‘A Dual-Frequency Antenna Using a Single Patch and an Inclined Slot,’’ Microwa¨e Opt. Technol. Lett., Vol. 8, Apr. 20, 1995, pp. 309]311.
3. C. L. Tang, H. T. Chen, and K. L. Wong, ‘‘Small Circular Mi-crostrip Antenna with Dual-Frequency Operation,’’ Electron. Lett., Vol. 33, June 19, 1997, pp. 1112]1113.
Q 1998 John Wiley & Sons, Inc. CCC 0895-2477r98
INTEGRATION NETWORK FOR
WIRELESS COMMUNICATION AND
CATV BROADCASTING WITH
FIBER-OPTIC STAR-RING
HIERARCHICAL STRUCTURE
Yang-Han Lee1and Jingshown Wu2
1Department of Electrical Engineering Tamkang University
Tamsui, Taipei Hsien, Taiwan, R.O.C. 2
Department of Electrical Engineering National Taiwan University
Taipei, Taiwan, R.O.C.
Recei¨ed 12 No¨ember 1997
ABSTRACT: In this paper, we make use of the fiber-opticrcoaxial CATV network for wireless communications with a star-ring topology to distribute broadcasting cable TV programs and simultaneously to pro¨ide bidirectional transmissions for wireless signals. This network utilizes the
(
hierarchical structure with the fiber hub uplink and downlink both by
) (
fiber cable , the semifiberhub uplink by fiber cable and downlink by
) (
coaxial cable , or the coaxial hub uplink and downlink both by coaxial )
cable to increase the system capacity effecti¨ely. Three examples, which co¨er an area of 10 km radius and utilize the GSM scheme, are gi¨en:
)
1 for the single-star ring topology, the system supports 8 hubs and 1000 )
wireless users; 2 for the multistar ring topology, the system supports 40 )
hubs and 5000 wireless users; and 3 for the extension topology, the system supports 160 hubs and 20000 wireless users.Q 1998 John Wiley & Sons, Inc. Microwave Opt Technol Lett 18: 132]141, 1998. Key words: wireless communications; cable TV; fiber optics
I. INTRODUCTION
Recently, there have arisen many new challenges for integra-tion of the embedded hybrid fiber-opticrcoaxial CATV net-work to provide wireless communication services and two-way data communication between the subscriber and the head
w x
end 1, 2 . A passive opticalrcoaxial hybrid network for delivery of CATV, telephony, and data services is proposed in w x3 . The CATV network utilizes the simulcasting protocol for
w x
wireless personal communication 4 and two-way data com-munication services between the subscriber and the head end, e.g., pay TV, teleshopping, alarm and guard facilities, or
w x
interactive videotex 5]7 . Because of the high-speed trans-mission characteristics of the optical fiber cable, we can eliminate the modulator and demodulator used in the tradi-tional coaxial microcellular system. Therefore, we can design a compact sized and cost-effective antenna tower with an
w x
optical fiber microcellular distribution system 8]13 . We propose a star-ring fiber-optic network. This network can distribute broadcasting cable TV programs, and
simulta-neously provide duplex transmission of wireless signals. It employs the star topology for the downlink with direct detec-tion and the ring structure for the uplink with coherent
. detection. The proposed system has some benefits: 1 it provides wireless bidirectional communication via the existing
.
hybrid optic-fiberrcoaxial CATV network; 2 a fiber to the hub system, with M subscribers and X wireless users, shares
. the same photodetector and phase modulator; and 3 the hybrid fiber-opticrcoaxial system is more economical. 1.1. System Description. The proposed star-ring fiber-optic network is shown in Figure 1 which employs the star topology for the downlink and the ring structure for the uplink. At the
Ž .
communication head end as shown in Fig. 2 , there are two lasers: one for the downlink with power of P , and the otherD
for the uplink with power of P . A 1U = 2 coupler is
con-nected to the output of the downlink laser to split the light into two parts. One part is used as the local oscillator for the uplink by coherent detection; the other part is externally modulated by the combined TV and wireless signals, then distributed via a 1= N star coupler to N hubs. The other laser connects to the ring network to provide an optical carrier to all hubs for uplink signals. At the same time, the optical signal carrying the upstream messages from the other side of the ring is mixed with the local oscillator and detected by the photodetector to recover the messages. Each hub uses a photodetector to detect the TV programs and downlink
Ž . w x
wireless messages via subcarrier multiplexing SCM 14 , then distributes the TV programs by coaxial cable to sub-scribers and wireless messages to a number X of wireless users by antenna. The hub also utilizes a phase modulator to transmit the uplink wireless data from the antenna via the fiber ring network with the cascaded phase modulator scheme w x15 .
1.2. Design of the Up]Down Con¨erters. While transmitting the wireless signals torfrom the hub based on the common RF band, we utilize up]down frequency-converting tech-niques for the transmission of the multiple hubs’ wireless signals with the same fiberrcoaxial cable between the head end and hubs. In order to transmit the dedicated signals to the destination hub, we use the up]down frequency con-verter.
There are six different types of uprdown converters as Ž .
shown in Figure 3: Type A}DORdown-converts the optical fiber cable spectrum into the RF spectrum, and transmits wireless downlink signals from the photodetector to the
an-Ž .
tenna via the star fiber network; Type B}UROup-converts the RF spectrum into the optical fiber cable spectrum, and transmits wireless uplink signals from the antenna to the
Ž . phase modulator for the ring fiber network; Type C}UCR
up-converts the coaxial cable spectrum into the RF spectrum, and transmits wireless downlink signals from the coaxial Ž . cable to the antenna via the coaxial cable network; Type D }DCRdown-converts the RF spectrum into the coaxial cable spectrum, and transmits wireless uplink signals from the antenna to the coaxial cable for the coaxial cable network;
Ž .
Type E}DOCdown-converts the optical fiber spectrum into the coaxial cable spectrum, and transmits wireless downlink signals from the photodetector to the coaxial cable for the
Ž .
coaxial cable network; Type F}UCO up-converts the coax-ial cable spectrum into the optical fiber cable spectrum, and transmits wireless uplink signals from the antenna to the phase modulator for the ring fiber network.
Figure 1 Schematic diagram of the star-ring fiber-optic CATV network
1.3. The Hub Structures. There are four different types of Ž .
hub structure as shown in Figure 4. Type A }Fiber hub ŽFH with antenna: Receiving the optical signals from the. fiber star network and down-converting the wireless signal with DORto the antenna, it can also up-convert the wireless signal with URO to modulate the phase modulator for the
Ž .
fiber ring network. Type B}FH as dropperrconcentrator: Receiving the optical signals from the fiber star network and down-convertingrdropping the wireless signals with D s toOC
their destination antenna, respectively. It can also up-con-vertrconcentrate the wireless signals with U s to modulateCO
the phase modulator for the fiber ring network. Type ŽC.}Semifiber hub SFH with antenna: Receiving the RFŽ . signals from the dropper of the coaxial cable network and up-converting the wireless signals with UCRs to the antenna, it can also up-convert the wireless signals with UROs to modulate the phase phase modulator for the fiber ring
net-Ž . Ž .
work. Type D}Coaxial hub CH with antenna: Receiving the RF signals from the dropper of the coaxial cable network and up-converting the wireless signals with UCRs to the an-tenna, it can also down-convert the wireless signals with DRCs to the coaxial cable network.
1.4. The Head-End Structure. The head end receives the Ž
downlink wireless signals from the PSTN Public Switching .
Telephone Network , and sends them to the corresponding antenna via the fiber star network. The head end collects the uplink wireless signals via the fiber ring network, then trans-mits them to the PSTN.
1.5. The CATV-Cellular Structures. There are two types of Ž .
CATV-cellular structure. Type A}Head end with antenna Ž .
for wireless cellular communication: In Figure 5 a , we give an example of a CATV-cellular structure with seven cells Žone head end together with six hubs . The spacing between.
Ž .
Figure 2 Communication head-end structure
Ž .
head end: In Figure 5 b , we have shown the remote head-end CATV-cellular structure where the distance between the head end and the hub can be larger than the cell radius. 1.6. Design of Hub and Head End. While transmitting the wireless signals torfrom the hub based on the common RF band, we utilize up]down frequency-converting techniques for the transmission of the multiple hubs’ wireless signals with the same fiberrcoaxial cable between the head end and hubs.
Ž
In our network, we may use the fiber hub uplink and
. Ž
downlink both by fiber cable , the semifiber hub uplink by .
fiber cable and downlink by coaxial cable , and the coaxial
Ž .
hub uplink and downlink, both by coaxial cable as defined in Figure 4 for four different types of hub structure. Because
the fiber hub and the semifiber hub are more expensive than the coaxial hub, we can increase the system capacity in a more economical way.
The head end receives the downlink wireless signals from
Ž .
the PSTN Public Switching Telephone Network , and sends them to the corresponding antenna via the fiber star network. The head end collects the uplink wireless signals via the fiber ring network, then transmits them to the PSTN.
2. ANALYSIS
2.1. Carrier-to-Noise Ratio for Uplink. For the uplink, we use the coherent detection as
Ž . Ž Ž . . Ž .
Figure 4 Different types of hub structure
where R is the responsivity of the photodetector and fIF is the frequency difference between the downlink and uplink lasers. P and PS LO are the received optical signal power and
Ž N .
local oscillator power given as PSs P r LU PMLR and PLOsaP , respectively. a is the power ratio of the localD
Ž .
oscillator laser over the downlink laser. u t is the uplinkU
wireless signals given as
N X
Ž . Ž Ž . . Ž .
u t sU
Ý Ý
bUi , jsin 2p fU i , jtqcU i , j t 2is1 js1
where bUi, j, fU i, j, and cU i, j are the modulation index, the subcarrier frequency, and phase for the uplink wireless sig-nals. 10 log10LP M is the insertion loss of the phase modula-tor, assumed to be 3 dB, and LR is the propagation loss of
Ž the uplink fiber for a ring topology, assumed to be 2p r q
.
2 r afiber dB, r is the radius between the head end and hub, and afiber is the fiber loss.
Assuming that the upstream signals are a single-octave Ž
system for GSM, the system’s uplink band is from 935 to 960
. Ž .
MHz , then the carrier-to-noise-ratio CNR at the upstream w x receiver is given by 16 0.5R2P P b2 LO S U Ž . CNRUs 2 2 2 6 3 Žs q s B q h K R P P b r32sh th. U 3 3 LO S U Ž . Ž .
where J1 bU and J0 bU have been given approximately by b r2 and 1, respectively. Thermal and shot noises are given,U
respectively, bys2s 2 eRP and s2s NFkTrR . e is the sh LO th L
electron charge, BU is the transmission bandwidth for uplink
Ž .
wireless signals, NF is the amplifier noise figure 3 dB , k is
Ž .
Figure 5 CATV-cellular structure
is the load resistance. The largest number of the third
inter-Ž .
modulation distortion IMD , which falls on the central3
w x
channel 17 , is given as
2
Ž . Ž . Ž .
K3s N N r2 q 1 r4 q N y 3 y 5 r4U U
Ž
U.
4 where NUs N = X is taken to be even. h is the effective3factor of IMD power within the desired signal band, and is3
w x
equal to 0.66 16 . The optimal modulation index for the uplink wireless signal is
1r6 2 2 Ž . 16 s q s Bsh th D ŽbU.opts
ž
h K R P2 P/
. Ž .5 3 3 LO S2.2. Carrier-to-Noise Ratio for Downlink. For the downlink, the detected photocurrent at the hub is given by
Ž . Ž Ž . . Ž .
iD t s RPr 1 q sinu tD 6
Ž .
where Pr is the received dc optical power as Prs 1ya
Ž .
PDr L L L . 10 log L in decibels is the insertion loss ofB C S 10 B
w x
the BBI modulator 18 , and 10 log10LS is the propagation loss of the fiber link for star topology. Both are assumed to
w x be 3 dB and rafiber dB, respectively. 10 log10LC dB is the splitting loss of the 1= N star coupler, with L being equalC
Ž .
to N.u t is the combined TV programs and wireless signalsD
for the downlink with the total number of P channels and NX wireless users, respectively, as given by
P Ž . Ž Ž . . u t sD
Ý
b sin 2p fl TVltqcTVl t ls1 N X Ž Ž . . Ž . qÝ Ý
bDi , jsin 2p fD i , jtqcD i , j t 7 is1 js1 Ž . Ž . Ž .where b , bl Di, j fTVl, fD i, j and c , cTVl D i, j are the modu-lation index, the subcarrier frequency, and the subcarrier phase for the downlink TV and wireless signals, respectively. The modulation indexes for all channels within TV programs
and wireless users are chosen to be the same as b s bl TV
Ž .
and bDi, jsb , respectively; then the u t is given asD D
P Ž . Ž Ž . . u t s bD TV
Ý
sin 2p f V t q c tT l l ls1 q Ž Ž . . Ž . qbDÝ
sin 2p f t q cDk Dk t 8 ks1 Ž Ž ..where qs NX and f ,Dk cDk t is one-to-one mapped into
ŽfDi, j,cD i, jŽ ..t . Then we can express u t in terms of aDŽ .
Bessel function extension as Ž . sinu tD ` Ž . Ž . s
Ý
???Ý
Jnl1 bTV ??? Jnlp bTV nisy` Ý nliqÝn sODDki Ž . Ž . w Ž .x = Jnk1 b ??? JD nkq b sin n vD l1 TV1tqcTV1t Ž . q ??? qnlp vTVptqcTVp t w Ž .x Ž . q nk1 v t q c t q ??? qnD1 D1 kq v t q c tkq Dq . Ž .9 Here, the TV signal band is put away from the wireless signal band; therefore, their cross talk can be ignored. For example, the CATV band is from 50 to 550 MHz, and the downlink of the AMPS system is from 869 to 894 MHz. We use theŽ . Ž .
approximation J0 x f 1 and J x f xr2, for x < 1. For1
the BBI modulator being biased at the quadrature points such that composite second-order distortion becomes
negligi-w x w x
ble 18 , the CNR for downlink wireless and TV signals 16 , respectively, is R2Pr2b2r2 D CNRDs 2 2 2 2 2 6 s q s q s B q h K R Prb r32
Ž
sh th RIN.
D D 3 D 3 D Ž10.where B , hD D3, KD 3 and BTV, hTV3, KTV3 are the transmis-sion bandwidth, IMD ’s power ratio, and IMD ’s number for3 3
2
downlink wireless and TV signals, respectively. s s 2 eRPr.sh
s2 s RIN R2Pr2. RIN represents the relative intensity RIN
Ž
noise of the laser here taken as y165 dBcrHz for an w x.
Nd:YAG laser 18 . And the CNRTV of TV signals is the same as the above equation, except that we replace the b ,D
B , hD D3, and KD 3 asb , B , hTV TV TV3, and KTV3, respectively. The largest numbers of IMD s falling on the central channel3
w x16 are given, respectively, as
2 Ž . Ž . Ž . KD3s N N r2 q 1 r4 q N y 3 y 5 r4D D
Ž
D.
11 2 Ž . Ž . Ž . KTV3s NTV NTVr2 q 1 r4 q N y 3 y 5 r4 12Ž
TV.
where NDs N = X and NTV are the number of downlink wireless signals and TV programs, respectively.
And the optimal modulation index for the downlink wire-less signals is 1r6 2 2 2 16
Ž
s q s q ssh th RIN.
BD ŽbD.optsž
h K R Pr2 2/
. Ž13. D3 D 33. NUMERICAL RESULTS AND DISCUSSIONS
3.1. System Parameters. Considering the system with parame-ters given asa s 0.01, P s P s 200 mW, N s 75, r s 1,U D TV
Ž
5 km for the macrocellular and microcellular range from .
2 to 5 km and from 0.5 to 1 km, respectively , and afibers
Ž w x.
0.4 dBrkm including the connector loss 19 . In our system, Ž we use two independent lasers and two fiber networks uplink
.
ring and downlink star for bidirectional wireless data
trans-w x
mission. Now, taking the GSM system 20, 21 as an example, we have an uplink frequency band from 935 to 960 MHz and a downlink frequency band from 890 to 915 MHz for a
channel spacing of 200 kHz. That is, the corresponding sys-tem parameters are Xs 125, B s B s 200 kHz.U D
The system spectra are shown in Figure 6 as follows. Ž .a The optical fiber cable spectra for the downlink star network are 50]550 MHz for the 75 TV broadcasting chan-nels, and 2]4 GHz for supporting 80 antenna bands of the downlink wireless signals. Therefore, we need an external modulator with a wide modulation bandwidth from 50 MHz
Ž .
to 4 GHz. b The optical fiber cable spectra for the uplink ring network are 2]4 GHz for supporting 80 antenna bands of the uplink wireless signals. Therefore, we need a phase modulator with a modulation bandwidth from 2 to 4 GHz. Ž .c The coaxial cable spectra for the bidirectional cable network are 50]550 MHz for the 75 TV broadcasting chan-nels, 550]650 MHz for supporting four antenna bands of the downlink wireless signals, and 650]750 MHz for supporting four antenna bands of the uplink wireless signals, Therefore, we need a bidirectional coaxial cable system with a bandwidth from 50 to 750 MHz.
3.2. Numerical Results
A. Single Star-Ring Topology. We have obtained the total hub number versus the radius between the head end and the hub
Ž .
as shown in Figure 7 a for a single star-ring topology. For CNRU larger than 15 dB, the uplink transmission capacity
Ž . Ž
of Type A , head end with antenna, varies from Ns 2 r s
. Ž . Ž .
22 km to Ns 20 r s 2 km , and that of Type B , remote
Ž . Ž
head end, changes from Ns 2 r s 90 km to N s 20 r s .
10 km . For CNRTV of the downlink with TV signals larger than 50 dB, the downlink transmission capacity is from Ns 2 Žrs 25 km to N s 20 r s 1 km , while the CNR larger. Ž . D
than 15 dB is not the limiting factor. Ž .
From Figure 7 b , we notice that there are some different hub numbers between the uplink and downlink, i.e., from Ns 20 reduced to N s 8 and from N s 18 reduced to Ns 3 at r s 10 and 20 km, respectively. Therefore, we
Ž . Ž . Ž . Figure 7 a Value of radius versus the total hub number for downlink TV, uplink Type A head end with antenna, and Type B
Ž . Ž .
remote head end, respectively. b Total hub number versus the value of radius for downlink TV and uplink Type B remote head end
propose the multistar-ring and extension system which can utilize the uplink hub to increase the system capacity.
B. Multistar-Ring Topology. Some hubs located in the same area may be considered as one group with their correspond-ing star-rcorrespond-ing subnetwork to interconnect the up- and down-links. In Figure 8, the whole network consists of eight multi-star-ring subnetworks. The distance between the head end
Ž Ž . .
and the first-level hub Type B FH is 10 km, while the distance between the first-level hub and the second-level hub ŽType C SFH is 0.5 km. The first-level hub receives theŽ . .
optical TV and downlink wireless signals by the photodetec-tor, then distributes those signals to the second-level hub by the coaxial cable. The second-level hubs collect the uplink wireless signals by the fiber ring with the cascaded phase modulators, which are then concentrated at the first-level hubs for transmitting toward the head end by a single pair of
Ž .
fibers. In Figure 8, we use one downlink laser 200 mW to
Ž . Ž .
provide eight Type B FHs and two uplink lasers 200 mW ,
Ž Ž . Ž .
each supporting 20 hubs four Type B FHs and 16 Type C .
Figure 8 Multistar-ring CATV cellular structure with Zs 8
Ž .
multistar-ring system can support 5000 Ns 40 and X s 125 wireless users with a frequency reuse number of 4 for cover-ing an area of radius 10 km.
C. Extension System. In our network, we may use the fiber
Ž .
hub uplink and downlink both by fiber cable , the semifiber
Ž .
hub uplink by fiber cable and downlink by coaxial cable , and
Ž .
the coaxial hub uplink and downlink both by coaxial cable as defined in Figure 4. Because the fiber hub and the semi-fiberhub are more expensive than the coaxial hub when using a phase modulator for uplink transmission, we can extend the system capacity in this economical way. For example, there are 8 FHs and 32 SFHs in Figure 8.
The performance of the overall system is limited by the
Ž .
downlink TV CNRTV and the uplink wireless transmission ŽCNRU.as shown in Figure 7 for the radius of transmission area versus the total hub number. For the downlink TV, the total hub numbers are 20 and 1 FHs within a radius of 1 and
Ž .
30 km areas, respectively. For the uplink Type A head end, the total hub numbers are 21 and 2 FHs within a radius of 1
Ž . and 22 km areas, respectively. For the uplink Type B head end, the total hub numbers are 20 and 2 FHs within a radius
Ž . of 10 and 90 km areas, respectively. The Type B system
Ž .
outperforms the Type A system for considering the location neighborhood.
Ž .
From Figure 7 b , we can design the extension system with a more systematic method. The difference in the number of
Ž .
hubs between Type B and downlink TV is the number of SFHs which can be added in the extension system to increase the total system capacity.
Designing the high-capacity system, we can use the FH as
Ž Ž . .
a dropperrconcentrator Type B FH together with the CH
Ž Ž . .
as an antenna Type D CH . For covering an area of radius
Ž .
of 10 km, we utilize one downlink laser 200 mW to provide
Ž . Ž .
eight Type B FHs and one uplink laser 200 mW to support
Ž . Ž .
eight Type B FHs. One Type B FH can support 20 Type ŽD CHs; therefore, the total number of hubs in this high-.
Ž .
capacity system is 160 Type D CHs. This system can support
Ž .
20,000 Ns 160 and X s 125 wireless users for covering an area of radius 10 km.
The system capacity in terms of the radius of transmission area versus the total hub number is limited by CNRTVof the downlink TV signals and CNRU of the uplink wireless signals
Ž . Ž .
as shown in Figure 7 a . From Figure 7 b , we can design the extension system with a more systematic method. The
differ-Ž . ence in the number of the hubs between Type B and downlink TV is the number of SFHs which can be added to the extension system to increase the total system capacity.
Designing the high-capacity system, we can use the FH as
Ž Ž . .
the droprconcentrator Type B FH together with the CH
Ž Ž . .
with the antenna Type D CH . For covering an area of
Ž .
radius to 10 km, we utilize one downlink laser 200 mW to
Ž . Ž .
provide eight Type B FHs and one uplink laser 200 mW to
Ž . Ž .
support eight Type B FHs. A Type B FH can support 20 Ž .
Type D CHs. Therefore, the total hub number in this Ž .
high-capacity system is 160 Type D CHs which can support
Ž .
20,000 Ns 160 and X s 125 wireless users. 4. CONCLUSION
The proposed star-ring fiber-optic network to distribute broadcasting cable TV programs and simultaneously provide bidirectional transmission of wireless signals is investigated. This system employs the star topology together with an external modulator for downlink direct detection, and a ring structure with cascaded phase modulators for uplink coher-ent detection. In our network, we may use the fiber hub, the semifiber hub, and the coaxial hub for increasing the system capacity in a more economical way. For the multistar-ring topology, the extension system can support 160 hubs and 20,000 wireless users of the GSM system for covering an area of 10 km.
ACKNOWLEDGMENT
This work was supported by the National Science Council of the Republic of China under Grant NSC 85-2213-E-032-002. REFERENCES
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Q 1998 John Wiley & Sons, Inc. CCC 0895-2477r98
EFFECTS OF COMPENSATION
VALUE OF DISPERSION
COMPENSATION FIBER ON
PRECOMPENSATION SYSTEM
Jianjun Yu,1Kejian Guan,1and Bojun Yang1 1Beijing University of Posts and Telecommunications P.O. Box 192
Beijing 100088, P.R. China
Recei¨ed 3 No¨ember 1997
ABSTRACT: Employing the nonlinear compensation technology of ha¨ -ing dispersion compensation fiber first, the effects of different compensa-tion ratios on the system performance are numerically analyzed. When the input power is large, and the transmission is an amplifier spacing or
long transmission distance, the best system performance can be obtained by employing proper undercompensation. O¨ercompensation and exces-si¨e undercompensation are not suitable for long-distance transmission no matter how much the input power is. The larger the input power is, the shorter is the requirement of DCF length.Q 1998 John Wiley & Sons, Inc. Microwave Opt Technol Lett 18: 141]143, 1998. Key words: dispersion compensation; single-mode fiber; optical fiber communication
1. INTRODUCTION
Dispersion management using dispersion compensation fiber ŽDCF is proving to be an efficient technique for upgrading. the dispersion-limited performance of embedded standard
Ž . w x
single-mode fiber SMF at high bit rates 1]9 . The perfor-mance improvement of having the DCF first was highlighted
w x
in 1 . In a bidirectional transmission system, we have to consider the dispersion compensation of having the DCF first. The dispersion management can be classified into:
. Ž .
1 DCF followed by standard SMF DCF first and standard
Ž .
SMF followed by DCF SMF first according to DCF’s posi-w x .
tion 2 ; 2 nonlinear dispersion management or linear
disper-Ž .
sion management according to the input DCF power PDCF
w2]4 ; and 3 full compensation, overcompensation, and un-x . dercompensation according to the dispersion value of DCF w x3 . Linear dispersion management has been widely studied w5, 6 . For nonlinear dispersion management, the characteris-x
w x
tics of SMF followed by DCF were analyzed in 3 ; the results showed that increasing the launching power into the DCF and proper undercompensation led to improving the
signal-Ž .
to-noise rate SNR . The nonlinear compensation of DCF w x
first and SMF first were compared in 2 , where it was found that the optimum channel power can be increased by 6 dB
Ž . with the DCF first. Different compensation ratios CR with the DCF first in nonlinear propagation are compared in this paper. It is found that the best performance can be obtained when proper undercompensation of DCF first is used. The
w x results are similar to the SMF first as in 3 . 2. NUMERICAL MODEL
We numerically analyze two models as shown in Figure 1. Ž .
The system configuration in Figure 1 a includes two
erbium-Ž .
doped fiber amplifiers EDFA , a 100 km SMF, and 16]18 km DCFs with CRs 0.94]1.06. The fiber’s parameters are shown in Table 1. The optical input mean power into the DCF PDCF
is chosen as 1, 5, 10, or 15 mW, respectively. The optical input power into SMF PSMF is continually tunable, but PSMF
is not smaller than PDCF subtracting the loss of DCF. In Ž .
Figure 1 b , we consider long-distance transmission. An EDFA, 100 km SMF, and some DCFs are included in each amplifier span. Each amplifier applies a gain G equal to the fiber loss of the following section.
The amplification process is obtained by multiplying the electrical field for the total gain
'
G , and by adding to eachTspectral component of the signal-independent noise terms whose real and imaginary parts are independent Gaussian
2 Ž .
variables with variances s N hn G y 1 Dnr2, where Nsp T sp
Ž
accounts for incomplete population inversion Nsps 1 for
. complete inversion; Nsps 2 is considered in this work , h is
the Planck constant,n is the signal carrier frequency, and Dn is the bandwidth occupied by each Fourier component of the discrete Fourier spectrum.
Ž .
An optical second-order Butterworth filter BWF is used in this work. The transfer function of the optical BWF placed
