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 ...
13 Markodiverzita handover
V mobilních systémech dochází vlivem šíˇrení vln vlivem vlastností pˇrenosového kanálu tzv. Thus, the signal envelope variations with complex spreading are
Figure 6.5 1.6.
The efficiency the power amplifier remains constant irrespective the power
difference between DPDCH and DPCCH. The GSM
modulation GMSK (Gaussian Minimum Shift Keying) which has constant envelope and
is thus optimised for amplifier peak-to-average ratio. the other hand, WCDMA uses fast
power control the uplink, which reduces the average required transmission power. Pod pojmem diver-
zitního pˇríjmu rozumí vytváˇrení nˇekolika pˇrenosových cest pro pˇrenos informace pomocí r˚uzných technik. G
denotes the power difference between DPCCH and DPDCH
108 WCDMA for UMTS
Obrázek 3. This method further reduces
the peak-to-average ratio the transmitted signal from the normal QPSK transmission. I-Q/code multiplexing with complex scrambling
G 0.Systémy mobilních komunikací 88
This has been avoided using complex-valued scrambling operation after the spreading
with channelisation codes. Their constellation the
same for rotated QPSK.0 and one bit combination for DPDCH when there is
no data transmitted.
The signal constellation the I-Q/code multiplexing before complex scrambling shown
in Figure 6.
filtr
I
Q
Q
I
Odhad
kanálu
Fázová
zpoždˇení
Kompenz. denotes the relative
gain factor between DPCCH and DPDCH branchesObrázek 3.34: Konstelaˇcní diagram skramblování
τ1, τ2, τ3, τ4
Pˇrizp.
Limiting the number possible values 4-bit representation necessary make the
terminal transmitter implementation simple.7.33: 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.5 and 0.5 the possible constellation
points are only circles only crosses during one symbol period.
The power difference between DPDCH and DPCCH has been quantified UTRA
physical layer specifications 4-bit words, i.7 the
transmitter power amplifier efficiency remains the same for normal balanced QPSK
transmission general.8.0
Figure 6.
DPDCH
(data)
DPCCH
(control)
Channelisation
code cc
Channelisation
code Complex
scrambling code
I+jQ
I
Q
G
*j
Figure 6.e. different values.8,
which shows the signal constellation for the I-Q/code multiplexed control channel with
complex spreading.4. practice, the efficiency the WCDMA power amplifier is
slightly lower than that the GSM power amplifier.6. Narrowband amplifiers are also
easier linearise necessary.
Korelátor
Generátor
rotace
kód˚u
Obrázek 3. The full
180
rotation can happen only between consecutive symbols. The power differences can have different
values between À23.
UTRA will face challenges amplifier efficiency when compared GSM. The complex scrambling codes are formed such way that the
rotations between consecutive chips within one symbol period are limited Æ90
. narrowband system, the GSM
signal can spread relatively more widely the frequency domain. Figure 6. This can explained with Figure 6.
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
.
The transmission two parallel channels, DPDCH and DPCCH, leads multicode
transmission, which increases the peak-to-average power ratio (crest factor). The same constellation obtained after descrambling the receiver for the
data detection. the middle constellation with 0. 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. rychlým úni-
k˚um. using the spreading modulation solution shown Figure 6. Signal constellation for I-Q/code multiplexed control channel with complex scrambling.35: Blokové schéma rake receiveru
3. Constellation I-Q/code multiplexing before complex scrambling. This allows the use a
less linear amplifier with better power conversion efficiency.6
the peak-to-average ratio changes when (the relative strengths the DPDCH and
DPCCH) changed. Proto omezení jejich dopadu kvalitu pˇrenosu výhodné používat diverzitní pˇríjem
