WIRELESS SYSTEM AND NETWORKING

Transcription

1 LECTURE 6 WIRELESS SYSTEM AND NETWORKING References: Rappaport (Chapter 9 and 10) Bernhard (Chapter 3, 4 and 5) Garg (Chapter 8 and 9) Kaarenen (Chapter 1-5 and 9)

2 WIRELESS EVOLUTION Japan Europe Americas 1st Gen TACS NMT/TACS/Other AMPS 2nd Gen PDC GSM TDMA CDMA 3rd Gen W-CDMA/EDGE (EDGE in Europe and Asia outside Japan) EDGE cdma2000

3 GSM Formerly: Groupe Spéciale Mobile (founded 1982) but now: Global System for Mobile Communication Pan-European standard (ETSI, European Telecommunications Standardisation Institute) Simultaneous introduction of essential services in three phases (1991, 1994, 1996) by the European telecommunication administrations - seamless roaming within Europe possible Today many providers all over the world use GSM (more than 170 countries in Asia, Africa, Europe, Australia, America) More than 500 million subscribers (April 2001)

4 GSM - Network Architecture

5 GSM - Protocol Stack

6 GSM - Logical Channel

7 GSM - Control Channel Control channels fall into three categories: Broadcast: BCCH, FCCH, SCH One way, from base to mobile Common Control: RACH, AGCH, PC One way, some from base to mobile and some from mobile to the base Dedicated: SDCCH, SACCG, FACCH Two-way, stand-alone or embedded in the traffic channels All signaling channels share one carrier in a cell the dedicated control channels may be transmitted on traffic carriers Broadcast Channels Frequency Correction Channel (FCCH) Carries information for frequency correction Synchronization Channel (SCH) Carries information for frame synchronization and for identification of the BTS Broadcast Control Channel (BCCH) Broadcasts general information on the BTS Broadcasts cell-specific information, e.g. control channel organization, frequency hopping sequences, cell identification, etc.

8 GSM - Control Channel Common Control Channels Paging Channel (PCH) - downlink only downlink only for paging purposes Random Access Channel (RACH) - uplink only uplink only used by any MS to request allocation of a signalling channel (SDCCH) a slotted Aloha protocol is used, so collisions among MSs may happen Access Grant Channel (AGCH) - downlink only used to allocate a SDCCH or a TCH Notification Channel (NCH) - downlink only notify MS of voice group and voice broadcast calls (ASCI feature) Dedicated Control Channels Stand Alone Dedicated Control Channel (SDCCH) used for call setup (authentication, signaling, traffic channel assignment), location updates and SMS Slow Associated Control Channel (SACCH) always coupled with a SDCCH or TCH for communicating measurement data and control parameters Fast Associated Control Channel (FACCH) to response to increased signaling demand, e.g. during handover bandwidth (bit slots) are stolen from the associated TCH (traffic data are preempted)

9 GSM - Traffic Channel GSM support two types of traffic channels full rate (TCH/F): 22.8 kbps half rate (TCH/H): 11.4 kbps Mapping to physical channel full rate traffic channel - 1 timeslot half rate traffic channel - 1 timeslot in alternating frames Full rate channel may carry 13 kbps speech or data at 2.4, 4.8 or 9.6 kbps Half rate channel may carry 6.5 kbps speech or data at 2.4 or 9.6 kbps The carriers in a given cell are separated by Nx200 khz N is the frequency reuse cluster size (4 in GSM) The traffic carriers have 26-multi-frame structure The control carrier has 51- multi-frame structure The control carrier has higher energy than traffic carriers

10 GPRS Reuse the existing GSM infrastructure Introduce packet-switched routing functionality Better data transfer rates Low cost and connectivity-oriented Migration Path to 3G Networks Share radio resources: users share a pool of channels Channels are allocated to users only when packets are to be sent or received Users can use several time slots (packet data channels) simultaneously Volume-charging: charging is based on traffic volume instead of the duration of a session Comparison Packet-switched High bit rates (up to 170kbit/s) Short access times Friendly bill (based on volume) Robust application support Frequent transmission of small volumes Infrequent transmission of small or medium volumes

11 GPRS ARCHITECTURE New components introduced for GPRS services: SGSN (Serving GPRS Support Node), GGSN (Gateway GPRS Support Node) and IP-based backbone network Old components in GSM upgraded for GPRS services: HLR, MSC/VLR and Mobile Station SGSN At the same hierarchical level as the MSC. Transfers data packets between mobile stations and GGSNs. Keeps track of the individual MSs location and performs security functions and access control. Participates into routing, as well as mobility management functions. Detects and registers new GPRS MSs located in its service area GGSN Provides inter-working between PLMN and external packet-switched networks. Converts the GPRS packets from SGSN into the appropriate packet data protocol format (e.g., IP or X.25) and sends out on the corresponding packet data network. Participates into the mobility management. Maintains the location information of the mobile stations that are using the data protocols provided by that GGSN. Collects charging information for billing purpose.

12 GPRS Circuit-switched Architecture Low bit rates (maximum 14.4kbit/s) Long access times Unfriendly bill (based on duration) Limited application support Large volumes

13 GPRS ARCHITECTURE Backbone network Tunnels of data and signaling messages between GPRS support nodes. Protocol architecture based on the Internet Protocol (IP). GTP (GPRS Tunneling Protocol) used to tunnel user data and signaling between GPRS Support Nodes. All PDP (Packet Data Protocol) PDUs (Protocol Data Units) shall be encapsulated by GTP. Two kinds of GPRS backbone Network: Intra-PLMN backbone network: The IP network interconnecting GSNs within the same PLMN. Inter-PLMN backbone network: The IP network interconnecting GSNs and intra-plmn backbone networks in different PLMNs. Two intra-plmn backbone networks are connected via the Gp interface using Border Gateways and an inter-plmn backbone network. Border Gateway handles the packet transfer between GPRS PLMNs. HLR Enhanced with GPRS subscription data and routing information. Accessible from the SGSN via the Gr interface and from the GGSN via the Gc interface.

14 GPRS ARCHITECTURE - Backbone Packet Data Network Gi Inter-PLMN Backbone Gp Gi GGSN BG BG GGSN Intra-PLMN Backbone Intra-PLMN Backbone SGSN SGSN SGSN

15 GPRS ARCHITECTURE MSC/VLR Not needed for routing of GPRS data. Needed for the co-operation between GPRS and the other GSM services. e.g., Paging for circuit-switched calls that can be performed more efficiently via the SGSN Combining GPRS and non-gprs location updates Receives location information from SGSN or sends paging requests to SGSN via the Gs interface. Mobile Station GPRS MS includes two components: MT (Mobile Terminal). Typically a handset used to access the radio interface. TE (Terminal Equipment). Typically a laptop or a Personal Digital Assistant (PDA). Could be one unit combing the functionalities of a MT and a TE. Three types of MS: Class-A: Could be attached to both GPRS and other GSM services, and the MS supports simultaneous operation of GPRS and other GSM services. Class-B: Could be attached to both GPRS and other GSM services, but the MS can only operate one set of services at a time. Class-C: Could be exclusively attached to one service type at a given time.

16 GPRS - Protocol Stack

17 UTRAN - Architecture

18 UTRAN - Protocol Stack

19 INTRODUCTION

20 INTRODUCTION