Comparison of different scenarios for path diversity packet wireless networks

INFORMATION AND COMMUNICATION TECHNOLOGIES AND SERVICES VOLUME: 10 | NUMBER: 4 | 2012 | SPECIAL ISSUE © 2012 ADVANCES IN ELECTRICAL AND ELECTRONIC ENGINEERING 199 COMPARISON OF DIFFERENT SCENARIOS FOR PATH DIVERSITY PACKET WIRELESS NETWORKS Pe CHLUMSKY1, Zbynek KOCUR1, Ji i VODRAZKA1 1Depa men o Telecommunica ion Enginee ing, Facul y o Elec ical Enginee ing, Czech Technical Uni e si y in P ague, Technicka 2, 166 27 P ague 6, Czech Republic [email p o ec ed], zbynek.kocu @ el.c u .cz, [email p o ec ed] u .cz Abs ac . This a icle discusses he use o he p inciples o ne wo k coding in wi eless ne wo ks o inc ease he o e all obus ness o he ansmission. Pa h di e si y on he packe le el is in es iga ed as a so wa e al e na i e o classical di e si y echniques commonly used o imp o e wi eless de ices communica ion. The a icle desc ibes he ini ial s age o he esea ch o ne wo k coding in elemen a y o m wi h ne wo k a ic duplica ion. Objec s o in es iga ion a e wo di e en ypes o ansmission in wo scena ios, whe e he esul ing ansmission loss is e alua ed wi h dependency on he packe leng h. Keywo ds Op imiza ion, pa h di e si y, wi eless ansmission. 1. In oduc ion Op imiza ion o wi eless ne wo ks is a e y b oad ield; ou wo k is ocused on he op imiza ion wi hin he meaning o ensu ing he desi ed balance be ween he ne wo k h oughpu , delay and packe loss size. The e a e si ua ions when maximal h oughpu and minimal delay a e equi ed (e.g. oice se ices), howe e , he e a e si ua ions when e e y single packe is impo an and mus be deli e ed o i s des ina ion (e.g. ile ans e ). Ou app oach is o ind he app op ia e connec ion scheme o unicas ne wo k using he pa h di e si y. Fu he mo e, a ious packe loss p obabili ies in sepa a e channels, esul ing om he usage o mo e o less obus modula ion echniques, a e an in eg al pa o he design o wo indi idual schemes. This a icle compa es hese wo di e en ansmission schemes wi h espec o p obabili y o packe loss. 2. Op imiza ion Design The i s pa o his chap e consis s o di e en ways o op imize he da a ansmission, and hen ocuses on he desc ip ion o ou ansmission schemes. 2.1. Rela ed Wo k A common way o imp o e he ansmission cha ac e is ics in he physical laye is he MIMO echnology (Mul iple-Inpu Mul iple-Ou pu ), i.e. he use o mul iple an ennas a he ecei e and ansmi e . MIMO has wo a ian s; he i s one is based on he spa ial di e si y which means ansmi ing he same da a h ough se e al an ennas. Spa ial mul iplexing is he second one and i s co e unc ion is based on he sending di e en da a h ough he each o an ennas [1]. O he op imiza ion echniques in he physical laye a ea o wi eless ne wo ks a e, o example, dynamic subca ie assignmen , adap i e powe alloca ion 0, o in e e ence cancela ion [3]. Op imiza ion in he link laye is ypically based on some kind o adap abili y in o de o adjus he p o ocol pa ame e s o he ac ual ne wo k condi ions [4], scheduling [5], o di e en back o mechanisms [6]. Di e en ype o a icles ocused on he ne wo k op imiza ion co e s new ou ing me hods, such as dispe si y ou ing. Unlike con en ional di ec o y ou ing p ocedu es, which ou e a message along a pa icula pa h be ween he sou ce and des ina ion, his ou ing mechanism sub-di ides he message and dispe ses i h ough he maze o pa hs comp ising he ne wo k [7]. 2.2. T ansmission Schemes In he ollowing sec ion is discussed wo sepa a e wi eless channels sys em op imizing da a ansmission. Op imiza ion o h oughpu o esilience, in sys ems wi h pa h di e si y in use, has i s e lec ion in MIMO me hods o spa ial di e si y and mul iplexing. P oposed echniques o ou wo k, on he con a y, a e in ended o be uni e sal and independen on he physical laye . INFORMATION AND COMMUNICATION TECHNOLOGIES AND SERVICES VOLUME: 10 | NUMBER: 4 | 2012 | SPECIAL ISSUE 200 © 2012 ADVANCES IN ELECTRICAL AND ELECTRONIC ENGINEERING 1) Load Balance Sys em Model Conside a ansmission sys em wi h wo sepa a e channels as depic ed in Fig. 1. Sys em wi h uni o mly dis ibu ed load elies on he assump ion ha i he e a e wo pa allel da a s eams and each will ansmi s he hal o inpu da a, hen, hanks o a lowe bi a e o a single da a channel will be achie ed highe esis ance using mo e obus modula ion. O e all h oughpu will be he same as in he basic sys em wi h a single channel. he impac o ype o modula ion on he packe e o a e (PER). The bi e o a e depends on he bi o symbol mapping, o SNR >> 1 (Signal- o-noise a io) and G ay- coded assignmen is possible o assume ha each symbol e o causes only one bi e o ; hen he p obabili y o bi - e o pe ca ie is [8]: n bb SNR b e c b PER                   22 3 2 1 1 2 11 1 2 , (1) Fig. 1: Load balance ansmission sys em. 2) Backup Sys em Model Sys em wi h da a mi o ing (see Fig. 2) akes ad an age o he si ua ion ha wo pa allel channels ansmi s he comple ely same da a. The e is necessa y o ha e a less obus modula ion, compa ed o he p e ious me hod, which is capable o ansmi da a wi h he same o e all h oughpu . Fo example, i he e is a ne wo k wi h wo channels based on he s anda d IEEE 802.11g and eques o a 24 Mbps h oughpu , hen wi h he i s sys em is necessa y o ha e a wo QPSK (Quad a u e Phase Shi Keying) channels (s anda d de ines bi a e o 12 Mbps). Wi h he second sys em, one can use a less obus 16- QAM (Quad a u e Ampli ude Modula ion) modula ion which is de ined o he bi a e o 24 Mbps in he men ioned s anda d (see Tab. 1). The o al bi a e will no inc ease, because o he selec ion jus o he o iginal da a a he des ina ion, bu due o pa allel ansmission o da a will be p ese ed high du abili y and e y low e o a e despi e highe e o a e pe channel caused by less esilien modula ion echnique. whe e b is numbe o bi s pe symbol; numbe o symbols in modula ion cons ella ion M = 2b, n is packe leng h in bi s and e c(x) is Gaussian complemen a y e o unc ion. Modula ion echniques and coding a es, which indica es he a io o he numbe o bi s o use ul in o ma ion o he o al numbe o bi s (including he added edundancy), o each ype o modula ion is de ined by IEEE s anda d 802.11g [9] and p esen ed in Tab. 1. 3. Compa ison o Schemes o Di e en Scena ios Ou compa ison o p esen ed schemes in e ms o packe loss wi h espec o packe leng h is di ided in o wo scena ios. The i s one deals wi h addi i e whi e Gauss. Fig. 2: Backup ansmission sys em. 2.3. Packe E o and Th oughpu The backg ound o his comes om he ac ha obus ness is dec eased wi h he g ea e numbe o symbols in modula ion cons ella ion. Equa ion 1 shows noise and wi h di e en modula ions in use o backup and load balance sys em. The second one is based on he same p obabili ies o in e up o bo h sys ems and shows how hese sys ems a e capable o deal wi h hem. INFORMATION AND COMMUNICATION TECHNOLOGIES AND SERVICES VOLUME: 10 | NUMBER: 4 | 2012 | SPECIAL ISSUE © 2012 ADVANCES IN ELECTRICAL AND ELECTRONIC ENGINEERING 201 3.1. Packe Loss o Gaussian Noise Only addi i e whi e Gaussian noise is conside ed in he i s scena io. The di e ence be ween load balance and backup sys em is app oxima ely ou o de s o magni ude g ea e in a o o he load balance sys em. This is so because sys ems a e designed o ope a e wi h di e en modula ions and, he e o e, is impo an o wo k wi h app op ia e p obabili ies o bi e o . These a e possible o ge om well-known equa ions o a pa icula ype o modula ion (mo e in [8]). Fo his compa ison, we ha e chosen 16-QAM modula ion o he backup sys em channels and he QPSK modula ion o he load balance sys em. App op ia e bi e o p obabili ies o 15 dB SNR a e shown in Fig. 3. Tab.1: Th oughpu o modula ion echniques and coding a es de ined in IEEE s anda d 802.11g. Modula ion Coding a e Bi a e BPSK 1/2 6 Mbps BPSK 3/4 9 Mbps QPSK 1/2 12 Mbps QPSK 3/4 18 Mbps 16-QAM 1/2 24 Mbps 16-QAM 3/4 36 Mbps 64-QAM 2/3 48 Mbps 64-QAM 3/4 54 Mbps Fig. 3: Bi e o p obabili ies o QPSK and 16-QAM modula ion. Figu e 4 shows how looks he si ua ion wi h di e en modula ions in use. The load balance sys em is signi ican ly mo e esilien agains bi e o s. This is caused by g ea di e ence o p obabili ies o e o o QPSK and 16-QAM modula ion. 3.2. Packe Loss o In e up and In e e ence in Wi eless Channel Fo compa ison which o schemes is mo e obus and less e o -p one is good o know how is p obable ha an e o will happen. The packe e o should be mo e p obable in he load balance sys em because i is su icien ha e o occu ed only a one o channels and he packe is los . On he con a y, when he packe is los in one channel o he backup sys em, is s ill deli e ed o i s des ina ion by he second channel. These wo di e en beha iou s a e desc ibed in ollowing equa ions. Fig. 4: Compa ison o sys ems wi h di e en modula ions in use. The p obabili y ha an e o occu s in he in e al o he packe leng h n in he load balance sys em is:          nn LppP 21 1111         nn pp 21 1111  . (2) The p obabili y ha an e o occu s in he in e al o he packe leng h n in he backup sys em is:         nn BppP 21 1111  . (3) whe e p1 and p2 a e p obabili ies o e o in one bi . Compa ison o hese equa ions o a ious packe leng hs and o he same in e up e o a e 10-5 o bo h sys ems is depic ed in Fig. 5. The di e ence be ween load balance and backup sys em is app oxima ely h ee o de s o magni ude g ea e in a o o he backup sys em. The e o e, o a wi eless ansmission a ec ed by ading o an enna shading [10] is a backup sys em mo e app op ia e. INFORMATION AND COMMUNICATION TECHNOLOGIES AND SERVICES VOLUME: 10 | NUMBER: 4 | 2012 | SPECIAL ISSUE 202 © 2012 ADVANCES IN ELECTRICAL AND ELECTRONIC ENGINEERING Fig. 5: Compa ison o sys ems o in e up in channel. 4. Conclusion This a icle p esen s wo di e en pa h di e si y wi eless ansmission schemes and hei compa ison o packe loss o a ious packe leng hs. The i s scheme is based on load balancing o sen da a in o wo sepa a e channels. Thanks o lowe bi a e o a single da a channel is achie ed highe esis ance using mo e obus modula ion. The second scheme uses bo h ansmission channels o pa allel sending o he same da a. The e o e, high esis ance agains e o is achie ed by da a backup. Compa ison o hese schemes is done om wo poin s o iew. Fi s ly, o he addi i e whi e Gaussian noise channel model i is shown ha load balance sys em is a mo e esilien o all es ed packe leng hs. Subsequen ly, o he si ua ions wi h signal in e up (e.g. shaded an enna) he backup sys em p o ed o be mo e sui able. These esul s will be used o u he wo k on hese schemes and i s usage o speci ic pu poses. Acknowledgemen s This wo k was suppo ed by he G an o he Minis y o he In e io o he Czech Republic, No. VG20122014095, „De elopmen o adap able and da a p ocessing sys ems o high-speed, secu e and eliable communica ion in ex eme condi ions“, and was esea ched in coope a ion wi h CERTICON and he S uden ´s g an o Czech echnical uni e si y in P ague, No. SGS11/124/OHK3/2T/13. Re e ences [1] GESBERT, D., M. SHAFI, P. SMITH and A. NAGUIB. F om heo y o p ac ice: An o e iew o MIMO space- ime coded wi eless sys ems. IEEE jou nal on Selec ed A eas in Communica ions. Ap il 2003, ol. 21, iss. 3, pp. 281-302. ISSN 0733-8716. DOI: 10.1109/JSAC.2003.809458. [2] GUOCONG, Song and Ye LI. C oss-laye op imiza ion o OFDM wi eless ne wo ks-pa I: Theo e ical amewo k. IEEE T ansac ions on Wi eless Communica ions. Ma ch 2005, ol. 4, iss. 2, pp. 614-625. ISSN 1536-1276. DOI: 10.1109/TWC.2004.843065. [3] SHABADANOV, S., P., MITRAN and C. ROSEMBERG. 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In: P oceedings o ICC '75. San F ancisco. 1975, pp. 10-13. [8] DOBES, Jose a Vacla ZALUD. Mode n Radio Enginee ing [in Czech]. P aha: BEN, 2006. ISBN 80-7300-132-2. [9] IEEE S anda d o In o ma ion Technology-Pa 11: Wi eless LAN Medium Access Con ol (MAC) and Physical Laye (PHY) Speci ica ions. 2007. A ailable a : h p://s anda ds.ieee.o g/ge ieee802/download/802.11- 2007.pd . [10] CHLUMSKY. P., Z. KOCUR and V. MACHULA. Simula ion o da a ans e om he ae oba ic plane. In: Knowledge in Telecommunica ion Technologies and Op ics 2011 P oceedings. Szczy k: VSB-Technical Uni e si y o Os a a, 2011, pp.113-116. ISBN 978-80-248-2399-7. Abou Au ho s Pe CHLUMSKY was bo n in 1985. He ecei ed his M.Sc. om he Czech Technical Uni e si y in P ague in 2010. Since 2010 he has been s udying Ph.D. deg ee. His esea ch in e es s include wi eless ansmission, ne wo k coding and ne wo k simula ion. He is eaching ne wo k echnologies, da a ne wo ks and digi al enginee ing. He is cu en ly in ol ed in p ojec ocused on de elopmen and op imiza ion o modules o simula ion o communica ion ne wo ks. Zbynek KOCUR was bo n in 1982. He ecei ed his M.Sc. deg ee in elec ical enginee ing om he Czech Technical Uni e si y in P ague in 2008. Since 2008 he has been s udying Ph.D. deg ee. He is eaching communica ion in da a ne wo ks and ne wo king echnologies. His esea ch is ocused on wi eless ansmission and da a low analysis, simula ion and op imiza ion. He is cu en ly ac i ely in ol ed in p ojec s ocused on high speed da a ansmission om as mo ing objec s and da a op imiza ion ia sa elli e ne wo k. INFORMATION AND COMMUNICATION TECHNOLOGIES AND SERVICES VOLUME: 10 | NUMBER: 4 | 2012 | SPECIAL ISSUE © 2012 ADVANCES IN ELECTRICAL AND ELECTRONIC ENGINEERING 203 Ji i VODRAZKA was bo n in P ague, Czech Republic in 1966. He joined he Depa men o Telecommunica ion Enginee ing, FEE, CTU in P ague in 1996 as a esea ch assis an and ecei ed his Ph.D. deg ee in elec ical enginee ing in 2001. He has been he head o he T ansmission Media and Sys ems scien i ic g oup since 2005 and became Associa e P o esso in 2008. He pa icipa es in nume ous p ojec s in coope a ion wi h ex e nal bodies. Cu en ly he ac s also as ice-head o he Depa men .