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Public Mobile Radio Systems
GSM-an overview
GSM System Architecture
PSTN
Data Terminal
HLR/VLR
MSCBSC
OMC(Operation & Maintenance
Center)
OperationTerminal
BTS
HandsetA
X.25
A-bis SS7
Network sub-system PSTNRadiosub-system
Mobilestation
UM
SIMcard
Mobile System network
• Two Components– Fixed Installed Infrastructure (network)– Mobile Subscribers (who uses the services of
network)
Fixed Installed Infrastructure (network)
• Divided into subnets known as subsystems
1. Radio Networks
2. Mobile switching network
3. Management Network
Subsystems
Radio Networks
Base Station
Subsystems
(BSS)
Mobile switching networkSwitching and Management
Subsystem (SMSS)
Management NetworkOperation and Management
Subsystems (OMSS)
GSM Network Elements
• Handset• BTS: Base Transceiver Station
• MSC: Mobile Switching Center
• BSC: Base Station Controller
• HLR/VLR: Home Location Register/Visiting Location Register
• SIM Card: Subscriber Identity Module Card
Subsystem-BSS
• BSS-two components1. Base Station Controller (BSC)
2. Base Transceiver Station/Base Station (BTS/BS).
BSS- BTS
• BTS-provides interface– Mobile’s interface to the network– A BTS is usually located in the centre of a cell.– The BTS provides the radio channels for
signaling and user data traffic in the cells.– A BS has between 1 and 16 transceivers, each
of which represents a separate radio frequency channel
BSS- BTS
• BSC-Controller– frequency administration– control of the BTS– The BSC also translates the 13 kbps voice
channel used over the radio link to the standard 64 kbps channel used by the Public Switched Telephone Network or ISDN
• Connected to MSC
Mobile switching network
• MSN consists of – Mobile Switching Centres (MSC) and
– Databases, which store the data required for routing and service provisions (HLR, VLR)
• Responsibilities– In addition to switching it also provides all the
functionality needed to handle a mobile subscriber, such as registration, authentication, location updating, handovers, and call routing to a roaming subscriber
MSC
• Gateway MSC (GMSC)– This passes voice traffic between fixed
networks and mobile networks– GMSC requests the routing information from
the Home Location Register (HLR) and routes the connection to the local MSC in whose area the mobile station is currently staying
Databases
• Home Location Register (HLR)– Stores the identity and user data of all
subscribers belonging to the area of the related GMSC
– Permanent data such as the International Mobile Subscriber Identity (IMSI). permitted supplementary service
– Temporary data such as address of the current VLR
Databases-VLR
• Visitor Location Register (VLR)– Stores the data of all MS’s that are currently
staying in the administrative area of the associated MSC
Mobile Handset (MH)
• Used by the subscriber to access the GSM network via the air interface
• Contains the hardware and software specific to the radio interface
• Need a Subscriber Identity Module (SIM) which contains the subscriber-specific data to access GSM network, except emergency call
Subscriber Identity Module (SIM)
• Subscriber Identity Module– Contains
• phone number (MSISDN)
• international mobile subscriber identity (IMSI)
• status of SIM
• service code
• authentication key
• PIN (personal identification code)
• PUK (personal unlock code)
GSM Frame Structure
3 57 26 57 8.251 1 3
0 7
...
...Superframe6.12 sec
120 msec
4.615 msec
0.57692 msec156.25 bits
51 Multiframe
26 Frames
8 Multiframe
Coded data Midamble
Tail bit Stealing Flag Guard period
• There are two types of multiframe– 26 TDMA-frame multiframe is used to carry
TCH, SACCH and FACCH(TCH0-11,13-24)SACCH12,25,NO DATA
– 51 TDMA-frame multiframe is used to carry BCCH, SCH,FCCH,AGCH,RACH
– FCCH IS ALWAYS IN 0,10,20,30,40 SCH IS IN 1,11,21,31,AND 41 AND BCCH 2-5
– PAGCH AND RACH according to load
Frame Types
Burst• The information contained in one time slot is a
burst• Five types of burst
– Normal Burst (NB)• To carry information on traffic and control channels
– Frequency Correction Burst (FB)• To synchronize the frequency of the mobile
– Synchronization Burst (SB)• To synchronize the frames of the mobile
– Access Burst (AB)• For random and handover access
– Dummy Burst• For padding the frame
GSM Frame Structure Per Channel
3 57 26 57 8.251 1 3
0 74.615 msec
0.57692 msec156.25 bits
8 Multiframe or bursts
Coded data Training
Tail bit Flag Speech/data Or Signaling Guard period
Channels
• Physical Channels– Associated with frequency bands, time slots, codes
– Physical channels transfer bits from one network element to another
• Logical Channels– Distinguished by the nature of carried information and the
way to assemble bits into data units
– Three types• one-to-one: traffic channels between a BTS and a MS• one-to-many: synchronization signals from BTS to MSs in a cell• many-to-one: from MSs to the same BTS
Trafficchannels(TCH)
Signalingchannel
TCH/F: Full-rate Traffic Channel
TCH/H: Half-rate Traffic Channel
FCCH: Frequency correction
SCH: Synchronization
BCCH: Broadcast control
PCH: Paging
AGCH: Access grant
RACH: Random access
SDCCH: Stand-alone dedicated control
SACCH: Slow associated control
FACCH: Fast associated control
Two-way
Base-to-mobile
Two-way
Logical Channel List
BCH
CCCH
DCCH
Logical Channels
• Control Channels– Broadcast Channels (BCH)– Common Control Channels (CCCH)– Dedicated Control Channels (DCCH)
• Traffic Channels (TCH)– Full Rate (TCH/F)– Half Rate (TCH/H)
UP / Down-Link
• Down-link: the transmission path from Base Station to Mobile Station
• Up-link: the transmission path from Mobile Station to Base Station
Control Channels• Broadcast Channels (BCH)
– Frequency Correction Channel (FCCH)– Synchronization Channel (SCH)– Broadcast Control Channel (BCCH)
• Common Control Channels (CCCH)– Paging Channel (PCH)– Random Access Channel (RACH)– Access Grant Channel (AGCH)
• Dedicated Control Channels (DCCH)– Stand alone Dedicated Control Channel (SDCCH)– Cell Broadcast Channel (CBCH)– Slow Associated Control Channel (SACCH)– Fast Associated Control Channel (FACCH)
Broadcast Channels (BCH)
• To help the MS (Mobile Station) measures– to listen for the cell information
• to start roaming, waiting for calls to arrive, making calls
– Because BTSs are not synchronized with each other, every time a MH decides to camp to another cell, its FCCH, SCH, and BCCH must be read.
Frequency Correction Channel (FCCH)
• Provide MS with the frequency reference of the system– To enable the Mobile Handset (MH) to
synchronize with the frequency
• Transmission properties– Transmit on the down-link– Point to multi-point.
Synchronization Channel (SCH)• MS synchronize with the structure within the
locative cell– MS can receive information from the proper time slots
on the TDMA structure
• Transmission properties– Transmit on down-link– Point to multi-point.
Broadcast Control Channel (BCCH)
• BTS broadcast cell information to MS– LAI ( Location Area Identity), to start roaming,
waiting for calls to arrive, making calls– maximum output power allowed in the cell– information about BCCH carriers for the
neighboring cells• Transmission properties
– Transmit on down-link– Point to multi-point
Common Control Channels (CCCH)
• CCCH support the establishment of a dedicated communication path (dedicated channel) between the MS and the BTS
• Three types of CCCH– Paging Channel (PCH)– Random Access Channel (RACH)– Access Grant Channel (AGCH)
Paging Channel (PCH)• Used by BTS to page particular MS in the cell
– MH actively listen to PCH to check contact info within certain time
– Contact could be incoming call or short message
• Contact info on PCH include– IMSI (MH’s identity number), or– TMSI (temporary number)
• Transmission properties– Transmit on down-link– point to point
Random Access Channel (RACH)
• Used by MS to request a dedicated channel for call setup– Shared by any MS attempts to access the
network– Channel request message contains the reason
for the access attempt
• Transmission properties– Transmit on up-link– Point to pint.
Access Grant Channel (AGCH)
• The network assigns a signaling channel via AGCH– A Stand alone Dedicated Control Channel
(SDCCH) is assigned
• Transmission properties– Transmit on down-link– Point to point
Dedicated Control Channels (DCCH)
• DCCH are used for transferring nonuser information between the network and the MS Messages on DCCH Including
• channel maintenance• mobility management• radio resource management
• Three kinds of DCCH– Stand alone Dedicated Control Channel (SDCCH)– Slow Associated Control Channel (SACCH)– Fast Associated Control Channel (FACCH)
Stand alone Dedicated Control Channel (SDCCH)
• Transfer signaling information between the BTS and the MS
• Typically used for location updating prior to use of a traffic channel
• Transmission properties– Bi-directional channel, transmit on both up and
down-link– Point to point.
Slow Associated Control Channel (SACCH)
• Carries control and measurement parameters along with routine data necessary to maintain a radio link between the MS and the BTS– On the uplink, MS sends averaged measurements
(signal strength and quality) of current and neighboring BCCH
– On downlink, MS receives information about transmitting power to use and an instruction with time advance/retard
• Transmission properties– Bidirection channel, transmit on both up and down link– Point to point
Fast Associated Control Channel (FACCH)
• An FACCH is used over a TCH where it steals time slots from a TCH– a 20 ms segment of speech is stolen to carry
handover signaling information
• Appears on demand
Traffic Channels (TCH)
• TCH transport user information (speech/data)
• TCH are bi-directional dedicated channels between the network and the MS
Traffic Channels (TCH)
• TCH- Two types– Full-rate TCH (TCH/F): provides transmission
speed of 13 kbps for speech or 9.6, 4.8 or 2.4 kbps for data.
– Half-rate TCH (TCH/H): allows transmission of 6.5Kbps speech or 4.8 or 2.4 Kbps of data.
Handoff/Handover
A process, which allows users to remain in touch, even while breaking the
connection with one BS and establishing connection with another BS.
Old BS New BS
MSC
Old BS New BS
MSC
MSC
Old BS New BS New BSOld BS
MSC
Handoff To keep the conversation going, the Handoff procedure
should be completed while the MS (the bus) is in the overlap region.
G
Old BS New BS
Cell overlap region
Handoff detection strategies
Mobile-Controlled handoff (MCHO)
Network-Controlled handoff (NCHO)
Mobile-Assisted handoff (MAHO)
Mobile-Controlled Handoff (MCHO)
In this strategy, the MS continuously monitors the radio
signal strength and quality of the surrounding BSs.
When predefined criteria are met, then the MS checks for
the best candidate BS for an available traffic channel and
requests the handoff to occur. MCHO is used in DECT
and PACS.
Network-Controlled Handoff (NCHO)
In this strategy, the surrounding BSs, the MSC or both monitor the radio signal. When the signal’s strength and quality deteriorate below a predefined threshold, the network arranges for a handoff to another channel. NCHO is used in CT-2 Plus and AMPS
Mobile-Assisted Handoff (MAHO)
It is a variant of NCHO strategy. In this strategy, the network
directs the MS to measure the signal from the surrounding
BSs and to report those measurements back to the network.
The network then uses these measurements to determine
where a handoff is required and to which channel. MACHO is
used in GSM and IS-95 CDMA.
Handoff types with reference to the network
Intra-system handoff or Inter-BS handoff
The new and the old BSs are connected to the
same MSC.
Old BS New BS
MSC
Handoff types with reference to the network
Intersystem handoff or Inter-MSC handoff
The new and the old BSs are connected to
different MSCs
Old BS New BS
MSCMSC
Handoff types with reference to link transfer
Hard handoff
The MS connects with only one BS at a time, and there is
usually some interruption in the conversation during the link
transition
Soft handoff
The two BSs are briefly simultaneously connected to the MU while
crossing the cell boundary. As soon as the mobile's link with the new BS
is acceptable, the initial BS disengages from the MU.
Handoff types with reference to link transfer
Soft handoff
1. MU sends a pilot strength measurement message to the old BS,
indicating the new BS to be added.
2. The old BS sends a handoff request message to the MSC. If the
MSC accepts the handoff request, it sends a handoff request
message to the new BS.
3. The BS sends a null traffic message to the MU to prepare the
establishment of the communication link.
Handoff types with reference to link transfer
Soft handoff
4. The new BS sends a join request message to the MSC.
The MSC bridges the connection for the two BSs, so
that the handoff can be processed without breaking
the connection.
5. The new BS sends a handoff ack message to the old
BS via the MSC. The old BS instructs the MU to add a
link to the new BS by exchanging the handoff
command and handoff complete messages.
Handoff types with reference to link transfer
Soft handoff
6. The old BS and the MSC conclude this procedure by
exchanging the required handoff information. The quality
of the new link is guaranteed by the exchange of the pilot
measurement request and the pilot strength measurement
message pair between the MU and the new BS.
Handover in GSM (2.11)
3 possible types
• Intra-Cell Handover
between traffic channels within cell
• Inter-Cell Handover
between traffic channels on different cells
• Inter-MSC Handover
between cells belonging to different MSCs
Handover Situations
• To maintain Link Quality
• To minimize Interference
• Traffic Management
Four security measures in GSM
1) PIN code (authentication of user using terminal => local security measure, network is not involved)
2) SIM authentication (performed by network)
3) Ciphering of information sent over air interface
4) Usage of TMSI (instead of IMSI ) over air interface
IMSI = International Mobile Subscriber Identity(globally unique identity)
TMSI = Temporary Mobile Subscriber Identity(local and temporary identity)
CDMA
CDMA Is a Spread-Spectrum System
Traditional technologies try to squeeze the signal into the minimum required bandwidth
Direct-Sequence Spread spectrum systems mix their input data with a fast spreading sequence and transmit a wideband signal
The spreading sequence is independently regenerated at the receiver and mixed with the incoming wideband signal to recover the original data
Spread SpectrumTRADITIONAL COMMUNICATIONS SYSTEM
SlowInformation
Sent
TX
SlowInformationRecovered
RX
NarrowbandSignal
SPREAD-SPECTRUM SYSTEM
FastSpreadingSequence
SlowInformation
Sent
TX
SlowInformationRecovered
RX
FastSpreadingSequence
Wideband Signal
Spread Spectrum Principles
1.25 MHz30 KHz
Power is “Spread” Over a Larger Bandwidth
MATHHAMMER
MATHHAMMER
Spread Spectrum Principles
Many code channels are individually“spread” and then added together tocreate a “composite signal”
CDMACode division Multiple Access is a digital technology pioneered by QUALCOMM that provides crystal clear voice quality in new generation wireless communication systems
CDMA provides better and most cost effective
Voice quality
Privacy
System capacity
Flexibility.
SMS
Internet
Diversity in CDMA
Three types of Diversity
Frequency
Spatial Diversity
Time Diversity
Frequency Diversity
• Inherent feature of CDMA due to wide part of spectrum covered by each signal
• Multipath fading is caused by different delays among alternative paths between a mobile and base station
• Use of Rack Receivers to get benefits from multipath propagation
Spatial Diversity
• Both in TDMA and CDMA
• Use of multiple antennas at the base stations
• Two antennas far apart at the receiver make it unlikely to receive the faded signal at the same instant
• CDMA allows multiple base stations to transmit to single mobile thus making soft handover possible
Time Diversity
• Channel coding and interleaving are used in GSM for time diversity
• CDMA also uses time diversity
• The Forward channel in IS-95 standard employs half-rate convolutional coding, which doubles the number of bits
• The reverse channel also employs one-third rate convolutional coding
Continue…..
• All the bits, both information and redundant, are interleaved thus separating the adjacent information bits
• At the receiver end of channel, a Viterbi decoder is used with soft decision point
• Only makes 1 or 0 bit decision as demodulator already marks noisy symbols
• Decoder simply ignores bad symbols instead of working on them
Features and Advantages of CDMA
Universal Frequency Reuse
Fast and accurate Power Control
Rake Receiver
CDMA Hand off
FDMA/TDMA Frequency Reuse Frequency Reuse
CD CDMA MA Frequency Reuse
CDMA Frequency Reuse
CDMA Power Controlwithout
CDMA Rake Receiver
Multipaths
Multipaths
Multipaths
CDMA RAKE Receiver
CDMA RAKE Receiver
CDMA RAKE Receiver
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)
Handoff in CDMA System
• Soft Handoff– Mobile commences Communication with a new BS without
interrupting communication with old BS– same frequency assignment between old and new BS– provides different site selection diversity
• Softer Handoff– Handoff between sectors in a cell
• CDMA to CDMA hard handoff – Mobile transmits between two base stations with different
frequency assignment
Soft Handoff
Soft Handoff Advantages
Hand Off
Hand off in GSM
a)Hard Hand Off
b)Soft Hand OffHand off in CDMA
a)Soft Hand off
b)Softer Hand off
Practical Handoff Problems
• (1)Problem Caused by high speed mobility: More handoffs are required to handle high speed mobility of MS
during a call. It will cause load on the system as well as call drops.
• (2) Problem Caused by low speed mobility: Cell dragging:
In the line of sight and smooth area signal does not drop sharply for pedestrian users so user goes on using the frequency of the previous cell in to the new cell. This causes increase in the co-channel interference.
Solution For More Handoffs• Umbrella Cell Approach: Micro cells inside A macro cell.
---- Macro cell is defined by high power and lengthy tower. ---- Micro cells are defined inside the macro cell with less power and less height towers.
---- High speed MS are handled by macro cell and low speed subscribers are handled by micro cells. ---- This strategy increases the no of capacity channels per unit area and decreases the no of handoffs.
Umbrella Cell Approach
Solution For Cell Dragging
• Handoff threshold
----and radio coverage parameters must be adjusted carefully according to the environment .
88
Forward Link Channels
89
Forward Link Channels
90
Forward Link Channels• Channels
– A channel may be voice data or overhead control data.
• Forward Link Channels– On the forward link there are 4 types of channels used to transmit control and
voice data to the mobile.
– These channels are:• Pilot• Sync• Paging• Traffic
91
Forward Link Channels
92
• Pilot Channel
– The pilot channel is constantly transmitted.
– The mobile uses the pilot signal to acquire the system. After the mobile has acquired the system the pilot is used for signal strength measurement.
– The strength of the pilot is used to determine the power required for mobile transmit.
– The pilot contains no information but it is the strongest signal on the forward link, containing at least 20% of the total power on the forward link. The power of the pilot is an indication to the mobile of its ability to successfully use the signals from the base station transmitting that pilot.
– After this, the phone looks for the sync channel
Forward Link Channels
93
• Sync. Channel
– The sync channel is constantly transmitted providing critical timing information to the mobile.
– The mobile will decode the Sync. channel message during the power up sequence.
– It repeatedly transmits a sync channel message which contains information about the cell and the phone system, and also contains information which permits the phone to determine the absolute clock time
– Once the sync channel message has been processed, the phone has sufficient information to begin to process the paging channel and to register
– Once the mobile is synchronized with the base station the sync channel is ignored.
Forward Link Channels
94
• The Sync Channel
– Mobiles must acquire the Sync Channel and decode its message in order to synchronize with the system.
– The Sync message is spread with Walsh code 32 and is broadcast continuously.
– The Sync message includes the following information:• System time• System ID• Network ID• Many more
Forward Link Channels
95
Paging Channel
– A base-to-mobile forward-link communications channel used to send control, call set-up, and paging messages when the mobile is not in the traffic mode.
– The paging channel is used to transmit overhead information (i.e. commands and pages) to the mobile.
• When a call is being set up the commands and traffic channel assignment are sent on the paging channel.
• Once a traffic channel is established the paging channel is ignored by the mobile.
Forward Link Channels
96
• Paging Channels
• A Paging Channel is used by the CDMA system to transmit overhead messages and mobile directed messages. Walsh codes 1 through 7 may be used for Paging Channels. A system operator may choose to support less than seven Paging Channels. In this case, unused codes may be assigned to Traffic Channels.
• A Paging Channel transmits the configuration messages:– System Parameters message– Access Parameters message– CDMA Channel List message– housekeeping information such as the PN Offsets of all nearby
cells and sectors.– Many more
Forward Link Channels
97
– While the mobile is not in the traffic mode, the base sends orders and messages to the mobile on the paging channel. It receives responses and requests via the mobile's Access Channel.
Forward Link Channels
98
• Forward Traffic Channel– The forward traffic channel is used when there is a call.
Forward Link Channels
99
Forward Traffic Channels
100
Reverse Link Channels
101
Reverse Link Channels
102
The reverse link in an IS-95 system is any link from a mobile subscriber to a base station.
On the reverse link there are two types of channels used to transmit control and voice data to the mobile.
These channels are: Access Traffic
Reverse Link Channels
103
Reverse Link Channels
104
• Access Channel– The access channel is used by the mobile when not
assigned to a traffic channel.– A mobile-to-base communications channel used
primarily for control and sending messages such as call origination, page response, and registration.
– The access channel is used by the mobile to • register with the network• originate calls• respond to pages and commands from the base station• transmit overhead messages to the base station.
Reverse Link Channels
105
• After the mobile initially acquires the pilot of a base station and reads the data on the Synchronization channel, it transmits to the base station on an Access Channel.
• This is the first indication that the base station has that the mobile is present and active.
• All communications with the base station occur using the Access Channel until the mobile is placed in the traffic mode.
Reverse Link Channels
106
• Reverse Traffic Channel– The reverse traffic channel is used when there is a call.
Reverse Link Channels
107
Problems in a CDMA Channel
108
Problems in a CDMA Channel• Near-Far Problem
– If all mobiles transmitted at the same power level, signals received by the base station from mobiles further away would be weaker than those signals received from mobiles which were closer to the cell. This issue reduces, if not resolved, the capacity of a CDMA system.
• Path Loss– The more distance between the cell and a phone the weaker the
signal becomes.• Fading
– Fading occurs when more than two signals from the same transmitter are received due to multipath.
109
Advantages of CDMA
110
Advantages of CDMA
• Coverage
• Capacity
• Clarity
• Cost
• Compatibility
• Customer Satisfaction
111
FDMA / TDMA / CDMA Coverage
112
Coverage
• Coverage Issues– Providing adequate coverage is a basic requirement of a wireless system.
– Coverage of a BTS or network is impacted by the capacity requirements of the system, terrain of the area, and power of the base station and mobiles.
• CDMA Advantage– Forward and reverse link power control helps a CDMA network dynamically
expand the coverage area.
– The coding and interleaving techniques used in CDMA provide the ability to cover a larger area for the same amount of available power used in other systems.
– Under line of sight conditions CDMA has a 1.7 to 3 times more coverage than TDMA.
113
Capacity
114
Clarity
115
• Rake Receiver– Combines multipath and softer handoff signals to reduce
errors and power requirements.
• Variable Rate Vocoder– The dynamic rate of the vocoder reduces the amount of
data transmitted for each person and reduces the interference.
Clarity
116
• Soft Hand-off– The soft hand off in CDMA reduces the interference and power
requirements for maintaining the link. Multiple received signals can be combined to reduce the possibility of errors resulting from interference and fading.
• Power Control– Dynamic power control reduces errors by keeping the power at an
optimal level.• Wideband Signal
– CDMA’s wideband signals does not suffer from the same effects of fading experience in an FDMA or TDMA system.
• Encoding and Interleaving– Strong encoding and interleaving reduces the effects of fading.
Clarity
117
Major Mobile Radio standards in North America
Spectrum Allocation by PTA
PMR
Key features of professional mobile radio systems can include:
• Point to multi-point communications (as opposed to cell phones)
• Push to Talk, release to listen — a single button press opens communication on a radio frequency channel
• Large coverage areas
• Closed user groups
• Use of VHF or UHF frequency bands
Private Mobile Radio (PMR) System
• System setup by a company or group of users for that group of user alone
• Walkie-talkie is simplest form where there is no need of base station
• Simple to setup and cheap to run
• But lack flexibility as calls to other networks or users is impossible
• A new service called PMR446, which can support upto about 1 or 2 million users in UK
• The channels are unlicensed, hence no guaranteed access
• PMR446 equipment is not permitted to be connected with public telephone network
• The USA has a similar system called called family radio service (FRS)
• In public mobile access radio (PAMR) users may group together to run joint systems
• PAMR systems are shared by number of different users
• PAMR or PMR systems with a common standard and internetworking arrangement has advantage of direct calls
• It is useful for services in neighboring countries
Problems
• Delays as Interworking arrangement routes calls through a fixed network
• Direct mode operation without base station is impossible
• Development of good public cellular system which undermine the advantages( adequate coverage, reduce cost, supplementary services) of PMR system
• Coverage in GSM exceeds the dedicated coverage provided by PMR
• The cost of public systems has decreased drastically due to competition and innovations
• PMR handsets becoming more costly due to move to digital and drive to increase flexibility, capacity and security
• Cellular users have economies of scale due to large market
The PMR User Community
• Public Safety
Emergency Services( Police, Fire, ambulance)
• Non-safety National Govt
Customs etc
• Non safety local Govt.
• Transport
Railways, Buses, Taxis
• Other Utilities
Water, Electricity, Gas, Coal
• On-site PMR
Construction site
• PAMR
Requirements of PMR Services
• Reliability
Service availability is extremely important
• Voice and Data Capability
Data services are increasing exponentially
• Centralized and De-centralized operations
• Pt to Pt, Group and Broadcast Calls
Flexible group call structure
• Fast Call Setup
Particularly important in emergency services, push to talk, no need of dialing
• Good Coverage
Mountain rescue service
• Long Battery life
• Flexibility
Ability of system to change with the need, scalable
• Low Total Cost of ownership
Lower Capital plus maintenance cost
• Others Requirements in some cases include Security, Call priorities, Ease of licensing
PMR Configurations (3.4)
• Point to point Direct terminal communication
• Dispatch operation
• Talk through Repeater Operation
• Use of Radio port to fill blackspot
• Vehicle mounted Repeater for local handheld coverage
• Wide area coverage using several base sites
• Cellular PMR Configuration
Comparison Between PMR and Cellular
• Group call..required in PMR but not so frequent in Cellular
• Dispatcher Operation…. Many PMR needs dispatcher for controlling and monitoring, not in Cellular
• Decentralized Operation…PMR works in direct mode without the need of fixed base station and network infrastructure
• Fast Call Set-up…. PMR fast as no need to wait to be connected
• Supplementary Services….Additional call services…now equally good in Cellular
• Traffic Patterns….Calls are short in PMR, PMR calls are mostly intended for the users on the same network
• Capacity…Cellular user base is larger, need more base stations, small cells, high re-use and efficient air interface techniques. PMR operator want to minimize infrastructure cost so larger cells.
• Freq Planning… Needed in Cellular
• Control, billing and authentication…User is authenticated and bill for each call as contrast to PMR
• Relationship between the service provider and the user…QOS is directly in control of user in PMR, Cellular will provide a standard service
• Coverage….PMR operator require coverage over predefined areas of operation, Cellular may use over as wide area as possible including internationally.
PMR Standards
• Analog
• Digital
Analog PMR
• Early systems were analog and proprietary
• Later on, some standards introduced for infrastructure cost and spectrum sharing
• One such system is LTR (Logic Trunk Radio)
• Another major Analog standard is MPT1327 developed in UK in 1980s but implemented worldwide
• MPT1327 is complex and expensive but efficient in spectrum use as well as offer data services
• Difficult to replace or upgrade due to cost
Digital PMR
Advantages are
• Ability to recover the signal completely as long as noise is below threshold level
• Direct sending of data without need for a modem and trunking due to easy manipulation of digital signal
• Lower spectrum required as digital modulation allows use of efficient compression techniques
• Increased Flexibility
• Increased availability of services
• Improved efficiency
• High QoS
Digital PMR Standards
• EDCAS..Enhanced Digital Access Communication System
• Geotek-FHMA
• APCO25
• iDEN
• GSM Derivatives
• TETRAPOL
• TETRA
Terrestrial Trunked Radio (TETRA)
• Open standard within ETSI
• Feature rich system from specialized safety services to cellular operating modes
• Wide selection of data services
• More efficient use of spectrum due to TDMA access technique
• Number of operating modes with wide coverage