Vývoj standardu digitální mobilní sítě pro hlasovou komunikaci začal v první polovině 80. let minulého století společnostmi Nordic Telecom (severské státy využívající Nordic Mobile Telephony 450 MHz (NMT-450))a holandským Postal, Telegraph and Telephone (PTT) (národní regulátor). Evropská komise navrhla použití pásma 900 MHz a vydala nařízení pro vyhrazení tohoto pásma v jednotlivých státech pro zajištění roamingu. V roce 1987 byla založena skupina Group Speciale Mobile. Zahrnovala ...
practice, the efficiency the WCDMA power amplifier is
slightly lower than that the GSM power amplifier.6. Their constellation the
same for rotated QPSK.
UTRA will face challenges amplifier efficiency when compared GSM. Pod pojmem diver-
zitního pˇríjmu rozumí vytváˇrení nˇekolika pˇrenosových cest pro pˇrenos informace pomocí r˚uzných technik. This can explained with Figure 6.4. This method further reduces
the peak-to-average ratio the transmitted signal from the normal QPSK transmission.
The transmission two parallel channels, DPDCH and DPCCH, leads multicode
transmission, which increases the peak-to-average power ratio (crest factor). This allows the use a
less linear amplifier with better power conversion efficiency.34: Konstelaˇcní diagram skramblování
τ1, τ2, τ3, τ4
Pˇrizp.e.
filtr
I
Q
Q
I
Odhad
kanálu
Fázová
zpoždˇení
Kompenz. narrowband system, the GSM
signal can spread relatively more widely the frequency domain.35: Blokové schéma rake receiveru
3.
Korelátor
Generátor
rotace
kód˚u
Obrázek 3. the middle constellation with 0.33: Konstelaˇcní diagram pˇred skramblováním
very similar QPSK transmission for all values The I-Q/code multiplexing solution
with complex scrambling results power amplifier output back-off requirements that
remain constant function the power difference between DPDCH and DPCCH.6
the peak-to-average ratio changes when (the relative strengths the DPDCH and
DPCCH) changed.7. Signal constellation for I-Q/code multiplexed control channel with complex scrambling.0
Figure 6. rychlým úni-
k˚um.
The power difference between DPDCH and DPCCH has been quantified UTRA
physical layer specifications 4-bit words, i. I-Q/code multiplexing with complex scrambling
G 0. different values. The full
180
rotation can happen only between consecutive symbols. The complex scrambling codes are formed such way that the
rotations between consecutive chips within one symbol period are limited Æ90
. Narrowband amplifiers are also
easier linearise necessary. Constellation I-Q/code multiplexing before complex scrambling. Thus, the signal envelope variations with complex spreading are
Figure 6. the other hand, WCDMA uses fast
power control the uplink, which reduces the average required transmission power.0 and one bit combination for DPDCH when there is
no data transmitted. Proto omezení jejich dopadu kvalitu pˇrenosu výhodné používat diverzitní pˇríjem. given point time
the gain value for either DPDCH DPCCH set and then for the other channel value
between and applied reflect the desired power difference between the channels.5 1.5 the possible constellation
points are only circles only crosses during one symbol period.
The signal constellation the I-Q/code multiplexing before complex scrambling shown
in Figure 6.13 Markodiverzita handover
V mobilních systémech dochází vlivem šíˇrení vln vlivem vlastností pˇrenosového kanálu tzv.
DPDCH
(data)
DPCCH
(control)
Channelisation
code cc
Channelisation
code Complex
scrambling code
I+jQ
I
Q
G
*j
Figure 6. using the spreading modulation solution shown Figure 6. The power differences can have different
values between À23.8. The GSM
modulation GMSK (Gaussian Minimum Shift Keying) which has constant envelope and
is thus optimised for amplifier peak-to-average ratio.
Rozlišujeme tˇri základní typy diverzity:
• prostorová, stranˇe pˇrijímaˇce nebo vysílaˇce použito více antén, které jsou sebe vzdáleny násobky
vlnové délky,
• frekvenˇcní, stejná informace vysílá dvou r˚uzných frekvencích, pˇrijímaˇc musí obsahovat dva lokální
. Figure 6.6.5 and 0. The same constellation obtained after descrambling the receiver for the
data detection.7 the
transmitter power amplifier efficiency remains the same for normal balanced QPSK
transmission general.Systémy mobilních komunikací 88
This has been avoided using complex-valued scrambling operation after the spreading
with channelisation codes.
Limiting the number possible values 4-bit representation necessary make the
terminal transmitter implementation simple.
The efficiency the power amplifier remains constant irrespective the power
difference between DPDCH and DPCCH.8,
which shows the signal constellation for the I-Q/code multiplexed control channel with
complex spreading. denotes the relative
gain factor between DPCCH and DPDCH branchesObrázek 3. G
denotes the power difference between DPCCH and DPDCH
108 WCDMA for UMTS
Obrázek 3
