GSM
GSM
01
TECHNICAL March 1997
ICS: 33.020
Key words: Digital cellular telecommunications system, Global System for Mobile communications (GSM)
ETSI
European Telecommunications Standards Institute
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Contents
Foreword .......................................................................................................................................................5
1 Scope ..................................................................................................................................................7
1.1 Normative references ..........................................................................................................7
1.2 Abbreviations .......................................................................................................................8
2 Set of channels....................................................................................................................................8
8 Modulation.........................................................................................................................................15
11 Performance......................................................................................................................................17
History..........................................................................................................................................................20
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Foreword
This Global System for Mobile communications Technical Specification (GTS) has been produced by the
Special Mobile Group (SMG) Technical Committee (TC) of the European Telecommunications Standards
Institute (ETSI).
This GTS is an introduction to the 05 series of the digital mobile cellular and personal communication
systems operating in the 900 MHz (P-GSM, E-GSM, R-GSM) and 1 800 MHz band (GSM 900 and
DCS 1 800).
This GTS is a TC-SMG approved GSM technical specification version 5, which contains GSM Phase 2+
enhancements/features to the version 4 GSM technical specification. The ETS from which this Phase 2+
GTS has evolved is Phase 2 GSM ETS 300 573 edition 4 (GSM 05.01 version 4.6.0).
GTS are produced by TC-SMG to enable the GSM Phase 2+ specifications to become publicly available,
prior to submission for the formal ETSI standards approval procedure to become European
Telecommunications Standards (ETS). This ensures the earliest possible access to GSM Phase 2+
specifications for all Manufacturers, Network operators and implementors of the Global System for Mobile
communications.
The contents of this GTS are subject to continuing work within TC-SMG and may change following formal
TC-SMG approval. Should TC-SMG modify the contents of this GTS it will then be republished by ETSI
with an identifying change of release date and an increase in version number as follows:
Version 5.x.y
where:
y the third digit is incremented when editorial only changes have been incorporated in the
specification;
x the second digit is incremented for all other types of changes, i.e. technical enhancements,
corrections, updates, etc.
The specification from which this GTS has been derived was originally based on CEPT documentation,
hence the presentation of this GTS may not be entirely in accordance with the ETSI rules.
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1 Scope
This Global System for Mobile communications Technical Specification (GTS) is an introduction to the
05 series of the GSM technical specifications for GSM and DCS 1 800. It is not of a mandatory nature, but
consists of a general description of the organization of the physical layer with reference to the technical
specifications where each part is specified in detail. It introduces furthermore, the reference configuration
that will be used throughout this series of technical specifications.
This GTS incorporates by dated and undated reference, provisions from other publications. These
normative references are cited at the appropriate places in the text and the publications are listed
hereafter. For dated references, subsequent amendments to or revisions of any of these publications
apply to this GTS only when incorporated in it by amendment or revision. For undated references, the
latest edition of the publication referred to applies.
[1] GSM 01.04 (ETR 350): "Digital cellular telecommunications system (Phase 2+);
Abbreviations and acronyms".
[2] GSM 03.03 (ETS 300 927): "Digital cellular telecommunications system
(Phase 2+); Numbering, addressing and identification".
[3] GSM 03.20 (ETS 300 929): "Digital cellular telecommunications system;
Security related network functions".
[4] GSM 03.22 (ETS 300 930): "Digital cellular telecommunications system;
Functions related to Mobile Station (MS) in idle mode and group receive mode".
[5] GSM 04.03: "Digital cellular telecommunications system (Phase 2+); Mobile
Station - Base Station System (MS - BSS) interface; Channel structures and
access capabilities".
[6] GSM 04.08 (ETS 300 940): "Digital cellular telecommunications system
(Phase 2+); Mobile radio interface layer 3 specification".
[7] GSM 04.21 (ETS 300 945): "Digital cellular telecommunications system; Rate
adaption on the Mobile Station - Base Station System (MS - BSS) interface".
[8] GSM 05.02 (ETS 300 908): "Digital cellular telecommunications system
(Phase 2+); Multiplexing and multiple access on the radio path".
[9] GSM 05.03 (ETS 300 909): "Digital cellular telecommunications system
(Phase 2+); Channel coding".
[10] GSM 05.04 (ETS 300 959): "Digital cellular telecommunications system;
Modulation".
[11] GSM 05.05 (ETS 300 910): "Digital cellular telecommunications system
(Phase 2+); Radio transmission and reception".
[12] GSM 05.08 (ETS 300 911): "Digital cellular telecommunications system
(Phase 2+); Radio subsystem link control".
[13] GSM 05.10 (ETS 300 912): "Digital cellular telecommunications system
(Phase 2+); Radio subsystem synchronization".
[14] GSM 03.30 (ETR 364): "Digital cellular telecommunications system; Radio
network planning aspects".
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1.2 Abbreviations
2 Set of channels
The radio subsystem provides a certain number of logical channels that can be separated into two
categories according to GSM 04.03 [5]:
1) The traffic channels (TCH): they are intended to carry two types of user information streams:
encoded speech and data. Two types of traffic channels are defined: Bm or full-rate (TCH/F) and
Lm or half-rate (TCH/H) traffic channels. For the purpose of this series of technical specifications,
the following traffic channels are distinguished:
All channels are bi-directional unless otherwise stated. Unidirectional downlink full rate channels,
TCH/FD are defined as the downlink part of the corresponding TCH/F. Unidirectional uplink full rate
channels are FFS.
Multislot configurations are defined as multiple (1 up to 8) full rate channels allocated to the same
MS. At least one channel shall be bi-directional (TCH/F). The multislot configuration is symmetric if
all channels are bi-directional (TCH/F) and asymmetric if at least one channel is unidirectional
(TCH/FD).
High Speed Circuit Switched Data (HSCSD) is an example of multislot configuration, in which all
channels shall have the same channel mode.
NOTE: For the maximum number of timeslots to be used for a HSCSD configuration, see
GSM 03.34.
2) The signalling channels: these can be sub-divided into BCCH (broadcast control channel), CCCH
(common control channel), SDCCH (stand-alone dedicated control channel) and ACCH (associated
control channel). An associated control channel is always allocated in conjunction with, either a
TCH, or a SDCCH. Two types of ACCH are defined: continuous stream (slow ACCH) and burst
stealing mode (fast ACCH). For the purpose of this series of technical specifications, the following
signalling channels are distinguished:
- stand-alone dedicated control channel, four of them mapped on the same basic physical
channel as the CCCH (SDCCH/4);
- stand-alone dedicated control channel, eight of them mapped on a separate basic physical
channel (SDCCH/8);
All associated control channels have the same direction (bi-directional or unidirectional) as the
channels they are associated to. The unidirectional SACCH/MD is defined as the downlink part of
SACCH/M.
When there is no need to distinguish between different sub-categories of the same logical channel, only
the generic name will be used, meaning also all the sub-categories (SACCH will mean all categories of
SACCHs, SACCH/T will mean both the slow, TCH associated, control channels,…).
The logical channels mentioned above are mapped on physical channels that are described in this set of
technical specifications. The different physical channels provide for the transmission of information
pertaining to higher layers according to a block structure.
3 Reference configuration
For the purpose of elaborating the physical layer specification, a reference configuration of the
transmission chain is used as shown in annex A. This reference configuration also indicates which parts
are dealt with in details in which technical specification. It shall be noted that only the transmission part is
specified, the receiver being specified only via the overall performance requirements. With reference to
this configuration, the technical specifications in the 05 series address the following functional units:
This reference configuration defines also a number of points of vocabulary in relation to the name of bits
at different levels in the configuration. It must be outlined, in the case of the encrypted bits, that they are
named only with respect to their position after the encryption unit, and not to the fact that they pertain to a
flow of information that is actually encrypted.
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NOTE 2: For half rate speech, the block is divided into two classes according to the importance of
the bits (95 bits for class I and 17 bits for class II).
NOTE 3: For data services, the net bit rate is the adaptation rate as defined in GSM 04.21.
NOTE 4: On SACCH, 16 bits are reserved for control information on layer 1, and 168 bits are used
for higher layers.
NOTE 5: CCCH channels are common to all users of a cell; the total number of blocks (m, n, p, r)
per recurrence period is adjustable on a cell by cell basis and depends upon the
parameters (BS_CC_CHANS, BS_BCCH_SDCCH_COMB, BS_AG_BLKS_RES and
NCP) broadcast on the BCCH and specified in GSM 05.02 and GSM 04.08.
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The basic radio resource is a time slot lasting ≈ 576,9 µs (15/26 ms) and transmitting information at a
modulation rate of ≈ 270.833 kbit/s (1 625/6 kbit/s). This means that the time slot duration, including guard
time, is 156,25 bit durations.
We shall describe successively the time frame structures, the time slot structures and the channel
organization. The appropriate specifications will be found in GSM 05.02 (multiplexing and multiple
access).
A diagrammatic representation of all the time frame structures is in figure 1. The longest recurrent time
period of the structure is called hyperframe and has a duration of 3 h 28 mn 53 s 760 ms (or 12 533,76 s).
The TDMA frames are numbered modulo this hyperframe (TDMA frame number, or FN, from 0 to
2 715 647). This long period is needed to support cryptographic mechanisms defined in GSM 03.20.
One hyperframe is subdivided in 2 048 superframes which have a duration of 6,12 seconds. The
superframe is the least common multiple of the time frame structures. The superframe is itself subdivided
in multiframes; two types of multiframes exist in the system:
- a 26-frame multiframe (51 per superframe) with a duration of 120 ms, comprising 26 TDMA frames.
This multiframe is used to carry TCH (and SACCH/T) and FACCH.
- a 51-frame multiframe (26 per superframe) with a duration of ≈ 235,4 ms (3 060/13 ms), comprising
51 TDMA frames. This multiframe is used to carry BCCH, CCCH (NCH, AGCH, PCH and RACH)
and SDCCH (and SACCH/C).
A TDMA frame, comprising eight time slots has a duration of ≈ 4,62 (60/13) ms.
The time slot is a time interval of ≈ 576,9 µs (15/26 ms), that is 156,25 bit durations, and its physical
content is called a burst. Four different types of bursts exist in the system. A diagram of these bursts
appears in figure 1.
- normal burst (NB): this burst is used to carry information on traffic and control channels, except for
RACH. It contains 116 encrypted bits and includes a guard time of 8,25 bit durations (≈ 30,46 µs).
- frequency correction burst (FB): this burst is used for frequency synchronization of the mobile. It is
equivalent to an unmodulated carrier, shifted in frequency, with the same guard time as the normal
burst. It is broadcast together with the BCCH. The repetition of FBs is also named frequency
correction channel (FCCH).
- synchronization burst (SB): this burst is used for time synchronization of the mobile. It contains a
long training sequence and carries the information of the TDMA frame number (FN) and base
station identity code (BSIC, see GSM 03.03). It is broadcast together with the frequency correction
burst. The repetition of synchronization bursts is also named synchronization channel (SCH).
- access burst (AB): this burst is used for random access and is characterized by a longer guard
period (68,25 bit durations or 252 µs) to cater for burst transmission from a mobile which does not
know the timing advance at the first access (or after handover).This allows for a distance of 35 km.
In exceptional cases of cell radii larger than 35 km, some possible measures are described in
GSM 03.30. The access burst is used in the RACH and after handover, as well as on the uplink of a
channel used for a voice group call in order to request the use of that uplink.
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1 hyperfram e = 2 048 superfram es = 2 715 648 T D M A fram es (3 h 28 m n 53 s 760 m s)
0 1 2 3 47 48 49 50
0 1 24 25
1 (26-frame) multiframe = 26 TDMA frames (120 ms) 1 (51-frame) multiframe = 51 TDMA frames (3060/13 ms)
0 1 2 3 4 22 23 24 25 0 1 2 3 46 47 48 49 50
0 1 2 3 4 5 6 7
TB Fixed bits TB GP
Frequency correction burst (FB) 3 8.25
3 142
The channel organization for the traffic channels (TCH), FACCHs and SACCH/T uses the 26-frame
multiframe. It is organized as described in figure 2, where only one time slot per TDMA frame is
considered.
(a) T T T T T T T T T T T T A T T T T T T T T T T T T -
26 frames = 120 ms
(b) T t T t T t T t T t T t A T t T t T t T t T t T t a
(a) case of one full rate TCH (b) case of two half rate TCHs
T, t: TDMA frame for TCH -: idle TDMA frame A, a: TDMA frame for SACCH/T
The FACCH is transmitted by pre-empting half or all of the information bits of the bursts of the TCH to
which it is associated (see GSM 05.03).
The channel organization for the control channels (except FACCHs and SACCH/T) uses the 51-frame
multiframe. It is organized in the downlink and uplink as described in figure 3.
The principle of slow frequency hopping is that every mobile transmits its time slots according to a
sequence of frequencies that it derives from an algorithm. The frequency hopping occurs between time
slots and, therefore, a mobile station transmits (or receives) on a fixed frequency during one time slot
(≈ 577 µs) and then must hop before the time slot on the next TDMA frame. Due to the time needed for
monitoring other base stations the time allowed for hopping is approximately 1 ms, according to the
receiver implementation. The receive and transmit frequencies are always duplex frequencies.
The frequency hopping sequences are orthogonal inside one cell (i.e. no collisions occur between
communications of the same cell), and independent from one cell to an homologue cell (i.e. using the
same set of RF channels, or cell allocation). The hopping sequence is derived by the mobile from
parameters broadcast at the channel assignment, namely, the mobile allocation (set of frequencies on
which to hop), the hopping sequence number of the cell (which allows different sequences on homologue
cells) and the index offset (to distinguish the different mobiles of the cell using the same mobile
allocation). The non-hopping case is included in the algorithm as a special case. The different parameters
needed and the algorithm are specified in GSM 05.02.
In case of multi band operation frequency hopping channels in different bands of operation, e.g. between
channels in GSM and DCS, is not supported. Frequency hopping within each of the bands supported shall
be implemented in the mobile station.
It must be noted that the basic physical channel supporting the BCCH does not hop.
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BCCH + CCCH
(downlink) F S B C F S C C F S C C F S C C F S C C -
BCCH + CCCH
R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R R
(uplink)
51 fra m es ≈ 23 5.38 m s
8 SDCCH/8 D 0 D 1 D 2 D 3 D 4 D 5 D 6 D 7 A 0 A 1 A 2 A 3 - - -
(downlink) D 6 A 6 A 7 - - -
D 0 D 1 D 2 D 3 D 4 D 5 D 7 A 4 A 5
8 SDCCH/8 A 5 A6 A 7 - - - D 0 D 1 D 2 D 3 D 4 D 5 D 6 D 7 A0
(uplink) A 1 A 2 A 3 - - - D 0 D 1 D 2 D 3 D 4 D 5 D 6 D 7 A 4
BCCH + CCCH
F S B C F S C C F S D 0 D 1 D 2 D 3 F S A 0 A 1 -
4 SDCCH/4
(downlink) F S B C F S C C F S D 0 D 1 D 2 D 3 F S A 2 A3 -
BCCH + CCCH D 0 D 1
D 3 R R A 2 A 3 R R R R R R R R R R R R R R R R R R R R R R R R R D 2
4 SDCCH/4
(uplink) D 3 R R A 0 A 1 R R R R R R R R R R R R R R R R R R R R R R R D 0 D 1 R R D 2
F: TDMA frame for frequency correction burst S: TDMA frame for synchronization burst
B: TDMA frame for BCCH C: TDMA frame for CCCH
D: TDMA frame for SDCCH A: TDMA frame for SACCH/C
R: TDMA frame for RACH
After coding the different channels (except RACH and SCH) are constituted by blocks of coded
information bits plus coded header (the purpose of the header is to distinguish between TCH and FACCH
blocks). These blocks are interleaved over a number of bursts. The block size and interleaving depth are
channel dependent. All these operations are specified in GSM 05.03.
NOTE 2: The 3 parity bits for TCH/FS detect an error on 50 bits of class I.
NOTE 3: The 3 parity bits for TCH/HS detect an error on 22 bits of class I.
8 Modulation
The modulation scheme is gaussian MSK (GMSK) with BT = 0,3. As already mentioned the modulation
rate is 1 625/6 kbit/s (≈ 270,83 kbit/s). This scheme is specified in detail in GSM 05.04 (Modulation and
demodulation).
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ii) Extended GSM 900 Band, E-GSM (includes Standard GSM 900 band);
For Extended GSM 900 Band, the system is required to operate in the following frequency band:
880 - 915 MHz: mobile transmit, base receive
925 - 960 MHz: base transmit, mobile receive
iii) Railways GSM 900 Band, R-GSM (includes Standard and Extended GSM 900 Band);
For Railways GSM 900 Band, the system is required to operate in the following frequency band:
NOTE: The term GSM 900 is used for any GSM system which operates in any 900 MHz band.
Operators may implement networks on a combination of the frequency bands above to support multi band
mobile stations which are defined in GSM 02.06.
The RF channel spacing is 200 kHz, allowing for 194 (GSM 900) and 374 (DCS 1 800) radio frequency
channels, thus leaving a guard band of 200 kHz at each end of the subbands.
The specific RF channels, together with the requirements on the transmitter and the receiver will be found
in GSM 05.05 (Transmission and reception).
In order to allow for low power consumption for different categories of mobiles (e.g. vehicle mounted,
hand-held, ..), different power classes have been defined. For GSM 900 there are four power classes with
the maximum power class having 8 W peak output power (ca 1 W mean output power) and the minimum
having 0,8 W peak output power. For DCS 1 800 there are three power classes of 4 W peak output
power, 1 W peak output power (ca 0,125 W mean) and 0,25 W peak output power.
Multi band mobile stations may have any combinations of the allowed power classes for each of the bands
supported.
The requirements on the overall transmission quality together with the measurement conditions are also in
GSM 05.05.
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1) The power control mechanisms which adjust the output level of the mobile station (and optionally of
the base station) in order to ensure that the required quality is achieved with the less possible
radiated power. Power levels with 2 dB steps have been defined for that purpose. This is described
in GSM 05.08 (radio subsystem link control) and GSM 05.05.
2) The synchronization of the receiver with regard to frequency and time (time acquisition and time
frame alignment). The synchronization problems are described in GSM 05.10 (synchronization
aspects).
3) The hand-over and quality monitoring which are necessary to allow a mobile to continue a call
during a change of physical channel. This can occur either because of degradation of the quality of
the current serving channel, or because of the availability of another channel which can allow
communication at a lower Tx power level, or to prevent a MS from grossly exceeding the planned
cell boundaries. In the case of duplex point-to-point connections, the choice of the new channel is
done by the network (base station control and MSC) based on measurements (on its own and on
adjacent base stations) that are sent on a continuous basis by the mobile station via the SACCHs.
The requirements are specified in GSM 05.08 (radio subsystem link control).
4) The measurements and sub-procedures used in the first selection or reselection of a base station
by a mobile are specified in GSM 05.08 (radio subsystem link control). (The overall selection and
reselection procedures, together with the idle mode activities of a mobile are defined in GSM 03.22
(functions related to MS in idle mode).)
5) The measurements and sub-procedures used by an MS in selecting a base station for reception of
a voice group or a voice broadcast call are specified in GSM 05.08 (radio subsystem link control).
The overall voice group and voice broadcast cell change procedures, being similar to the
reselection procedures related to the idle mode activities of an MS, are defined in GSM 03.22
(functions related to MS in idle mode).
11 Performance
Under typical urban fading conditions (i.e. multipath delays no greater than 5 µs), the quality threshold for
full-rate speech is reached at a C/I value of approximately 9 dB. The maximum sensitivity is approximately
-104 dBm for base stations and GSM mobiles and -102 dBm and -100 dBm for GSM 900 small MSs (see
GSM 05.05) and DCS 1 800 hand-helds, respectively.
Multi band MSs shall meet the requirements on each band of operation respectively.
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Annex A (informative): Reference configuration
R e c .0 5 .0 3
(4 ) b u rs t bu rs t (5 ) d iffe re n tia l
m o du la tio n tra ns m itte r
bu ilding m ultip lexin g e n co ding
a ir
R e c .0 5 .02 R e c .0 5.0 4 an te nn a
inte rfa c e
Reference configuration
Annex B (informative): Relations between specification
06 s e rie s 05 .1 0
C O D E R /D E C O D E R S Y N C H R O N IZ A T IO N
to a ll blo c k s
SPEECH
0 5.0 3 05 .0 2 05 .0 4 0 5.0 5
IN T E R L E A V IN G 0 3 .20 & 0 3 .2 1 ACCESS DE M O D ULATO R R E C E IV E R
C O D E R /D E C O D E R E N C R Y P T IO N & M U LT IP L E AND AND
CHANNEL M U L T IP L E X IN G MODULATOR T R A N S M IT T E R
0 4 .0 4
PR O TO CO LS
LAY ER 1
0 4 .0 5 & 04 .0 6
03 .0 9 & 0 5.0 8 & 0 3 .22
PR O TO CO LS
(H A N D -O V E R , P O W E R C O N TR O L )
LA Y E R 2
L IN K C O N T R O L
0 4 .0 7 & 04 .0 8
PR O TO CO LS Relations betw een specifications
LA Y E R 3
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History
Document history
April 1996 Creation of version 5.0.0 (CRs A007,A018, A019, A020)