CDMA Call Processing
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Transcript of CDMA Call Processing
CDMACALL PROCESSING
0 1 2 16 31
We have 32 Time slots for E1I,e TS 0 to TS 31Each slot having data rate of 64 Kbps.
PSTN
AM
CM
SM-2000E1
5ESS SWITCH
E1
D.L
ECPCOMPLEX
D.L
SS7
AM
CM
SM-2000 SM-2000 SM-2000
ATM
PSTN
CELL
ECPCOMPLEX
PSTN
IWF IFRPH
IBC
SVC CELL
555
SMPSTN
DLTU2
PSU 2PHV
0
16
PHV
16
0
FRPH
0
30
TSICELL SITE
DLTU 2
1
64
DFI
ECSU
TSI
PP
DATAFANOUT
VOCODER
PHV
PCM VOICE
CDMA PACKET
PACKET
BUS
PACKET HANDLER FOR VOICE
PHV 1: 8Kbps (9.6Kbps)PHV 2: 13Kbps(14.4Kbps)
PHV 3: Both 8Kbps & 13Kbps
100Mbps
A Data channel employs Radio Link Protocol(RLP), which enhances delivery of user dataacross air link by detecting missing user data and retransmitting it.
Mobile originated calls(Ckt-mode) : The mobile down loads its stored modem configuration in to the IWF.(Ex: Tel No. of PSTN-connected modem etc.)
SH
PHV
FRAMESELECTOR
FRPH PHA
ATM
PHA
TSI
SM X
CMAM
PSTN DFI DFI SITE
SM Y
CDN
CDNSS7
SS7
RPCN
CSN
CSN
IMS RING
DATA LINKS
RPCN :RING PERIPHERAL CONTROL NODE
Interconnects the ECP and IMS Ring.
CSN : Cell site Node Terminates up to 8 Cell site data links.
CDN : Call processing/data base node Performs many of the call processing functions.
PHV FRPH IFRPH
DFI
ISDNPRI
ISDNFRAMERELAY
IWF
CELL
PSTN
FRAMESELECTOR
DATACHANNEL
FOR DATA
PSTN TO IWF : ANALOG TONESIWF TO MOBILE : DIGITAL DATA
VSC
PHV PHV FRPH FRPH
DATA FAN OUT
PACKET BUS
PSU-2
DFI
DFI
DFI
DFI
DFI
DLTU
TSI
ECP CELL SITE
DCS
PSTN
PSTN TO MOBILE STATION
PCM VOICE(64kBPS)
SIGNALLING(DL-0 & DL 1)
VOICE PACKETS (In the form of DS0)
One P.P with PHV 1
One P.P with PHV 2
DS0 s (64Kbps)
2
3
4
5
6
7
8
6
30
26
22
18
14
10
22
19
16
13
10
7
4
PHV PHV FRPH FRPH
DATA FAN OUT
PACKET BUS
PSU-2
DFI
DFI
DFI
DFI
DFI
DLTU
TSI
ECP CELL SITE
DCS
DFILAT
CELL SITE
MOBILE STATION TO MOBILE STATIONCALL IN THE SAME SM
DFI
PHV3
FRPH
ChanlGroups
PSU 2
TSI DFIIn D L T U 2
12..89..1617..222425
23
8
10
PP
12
CSN
IMS
Acculink
1
8
1
32
DFIE1
1
24
DL -0
SWITCH SIDE CELL SIDE
DFI
CCC8
CCC10
CCC12
E1 MAPPING FOR 1st E1.
LN 00
DFI
PHV3
FRPH
ChanlGroups
PSU 2
TSI DFIIn D L T U 2
12..8
23
14
PP
CSN
IMS
Acculink
1
8
1
32
DFIE1
1
24
DL -1
SWITCH SIDE CELL SIDE
DFI
CCC14
E1 MAPPING FOR 2nd E1.
LN 32
DFI
PHV3
FRPH
ChanlGroups
PSU 2
TSI DFIIn D L T U 2
12..89..1617..24
25
31
20
22
PP
24
SWITCH SIDE CELL SIDE
DFI
CCC20
CCC22
CCC24
E1 MAPPING FOR 3rd E1.
16
CCC16
DFI
PHV3
FRPH
ChanlGroups
PSU 2
TSI DFIIn D L T U 2
12..89..1617..24
25
31
26
28
PP
30
SWITCH SIDE CELL SIDE
DFI
CCC26
CCC28
CCC30
E1 MAPPING FOR 4th E1.
18
CCC18
AM
CM
SM
PSTN
CELL SITE
SM SM
ACCULINK DACS
IMSDLN RPCN
ACDN CDN
SS 7 CSN
ECP
OMP
AUTO PACE
CELL SITE P.Ps
CELL SITE DATA LINKS(BX.25)
DCS
Dual X.25
DS1 0 or DL-0 or Ist E1
DS0 0 1-8 9-16 17-22 23 24-25 26-31SYNCP.P 8 10 12 NOT USEDDL 0 12
No. DS0s 1 8 8 6 1 2 6
DS1 1 or DL-1 or 2nd E1
DS0 0 1-8 9-22 23 24-31SYNCP.P 14 DL 1
No. DS0s 1 8 14 1 8
NOT USED NOT USED
P.P POSITION IN E1
DS1 2 or 3rd E1
DS0 0 1-8 9-16 17-24 25-31SYNCP.P 20 22 24 16
No. DS0s 1 8 8 8 7
DS1 3 or 4th E1
DS0 0 1-8 9-16 17-24 25-31SYNCP.P 26 28 30 18
No. DS0s 1 8 8 8 7
8DS 0s : 30 Calls7DS 0s : 26 Calls
CCC CCU1
CCU2
CCU3
ACU BCR
BIUBBA
TxRx0
Rx1
RCC
DFI
SCT
E1
RFTG
GPS ANTENNA
CDMA CLUSTER
CBUS
TDM BUS
19.66MHZ,2PPSGPS TIME
15MHZ,1PPSGPS TIME
CELL SITE
CCU : Performs the digital base band signal functions
BIU : Controls ACU,BCR and provides TDM bus to RCC
ACU : Converts the signals from one or two CCCs to Analog Base band signals.
BCR : Converts Analog base band signals from up to 3 ACUs to RF Signals. To antenna faces.
CCC8
CCC10
CCC12
ACU
ACU
ACU
BCR
BCR
BCR
BIU
BIU
BIU
DFIE1
E1
SCT RFTG GPSRECEIVER
GPS ANTENNA
TDM BUS
1.2Kbps
2.4Kbps
4.8Kbps
9.9Kbps
1.8Kbps
3.6Kbps
7.2Kbps
14.4Kbps
8Kbps VocodedSpeech data(20msec block)
13Kbps VocodedSpeech data(20msec block)
1/2Rate
3/4Rate
Interleaver
19.2Kbps
19.2Kbps
Encoder &Code repetition
Scrambling
Long CodeGenerator
Decimator
19.2Kbps
1.23Mbps
MUX
Pwr controlbit position
800bps
Power control Bits(800bps)
Walsh codeGenerator
64 Bits
I-Chl PilotPN offset
Q-Chl PilotPN offset
1.23Mbps
1.23Mbps
1.23Mbps
CALL PROCESSING IN CELL SITE
CDMA FRAME FORMATS
1 1719.6Kbps Frame
4.8Kbps Frame
2.4Kbps Frame
1.2Kbps Frame
12 8
1 79 88
1
1 15
39 8
8
: Mixed mode bit
: Information bits
: CRC(Cyclic redundancy check)
: Encoder tail bits.
Total Bits 1+171+12+8=192 Bits in 20ms Block
Total Bits 1+79+8+8=96 Bits in 20ms Block
Total Bits 1+39+8=48 Bits in 20ms Block
Total Bits 1+15+8=24 Bits in 20ms Block
20ms FRAMES
WALSH CODES REPRESENTATION IN CDMA BAND
23 54 49 28 8 60 59 56 41 24 20 2 25 16 40 30 16 46 9 15 13 32 14 48 21 64 7
1.25MHz
Walsh Code 0 : Pilot Channel
Walsh Code 1-7: Paging Channel
Walsh Code 32 : Sync Channel
Walsh Code 8-63: Forward Traffic channel except 32
CDMA Carrier
PILOT PN Sequence Offset 0
PILOT PN Sequence Offset 1
PILOT PN Sequence Offset X
PILOT PN Sequence Offset 510
PILOT PN Sequence Offset 512
FORWARD CDMA Chal
PILOT Chal PAGING Chal SYNC ChalTRAFFIC
ChalTRAFFIC
Chal
We have 4 channels
160 Chl No. 4201 Chl No. 3242 Chl No. 2283 Chl No. 1
Concerned Down link Frequencies for the above channels are
160 X 0.03 MHz + 870 MHz = 874.8 MHz
201 X 0.03 MHz + 870 MHz = 876.03 MHz
242 X 0.03 MHz + 870 MHz = 877.26 MHz
283 X 0.03 MHz + 870 MHz = 878.49 MHz
Each Band contains 41 ChannelEach Channel is 30 KHz or 0.03 MHzSo channel separation is 41 X 0.03 MHz = 1.23 MHz
Note: Down link is Base station to Mobile.
Concerned Up link Frequencies for the above channels are
160 X 0.03 MHz + 825 MHz = 829.8 MHz
201 X 0.03 MHz + 825 MHz = 831.03 MHz
242 X 0.03 MHz + 825 MHz = 832.26 MHz
283 X 0.03 MHz + 825 MHz = 833.49 MHz
Up link down link separation is 45 MHz.
Total down link bandwidth is 870 - 885 MHzand Up link bandwidth is 825 - 840 MHz
Note : Up link is Mobile to Base station.
140
160
180
181
201
221
222
242
262
263
283
303
Chl 4 Chl 3 Chl 2 Chl 1
139
131
304
312
GuardBand
GuardBand
41 FDMA Chls (1.23MHz)
U.L: 829.8MHzD.L: 874.8MHz
41 FDMA Chls (1.23MHz)
U.L: 831.03MHzD.L: 876.03MHz
41 FDMA Chls (1.23MHz)
41 FDMA Chls (1.23MHz)
9 Chls (0.27MHz)
U.L: 832.26MHzD.L: 877.26MHz
U.L: 833.49MHzD.L: 878.49MHz
9 Chls (0.27MHz)
NOTE : U.L :Up Link D.L : Down Link
Total B.W required for 4 Chals is 1.23 MHz x 4 = 4.92 MHzGuard Band 0.27 MHz x 2 = 0.54 MHz
= 5.46 MHz
FORWARD LINK CHANNEL FORMAT
PN SpreadingPN Spreading
PN SpreadingPN Spreading
PN SpreadingPN Spreading
PN SpreadingPN Spreading
D/A ConvertD/A Convert
D/A ConvertD/A Convert
D/A ConvertD/A Convert
D/A ConvertD/A Convert
PILOT Chal
SYNC Chal
PAGING Chals1 up to 7 Chals
TRAFFIC Chals1 up to 55 Chals
All 0’s
Walsh code 0
Walsh code 32
Walsh code 1 to 7
Walsh code 8-31,33-63
4.8Kbps
19.2Kbps
19.2Kbps
1.23Mbps
1.23Mbps
1.23Mbps
1.23Mbps
I
Q
I Data
Q Data
Q Data
Q Data
Q Data
I Data
I Data
I Data
CDMA REVERSE TRAFFIC CHANNEL
1.2Kbps
2.4Kbps
4.8Kbps
9.9Kbps
1.8Kbps
3.6Kbps
7.2Kbps
14.4Kbps
8Kbps VocodedSpeech data(20msec block)
13Kbps VocodedSpeech data(20msec block)
1/3Rate
1/2Rate
Interleaver
28.8Kbps
28.8Kbps
Encoder &Code repetition
Long CodeGenerator
1.23Mbps
IPN offset 0
307.2Kbps
Code 63
Code 62
Code 61
Code 1
Code 2
Code 0Q
PN offset 0
1.23Mbps
1.23Mbps
D/AConvert
D/AConvert
T/2
Q
I64-Ary Mod
64-ary Modulation
W 63=……………………..
W 0 =……………………..
W 1 =……………………..
64 Bits
W 2 =……………………..
101100110100111000010
Decimal value of Last 6 bits is 2. This will mapp in to Walsh code 2(Consistes 64 bits)
I/p Data rate is 28.8 Kbps
O/p Data rate is 28.8 Kbps x 64 bits
6 Bits = 307 Kbps
ADVANTAGES :
Different ratings of Coders.(When users assigned to CDMA carrier are not talking, all other on the same carrier benefit with less interference.)
Frequency reusage factor : 1
Low RF Power.
Multipath fading can avoid using rake receiver.
Soft hand off: A call to be carried by the two or six cells or sectorsat the same time.
Security : It is spread spectrum Technology.
Each OMNI Cell /Cell sector operating on CDMA carrier is identified by PN sequenceoffset. There are 512 Pilot PN sequences offsets (0 to 511) Forward chals on one CDMAcarriers.
Primary CDMA carrier is 283.
Each PN consists 64 Chips
PILOT PN sequence is Quadrature pair of identical PN binary codes operating at 1.23Mbpsfor F.W and Reverse CDMA Chals.
Each PN sequence is Maximum length binary sequence of :
512 Offsets X 64 Chips = 32768 in 26.7 msec.
Note: Forward CDMA Chal always contains one PILOT may be one SYNC may be seven PAGING up to 63 TRAFFIC Chanals
Number of Walsh codes : 64 (0 to 63)Each Walsh code contains 64 Bits. Long and operating 1.23Mbps
Walsh functions are orthonagal
0 : PILOT1 to 7 : Paging or Traffic32 : SYNCRemains Traffic.
All codes are Information Bearing Chals Except PILOT Chal consists 64 Zeros.
A Mobile initially acquires the CDMA system by searching and locking on to strongest PILOT Chal.
REVERSE CDMA CHANNEL
CDMA CARRIER
PN SequenceOffset 0
REVERSR CDMA Chal
ACCESSChal 1
ACCESSChal N
TRAFFICChal 1
TRAFFICChal N
REVERSE CDMA Chal is sum of all MS transmission on a CDMA Carrier.
N : Number of Mobiles currently accessing the CDMA system on the CDMA Carrier.
Common CDMA carrier(283) has its own PILOT,SYNC,PAGING and TRAFFIC channels.
FORWARD
Non common CDMA carriers(160,201,242) has own PILOT& TRAFFICChannels. It may or may not have sync and paging Chals.
For every paging Chal in Forward atleast on Access chal in reverse.
42 Bit Long code is for 1) Identify the traffic (Reverse) 2) Paging and Traffic chal scrambling.
Each code binary sequence of 4.4 Trillion (42 days)REVERSRECommon carrier has its own Paging & Traffic ChalsBit other carriers has its own Traffic chals but may or may not have ownAccess Chals.
Global Positioning System
The start of CDMA system time coincides with GPS time.(Jan 6,1980 00:00:00)
The present CDMA time is Number of seconds elapsed from the above time.
Cell Site
MS
MS
Cell Site
5micro Sec/mile 5micro Sec/mile
CDMA Call is processed by different stages Stage 1 : MSC : It is combination of DCS and ECP Complex
Stage II: Cell site
Here ECP complex consists ECP,IMS token ring and OMP
ECP is heart of heart of Call processing. It controls call processing in DCS via SS7 link and Cell site via Data links.
Each SM-2000 consists 1) Packet handler for Voice(PHV)
Each Packet Handler can have of 16 Vocoders(or Speech handlers(SH)) Each Vocoder process one call and it converts PCM 64Kbps to 9.6/14.4Kbps
packets or vice versa. Each SH will also have function of Frame selector, which selects best
frame(by CRC)in Softhandoff reverse call process.
2) PH4(FRPH) Each FRPH can handle 64 calls or 32 DS0s. Since our network Packet
Pipe(PP) consists 8DS0s(equal to 30 calls), each FRPH may handle two PPs
3) Packet Bus(100Mbps)
4) PHA(Packet handler for ATM) for SM to SM call processing.
In forward call processing E1 lands on SM/DLTU, which consists of DFI cards(up to 20)and ECSU.During data compression(By Vocoders) there will be some time delay. Because of this ECHO may
raise. To avoid ECHO, we have ECSU(Echo cancelled and signaling unit). The signaling information from E1 goes to ECP complex via DCS.
Now each Vocoder(SH) takes one 64Kbps PCM line and compress the data rate to PHV1(9.6Kbps) orPHV2(14.4Kbps) or PHV3(both 9.6 (EVRC)& 14.4Kbps) Packets, depends upon the rate set of
Vocoder
The vocoded data can be Full rate(9.6Kbps),Half rate(4.8Kbps),quarter rate(2.4Kbps) or 1/8th rate(1.2Kbps), depends upon the voice rate.
This CDMA packets from different Vocoders go to FRPH via Packet Bus(100Mbps). CDMA packetsfrom PHVs to FRPH (& from FRPH to PHVs) is Dynamic.
FRPH converts these packets in to Packet pipe.(We have 12 Packet pipes for each cell site. I.e. 8,10,12,14,16,18,20,22,24,26,28 and 30)
These Packet pipes are going to DLTU, where DFI mux the Packet pipes and Datalink(it is coming from Cell site node of IMS ring) and forms E1. For each cell site 4E1s are allotted.
Only Ist and 2nd E1 for each cell site requires Data links. D.L(Data link)-0 will go along with Ist E1 and D.L-1 go along with 2nd E1. 3rd and 4th E1s consists only PPs.
In the reverse link DFI extracts the D.Ls coming from Ist and 2nd E1s and sent to CSNs.and sends PPs to concerned FRPHs. Here PPs from FRPH to DFI is static. The particular
FRPH,DFI at SM in DCS is constant for particular cell site.
FRPH converts PPs to Packets and sends to PHV via packet bus, in case the call is to PSTN. The Frame selector selects good frame(20msec) in case the call is from more than one cell sites or sectors.
The Vocoder now decodes CDMA packets to 64Kbps PCM line.
In case the call is within DCS and with in same SM, then first CDMA packet from FRPH goes to PHVconverts to 64Kbps data, goes to DFI and loop back to again DFI(Called loop around trunk:LAT) and goes to PHV and converts to CDMA packet and goes to FRPH , and from there to concerned cell site.
In case the call is within DCS and different SM, then concerned CDMA packet to PHA and lands ondifferent PHA,which is located in different SM. The SM to SM connection is trough ATM.
ECP complex consists ECP,IMS Token ring and OMP. IMS ring nodes having protection byLink node 00(LN00) and and Link node 32(LN 32). Each Link Node consists 1) CSNs(Cell site Nodes)
2) CDNs(Call Processing & data base node) 3) SS7 node
4) RPCN(Ring peripheral and control node)
CSNs controls the cell site by Data links. Each cell CSN can have up to 8 D.Ls. LN00 CSN haveeight D.L-0s and LN32 CSN have eight D.L-1s. So one pair of CSNs will manage eight cell sites.
If sites are more than eight then we have to go for one more pair of CSNs.
SS7 Node in IMS ring control call process in DCS. The signaling information from PSTN will cometo IMS ring via this SS7 link. Both Link nodes in IMS ring has SS7 nodes for protection.
CDNs in IMS ring will do call processing.
RFCN will connect IMS ring to ECP. Even RFCN is duplicated for protection.
Now CSN will have eight D.Ls. These Data links are connected to ACCULINK, where it formsE1. Acculink even gets D.Ls from other CSN. This E1 is connected to DFI, which is available
in DLTU of SM.
DIFFRENCE BETWEEN DATA & VOICE CHANNELS
FRAME SELECTOR
FRAME SELECTOR
VOCODERDATA CHAL
PHV PHV
PACKET SWITCHING N.W(VOICE) CKT MODE DATA
(DATA)
For Voice PHV contains VOCODER with Frame selectorFor Data PHV contains DATA Channel with Frame selector.
One PHV can support three Data channels with reducing its any of its voice processing capacity.Service option 3 uses for EVRC(Bot rate sets)
Service option 4 : Asynchronous data service for Computer at CDMA NIU with rate set 1(9.6Kbps)This can connects with existing asynchronous modem in the PSTN. This requires IWF
A Data channel can support any circuit-mode data.
Service option 5: Asynchronous data access to fax for rate set-1. It can connect with Group-3 Fax in PSTN.
It requires IWF(Inter Working Function) & down loading radio link protocol(RLP) on to existing PHV boards.
Service option 6 : It is for sending “SHORT MESSAGE SWITCH(SMS)” to NIU.
Service option 12 : Asynchronous data service for Computer at CDMA NIU with rate set2(14.4Kbps)
Service option 13 : Asynchronous data access to fax for rate set-2. It can connect with Group-3 Fax in PSTN.
IWF provides protocol conversion between protocols carried over air interface and modemprotocols required for voice-band data in the PSTN path.
TIA STANDARDS
IS-95A : For Air-Interface Packet-switched service.(@ 800Mhz)IS-95B : For Air-Interface Packet-switched service.(@ 800Mhz & 1900Mhz)
IS-99 : CDMA Air interface for Ckt-mode data service with rate set-1IS-707 : CDMA Air interface for Ckt-mode data service with rate set-2
IS-658 : Defines interface between IWF & MSC
CSN to DFI uses BX.25
Mobile data path : Mobile to/from IWFAnalog Modem tones IWF to/from PSTN.
IWF supplied by 3-com communication corporation.
In case of Data channel the CDMA packet which is coming from P.P goes toPHV, it sends to IFRPH(ISDN FRPH), where it can handle 40 simultaneous Ckt-mode Data calls. Each Ckt-mode data call requires one SVC(Switched Virtual circuit) for on
an IFRPH for sending Data call to IWF. It converts to ISDN B Chal(IBC) and enters PSTN environment.
A Data channel employs Radio Link Protocol(RLP), which enhances delivery of user dataacross air link by detecting missing user data and retransmitting it.
Mobile originated calls(Ckt-mode) : The mobile down loads its stored modem configuration in to the IWF.(Ex: Tel No. of PSTN-connected modem etc.)
Each cell site caters 4 E1s. These E1s lands on DFI card in cell site and from there toBUS 0 and BUS 1(These two bus are connected to RCC(Radio control complex). Now
all the 12 CCC(In CDMA Cluster complex) are connected to BUS 0 and/or Bus 1. TDMBus supplies Clock,frequency and data to the each CCC. Now CCC extracts one Packetpipe from E1. So One packet pipe from FRPH in DCS will serve on one CCC in cell site.
We have three ECU's(Enhanced channel unit) for each CCC. CCC demux the Packetpipe and disassemble packets and sends to ECU. Now each ECU consists 10 Channel
elements. So one CCC can handle 30 Channel elements.(CE s)
CCC = 3 ECU's = 10 X 10 CE = 30 CE s
One CE in cell site is equal to one trunk(connects on vocoder/SH) in DCS.
In reverse Call processing packets coming from different CE s assemble and become Packet pipe(P.P) at CCC and mux in to E1 and goes to DCS via ADM.
CCU performs the Digital base band signal functions.
CE performs the Digital band signal processing for a single CDMA channel.In CE the packet which contains 9.6Kbps Data(Can be full rate,half rate,quarter
rate,1/8 rate depends upon vocoder data rating) will be doubled i ,e 19.2Kbpsand scramble with 42Bit register Long code. This PN code is users algorithm
A long code sequence is a PN sequence, operating at 1.23Mbps used to spread the access and reverse traffic channels and to scramble the paging and forward traffic channels. The long
code uniquely identifies access channels on the same CDMA carrier and uniquely identifies amobile station on both reverse and forward traffic channels.
Each Long code sequence is maximum length binary sequence repeats every 4.4 Trillion(Approx........ 42 days), this also called as long PN code. Where PN is pseudo Noise on CDMA carrier.
This 1.23Mbps long code decimated by 64 and gives 19.2Kbps and this will scramble the originaldata, so that the resultant data becomes coded data at the rate of 19.2Kbps. From the same Long
code for every 800 or for every 1.25msec bits one bit will be inserted( I ,e 1/800=1.25msec) into the data for increasing and decreasing the power depends upon the NIU requirement.
Tx power + Rx power = -75 dBm.
NIU will extract this bit from data for every 1.28msec and increases/decreases the power byone d B depends upon the bit one or zero.
The narrow band signals are associated with code channel are spread by specialized binary sequencecalled Walsh functions and then spread by the Pilot PN sequence operating at an signed time
offset. There are 64 different Walsh functions, 0 to 63, each 64 bits long and operating at1.2288Mbps. Code Channel 0 is spread by Walsh function zero, code channel 1 is spread by Walsh function 1,…
and code channel 63 is for Walsh function 63.
Code channel zero is assigned to the pilot channel. Code channels 1 through7 may be assigned to either the paging channels or the traffic channels. Code
Channel 32 may be assigned to either a sync channel or a traffic channel. The Remaining code channels may be assigned to traffic channels.All code
channels are information-bearing channels except the pilot channel. The pilot channel is un modulated by information and is assigned Walsh
function zero, which consists of 64 zeros. Thus, the pilot channel signal consists only of the pilot PN sequence operating at an assigned time offset.A mobile initially acquires the CDMA system by searching and locking onto
the strongest pilot channel, which typically corresponds to the nearest cell site. During a call, the mobile
distinguishes its particular signal by despreading the received data with a synchronized representation of the same Walsh function used to spread
the signal at the cell.
The primary carrier(Carrier 283 consists sync) and noncommon(160,201 242)carriers may or may not have sync and paging channels. The Walsh
functions, themselves, are aligned to the locally generated Pilot PN sequence.
Now this 1.23Mbps(19.2Kbps X 64 = 1.23Mbps wide spread) is divided in to I(Inphase) and Q(Quadrature phase) digital channels.
From GPS antenna We are getting GPS Clock one PPS(1 Hz)and GPS timingto GPS Antenna and it is generating 15 Mhz and 1PPS. This is going to RFTG
(Reference Frequency and Timing Generator). We have two Reference generatorsRG-0 and RG-1(Protection). This will give clock and frequency to SCT(Synchronised
clock and tone), where it gives 19.6608MHz and clock 2PPS(one pulse for twoseconds:0.5Hz) to TDM Bus. We have duplicated SCTs for protection for each Growth
Frame. Each Frame caters for six CCCs. This SCT output goes to CCC complex forcall processing. The start of CDMA system time coincides with of GPS time, Jan 6th,1980 00(Hr):00(Min):00(Sec)UTC(Universal time code). The present CDMA time is
number of seconds elapsed from the above time.Mobile receives time with SYNC Chal from the Base station.
Pilot PN sequence is getting time from GPS. We have time difference from place to place. By creating time offset one sector carrier to another sector carrier and from
one cell site to another cell site, even we use same carrier in all the three sectorscarrier interference will not happen. That is the reason why CDMA carrier reusage
factor is 1. We are maintaing sector to sector same carrie offset is 168.
Pilot PN sequence, which is Quadrature pair of identical PN binarycodes operating at 1.23Mbps for Forward and Reverse CDMA channels.Each sector(Alpha,Beta and gamma) transmits same PN sequence but
with different time offset.
We have 512 offset 0 to 511, each offset having 64 chips. So Maximum length of binary sequence is 32768 (512 offsets X 64 Chips) and repeats
every 26.7msec.
00
11
10
01
I
Q
PN SequenceOffset
I
Q
Example for one C.E Pilot PN offset coding
The Forward (Base station to Mobile) CDMA channel contains Pilot channel and may carry up to one Sync and up to seven paging and up to 63 traffic channels.
All code channel are information bearing channels except Pilot channel(Unmodulated by information) consists all 64 Zeros. A mobile initially acquires the
CDMA system by searching the strongest the PILOT channel.
Now In Radio Unit contains BBA trio(Base Band) which includes BIU(BusInterface Unit),ACU(Analog conversion unit) and BCR(Base band combiner &
Radio).
CCC
CCU
CCU
CCU
CE 0
CE 1
CE 9ACU
ACU converts all CE digital base band signals to single Analog Base band signal.BIU controls both ACU and BCR and also connected to TDM bus.
In BCR the Analog base band signal which is coming from particular ACUcup converts to required Radio Frequency(RF) and goes to concerned Sector.
Since each carrier serves 3 CCCs, BCR of a Alpha sector even connected to ACU of another BBA
Here for 283 carrier CCC 8,10,12 is connected. Like for carrier 160 CCC14,16,18and for carrier 242 CCC 20,22,24 and for carrier 201 CCC 26,28,30 are connected.
CCC 8 ACU BCR
CCC 10
CCC 12 ACU
ACU
BCR
BCR
Example on 283 Carrier
Alpha
Beta
Gamma
CDMA Overhead Channels and Overhead CEsCDMA overhead channels are the control channels used by a CDMA system to establish call setup prior to assigning the call to a traffic channel. There are four types of CDMA overhead
channels:1)Pilot channel The pilot channel is an unmodulated, direct-sequence spread-spectrum signal transmitted continuously by each sector of a CDMA cell. It allows the mobile to acquire the timing of the forward control channels and provides a coherent carrier phase reference for
demodulating the sync and paging channels.2)Sync channel The sync channel provides time-of-day and frame synchronization
to the mobile. The mobile uses this channel to acquire cell and sector-specific information.3)Paging channel The paging channel transmits control information to idle mobiles during mobile power-up and when a mobile is acquiring a new cell site. It conveys
pages to the mobiles.4)Access channel The access channel is a CDMA reverse channel used for short
signaling message exchange such as mobile registration, mobile call origination, and response to pages..In the Lucent Technologies CDMA system, a CE can be configured as an overhead channel or a traffic channel. There are three types
of overhead CEs: an overhead CE configured as the pilot/sync/access channel, known as the P/S/A CE, an overhead CE configured as a pilot only channel, known
as the pilot CE, and an overhead CE configured as the paging channel, known as the page CE.
In the reverse CDMA call, vocoded 20msec data(May be 9.6Kbps for Rate set-1) becomes 28.8Kbps by one third rate by code repetition & encoder. We have 64 Ary modulator, where
it 64 codes, and each code contains 64 bits. Ex W1,W2….W63. The decimal value of last 6bits in the Data, will decide which W code represents this data. For example the decimal
value of lst 6 bits for a frame is 000011, it is equivalent of decimal 3. So W 3 converts this bits its coded 64 bits. So for 28.8Kbps data 28.8Kbps X 64 Bits
6 BitsEqual to 307.8Kbps. With this data the users mask(Long code )which at the rate 1.23Mbps
will be mixing. The resultant data i.e. 1.23Mbps. This Data is again dividing in to I & Qchannels. Here with zero offset of Pilot PN sequence it will modulate the data. Unlike in
forward channel, here the Q channel will be delayed by T/2 for OQPSK modulation.