2G (GSM) Evolution By Saroj Dhakal. 2G (GSM) Evolution Limits of GSM limited capacity at the air...
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Transcript of 2G (GSM) Evolution By Saroj Dhakal. 2G (GSM) Evolution Limits of GSM limited capacity at the air...
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2G (GSM) Evolution
By Saroj Dhakal
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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)
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Circuit Switching Vs Packet Switching
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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.
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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
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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
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The Requirement for Mobile Data
• Requirement to develop additional revenue-generating streams• Exponential growth in Internet Access• Evolution towards 3G services
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Emerging Mobile Data Technologies
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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
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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
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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
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GSM/GPRS Mobile Terminal (MT)
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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• Data coding / decoding • Forward error correction (convolution coding)• Air interface interleaving• Radio management
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GPRS Core Network ElementsThe 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
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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
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Serving GPRS Support Node (SGSN)
Functions:• Packet routing• MS Session management • Authentication and Ciphering• Mobility management • Billing information collection
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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
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GPRS architecture and interfaces
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GPRS Air Interface • GPRS Um Air Interface
– 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
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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
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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
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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
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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)
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GPRS services• 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)
• 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
• Adaptive Coding Schemes(adaptive Forward Error Control –FEC)– 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
– 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.
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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)
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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
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Preview: UMTS system architecture (Release 3)
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UMTS/GSM Network Architecture
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Thank you………………………………..