Pulse Interval Modulation Dual Header (PIM-DH)

Transcription

1 Pule Interval Modulation Dual Header () N. Aldiiat, Z. Ghaemlooy, and R. Saatchi Electronic Reearch Group, School of Engineering Sheffield Hallam Univerity Sheaf Building, Pond Street Sheffield S WB United Kingdom z.f.ghaemlooy@hu.ac.uk Atract hi paper introduce digital pule interval modulation with dual header, a new form of digital pule time modulation cheme offering increae tranmiion capacity, requiring le tranmiion andwidth, and it ha uilt-in frame and lot ynchroniation capaility. heoretical expreion are decriing the code characteritic and howing the advantage of thi new cheme. Matla i ued to imulate the propoed cheme and a election of waveform are alo preented.. Introduction Digital pule time modulation technique (PM) have een uggeted for long-haul point-to-point optical communication link and for optical wirele communication ytem ecaue of improved receiver enitivity, aility to trade andwidth againt noie performance and relatively le complex circuitry compared with other digital modulation technique []. wo uch cheme are digital pule poition modulation (PPM) and digital pule interval modulation (PIM). he former exploit the wide andwidth of optical fire in a more efficient way to deliver the ame performance a that of PCM ut at reduced receiver enitivity [-4]. It alo achieve very good average power efficiency, which i deirale in optical wirele ytem. However, ince it i an iochronou in nature, having a fixed frame length, then it require oth lot and frame ynchroniation. he later not only olve the prolem of frame ynchroniation y locating a hort duration pule at the tart of each frame ut alo improve the tranmiion andwidth y eliminating the unued time lot a in PPM [5]. In thi paper we propoe a new digital pule interval modulation with dual header () offering horter frame length and requiring le tranmiion andwidth compared to exiting PIM and PPM cheme. It alo offer improved frame ynchroniation y initiating each frame with one of two different type of header pule. Analytic reult for the tranmiion capacity, lot duration, andwidth and power pectral denity are preented and where appropriate compared with other ytem.. Sytem heory In PIM [6] and, each frame conit of a numer of dicrete time lot where a hort duration pule, with duration one time lot, i located at the tart of a frame. A ymol i therefore repreented y a dicrete time interval etween two ucceive pule elonging to two conecutive frame. A pule repreent the dual role of frame initiation and time reference for the proceeding and ucceeding frame. In, for an M it on-off keying (OOK) word, the maximum numer of time lot in each ampling period i n = M. Depending on the mot ignificant it (MSB) the frame generated will have different header and information time lot. For MSB = each frame conit of a header of γ time duration diplaced from the previou header y a numer of time lot proportional to the decimal value of the input data. For MSB = each frame tart with a header of γ time duration pule, where the duty cycle < γ < γ, followed y a numer of time lot correponding to the decimal value of input data after taking it complement, a hown in Fig..a. hu the generated i compoed of variale frame length having ame/or different header followed y a numer of information time lot. o avoid zero length frame an additional time lot i added to each frame to act a a guard and. At the demodulator each individual frame length i determined y imply counting the numer of time lot etween the received pule (or header), a proce which require no frame ynchroniation to correctly interpret the encoded value. Depending on the

2 type of header, it i required to take the complement of the recovered data, ee Fig... M it MSB= No Enale Ye ' complement Enale (a) H B/D H frame generator output and with the latter diplaying on average horter ymol length. he minimum, maximum and average frame length of are given a: L min = [ ] M L = ( + ) ] max [ M L = ( + ) ] avg [ he lot duration i defined a where M. f () / L = f max, = i the OOK frame duration and i the it duration. PLL circuit ale. Mapping of OOK code to tranmitted ymol for PPM, PIM and data in Delay. Header width Edge detection Reet Counter Data latch Switch OOK PPM PIM lot rate i given y: ' complement data out () Fig. Sytem lock diagram (a) tranmitter, and () receiver R where, M = / = [( + ). R / M ] () R / = i the it rate. Fig. how the average frame length of each of the aove-mentioned digital ytem veru the OOK it reolution, with offering the hortet frame length in particular at higher it reolution, a expected. hi i achieved y taking the complement of the input data equence with MSB =. hi cheme offer all the attractive feature of the PPM without the need for frame ynchroniation, and at the ame time offering higher tranmiion capacity y virtue of eliminating all the unued time lot, and requiring far le andwidth than oth the exiting PIM and PPM ecaue of horter average frame length. Average frame length [t] OOK PIM 3. Code Propertie (i) Frame tructure ale how the mapping of the ource code (OOK) to tranmitted ymol for PPM, PIM OOK it reolution Fig.. Average frame length V it reolution

3 (ii) ranmiion capacity and andwidth (iii) Average power he tranmiion capacity i given a [6,7]: C PIM DH = ( Lmax / Lavg). R.log ( M M C PIM DH= M. R.(+ )/( + ) [it/ec] (3) Fig. 3 how the tranmiion capacity of PIM- DH, PIM, PPM normalied to that of OOK. From the figure we ee that oth PIM and PIM- DH diplay much higher tranmiion capacity compared to PPM. However, at lower it reolution diplay marginally lower tranmiion capacity compared to PIM, reaching the ame value at higher it reolution. he tranmiion andwidth of all digital PM cheme i determined y the frequency characteritic of the pule [8]. In the aic pule ha a minimum duration of M γ = γ /( + ) and therefore it f tranmiion andwidth i given y B = /( γ. ) PIM DH. Fig 3 alo how the normalied tranmiion andwidth veru it reolution for all three cheme, with howing conideraly lower andwidth requirement compared to PPM and PIM. hi i ecaue ha wider lot duration due to horter frame length characteritic..5 M ) 5 Mathematically the ignal may e written a [6]: i x ( t) = v. y[ t (. i + S ) ] (4) i i= m m= where, y(t) repreent the pule hape (rectangular) of duration γ. and amplitude v i. S m i the numer of empty time lot in th the m frame repreenting encoded information. For a given code word ha different energie per frame depending on the type of header ued, unlike PPM and PIM where all the frame have equal energy. With having wider lot duration, the normalied average power will e marginally higher than thoe of PPM and PIM a given y: γ P( t) = x( t) dt (5) Lave Fig. 4 how the average power relative to OOK for a range of it reolution for all threemodulation cheme. he average duty cycle of 5% and 75% were aumed for PPM/PIM and, repectively. diplay a higher power requirement ~ 3.5 db and 4.5 db compared to PIM and PPM, repectively. hi i ecaue ha a much wider lot duration, ~.6 time higher, compared to PPM and PIM [9]. Normalied tranmiion capacity.5.5 P I M P I M - D H P P M C a p a c i t y B a n d w i d t h P P M P I M P I M- D H 5 5 Normalied tranmiion andwidth Average power relative to OOK [db ] PPM PIM O O K i t r e o l u t i o n OOK it reolution Fig. 3. ranmiion capacity & andwidth for, PIM and PPM modulation ytem Fig. 4. Normalied average power V it reolution

4 4. Simulation Reult he complete ytem, hown in Fig. wa imulated uing MALAB. o demontrate it capailitie, white Gauian noie wa added to the pule train and at the receiver, a pre-detection matched filter wa employed to reduce the noie power. Fig. 5 how elected imulated time domain waveform. o invetigate it pectral characteritic, random data ample of 5 random frame with rectangular hape header pule having duty cycle of γ = 5 % and γ = % were generated, and the reult are hown in Fig. 6. Frequency axi i normalied to the lot frequency. he pectra contain a ditinct lot component which can e extracted uing a phae-locked-loop (PLL) at the receiver for lot ynchroniation. he location and amplitude of the lot component depend on the pule duty cycle. If all the generated frame have the ame header with % duty cycle, then the lot component will coincide with the firt zero croing point thu making clock recovery, uing PLL, quite difficult. However, thi i very unlikely event x ( c ) x t [Sec] x -5 ( d ).5 ( a ) ( )..4.6 ime [S].8. x -5 Fig. 5. Selected imulated waveform: (a) tranmitted, () with noie (c) output of the matched filter, and (d) recovered ignal. Power Spectrum Denity (db) Normalied frequency Fig. 6. Power pectral denity of ignal 5. Concluion A new digital pule time modulation technique known a ha een preented in thi paper. Reult how that diplay imilar tranmiion capacity to that of PPM and PIM, ut offer horter frame length and therefore requiring le tranmiion andwidth compared to PPM and PIM. It require no complex frame ynchroniation at the receiver, in contrat to PPM. Simulated reult how the potential of thi new cheme for application where andwidth requirement i at a premium. Reference: [] B. Wilon, and Z. Ghaemlooy: 'Pule ime Modulation echnique for Optical Communication: a Review', IEE Proceeding J, Vol. 4, No. 6, pp , Dec [] R. A. Cryan, R.. Unwin, A. J. Maarella, M. J. N. Siley,: A comparion of coherent digital PPM with PCM, European ranac. on elecom, 3, (4), pp 33-34, July, 99. [3] J. D. Martin, H. H. Hauien,: PPM veru PCM for optical local-area network, IEE Proceeding-I, 39, (3), pp4-5, 99. [4] N. M. Calvert et-al,: Experimental optical fire digital PPM ytem, Electronnic Letter, 4, (), pp. 9-3, 988. [5] R. Reher, Z. Ghaemlooy, A. Simmond, R. Saatchi, A novel digital modulation ytem uing Pule interval code modulation (PICM) and pule interval width code modulation (PIWCM), 3rd International Sympoium on Communication heory and Application, UK, pp , July 995.

5 [6] E. D. Kaluarachchi,: Digital pule interval modulation for optical communication, PhD hei, Sheffield Hallam univerity, UK, 997. [7] M. Sato, M. Murata,. Namekawa, New optical communication ytem uing the pule interval and width modulated code, IEEE tran. on Cale televiion, Vol. catv- 4, no., pp. -9, January 979. [8] J. Proaki, M. Salehi, 'Communication Sytem Engineering', New Jerey: Prentice-Hall International, 994. [9] Z. Ghaemlooy, A.R. Haye, N.L. Seed, and E. D. Kalurachchi, 'Digital Pule Interval Modulation for Optical Communication', IEEE Communication Magazine, Vol. 36, No., pp , Decemer 998. Acknowledgement N. Aldiiat i grateful to the Aga Khan Foundation (AKF) for receiving a cholarhip.