Part 5. 2G and 2.5G Mobile Communication Systems

Transcription

1 Part 5. 2G and 2.5G Mobile Communication Systems p. 1

2 GSM (Global System for Mobile Communications) p. 2

3 Global GSM Subscribers 3000 Number of GSM Subscribers (Million) Year p. 3

4 History (1) Groupe Special Mobile established by CEPT Several proposals for GSM multiple access: wideband TDMA, narrowband TDMA, DS-CDMA, hybrid CDMA/FDMA, narrowband FDMA Eight prototype systems tested in CNET laboratories in France; Permanent nucleus set up Basic transmission principles selected: 8- slot TDMA, 200-kHz carrier spacing, frequency hopping; MoU signed GSM (Global System for Mobile communications) became an ETSI technical committee GSM phase 1 specifications frozen (drafted ) GSM1800 standardization began GSM 1800 specifications frozen; commercial operation delayed due to the lack of terminals; GSM: God Send Mobiles p. 4

5 History (2) GSM900 commercial operation started; GSM phase 2+ development started GSM submitted as a PCS technology candidate to the United States; PCS1900 standard adopted in the United States Enhanced full rate (EFR) speech codec standard ready; 14.4-Kbps standard ready; GSM1900 commercial operation started HSCSD standard ready; GSM cordless system (home base station) standardization started; EDGE standardization started GPRS standard ready; WCDMA selected as the third generation air interface EDGE standard ready GSM standardization moved to 3GPP and TSG GERAN established p. 5

6 Some Facts For providing telephone and ISDN services. Initially designed to unite mobile communication standards that were previously used over European countries. Huge success achieved afterwards. Became deployed globally. Advantages over 1G analog systems from users viewpoint: Higher digital voice quality and low cost alternatives to making calls such as text messaging Introduction of Subscriber Identity Module (SIM): a memory device that stores information such as subscriber s identification number, networks that can be used, and other user-specific information; offering convenience to users. Improved on-the-air privacy due to data encryption. p. 6

7 GSM System Architecture Home Location Register Visitor Location Register Authentication Center Mobile Station Base Station Controller Base Transceiver Station Operation and Maintenance Center Mobile Switching Center p. 7 All copied from Rappaport s Wireless Communications

8 BSS Consists of many BSCs which connect to a single MSC Provides and manages radio transmission paths between MSs and MSCs. Also manages the radio interface between MSs and other GSM subsystems. BSC Terminologies (1) May co-locate with a BTS Connects to remote BTSs by microwave links, leased lines or optical fibers. Controls up to several hundred BTSs. Controls handovers when BTSs involved are under the control of the same BSC, thereby alleviating the burden of the MSC in handling handovers. p. 8

9 Terminologies (2) NSS Manages the switching functions of the system. Allows MSCs to communicate with other networks such as PSTN and ISDN. MSC Is the central unit in NSS. Controls the traffic among all BSCs p. 9

10 Example When the car moves from the cell covered by BTS1 to the cell covered by BTS2, a so-called handoff operation is needed to transfer the communication with the MS from BTS1 to BTS2. Which function blocks are involved in this operation? What about when the car moved from BTS3 to BTS4? p. 10

11 Terminologies (3) HLR Is a database that contains subscriber information and location information for each user who resides in the same city as the MSC. Contains the International Mobile Subscriber Identity (IMSI) for each user, used to identify each home user. p. 11

12 VLR Terminologies (4) Is a database which temporarily stores the IMSI and customer information for each roaming subscriber who visits the coverage area of a particular MSC. Is linked between several adjoining MSCs in a particular market or geographic region. [When a roaming mobile is logged onto a particular VLR, the MSC sends the necessary information to the visiting subscriber s HLR so that calls to the roaming mobile can be appropriately routed over the PSTN by the roaming user s HLR.] p. 12

13 Terminologies (5) AUC Is a strongly protected database that handles the authentication and encryption keys for every single subscriber in the HLR and VLR. Contains a register called the Equipment Identity Register (EIR) which identifies stolen or fraudulently altered phones that transmit identity data that do not match with information contained in either the HLR or VLR. p. 13

14 Example Suppose that you are a local customer of GSM services provided by Hutchison in Hong Kong. In which function block of Hutchison s local GSM network will your subscriber information and location information be stored? If you travel to Paris and enjoy the international roaming mobile service, in which function block of the network in Paris will your information be stored? If your phone is lost and Hutchison disables your phone number as you requested, where will this number be stored in the network? p. 14

15 Terminologies (6) OSS Supports the operation and maintenance of GSM. Allows engineers to monitor, diagnose and troubleshoot the system. Main functions: to maintain all telecom hardware and network operations with a particular market to manage all charging and billing procedures to manage all mobile equipment in the system p. 15

16 Radio Air Interface Abis Interface carries traffic and maintenance data A Interface uses an SS7 protocol called the signaling correction control part (SCCP) supports communication GSM System Interfaces between the MSC and the BSS, and network messages between the individual subscribers and the MSC SS7 (Signaling System 7) All copied from Rappaport s Wireless Communications is a set of telephony signaling protocols which are used to set up the vast majority of the world's public switched telephone network telephone calls. p. 16

17 Frequency domain Radio Interface (1) Two bands of 25MHz Divides into 200kHz wide channels called ARFCNs (Absolute Radio Frequency Channel Numbers) Each channel is time shared between 8 subscribers using TDMA 25MHz 200kHz 25MHz MHz f (MHz) for reverse link (Uplink) for forward link (Downlink) Multiple Access Method Combination of TDMA and FDMA p. 17

18 Time domain Radio Interface (2) 8 time slots (TSs) per frame; each frame occupies 4.615ms; each time slot has µs. modulation data rate: bits kbps µ s = p. 18

19 Radio Interface (3) Collision of received signals MSs at different distances from the BS: different round trip delay Collision of the signals from mobiles assigned to adjacent time slots p. 19

20 Solution: Time Advance Radio Interface (4) Transmit and receive time spacing: 3 time slots Time Advance: BS commands MSs to advance their transmission by the round trip delay p. 20

21 Radio Interface Summary FDD (frequency division duplex) ARFCN (Absolute Radio Frequency Channel Number) Specifies the carrier frequency that is used. Each radio channel occupies 200kHz. p. 21 Copied from Rappaport s Wireless Communications

22 Physical channel: Channel Types Is the combination of a TS number and an ARFCN. Is the channel that is used by a user. E.g., user 3 is assigned a pair of physical channels TS2-ARFCN3 and TS7-ARFCN1000 Logical channel: Each specific time slot of frame may be dedicated to either handling traffic data, signaling data, or control channel data. link the physical layer with the data link layer Traffic channel (TCH): is used to carry digitized speech or data for a user. Control channel (CCH): Carries signaling or synchronizing commands between the BS and MS. p. 22

23 Multiframe structure for TCH Traffic Channels (1) 26 frames per multiframe; each multiframe occupies 120ms data are broken up every 13th frame by SACCH or idle frames the 26th frame contains idle bits when full-rate TCHs are used and contains SACCH data when half-rate TCHs are used p. 23

24 Traffic Channels (2) carrying speech: Full-Rate TCH: channel data rate: 22.8kbps; Full-Rate Speech Channel (TCH/FS): carries user speech digitized at a raw data rate of 13kbps Half-Rate TCH: channel data rate: 11.4kbps; Half-Rate Speech Channel (TCH/HS): carries digitized speech sampled at a rate half that of a full-rate channel, 6.5kbps Half-rate is an optional feature of GSM Used when the cell is nearly congested or when MS has low battery since it saves 30% more energy Could double the network capacity for voice traffic, at the expense of quality carrying data: Data Channel for 9600bps (TCH/F9.6) Data Channel for 4800bps (TCH/F4.8) Data Channel for 2400bps (TCH/F2.4) p. 24

25 Traffic Channels (3) Example of system state at arbitrary time p. 25

26 Three main control channels Broadcast Channel (BCH) Control Channels operates on the forward link of a specific ARFCN within each cell, and transmits data only in TS0 other seven timeslots for the same ARFCN are available for TCH data or DCCH data provides synchronization for all mobiles within the cell Common Control Channel (CCCH) occupies TS0 that is not otherwise used by the BCH or the Idle frame most commonly used control channels used to page specific subscribers, assign signaling channels to specific users, and receive mobile requests for service Dedicated Control Channel (DCCH) may exist in any time slot and on any ARFCN except TS0 of the BCH ARFCN bidirectional, forward and reverse link p. 26

27 BCH Broadcast Control Channel (BCCH) occupies frame 2 to frame 5 of a control channel multiframe (illustrated later) broadcast information: cell and network identity, operating characteristics of the cell (current control channel structure, channel availability and congestion) broadcast a list of channels that are currently in use within the cell Frequency Correction Channel (FCCH) occupies TS0 for the very first frame (frame 0) and is repeated every ten frames within a control channel multiframe allows each MS to synchronize its local oscillator to the exact frequency of BS Synchronization Channel (SCH) occupies TS0 of the frame immediately following the FCCH frame allows each MS to frame synchronize with the BS broadcast frame number (FN), base station identity code (BSIC), time advancement commands p. 27

28 CCCH Paging Channel (PCH) (forward) provides paging signals from the base station to all mobiles in the cell notifies a specific mobile of an incoming call which originates from the PSTN provides cell broadcast text message to all subscribers, SMS feature Random Access Channel (RACH) (reverse) used by a MS to acknowledge a page from the PCH used by a MS to originate a call uses a slotted ALOHA access scheme Access Grant Channel (AGCH) (forward) used by the BS to respond to a RACH sent by a MS carries data which instructs the MS to operate in a particular physical channel (time slot and ARFCN) the final CCCH message sent by the BS before the MS is moved off the control channel p. 28

29 DCCH Standalone Dedicated Control Channel (SDCCH) bidirectional, ensures that the MS and the BS remain connected while the BS and MSC verify the MS and allocate resources for the MS an intermediate and temporary channel used to send authentication and alert messages Slow Associated Control Channel (SACCH) associated with a TCH or a SDCCH forward link: send slow but regularly changing control information, like transmit power level instructions and specific timing advance instructions reverse link: carries information about the received signal strength and the quality of the TCH Fast Associated Control Channel (FACCH) carries urgent messages, same type of information as the SDCCH replaces all or part of a TCH when there is a need for some heavy-duty signaling (e.g., a handoff request) p. 29

30 Example of Control Channel Multiframe channel combination: FCCH+SCH+CCCH+BCCH p. 30

31 Examples of How a MS Behaves Synchronization with the Network When MS is turned on Search for the BCH: BCH operates at a specific ARFCN, just search for the freq. channel with the highest power level Search for the FCCH: BS transmits, during certain known intervals, a pure sine wave for the period of exactly one time slot; the received signal exhibits a tone at 1/4th of the GSM symbol rate, i.e., 67kHz Search for the SCH: SCH is in the time slot following FCCH Read broadcast info. in BCCH: location of the cell, how to access BS, etc.. 2. FCCH 1. p. 31

32 Registration A procedure that the MS informs its presence to the network when the MS is switched on. RACH AGCH SDCCH SDCCH SDCCH SDCCH SDCCH SDCCH p. 32 Copied from An Introducation to ELEC6040 Mobile Radio Communications, GSM Dept. of E.E.E., HKU

33 Call Establishment (MOC) Mobile-originated call (MOC) Mobile-terminated call (MTC) Procedure almost identical RACH AGCH SDCCH SDCCH SDCCH SDCCH SDCCH SDCCH SDCCH SDCCH FACCH FACCH FACCH FACCH Copied from An Introducation to GSM p. 33 TCH

34 Call Establishment (MTC) Mobile-originated call (MOC) Mobile-terminated call (MTC) Procedure almost identical Copied from An Introducation to GSM p. 34

35 Speech Transmission Copied from Rappaport s Wireless Communications p. 35

36 Physical Layer (1) Speech coding Based on Residually Excited Linear Predictive Coding (RELP) Yields 260 bits per 20ms block of speech Gives a bit rate of 13kbps. Discontinuous Transmission Mode (DTX) Exploits the fact that a normal person speaks for only 40% of time. No transmission during silent period => a longer subscriber battery life and less instantaneous radio interference Relative importance of speech-coder outputs Ia bits: the most important 50 bits out of 260 bits of speech Ib bits: the 132 bits that are less important than Ia bits Type II bits: the rest of 78 bits out of 260 bits p. 36

37 Channel coding for the speech signal: 50 Ia bits appended with 3 parity check bits 50 Ia bits & 3 parity bits & 132 Ib bits are altogether coded by a convolutional code with rate 1/2 and constraint length 5. The 78 Type-II bits are unprotected. The resultant gross data rate of the GSM speech with channel coding is 22.8kbps. Physical Layer (2) p. 37 Copied from Rappaport s Wireless Communications

38 Physical Layer (3) Channel coding for data channel: half rate punctured convolutional code Channel coding for control channel: a shortened binary cyclic fire code followed by a half rate convolutional code Interleaving To mitigate the effect of sudden fade. Copied from Rappaport s Wireless Communications 456 encoded bits for each 20ms speech frame are broken into eight 57-bit subblocks. The 8 sub-blocks are transmitted over eight consecutive traffic-channel (TCH) time slots. Each TCH time slot carries two 57-bit blocks for two segments of 20ms speech. p. 38

39 Burst formatting Physical Layer (4) Adds binary data to the cipher text to help synchronization and equalization. Ciphering Security achieved by encryption Encryption algorithm changed from call to call. Modulation 0.3 GMSK (Gaussian minimum shift keying) [0.3 means the 3dB bandwidth of the Gaussian pulse shaping filter with relation to the bit rate is BT = 0.3.] Binary ones and zeros are represented by shifting the RF carrier by ±67.708kHz, one fourth of the channel data rate of GSM ( kbps). Refer to Proakis s Digital Communications p. 39

40 Physical Layer (5) Frequency hopping To avoid persistent staying at a bad channel. Maximum hopping rate is hops per second Maximum number of hopping frequencies = 64 p. 40

41 Physical Layer (6) Multipath Channel: H(t,τ) Transmitted Signal D D D h(t,τ 0 ) h(t,τ 1 ) h(t,τ 2 ) h(t,τ L-1 ) Received Signal Channel equalization To combat against the adverse effects due to multipath propagation and fading With the help of training sequences in the midamble of every time slot. Received Signal Channel Equalization Recovered Signal inverse the channel effect: H -1 (t,τ) p. 41

42 Handover (1) The MS continuously monitors the neighboring cells perceived power levels. The home BS gives the MS a list of channels of other BSs for measurement. The measurement report is periodically sent from the MS back to the home BS. Different types of handover situations: Handover between BTSs under the control of the same BCS. [The MSC is not troubled to handle handover, so that MSC is relieved in the handover burden. But the MSC has to be notified about the switching of BTSs.] Handover between BTSs under the control of different BSCs but the same MSC. [The MSC has to control the handover procedure.] Handover between BTSs under the control of different MSCs (and, implicitly, different BSCs). [Communications between different MSCs required.] p. 42

43 Handover (2) p. 43 Copied from An Introducation to GSM

44 Handover (3) p. 44 Copied from An Introducation to GSM

45 Summary GSM system architecture is important. It is the base of other mobile ratio communication systems. BSC, MSC, HLR, VLR, AUC: full names and main functions. Main system parameters of GSM: in frequency domain, each channel occupies 200kHz bandwidth. And each frequency channel is further divided into 8 time slots, shared by 8 subscribers using TDMA. Collision of received signal in GSM: reason and solution. Half rate codec: advantages and disadvantages. Logical channels: BCCH, FCCH, SCH, PCH, RACH: full name, main function. How are these channels used when the MS synchronizes with network, register, and establish a call? Discontinuous transmission: reason and benefits Interleaving: combat sudden fade Frequency hopping: combat frequency selective fading p. 45

46 IS-95 (cdmaone) p. 46

47 Frequency Spectrum IS-95: cdmaone Key player: Qualcomm Use direct-sequence spread-spectrum technique Frequency reuse factor = 1 so that No frequency planning is required. System capacity is increased. Each CDMA channel occupies 1.25MHz. Chip rate = M chips per second. p. 47

48 IS-95 System Architecture MS BTS BTS BSC MSC MSC IWF VLR HLR/AC EIR VLR Equipment Identity Register BTS BSC PSTN Internet p. 48 Interworking Function (IWF): a technique for interfacing data between a wireless system and the telephone network; involves the use of modems or data terminal adapters to convert the data transmitted over the air interface and mobile network to a format that can be recognized and carried by the public telecommunications network.

49 Forward channel: Forward Channel (1) BS simultaneously transmits the user data for all mobiles in the cell by using different spreading sequences for mobiles. A pilot signal, spread by a specific code, is transmitted from the BS for channel estimation and enabling coherent detection at the receivers. Coherent detection at the MS forward link: BS MS time One pilot signal for all MSs in the cell; simple and efficient p. 49

50 Forward channel: Forward Channel (2) Spread by one of 64 orthogonal spreading sequences (Walsh codes) Orthogonality among all users signals is maintained as the signals are synchronously transmitted. Scrambled by a cell-specific long pseudorandom sequence (2 15 ) to reduce the interference between mobile using the same spreading sequence in different cells Frame length: 20ms p. 50

51 Forward Channel (3) Forward Link Channel Structure p. 51

52 Reverse channel: Reverse Channel (1) Mobiles signals are asynchronously transmitted. Orthogonality among all users signals is destroyed as a result of asynchronous transmission. no pilot signals, non-coherent detection at BS reverse link: MS BS time Coherent: each MS needs a pilot signal; inefficient and complicated p. 52

53 Reverse channel: Reverse Channel (2) Power control enables all mobiles to transmit with power levels such that received power levels of all signals are nearly the same. Orthogonal modulation: Each block of six encoded symbols of a user s data stream is mapped to one of the 64 orthogonal Walsh functions, resulting in 64-ary orthogonal signaling. Frame length: 20ms encoded user data stream: orthogonal Walsh functions p. 53

54 Reverse Channel (3) Reverse Link Channel Structure p. 54

55 Forward Link All copied from Rappaport s Wireless Communications p. 55

56 Reverse Link p. 56

57 Rate Sets Illustration of Main Functions (1) Rate Set 1: 9600, 4800, 2400, 1200bps Rate Set 2: 14400, 7200, 3600, 1800bps Speech coding: Original: Qualcomm 9600 bps Code Excited Linear Predictive (QCELP) coding; coding rate: 9600 bps (for Rate Set 1) Detects voice activity; Reduces to 1200 bps during silence periods. Enhanced: QCELP13; introduced in 1995; coding rate: 14.4 kbps (for Rate Set 2) Channel coding: Forward link: convolutional code with rate 1/2 and constraint length 9 (for Rate Set 1), punctured convolutional code with 3/4 (for Rate Set 2) Reverse link: convolutional code with rate 1/3 and constraint length 9 (for Rate Set 1), convolutional code with rate 1/2 (for Rate Set 2) p. 57

58 Illustration of Main Functions (2) Repetition of symbols: Repetition of coded symbols is required in order that a constant coded rate of symbols per second is obtained for all possible information data rates. Required because IS-95 supports variable-rate transmission: 1200bps, 2400bps, 4800bps, 9600bps. Block interleaver: 20ms block interleaver a 24 by 16 array for forward link, a 32 by 18 array for reverse link To randomize the data errors in a fading channel, so that channel coding can perform better RAKE receiver at both the MS and BS To exploit multipath diversity by means of spread-spectrum transmission. p. 58

59 Tight power control: Power Control (1) CDMA: interference limited system BS: noncoherent detection, interference on reverse link is more critical than it would be on the forward link Performance criterion target SIR is not sufficient, certain FER (0.2%~3%) should be maintained Near-far problem solved by a combination of open-loop and fast, closedloop power control. Fast power control s update rate is 800 updates per second. A simple up or down request is sent for each update. p. 59

60 1. BS Power Control (2) Reverse link open loop power control Aims to compensate the long-term channel variations caused by distance and shadowing Principle: the MS closer to the BS needs to transmit less power as compared to a MS that is farther away from the BS The MS adjusts its transmit power based on total power received in the forward link. If the received power is high (low), the MS reduces (increases) its transmit power BS is not involved forward link MS 2. MS: Measure received power. Decide to reduce or increase the transmit power 3. BS reverse link MS: Transmit signal with adjusted power p. 60

61 Power Control (3) Reverse link open loop power control Simple but significant error due to Assumption of reciprocity on the forward and reverse links Use of total received power including power from other BSs Too slow response time ~30ms to counter fast fading Reverse link closed loop power control Aims to compensate the short-term channel variations caused by fast fading Provides correction to the open loop power control Quick response time 1.25ms Consists of two parts inner-loop: keep the MS as close to its target SIR as possible outer-loop: adjust the BS target SIR for a given MS p. 61

62 Power Control (4) Reverse link closed loop power control p. 62

63 Forward link power control Power Control (5) aim at reducing interference on the forward link limit the in-cell interference, reduce other cell/sector interference set each traffic channel transmit power to the minimum required to maintain the desired FER at the mobile The MS continuously measures forward traffic channel FER, and reports this measurement to the BS periodically. After receiving the measurement report, the BS takes the appropriate action to increase or decrease power on the measured logical channel. 1. BS forward link MS: Measure FER on the forward link Adjust the transmitting power according to the measurement report BS :BS reverse link forward link MS: MS Report the measured FER to BS p. 63

64 Hard handofff Soft Handoff (1) A definite decision is made on whether to handoff or not Is initiated and executed without the user attempting to have simultaneous traffic channel communications with the two base stations Break before make strategy. The connection with the old traffic channel is broken before the connection with the new traffic channel is established Soft handoff A conditional decision is made on whether to handoff or not The user has simultaneous traffic communication with all candidate BSs. Depending on the changing pilot signal strength for the BSs involved, when it is evident that the signal from one BS is considerably stronger than those from the others, a hard decision will be made to communicate with only one. Make before break, universal frequency reuse of CDMA Diversity gain p. 64

65 Soft Handoff (2) Hard Handoff Soft Handoff New BS New BS Old BS Old BS New BS Soft handoff Forward link: multiple BSs transmit signal for one MS, MS uses Rake to achieve diversity gain, extra interference Reverse link: multiple BSs receive signal from one MS, selection combining is used to provide diversity gain, no additional interference p. 65

66 Soft Handoff (Illustration) p. 66 Copied from CDMA Systems Engineering Handbook.

67 Procedure: Summary-Soft Handoff Make before break during switching. Advantages Contacting the new base station before switching avoids mobile stations from losing contact with the system and hence avoids calls dropped. Diversity combining of multiple signals is possible; performance enhanced. Ping-pong effect in base station switching is avoided. The system is relieved from the burden of determining signal strengths, as it is done at mobile stations. Note: Carrier frequency is not required to be changed during soft handoff. p. 67

68 2.5G Data Services p. 68

69 2.5G Operators have invested a lot of money on the existing infrastructure. Before 3G can be deployed, a rapid way to upgrade the existing 2G infrastructure to support high-data-rate transmission and packet switching is essential because of the explosive demand on the Internet access. Evolved standards: GPRS (General Packet Radio Services) EDGE (Enhanced Data Rates for GSM and TDMA/136 Evolution) IS-95B p. 69

70 GSM Migration Paths HSCSD: high-speed circuit-switched data service, combines two to four of the time slots (out of a total of 8 in each frame) to provide service from 28.8 Kbps to 56 Kbps, attractive to carriers because it requires minimal new infrastructure Copied from /htyo/54/index.shtml p. 70

71 GPRS - Introduction (1) As a service providing optimized access to the Internet, while reusing to a large degree existing GSM infrastructure. Introduce packet-switched services into GSM: Many new protocols and nodes are added to the GSM network Primary features: Circuit- and packet-switched services in one mobile radio network circuit-switched: a data connection establishes a circuit, and reserves the full bandwidth of that circuit during the lifetime of the connection B Data waiting A Data Data C D Data waiting time p. 71

72 Primary features (Cont') GPRS - Introduction (2) packet switched: multiple users share the same transmission channel, only transmitting when they have data to send; the total available bandwidth can be immediately dedicated to those users who are actually sending at any given moment, providing higher utilisation where users only send or receive data intermittently; the data is transmitted in small parts called packages, ideal for bursty traffic, cost efficient and optimize the use of radio and network resources A Data Data Data B C Data D time p. 72

73 Primary features (Cont') GPRS - Introduction (3) Seamless connection to other external packet data networks, based on IP or X.25 Fast setup/access times: typically from 0.5~1s Support of QoS. Volume-based charging, GSM: time-based charging new GRPS radio channels: flexible allocation of timeslots per TDMA frame GSM: one timeslot for one user, 9.6 and 14.4kbps GPRS: one to eight timeslot for one user, increase data rate, 9-150kbps p. 73

74 GPRS network structure GPRS Network Structure (1) Copied from sumstoff2004/gprs_tutorial.pdf p. 74

75 Upgraded BSC GPRS Network Structure (2) adding a Packet Control Unit (PCU) PCU: differentiates data destined for the standard GSM network (or circuit switched data) and for the GPRS network (or packet switched data) Two new functional elements Serving GPRS supporting node (SGSN) routing, handover and IP address assignment Gateway GPRS supporting node (GGSN) basically a gateway, router and firewall rolled into one GPRS tunneling protocol (GTP) the connection between SGSN and GGSN, sits on top of TCP/IP, responsible for the collection of mediation and billing information p. 75

76 Handset Classes GPRS Handset Classes Class A: have two transceivers, allow to send / receive data and voice at the same time, example: Nokia N93 may be required to transmit on two different frequencies at the same time, and thus will need two radios. To get around this expensive requirement, a GPRS mobile may implement the dual transfer mode (DTM) feature. Class B: can send / receive data or voice but not both at the same time, During GSM service (voice call or SMS), GPRS service is suspended, and then resumed automatically after the GSM service (voice call or SMS) has concluded. Most GPRS mobile devices are Class B. Class C: connected to either GPRS service or GSM service. Must be switched manually between one or the other service, such as a GPRS PCMCIA card in a laptop p. 76

77 Coding Schemes GPRS Coding Schemes GPRS provides a number of coding schemes with different levels of error detection and correction. Different coding schemes are used according to channel conditions and service requirement. Coding Schemes CS-1 Coding Rate 1/2 Data Rate (using one timeslot) 8.0kbps CS-2 2/3 12.0kbps CS-3 3/4 14.4kbps CS-4 1 (no coding) 20.0kbps p. 77

78 The QoS profile An Example of GPRS QoS Copied from R. Kalden, I. Meirick and M. Meyer, Wireless Internet access based on GPRS, IEEE Personal Communications, pp. 8-18, Apr Parameters Precedence Reliability Delay for packets of 128 octets Maximum bit rate Mean bit rate GPRS limit (in 2000) Values High, normal, low Packet loss probability: e.g., 10-9, 10-4, 10-2 Coding schemes Mean (s) 95% (s) 160kbps CS-1 <0.5 8kbps~2Mbps 0.22bps~111kbps CS-2 <5 CS-3 <50 CS-4 Best effort <1.5 <25 <250 Best effort p. 78

79 EDGE - Introduction Enhanced Data rates for GSM Evolution (EDGE) or Enhanced GPRS (EGPRS): a new TDMA-based radio access technology for both TDMA/136 (or D-AMPS) and GSM systems for providing good Internet access to mobile users. Objective increase data transmission rates and spectrum efficiency facilitate new applications and increased capacity for mobile use A method to increase the data rates on the radio link for GSM support circuit- and packet-switched services add new modulation and channel coding to GPRS make adjustments to the radio link protocols offer significantly higher throughput and capacity. p. 79

80 EDGE - Network Structure EDGE is an add-on of GPRS and cannot work alone. A new physical layer with new modulation and channel coding techniques. Data rate: up to 384kbps Copied from Ericsson, "EDGE Introduction of highspeed data in GSM/GPRS networks", white paper. p. 80

81 EDGE - Basic Radio Parameters Copied from T. Ojanpera and R. Prasad, WCDMA: Towards IP Mobility... p. 81

82 EDGE - MCS MCS: Modulation Coding Schemes Modulation Coding Schemes Modulation Technique Coding Rate Data Rate (using one timeslot) MCS-1 GMSK kbps MCS-2 GMSK MCS-3 GMSK MCS-4 GMSK 1.0 (no coding) 17.6 MCS-5 8-PSK MCS-6 8-PSK MCS-7 8-PSK MCS-8 8-PSK MCS-9 8-PSK p. 82

83 Comparison GPRS and EDGE: a comparison of technical data p. 83 Copied from Ericsson, "EDGE Introduction of highspeed data in GSM/GPRS networks", white paper.

84 CDMA Migration Path G 2.5G 3G CDMA IS-95A IS-95B 1xRTT Data Only 1xEV-DO Data and Voice 1xEV-DV CDMA2000 3xRTT CDMA2000 family p. 84

85 IS-95B (1) Is an enhancement to IS-95A standard Offers the highest possible performance using the same air interface design as IS-95A IS-95A supports 9.6 kb/s using RS1 (Rate Set 1) 14.4 kb/s using RS2 (Rate Set 2) IS-95B uses, instead of one code channel, up to 8 code channels for high-rate data transmission, so that it supports kb/s at RS kb/s at RS2 p. 85

86 Enhancement over IS-95A IS-95B (2) Forward code channels: Up to eight walsh codes (1 walsh code per code channel) are assigned for the data burst to the high rate user Reverse code channels: Each reverse supplemental channel is assigned a different PN sequence mask derived from its fundamental PN sequence mask. Each mask corresponds to a different PN sequence shift. Power control: Power control for the supplemental code channels is derived from the fundamental code channel. That is, there is no independent power control loop for the supplemental code channels. Permitted code rates: During a data burst, all the code channels are transmitted at full rate; partial rates are not permitted. Due to "time-to-market" reasons, IS-95B is not popular. Most operators skip IS-95B and go directly to CDMA20001xRTT Source: D.N. Knisely, etc., "Evolution of wireless data services: IS-95 to cdma2000". IEEE Comm. Mag.. p. 86

87 p. 87 CDMA2000 1XRTT CDMA2000 1xRTT (1) 1X: the number of 1.25 MHz wide radio carrier channels used RTT: radio-transmission technology a convenient stepping stone for CDMA carriers moving to 3G, can also be thought of as a 2.5G technology since it uses the same 1.25 MHz bandwidth as IS-95 can be deployed in existing spectrum to double voice capacity with only a modest investment in infrastructure (fast forward power control, lower code rates, a coherent reverse link) Improvements over IS-95A: more sophisticated power control, new modulation on the reverse channels, improved data encoding methods => significantly higher capacity, provide IP-based packet-data rates of up to 144 Kbps Offers 50% longer stand by times: supported by Quick Paging Channel Backward and forward compatible with IS-95A/B Source: D.N. Knisely, etc., "Evolution of wireless data services: IS-95 to cdma2000". IEEE Comm. Mag..

88 CDMA2000 1xRTT (2) Main differences between IS-95 and CDMA2000 1xRTT 64 more traffic channels on the forward link that are orthogonal to the original set Some changes were also made to the data link layer to accommodate the greater use of data services CDMA-2000 has media and link access control protocols and QoS control. In IS-95, none of these were present, and the data link layer basically consisted of a "best effort delivery" RLP this arrangement is still used for voice. p. 88 Source: D.N. Knisely, etc., "Evolution of wireless data services: IS-95 to cdma2000". IEEE Comm. Mag..

89 Summary Main system parameters of IS-95: in frequency domain, each CDMA channel occupies 1.25M bandwidth. The chip rate is Mbps. Frequency reuse factor is one. Power control: reverse link, forward link Hard handoff and soft handoff GPRS introduces packet switched services to GSM. System architecture is modified: PCU, SGSN and GGSN are added. Measures employed by GPRS to provide higher data rates than GSM: various coding rate, multi-time slot transmission Measures employed by EDGE to provide higher data rates than GSM: new modulation (8PSK) schemes, various coding rate, multi-time slot transmission Measures employed by IS-95B to provide higher data rates than IS-95A: multi-code transmission p. 89