Efficient bit-level design of an on-board digital TV demultiplexer
Abstract
A bit-level description of the signal processing stage of an on-board integrated VLSI multi-carrier demodulator is presented in this paper, along with a description of the optimization procedure that has been developed for the signal processing functions1. The demultiplexer is capable of handling a varying number of carriers in a 36 MHz bandwidth on the satellite up-link. Its architecture has been optimized at bit-level in a way dependent on the known input signal statistics and carrier distributions allowed by the frequency plan.
Full text
EFFICIENT BITLEVEL DESIGN OF AN ONBOARD
DIGITAL TV DEMULTIPLEXER
S. Cal o J.Sala A. Pages G. Vazquez
Dep . o Signal Theo y and Communica ions Uni e si a Poli ecnica de Ca alunya
c Jo di Gi ona 13 Modul D5114b
08034 Ba celona SPAIN
Tel 3434015894 Fax 3434016447
email
se gioal a ez
g
gps. sc.upc.es
ABSTRACT
A bi le el desc ip ion o he signal p o cessing s age o
an onb oa d in eg a ed VLSI mul ica ie demo dula o
is p esen ed in his pap e along wi h a desc ip ion o he
op imiza ion p o cedu e ha has b een de elop ed o he
signal p o cessing unc ions
1
.The demul iplexe is capa
ble o handling a a ying numb e o ca ie s in a 36 MHz
bandwid h on he sa elli e uplink. I s a chi ec u e has
been op imized a bi le el in away dep enden on he
known inpu signal s a is ics and ca ie dis ibu ions
allowed by he equency plan.
1INTRODUCTION
Space Digi al Video B oadcas ing Sys ems a e e ol ing
owa d he DVB Digi al Video B oadcas ing S anda d
based on MPEG2. An inc easingly la ge amoun o
p o cessing is b eing mo ed owa d he space segmen so
ha complex egene a i epayloads shall ha e o beca
ied by he o hcoming sa elli e gene a ion. This pap e
desc ib es he a chi ec u e ha has b een de eloped o
an OB Mul ica ie Demul iplexe ASIC p o o ype o
p o ide se ices o digi al ele ision and mul imedia in
he ame o he HISPANET ne wo k p o jec . HISPA
NET is aimed a p o iding b oadcas ing o digi al mul i
p og amme ele ision o Spanishsp eaking communi ies
in Eu op e and Ame ica. The basic concep is o p o ide
access o indi idual b oadcas e s and se ice p o ide s
h ough sp ecic ansp onde s ca ied by he HISPASAT
sa elli e. One ca ie con eying all p og ammes ecei
ed on he indi idual uplinks Mul i equency TDMA
is ansmi ed on he downlink. The e o e demul iple
xing and demo dula ion no conside ed in his pap e
mus b e ca ied ou onb oa d.
The design o digi al onb oa d sys ems and speci
cally o he l e ing s ages o he digi al demul iplexe
ha e okeep p owe consump ion ga e coun and imple
men a ion losses o a minimum while main aining ac
cep able sys em pe o mance. A sp ecial c i e ion ha
1
This esea chwo k has b een pa ially suppo ed by he Na i
onal Resea ch Plan o Spain CYCIT TIC951022C0501 and
TIC960500C1001 and he Ca alonian Regional Go e nmen
CIRIT 1996SGR00096.
akes in o accoun he s uc u e o he in e e ing ad
jacen ca ie s has b een de elop ed 4 o de i e sui able
decima ion l e s o he demul iplexing unc ion. The
c i e ion op imizes join ly he l e esponse in he pass
ansi ion and s opbands o a gi en numbe o coe
cien s as he complexi y o l e ing is exp onen ial in he
l e leng h. In his ollowup pape we conside he
bi le el design o he a chi ec u e he ein desc ib ed. A
sys em o e iew is p esen ed in sec ion 2 Sys em Des
c ip ion. Sec ion 3 p esen s he app oach ollowed in
bi le el design o VLSI in eg a ion. Resul s and Con
clusions a e shown in Sec ion 4.
2 SYSTEM DESCRIPTION
The a chi ec u e o he digi al onb oa d demul iplexe
shall ha e o deli e any ca ie combina ion o hose
allowed see Fig. 2.1 and 2.2 o he ollowing signa
ling a es
R
s
2
R
s
3
R
s
and 4
R
s
wi h
R
s
he lowes
signaling a e. Each ca ie is QPSK mo dula ed wi h
a squa e o o aised cosine pulse ollo 0.35. Two
p ossible equency plans ha e been ailo ed o acili a e
he demul iplexing scheme whe e he sepa a ion wi h
adjacen ca ie s is 1.5
R
s
. In he nal a chi ec u e
b o h equency plans depic ed in Fig. 2.1 and Fig. 2.2
a e p ocessed by wo independen demul iplexe s ha
can b e in e nally congu ed o deal wi h ei he o hem.
The o e all bandwid h 36 MHz can con ain up o 18
small ca ie s a he
R
s
signaling a e. The sampling
scheme is IF sampling a
s
36
R
s
44.64 MHz. Bo h
equency plans ha e been de ised o con ain he ou
p ossible men ioned signaling a es wi h wo cons ain s
a ha e y simple equency shi ing ope a ions should
b e ca ied ou and b ha he ou pu sampling a e o
each ca ie should be he same in samples pe sym
b ol o all a es. These wo cons ain s ha e led o he
cons uc ion o wo equency plans and he design o
he demo dula o s a 3 samples p e symb ol. The inne
a chi ec u e o he demul iplexe consis s o in e com
munica ing p olyphase p ocesso s ina ee scheme. In
p inciple i would ha e b een p ossible o dene a com
mon a chi ec u e capable o p ocessing bo h equency
plans. No e in gu es 2 and 2 ha i should only be
neccessa y o in o duce he inpu signal a a decima ion
by wo o a a decima ionby h ee block. Ne e heless
he impac his app oachhas a bi le el is conside a
ble as each p o cessing blo ck mus be dimensioned o
handle complex signals a sucien a e. In he end i
was op ed o implemen ing each ees ha dwa e sepa
a ely. Then ha dwa e op imiza ion is mo e s aigh
o wa d and can b e handled mo e eec i ely using he
echniques desc ib ed in he sec ion on Bi Le el Design.
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
H
H
H
H
H
H
H
H
H
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
H
H
H
H
H
H
H
H
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
0
222222222
666
0
4 4 4 4 2
8 8
Figu e 1
F equency Plan No. 1 and No. 2 ab o e 2.1
Mbps and 6.3 Mbps ca ie s b elow 2.1 Mbps 4.2 Mbps
and 8.4 Mbps ca ie s.
Demul iplexing is ca ied ou acco ding o he scheme
dened in gu es 2 and 2
1/2 band 21/2 band 2
1/2 band 2
1/2 band 2
1/3 band 3
1/3 band 3
1/3 band 3
h
1
n
[]
j
−n
h
1
n
[]
j
n
h
0
n
[]
j
n
e
−j
π
n
h
1
n
[] k
6
=0
k
6
=1
k
6
=−
1
e
−j
π
k
6
n
h
2
n
[]
e
−jn
π
/3
h
2
n
[]
e
jn
π
/3
h
2
n
[] ′
k
2
=0
′
k
2
=1
′
k
2
=−
1
e
−j
π
′
k
2
n
6 Mbps 2 Mbps
Figu e 2
Fil e ing and Decima ion s uc u e o T ee no.
1 o 223. Each blo ck is a p olyphase p ocesso consis ing
o a decima ed l e bank and a IDFT op e a ion. Bi le el
op imiza ion is ca ied ou sepa a ely a b o h blo cks
The a chi ec u e o he 322 congu a ion is dis
played in gu e 2. Each blockis implemen ed wi h a
p olyphase p o cesso ha pe o ms demul iplexing o 6
and 4 ca ie s wi h a decima ion a io o 3 and 2 es
p ec i ely. No e ha he wo king a e o each p o cesso
is wice as as i compa ed o ha o acon en ional
p olyphase p ocesso he decima ion a io is only hal
he numbe o ca ie s. This only aec s he IDFT
pa o he p olyphase as he same ou pu s o he l e
bank maybeused wice a die en inpu p osi ions o
he IDFT o e alua e odd ou pu samples. Only some
1/2 band 2
1/2 band 2
1/2 band 2
1/2 band 2
1/3 band 3
1/3 band 3
1/3 band 3
h
3
n
[]−
1
()
n
h
3
n
[]
e
jn
π
3
h
3
n
[]−
1
()
n
e
−jn
π
3
k
8
=1
k
8
=0
k
8
=−
1
e
−j
π
k
8
n
h
4
n
[]
e
−jn
π
/4
h
4
n
[]
e
jn
π
/4
′
k
4
=−
1
′
k
4
=1
h
5
n
[]
e
−jn
π
/4
h
5
n
[]
e
jn
π
/4
′
k
2
=1
′
k
2
=−
1
e
−j
π
′
k
4
/2⋅n
e
−j
π
′
k
2
/2⋅n
8 Mbps 4 Mbps 2 Mbps
Figu e 3
Fil e ing and Decima ion s uc u e o T ee no. 2
o 322
o he ou pu s o each p ocesso con ain use ul da a de
p ending on he equency plan so ha inhibi ed ou
pu s will no be syn hesized in he nal ha dwa e.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
4
4
4
4
T
T
T
h2
h1
h3
h2
h0
h3
h1
T
T
h0
z1
z3
z0
z2
IDFT
xn
x0
x1
x2
x3
Figu e 4
A chi ec u e o he 2 decima ionby wo p o
cesso l e bank. The ou pu ec o
y
is ed in o a IDFT
p o cesso . The ou die en subl e s cons i u e he de
cima ed e sions o he ca ie demul iplexing l e
h
n
hi
h
4
n
i
. Fo his pa icula applica ion we ha e
h
4
n
1
n
L
and
h
4
n
3 0. Upp e lowe b anc
hes o he ou logic mul iplexe s a e selec ed acco ding o
e eno dd IDFT ou pu samples ec o
z
. T
he3p ocesso
is designed in a simila way.
3 BITLEVEL DESIGN
Bi le el designs o signal p o cessing algo i hms o en
equi e ca e ul wo dleng h dimensioning in eachnodeo
he a chi ec u e. The o e all pe o mance o he sys em
in e ms o a dis o ion c i e ion dep ends on wo ac o s
a he wo dleng h assigned o eachin e nal a iable and
b he numb e o quan iza ion le els a he inpu . The
usual c i e ion is hus o op imize p e o mance o a e
asonable complexi y. I is use ul o conside se e al op
imiza ion le els in he design o a digi al a chi ec u e
a op le el whe e algo i hmical op imiza ion is ca ied
ou choice o he algo i hm b bi le el o egis e
ans e le el RTL whe e he op imiza ion p o cedu e
desc ib ed in his pap e applies and c ga e le el whe e
he RTL sp ecica ion is syn hesized in o an in e connec
ion o ga es egis e s. T adeos mus be me du ing
he design phase. The e o e i is a usual p o cedu e in
he p o ision o he sys em sp ecica ions o s a e he
maximum ole a ed le el o implemen a ion loss e alu
a ed in dB. We ha e chosen his he e o e as he dis
o ion c i e ion unde which he a chi ec u e mus b e
op imized. The implemen a ion loss is dened acco ding
o
L
I
10log
1
0
E
b
N
o
a ch
E
b
N
o
ue
dB 1
wi h
E
b
N
o
a ch
he bi ene gy o noise sp ec al p owe
densi y a io ob ained a he ou pu o he a chi ec u e
nally implemen ed and
E
b
N
o
ue
he ue a io o
he ideal signal mo del.
P e iouslyweha e desc ib ed he highle el a chi ec
u e o he digi al TV demul iplexe in e ms o a p olyp
hase ee. The nex s ep in he design p o cess is o
ansla e his algo i hmics o RTL VHDL p imi i es.
Sp ecica ions o he p esen sys em in e ms o he
numbe o ca ie s o be p o cessed he ou admissi
ble symb ol a es o each ca ie and he a ying inpu
dynamics mus b e app oached wi h a sui able s a egy
a he a i hme ical and logic le els. The complexi yo
he o e all sys em dep ends on a la ge deg ee on he
numbe o bi s assigned o each node in he a chi ec
u e. I is he e o e imp o an oiden i y hose p oin s
in he a chi ec u e ha a e mo e c i ical in e ms o he
implemen a ion loss in o duced.
This ob jec i e is usually achie ed a e ecu en si
mula ions using p obing sequences p e iously dened o
anumb e o scena ii we e e he e o hose c i ical ca
ses dened in he sys em sp ecica ions. Tables a e p o
duced showing he implemen a ion loss asso cia ed wi h
each node in e ms o he implica ed complexi yanda
nal decision is eached o he i s p op e dimensioning.
A close unde s anding o he b eha iou o bi dynamics
in e ms o he da a s a is ics can p o ide sho cu s o
his p o cedu e. In ou se ing da a s a is ics can be
in ui i ely ela ed o he spec um o equency plan
p esen a he inpu o each p olyphase p ocesso .
The wo king ma gin o each p ocesso can b e dened
as ha ange in e ms o signal p owe ha is p esen ed
o i om he p eceding s age in he a chi ec u e. P o i
ded ha his condi ion is me ha pa icula p o cesso
will wo k acco ding o sp ecica ions. In his pa icula
case he whole demul iplexing ee is implemen ed as a
cascade o polyphase p o ceso s so ha ca e ul moni o
ing o signal dynamics is c ucial o gua an ee ha each
p olyphase p o cesso is nea i s op imum wo king p oin .
Bi le el dynamics dep end hea ily on he inpu da a
s a is ics. In pa icula cascaded a chi ec u es a e ex
emely sensi i e o his eec . Bi le el p imi i es a e
implemen ed as xedp oin op e a ions so ha ecu en
p o cessing on he inpu da a ec o esul s in signal a
enua ion along he cascade. This a enua ion eec
being de imen al o sys em p e o mance in e ms o
he quan iza ion SNR o implemen a ion loss
L
I
is
hea ily dep enden on he inpu da a sp ec um.
The app oach ha has b een aken o his design is
o moni o he da a his og am along he cascade as p o
bing sequences a e ed h ough. This a enua ion can b e
elimina ed i xedp oin amplica ion is implemen ed a
key poin s in he a chi ec u e. The choice o he ampli
ca ion ac o s is c i ical in he sense ha only a p ecise
unde s ading o he signal s a is ics can p o ide a sui
able alue o he whole ange o ca ie dis ibu ions
con empla ed in he equency plan. Asui able alue
mus b e chosen o p e en ei he sa u a ion o a i hme
ics o an excessi ely low signal o quan iza ion noise
a io o he sp ecied ca ie p owe s.
The e o e in o de o de e mine he b eha iou o one
a ge a chi ec u e i is only necessa y o de e mine
hose inpu da a dis ibu ions o sp ec a ha deli e
a he ou pu he maximally and minimally a enua ed
signal powe o cons an inpu signal powe . I can
be shown ha he a enua ion induced by he a chi
ec u e dep ends on he andomness o he inpu signal
sp ec um. All op e a ions in ol ed in demul iplexing he
ca ie se a e linea op e a ions. I is s aigh o wa d o
p o ide an in ui i e jus ica ion le
x
i
i
2Ig
be a
se o inpu co ela ed and bounded andom a iables
and le us p e o m a linea op e a ion
L
on hese a i
ables
y
L
x
1
x
N
. Then he p obabili y densi y
unc ion o he andom a iable
Y
0
p
Y
0
y
0
y
0
de
y
max
y
2
is a e he mo e hose inpu andom a iables a e co
ela ed his can be jus ied om he Cen al Limi
Theo em. In o he wo ds absence o co ela ion a
he inpu can be in e p e ed as he ou pu aking i s
maximum alues wi h anishing p obabili y.
The e o e wo dleng h dimensioning is c i ical in
e ms o he da a s a is ics o gua an ee minimum im
plemen a ion loss. The mos signican bi s a se e al
poin s in he a chi ec u e can be d opp ed as hey will
only ac i a e wi h negligible p obabili y dep ending on
he da a s a is ics. Thus he necessa y logic o e alu
a e hose bi s can be ob ia ed in he syn hesis p o cess
leading o a ea and ga e delay educ ions in he nal
implemen a ion. Tha is ue a adeo shall ha e o
be es ablished be ween he clipping p obabili y hose
MSB bi s ha would ac i a e and he logic complexi y.
In he nal ha dwa e simple scaling ope a ions wi h
ac o s
1 shi bi s o he uppe p osi ions. Rounding
is p e o med a e wa ds o limi he wo dleng h passed
on o he nex p o cesso .
In conclusion he use o his og ams and cha ac e is
ic p obing sequences has p o ided he necessa y means
Ga es
s age 1 s age 2 s age 3
T ee 223
5229 12477 13698
T ee 322
31185 25252 27235
Table 1 Numb e o ga es used by hein eg a ed ci cui
o each ee. T ees 223 and 322 o al 31404 and
83672 ga es esp ec i ely. T ee 322 displaysahea ie
compu a ional load.
o educe he digi al a chi ec u e complexi y o he de
mul iplexe o an accep able le el.
4RESULTS
His og ams and sp ec a a e shown a key p oin s in he
a chi ec u e. We ha e conside ed wo die en scena
ii a one ca ie congu a ion con aining all nine 2.1
Mbps ca ie s and b one ca ie congu a ion con ai
ning wo 8.4 Mbps ca ie s and one 2.1 Mbps ca ie . In
his way we can show heeec o da a s a is ics and
he sp ec um a hose p oin s o in e es in he a chi ec
u e. Pa icula lyweha echosen he inpu o eacho
he p olyphase p o cesso s. The dynamic ange is always
sp ecied as
1
=
2
;
1
=
2.
−0.5 −0.4 −0.3 −0.2 −0.1 0 0.1 0.2 0.3 0.4 0.5
10
−4
10
−3
10
−2
10
−1
(1)
−0.5 −0.4 −0.3 −0.2 −0.1 0 0.1 0.2 0.3 0.4 0.5
10
−4
10
−3
10
−2
10
−1
(2)
(b)
(b)
(a)
(a)
Figu e 5
His og ams a and b a he ou pu o he s
1 and second 2 s ages. No e ha his og am b is mo e
sp ead han a as he numb e o indep enden ca ie s he
ein con ained is ou imes lowe han a. I is ad isable
o moni o he dynamics asso cia ed wi h b o keep a su
cien ly low clipping p obabili ywhileawillbep one o
g anula noise. No e also han in 2 his og am b is al eady
depa ing om he Gaussian shap e.
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
10
−3
10
−2
10
−1
10
0
10
1
10
2
10
3
(b)
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
10
−3
10
−2
10
−1
10
0
10
1
10
2
10
3
(a)
2.1 Mbps
Figu e 6
ab o e sp ec um o he b congu a ion and
b elow sp ec um o he a congu a ion. The equency
axis is no malized o he sampling equency o 44.64 MHz.
Ex ensi esimula ions ha e been un o ob ain he
wo dleng h assignmen o each p olyphase p ocesso
capable o mee ing he sp ecica ions. A 8bi analog o
digi al con e e ADC is used o IFsample he inpu
signal. Wo dleng hs passed b e ween p olyphase p o ces
so s a e limi ed o 8 bi s. The complexi yo each s age
is p esen edin able4ase alua ed om he VHDL syn
hesis p o cess. No e ha T ee 322 is mo e complex due
o mo e demanding compu a ional equi emen s. Fo
compa ison see gu es 2 and 2
5Conclusions
I has been shown ha linea signal p o cessing op e a
ions can be ecien ly syn hesized on o an in eg a ed
ci cui when he s a is ical dep endence be ween da a is
aken o ad an age in he design p o cess. The educ ion
in complexi ymus be aded o agains clipping p o
babili y. The e o e sa u a ing a i hme ics is necessa y
o a oid excessi e dis o ion.
Re e ences
1
J.Sala A. Pages J.Riba S.Cal o G. Vazquez
M.A.Rey. Algo i hms S udy and Simula ion Re
sul s. Rep o AEO001887 300697 submi ed
o he Eu op ean Space Agency unde con ac
ESAESTEC1209296NLUS.
2 J.P a A. Ro d guez F.O ega M.A.Rey.
Digi al A chi ec u al Design. Repo AEO
0018487 300697 submi ed o he Eu op ean
Space Agency unde con ac ESAESTEC
1209296NLUS.
3 F. O ega A. Ro d guez e al. An ad anced
Mul iCa ie Demo dula o o he ESA OBP Sys
em. P o ceedings o he Fi h ESA In e na io
nal Wo kshop on Digi al Signal P o cessing Tech
niques Applied o Space Communica ions.
4 J. Sala A. Pages S. Cal o J. P a . Design
and Implemen a ion o aDVB OnBoa d Mul i
Ca ie Demo dula o . P o ceedings o ICASSP98
COMM10.8.