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WIRELESS LOCAL LOOP
AN OVERVIEW
Mian Ahmed YaserDE (Computer & Data Services)
Definition
• WLL is a system that connects the subscribers to the PSTN using radio system as a substitute for the copper for all or part of the connection between subscriber and switch.
Wireless local loop
• Replaces:– Traditional twisted pair
• Also called:– Fixed wireless access
WLL alternatives
• Narrowband– Replaces existing telephony services
• Broadband – Provides high speed two way voice and data
WHY WLL?
• Congested urban areas
• Far flung rural areas
• Fast installation
• Less maintenance
• Easy operation
• Less establishment problems
Role of WLL
• WLL services one or two cells• A cell has a base station antenna installed on
the top of a tall building or a tower• Customers’ antennas are installed atop their
houses or separate poles such that there is an unobstructed line of sight with the base station
• Base station is linked to the switching center wirelessly or wired
• An ISP is linked to the switch using a high speed link
Advantages of WLL1. Cost of installation and maintenance of WLL is lower
than cable network
2. Installation time is less in case of WLL
3. Selective installation: Installation for those who require connection at a certain time
4. Quality of wireless technologies have improved to nearly equal the contemporary wired options which do face problems like longer distances in xDSL and lack of infrastructure, so WLL offers tough competition
5. Cellular systems are too expensive with lesser signal quality than fixed broadband wireless which uses directional antennas
REQUIREMENTS FROM PTA
• Radio Frequency bands allocated by PTA– 1.9 GHz– 3.4 to 3.6 GHz– 450 MHz– 479 MHz
Radio Spectrum Band Information sheet 1.9 GHz
Spectrum Block size (Transmit + Receive)
MHz
Number of available blocks
Maximum blocks available per applicant and affiliates
One time fee per block upon lisencing by Region (US $ and Pak Rs)
Annual renewal fee per block per region (US $ and Pak Rs)
Roll out commitment in region
Rollout commitment compliance
5+5
1.25 x3+
1.25 x3
1890-1895
1970-1975
1 1 Area 1
Area 2
US $ 250,000 or Pk Rs. 14,500,000
US $75,000or
Pk Rs. 4,350,000
Area 1
Area 2
US $75,000or
Pk Rs. 4,350,000
US $ 25,000 or Pk Rs. 1,450,000
1.Atleast one base station that is in ongoing operational as part of licensee’s network
2. One or more base stations providing service to atleastt 5 customers
1. Initially by 18 months from effective date. 2. On an ongoing basis thereafter
1.9 GHz band
• 1880-1885 ; 1960-1965 MHz will be available if not used by CMTS– AREA 1
• Karachi, Lahore, Islamabad
– AREA 2• FTR, HTR, GTR, RTR, WTR, STR-I, STR-V, MTR,
NTR-I, NTR-II and CTR
Radio Spectrum Band Information sheet 3.4-3.6 GHz
Spectrum Block size (Transmit + Receive)
MHz
Number of available blocks
Maximum blocks available per applicant and affiliates
One time fee per block upon lisencing by Region (US $ and Pak Rs)
Annual renewal fee per block per region (US $ and Pak Rs)
Roll out commitment in region
Rollout commitment compliance
10.5+10.5
3.5 x21+
3.5 x21
Blocks located within
3410-3497.5
3510-3597.5
7 1 Area 1
Area 2
US $ 25,000 or Pk Rs. 1,450,000
US $10,000or
Pk Rs. 580,000
Area 1
Area 2
US $ 25,000 or Pk Rs. 1,450,000
US $10,000or
Pk Rs. 580,000
1.Atleast one base station that is in ongoing operational as part of licensee’s network
2. One or more base stations providing service to atleastt 5 customers
1. Initially by 18 months from effective date. 2. On an ongoing basis thereafter
– AREA 1• Karachi, Lahore, Islamabad
– AREA 2• FTR, HTR, GTR, RTR, WTR, STR-I, STR-V, MTR,
NTR-I, NTR-II and CTR
Radio Spectrum Band Information sheet 450 MHz
Spectrum Block size (Transmit + Receive)
MHz
Number of available blocks
Maximum blocks available per applicant and affiliates
One time fee per block upon lisencing by Region (US $ and Pak Rs)
Annual renewal fee per block per region (US $ and Pak Rs)
Roll out commitment in region
Rollout commitment compliance
5+5
1.25 x3+
1.25 x3
452.5-457.457;
462.5-467.457
1 1 Area 1
Area 2
US $ 75,000 or Pk Rs. 4,350,000
US $37,500or
Pk Rs. 2,175,000
Area 1
Area 2
US $50,000or
Pk Rs. 2,900,000
US $ 25,000 or Pk Rs. 1,450,000
1.Atleast one base station that is in ongoing operational as part of licensee’s network
2. One or more base stations providing service to atleastt 5 customers
1. Initially by 18 months from effective date. 2. On an ongoing basis thereafter
– AREA 1• Karachi, Lahore, Islamabad
– AREA 2• FTR, HTR, GTR, NTR-I,RTR
– AREA 3• WTR, STR-I, STR-V, MTR, NTR-II and CTR
– PTCL has been allocated 1.25 MHz band in this area 3, rest of the 3.75 MHz is available for new LL operators in area 3
– License fee given for area 2 will apply
Radio Spectrum Band Information sheet 479 MHz
Spectrum Block size (Transmit + Receive)
MHz
Number of available blocks
Maximum blocks available per applicant and affiliates
One time fee per block upon lisencing by Region (US $ and Pak Rs)
Annual renewal fee per block per region (US $ and Pak Rs)
Roll out commitment in region
Rollout commitment compliance
5+5
1.24 x3+
1.24 x3
479-483.48
489-493.48
1 1 Area 1
Area 2
US $ 75,000 or Pk Rs. 4,350,000
US $22,500or
Pk Rs. 1,305,000
Area 1
Area 2
US $50,000or
Pk Rs. 2,900,000
US $ 15,000 or Pk Rs. 870,000
1.Atleast one base station that is in ongoing operational as part of licensee’s network
2. One or more base stations providing service to atleastt 5 customers
1. Initially by 18 months from effective date. 2. On an ongoing basis thereafter
SPECIFICATIONS FROM PTCL
• Technologies and Standards Wing PTCL HQ
• No. T&S / TR-133B/03
• CDMA 2000 1x based on– TIA/EIA/IS-2000 standard– 3GPP2 standard– ITU-RM 1457 standard
Requirements of Specifications
• To Provide– Toll Quality Voice service– Wireless Pay Phone– Internet access
– Maximum rate of 144 Kbps and at least 30 Kbps packet mode data
– 14.4 Kbps of voice band data in circuit mode
Main Parts of the system
• MSC- Main Switching Center
• BSC- Base Station Controller
• BTS- Base Transceiver Station
• FWT (Fixed Wireless Terminal) or Mobile terminal
Frequency Spectrum
• Rural Areas– 450 MHz band i.e.
• 452.5-457.475 MHz :Uplink• 462.5-467.475 MHz :Downlink
– 1-3 RF carriers 1.25 MHz each
• Urban Areas – 1900 MHz band (If available) i.e.
• 1890-1895 MHz : Uplink• 1970- 1975 MHz: Downlink
– 1-4 RF carriers 1.25 MHz each
Standards
• Air Interface Standard– TIA/EIA/IS-2000
• Frame st. standard– TIA/EIA/IS-2000
Compatibility
• Backward Compatibility– IS-95
• Forward Compatibility– CDMA 2000 1x EV DO
• 2.4 Mbps Multimedia
Vocoders
• Codec (EVRC) (EIA/TIA ISO 127-2)
• 3GPP2 standard CS0014-0-2
• 13.4 Kbps QCELP (IS-733) vocoder
• SMV (Selective Multirate Vocoders)
– Dynamic allocation of Vocoders required – Should also be software configurable
Duplexing method
FDD/TDD
Frequency division duplex/Time division duplex
Traffic Capacity of system
• In Erlangs/sector/MHz for 1% GOS with 98% active voice calls and 2% active data calls at 144 Kbps to be specified by the vendor:
Traffic Capacity of a BSC
• Capacity of BSC for an average traffic of 0.05 Er./Subscriber and 1%GOS. BHCA/sub shall be 4.
Capacity of Base Station
• Minimum 110 Erlang /FA / 3 sectors assuming all Remote Stations are FWTs using voice only.
Coverage Radius of BTS
• 20 to 25 Km, extendable to double this value
BTS sensitivity
-125 dBm
BSC
• The BSC should adopt ATM or IP platform.
• Switching capability of BSC is in Gbps
Power Supply
• To BTS, BSC and MSC is
-48 V (-44 V - -56.4 V)
Requirements from FWT
• Voice supporting RJ-11 Interface
• Group 3 fax at RJ-11 Interface
• Voice band data upto 14.4.kbps in circuit mode
• 144 kbps data in packet mode
• Subscriber’s Call Charge Meter (Home Meter)
Requirements from Handheld terminal
• Voice
• Voice band data upto 14.4.kbps in circuit mode
• 144 kbps data in packet mode
• Extended antenna support
• SMS
• Address book
Generic Model of CDMA 2000 1x WLL
HLR
IWF
OMC-S
AAA
OMC-P
BTSRS
PDSN
BSC MSC
NMC
Core Network (CN)
Radio Network (RN)
OMC-R
Packet SwitchedCore Network(PCN)
Um
Abis
A10/A11
A1/A2
L
HLR
IWF
OMC-S
AAA
OMC-P
BTSRS
PDSN
BSC MSC
NMC
Core Network (CN)
Radio Network (RN)
OMC-R
Packet SwitchedCore Network(PCN)
Um
Abis
A10/A11
A1/A2
L
WLL solution by Huawei
CDMA 2000 1x WLL Huawei solution
• Basically this is a complete solution for a PLMN: Public local mobile network
• Only minor changes in the software can change this WLL network into a mobile system
Expected Network in Pakistan
• Islamabad: Centralized control
• Peshawar
• Lahore
• Quetta
• Karachi
• Multan
Equipment to be available at sites
• MSC: Mobile Switching center
• BSC : Base Station Controller
• BTS : Base Transceiver Station
• HLR/AuC : Home Location Register/ Authentication Center
Interfaces
• Between MSC and BSC: V 5.2
• Between BSC and BTS: E1
– No. of max. BTS that can be connected to a BSC: 14
– No. of BSC that can be connected to a MSC:
BSC Capabilty
• ATM broadband packet platform with switching capacity of 25Gbps
• Convenient to upgrade to 1x EV only by upgrading the software of BSS and adding 1x EV channel board to BTS;
Evolution to EV-DO
• Patent radio resource management algorithm
• Variable step length power control technique to improve receiving sensitivity and fulfill the performance requirements for future evolution to EV-DO
CDMA 2000 1x and EV-DO mixed Networking
CDMA IS-95 Standard
• Introduced in: 1993• Access Method: CDMA• Uplink band: 869 to 894 MHz• Downlink band: 824 to 849 MHz• Forward rev. spacing: 45 MHz• Channel Bandwidth: 1250 KHz• No. of duplex channels: 20• Max. power of mobile: 0.2 Watts• Users per channel: 35
CDMA IS-95 Standard (Contd.)
• Modulation: QPSK
• Carrier bit rate: 9.6 Kbps
• Speech coder: QCELP
• Speech coding bit rate: 8,4,2,1 Kbps
• Frame size : 20 m sec
• Error control coding: Convolutional1/2 rate forward; 1/3 rate reverse
Development of Mobile Communications
1st Generation 1980s (analog)
2nd Generation 1990s (digital)
3rd Generation current (digital)
3G provides: Complete integrated service solutions High bandwidth Unified air interface Best spectral efficiency and ……………… a step towards PCS
AMPS
Analog to DigitalTACS
NMT
OTHERS
GSM
CDMA IS95
TDMA IS-136
PDC
UMTS WCDMA
CDMA 2000
TD-SCDMA
Voice to Broadband
Transmission TechniquesTraffic channels: different users are assigned unique code and transmitted over the same frequency band, for example, WCDMA and CDMA2000
Traffic channels: different frequency bands are allocated to different users,for example, AMPS and TACS
Traffic channels: different time slots are allocated to different users, for example, DAMPS and GSM
FrequencyTime
Power
FrequencyTime
Power
FrequencyTime
Power
FDMA
TDMA
CDMA
User
User
User
User User
User
TDMA
Frequency
Time
Power
use
r
use
r
use
r
use
r
use
r
3G Objectives
3G is developed to achieve:• Universal frequency band for standard and seamless
global coverage • High spectral efficiency• High quality of service with complete security and
reliability• Easy and smoothly transition from 2G to 3G, compatible
with 2G• Provide multimedia services, with the rates:
– Vehicle environment: 144kbps– Walking environment: 384kbps– Indoor environment: 2Mbps
Standards for 3G
3G system
CDMA2000
3GPP2
FDD mode
WCDMA
3GPP
FDD mode
TD-SCDMA
CWTS
TDD mode
A Comparison b/w 3G standardsWCDMA CDMA2000 TD-SCDMA
Receiver type RAKE RAKE RAKE
Close loop power control Supported Supported Supported
Handoff Soft/hard handoff
Demodulation mode Coherent
Chip rate (Mcps) 3.84 N*1.2288 1.28
Transmission diversity mode
TSTD, STTDFBTD
OTD, STS No
Synchronizationmode
Asynchronous Synchronous Asynchronous
Core network GSM MAP ANSI-41 GSM MAP
CoherentCoherent
Soft/hard handoff Soft/hard handoff
Development of CDMA
IS95A 9.6kbps
IS95A 115.2kbps
CDMA2000 307.2kbps
Heavier voice service capacity ;
Longer period of standby time
CDMA2000 3X
CDMA2000 1X EV
1X EV-DO
1X EV-DV
1995 1998
20002003
• Higher spectrum efficiency and network
capacity
• Higher packet data rate and more diversified
services
• Smooth transit to 3G
CDMA2000 1X Network Structure
• MS: Mobile Station BTS: Base Transceiver Station• BSC: Base Station Controller MSC: Mobile Switching Center• HLR :Home Location Register VLR: Visitor Location Register• PCF: Packet data Control Function PDSN: Packet Data Service Node • HA: Home Agent FA: Foreign Agent • SCP: Service Control Point Radius: Remote Authentication Dial-in User Service
Abis
A1(Signaling)
A2(Traffic)
A11(Signaling)
A10(Traffic)
A3(Signaling &
Traffic)
A7(Singaling)
Correlation
(a)
(b)
+1
-1
+1
-1
+1
-1
+1
Correlation 100% so the functions are parallel
Correlation 0% so the functions are
orthogonal
Orthogonal Function
• Orthogonal functions have zero correlation. Two binary sequences are orthogonal if their “XOR” output contains equal number of 1’s and 0’s
0000
0101
0101
EXAMPLE:
1010
0101
1111
Information spreading over orthogonal codes
1 0 0 1 1
0110 0110 0110 0110 0110
1001 0110 0110 1001 1001
User Input
Orthogonal Sequence
Tx Data
+1
-1
+1
-1
Information recovery
1 0 0 1 1+1
-1
Rx Data 1001 0110 0110 1001 10010110 0110 0110 0110 01101111 0000 0000 1111 1111
Correct Function
? ? ? ? ?
Rx Data 1001 0110 0110 1001 10010101 0101 0101 0101 01011100 0011 0011 1100 1100
Incorrect Function
Spreading and De-spreading
information pulse interference White noise
The improvement of time-domain information rate means that the bandwidth of spectrum-domain
information is spread.
S(f) is the energy density.
f
S ( f)
The spectrum before spreading
information
f0
The spectrum before despreading
informationInterference/noise
S ( f)
f0 f f0
The spectrum after despreading
information
Interference/noise
S ( f)
f
The spectrum after spreading
information
f0
S ( f)
f
Signal flow
InterleavingSource coding
Convolution &Interleaving
Scrambling Spreading Modulation
RF transmission
Source decoding
deinterleavingDecovolution &Deinterleaving
Unscrambling De-spreading Demodulation RF receiving
Common Technical Terms
• Bit, Symbol, Chip:– A bit is the input data which contain information– A symbol is the output of the convolution, encoder, and the
block interleaving– A chip is the output of spreading
• Processing Gain:– Processing gain is the ratio of chip rate to the bit rate. – The processing gain in IS-95 system is 128, about 21dB.
• Forward direction: Information path from base station to mobile station
• Reverse direction: Information path from mobile station to base station
Source Coding
• Vocoder: – 8K QCELP– 13K QCELP– EVRC
• Characteristics– Support voice activity
In a typical duplex call, the duty ratio is less than 35%. To achieve
better capacity and low power consumption, base station reduces its
transmission power.
Channel Coding
Convolution code or TURBO code is used in channel encoding
Constraint length=shift register number+1.
Encoding efficiency= (total input bits / total output symbols)
convolution encoder
Input (bits)
Output (symbols)
Turbo Code
Turbo code is used during the transmission of large data packet.
• Characteristics of the Turbo code: – The input information is encoded twice and the
two output codes can exchange information with each other during decoding.
– The symbol is protected not only by the neighborhood check bits, but also by the separate Check Bits.
The performance of a Turbo code is superior to that of a convolution code.
Interleaving
The direction of the data stream
1 2 873 64 5
1 2 873 64 5
1 2 873 64 5
1 2 873 64 5
1 2 873 64 5
1 2 873 64 5
1 2 873 64 51 2 873 64 51 2 873 64 5
1 2 873 64 5
1 1 111 11 1
2 2222
7 7 777 77 7
6 6 666 66 6
3 3 333 33 3
4 4 444 44 4
1 2 873 64 51 2 873 64 55 5 555 55 5
8 8 888 88 8interleaving
2 2 2
Scrambling (M) sequence
Out
0 0 1
1 1 0
• Two points are important here: – Maximum number of shift register (N)– Mask
• The period of out put sequence is 2N-1 bits• Only sequence offset is change when the mask is
changed• PN stands for Pseudorandom Noise sequence
Long Code
• The long code is a PN sequence with period of 242-1chips
• The functions of a long code: – Scramble the forward CDMA channel– Control the insertion of power control bit– Spread the information on the reverse
CDMA channel to identify the mobile stations
Short Code
• Short code is a PN sequence with period of 215 chips– Sequence with different time offset is used to distinguish different
sectors
– Minimum PN sequence offset used is 64 chips, that is, 512 PN offsets are available to identify the CDMA sectors (215/64=512).
PNa
PNc
PNb
Walsh Code
W2n=Wn Wn
Wn Wn
W1=0
W2= 0 0
0 1
W4 =
0 00 1
0 00 1
0 00 1
Walsh code
64-order Walsh function is used as a spreading function and each Walsh code is orthogonal to other.
Walsh Code is one kind of orthogonal code.
A Walsh can be presented by Wim where ith (row) is the
position and m is the order. For example, W24 means 0101
code in W4 matrix
1 11 0
Walsh Code
• In forward direction, each symbol is spread with Walsh code
• Walsh code is used to distinguish the user in forward link
• For IS95A/B, in the reverse, every 6 symbols correspond to one Walsh code. For example, if the symbol input is 110011,the output after spreading is W51
64 (110011=51).
• For CDMA2000, in the reverse, Walsh function is used to define the type of channel (RC 3-9)
Variable Walsh codes
64
48
16
32
12
9600 19200 38400 76800 153600 307200 614400
Data rate -bps-
W01 =0
W02 =00
W12 =01
W04 =0000
W24 =0011
W14 =0101
W34 =0110
W08 =00000000
W48 =00001111
W28 =00110011
W68 =00111100
W18 =01010101
W58 =01011010
W38 =01100110
W78 =01101001
( W016 ,W8
16)
( W416 ,W12
16 )
( W216 ,W14
16 )
( W616 ,W14
16 )
( W116 ,W9
16 )
( W516 ,W13
16 )
( W316 ,W11
16 )
( W716 ,W15
16 )
The different Walsh codes corresponding to different data rates
Modulation-QPSK
I
Q
I channel PN sequence1.2288Mcps
Q channel PN sequence
1.2288Mcps
Baseband filter
Baseband filter
Cos(2pfct)
Sin(2pfct)
I(t)
Q(t)
s(t)A
1.2288Mcps: the PN chip rate of the system.
After being spread, all the forward channels in the same carrier are
modulated by means of QPSK(OQPSK in the reverse), converted
into simulation signals and transmitted after clustering.
CDMA mobile parameters
Power Control Handoff Diversity and RAKE
Power Control
• Reverse power control– Open loop power control– Closed loop power control
• Inner loop power control: 800 Hz• Outer loop power control
• Forward power control– Message transmission mode:
• threshold transmission• periodic transmission
– Closed loop power control
Reverse Open Loop Power Control• The transmission power required by the mobile station is determined by
the following factors:
Distance from the base station
Load of the cell
Circumstance of the code channels
• The transmission power of the mobile station is relative to its received
power.
BTSMobile
Reverse Open LoopPower Control
BTS
BTS
Transmitting Power
Reverse Closed Loop Power Control
BTS
Power Control Bit
Eb/Nt Value FER Value
Inner Loop Power Control
Outer Loop Power Control
Change in Eb/Nt Value
BSC
BTS
Forward Power Control
MS measures the frame quality and informs the base station to the result i.e. whether it is in the threshold or periodical mode. Base station determines whether to change the forward transmitting power or not.
In IS-95 system, the forward power control is slow but in CDMA2000 system it is fast.
Message Transmission Mode
Forward Closed Loop Power Control
•Compared with IS-95 system,
CDMA2000 the forward quick
power control is fast.Power Control Bit
Eb/Nt Value
BTS
Handoff
• Soft handoff–It is a process of establishing a link with a target sector before breaking the link with the serving sector
• Softer handoff–Like the soft handoff, but the handoff is occurred between multi-sectors in the same base station
• Hard handoff–Hard handoff occurs when the two sectors are not synchronized or are not on the same frequency. Interruption in voice or data communication occurs but this interruption does not effect the user communication
Soft/Softer Handoff• Multi-path combination in the BSC during soft handoff
• Multi-path combination in the BTS during softer handoffs
Combine all the power from each
sector
Power received from a single sector
Pilot Set
ActiveSet
CandidateSet
NeighborSet
Remaining Set
The pilot set, corresponding to the base station being connected
The pilot set, not in the active set but potential to be demodulated
Other pilot sets
the set of the pilots having same frequency but different PN sequence offset
T_ADD,T_DROP,T_TDROP
Time
Ec/Io
Sector A Sector
B
Guard Time(T-TDROP)
Add Threshold (T_ADD)
DropThreshold (T_DROP)
Soft Handoff Region
T_ADD, T_DROP and T_TDROP affect the percentage of MS in handoff.
T_ADD & T_DROP is the standards used to add or drop a pilot.
T_DROP is a timer.
Comparison Threshold
Pilot P1
Pilot P2
t0
T_COMP×0.5dB
t1 t2
T_ADD
P0-Strengh of Pilot P0 in Candidate Set.
P1,P2-Stength of Pilot P1,P2 in Active Set.
t0-Pilot strength Measurement Message Sent, P0>T_ADD
t1-Pilot strength Measurement Message Sent, P0>P1+T_COMP*0.5dB
t2 -Pilot strength Measurement Message Sent, P0>P2+T_COMP*0.5dB
Transition Between Pilot Sets
T_ADD
T_DROP
Pilot 1
Pilot strength
Pilot 2
T_TDROP
T_TDROP
NeighborSet
CandidateSet
ActiveSet
CandidateSet
NeighborSet
TIME1 2 3 4 5 6 7 8
Transmit Diversity
• Time diversity– Block interleaving, error-correction
• Frequency diversity– The CDMA signal energy is distributed on the whole
1.23MHZ bandwidth.
• Space diversity– The introduction of twin receive antennas .– The RAKE receivers of the mobile station and the base
station can combine the signals of different time delay.– During a handoff, the mobile station contacts multiple base
stations and searches for the strongest frame
Transmission Diversity
• The forward transmission diversity types in CDMA2000 1X are– TD (Transmit Diversity)
• OTD (Orthogonal Transmit Diversity)– The data stream is divided into two parts, which will
be spread by the orthogonal code sequence, and transmitted by two antennas.
• STS (Space Time Spreading)– All the forward code channels are transmitted by the
multi-antennas.– Spread with the quasi-orthogonal code
–Non-TD
Transmission DiversityTransmission Diversity
The Transmission Diversity Technology enhances the receive performance of MS.
Transmission diversity
processing
Data stream 1
Data stream 2
Data stream Restoring data stream
Path 1
Path 2
Antenna 2
Antenna 1
The Principle of RAKE Receiver
RAKE antennas help to overcome on the multi-path fading and enhance
the receive performance of the system
Receive set
Correlator 1
Correlator 2
Correlator 3
Searcher correlator Calculate the time delay and signal strength
Combiner The combined signal
tt
s(t) s(t)
A typical CDMA Network
MS BS MSC
HLRAC
EIR
VLR
PSTN
ISDN
MC
Um A
BC
D
E
H
Ai
Di
MSC
F
VLR
MCSMESME
GN
MMM
Q
SCPSCP SSP
Ai
T1T8
IP HLR IP ISDNDi
T2T3T5
T9
CDMA Interfaces
MSC: Mobile-service Switching Center BSC: Base Station ControllerMC: Short Message Center HLR: Home Location RegisterBTS: Base Transceiver Station VM: Voice MailboxVLR: Visitor Location Register OMC: Operation & Maintenance Center AC: Authentication Center SCP: Service Control Point
MSC: Mobile-service Switching Center BSC: Base Station ControllerMC: Short Message Center HLR: Home Location RegisterBTS: Base Transceiver Station VM: Voice MailboxVLR: Visitor Location Register OMC: Operation & Maintenance Center AC: Authentication Center SCP: Service Control Point
Other MSCs
MC/VM
MSC/SSP/VLR
OMC
HLR/AC
SDH
GMSC/SSP
SCP
STP
IOS4.0
SS7
IS-41
IS-41
IS-41
IS-41
Mobile Customer Service Center
SS7
TCP/IP
SS7IS-41
BTS
BTS
BSC
MSINTERNET
Other PLMNs
PSTN/ISDN
Network InterfaceMSC/VLR GMSC
HLR/AuC
PDSN
PSTN
GPRS IP骨干网
SS7
SCPBSS
HA
A1/A2
BSSAP
SCCP
MTP
Physical layer
IP backbon
e network
A10/A11
A11 signaling
UDP
IP
Link layer
Physical layer
A10 service
GRE
IP
Link layer
Physical layer
CN
CDMA Services
Businesses, enterprises•Mobile virtual private network•Mobile high-speed network access•Advertising services•Free phone
Family•Familiarity number•Life & amusement
Schools, groups•Universal account number•Sectorized and time-shared charge•Broadcast news
Individuals•Individualized services•Privacy
CDMA2000---Data Services
0
32
64
9.6
128
144
384
2,000 Video StreamingVideo Streaming
VoiceVoice
Text Text MessagingMessaging
Still ImagingStill Imaging
Audio StreamingAudio Streaming
Electronic newspaper
High-quality videoconference
Telephone (Voice)
Voice Mail
E-MailFax
Electronic book
Sports, news and weather report on
demand
Singing room
Low-quality videoconference
JPEG Still Photos
Mobile Radio
Video Surveillance,Video Mail, Travel
Image
Data
Weather, transportation, news, sports and securities
Mobile TV
E-commerce
RemoteMedical Service
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Locating Services
3GPP2 uses the following 3 standards for MS location:
• GPS-aided measurement
– Accuracy: suburbs---10m.
City zone---30~70m.
Indoor --unable to locate
– Response time: 3~10s
• Measurement of base station pilot phase
– Accuracy: 50~200m
– Response time: 3~6s
• Locating of a cell ID
– Accuracy: depends on the size of a cell
– Response time: within 3s
Locating Services
110! Bandit!
• The system transfers the alarm to the nearest alarm processing center based on the location.
• An emergency button can be set on a user’s mobile phone to so that an alarm can be reported without any conversation or delay.
Review
• Chips rate: 1.2288Mcps• IS-95A/B is a subset, RC1/RC2 • Apply the coherent demodulation to the reverse pilot channel• Forward transmit diversity: OTD and STS• Forward quick power control at 800HZ rate• Improve the standby time by introducing the quick paging
channel.• Variable frames: 5ms, 20ms, 40ms and 80ms• Introduce TURBO code into channel encoding• The maximum rate of a physical layer is up to 307.2K
A Simple CDMA 1X BSS Network
PSTNMSC
PDSN
Abis A10/A11
A1/A2
A3/A7
BSC
PCF
A8/A9Um
CDMA2000 1X BSS
MS
MS
BTS
BTS
BTS
BTS
BTS
BTS
BSC
Description of Interfaces
• Um interface carries all signaling & services between MS and
BTS over radio links.
• Abis interface carries signaling & services between BTS and
BSC.
• A1 interface carries call control signaling between MSC and
BSC.
• A2 interface provides 64kbit/s PCM speech channels between
MSC and BSC.
• A3 interface has two functions: Signaling and traffic. A3
signaling is used to control and allocate the transmission
channels for user traffic.
Description of Interfaces
• A7 interface carries signaling between source BSC and
target BSC.
• A8 interface carries user traffic between BSC and PCF.
• A9 interface carries signaling between BSC and PCF.
• A10 interface carries user traffic between PCF and PDSN.
• A11 interface caries signaling between PCF and PDSN.
A CDMA Network
BTS: Base Transceiver Station MSC: Mobile Switching Center
BSC: Base Station Controller PDSN: Packet Data Service Node
PCF: Packet data Control Function MS: Mobile Station
Rack Distribution in BSC
Large capacity BSC is divided into following functional blocks. In
general each block corresponds to single subrack. These are:
• CDMA Switch Subrack (CSWS)• CDMA Integrated Processing Subrack (CIPS) • CDMA Resource and Packet Subrack (CRPS) • CDMA Packet Module Subrack (CPMS)• CLocK processing Module (CLKM)• CDMA Integrated Management System (CIMS)
Rack DistributionTo/from MSC
To / from PDSN
Optical fiber
To / from NMSLAN
E1
GE
Ethernet
Optical fiber
Optical fiber
CIPS
CIMS
CPMS
CRPS
CSWS
CLKM
To / from PDSNGE
Configuration for 120,000 Subscribers
• BHCA: 240k• Voice traffic volume: 2,400Erl• Um interface: 54,000TCE (traffic channel element)• A-interface: 38400CIC,1280E1• Abis interface: 960E1
•3840 Sector Carriers•1,200k Voice Subscribers(0.02Erl/sub)•70,000 PPP connections•5,000 active PPP connections•Total flow of packet data: 200Mbps
CCTR (CDMA Controller Rack)
CBUR (CDMA BUsiness Rack)
Overview
Power distribution box
Cabling Through
Air guide subrackFan box
Cable trough
Air guide subrack
Fan boxCable trough
Keyboard
Dummy panel
Lanswitch
Dummy Panel
CLKM
Lanswitch
BAM Server
BAM ServerBAM Server
LCD
CSWS
CRPS/CRMS
CLKM
Cabling though
Dummy panel
Air guide subrackFan box
Cable trough
Power distribution box
Fan boxCable trough
Fan boxCable trough
Air guide subrack
CIPS/CPMS
CIPS/CPMS
CIPS/CPMS
A Wireless Network
BTS3612 Cabinet & Functional Distribution
BC IM
BC IM
BCPM
BCPM
BCPM
BCPM
BCPM
BCPM
BRDM
BRDM
BCKM
BCKM
BRDM
BRDM
BCPM
BCPM
BCPM
BCPM
BCPM
BCPM
BRDM
BRDM
Fan box 1 Fan box 2
Power distribution room
PSU
BHPA
BTRM
RLDU
CDU
PSU
PSU
PSU
PSU
RLDU RLDU
BHPA
BTRM
BHPA
BTRM
BHPA
BTRM
BHPA
BTRM
BHPA
BTRM
BHPA
BTRM
BHPA
BTRM
BHPA
BTRM
BHPA
BTRM
BHPA
BTRM
BHPA
BTRM
CDU/DFU CDU/DFUCDU CDU/DFU CDU
RF subrack
CDU/RLDU subrack
Fan subrack
Baseband subrack
RF subrack
Power subrack
Interface Protocol Stack
Abis signaling
TCP/IP
IPOA
AAL5
ATM
OML signaling
TCP/IP
IPOA
AAL5
ATM
Abis traffic
AAL2
ATM
Abis signaling OML signalingAbis traffic
IS-2000.2
Um
Command line
TELNET
802.3
MMI command
Introduction
• BTS antenna & feeder subsystem consists of two parts:
RF antenna & feeder, and dual-satellite synchronization
antenna & feeder.
• RF antenna & feeder transmits the modulated RF signals
and receives MS signals, while the dual-satellite
synchronization antenna & feeder provides precise
synchronization for CDMA system.
RF Antenna &Feeder
Inner cable
TX/RXMA
NT
RXD
CDU/DFU
Sect
or ¦A
Sect
or¦A
Sect
or¦A
Antenna
Feeder
Jumper
Jumper
BTS cabinet
Dual-satellite Synchronization Antenna & Feeder
Note: BTS3612 receiver is provided by CLK on BCKM.
Inner cable
Receiver on BCKM
GPS/GLONASS receiving antenna
Feeder
Jumper
BTS3612 cabinet
Jumper
Lighting arrester
Lighting arrester
Lighting arrester
Resource Pool 、 Carrier 、 Sector and Frequency
Resource Pool1
BTRM0 BTRM1 BTRM2 BTRM3
BTRM4 BTRM5 BTRM6 BTRM7
BTRM8 BTRM9 BTRM10 BTRM11
SECTOR0
SECTOR1
SECTOR2
CARRIER1 CARRIER2 CARRIER 3 CARRIER 4
BTS3612
Resource Pool2
Resource Pool3
Resource Pool4
Configuration SchemeCabinet Configuration Scheme-01 or S1Cabinet Configuration Scheme-01 or S1
CDU/DFU
RLDURLDU RLDU
BHPA
BTRX
CDU/DFU
PSU
PSU
PSU
PSU
PSU
PSU
F A N F A N
Baseband frame
BHPA
BTRX
BHPA
BTRX
BHPA
BTRX
BHPA
BTRX
BHPA
BTRX
BHPA
BTRX
BHPA
BTRX
BHPA
BTRX
BHPA
BTRX
BHPA
BHPA
BHPA
BTRM
BHPA
BTRX
CDU/DFU
CDU/DFU
CDU/DFU
CDU/DFU
CDU/DFU
• 1HPA + 1BTRM• 1 DFU/CDU/DDU• 1RLDU• PSU 1+1 standby
Configuration Scheme
CDU/DFU
RLDU
BHPA
BTRX
CDU/DFU
PSU
PSU
PSU
PSU
PSU
PSU
F A N F A N
Baseband frame
BHPA
BTRX
BHPA
BTRX
BHPA
BTRX
BHPA
BTRX
BHPA
BTRX
BHPA
BTRX
BHPA
BTRX
BHPA
BHPA
BHPA
BTRM
BHPA
BTRX
CDU/DFU
CDU/DFU
CDU/DFU
CDU/DFU
BHPA
BHPA
BHPA
BTRM
BHPA
BHPA
BHPA
BTRM
RLDURLDU RLDU
Cabinet Configuration Scheme- S111Cabinet Configuration Scheme- S111
• 3HPA + 3BTRM• 3CDU/DFU/DDU• 3RLDU• PSU1+1 standby
Sector 0 Sector 1 Sector 2
Configuration SchemeCabinet Configuration Scheme-S222Cabinet Configuration Scheme-S222
• 6HPA+6BTRM
• 3CDU/DDU• 3RLDU• PSU
2+1backupCDU/DFU
RLDU
BHPA
BTRX
CDU/DFU
PSU
PSU
PSU
PSU
PSU
PSU
F A N F A N
Baseband frame
BHPA
BTRX
BHPA
BTRX
BHPA
BHPA
BHPA
BTRM
CDU/DFU
CDU/DFU
CDU/DFU
CDU/DFU
BHPA
BHPA
BHPA
BTRM
BHPA
BHPA
BHPA
BTRM
RLDURLDU RLDU
BHPA
BTRX
BHPA
BTRX
BHPA
BTRX
BHPA
BHPA
BHPA
BTRM
BHPA
BHPA
BHPA
BTRM
BHPA
BHPA
BHPA
BTRM
Product Performance (1)
• Abis interface– Use the IMA technique and support the E1 interface (16E1s)– Support the E1 mode in SDH– Support ATM over SDH (compatible interface)
• The traffic and control bus adopt CELLBUS.– Switching bus– AAL2 transports the traffic data and AAL5 transports the signaling data– Bus clock is 25MHz
• External interfaces include:– RS485 power monitoring interface– RS485 interface to support the environment monitoring– External time reference interfaces (RS485 and RS232)– 10MHz, PP2S interfaces used for instrument testing
Product Performance (2)
Built-in GPS and GLONASS receiver
Built-in testing functions Perfect heat dissipation: upper and lower ducts
Product Performance (3)Technical Features of Power Supply subrackTechnical Features of Power Supply subrack
• Input voltage: -48V• Output voltage: +25V ± 0.5V ~ +29V±0.5V• Power modules: 1800W each module 9000W in
total• Power efficiency: 85%• Heat dissipation: upper and lower grid with fans• Hot swappable• Provides RS485 monitoring interfaces
Product Performance (4)
Technical Features of RF ModuleTechnical Features of RF Module
•Modular architecture•Each cabinet supports 12 antennas and 6-sectors application•BTRM supports the digital intermediate frequency technology•BTRM offers the fiber interface to support remote RF module•BTRM supports receiving and transmitting diversities•Each sub-module fulfills the blind mate•Provides the power monitoring RS485 interface which is used for remote RF modules
Product Performance (5)Technical Features of RF ModuleTechnical Features of RF Module
• RF front end adopts the CDU/DFU+RLDU mode
• Each cabinet supports 6 sectors
• Each sector supports the 4FA/2 antenna and space receiving
diversity
• Supports the transmitting diversity
• HPA and BTRM modules with fans follows the combination
structure with front and rear ducts
• Front cabling makes installation and maintenance convenient
Product Performance (6)
Thermal Design of Integrated EquipmentThermal Design of Integrated Equipment
•The dissipation power of the integrated equipment is about 7000W.•Thermal design of large power module.•Front/rear duct and independent duct.•The distribution structure is adopted to reduce the heat generation density at certain point.•Holes at both the front and rear doors for ventilation.•The small power modules adopt upper and lower ducts to reduce the number of cascades.•Automatic speed controller to regulate the fans speed.
Frequency bands
• 15 frequency bands allocated by FCC
• 2 GHz-40 GHz i.e. higher than cellular systems
i.e. millimeter wave frequencies
Freq (GHz) Usage
2.15-2.162 Licensed MDS and MMDS, two bands 6MHz each
2.4-2.483 Unlicensed ISM
2.596-2.644 Licensed MMDS, eight bands of 6MHz each
2.65-2.656 Licensed MMDS
2.662-2.668 Licensed MMDS
2.674-2.68 Licensed MMDS
5.725-5.875 Unlicensed ISM-UNII
24-24.25 Unlicensed ISM
24.25-25.25 Licensed
27.5-28.35 Licensed LMDS (Block A)
29.1-29.25 Licensed LMDS (Block A)
31-31.075 Licensed LMDS (Block B)
31.075-31.225 Licensed LMDS (Block A)
31.225-31.3 Licensed LMDS (Block B)
38.6-40.0 Licensed
Propagation considerations
• Millimeter wave range used is defined as frequencies above 10 GHz up to 300 GHz
• Because:– Availability of wide unused frequency bands
above 25 GHz– Wide channel bandwidths available for high
data rates at higher frequencies– Small size transceivers with adaptive
antennas can be used
Disadvantages of millimeter range
• Free space loss increases with the square of frequency
• Attenuation due to rainfall and atmospheric absorption is significant after 10 GHz
• Multi-path losses are high because:
Because:
• Reflection occurs when an EM signal encounters a surface larger relative to the wavelength of the signal
• Scattering occurs if the size of obstacle is of the order of the wavelength of the signal
• Diffraction occurs if wave front encounters the edge of the obstacle that is large compared to wavelength
Fresnel zone
• Space around the direct path between transmitter and receiver that should be clear of obstacles
• Basis:– Any small element of space in the path of EM
wave may be considered as the source of a secondary wavelet. Radiated field is build up by superposition of these wavelets
Fresnel zone (contd.)
• Objects lying within a series of concentric circles around the direct line of sight between two transceivers have constructive or destructive effects on communication
• Objects falling in the first circle have the most negative effect
Fresnel zone (contd.)
R= λSD√ S+D
S=Distance from transmitterD=Distance from receiver λ=Wavelength of signal
S,R and D are in same units
or
Rm =17.3 SkmDkm
√ fGHz(Skm+Dkm)
S and D are distances in Km,R is in metersf is in Giga Hertz
Attenuation due to Fresnel zone is negligible if :
• Obstruction does not lie within 0.6 times the radius of first Fresnel
zone
ATMOSPHERIC ABSORPTION
• Molecular absorption significant above 10 GHz• Peak of water vapor absorption at 22 GHz• Oxygen absorption peak is at 60 GHz• So, favorable window is in between 28-42 GHz
with attenuation of the order of 0.13dB/km• Another favorable window is between 75 GHz-
95 GHz with attenuation of the order of 0.4dB/km
Effect of rain
• Rain severely degrades the performance of communication links
• It out-weighs all other factors• Depends upon drop shape, size, rain rate and
frequencyA=aRb
R= rate of rain
A=attenuation measured in dB/km
a & b depend upon distribution of drop sizes and frequency
Temperature dependency of air absorption at 28 GHz
0% 50% 100%
00 0.02 0.05 0.08
100 0.02 0.08 0.14
200 0.02 0.12 0.25
300 0.02 0.2 0.44
400 0.01 0.33 0.79
Relative humidity
Temp (0C)
Values of a and b for horizontal and vertically polarized EM waves
Freq(GHz) ah av bh bv
1 .0000387 .0000352 0.912 0.880
2 0.000154 .000138 0.963 0.923
6 0.00175 0.00155 1.308 1.265
10 0.0101 0.00887 1.276 1.264
20 0.0751 0.0691 1.099 1.065
30 0.187 0.167 1.021 1.000
40 0.350 0.310 0.939 0.929
50 0.536 0.479 0.873 0.868
Effect of vegitation
• Trees can cause multipath fading due to diffraction and scattering
• Attenuation of:– Regularly planted orchards is 12-20dB– Deciduous trees up to 40dBs– Conifer trees 1 to 3dBs
• If foliage lies within 60% of first fresnel zone
Presence of trees does not preclude communication,
• So methods like forward error correction should be employed
WLL SYSTEM TECHNOLOGIES
1. ANALOG CELLULAR
2. DIGITAL CELLULAR
3. PERSONAL COMMUNCATIONS SERVICES / NETWORK (PCS/PCN)
4. DIGITAL CORDLESS SYSTEMS
5. PROPRIETARY IMPLEMENTATIONS
1. Analog Cellular
• Three of its system types operating in the world, AMPS and NAMPS with 69% of
subscribers, while TACS has 23% and NMT has only 8%.
• These systems use conventional FM on either 25 or 30 kHz channels in 800 or
900MHz mobile bands. Most recently AMPS operate in 1800-2000MHz band.
• Best suited to serve low or medium density markets, with long range up to 70km, with
fixed units having high gain antennas.
• Narrow band analog transmission results in low speed.
• Since the access method is FDMA, the subscriber unit cannot support more than one
line per radio tranceiver.
• Relatively low capacity in terms of number of channels.
AMPS Parameters
• Base Station Transmission band
• Mobile unit transmission band
• Spacing between forward and reverse channels
• Channel bandwidth
• Number of full duplex voice channels
• Mobile unit maximum power
• Cell size, radius
• Modulation voice channel
• Modulation, control channel
• Data transmission rate
• Error control coding
• 869 to 894 MHz
• 824 to 849 MHz
• 45 MHz
• 30 KHz
• 790
• 3 watts
• 2 to 20 Km
• FM, 12 KHz peak deviation
• FSK, 8 KHz peak deviation
• 10 Kbps
• BCH (48,36,5) and (40,28,5)
2. Digital Cellular
• Major worldwide digital cellular standards include GSM, D-AMPS (American) & GSM/DCS
(European), TDMA and CDMA.
• It is forecasted that approximately one-third of the installed WLL will use digital cellular
technology in the year 2000. • Digital cellular can support higher capacity and better functionality than analog cellular and
wireline networks.
• Digital cellular systems are encrypted and provide high speech security with no impact on quality.
• Both DAMPS and GSM use TDMA and support multiple lines from a single subscriber unit.
• Some of these systems has general confusion over industry standards.
• GSM currently dominates mobile cellular industry, but there has been little activity in using GSM
as a WLL platform.
TDMA and Point to Multipoint Systems
• These System are relatively well suited for rural use, because they provides
service coverage over a wide area.
• TDMA standards are IS-54 and IS-136, triples the capacity of cellular
frequencies, by dividing a 30 kHz cellular channel into 3 timeslots.
• Proven and reliable technology.
• Designed to support subscribers in sparsely populated rural areas.
• A typical base station has 30 or 60 traffic channels and could support 256 to
1800 residential subscribers respectively.
• Relatively long range (over 70km) but requires a line-of-sight path between
RBS and all subscriber units.
Digital Cellular GSM IS-136 IS-95
Year Introduced 1990 1991 1993
Access Method TDMA TDMA CDMA
Base Station Transmission band 935 to 960 869 to 894 869 to 894
Mobile Station Transmission band 890 to 915 824 to 849 824 to 849
Spacing between forward and rev. 45 MHz 45 MHz 45 MHz
Channel bandwidth 200 KHz 30 KHz 1250 KHz
Number of duplex channels 125 832 20
Mobile unit maximum power 20 W 3 W 0.2 W
Users per channel 8 3 35
Modulation GMSK Pi/4 DQPSK QPSK
Carrier bit rate 270.8 Kbps 48.6 Kbps 9.6 Kbps
Speech coder RPE-LTP VSELP QCELP
Speech coding bit rate 13 Kbps 8 Kbps 8,4,2,1 K
Frame size 4.6 ms 40 ms 20 ms
Error control coding Conv 1/2 Conv 1/2 Conv 1/2f,1/3r
CDMA (Code Division Multiple Access)
• CDMA is a "spread spectrum" technology, it spreads the information contained in a particular signal over a much greater bandwidth than the original signal.
• A CDMA call starts with a standard rate of 9.6kb/s. This is then spread to a transmitted rate of about 1.23 Mb/s.
• It offers 3-6 times more capacity than the other digital standards and 10-15 times greater than analog cellular.
• Improved spectral efficiency in a multi-cell environment - mainly due to interferer diversity.
• Flexible cell sizes and service provisions - for a given data rate, range is increased as traffic density is reduced.
• Speech delay can be minimized - fast power control tracks and minimize fading.
• Multi-path fading is reduced due to inherent frequency diversity, which is common in mountainous terrain and dense urban areas.
• CDMA-WLL based on new US cdma-One (IS-95) standard is presently used.
3. Personal Communications Services/ Network (PCS/PCN)
• PCS starts to operate in the 1800 MHz frequency band. PCS/PCN incorporates
elements of digital cellular and cordless standards as well as newly developed RF
protocols.
• Its purpose is to offer low-mobility wireless service using low-power antennas.
• The main weakness of PCS/PCN is that it is not yet commercially available.
• The candidate standards are CDMA, TDMA, GSM, personal access communication
systems (PACS), Personal handyphone system (PHS), and digital cordless telephone
United States (DCT-U).
• PHS technology and terminal equipment reduces the WLL system cost as it uses
32kb/s ADPCM voice coding system.
• PHS-WLL system is superior in terms of speech quality and economy for urban and
suburban applications. It also offers extensibility to mobile service in the future.
4. Digital Cordless Systems
• CT2 (Cordless telephone 2nd generation) and DECT (Digital Enhanced / European
cordless telephone systems are its types.
• CT2 provides the user with a single 32kb/s duplex channel, but it has not been
universally adopted.
DECT• DECT is a picocellular wireless system for very dense subscriber environments
where demand per km is high and cell coverage area is not a critical requirement.
• DECT supports ISDN services and also comprehensive security provisions including
authentication and encryption.
• The DECT radio interface is based on TDMA technology. It operates over 10 radio
carriers in the 1880 to 1900 MHz band. • It uses dynamic channel selection, an automated frequency-planning mechanism,
which provides least interference from neighboring cells.
Comparison of DECT and PWT
• DECT• 20 MHz bandwidth• 1.88 to 1.9 GHz band• TDD/TDMA/FDMA• 1.728 MHZ carrier
bandwidth• 10 number of carriers• 12 channels per carrier• Number of channels,120• Transmitted data rate:
1.152Mbps• Speech rate:32 Kbps
• PWT• 20 MHz bandwidth• 1.91 to 1.92GHz band• TDD/TDMA/FDMA• 1.25 MHz
• 8• 12• 120• 1.152
• 32 Kbps
Comparison of DECT and PWT
• Speech coding: ADPCM
• Modulation: Gaussian FSK
• Peak output power: 250 mW
• Maximum cell radius: 30 to 100 meters
• ADPCM
• Pi/4 DQPSK
• 90 mW
• 30 to 100 meters
DECT
• System has frequency reuse limitations, so the maximum number of voice channels
available for a single cell site in a multi-cell environment is 60.
• DECT system transmits at low power using low antenna heights.
• DECT does not appear to be ideally suited for long range rural or low-density
applications.
• Its normal range is 3-5 Km with a capacity up to 100,000 subscribers per km2.
• As compared to cellular technology, DECT is capable of carrying higher levels of
traffic and data.
• The micro-cell architecture of DECT allows it to be deployed in smaller increments
that more closely match the subscriber demand, with reduced initial capital
requirements.
5. Proprietary Implementations
• These systems are considered proprietary because they are not available
on public wireless networks and are typically customized for a specific
application.
• They generally do not provide mobility, and are most effective in terms of
time and cost. • Proprietary systems like broadband CDMA and fixed radio access are
designed from vendors like Interdigital, Ionica and NORTEL. Equipment
providers include corporate giants such as Motorola, Ericsson, Lucent,
Siemens, NEC, Qualcomm and Hughes Network Systems as well as many
other smaller companies
OFDM
• Orthogonal frequency division multiplexing
• Also called Multi carrier modulation
• Sending some of the bits on each channel
• All sub channels are dedicated to a single data source
Suppose we have:
• Data stream operating at R bps
• Available bandwidth is N∆f centered at f0
• Entire bandwidth used to send data stream for which each bit duration is 1/R
• Alternatively split the data stream to N sub-streams using serial to parallel converter
• Each sub-stream has a data rate of R/N bps transmitted on a separate carrier
• Spacing between individual sub-carriers is ∆f
• Now the bit duration is N/R
Advantages of OFDM:
• Frequency selective fading only affects a few channels and not the whole signal so it can be easily handled by forward error correction techniques
• OFDM can handle Inter-symbol interference in multipath environment– ISI is more effective at higher bit rates as the distance
between the bits is smaller– OFDM reduces the data rate by a factor of N thus
symbol period increases by the factor N so effect of ISI is reduced
– So equalizers do not remain essential
Modulation scheme for OFDM
• QPSK– There are two bits representing one symbol
MMDS
• Multichannel multipoint Distribution service• Occupies 6 MHz made up of 512
individual carriers with carrier saparation of 12 kHz
• Data transmitted in bursts• Cyclic prefix attached to each burst to
reduce transients from previous bursts caused by multipath
MMDS (contd.)
• 64 symbols constitute cyclic prefix • Followed by 512 QPSK symbols per burst• So on each sub-channel, QPSK symbols are
separated by a prefix of duration 64/512 symbol times
• By the time prefix is over, the resulting waveform is independent of the previous burst
• So ISI is nil
MMDS contd.
• Frequency range 2.15 GHz to 2.68 GHz– 2.15-2.162 and 2.4-2.4835 GHz bands called
Multipoint distribution service for 6MHz TV broadcast.
– In 1996 FCC increased the allocation up to 2.68 GHz for MMDS
– MMDS is used to provide TV service where broadcast TV or cable can not reach in rural areas
– So, MMDS is also called wireless cable
MMDS contd.
• Range: 50km
• MMDS also used for two-way broad band data services and Internet access
Disadvantages of MMDS
• Lesser bandwidth than LMDS• Data rates:
– 27 Mbps for up-stream per channel– 300kbps to 3 Mbps individual subscriber rates
Used by residential or small business customers
Advantages of MMDS over LMDS
• Larger wavelengths i.e.10cm or more, so travel farther, so larger cells
• Less expensive equipment than LMDS• Signals more susceptible to rain
absorption• Signals do not get easily blocked by
objects
LMDS
• Local Multipoint Distribution service
• TV and two way broadband communication
• Millimeter frequencies
• At 30 GHz in USA and 40 GHz in Europe
Advantages of LMDS
• High data rates i.e. in Mbps
• Capability of video, telephony and data
• Lower cost than cable alternatives
Disadvantage
• SHORT RANGE
Antenna coverage
• 600 to 900 coverage sector so 4 to 6 antennas required for full coverage
• Typical radius of 2 to 4 km• Per customer data rates:
– 1 Mbps upstream– 36 Mbps down stream
• Buildings, trees and foliage affect the communication too much so overlapping cells or the use of repeaters and reflectors is required
FIXED WIRELESS BROADBAND ACCESS
• STANDARD
– IEEE 802.16
• Working group developed in 1999
CHARTER OF IEEE 802.16
• Use of microwave or millimeter wave radio for wireless links
• Use of licensed spectrum• Standards of metropolitan scale• Provide public network service to fee paying
customers• Point to multipoint architecture for roof top or
tower mounted antennas• Efficient transport of heterogeneous traffic with
QoS• Broad band capability i.e. >2 Mbps
IEEE 802.16 working groups
• IEEE 802.16.1:• Air Interface for 10 to 66 GHz
• IEEE 802.16.2:• Co-existance of Broadband wireless access
systems
• IEEE 802.16.3:• Air Interface for licensed frequencies 2 GHz to 11
GHz