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 .
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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.
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© 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.
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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.
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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 .