Transcript 1.2G Evolution first

2G (GSM) Evolution
By
Saroj Dhakal
2G (GSM) Evolution
• Limits of GSM
• limited capacity at the air interface:
• Data transmission standardized with only 9.6kbit/s
• advanced coding allows 14,4kbit/s
• not enough for Internet and multimedia applications
• Extensions
• HSCSD (High-Speed Circuit Switched Data)
• GPRS (General Packet Radio Service)
• EDGE (Enhanced Data Rate for GSM Evolution)
• EGPRS (EDGE and GPRS)
• GERAN (GSM Interface to UMTS)
Circuit Switching Vs Packet Switching
Circuit Switching Vs Packet Switching
• Advantages of Circuit Switching
– More suited to time-sensitive applications
– Less data overheads for routing requirements
– Compatibility with existing circuit-switched
networks (eg PSTN/ISDN)
• Advantages of Packet Switching
– More efficient use of existing bearers
– More suited to bursty-type traffic such as Internet
access.
Packet Routing Strategies
• Connection-Orientated (CONS):
– Packet route established prior to data transfer
– Supports flow control
– Supports QoS functions
• Connectionless (CNLS)
– No predefined route -packets routed individually
– No guarantee of delivery
– Difficult to implement QoS
Virtual Circuit Connections
• Permanent Virtual Circuit (PVC):
– Dedicated resource for specific user
– Connectionless
• Switched Virtual Circuit (SVC):
– Setup on request
– Temporary allocation of resources
– Cleared on completion of session
The Requirement for Mobile Data
• Requirement to develop additional revenue-generating streams
• Exponential growth in Internet Access
• Evolution towards 3G services
Emerging Mobile Data Technologies
HSCSD (High-Speed Circuit Switched
Data)
• continuous use of multiple time slots
• asynchronous allocation of time slots
• gain: net data rate up to 115.2 kbps (allocation of all 8
traffic channels)
• Mainly software update
• additional HW needed if more than 3 slots are used
– advantage: constant quality, simple
– disadvantage: channels blocked for voice transmission
GPRS (General Packet Radio Service)
• What is GPRS?
– Packet-switching technology
– Transparent end-to-end data transport of data packets
over a modified GSM network
– Shares Radio Resources with GSM
– New GPRS core network distinct from GSM
– using free slots only if data packets ready to send
(e.g., 115 kbit/s using 8 slots temporarily)
– standardization 1998, introduction 2001
– advantage: one step towards UMTS, more flexible data
services
– disadvantage: more investment needed
GPRS -Conceptual View
• Key GPRS Features: Introduces new air interface
coding schemes, Supports SMS over GPRS and Allows
for shared usage of GSM control functions
GSM/GPRS Mobile Terminal (MT)
System Modifications
• GPRS Mobile Station (MS) Modifications
– New Mobile Stations will be required
– Backward compatibility with GSM
– SIM Card updates to include GPRS functionality
• Base Station Subsytem (BSS) Modifications
– BTS Requires software upgrade
– Inclusion of a CCU in the BTS
– BSC requires software upgrade and addition of Packet
Control Unit Support Node (PCU)
– Packet Control Unit (PCU) Functions
• Provides physical and logical data interface out of the BSS for packet
data traffic
• LLC layer PDU segmentation/reassembly
• Packet data transfer scheduling
• Radio channel management function
– Channel Codec Unit (CCU) Functions
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Data coding / decoding
Forward error correction (convolution coding)
Air interface interleaving
Radio management
GPRS Core Network Elements
The following GSM network changes are
required:
• New GPRS entities:
– Serving GPRS Support Node (SGSN)
– Gateway GPRS Support Node (GGSN)
• Modified GSM entities:
– HLR
– MSC/VLR
– SMS-GMSC
Databases –VLR/HLR
• GPRS can share GSM database resources
• Database software upgrades required to
accommodate new GPRS functionality and
parameters when interacting with GSM
• SGSN acts as VLR for GPRS-specific VLR
functions
• EIR/AuC will also require software upgrades
for GPRS-specific authentication/authorization
Serving GPRS Support Node (SGSN)
Functions:
• Packet routing
• MS Session management
• Authentication and Ciphering
• Mobility management
• Billing information collection
Gateway GPRS Support Node (GGSN)
• Interface between GPRS backbone and
external PDNs.
• PDP Conversion
• IP address assignment management
• Packet routing to/from SGSNs
• Billing information collection
GPRS architecture and interfaces
GPRS Air Interface
• GPRS Um Air Interface
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New Packet logical channels defined
New multi frame structure defined
Ability for multiple users to share single or multiple timeslots
Dynamic Resource Allocation
Four new channel coding schemes
• GPRS Logical Channels
– GPRS shares GSM for many logical common control channel functions
(e.g. FCCH, SCH)
– New GPRS logical dedicated control channels are used (e.g. PDTCH
:Packet Data Traffic Channel, PACCH: Packet Associated Control
Channel and PTCCH: Packet Timing Advance Control Channel
– Packet control channels are optional
– GSM control channels may be substituted
GPRS Coding Schemes
• 4 coding schemes have been defined for
GPRS as shown in table.
– CS-1 is mandatory for the BSS
– CS-1 to 4 are mandatory for the MS
Protocols
• A protocol is a set of rules, agreed by both sides, to allow
meaningful communication to take place. Protocols are needed
whenever systems need to pass information from one to another.
• Data Tunneling: A tunnel is a point-to-point (PTP) virtual connection
between two end points across a network through which data
packets can be transported, transparent to the bearer network
• GPRS Protocol Stacks
• Transmission Protocol Stack
• Network Access Signalling Protocol Stack
• Core Network Signalling Protocol Stack
GPRS Mobility Management (GMM)
States
• GPRS defines 3 GMM states:
– Idle -camped on but not attached
– Standby -attached but not in data transfer mode
– Ready -able to transmit/receive packet data
MM State Change Conditions
• Idle to Ready:
– GPRS attach
• Ready to Standby:
– Ready timer expired
– Forced to Standby
• Standby to Ready:
– Packet transmission
/reception required
• Ready to Idle:
– GPRS detach
– Location cancelled (SGSN context)
• Standby to Idle:
– detach (SGSN context)
– Location cancelled (SGSN context)
GPRS services
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Quality-of-Service Parameters: Reliability, Throughput, service priority
End-to-End packet switched traffic(peak channel rates)
– 28kbps (full use of 3 time slots, FEC)
– 171.2 kbps (full use of 8 time slots, no FEC)
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Average aggregate throughput of a cell (Source: H. Menkes, Wireless Web, Aug.
2002)
– 95 kbps (for both up and downlink)
– Assumptions: 1/3 reuse, realistic RF conditions, random traffic
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Adaptive Coding Schemes(adaptive Forward Error Control –FEC)
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CS 1:9.05 Kbps/slot
CS 2:13.4 Kbps/slot
CS 3: 15.6 Kbps/slot
CS 4: 21.4 Kbps/slot (no Forward Error Correction)
(current systems implement CS1 and 2 only)
Problems and limits
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IP-based network=> high latency, no guarantees
Limited data rate: 28 kbps(3 slot/CS-1) -64.2 kbps(3 slot/CS-4)
Latency/flow control problems with TCP
Cell capacity.
Sub-optimal modulation technique.
EDGE (Enhanced Data Rates for GSM
Evolution)
• Spectral efficiency depends on:
– Size of frequency band
– Duration of usage
– Level of interference to others (power)
• EDGE:
– Adaptation of modulation depending on quality of radio path
• GMSK (GSM standard–1 bit per symbol)
• 8-PSK (3 bits per symbol)
– Adaptation of coding scheme depending on quality of radio
path (9 coding schemes)
– Applied to a GSM channel, EDGE allows a maximum data rate of
48 kb/s per timeslot, giving the quoted figure of 384 kb/s per
carrier (8 timeslots)
EDGE
– Gain: data rate (gross) up to 69,2kbps (compare to
22.8kbps for GSM)
– complex extension of GSM!
• EDGE can be applied to HSCSD (ECSD) and GPRS
(EGPRS)
• EDGE will be expensive for operators to
implement:
– Each base station will require a new EDGE transceiver
– Abis interface between BTS and BSC must be
upgraded
– New EDGE-enabled handsets required
Preview: UMTS system architecture
(Release 3)
UMTS/GSM Network Architecture
Thank you………………………………..