Mobile Communications

Transcription

1 October 21, 2009

2 Agenda Topic 2: Case Study: The GSM Network 1 GSM System General Architecture 2 GSM Access network. 3 Traffic Models for the Air interface 4 Models for the BSS design. 5 UMTS and the path towards 4G 6 UMTS cell design

3 General Scheme The network is divided into three major parts: Switching System (SS) Base Station System (BSS) Operation and Maintenance Center (OMC) Each of these contains a number of functional units which make up the entire system. The functional units are parts in the various hardware units. Next slide shows a scheme of the structure of a GSM network.

4 General Scheme

5 Functional Element Description: MSC The Mobile services Switching Center (MSC) performs the telephony switching functions of the system. It also controls calls to and from other telephony and data systems, such as the Public Switched Telephone Network (PSTN) and Public Land Mobile Network (PLMN). In most GSM system, the VLR (see next section) is integrated with the MSC in a MSC/VLR. The MSC is responsible of the following functions Setting up and controlling calls Handling speech path continuity of moving subscribers (handover). Location updating and location canceling in the location registers.

6 Functional Element Description: MSC Provision of functions for signaling to and from BSC, MSs other GSM entities, other networks such as PSTN or ISDN. Administrative functions for defining data and handling of the mobile subscribers. Security related functions which perform authentication. Functions for IMEI check. Receiving and delivering short messages from and to the MS. charging and accounting.

7 Functional Element Description: Example of MSC This a typical MSC machine (In this case of Siemens). Processor, Switching Matrix,BSC port interfaces. Of course, the building. Between 5-6 Million Euros (Depends on the vendor, the country, the operator)

8 Functional Element Description: VLR The Visitor Location Register (VLR) is a database containing information about all MSs currently located in the MSC service area. The information is temporary and needed by the MSC to provide service for visiting subscribers. It can be seen as a distributed HLR. When a MS roams into a new MSC service area, the VLR requests data about the MS from the HLR. If the MS makes a call, the VLR already has the information needed for call set-up. This makes signaling between the two nodes over the network unnecessary

9 Functional Element Description: GMSC The Gateway MSC (GMSC) is the point in the PLMN where calls to mobile subscribers enter/leaves the GSM network. Each mobile terminating call must be routed via a GMSC in the home PLMN of the called MS. It is required to distinguish between the element and the signalling function. The Gateway element is the physical element used as interface to other networks The signalling function is the functionality that asks the HLR about the position of the MS. In most cases both things are implemented in the MSC.

10 Functional Element Description: HLR The Home Location Register (HLR) is a database that stores and manages subscriptions. In a PLMN there usually is one, maybe two for security issues. For each subscriber, the HLR contains permanent data like: 1 The associated numbers - MSISDN and IMSI. 2 The customer portfolio. The HLR also stores and updates dynamic data of the customer.

11 Functional Element Description: HLR functionality The HLR provides the following functions (among others): 1 Definition of subscriber data. 2 Maintenance of a database of mobile subscribers a 3 Subscription to basic/supplementary services. 4 Activation/deactivation of supplementary services. 5 Functions for analysis of mobile subscriber numbers 6 Handling of authentication data for mobile subscribers 7 Communication with Authentication center. 8 Functions for communication with GMSC and VLR using the SS7. 9 Statistical functions for collecting data regarding the performance of the system.

12 Functional Element Description: AUC and EIR The Authentication Center AUC is a database which contains the authentication keys. These keys are generated any time the HLR request it, and forwards them to the VLR. These keys are checked with the MS at each access attempt. The Equipment Identity Register (EIR) is a data base which stores the International Mobile station Equipment Identity (IMEI) for each MS equipment. It is verified in each access.the main objective is to ensure that the equipment is not stolen. It has four lists: 1 White listed (permitted for use) 2 Gray listed (should be tracked for evaluation) 3 Black listed (barred) 4 Unknown equipment

13 Functional Element Description: SMS Center Although it is part of the Network Switching subsystem it is not shown in the figure of the first slide. As its name shows the Short Message Service Center (SMSC) is a node dedicated to handle with the SMS service. It has to receive and deliver SMS from MS inside and outside de PLMN. The messages received are stored in the SMSC and they are not sent to the ending MS until the network is under a specified using threshold. The cost of a SMSC is about 1-3 Millions Euros.

14 Functional Element Description: Base Station The Base Station (BS) handles the radio interface to the MS. It is the radio equipment (transceivers and antennas) needed to serve the users in its coverage area in the network. We have to distinguish between the following concepts: 1 Site: It is composed of the civil engineering and the support and facilities to hold the equipment. 2 BTS/BS/RBS is the set of equipment in the site. Usually a single site may be composed of a BTS for 900 MHz, and a BTS for 1800 MHz in GSM system. 3 Sector or cells. Normally the Base Station are divided into sectors, each one of them composes a cell. 4 TRX, Transmitter: It defines a radiochannel that is the set of a frequency (FDMA) and the time multiple access (TDMA).

15 BTS types The base stations/cells are usually classified attending to the type of cell they are handling. A classical division is the following. Macrocells. With a coverage radius between 1.5 to 20 Km, mainly for rural environments with low traffic. Minicells.Coverage radius between 0.7 to 1.5 Km for suburban and urban areas. Microcells. Coverage radius between to Km for urban areas with high traffic. Picocells. Coverage radius up to 0.5 km. They are used in dense urban areas with high traffic or to cover special places like males or airport. They are usually traffic driven.

16 BTS types Figure: Macrocell for Rural Areas Figure: Microcell for Urban-Suburban Areas Figure: Picocell for Dense Urban Areas

17 BTS types and costs The total cost of a site is the sum of several amounts and depends, of course on the type of BTS. 1 Site acquisition and preparation: Between 30KEuros (Picocell) - 80 KEuros (Rural Macrocell) 2 BTS equipment, from 15KEuros (Picocell)- 40KEuros (Macrocell). It may additionally be increased by the number of sectors. 3 TRX, with an average cost of 3-4 KEuros. Therefore the cost of the BTS can be estimated by. C BTS = C S + C BTS N Sectors + C TRX N TRX N Sectors

18 BTS Functions Radio transmission to and radio signal reception from MSs, Equalizing and diversity functions to compensate for fading effects. Quality measurements: uplink, downlink and neighboring BSs. Report measurements to the BSC. Time alignment measurements. Transceiver and MS power control. Broadcasting system information and paging messages. Receiving channel requests from MSs.

19 Base Station Controller The BSC handles all radio related functions and is the BSSs center point. The BSC manages the entire radio network including: 1 Configuration of the network. 2 Administration and remote control of the RBSs. 3 Handling connections to MSs including handovers. The capacity of a BSC is about 256 BTS, 512 cells and 1020 TRX. Sometimes the BSC may be integrated with the MSC in the same location. Anyway, from the logical point of view, they continue being separate elements. This usually happens in countries with customer concentrates in some points (large cities).

20 BSC example The cost of a BSC rounds 3 Million Euros. Figure: Example of BSC Figure: Typical values of BSC features

21 Mobile Station and MSISDN The mobile station (our mobile phone) is the only part in the mobile network that is, in fact, mobile. The mobile is physically divided into the Terminal Equipment (TE) and the Subscriber Identification Module (SIM) The SIM contains customized information about the subscriber and is the part that provides the mobility to the user. Of course it contains the MSISDN and the corresponding authentication Keys. The MS is functionality divided into three parts. 1 Mobile Termination, which includes the Radio Modem, the User interface and the set of RF equipment. 2 Terminal Adaptor (TA): It connects different data terminals to the MT. It performs the protocol adapting functions. 3 Terminal equipment (TE): With two types, TE1 for ISDN interfaces and TE2 for no ISDN.

22 Mobile Station and MSISDN The MSISDN number uniquely identifies a mobile telephone subscription in the public switched telephone network numbering plan. It is composed by: Country Code National Destination Code Subscriber Number

23 Operation and Support System There are some part of the GSM network that are not typically shown in the lectures: The Management Part and the Intelligence Network. We will give a short look into them. OMC offers the customer cost effective support for centralized, regional and local operations and maintenance activities required by a cellular network. OMC is the functional entity from which the network operator monitors and controls the system. Most of OMC s in Mobile Networks are are based on Telecommunication Management Network (TMN). TMN is a model for telecommunication networks management. The most important parts are: 1 Configuration management 2 Fault management 3 Performance management

24 Intelligent Network Intelligent Network(IN) techniques are a flexible and convenient way to provide a large number of more varied services to the customer IN also allows highly personalized new services to be offered. The basic functions needed for IN services are 1 Triggering function used to determine if this is an IN call or not. 2 Functionality to store information about the IN services. 3 Functionality to provide access to the IN services. 4 Functionality to carry out the service.

25 Intelligent Network

26 Intelligent Network Functionalities Now we show the main functionalities of the IN. 1 Service Control Function (SCF): contains the service logic and processing capability that is required to execute an IN service. 2 Service Switching Function (SSF): is the functional entity that provides the mobile network with access to the IN services that reside in the Service Control Function (SCF). 3 Service Data Function (SDF): is the database function of the Intelligent Network. The SDF stores IN subscriber data and network data. These data are accessed by the SCF during the execution of the service. 4 Specialized Resource Function (SRF): provides special capabilities for the execution of some IN services.

27 Intelligent Network Nodes The above functionalities can be implemented in a MSC/VLR or as stand alone nodes. In this last case: 1 Service Control Point (SCP): Implements the SCF and often also the SDF. 2 Service Switching Point (SSP): Implements the SSF. 3 Service Switching Control Point (SSCP): Implements SSF, SCF, and usually also the SDF. 4 Service Data Point (SDP): Implements the SDF on a UNIX station. 5 Intelligent Peripherals (IPs): Special hardware implementing the SRF

28 Intelligent Network Nodes The list of IN services is as long as detailed as you (or better said the operator) want. A short list of them is: 1 Personal Number 2 Prepaid Services 3 Virtual Private Network 4 Information and Business Services (Free numbers, Universal Access Number and Premium Rate)