1. 1. GSM NETWORK PLANNING- TRANSMISSION OVERVIEW/PLANNING STUDENT TEXT EN/LZT 123 6914/2 R3A
2. 2. GSM Network Planning - Transmission Overview/Planning DISCLAIMER This book is a training document and contains simplifications. Therefore, it must not be considered as a specification of the system. The contents of this document are subject to revision without notice due to ongoing progress in methodology, design and manufacturing. Ericsson assumes no legal responsibility for any error or damage resulting from the usage of this document. This document is not intended to replace the technical documentation that was shipped with your system. Always refer to that technical documentation during operation and maintenance. This document was produced by Ericsson Radio Systems AB. It is used for training purposes only and may not be copied or reproduced in any manner without the express written Copyright 2002 by Ericsson Radio Systems AB consent of Ericsson. This document number, EN/LZT 123 6914/2, R3A supports course number LZU 108 3816/2. EN/LZT 123 6914/1 R3A
3. 3. Revision Record REVISION RECORD Date Revision No. Chapters Affected 2002-11-03 R3A All EN/LZT 123 6914/2 R3A
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5. 5. Table of Contents GSM Network Planning-Transmission Overview/Planning Table of Contents Topic Page 0. Table of Contents..............................................................................0 1. GSM Introduction-Interface and Node Hierarchy ..............................1 2. Media ..............................................................................................33 3. Techniques......................................................................................53 4. Bearer Networks .............................................................................69 5.1 Ericsson Products 5.1 ...................................................................129 5.2 Ericsson Products 5.2 ...................................................................165 6. Introduction to Network Planning-The Traffic Model .....................189 7. Access Network Topologies..........................................................211 8. Choice of Transmission Media ......................................................275 9. Project Management .....................................................................287 10. Network Design.............................................................................295 11. LoS Survey....................................................................................317 12. Detailed Planning of Microwave Links...........................................329 EN/LZT 123 6914/2 R3A -i -
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7. 7. GSM Introduction - Interfaces and Node Hierarchy Chapter 1 This chapter is designed to provide the student with an introduction to the GSM system. OBJECTIVES: Upon completion of this chapter the student will be able to: Draw a PLMN comprising classical GSM nodes and GPRS nodes SGSN-G 3.0 and GGSN 4.0. List the interfaces in a GSM PLMN Explain how user data is mapped in each interface
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9. 9. 1 GSM Introduction - Interfaces and Node Hierarchy 1 GSM Introduction - Interfaces and Node Hierarchy Table of Contents Topic Page SYSTEM ARCHITECTURE IN ERICSSONS GSM SYSTEM...............1 NODES ...........................................................................................................................3 INTERFACES...............................................................................................................10 OPERATION AND MAINTENANCE CENTRE.............................................................14 AIR INTERFACE (Um) ........................................................................18 CARRIERS, TIMESLOTS, AND TDMA FRAMES........................................................18 LOGICAL CHANNELS..................................................................................................20 CHANNEL COMBINATIONS........................................................................................23 Abis INTERFACE................................................................................24 Ater INTERFACE AND REMOTE BSC...............................................27 RBS2000..............................................................................................28 MULTIDROP.................................................................................................................29 DIGITAL CROSS CONNECT ..............................................................30 NODE HIERARCHY.............................................................................31 EN/LZT 123 6914/2 Rev R3A i
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11. 11. 1 GSM Introduction - Interfaces and Node Hierarchy SYSTEM ARCHITECTURE IN ERICSSONS GSM SYSTEM The GSM R9 network will be a multi-service network. It will accommodate the growing number of interconnections between a variety of networks circuit-switched and packet-switched, narrowband and broadband, voice and data, fixed and mobile. For the operator, the GSM R9 network means continuity of services, optimized end-user application portfolios and significant cost reductions in transmission, operation and maintenance. Examples of private corporate applications LAN/MAN interconnect, file transfer, CAD/CAM PBX extensions and tie line, Fax G3/G4 Corporate multimedia, video conference X-rays Examples of coding PCM MPEG2 ADPCM Transfer mode; Bearer network Circuit mode Private ISDN, Private voice network BGS (ISDN, PSTN), VPN (ISDN, PSTN), leased lines, Private cellular (DECT) Packet mode Private X.25, PVC X.25, Private ISDN (X.25), Mobitex Frame mode Private frame relay, Private PVC (FR), Private ISDN (FR) Cell mode Private ATM, VLL, Private DQDB Examples of transmission access techniques Baseband Modem PDH, SDH, TDMA, CDMA, HDSL, ADSL, FDM Medium Copper pair Fibre (FTTO, FTTR, FTTC...) Radio (macrocell, microcell, pico cell, radio P-P...) Satellite Coax Figure 1-1: Private, virtual private and business access. The Core Network of the GSM R9.1 is an evolved GSM R8 (and R9.0) core network. It supports both Circuit Switched and Packet Switched services. Figure 1-2 shows Ericssons GSM/WCDMA system for CN2.0/R9.1. The overall aim of CN2.0 is the introduction of the new node and layered network architecture. The physical split between circuit mode servers and MGWs is implemented. Ericsson has developed Cello-ased MGW R2 as an external MGW. R9.1 includes functions that, although not related to the architecture split, are dependent upon its implementation. It also includes features that could not be implemented in R9.0. EN/LZT 123 6914/2 Rev R3A 1
12. 12. GSM Network Planning - Transmission Overview/Planning CN2.0/R9.1 is the first combined WCDMA Systems/GSM release that will reach full GA for WCDMA. The release is based on 3GPP R99 June-01. It is permitted to combine GSM and WCDMA systems access technologies within the same node. IP Backbone Cello MGw IP SDH Network Cello MGwATM Backbone STM/TDM Based Transit Network PSTN ISDN PLMN Internet, Intranet HLR AuC FNR BSC RNC MSC server SGSN G SGSN W MSC server AXE MGw GMSC server AXE MGw GMSC server GGSNR IP R IP R Note: Not all nodes shown and named . Figure 1-2: Ericssons GSM/WCDMA System for CN2.0/R9.1 To create the architecture split (layered network architecture), the software of the existing MSC is upgraded to implement an internal split in MSC Server and AXE based Media Gateway, which will continue to serve the GSM BSS (and part of the WCDMA Systems traffic). This split also facilitates the utilization of the MSC Server part for controlling the WCDMA Systems traffic in the stand-alone Cello based MGW. When WCDMA Systems traffic increases further, there will typically be a need for additional call/session handling capacity. This can be achieved by deploying the stand-alone MSC Servers (without AXE media gateway function). MSC may have different configuration scenarios to support both 2G and 3G networks. 2 EN/LZT 123 6914/2 Rev R3A
13. 13. 1 GSM Introduction - Interfaces and Node Hierarchy MSC/VLR GSMTDM (Cello) CC MSC/MGW UMTSTDM ATM GSM MSC/VLR GSMTDM MSC-Server (Cello) MGW ATM UMTS TDM UMTS TDM UMTS ATM UMTS TDM/ATM UMTS/GSM-TDM UMTS/GSM-ATM UMTS-TDM/GSM-ATM UMTS-ATM/GSM-TDM UMTS/GSM-TDM/ATM UMTS/GSM-TDM UMTS-ATM/GSM-TDM UMTS TDM UMTS ATM UMTS TDM/ATM GSM-TDM GSM only GSM and WCDMA WCDMA only MSC-Server (Cello) MGW ATM UMTS TDM Figure 1-3: Different MSC Configuration Scenarios NODES GMSC VLR GMSC VLR GG SNGG SN HLRHLR EIREIR AU CAU C SMS- IW MSC SMS- IW MSC SMS- GMSC SMS- GMSC SGSNSGSN MSC VLR MSC VLR ISDN PSTN PSPDN CSPD N PDN: -Intranet -Extranet -Internet BSC RBSSIM SIM MS MS BSC RBSSIM SIM MS MS Core NetworkBSS DTI SOG BGW FNR MIN Note: Not all nodes and interfaces are shown and named Figure 1-4: Ericssons GSM Model EN/LZT 123 6914/2 Rev R3A 3
14. 14. GSM Network Planning - Transmission Overview/Planning The GSM/GPRS system contains the following components: Base Station System (BSS) Radio Base Station (RBS) Base Station Controller (BSC) Core Network (CN) Mobile services Switching Center (MSC) Gateway MSC (GMSC) Visitor Location Register (VLR) Home Location Register (HLR) Authentication Center (AUC) Equipment Identity Register (EIR) Short Message Service - Gateway MSC (SMS-GMSC) Short Message Service - InterWorking MSC (SMS- IWMSC) Serving GPRS Support Node (SGSN ) Gateway GPRS Support Node (GGSN ) Data Transmission Interworking unit (DTI) Flexible Number Register (FNR) Additional items possibly connected - Mobile Intelligent Network (MIN) - Billing Gateway (BGW) - Service Order Gateway (SOG) Base Station System (BSS) The Base Station System (BSS) consists of the functional units described in the following sections. Radio Base Station (RBS) A Base Transceiver Station (BTS) is the GSM radio equipment required to serve one cell. It contains the antenna system, radio frequency power amplifiers, and digital signaling equipment. The Ericsson product for the BTS is the Radio Base Station (RBS). 4 EN/LZT 123 6914/2 Rev R3A
15. 15. 1 GSM Introduction - Interfaces and Node Hierarchy The system versions are: RBS 2000 for GSM 900, GSM 1800, and GSM 1900 RBS 200 for GSM 900 and GSM 1800 Base Station Controller (BSC) The BSC controls and supervises a number of RBS and radio connections in the system. It handles the administration of cell data, the locating algorithm, and orders handovers. The node is based on Ericsson Digital Switching System AXE 10 switch. Transcoder Controller (TSC) The TRC performs speech coding and decoding functions and rate adaptation for data calls. The TRC is not a standard GSM network element and in Ericssons implementation it can be a stand-alone node or it can be integrated. Core Network The Core Network contains the functional units described in the following sections. Mobile Services Switching Center (MSC) The MSC is responsible for setting up, routing, and supervising calls to and from the mobile subscriber (mobility management, handover, ). Short messages, routed from the SMS-GMSC or sent from the Mobile Station (MS), are relayed in the MSC. The MSC is implemented using an AXE 10 switch or AXE 810 switch. AXE 810 is the name of the AXE version that will be available to the market in CN2.0/R9.1. Gateway MSC (GMSC) The GMSC is an MSC serving as an interface between the mobile network and other networks, such as the Public Switched Telephony Network (PSTN) and Integrated Services Digital Network (ISDN) for mobile terminating calls. It contains an interrogation function for retrieving location information from the subscribers HLR. The GMSC contains functions for rerouting a call to the mobile subscriber according to the location information provided by the HLR. EN/LZT 123 6914/2 Rev R3A 5
16. 16. GSM Network Planning - Transmission Overview/Planning The GMSC is implemented using an AXE 10 switch or AXE 810 switch. Visitor Location Register (VLR) The VLR temporarily stores information about the MS currently visiting its service area. In an Ericssons GSM network, the VLR is integrated with the MSC in the same AXE 10 switch or AXE 810. Home Location Register (HLR) The HLR database stores and manages all mobile subscriptions belonging to a specific operator. The HLR stores permanent data about subscribers, including the subscriber's supplementary services, location information, and authentication parameters. When a person buys a subscription, it is registered in the operators HLR. The HLR can be implemented with the MSC/VLR or as a stand-alone database. The HLR uses Mobile Application Part (MAP) signaling to the other nodes (Except for PC-based AUC). Flexible Number Register (FNR) FNR was introduced with Ericssons release to provide a flexible number function which enables mobile operators to allocate subscriber MSISDN freely without restricting it to the MSISDN series, held in the HLR where the corresponding IMSI series are held. FNR is modified to provide the function of number portability with GSM R7 in addition to flexible numbering. Number portability is a network feature that allows the subscribers to retain their MSISDN when they change their service provider within one country, based on the agreement between different network operators. FNR is a database which stores all the information needed to perform SCCP message translation before rerouting an incoming call to the correct HLR. The FNR has the same platform as HLR. It can be implemented as a stand-alone node or can be co-located with the other As (Application Module). 6 EN/LZT 123 6914/2 Rev R3A
17. 17. 1 GSM Introduction - Interfaces and Node Hierarchy Authentication Center (AUC) The AUC database is connected to the HLR. The AUC provides the HLR with authentication parameters and ciphering keys by generating triplets or quintuplets depending on the GSM release. Using these triplets or quintuplets, ciphering of speech, data, and signaling over the air-interface is performed. Both provide system security. The AUC is available as a PC or VAX-based system or as an integrated AUC. The PC-based version is connected to the Input/Output Group 20 (IOG20) similar to an operator terminal. The VAX-based version uses MAP signaling and is connected via S7 signaling links. The integrated AUC is implemented on an RPD or RPG within the AXE 10 or AXE 810 and can be co- located with a MSC/VLR. A new and more powerful RPG (RPG3) was built for AXE 810 switch. The RPG/RPG2 have more than four times the processing capacity of their predecessor RPD, and RPG3 has more than 12 times the processing capacity of the RPD. Equipment Identity Register (EIR) The EIR database validates mobile equipment. The MSC/VLR can request the EIR to check if an MS has been stolen (black listed), not type-approved (gray listed), normal registered (white listed), or unknown. The EIR is connected to the VLR via the S7 network and uses MAP signaling. The EIR is implemented as a UNIX operating system or as a VAX computer platform. Data Transmission Interworking Unit (DTI2) The DTI2 provides the interface necessary for fax and circuit- switched data communication. Short Message Service - Gateway MSC (SMS-GMSC) The SMS-GMSC routes MS-terminated short messages. For signaling to GSM entities, MAP signaling is used. For signaling to an Ericsson SC, an Ericsson variant of MAP is used. Any MSC/GMSC can be implemented as an SMS-GMSC. EN/LZT 123 6914/2 Rev R3A 7
18. 18. GSM Network Planning - Transmission Overview/Planning Short Message Service - InterWorking MSC (SMS-IWMSC) The SMS-IWMSC routes MS-originated short messages to the SC for delivery. For signaling to GSM entities, MAP signaling is used. For signaling to an Ericsson SC, an Ericsson variant of MAP is used. Any MSC/GMSC can be implemented as an SMS-IWMSC. Serving GPRS Support Node - SGSN The Serving GPRS Support Node is a primary component in the GSM network using GPRS. It forwards incoming and outgoing IP packets addressed to/from an MS that is attached within the SGSN service area. The SGSN handles packet routing and serves all GSM subscribers that are physically located within the geographical SGSN service area. The (packet-switched) traffic is routed from the SGSN to the BSC, via the BTS to the user equipment. Gateway GPRS Support Node GGSN The Gateway GPRS Support Node is the second new node type, introduced to handle GPRS connections. The GGSN handles the interface to the external IP packet networks and acts like a router for the IP addresses of all GPRS subscribers in the network. Additional Nodes Mobile Intelligent Network (Mobile IN) Mobile IN is used in conjunction with the Public Land Mobile Network (PLMN). It consists of service nodes that provide advanced services to subscribers. Mobile IN functions include the Service Switching Point (SSP) and the Service Control Point (SCP), or a combined Service Switching and Control Point (SSCP). The mechanism to support operator-specific services which are not covered by standardized GSM services, even while the UE is roaming outside the Home PLMN, is provided by the Customized Applications for Mobile network Enhanced Logic (CAMEL). 8 EN/LZT 123 6914/2 Rev R3A
19. 19. 1 GSM Introduction - Interfaces and Node Hierarchy The SSP function determines whether the SCP function is required. The SCP function provides the service. The SSP is typically located in an MSC. The SCP function may be located in the SSP node or it may be a stand-alone node. SSP-SCP communication occurs via the Ericsson Intelligent Network Application Part (INAP) protocol CS 1+. INAP CS 1+ is compatible with the standard protocol INAP CS 1, but offers additional functions. When the SSP and SCP are co-located, INAP messages are carried on internal AXE software signals. When the nodes are remote, INAP messages are carried on S7 links and use the Transaction Capabilities Application Part (TCAP) function. An example of an advanced service provided by Mobile IN is Virtual Private Network (VPN). The VPN service gives the corporate customer a private numbering plan within the PLMN network. The Mobile IN functions are implemented on AXE 10 or AXE 810 platforms. Service Center (SC) The SC receives, stores, and forwards a short message between the message sender and the MS. Ericsson offers the SC as a combined messaging system, for example, voice and fax on an MXE platform. Billing GateWay (BGW) The BGW collects billing information, Call Data Records (CDRs), in files from the network elements and immediately forwards the information to post-processing systems that use CDR files as input. The BGW acts as a billing interface to all network elements in an Ericsson network. The flexible interface of the BGW easily adapts to new types of network elements. Service Order Gateway (SOG) The SOG connects a Customer Administrative System (CAS) and a set of Ericsson Network Elements (NEs) to allow the CAS to exchange service data with the NEs. It provides a safe and reliable connection for updating the GSM network database and EN/LZT 123 6914/2 Rev R3A 9
20. 20. GSM Network Planning - Transmission Overview/Planning eliminates the operators need to create his own interface to each of the NEs. The SOG provides a remote interface to the HLR, the AUC, and the EIR. This combines the subscription management functionality of the HLR/AUC and the equipment management functionality of the EIR. Mobile Station (MS) The MS allows the subscriber to access the network through the radio interface. It is not specified as a network node in Ericssons GSM network. The MS consists of: Mobile Equipment (ME) The ME consists of radio processing functions and an interface to the user and other terminal equipment. Subscriber Identity Module (SIM) The SIM contains information regarding the user subscription and can be used with any MS. INTERFACES SGSN G MGW MSC Server Backbone Network ATM SGSN W MSC/VLR Gr Gn/Gom BSC GbAbis Gs Gf BS RNC Iu Iub Gr Gn/Gom Gf Backbone Network IP Other PLMN Gp GGSN Gi IP Network GsGSM BSS WCDMA Systems RAN HLRHLR AUCAUC FNR FNR BTS EIREIR MGW Iu MSC/VLR Other PLMN Fixed Network A Iu C C C H F to MSC Signaling Signaling and Traffic E Iu WCDMA Systems RAN GMSC SGSN G MGW MSC Server Backbone Network ATM SGSN W MSC/VLR Gr Gn/Gom BSCBSC GbAbis Gs Gf BS RNC Iu Iub Gr Gn/Gom Gf Backbone Network IP Other PLMN Gp GGSN Gi IP Network GsGSM BSS WCDMA Systems RAN HLRHLR AUCAUC FNR FNR BTS EIREIR MGW Iu MSC/VLR Other PLMN Fixed Network A Iu C C C H F to MSC Signaling Signaling and Traffic Signaling Signaling and Traffic E Iu WCDMA Systems RAN GMSC Note: Not all nodes and interfaces shown. Figure 1-5: Ericsson WCDMA/GSM Network Interfaces 10 EN/LZT 123 6914/2 Rev R3A
21. 21. 1 GSM Introduction - Interfaces and Node Hierarchy Um Interface The MS RBS (air-) interface uses GSM for the physical layer. For more information refer to section Um interface later in this chapter. Abis Interface The RBS - BSC interface is named Abis interface, which carries both signaling and traffic. For more information refer to section Um interface later in this chapter. A Interface The A Interface is the interface between the GSM access network and core network. GSM L1 GSM L1 Layer 1 Layer 1 LAPDm LAPDm LAPD LAPD MTP MTP MTP TU P / IS UP SCCP SCCPSCCP BTSMBTSMRR BSSAP RR BSSAP RR MM CM MAP TCAP RR MM CM Um Abis A MS C BS C BT S M S CM Connection Management MM Mobility Management RR Radio Resource Management CM,MM,RR = Radio Interface Layer 3 LAPDm Link Access Procedures for Dm-channel GSM L1 Air interface layer 1 BTSM BTS Management BSSAP Base Station System Application Part MAP Mobile Application Part TCAP Transaction Capabilities Application Part SCCP Signaling Connection Control Part ISUP ISDN User Part TUP Telephony User Part MTP Message Transfer Part Figure 1-6: GSM MS MSC Protocol EN/LZT 123 6914/2 Rev R3A 11
22. 22. GSM Network Planning - Transmission Overview/Planning C Interface The MSC Server HLR interface is a MAP interface used to perform the interrogation needed to set up calls to a mobile subscriber. To forward a short message to a mobile, the SMS gateway MSC interrogates the HLR to obtain routing information. F Interface The MSC - EIR interface is an optional MAP based interface for checking user equipment. H Interface The HLR - AUC interface is for retrieval of authentication parameters from the AUC. GSM L1 GSM L1 L1 bis L1 bis MAC MAC NS BSSGPBSSGPRLC LLCLLC GMM/SM Um Gb SGSNBSSMS LLC Logical Link Control RLC Radio Link Control MAC Medium Access Control BSSGP Base Station System GPRS Protocol GMM GPRS Mobility Management SM Session Management NS Network Service RLC NS GMM/SM Figure 1-7: GPRS MS SGSN Signaling 12 EN/LZT 123 6914/2 Rev R3A
23. 23. 1 GSM Introduction - Interfaces and Node Hierarchy Gb Interface The Gb interface between the SGSN and BSC (PCU) is used for both user data and signaling. The user data part carries end-user IP traffic encapsulated in LLC-PDU and transported over the FR network between the CN and the AN. GSM L1 GSM L1 L1 bis L1 bis MAC MAC NS L1 IPBSSGPBSSGPRLC TCP / UDP LLCLLC SNDCP IP Um Gb Gn GGSNSGSNBSSMS IP Internet Protocol SNDCP Sub-network Dependent Convergence Protocol LLC Logical Link Control RLC Radio Link Control MAC Medium Access Control BSSGP Base Station System GPRS Protocol GTP GPRS Tunneling Protocol TCP Transmission Control Protocol UDP User Datagram Protocol L1 Layer 1 L2 Layer 2 NS Network Service RLC Application NS SNDCP L2 GTP L1 L2 GTP IP IP TCP / UDP Gi Figure 1-8: GPRS Transmission Protocol Architecture Gn Interface The Gn interface is used for control signaling (for mobility and session management) between the SGSN and GGSN, as well as for tunneling of end-user data payload within the backbone network. On the Gn interface the GTP protocol is used for control signaling and for tunneling user plane data between SGSN and GGSN. EN/LZT 123 6914/2 Rev R3A 13
24. 24. GSM Network Planning - Transmission Overview/Planning Gi Interface The Gi interface is used to transport end-user IP data between the mobile network and external IP networks. It connects the GGSN to other networks. The Gi interface is also used for GGSN control signaling to SP servers located in IP networks such as the ISPs network. This usage involves external servers for end-user authentication and IP address allocation. Gp Interface The Gp interface is used for control signaling when the GSNs are located in different mobile networks. Gp provides a subset of Gn functionality. Gr Interface The SGSN supports the standard Gr interface to the HLR. MAP signaling is used over this interface in order to support storage/retrieval of subscriber data. Gs Interface The Gs interface is used towards the MSC server, with the BSSAP+ protocol. OPERATION AND MAINTENANCE CENTRE For centralized control of a network, the installation of a Network Management Center (NMC), with a subordinate Operation and Maintenance Centers (OMC) is advantageous. NMC staff can concentrate on system-wide issues, whereas local personnel at each OMC can concentrate on short-term, regional issues. The OMC and NMC functionality can be combined in the same physical installation, or implemented at different locations. The BTSs are supported through the BSC. Other Ericsson nodes including Message Center (MXE) can be supported. Core Network Operation and Support System (CN-OSS) is Ericssons implementation of OMC and/or NMC. CN-OSS management areas are based on the Telecommunication Management Network (TMN). TMN is a 14 EN/LZT 123 6914/2 Rev R3A
25. 25. 1 GSM Introduction - Interfaces and Node Hierarchy model for telecommunication networks management. The most important parts are: Operation and Support System NMC OMC OMC MIN MSC BSC BTS HLR AUC / EIR Figure 1-9: Central Supervision of All Network Elements. Configuration Management The Configuration Manager enables the operator to fully configure a node in a fast and efficient manner, enabling new nodes to be brought into service quickly, and existing nodes to be updated in a similar manner. Fault Management Ericssons Fault Management solution is designed to provide a completely integrated alarm and event handling solution, which provides the operator with element-level, sub-network as well as full network and service management. CN-OSS provides core/network support for all implementations of the FM solution. Performance Management The Performance Management solution is designed to provide comprehensive network performance management for all sub-network domains as well as specific sub-network level performance data analysis and reporting. CN-OSS offers the customer cost effective support for centralized, regional and local operations, and maintenance EN/LZT 123 6914/2 Rev R3A 15
26. 26. GSM Network Planning - Transmission Overview/Planning activities required by a cellular network. CN-OSS is the functional entity that allows the network operator to monitor and control the system. CN-OSS in Ericssons GSM system is based on the new CIF (Common Integration Framework) platform. The Common Integration Framework (CIF) from Ericsson is a unified platform that integrates common functionality of O & M applications for existing and new types of network elements. It provides operators with one solution to manage both their existing 2nd generation mobile network and their 3rd generation mobile network. CIF is a scalable platform that best meets the needs of the customer, thus avoiding costly over-dimensioning. Benefits The major CIF benefits are: CIF makes it possible to run, upgrade and maintain the O&M environment as one system. CIF is built on state of the art technology, thus creating a secure foundation upon which the O & M system can expand. CIF is a multi-technology platform consisting of commercial IT components facilitating integration in the operators existing IT environment. CIF provides a Configuration Service which stores a model of the network where changes can be performed on a planned configuration before applying to the network elements. CIF provides common security solution which the applications can use. CIF supports scalable O & M solutions for management of large networks. CIF supports distribution of O & M functionality over several servers. CIF maximizes return on investment by utilizing extensions of existing HW, rather than replacement. 16 EN/LZT 123 6914/2 Rev R3A
27. 27. 1 GSM Introduction - Interfaces and Node Hierarchy Description CIF provides numerous services (e.g. Object Request Broker, Web Server, Databases, Configuration Services, security) essential to network management. The different O & M systems exist as applications on top of CIF which acts as a bottom layer. The applications can be cellular planning tools, network consistency tools, alarm viewers, network topology viewers etc. EN/LZT 123 6914/2 Rev R3A 17
28. 28. GSM Network Planning - Transmission Overview/Planning AIR INTERFACE (Um) The Um interface is the interface between the MS and the BTS. Here, the communication is carried out using radio waves. Cell Allocation (CA) is the subset of the total frequency band that is available for one BTS. It can be viewed as the total transport resource available for the traffic between the BTS and its attached MSs. One carrier (pair of frequencies, one uplink and one downlink) of the CA is used to carry synchronization information and the Broadcast Control CHannel (BCCH). This carrier is known as the BCCH carrier or the c0 carrier. High efficiency and quality requirements have resulted in a rather complex way of utilizing the frequency resource. This chapter describes the basic principles of how to use this resource, from the physical resource itself to the information transport service offered by the BTS. CARRIERS, TIME SLOTS, AND TDMA FRAMES Table 1-1 shows the frequency bands allocated to each system. GSM 900 GSM 1800 GSM 1900 Uplink 890 - 915 MHz 1710 - 1785 MHz 1850 - 1910 MHz Downlink 935 - 960 MHz 1805 - 1880 MHz 1930 - 1990 MHz Table 1-1: Frequency Bands Carrier separation is 200 kHz, which provides: 124 carriers in the GSM 900 band 374 carriers in the GSM 1800 band 299 carriers in the GSM 1900 band Using Time Division Multiple Access (TDMA) each of these carriers are divided into eight Times Slots (TS). A TS has a duration of 3/5200 seconds (577 s). Eight TSs form a TDMA frame, with a duration of approximately 4.62 ms. At the BTS, 18 EN/LZT 123 6914/2 Rev R3A
29. 29. 1 GSM Introduction - Interfaces and Node Hierarchy the TDMA frames on all radio frequency channels in the downlink direction are aligned. The same applies to the uplink. The start of a TDMA frame on the uplink is, however, delayed by a fixed time corresponding to three time slot periods. The reason for this delay is to allow for the same TS number to be used in both uplink and downlink directions without requiring the MS to receive and transmit simultaneously. 9 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 Downlink Uplink offset TDMA frame No. TDMA frame No. MS to BTS transmission BTS to MS transmission Figure 1-10: TDMA Offset. One TS on a TDMA frame is called a physical channel, that is, on each duplex pair of carriers there are eight physical channels. A variety of information is transmitted between the BTS and the MS. The information is grouped into different logical channels. Each logical channel is used for a specific purpose such as paging, call set-up and speech. For example, speech is sent on the logical channel Traffic CHannel (TCH). The logical channels are mapped onto the physical channels. EN/LZT 123 6914/2 Rev R3A 19
30. 30. GSM Network Planning - Transmission Overview/Planning LOGICAL CHANNELS This section examines how the logical channels are used in the circuit switched communication between the MS and the RBS. GPRS channels are not covered in this document. Logical Channels Control Channels Traffic Channels BCH Broadcast CHannels CCCH Common Control CHannels DCCH Dedicated Control CHannels Half Rate Full Rate FCCH SCH BCCH PCH AGCH RACH SDCCH SACCH FACCH Figure 1-11: Logical Channels The logical channels can be divided into two categories, namely traffic channels and signaling/control channels. There are two forms of Traffic CHannels (TCH): Bm or full rate TCH (TCH/F). This channel carries information at a gross rate of 22.8 kbit/s. Lm or half rate TCH (TCH/H). This channel carries information at a gross rate of 11.4 kbit/s. Signaling channels are subdivided into three categories: Broadcast CHannels, BCH Common Control CHannels, CCCH Dedicated Control CHannels, DCCH The following sections describe specific channels within these categories. 20 EN/LZT 123 6914/2 Rev R3A
31. 31. 1 GSM Introduction - Interfaces and Node Hierarchy Broadcast Channels 1. Frequency Correction CHannel (FCCH) On the FCCH, bursts containing only zeroes are transmitted. This serves two purposes. Firstly, to ensure that this is the BCCH carrier, and, secondly, to allow the MS to synchronize to the frequency. The FCCH is only transmitted downlink on c0 Time Slot 0 (C0TS0). 2. Synchronization CHannel (SCH) The MS must synchronize to the time structure within this particular cell, and also needs to ensure that the chosen BTS is a GSM base station. By listening to the SCH, the MS receives information about the frame number in this cell and about the BSIC (Base Station Identity Code) of the selected BTS. The BSIC can only be decoded if the base station belongs to the GSM network. The SCH is only transmitted downlink on c0TS0. 3. Broadcast Control CHannel (BCCH) The MS must receive some general information concerning the cell to perform these functions: start roaming, wait for calls to arrive, or make calls. The required information is broadcast on the Broadcast Control CHannel (BCCH) and includes the Location Area Identity (LAI), maximum output power allowed in the cell, and the BCCH carriers for neighboring cells, on which the MS performs measurements. The BCCH is only transmitted downlink on c0TS0. Using FCCH, SCH, and BCCH, the MS tunes to a BTS and synchronizes with the frame structure in that cell. The BTSs are not synchronized to each other. Therefore, every time the MS decides to camp on another cell, it must listen to the FCCH, SCH and BCCH in the new cell. Common Control Channels (CCCH) 1. Paging CHannel (PCH) At certain time intervals, the MS listens to the PCH to check if the network wants to get in contact with the MS. The network may want to contact the MS because of an incoming call or an incoming short message. The information on the PCH is a paging message, including the MSs identity number (IMSI) or a temporary number (TMSI). The PCH is transmitted downlink on c0TS0 (possibly, also on other physical channels on c0). EN/LZT 123 6914/2 Rev R3A 21
32. 32. GSM Network Planning - Transmission Overview/Planning 2. Random Access CHannel (RACH) The MS listens to the PCH to know when it is paged. When the MS is paged, it replies by requesting a signaling channel on the RACH. The RACH can also be used if the MS wants to contact the network, for example, when setting up a call. The RACH is transmitted uplink on c0TS0 (possibly, also on other physical channels on c0). 3. Access Grant CHannel (AGCH) The network assigns a signaling channel (the Stand alone Dedicated Control CHannel, SDCCH) to the MS. This assignment is performed on the AGCH. The AGCH is transmitted downlink on c0TS0 (possibly, also on other physical channels on c0). Dedicated Control Channels (DCCH) 1. Stand alone Dedicated Control CHannel (SDCCH) The MS (as well as, the BTS) switches over to the assigned SDCCH. The call set-up procedure is performed on the SDCCH, as is the textual message transmission (short message and cell broadcast) in idle mode. The SDCCH is transmitted both uplink and downlink. The default in the Ericsson implementation is C0TS2 (possibly, also on any other physical channel) When call set-up is performed, the MS is told to switch to a TCH. 2. Slow Associated Control CHannel (SACCH) The SACCH is associated with the SDCCH or TCH (that is, sent on the same physical channel). On the uplink, the MS sends averaged measurements on its own BTS (signal strength and quality) and neighboring BTSs (signal strength). On the downlink, the MS receives information concerning the transmitting power to use and also instructions on the timing advance. The SACCH is transmitted both uplink and downlink. 3. Fast Associated Control CHannel (FACCH) If a handover is required, the FACCH is used. The FACCH works in stealing mode, which means that one 20 ms segment of speech is exchanged for signaling information necessary for the handover. Under normal conditions the subscriber 22 EN/LZT 123 6914/2 Rev R3A
33. 33. 1 GSM Introduction - Interfaces and Node Hierarchy does not notice the speech interruption because the speech coder repeats the previous speech block. CHANNEL COMBINATIONS Only certain combinations of logical channels are permitted according to the GSM recommendations. Figure 1-12 below shows the way in which logical channels can be combined onto Basic Physical Channels (BPC). The numbers appearing in parenthesis after the channel designations indicate sub-channel numbers. A sub-channel is formed by a specific subset of BPCs within a multiframe structure. (i) TCH/F + FACCH/F + SACCH/TF (ii) TCH/H(0.1) + FACCH/H(0.1) + SACCH/TH(0.1) (iii) TCH/H(0) + FACCH/H(0) + SACCH/TH(0) + TCH/H(1) (iv) FCCH + SCH + BCCH + CCCH (v) FCCH + SCH + BCCH + CCCH + SDCCH/4(0...3) + SACCH/C4(0...3) (vi) BCCH + CCCH (vii) SDCCH/8(0...7) + SACCH/C8(0...7) Where CCCH = PCH + AGCH + RACH Figure 1-12: Permitted Channel Combinations (DL). GPRS- Specific Channels Are Not Listed. SACCH/T indicates that the SACCH is associated with a TCH whereas SACCH/C is associated with a control channel. If the SMSCB is supported, the CBCH replaces the SDCCH sub-channel 2 in cases (v) and (vii) above. A combined CCCH/SDCCH allocation (case v) above can only be used when no other CCCH channel is allocated. The difference between channel combinations (ii) and (iii) is that combination (ii) addresses two different MSs, whereas combination (iii) addresses one single MS using both half rate traffic channels, for example, one for speech and the other for data. EN/LZT 123 6914/2 Rev R3A 23
34. 34. GSM Network Planning - Transmission Overview/Planning Abis INTERFACE The interface between the BSC and RBS is called Abis. The BSC and the RBS are connected via E1 links. Radio network planning provides information that is vital for planning the Abis part of the network, such as the number of E1 links required. When planning the radio network the cell planners consider, for example, the number of subscribers, subscriber behavior, grade of service (GoS), costs, possible sites for the RBSs, radio wave propagation, interference. The output will be the Channel Loading Plan (CLP): number of sites, site types (including number of TRUs/TRXs per site), and, possibly, also a map showing the location of the sites. Each TRX/TRU can handle a maximum of eight TCHs on the Um interface. Normally, the TRX/TRU for the c0 carrier handles six TCHs, plus two physical channels for signaling. The other TRXs/TRUs handles eight TCHs as long as no further physical channel is needed for signaling. MSC/VLR BSC RBS MS A interface Air interface A-bis Interface A-ter Interface TRC Figure 1-13: CS interfaces in a GSM network On the Abis interface, resources are allocated for each TRX/TRU. Normally, one TS (on the E1) is reserved for signaling (LAPD signaling) and two TSs (on the E1) are reserved for traffic (each TS carries four traffic channels). This means that three TSs on Abis are required for each TRX/TRU. 24 EN/LZT 123 6914/2 Rev R3A
35. 35. 1 GSM Introduction - Interfaces and Node Hierarchy BSC S = Signaling T = Full rate traffic S T S T T T T T TRX 1 S T S T T T T T T T T T T T T T TRX 2 T T T T T T T T 0 1 2 3 4 5 6 . 31 Synch S T T T T T T T T TRX 1 S T T T T T T T T TRX 2 c0 Figure 1-14: Um Abis relation. In the cell given in Figure 1-14, there are two carriers, that is, two TRXs. On the Um interface, TRX1 handles the c0 carrier (up- and downlink) with two physical channels for signaling and six for full rate traffic, and TRX2 handles eight full rate traffic channels. On the Abis interface three E1 TSs (64 kbit/s) are required for each TRX one for signaling and two for traffic. One E1 TS carries four full rate traffic channels (13 kbit/s for each traffic channel plus three kbit/s for inband signaling). =E1 frame synchronization S1 S2 S1 S2 T1 T1 T1 T1 T1 T1 T2 T2 T2 T2 T2 T2 T2 T2 .... S1 T1 T1 T1 T1 T1 T1 T1 .... S4 S3 T1 T1 T1 T1 T2 T2 T2 T2 T2 T2 T2 T2T1 T1 T1 T1 T1 T1 T1 T1 T3 T3 T3 T3 T3 T3 T3 T3 T4 T4 T4 T4 T4 T4 T4 T4 S2 S1 S3 S4 .... LAPD-M LAPD-C Figure 1-15: Um Abis , if the optional features LAPD- multiplexing and LAPD-concentration are used. The numbers refer to a specific TRX. EN/LZT 123 6914/2 Rev R3A 25
36. 36. GSM Network Planning - Transmission Overview/Planning LAPD concentration offers a more efficient usage of the signaling transmission between Base Transceiver Station (BTS) and Base Station Controller (BSC). The improved utilization of the signaling transmission is achieved by sharing the same 64 kbit/s time slot for several Transceivers with low signal transmission. By concentrating up to four LAPD signaling links upon one 64 kbit/s A-bis PCM timeslot, the required signaling transmission capacity can be reduced by approximately 25%. One TRX requires 2.25 TS in the PCM link. The LAPD concentration is most efficient for RBS sites with three TRXs or more per cell. LAPD concentration can be used when RBS 200 and RBS 2000 are cascaded in the same transmission link. This feature can not be used simultaneously with LAPD multiplexing. LAPD multiplexing offers another example of efficient usage of the signaling transmission between Base Transceiver Station (BTS) and Base Station Controller (BSC). This is especially useful for small sites (typically two TRXs or less). The improved utilization of the signaling transmission is achieved by multiplexing of A-bis LAPD signaling links and traffic links on the same 64 kbit/s link. One TRX requires two TSs on the PCM link. Sub rate switching on RBS site is required and it is only supported in RBS 2000. This feature can normally not be used together with LAPD concentration in the same DXU. See the next section. 26 EN/LZT 123 6914/2 Rev R3A
37. 37. 1 GSM Introduction - Interfaces and Node Hierarchy A-ter INTERFACE AND REMOTE BSC R7 introduced the A-ter interface between a distributed BSC and the TRC (Transcoder Controller) which allow the migration from a coverage solution to a high capacity solution in a cost efficient way. The introduction of a limited number of remote BSCs can be justified by savings in transmission cost due to the dynamic utilization of transmission resources on the interface between the remote BSCs and the Transcoders. The market- unique Ericsson feature, Dynamic Allocation of Transcoder Resources, makes it possible for up to 16 BSCs to share the same transcoders in the TRC (Transcoder Controller) node integrated with the central BSC. However, remote BSCs should be introduced at a limited number of strategically chosen locations when the transmission savings on the link from the remote BSC to the central BSC/TRC justifies the investment cost, the increased O&M costs and spare part costs associated with the remote BSC node. DXC Hub Node AA A Ring, Tree, etc. MSC BSC/TRC BSC DXC Hub Node AA A Ring, Tree, etc. MSC BSC/TRC BSC Figure 1-16: Remote BSC EN/LZT 123 6914/2 Rev R3A 27
38. 38. GSM Network Planning - Transmission Overview/Planning RBS2000 X-Bus PSUs Mains Supply DC System Supply Timing Bus Power Communication Loop External alarm OMT interface Test A-bis interface Local Bus Antenna System Interface Antenna System Interface RF-Path RF-Path CDU-Bus Antenna System Interface Antenna System Interface RF-Path RF-Path CDU-Bus Antenna System Interface Antenna System Interface RF-Path RF-Path CDU-Bus TRU TRU TRU TRU TRU ECU CDU CDU CDU Mobile Station Test Point (MSTP) Mobile Station Test Point (MSTP) Mobile Station Test Point (MSTP) Mobile Station Test Point (MSTP) Mobile Station Test Point (MSTP) Mobile Station Test Point (MSTP) DXUDXU TRU X-Bus PSUs Mains Supply DC System Supply Timing Bus Power Communication Loop External alarm OMT interface Test A-bis interface Local Bus Antenna System Interface Antenna System Interface RF-Path RF-Path CDU-Bus Antenna System Interface Antenna System Interface RF-Path RF-Path CDU-Bus Antenna System Interface Antenna System Interface RF-Path RF-Path CDU-Bus TRU TRU TRU TRU TRU ECU CDU CDU CDU Mobile Station Test Point (MSTP) Mobile Station Test Point (MSTP) Mobile Station Test Point (MSTP) Mobile Station Test Point (MSTP) Mobile Station Test Point (MSTP) Mobile Station Test Point (MSTP) DXUDXU TRU DXUDXU TRU Figure 1-17: Radio Base Station 2000 (RBS2000) There are two different RBS families: RBS 200 RBS 2000 The following overview relates to RBS 2000. The major functional units are (refer to Figure 1-17): The Distribution Switch Unit (DXU) provides an interface to the link towards the BSC. It is in charge of the link resources and connects the traffic between the BSC and the TRUs. The TRU includes all functionality needed for handling one radio carrier. Transceiver Unit (TRU) provides functionality for transmitting, receiving and signal processing for the TS handling on the radio interface. 28 EN/LZT 123 6914/2 Rev R3A
39. 39. 1 GSM Introduction - Interfaces and Node Hierarchy The Combining and Distribution Unit (CDU) is the interface between the TRUs and the antenna system. The Energy Control Unit (ECU) controls both power and climate (heating/cooling). MULTIDROP BSC RBS A B RBS A B RBS A B RBS A B RBS A B RBS A B RBS A B Figure 1-18: Multidrop In RBS 2000, the feature of cascading several RBSs is called multi-drop. The functionality is implemented in the TRI (Transmission Radio Interface) for RBS 200, and in the DXU for RBS 2000. The functionality enables the E1 to be passed on to the next site. The total number of TSs, required for the RBSs, must not exceed 31. The signaling to control the multi-drop facility in the DXU is sent together with LAPD signaling. Protection switching which forwards the incoming signal to the outgoing signal protects the chain in case one RBS goes down. EN/LZT 123 6914/2 Rev R3A 29
40. 40. GSM Network Planning - Transmission Overview/Planning DIGITAL CROSS CONNECT A DXC helps to organize the traffic, thereby reducing the need for transmission capacity. It facilitates the design of optimized network topologies. The network flexibility, introduced by a DXC and the variety of DXC interfaces, facilitates the smooth growth of the network. The following features can be accomplished using a DXC: Add-drop / Daisy chain. Traffic can be dropped and added within the capacity limit in the site. Grooming / Consolidation Traffic from various sites can be allocated in the same E1 frame, thus reducing the number of E1s required. Protection with ring configurations. Rerouting of traffic, in case of link failure, is required. This type of ring configuration may not be supported by all DXCs types. Voice compression (Adaptive Differential PCM, ADPCM). Used for conversion of analog transmission into digital transmission, and also for compression of the signal. Not all DXC types support ADPCM. 30 EN/LZT 123 6914/2 Rev R3A
41. 41. 1 GSM Introduction - Interfaces and Node Hierarchy NODE HIERARCHY BSC A HLR TGMSC TGMSC HLR TGMSC TGMSC MSC MSC MSC MSC MSC MSC PLMN, PSTN, ISDN, ... E TGMSC/TG MSC/VLR BTS BTS BSC/TRC A AREA A AREA B HLR TGMSC TGMSC HLR TGMSC TGMSC MSC MSC MSC MSC MSC MSC PLMN, PSTN, ISDN, ... E HLR TGMSC TGMSC HLR TGMSC TGMSC MSC MSC MSC MSC MSC MSC PLMN, PSTN, ISDN, ... E TGMSC/TG MSC/VLR BTS BTS BSC/TRC A AREA A AREA B BTS BTS BTS BTS BTS BTS BTS BTS BTS BTS BTS BTS BTS BTS DXCBSC A A A Backbone (Core) (Trunk) NW Access NW BSC A HLR TGMSC TGMSC HLR TGMSC TGMSC MSC MSC MSC MSC MSC MSC PLMN, PSTN, ISDN, ... E HLR TGMSC TGMSC HLR TGMSC TGMSC MSC MSC MSC MSC MSC MSC PLMN, PSTN, ISDN, ... E TGMSC/TG MSC/VLR BTS BTS BSC/TRC A AREA A AREA B HLR TGMSC TGMSC HLR TGMSC TGMSC MSC MSC MSC MSC MSC MSC PLMN, PSTN, ISDN, ... E HLR TGMSC TGMSC HLR TGMSC TGMSC MSC MSC MSC MSC MSC MSC PLMN, PSTN, ISDN, ... E TGMSC/TG MSC/VLR BTS BTS BSC/TRC A AREA A AREA B BTS BTS BTS BTS BTS BTS BTS DXCBSC A A A Backbone (Core) (Trunk) NW Access NW BTS BTS BSC/TRC A AREA A AREA B BTS BTS BTS BTS BTS BTS BTS BTS BTS BTS BTS BTS BTS BTS DXCBSC A A A Backbone (Core) (Trunk) NW Access NW Figure 1-19: National / Regional PLMN Architecture GSM networks are built in a hierarchical manner with independent regional areas with access networks, each one controlled by an MSC. In small PLMNs the MSCs are connected in a meshed network. However, as PLMN grow large the backbone network is divided into a transit layer and a regional MSC layer. In order to simplify routing and traffic prediction, a ring topology can be implemented in the transit layer. It is also recommended that all incoming and outgoing traffic be in the transit layer. This enables the operator to choose the most cost-effective solution in terms of far-end drop or near- end drop. Each regional MSC should be connected to at least two transit layer nodes. This is called dual homing and it enables them to have full protection or to have load sharing. The most common option is something in between. EN/LZT 123 6914/2 Rev R3A 31
42. 42. GSM Network Planning - Transmission Overview/Planning In the access network the RBSs are linked to the BSC directly or via chains or hubsites where DXC equipment can be used. Every BSC that is going to support packet switched traffic must be equipped with a packet control unit (PCU) that is connected to an SGSN via the Gb interface. With small or large BSCs there are a number of factors to be considered: Capacity factor, i.e. when will their capacity run out? Where should small BSCs be located in the network? O&M factor, i.e. does it cost more to have many small- capacity SCs compared to having a few large ones? Network robustness, i.e. would the network be more robust with many more BSCs rather than a few large ones? Transmission efficiency, i.e. is it more efficient to have concentrated large BSCs rather than many smaller ones? Spare parts handling, the practical issues with holding spare parts in different places and the management of spare parts. Other costs, such as the cost of new sites against co- location. Placing many small BSCs in the network would entail more site costs, especially if they are to be spread out geographically. Co-location must be considered. Would the network topology of one, which consists of a few large BSCs or one, that has many small BSCs be more flexible for expansion? 32 EN/LZT 123 6914/2 Rev R3A
43. 43. Media Chapter 2 This chapter is designed to provide the student with an introduction to the types of transmission media and their basic properties. OBJECTIVES: Upon completion of this chapter, the student will be able to: List two common types of copper wiring and list its features in terms of bandwidth and length List frequency and bridging distance of a typical radio link List the requirements on a geostationary satellite, and one disadvantages and one advantage that it has Make a comparison with low orbiting satellites and state one disadvantage and one advantage that they have List two wavelengths used in optical fiber communication systems List two reasons for attenuation and dispersion respectively in an optical fiber List two light sources and two light detectors used in optical fiber communication systems
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45. 45. 2 Media 2 Media Table of Contents Topic Page METAL CABLE ...................................................................................33 OPEN WIRE .................................................................................................................33 PAIRED CABLE............................................................................................................33 COAXIAL CABLE .........................................................................................................34 RADIO WAVES ...................................................................................36 RADIO LINK .................................................................................................................36 SATELLITE...................................................................................................................38 OPTICAL FIBER..................................................................................41 TYPES OF OPTICAL FIBER........................................................................................44 OPTICAL TRANSMITTERS AND RECEIVERS...........................................................46 WAVELENGTH DIVISION MULTIPLEXING (WDM) ...........................48 RECENT ADVANCES IN OPTICAL COMMUNICATIONS..................50 EN/LZT 123 6914/2 Rev R3A i
46. 46. GSM Network Planning - Transmission Overview / Planning Intentionally Blank ii EN/LZT 123 6914/2 Rev R3A
47. 47. 2 Media METAL CABLE OPEN WIRE In the early days of telegraph lines, the only transmission medium was the open wires in the form of non-isolated copper or iron wires. The first application example of open wires was the 60 km Washington-Baltimore telegraph line set up in 1845. Open wires were generally used in Frequency Division Multiplex (FDM) systems in the 1940s. They are still in use in some rural areas, but for only 3.1 kHz bandwidth voice communications. Figure 2-1: Open wire metal cables The advantages of using open wire cables are: Very low attenuation for voice frequencies Very simple and cheap Easy installation in rural areas The main disadvantage of this type of transmission media is that it is vulnerable to electromagnetic disturbances and mechanical damage. Figure 2-1 shows a well-known rural open wire application. PAIRED CABLE Twisted pair, an example of paired cable, is probably the most commonly used transmission media. An example from our daily life is the cable connecting our telephone to the wall socket. These types of cables are mainly used in access networks, between the subscribers and the exchange, and rarely in trunk EN/LZT 123 6914/2 Rev R3A 33
48. 48. GSM Network Planning - Transmission Overview / Planning networks between the exchanges. Figure 2-2 shows a typical paired cable structure. Paired cable can be found as 2, 5, 10, 100 and 500 etc. pairs in a plastic or paper cover and is generally buried underground. The conducting material is normally copper with a diameter of 0.4 to 0.8 mm diameter. The wires inside the cable are twisted together to form pairs with two conductors, or quads with four conductors. Figure 2-2: Paired cable There are two types of paired cable according to its shielding structure. If the cable core is covered with a metal sheath (lead or aluminium) inside the plastic cover structure, it is protected against mechanical external damage, electrical and electromagnetic interference. Sometimes metal sheath is armoured with steel wires to increase its mechanical strength. For aerial applications, paired cables are reinforced with a steel core. Electrical characteristics, for example attenuation, of paired cables strictly depend on their conductor diameter size, conductor material and the frequency used. Although they were originally developed for analog communications, they can also be used for digital communications with a maximum capacity of 100 kbps. The main disadvantage for this type is the cross talk between the conductors. COAXIAL CABLE Some well-known applications of coaxial cables are cable-TV networks, local data networks and radio antenna feeders. They are preferred for both analog FDM and digital TDM (Time Division Multiplexing) systems with a capacity up to 200 Mbps. Figure 2-3 shows a schematic of a coaxial cable and detailed cross-section. The cable consists of an inner conductor surrounded by a tube-shaped outer conductor. The best insulator 34 EN/LZT 123 6914/2 Rev R3A
49. 49. 2 Media between these conductors is air. However sometimes plastic materials are also used for the same purpose. Typical coaxial cable dimensions for telephony applications are 2.6/9.5 mm or 1.2/4.4 mm for inner/outer radius. The outer conductor also provides a shielding for surrounding effects such as electromagnetic interference. There are some coaxial cables with a multi-wire inner conductor, twisted multi-wire and plastic insulator between them. These types are very useful for applications requiring flexible cabling. Outer shield Insulator Conductor Figure 2-3: Coaxial cable schematic and cross-section details Previously coaxial cables were used mainly in trunk networks but today they are replaced by optical fibers and their main application area has shifted towards the access network. One important feature of coaxial cable is that the main electrical characteristics are completely governed by conductor diameters. Roughly speaking, the attenuation is inversely proportional to the conductor diameter. EN/LZT 123 6914/2 Rev R3A 35
50. 50. GSM Network Planning - Transmission Overview / Planning RADIO WAVES Radio as a transmission medium has great a many applications in telecommunications. It can be used, in local or intercontinental networks, for fixed or mobile communications between network nodes or between users and network nodes. The most well known applications are cordless, GSM and satellite mobile phones, radio and TV broadcasting, radar, etc. The radio spectrum shown in Figure 2-4 extends from 3 kHz to 300 GHz is a part of the electromagnetic spectrum, in the same way as infrared, visible, X-ray etc. spectrums. Very low frequency Low frequency Medium frequency High frequency Very high frequency Ultra-high frequency Super high frequency Extremely high frequency 3 k 30 k 300 k 3 M 30 M 300 M 3 G 30 G 300 G [Hz] f VLF LF MF HF VHF UHF SHF EHF Very low frequency Low frequency Medium frequency High frequency Very high frequency Ultra-high frequency Super high frequency Extremely high frequency 3 k 30 k 300 k 3 M 30 M 300 M 3 G 30 G 300 G [Hz] f VLF LF MF HF VHF UHF SHF EHF Figure 2-4: Radio spectrum The main feature of radio waves is that their propagation is strictly frequency-dependant. Radio waves having frequency below 30 MHz are reflected by certain layers of the atmosphere and the ground. Because of this, frequencies below 30 MHz are generally used in maritime radio, telegraphy and telex applications with a small information capacity. Certain parts of VHF and UHF bands are used for TV broadcasting, FM radio, mobile telephony, etc. Frequencies greater than 3 GHz suffer attenuation caused by the objects in their way, such as buildings. For this reason they require free line of sight to establish good communication between the transmitter and the receiver (e.g. radio links using the 2-40 GHz part of the spectrum and satellite communication systems using the 2-14 GHz frequency band). The information carried by these systems range from a few Mbps to several hundreds Mbps. In this chapter, we will give some details about radio link and satellite applications. RADIO LINK The radio links can be used for both analog and digital communications systems. The physical distance between the transmitter and the receiver is known as the hop length and is 36 EN/LZT 123 6914/2 Rev R3A
51. 51. 2 Media strictly dependant on which frequency, climate, output power, antenna size, antenna type and what quality objectives the hop is designed for. The information can also be transferred through several hops with active or passive nodes at both ends. In passive systems, the signal is neither regenerated nor amplified. Instead, it is received by the receiver antenna and directed to the transmitted antenna. The only thing changed in a passive station is the direction of the signal - in order to solve line of sight problems. A typical point-to-point radio link system is shown in Figure 2- 5. Figure 2-5: Point-to-point radio link The main advantages of radio link systems can be summarized as: Fast installation No fixed infrastructure requirement Easy access over difficult areas (compared to other techniques such as fiber) Need for only a few landowner permits Point-to-multi point systems are generally used in high-speed internet-intranet, LAN-LAN interconnection, TV broadcast, IP services, leased lines, etc. In other words, they are very useful and cost effective in providing communications to scattered populations compared to wire line or point-to-point systems. A typical point-to-multipoint radio system is shown in Figure 2-6. EN/LZT 123 6914/2 Rev R3A 37
52. 52. GSM Network Planning - Transmission Overview / Planning Figure 2-6: Point-to-multipoint radio system The main problems with radio links can be summarized as: Attenuation due to rain Refraction from atmosphere Reflection from ground and obstacles such as buildings SATELLITE Satellite communications had first been mooted with the prophetic article of Arthur C. Clarke Extra-Terrestrial Relays in 1945. In this article, Clark proposed three geostationary satellites to provide world coverage. After various experiments in USSR and US, the following historical developments took place: 1958 - Christmas greeting from SCORE satellite 1960 - First reflector satellite, ECHO 1960 - First satellite recorded message 1962 - First active communications satellites, TELSTAR and RELAY 1963 - First geostationary satellite, SYNCOM 1965 - First commercial geostationary satellite, INTELSAT 1 1965 - First Russian communications satellite, MOLNYA A satellite network in its simplest form consists of two earth stations communicating with each other via a satellite as shown in Figure 2-7. 38 EN/LZT 123 6914/2 Rev R3A
53. 53. 2 Media Figure 2-7: A typical satellite communication system There are several satellite services, which are classified as: Fixed satellite services Earth stations - Satellite(s) - Earth station Mobile satellite services Mobile earth stations Broadcasting satellite service TV and radio Earth exploration satellite service For example, meteorological Space research service Scientific and technical research The frequency range for satellite communications lies between L band (0.4-0.46 GHz) and Q band (33-50 GHz), but does not cover the whole range. The most commonly used frequencies are 6/4, 14/11 and 30/20 GHz for uplink/downlink. Satellites are placed at previously defined orbits in the space. A satellite remains in that orbit as long as its centrifugal force is in balance with the gravitational attraction of the earth and other cosmic influences. There are four distinct altitude ranges used for telecommunication satellites. These orbits are: Low Earth orbit (LEO) between 500 and 2000 km, approximately 14 ms signal delay Medium Earth orbit (MEO) between 5000 and 15000 km (also called intermediate circular orbit, (ICO)), approximately 100 ms signal delay EN/LZT 123 6914/2 Rev R3A 39
54. 54. GSM Network Planning - Transmission Overview / Planning Geostationary Earth orbit (GEO) at 35786 km (also called Clark orbit), approximately 240 ms signal delay Highly elliptical orbit (HEO) beyond GEO The main problems with satellite communications are: Attenuation due to atmosphere and ionosphere, Attenuation due to precipitation and clouds, Losses due to antenna depointing, Delay. 40 EN/LZT 123 6914/2 Rev R3A
55. 55. 2 Media OPTICAL FIBER Optical fibers have been extensively used in communications systems due to their unique features, such as: Low attenuation High capacity Small volume Low weight Insensitive to electromagnetic interference No cross-talk After the proposal of Gao and Hockham in 1966, the first low loss fiber (