GSM Spectrum Allocation P-GSM Spectrum (Primary GSM) E-GSM Spectrum (Extended GSM) DCS-1800 Spectrum PCS-1900 Spectrum 1.

GSM Spectrum Allocation P-GSM Spectrum (Primary GSM) E-GSM Spectrum (Extended GSM) DCS-1800 Spectrum PCS-1900 Spectrum 1

P-GSM Spectrum (Primary GSM) The initial allocation of spectrum for GSM provided 124 carriers with Frequency Division Duplex for uplink and downlink: Duplex sub bands of width 25 MHz - duplex spacing 45 MHz Uplink sub band: 890 MHz to 915 MHz Downlink sub band: 935 MHz to 960 MHz Frequency spacing between carriers is 200 kHz (0.2 MHz) One carrier is used for guard bands. Total number of carriers (ARFCNs) = (25 0.2) / 0.2 = 124 2

E-GSM Spectrum (Extended GSM) E-GSM allocated extra carriers at the low end of the spectrum. The ARFCN numbers of P-GSM were retained (with 0 now included) and new ARFCNs introduced for the lower end, numbered 975 1023. Duplex sub bands of width 35 MHz - duplex spacing 45 MHz (same as PGSM) Uplink sub band: 880 MHz to 915 MHz Downlink sub band: 925 MHz to 960 MHz Frequency spacing of 200 kHz One carrier used to provide guard bands 3 0

900 MHz Utilization in Jordan 4 ZainOrange MHz 880885 925930 890902.5 935947.5 Zain 915 960

DCS-1800 Spectrum Digital Communication System 1800 MHz introduced a further spectrum range for GSM, typically used for smaller microcells overlaid over existing macrocells. Duplex sub bands of width 75 MHz - duplex spacing 95 MHz Uplink sub band: 1710 MHz to 1785 MHz Downlink sub band: 1805 MHz to 1880 MHz Frequency spacing of 200 kHz One carrier used to provide guard bands 5

1800 MHz Utilization in Jordan 6 Umniah MHz 17101740 18051835 1755 1850 1785 1880

1800 MHz Utilization in UK 7

PCS-1900 Spectrum Personal Communication System 1900 MHz is used in USA and Central America to provide a service similar to GSM. Duplex sub bands of width 60 MHz - duplex spacing 80 MHz Uplink sub band: 1850 MHz to 1910 MHz Downlink sub band: 1930 MHz to 1990 MHz Frequency spacing of 200 kHz One carrier used to provide guard bands 8

Multiple Access Techniques Purpose: to allow several users to share the resources of the air interface in one cell Methods: FDMA - Frequency Division Multiple Access TDMA - Time Division Multiple Access CDMA - Code Division Multiple Access 9

FDMA - Frequency Division Multiple Access Divide available frequency spectrum into channels each of the same bandwidth Channel separation achieved by filters: Good selectivity Guard bands between channels Signalling channel required to allocate a traffic channel to a user Only one user per frequency channel at any time Used in analog systems, such as AMPS, TACS Limitations on: frequency re-use number of subscribers per area 10 Time Frequency Channel BW

TDMA - Time Division Multiple Access Access to available spectrum is limited to timeslots User is allocated the spectrum for the duration of one timeslot Timeslots are repeated in frames 11 Time Frequency TS0TS1TS2TS3TS4TS5TS6TS7 TS0TS1TS2TS3TS4TS5TS6TS7 Frame Time slot

CDMA - Code Division Multiple Access Each user is assigned a unique digital code (pseudo - random code sequence) Code is used at Mobile Station and Base Station to distinguish different users signals Many users communications can be transmitted simultaneously over the same frequency band Advantages: very efficient use of spectrum does not require frequency planning Used in IS - 95 (cdmaOne) Not used in GSM Wideband CDMA techniques used in UMTS 12 Time Frequency Code

higher GSM frame structures 935-960 MHz 124 channels (200 kHz) downlink 890-915 MHz 124 channels (200 kHz) uplink frequency time TS0TS1 TS2 TS3 TS4 TS5 TS6TS7 GSM TDMA frame GSM time-slot (normal burst) Physical Channel 4.615 ms 546.5 s 577 s tailuser dataTrainingS guard space Suser datatail guard space 3 bits57 bits26 bits 57 bits1 13 GSM - TDMA/FDMA 156.25 bit periods Using FDMA and TDMA techniques, each carrier is divided into 8 Physical channels (timeslots) 13

Uplink and Downlink Synchronization TDMA is used to provide a set of 8 physical channels (timeslots) on each carrier One cycle of 8 timeslots forms the TDMA frame of 4.615 ms duration Each timeslot lasts for 0.577 ms (156.25 bit periods) and can contain one of several types of data burst A mobile station cannot transmit and receive simultaneously. The MS transmit burst is delayed by 3 timeslots after the BTS burst. This delay allows the MS to compare signal quality from neighboring cells 14

GSM Channels A timeslot is the basic physical resource (channel) in GSM, which is used to carry all forms of logical channel information, both user speech/data and control signaling. Logical Channels - the various ways we use the resource- one physical channel may support many logical channels. logical channels are piggybacked on the physical channels Multiframe structures is used to provide all the logical channels required. Different structures of data burst are used in the timeslot for different purposes. 15

Logical Channels GSM uses a set of logical channels to carry call traffic, signaling, system information, synchronization etc. The logical channels are divided into traffic channels and control channels They can then be further divided as shown: 16 TCH Traffic Channels TCH/F Traffic Channel (full rate) (U/D) TCH/H Traffic Channel (half rate) (U/D) BCH Broadcast Channels FCCH Frequency Correction Channel (D) SCH Synchronization Channel (D) BCCH Broadcast Control Channel (D) CCCH Common Control Channels PCH Paging Channel (D) RACH Random Access Channel (U) AGCH Access Grant Channel (D) CBCH Cell Broadcast Channel (D) NCH Notification Channel (D) DCCH Dedicated Control Channels SDCCH Stand alone Dedicated Control Channel (U/D) SACCH Slow Associated Control Channel (U/D) FACCH Fast Associated Control Channel (U/D) U = Uplink D = Downlink

Traffic Channels (TCH) TCH carries payload data - speech, fax, data- normally time slots 1 - 7 if TS0 is used for control signaling Connection may be: Circuit Switched - voice or data or Packet Switched data TCH may be: o Full Rate (TCH/F) one channel per user 13 kbps voice, 9.6 kbps data or o Half Rate (TCH/H) one channel shared between two users (alternatively from frame to frame) 6.5 kbps voice, 4.8 kbps data 17

Broadcast Channels (BCH) BCH channels are all downlink and are allocated to timeslot zero some times called BCCH. The RF carrier used to transmit the BCCH is referred to as the BCCH carrier. BCH Channels are: o FCCH: Frequency correction channel sends the mobile a burst of all 0 bits which allows it to fine tune to the downlink frequency o SCH: Synchronization channel, t he SCH carries the information to enable the MS to synchronize to the TDMA frame structure and know the timing of the individual timeslots, it sends the absolute value of the frame number (FN), which is the internal clock of the BTS, together with the Base Station Identity Code (BSIC). o BCCH: Broadcast Control Channel sends radio resource management and control messages: Location Area Identity (LAI). List of neighboring cells that should be monitored by the MS. List of frequencies used in the cell. Cell identity. Power control indicator. DTX permitted. Access control (i.e., emergency calls, call barring... etc.). CBCH description. Some messages go to all mobiles, others just to those that are in the idle state. As the name suggests, the broadcast channels send information out to all mobiles in a cell. These channels are also important for mobiles in neighboring cells which need to monitor power levels and identify the base stations. 18

Common Control Channels (CCCH) CCCH contains all point to multi-point downlink channels (BTS to several MSs) and the uplink Random Access Channel: o CBCH: Cell Broadcast Channel is an optional channel for general information such as road traffic reports sent in the form of SMS. o PCH: Paging Channel sends paging signal to inform mobile of a call, (paging can be performed by an IMSI, TMSI or IMEI). o RACH: Random Access Channel is sent by the MS to request a channel from the BTS or accept a handover to another BTS. A channel request is sent in response to a PCH message. o AGCH: Access Grant Channel allocates a dedicated channel (SDCCH) to the mobile. o NCH: Notification Channel informs MS about incoming group or broadcast calls. The main use of common control channels is to carry the information needed to set up a dedicated channel. Once a dedicated channel (SDCCH) is established, there is a point to point link between the base station and mobile. Associated control channels carry additional signalling to support dedicated channels. SACCH is associated with either SDCCH or TCH. FACCH is only associated with TCH. 19

Dedicated Control Channels (DCCH) DCCH comprise the following bi-directional (uplink / downlink) point to point control channels: o SDCCH: Standalone Dedicated Control Channel is used for call set up, Authentication, location updating and also point to point SMS. o ACCH: Associated Control Channels can be associated with either an SDCCH or a TCH, they are used for carrying information associated with the process being carried out on either the SDCCH or the TCH. o SACCH: Slow Associated Control Channel conveys power control and timing information in the downlink direction (towards the MS) and Receive Signal Strength Indicator (RSSI), and link quality reports in the uplink direction during a call or operations associated with SDCCH. o FACCH: Fast Associated Control Channel is used (when needed) for signalling during a call, mainly for delivering handover messages and for acknowledgement when a TCH is assigned. 20

Multiframes To provide all the logical channel operations with the physical resources (timeslots) available, an additional time frame structure is required in which the logical channels are multiplexed onto the timeslots. This is the concept of multiframes. Multiframes provide a way of mapping the logical channels on to the physical channels (timeslots). A multiframe is a series of consecutive instances of a particular timeslot. GSM uses multiframes of 26 and 51 timeslots. 21

Traffic Channel Multiframe The TCH multiframe consists of 26 timeslots. This multiframe maps the following logical channels: TCH SACCH FACCH TCH Multiframe structure: 22 TCH is always allocated on the 26 frame multiframe structure shown above. During a call the mobile is continually monitoring power levels from neighboring base stations. It does this in the times between its allocated timeslot. Once each traffic channel multiframe there is a SACCH burst which is used to send a report on these measurements to the current serving base station. The downlink uses this SACCH burst to send power control and other signals to the mobile. Frame # T = TCH, S = SACCH, I = Idle FACCH is not allocated slots in the multiframe. It steals TCH slots when required - indicated by the stealing flags in the normal burst.

Control Channel Multiframe The control channel multiframe is formed of 51 timeslots. CCH multiframe maps the following logical channels: A basic BCCH multiframe is shown below which use TS0. The main reason for other structures is the allocation of SDCCH/SACCH. 23 DownlinkUplink FCCH RACH SCH BCCH CCCH (combination of PCH and AGCH)

Different Control Channel structures 24 TS0 TS1 While TS0 as in the previous slide

GSM hierarchy of frames 012204520462047... hyperframe 012484950... 012425... superframe 012425... 012484950... 0167 multiframe frame burst slot 577 s 4.615 ms 120 ms 235.4 ms 6.12 s 3 h 28 min 53.76 s control traffic control The timing of the hyperframe relates to the cycle of frame numbers transmitted on the synchronization channel (SCH). After 26 x 51 x 2048 = 2715648 frames, the frame number (which consists of 22 bits) resets to zero. 25

Types of Data Burst The 156.25 bit periods of a timeslot can hold different types of data burst: 26

Timing Advance Timing Advance is needed to compensate for different time delays in the transmission of radio signals from different mobiles. Signal from MS1 takes longer to arrive at BTS than that from MS2 Timeslots overlap - collision 27 Timing Advance signal causes mobiles further from base station to transmit earlier - this compensates for extra propagation delay

TA Cont. The maximum value of Timing Advance sets a limit on the size of the cell. Timing Advance is calculated from delay of data bits in the RACH burst received by the base station long guard period allows space for this delay 28 It is adjusted during the call in response to subsequent normal burst positions. TA signal is transmitted on SACCH as a number between 0 and 63 in units of bit periods TA value allows for round trip from MS to BTS and back to MS Each step in TA value corresponds to a MS to BTS distance of 550 metres Maximum MS to BTS distance allowed by TA is 35 km

TA Cont. Timing Advance value reduces the 3 timeslot offset between downlink and uplink 29 Uplink TA Actual delay The Timing Advance technique is known as adaptive frame alignment

GSM Modulation Technique Gaussian Minimum Shift Keying (GMSK): Frequencies are arranged so there is no phase discontinuity at the change of bit period. Data pulses are shaped using a Gaussian filter: Smoothes phase transitions Gives a constant envelope QPSK is used in IS-95 (CDMA). Comparison of GMSK and QPSK: GMSK requires greater bandwidth QPSK reduces interference with adjacent carrier frequencies GMSK is more power efficient - less battery drain from MS on uplink GMSK has greater immunity to signal fluctuations 30

Speech over the Radio Interface 31

Speech Coding GSM transmits using digital modulation - speech must be converted to binary digits Coder and decoder must work to the same standard Simplest coding scheme is Pulse Code Modulation (PCM): Sampling every 1/(2*4k)=125 s Assume each sample is mapped to an 8 bit codeword (256 levels of an equalizer) then this requires data rate of 8k*8=64 kbps This is too high for the bandwidth available on the radio channels 32

Advanced Speech Coding Several approaches to modeling human speech which requires less data than PCM have been attempted. Estimates are that speech only contains 50 bits per second of information Compare time to speak a word or sentence with time to transmit corresponding text Attempts to encode speech more efficiently: speech consists of periodic waveforms -so just send the frequency and amplitude model the vocal tract - phonemes, voiced and unvoiced speech Vocoder - synthetic speech quality 33

ASC Cont. Speech obviously contains far more information than the simple text transcription of what is being said. We can identify the person speaking, and be aware of much unspoken information from the tone of voice and so on. Early vocoders which reduced the voice to just simple waveform information lacked the human qualities which we need to hold a meaningful communication. Hybrid encoders give greater emphasis to these qualities by using regular pulse excitation which encodes the overall tone of the voice in great detail. 34

GSM Voice Coder 35 Sent as frequency and amplitude

Error Correction Coding To reproduce speech, decoder needs bit error rate no more than 0.1% Radio channel typically gives error rate of 1% - need error correction Two approaches to error correction: Backward error correction: Automatic Repeat Request (ARQ) Forward error correction 36

ARQ In backward error correction, we assume that if the known check bits have been transmitted correctly, the rest of the data is correct. If the check bits do not match what is expected, the system asks for re-transmission. Not suitable for speech as the timing could become unintelligible if several repeats were necessary. However, in normal conversation, we naturally apply backward error correction by asking the person to repeat something we have not understood. 37

FEC Coding is added to the information bits which enable the original to be reconstructed even if there are errors - redundancy Repeat transmission is not required - suitable for speech Two types of FEC: Block codes Convolutional codes GSM uses a combination of both code types 38

GSM Error Correction Scheme The GSM coding scheme is described as concatenated. It divides the data into three prioritized sections and applies different levels of coding to each, the resultant code is then put together (concatenated) for transmission. 260 bits from voice coder are divided into 3 classes, according to their importance for speech reproduction: Rate of coding describes the amount of redundancy in the coded data: 1/2 rate code transmits twice as many bits as actual data Data rate is halved 39

Interleaving The algorithms used to recover the data are based on an assumption that errors will be randomly distributed. In practice errors tend to clump together as the mobile passes in and out of fade regions. To overcome this, the data bursts are not sent in their natural order, but are interleaved according to a pseudo-random pattern among a set of timeslots within the multiframe. Interleaving is applied after error coding and removed at the receiver before the decoding. Thus the coding algorithm has a more random distribution of errors to deal with. 40

Protocol Stack 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 ISO 7-Layer OSI Reference Model: 41

Vertical vs. Horizontal Communications 42 Horizontal (Peer-to-Peer) Communication Vertical (Entity-to-Entity) Communication

Each layer requests a service from the layer below The layer below responds by providing a service to the layer above Each layer can provide one or more services to the layer above Each service provided is known as a service Entity Each Entity is accessed via a Service Access Point (SAP) or a gate. Each SAP has a unique SAP Identifier (SAPI) 43

GSM Protocols In the OSI Reference Model, the logical channels of the air interface are at the Service Access Point (SAP) of the Physical Layer (Layer 1) ISDN Reference Model divides the protocol plane into a Control Plane and a User Plane corresponds to the control and traffic channels of the logical channels some user data (notably SMS text messages) is carried by the control plane 44

Protocols on the GSM Air Interface 45

User Plane - Speech Transmission Speech is encoded at the MS by the GSM Speech Codec (GSC) using hybrid encoders to give a data rate of 13 kbps. Then Forward Error Correction (FEC) is applied At the BSS the FEC and any encryption is decoded by the TRX and the data is converted to the ISDN format (ITU-T A-law) by a Transcoding and Rate Adaption Unit (TRAU). The A-law format carries data at 64 kbps across the fixed network. The TRAU may be part of the BTS or part of the BSC. If the TRAU is located at the BSC, then up to 4 speech channels may be multiplexed at the BTS (MPX in the diagram) onto an ISDN B channel which reduces the bandwidth required across the Abis interface. 46

Control Plane-GSM Signalling Protocols 47 CM: Connection Management MM: Mobility Management RR: Radio Resources Management LAPD: Link Access Procedure D LAPDm: Link protocol adapted for air interface (Um) BTSM: Base Transceiver Station Management BSSMAP: Base Station System Management Application Part DTAP: Direct Transfer Application Part SCCP: Signalling Connection Control Part TCAP: Transaction Capabilities Application Part MTP: Message Transfer Part MAP: Mobile Application Part UP: User Part ITU-T G.703, G705, G.732: Protocols for digital transfer of signalling messages on the Abis and A interfaces at 2048 kb/s or 64 kb/

Protocols Functionality Layer 1 Physical Layer On the air interface, the physical layer uses FDMA/TDMA, multiframe structure, channel coding etc. to implement the logical control channels. Services provided by layer 1 are: Access capabilities multiplexing logical onto physical channels Error protection error detection / correction coding mechanisms Encryption Layer 2 LAPDm Link Access Procedure on Dm channels Data link protocol responsible for protected transfer of signalling messages between MS and BTS. LAPDm supports the transport of messages between protocol entities on Layer 3, in particular: BCCH, PCH, AGCH and SDCCH signalling. 48

Cont. Layer 3 - Network Sub-layers: Radio Resource Management (RR) Mobility Management (MM) Connection Management 3 entities: Call Control (CC) Supplementary Services (SS) Short Message Service (SMS) RR is responsible for: Monitoring BCCH and PCH Administering RACH Requests for and assignments of data and signalling channels Measurements of channel quality MS power control and synchronization Handover Synchronization of data channel encryption and decryption MM is responsible for: TMSI assignment Location updating Identification of MS (IMSI, IMEI) Authentication of MS IMSI attach and detach Confidentiality of subscriber identity 49 Within Connection Management, Call Control (CC) is responsible for: Set up of normal calls (MS originated, MS terminated) Set up of emergency calls (MS originated only) Terminating calls DTMF signalling Call related supplementary services Service modification during a call (e.g. speech/data, speech/fax)

Enhancing GSM AMR (Adaptive multi-rate) speech coder Trade off speech and error correction bits Fewer dropped calls DTX discontinuous transmission Less interference (approach 0 bps during silences) More calls per cell Frequency hopping Overcome fading Synchronization between cells DFCA: dynamic frequency and channel assignment Allocate radio resources to minimize interference Also used to determine mobiles location TFO Tandem Free Operation

Tandem Free Operation (TFO) Concepts Enchance GSM operation through Improve voice quality by disabling unneeded transcoders during mobile-to-mobile calls Operate with existing networks (BSCs, MSCs) New TRAU negotiates TFO in-band after call setup TFO frames use LSBits of 64 Kbps circuit to carry compressed speech frames and TFO signaling MSBits still carry normal G.711 (PCM)speech samples Limitations Same speech codec in each handset Digital transparency in core network (EC off!) TFO disabled upon cell handover, call transfer, in-band DTMF, announcements or conferencing

TFO Tandem Free Operation No TFO : 2 unneeded transcoders in path With TFO (established) : no in-path transcoder A BTS BSC TRAU Ater MSC TRAU BSC MS BTS Abis GSM CodingG.711 / 64 kbGSM Coding ADAD DADA ADAD DADA (**) or 7 bits if Half-Rate coder is used A BTS BSC TRAU Ater MSC TRAU BSC MS BTS Abis GSM Coding[GSM Coding + TFO Sig] (2bits) + G.711 (6bits**) / 64 KbGSM Coding ADAD TFOTFO TFOTFO DADA PSTN* (*) or TDM-based core network

GSM Evolution A lot of developments within GSM leads towards 3G technology and the high data rates which this is intended to offer. These technologies are collectively known as 2.5 or B2G Generation GSM technologies and include: High Speed Circuit-Switched Data (HSCSD) General Packet Radio Service (GPRS) Enhanced Data for GSM Evolution (EDGE) CAMEL (Customized Application for Mobile Enhanced Logic) 53

2.5 G In GSM data transmission standardized with maximum 9.6 kbit/s advanced coding allows 14,4 kbit/s not enough for Internet and multimedia applications Main requirement is for increased data rates Mobile access to: Internet E-mail Corporate networks 54

GSM Evolution for Data Access 1997200020032003+ GSM GPRS EDGE UMTS 9.6 kbps 115 kbps 384 kbps 2 Mbps GSM evolution3G

HSCSD (High-Speed Circuit Switched Data) Increases bit rate for GSM by a mainly software upgrade Uses multiple GSM channel coding schemes to give 4.8 kb/s, 9.6 kb/s or 14.4 kb/s per timeslot Multiple timeslots for a connection e.g. using two timeslots gives data rates up to 28.8 kb/s Timeslots may be symmetrical or asymmetrical, e.g. two downlink, one uplink, giving 28.8 kb/s downloads but 14.4 kb/s uploads HSCSD handsets are typically limited to 4 timeslots, allowing: 2 up / 2 down (28.8 kb/s in both directions) 3 down and 1 up (43.2 kb/s down 14.4 kb/s up) This limitation arises because the handset operates in half duplex and needs time to change between transmit and receive modes Advantage: ready to use, constant quality, simple Disadvantage: channels blocked for voice transmission 56

GPRS (General Packet Radio Service) Packet switching: Data divided into packets Packets travel through network individually Connection only exists while packet is transferred from one node to next When packet has passed a node, the network resources become available for another packet User sees an always on virtual connection through the network Using free slots only if data packets ready to send (e.g., 115 kbit/s using 8 slots temporarily) Standardization 1998, introduction 2000. Advantage: one step towards UMTS, more flexible Disadvantage: more investment needed 57

GPRS Network Elements GPRS network elements GSN (GPRS Support Nodes): GGSN and SGSN GGSN (Gateway GSN) interworking unit between GPRS and PDN (Packet Data Network) acts as an interface and a router to external networks. The GGSN contains routing information for GPRS mobiles, which is used to tunnel packets through the IP based internal backbone to the correct Serving GPRS Support Node. The GGSN also collects charging information connected to the use of the external data networks and can act as a packet filter for incoming traffic. SGSN (Serving GSN) responsible for authentication of GPRS mobiles, registration of mobiles in the network, mobility management, and collecting information for charging for the use of the air interface. GR (GPRS Register) user addresses 58

GPRS architecture and interfaces MS BSSGGSNSGSN MSC UmUm EIR HLR/ GR VLR PDN GbGb GnGn GiGi SGSN GnGn 59

GPRS modifications on GSM network GSM Network ElementModification or Upgrade Required for GPRS Mobile Station (MS)New Mobile Station is required to access GPRS services. These new terminals will be backward compatible with GSM for voice calls. BTSA software upgrade is required in the existing base transceiver site. BSCThe base station controller (BSC) requires a software upgrade and the installation of new hardware called the packet control unit (PCU). The PCU directs the data traffic to the GPRS network and can be a separate hardware element associated with the BSC. GPRS Support Nodes (GSNs)The deployment of GPRS requires the installation of new core network elements called the serving GPRS support node (SGSN) and gateway GPRS support node (GGSN). Databases (HLR, VLR, etc.)All the databases involved in the network will require software upgrades to handle the new call models and functions introduced by GPRS. 60

GPRS Circuit/Packet Data Separation 61

SS7 BTS BSC MSC VLR HLR AuC GMSC BSS PSTN NSS A E C D PSTN Abis B H MS BSS Base Station System BTS Base Transceiver Station BSC Base Station Controller NSS Network Sub-System MSC Mobile-service Switching Controller VLR Visitor Location Register HLR Home Location Register AuC Authentication Server GMSC Gateway MSC 2.5G Architectural Detail SGSN Serving GPRS Support Node GGSN Gateway GPRS Support Node GPRS General Packet Radio Service IP 2G+ MS (voice & data) PSDN Gi SGSN Gr Gb Gs GGSN Gc Gn 2G MS (voice only) 62

GPRS protocol architecture apps. IP/X.25 LLC GTP MAC radio MAC radio FR RLC BSSGP IP/X.25 FR UmUm GbGb GnGn L1/L2 MS BSSSGSNGGSN UDP/TCP GiGi SNDCP RLC BSSGP IP LLCUDP/TCP SNDCP GTP 63

GPRS Air Interface New Packet logical channels defined - PBCCH, PDTCH etc. New multiframe structure based on radio blocks of 4 timeslots Allows up to 8 mobiles to share a timeslot For high data rates, several physical channels may be allocated to one user 4 levels of channel coding schemes (CS-1 to CS-4): Decreasing level of error checking Greater data throughput rates Scheme selected according to interference level (C/I) 64

Enhanced Data rates for GSM Evolution (EDGE) Use 8 Phase-Shift Keying (8PSK) modulation - 3 bits per symbol Improved link control allows the system to adapt to variable channel quality - leads to slightly reduced coverage area Applied to GSM, 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 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 65

GSM Spectrum Allocation P-GSM Spectrum (Primary GSM) E-GSM Spectrum (Extended GSM) DCS-1800 Spectrum PCS-1900 Spectrum 1.

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