GSM/GRPS TrainingBasic GSM/GPRS Training
Mobile Communication (GSM)
Outline
Packet Data for the GSM World
GPRS Overview
The GPRS Protocol Stack
High Speed Circuit Switched Data (HSCSD)
Enhanced Data Rates for Global Evolution (EDGE)
* Nokia Mobile Phones July 9, 2002 Sascha Meyer CONFIDENTIAL
An Introduction to GSM
* Nokia Mobile Phones July 9, 2002 Sascha Meyer CONFIDENTIAL
GSM Overview
The Past…
The standardization of GSM (Global System for Mobile Communication)
was carried out by ETSI in the late 1980’s to provide an all
digital mobile communication system in the 900 MHz range to the
European market.
…and The Present
for different applications and frequency
ranges (R-GSM, E-GSM, PCS1900, …).
alternative solutions. The idea is to
achieve a high reuse factor of
the available frequencies.
GSM Overview
BSS
NSS
MS
Mobile Station and SIM
A Mobile Station (MS) consists of Mobile Equipment (ME) and SIM
card
Every MS performs the following tasks:
Mobile Equipment
Mobile Station and SIM
The Subscriber Identity Module (SIM) is a typical Smart Card
SIM cards are available as ID-1 and Plug-In SIM
SIM performs algorithms and stores data (see table for some
exambles).
Administrative Data
Security Related Data
A3 and A8 algorithms for authentication and Kc calculation Keys Ki
(subscriber‘s individual secret key) and Kc (session key)
Subscriber Data
Roaming Data
TMSI, Location updating status, LAI NCCs of restricted PLMNs and
NCCs of preferred PLMNs
PLMN Data
Home PLMN‘s NCC, MCC, MNC ARFCNs (Absolute Radio Freq. Channel
Numbers) of home PLMN (frequencies for which the home PLMN is
licensed)
* Nokia Mobile Phones July 9, 2002 Sascha Meyer CONFIDENTIAL
The Basestation Subsystem
Base Station Controller (BSC)
BSC was invented to relieve the MSC from radio related tasks like
access control or handover scenarios (-> do not require
contribution of MSC).
Base Transceiver Station (BTS)
The BTS connects the GSM network to the air interface and has
multiple radio related functions like interleaving, channel coding
and ciphering. Important: BTS broadcasts BCCH with constant output
power to supply surrounding mobile stations with cell specific
information and to serve as a beacon for handover decisions.
Transcoding Rate and Adaption Unit
The TRAU is used for speech compression and is transparent for data
connections. Since human speech is quite redundant, compression
rates of 1/4 (fullrate channel (FR)) and even 1/8 (halfrate channel
(HR)) are achieved.
* Nokia Mobile Phones July 9, 2002 Sascha Meyer CONFIDENTIAL
The Network Subsystem
Mobile services Switching Center (MSC)
The MSC is a digital switch that has been upgraded to suit the
requirements of a mobile network environment. In GSM, the MSC takes
care of resource management towards the BSC and is responsible for
call processing in MO Calls and MT Calls. The MSC can process
handover procedures between two and even three MSCs. Special
function: Gateway-MSC (G-MSC) provides access to external networks.
Other MSCs with more special functions for the processing of short
messages: SMS-IW-MSC, SMS-G-MSC.
Visitor Location Register (VLR)
Initially, the VLR was considered a different network element from
the MSC. Then the VLR became part of what is now called MSC/VLR.
Still, from the protocol perspective, the VLR takes care of
different tasks
(=> Mobility Management (MM)) than the MSC (=> Call Control
(CC)).
* Nokia Mobile Phones July 9, 2002 Sascha Meyer CONFIDENTIAL
The Network Subsystem
Home Location Register & Authentication Center (HLR/AuC)
The HLR is a huge database for permanent storage of subscriber
data. The different VLRs and MSCs within a PLMN will retrieve
subscriber and routing information and store it on an intermediate
bases. Integrated in the HLR is the AuC which holds every PLMN
subscriber‘s secret key (Ki) and the (also secret) algorithms of
GSM (A3, A8). The AuC supports the VLR during subscriber
authentication by computing the authentication triplet (Kc, RAND,
SRES).
Equipment Identity Register (EIR)
EIR was intended to track and so block stolen mobile terminals from
being used any further. Almost no operator has implemented the EIR
as the cost-value ratio is uninteresting for most operators. (And
because it‘s so rarely in use its even more pointless to implement
it in future).
* Nokia Mobile Phones July 9, 2002 Sascha Meyer CONFIDENTIAL
The GSM Air I/F
The GSM Burst (Power vs. Time Template)
GSM uses the Gaussian Minimum Shift Keying (GMSK) modulation
scheme. Each GSM carrier requires 200 kHz bandwidth and is divided
into 8 timeslots (each with a duration of 577 us).
* Nokia Mobile Phones July 9, 2002 Sascha Meyer CONFIDENTIAL
The GSM Air I/F
GSM features Time Division Multiple Access (TDMA) together with
Frequency Division Multiple Access (FDMA). TDMA timeslots are
organized in TDMA frames.
* Nokia Mobile Phones July 9, 2002 Sascha Meyer CONFIDENTIAL
The GSM Air I/F
A Hierarchy of Frames:
The GSM Air I/F
A Hierarchy of Frames:
Starting from the basic TDMA frame, the frame hierarchy comprises
Multiframes, Superframes, and Hyperframes. Each TDMA frame carries
a frame number (FN) uniquely identifying this frame in the
structure. The BTS needs an internal clocking system to establish
the frame hierarchy. This clocking system is also needed to
enable
Logical channel configuration
Physical Channels vs. Logical Channels
A GSM physical channel basically is one timeslot. In turn, a
logical channel is an application specific bearer channel defined
to carry GSM data traffic or signaling, and is mapped on one or
more physical channels. The multiframe structure is used to
identify, at which moment in time which logical channel is using a
physical channel
* Nokia Mobile Phones July 9, 2002 Sascha Meyer CONFIDENTIAL
The GSM Air I/F
A Hierarchy of Frames:
This Example shows one possible allocation of logical channels in
downlink direction on TS 0 of the BCCH carrier (uses
51-multiframe!):
* Nokia Mobile Phones July 9, 2002 Sascha Meyer CONFIDENTIAL
The GSM Air I/F
Frequency Correction Channel (FCCH)
„Lighthouse“ of the BTS
Broadcast Common Control Channel (BCCH)
Carries cell specific information to the mobile stations that are
currently camping on that BTS.
Common Control Channel (CCCH)
Mainly used to establish a dedicated channel (AGCH) or for paging a
mobile station (PCH)
Slow Associated Control Channels (SACCH)
Transmits signaling and information like timing advance, power
control information etc. Assigned to TCH (during call) with one
SACCH every 120 ms (26-multiframe) or to SDCCH with one SACCH every
235.38 ms (51-multiframe).
Fast Associated Control Channels (FACCH)
The FACCH transmits signaling during a connection but is only used
when no delay is acceptable.
Standalone Dedicated Control Channel (SDCCH)
Exchange of signaling information between MS and BTS for connection
setup, location update etc. (bidirectional PTP channels)
* Nokia Mobile Phones July 9, 2002 Sascha Meyer CONFIDENTIAL
The GSM Air I/F
Different Burst Types of GSM:
Since GSM is a TDMA system, transmission and reception is not
continuous but performed in so called bursts. Dependent on the
usage, five different types bursts have been defined:
Frequency Correction Burst (FB): consists of 142 bits, all coded
with ‚0‘ (plus head and tail), only used on the FCCH (the BTS
beacon).
Synchronization Burst (SB): is used on the Synchronization Channel
(SCH) and provides frame number and initial identification of the
cell.
* Nokia Mobile Phones July 9, 2002 Sascha Meyer CONFIDENTIAL
The GSM Air I/F
Different Burst Types of GSM:
Normal Burst (AB): carries almost every kind of information,
signaling and payload in uplink and downlink direction. Consists of
Payload (114 bit!), Training Sequence, and Stealing Flags (to
indicate if and which part of a burst has been stolen for
FACCH)
Access Burst (AB): used by the mobile station to determine the
current propagation delay (-> Timing Advance (TA)) in this cell.
The AB is shortened to ensure that it fits into the respective
receive window of the BTS (this method allows for a max. Distance
of 35 km between mobile station and BTS.
Dummy Burst (DB): serves a special function on the BCCH carrier
where all timeslots need to transmit permanently (because BCCH
carrier serves as reference for handover and cell selection
decisions), even without being in use. All not-used timeslots of
the BCCH therefore transmit dummy bursts whereas a dummy burst
consists of a pre-defined and fixed bit sequence.
* Nokia Mobile Phones July 9, 2002 Sascha Meyer CONFIDENTIAL
The GSM Air I/F
The Timing Advance Control:
The propagation delay varies with distance and is a critical issue
for a TDMA system on the uplink path. Accordingly, the network
needs to constantly tell the mobile station how to offset its burst
transmissions during a connection (-> SACCH). Otherwise, the
signals from different mobile stations would collide in the receive
window of the BTS.
* Nokia Mobile Phones July 9, 2002 Sascha Meyer CONFIDENTIAL
The GSM Air I/F
Channel Coding:
Transmission over the air interface is vulnerable against
interference. Adding redundancy to the data to be sent allows the
receiver to recover the original signal in case of errors. (Below
figure shows channel coding for the FR speech TCH)
* Nokia Mobile Phones July 9, 2002 Sascha Meyer CONFIDENTIAL
The GSM Air I/F
Interleaving:
Interleaving is another method to protect data during transmissions
over the air interface. By distributing a single block over
multiple bursts the hazard of a complete loss of one packet is
reduced.
* Nokia Mobile Phones July 9, 2002 Sascha Meyer CONFIDENTIAL
The GSM Air I/F
Authentication
Authentication is used to prevent fraudulent subscribers from
accessing the GSM network. The Authentication process is invoked by
the MSC/VLR which requests precalculated authentication triplets
from the HLR/AuC. Authentication consists of challenging the mobile
station by providing the RAND. As the next slide shows RAND an Ki
are the input parameters for the algorithm A3. The respective
output is SRES. The VLR will compare both values, the stored SRES
and the SRES coming from the mobile station to decide whether the
authentication process was successful.
Ciphering
Ciphering ensures data confidentiality during the transmission over
the air interface. Ciphering cannot be initiated without prior
authentication! Comparably to authentication, ciphering is based on
the calculation of RAND and Ki, but this time applying algorithm
A8. The respective output parameter Kc together with the current
frame number is used in algorithm A5 to determine the ciphering
sequence that is used for “XORing” the 114 bits of the output
burst.
* Nokia Mobile Phones July 9, 2002 Sascha Meyer CONFIDENTIAL
The GSM Air I/F
A3/8 computations during Authentication
The GSM Air I/F
Ciphering with the A5
* Nokia Mobile Phones July 9, 2002 Sascha Meyer CONFIDENTIAL
Packet Data for the GSM World
GPRS Overview
The GPRS Protocol Stack
GPRS Overview
GPRS is… Packet Switched High Speed Mobile Data
An Efficient Approach to Upgrade Existing GSM to a Packet Switched
System on the way to 3G
An Important Trial for 3G Mobile Networks
Being Online Permanently!!!
Mobile Bandwidth without Limits…
* Nokia Mobile Phones July 9, 2002 Sascha Meyer CONFIDENTIAL
GPRS Overview
Packet Switched vs. Circuit Switched:
Packet Switched transmission requires that every packet comes with
an individual header to provide address and routing information. No
allocation of dedicated resources is required.
Circuit switched transactions establish a permanent dedicated
connection that for the duration of a transaction is exclusively
used by only one user.
Inherently, GSM is a packet-switched system, considering that
transmission and channel coding is performed in bursts and blocks.
Of course, this applies only for the air interface.
* Nokia Mobile Phones July 9, 2002 Sascha Meyer CONFIDENTIAL
GPRS Overview
Cost Efficiency:
Reuse as much HW of the existing GSM infrastructure as
possible
Support of Multiple Packet Data Protocols:
GPRS Rel99 supports IP, PPP and IHOSS (Internet Hosted Opted Stream
Service)
Support Short Message Services (SMS)
Provide for Different Charging Options:
e.g.: charge per duration, volume, content
Ensure a Long Term Investment:
Ensure later network migrations to EDGE, IMT-2000
Compatibility to Alternative Air Interface Technologies:
Support IS-136+ and UWC
* Nokia Mobile Phones July 9, 2002 Sascha Meyer CONFIDENTIAL
GPRS Overview
GPRS Transmission Rates:
This table is taken from GSM 03.64. It considers RLC headers as
being part of the input for the encoder.
1 Timeslot
2 Timeslots
8 Timeslots
The GPRS Network
Implications for the GSM network:
The GSM Base Station Subsystem (BSS) should be left (almost)
unchanged
A Packet-Switched Core Network needs to be added to the GSM Network
Switching Subsystem (NSS)
* Nokia Mobile Phones July 9, 2002 Sascha Meyer CONFIDENTIAL
The GPRS Network
One Extension is needed in the BSS:
The Packet Control Unit (PCU) is added to interface data packets to
the unchanged GSM-BSS and to control and manage most of the radio
related functions of GPRS
Most vendors locate the PCU at the BSC. Other possible locations
are BTS or SGSN
* Nokia Mobile Phones July 9, 2002 Sascha Meyer CONFIDENTIAL
The GPRS Network
SGSNs, GGSN, BGs, etc.
The GPRS Network
The SGSN is a Packet Switch:
The SGSN needs to route incoming data to the right
destination
Data Compression:
SGSN applies data compression according to RFC 1144 (TCP/IP header
compression) and V.42 bis (for data compression).
Ciphering:
In GPRS the SGSN is responsible for data encryption, not the BTS
like in GSM.
Being the Ultimate Peer for the Mobile Station:
Within the GPRS core network, the SGSN is the main partner for the
mobile station
* Nokia Mobile Phones July 9, 2002 Sascha Meyer CONFIDENTIAL
The GPRS Network
Mobility Management:
The SGSN keeps track of a subscriber’s location down to the routing
area and, in ready state, even down to the BTS level.
Charging:
The SGSN needs to collect charging information related to the usage
of the own network and in particular related to the usage of the
air interface.
Handover/Cell Change:
In case of a cell change during an ongoing packet data transfer,
the SGSN needs to take care that not-acknowledged packets are
routed to the new cell and, in case of a change of the SGSN, that
the new SGSN receives the unacknowledged packets and all new
packets.
* Nokia Mobile Phones July 9, 2002 Sascha Meyer CONFIDENTIAL
The GPRS Network
Gateway to External Packet Data Networks:
As its name suggests, the GGSN interconnects a PLMN to external
packet data networks
Anchor Function During Packet Data Transactions:
Note that the GGSN will remain the anchor point for external packet
data networks even after the SGSN has changed due to a cell
change.
Charging:
Opposed to the SGSN, the GGSN collects charging information based
on the usage of external network resources.
Function of the Border Gateway (BG):
Message Screening / Security:
All transactions that involve the usage of external PLMNs are
screened by the BG to provide a maximum level of security for a
network operator.
* Nokia Mobile Phones July 9, 2002 Sascha Meyer CONFIDENTIAL
The GPRS Network
The Complete Picture:
* Nokia Mobile Phones July 9, 2002 Sascha Meyer CONFIDENTIAL
The GPRS Network
Class A:
The Mobile Station can simultaneously perform GSM circuit-switched
and GPRS packet switched transactions. (Currently NMP does not have
any such product on its roadmap).
Class B:
The Mobile Station can monitor circuit-switched and packet switched
services, but cannot operate them simultaneously. (8310, 6310,
6510, etc.)
Class C:
The Mobile Station can either monitor and operate circuit switched
services or GPRS. (see Nokia M2M platform)
* Nokia Mobile Phones July 9, 2002 Sascha Meyer CONFIDENTIAL
The GPRS Air I/F
The GPRS Air I/F
12 Radio Blocks for the different Packet Data Channels
(PDCHs)
Each Radio Block consists of 4 consecutive appearances of the same
timeslot within 4 consecutive TDMA frames.
Resource Allocation in Uplink and Downlink is done on Block
level
2 TDMA frames are reserved for Timing Advance Control (Propagation
Delay)
2 idle TDMA frames for interference measurements
* Nokia Mobile Phones July 9, 2002 Sascha Meyer CONFIDENTIAL
The GPRS Air I/F
One 52-multiframe represents 52 times the repetition of one
timeslot.
This figure represents the usage of TS 0
* Nokia Mobile Phones July 9, 2002 Sascha Meyer CONFIDENTIAL
The GPRS Air I/F
PDCHs are only used in 52-multiframe
PDCHs can be allocated dynamically by the system
PCCCH, PBCCCH are usually introduced in high load situations
* Nokia Mobile Phones July 9, 2002 Sascha Meyer CONFIDENTIAL
The GPRS Air I/F
PBCCH (Packet Broadcast Channel):
The PBCCH broadcasts GPRS related information about a cell to all
GPRS enabled mobile stations that are currently camping on that
cell. Opposed to the BCCH, the PBCCH can be configured on each
timeslot of each ARFCN.
PCCCH (Packet Common Control Channel):
PCCCH actually stands for the PRACH, PAGCH, PPCH and PNCH. Note
that packet-related control information can also be transmitted on
CCCH if there is no PCCCH allocated in a cell.
PRACH (Packet Random Access Channel):
Similar to the RACH in GSM, the PRACH is used to convey the initial
network access message from the mobile station to the network
(PCU). The PRACH is the only uplink PCCCH.
* Nokia Mobile Phones July 9, 2002 Sascha Meyer CONFIDENTIAL
The GPRS Air I/F
PAGCH (Packet Access Grand Channel):
Like the circuit-switched AGCH, the PAGCH is used to convey the
assignment of dedicated uplink or downlink resources to a mobile
station. The PAGCH belongs to the group of PCCCHs.
PPCH (Packet Paging Channel):
As its name suggests, the PPCH is used to transmit a paging message
for GPRS or circuit-switched services to the mobile station.
Additionally, the PPCH can be used in GMM state READY to send a
downlink resource allocation to the mobile station.
PNCH (Packet Notification Channel):
The PNCH is used to notify a mobile station about an upcoming
Point-to-Multipoint (PTM) transaction.
* Nokia Mobile Phones July 9, 2002 Sascha Meyer CONFIDENTIAL
The GPRS Air I/F
PDTCH (Packet Data Traffic Channel):
The PDTCH is the bearer for all packet data being transferred in
uplink and downlink direction. The GPRS mobile station may transmit
and receive simultaneously on one or more PDTCHs. Opposed to the
circuit-switched TCH, the PDTCH is unidirectional!
PACCH (Packet Associated Control Channel):
The PACCH is the only PDCH being available in both directions
during a unidirectional GPRS transaction. The PACCH is used to
transmit RLC/MAC control information between the PCU and the mobile
station.
PTCCH (Packet Timing Advance Control Channel):
Distinction needs to be made for the PTCCH/U (-> uplink) and the
PTCCH/D (-> downlink). The PTCCH is only applicable in the
52-multiframe positions 12 and 38 in uplink and downlink direction.
The PTCCH/U is divided into 16 subchannels within eight
52-multiframes serving 16 different MS. (Another possibility for TA
Control is to use control messages on PACCH when polled by the
network)
* Nokia Mobile Phones July 9, 2002 Sascha Meyer CONFIDENTIAL
Network Access and Packet Transmission
The Initial Access in GPRS:
The initial access is used to convey the reason for accessing the
network and to determine the distance between MS and network.
The initial access is done on the PRACH if a PCCCH is provided in a
cell or on the RACH if only the CCCH is available.
On the RACH, the regular CHAN_REQ message is used to convey the
reason for access.
On the PRACH, the PACK_CHAN_REQ message is used.
Independent of the number of information bits, each PACK_CHAN_REQ
needs to fit in the shortened access burst which may carry 36
information bits (-> puncturing).
* Nokia Mobile Phones July 9, 2002 Sascha Meyer CONFIDENTIAL
Network Access and Packet Transmission
One-Phase Packet Access
Requested and selected by the mobile station.
Initial access message is responded to by suitable resource
allocation in uplink direction (on one TS only if initiated on
RACH).
Even if MS requests One-Phase access, network may enforce Two-Phase
access by allocating only a single block to requesting MS (to
further specify its request).
Problem: initial access message cannot uniquely identify sending
MS
=> different MSs may try to start using same resource
allocation
=> Contention resolution required!
Two-Phase Packet Access
Selected by the MS by asking only for a single block allocation (on
RACH) or by explicitly requesting Two-Phase Packet Access (on
PRACH).
Two-Phase Packet Access is mandatory in case of Unack. RLC/MAC
transmission mode.
No Contention resolution required,
but Two-Phase Packet Access takes twice the time of One-Phase
Packet Access
=> Preferred procedure for high load situations
* Nokia Mobile Phones July 9, 2002 Sascha Meyer CONFIDENTIAL
Network Access and Packet Transmission
Example of Two-Phase Packet Access:
* Nokia Mobile Phones July 9, 2002 Sascha Meyer CONFIDENTIAL
Network Access and Packet Transmission
The Temporary Block Flow (TBF):
TBF is introduced to distinguish between ongoing packet
transactions
May involve more than one TS
TBF is uniquely identified by a Temporary Flow Identity (TFI)
TFI is part of each block sent up- or downlink
The TFI is unformatted and has a length of 5 bits.
* Nokia Mobile Phones July 9, 2002 Sascha Meyer CONFIDENTIAL
Network Access and Packet Transmission
The Trouble with Resource Allocation:
Packet Switched mobile networks do not deploy dedicated resources
but rather resources on demand. One PDCH or PDTCH is shared among
many users.
Downlink direction is not critical as the network may identify
addressed MSs in each downlink block.
Uplink direction is very critical -> With several MSs collisions
are probable.
=> Uplink Transmissions Need to be Scheduled and
Controlled by the Network!!!
Network Access and Packet Transmission
Fixed Allocation of Uplink Resources
Network sends bitmap to MS identifiying all blocks within several
consecutive 52-multiframes where the mobile station may
transmit.
There may be more than one bitmap in case of more than one TS
used.
More resources can be requested freely when the MS is in a fixed
allocation.
Dynamic Allocation of Uplink Resources
The Uplink State Flag (USF) regulates the resource
allocation.
The USF is part of every downlink data or control block sent by the
network.
USF of downlink block k identifies user of uplink block
(k+1).
(This is the preferred Resource Allocation method by
operators)
Extended Dynamic Allocation of Uplink Resources
Only optional for network and MS.
Only usable in multislot assignments.
Also utilizes USF for uplink transmission scheduling.
* Nokia Mobile Phones July 9, 2002 Sascha Meyer CONFIDENTIAL
Network Access and Packet Transmission
Complete Picture of Network Access and Resource Allocation
* Nokia Mobile Phones July 9, 2002 Sascha Meyer CONFIDENTIAL
Network Access and Packet Transmission
And what about Downlink Resource Allocation???
Downlink transmission scheduling is no issue as it is automatically
controlled by the network.
Downlink reception -> a mobile station cannot determine in
advance when packets will be sent by the network.
=> A mobile station needs to receive and decode all downlink
data blocks on all assigned timeslots while involved in a downlink
TBF!!!
A mobile station will identify its downlink data packets by
checking the TFI, which is part of each downlink block.
* Nokia Mobile Phones July 9, 2002 Sascha Meyer CONFIDENTIAL
The GPRS Protocol Stack
Some Facts about the GPRS Protocol Stack
Note: The BSC and BTS are (almost) transparent -> most packet
rel. tasks in BSS are handled by the PCU
Note: LLC is the lowest GPRS protocol independent from the
underlying air interface standard
* Nokia Mobile Phones July 9, 2002 Sascha Meyer CONFIDENTIAL
The GPRS Protocol Stack
RLC/MAC (Radio Link Control/Medium Access Control):
The MAC sublayer controls the access to the transmission medium
(access, sharing, release of the physical medium). RLC deals with
segmentation and de-segmentation of data units from higher layers
(-> LLC). RLC also ensures data protection by applying ARQ
measures. RLC/MAC best match with OSI layer 2 .
LLC (Logical Link Control):
LLC is the lowest GPRS protocol, independent from the used air
interface protocols (makes GPRS core network as independent as
possible from air I/F). LLC is an OSI layer 2 protocol and offers
encapsulation of higher layer PDUs, acknowledged and unacknowledged
operation, and GPRS ciphering. LLC is based on HDLC.
SNDCP (Subnetwork Dependent Convergence Protocol):
SNDCP is responsible for in-sequence delivery of SNDCP PDUs and for
the actual transmission between MS and SGSN. It interfaces to the
supported packet data protocols (IP, PPP, IHOSS). SNDCP does
compression/decompression of data and packet headers (in case of
TCP/IP).
* Nokia Mobile Phones July 9, 2002 Sascha Meyer CONFIDENTIAL
The GPRS Protocol Stack
FR (Frame Relay):
-> simple packet-switched networking protocol (no error
correction!) used on the Gb interface. Together with the Network
Service Control, FR forms the Network Service (NS). NS
administrates the virtual connections between SGSNs and PCUs.
BSSGP (Basestation Subsystem GPRS Protocol):
Takes care of transmission of radio related control information
between PCU and SGSN (like BSSMAP between BSC and MSC). It also
transparently transfers LLC frames between mobile station and
SGSN.
GTP (GPRS Tunneling Protocol):
Carries information between all GSNs (and the Charging Gateway
Function (GCF)): GTP signaling and application data transfer
* Nokia Mobile Phones July 9, 2002 Sascha Meyer CONFIDENTIAL
Outlook
Enhanced Data Rates for Global Evolution (EDGE) Overview
* Nokia Mobile Phones July 9, 2002 Sascha Meyer CONFIDENTIAL
High Speed Mobile Data
HSCSD Overview
HSCSD is circuit switched:
Resources are allocated permanently and cannot be used for another
transaction.
HSCSD combines TCHs:
HSCSD combines up to 4 fullrate TCHs to provide data rates up to
57.6 kbit/s. Operators usually offer not more than 38.4 kbit/s (to
limit HSCSD complexity)
* Nokia Mobile Phones July 9, 2002 Sascha Meyer CONFIDENTIAL
HSCSD Overview
HSCSD offers symmetric and asymmetric connections:
Symmetric connections use same data rates up- and downlink. On
asymmetric connections, the data rate in downlink direction is
(always!) higher than in uplink.
HSCSD offers transparent and non-transparent connections:
No error recognition and correction but higher data rates on
transparent connections. RLP (Radio Link Protocol) on
non-transparent connections for error recognition and
correction.
HSCSD Performance:
This table shows the HSCSD throuput rates depending on the
allocated number of fullrate traffic channels.
1 TCH
2 TCHs
3 TCHs
4 TCHs
9.6 kb/s
19.2 kb/s
28.8 kb/s
38.4 kb/s
14.4 kb/s
28.8 kb/s
43.2 kb/s
57.6 kb/s
EDGE Overview
EDGE migrates GPRS to EGPRS:
EDGE largely builds on the established GPRS network. The protocol
stack is left almost unchanged, but extensive adaptations in the
RLC/MAC layers are required. 8PSK and GSMK are deployed
simultaneously.
* Nokia Mobile Phones July 9, 2002 Sascha Meyer CONFIDENTIAL
EDGE Overview
EGPRS introduces nine new coding schemes:
Nine new Modulation and Coding Schemes (MCS) to enable data rates
of up to 59.2 kbit/s per timeslot.
Coding Scheme
EDGE Overview
EDGE deploys a new modulation scheme: 3/8 Offset 8-PSK
* Nokia Mobile Phones July 9, 2002 Sascha Meyer CONFIDENTIAL
EDGE Overview
EGPRS and 8PSK Modulation:
EDGE/EGPRS deploys 3/8 Offset 8-PSK modulation to limit spectrum
requirements to a minimum
Opposed to GMSK which (theoretically) contains no amplitude
modulation (AM),
8-PSK contains phase (PM) and amplitude modulation (AM).
Thus, 8-PSK modulated signals in EGPRS need to be transmitted with
smaller output power than GMSK to avoid that the power amplifier
becomes nonlinear (-> garbled signal).
Therefore, the coverage area of a BTS that deploys 8-PSK modulation
shrinks.
This effect increases with higher interference level.
* Nokia Mobile Phones July 9, 2002 Sascha Meyer CONFIDENTIAL
Thanks for Your Attention!
Nice-To-Know
Basestation Identity Code: BSIC = NCC (3 bit) + BCC (3 bit)
(Network and Basestation Color Codes)
Normal Burst:
* Nokia Mobile Phones July 9, 2002 Sascha Meyer CONFIDENTIAL
Nice-To-Know
Carries only signaling
Carries many control channels and serves many subscribers on one
TS
26er multiframe:
Pos 12 -> SACCH (TA, Power Control), needs 4 consecutive
26-multiframes
Pos 25 -> IDLE to allow measurement of neighboring SCHs =>
main reason for 26-multiframe structure: measurement in idle
position varies against 51-multiframes (that carry the SCH)
52er multiframe:
Network dynamically allocates 52-multiframes on TSs depending on
GPRS load
Never 26-multiframe and 52-multiframe on same TS
Hyperframe only because of ciphering, FN is input in ciphering
algorithm A5, repeats every 3.5 h
* Nokia Mobile Phones July 9, 2002 Sascha Meyer CONFIDENTIAL
Nice-To-Know
detect errors by adding checksum, repeat requests of erroneous
blocks
FEC Forward Error Correction:
Channel Coding:
TRAU Frame: Class 1a (highly protected), 1b (protected), 2 (no
protection)
Interleaving:
GPRS mixes 4 bursts of a radio block but does not mix bursts of
multiple radio blocks (-> signaling, time to react, etc.)
GSM data spreads 4 bursts over 22 bursts
½ Rate Convolution Coder: