Chapter 5 Acknowledgment:

Transcription

1 Chapter 5 Acknowledgment: This material is based on the slides formatted by Dr Sunilkumar S. Manvi and Dr Mahabaleshwar S. Kakkasageri, the authors of the textbook: Wireless and Mobile Networks, concepts and protocols. Most of the slides are used without any change. Some additional slides are taken and/or inspired by material from various paper and / or electronic resources. Some comments and/or additive information are directly enclosed in the original slides. Such comments are usually written with a different color. I apologize for any involuntary omission to other references if any.

2 Chapter 5 Wireless Wide Area Networks

3 Learning objectives To understand Wireless Wide Area Networks (WWANs) To study the WWAN standards To know the architectures of WWANs To study the protocols used in WWANS To illustrate the applications of WWANs

4 Principles of cellular networks (Contd..) Communication area is divided into hexagonal cells. Cell dimensions range from hundreds of meters till tens of kilometers. Each cell is served by a BS formed by a transceiver and a control unit. Each cell is allocated a frequency band for communication. Communication from MS to BS uses reverse link and communication from BS to MS uses forward link. Frequency reuse is a technique of reusing frequencies and channels within a cellular network to improve the network capacity. Cells that reuse the same frequency must be distant enough for avoiding interference.

5 Principles of cellular networks (Contd..)

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7 Handoff The procedure of moving from one cell to another, while a call is in progress, is called handoff. While performing handoff, the MS requires that the BS in the cell where it has moved allocates a channel. If channel is not available in the new cell, the handoff call is blocked and blocking is called handoff blocking.

8 Handoff (Contd..) The QoS (Quality of Service) of a cellular network is determined by new call and handoff blocking probabilities. Blocking probabilities can be reduced by increasing the capacity of the cellular networks. Capacity of Cellular networks can be increased by applying efficient power control algorithms or by reducing the size of the cells or by increasing the number of channels in each cell. High cost solution Reduced cells size Adding supplementary channels

9 Other methods to increase capacity in cellular networks Frequency borrowing: congested cells use frequencies taken from adjacent cells where less traffic is observed. Cell sectoring: cells are divided into sectors and each sector is allocated its own set of frequencies. BSs use directional antennas to cover sectors. Microcells and picocells: a microcell covers a range of about 500 m and a picocell covers a range of about 10 m.

10 Example A cellular network has a total bandwidth of 56 MHz. If two 35 KHz simplex channels are used to provide full duplex voice and control channels, compute the number of channels available per cell if a system uses (a) 4-cell reuse, (b) 7-cell reuse, (c) 12-cell reuse. Solution:

11 Example A cellular network has a total bandwidth of 56 MHz. If two 35 KHz simplex channels are used to provide full duplex voice and control channels, compute the number of channels available per cell if a system uses (a) 4-cell reuse, (b) 7-cell reuse, (c) 12-cell reuse. Solution: Given that the total available bandwidth is 56 MHz = 56,000 KHz. Channel bandwidth = 35 KHz x 2 simplex channels = 70 KHz/duplex channels. Total available channels = 56,000/70 = 800 channels. let N denotes cell reuse. (a) For N = 4, Total number of channels available per cell = 800/4 = 200 channels. (b) For N = 7, Total number of channels available per cell = 800/7 = 115 channels. (c) For N = 12, Total number of channels available per cell = 800/12 = 67 channels.

12 Example In a cellular network with hexagonal cells, it is forbidden to reuse a frequency band in an adjacent cell. If 915 frequencies are available, how many frequencies can be used in a given cell? Solution: Example scenario

13 Example In a cellular network with hexagonal cells, it is forbidden to reuse a frequency band in an adjacent cell. If 915 frequencies are available, how many frequencies can be used in a given cell? Solution: Given that the cell shape is hexagonal, hence it has six neighbors. If the central cell uses frequency group A, its six neighbors can use B, C, B, C, B, and C respectively. In other words, only 3 unique cells are needed. Therefore each cell can have (915/3) or 305 frequencies. Example scenario

14 Example Consider a cellular network with 64 cells. Each hexagonal cell has an approximate area 10 km 2. The total number of radio channels allotted for the network is 336. What is the total area covered by the cellular network. Find the total number of channels of the network, if (a) N = 4, (b) N = 7, (c) N = 12, where N denotes cell reuse. Solution:

15 Example Consider a cellular network with 64 cells. Each hexagonal cell has an approximate area 10 km 2. The total number of radio channels allotted for the network is 336. What is the total area covered by the cellular network. Find the total number of channels of the network, if (a) N = 4, (b) N = 7, (c) N = 12, where N denotes cell reuse. Solution: Total number of cells = 64. Each cell area = 10 km 2. The total area covered by the cellular network is, 64 X 10 = 640 km 2. It is given that the total available channels in the network = 336. (a) For N = 4, the available channels in a cell = 336/4 = 84 Total channels = 84 X 64 = 5,376 channels. (b) For N = 7, the available channels in a cell = 336/7 = 48 Total channels = 48 X 64 = 3,072 channels. (c) For N = 12, the available channels in a cell = 336/12 = 28 Total channels = 28 X 64 = 1,792 channels.

16 GSM Architecture GSM networks operate at various different radio frequencies: 900MHz and/or 1800MHz. USA and Canada operate at 850MHz and/or 1900MHz. Major components of a GSM network are: MS (Mobile Station), BSS (Base Station System), Operation and Maintenance Center (OMC), and Network and Switching Subsystem (NSS). GSM network architecture

17 GSM Architecture (Contd..) Mobile Station (MS): Mobile phone, PDA or a laptop. It consists of a subscriber identity module (SIM) and a mobile equipment (ME). The ME (the phone itself), is identified by International Mobile Equipment Identity (IMEI).

18 OMC Operation and Maintenance Center (OMC): manages the GSM functional blocks: Mobile Switching Center (MSC) and the BSC (and indirectly the BS). Maintains satisfactory operation of the GSM network based on observing the system load, blocking rates, handovers, etc.

19 NSS Network and Switching Subsystem (NSS): it contains Mobile Switching Center (MSC): used to facilitate communication between different MSs connected to different BSs.

20 NSS (Contd..) Interworking Functional Unit (IFU): allows the mobile stations (MSs) connected to a mobile switching center (MSC) to connect to public switched data network (PSDN), to public switched telephone network (PSTN) or the Internet.

21 NSS (Contd..) Equipment Identity Register (EIR): It contains a list of valid MS equipments within the network, where each MS is identified by its International Mobile Equipment Identity (IMEI).

22 Home Location Register (HLR): Database for management of mobile subscribers. Billing: must identify that every call is being made by either a home or a roaming user. Visitor Location Register (VLR): Manages roaming NSS (Contd..)

23 NSS (Contd..) Authentication Center (AuC): It is a protected database that has a copy of the secret key stored in each subscriber s SIM card. This key is used for authentication and encryption over the radio channel.

24 GPRS General Packet Radio Service (GPRS) is a non-voice value-added service that allows information to be sent and received across a mobile telephone network. It supplements today s circuit-switched data and SMS. GPRS is not related to the global positioning system (GPS), a similar acronym that is often used in mobile contexts.

25 GPRS Architecture General Packet Radio Service (GPRS) is an enhancement over the GSM and adds some nodes in the network to provide the packet switched services. These network nodes are called GPRS Support Nodes (GSNs) and are responsible for the routing and delivery of the data packets to and from the MS and external packet data network (PDN)

26 GPRS Architecture (Contd..) GSN: GPRS Support Node AuC: Authentication Center EIR: Equipment Identity Register TAF: Terminal Adaptation Function PLMN: Public Land Mobile Network

27 GPRS mobile station (MS) GPRS mobile station (MS) includes two components: MT (Mobile Terminal) and TE (Terminal Equipment). MT is typically a handset used to access the radio interface. It consists of ME, SIM, and Terminal Adaptation Function (TAF) TAF helps GPRS TE merely to use the radio system at hotspots. TE is typically a laptop or a Personal Digital Assistant (PDA).

28 GPRS mobile station (Contd..) Three different classes of MS have been defined: Class-A: supports simultaneous monitoring and operation of both GPRS (packet-switched) and GSM (circuitswitched) services. Class-B: supports simultaneous monitoring but not simultaneous operation of GSM (circuit-switched) and GPRS (packet-switched) services. Class-C: supports either GSM (circuit-switched) or GPRS (packet-switched) monitoring and operation at a given time.

29 GPRS Architecture Source: CSI 5171 (95.533) Network Architectures, Services, Protocols and Standards

30 Packet transfer Source: CSI 5171 (95.533) Network Architectures, Services, Protocols and Standards

31 SGSN (Serving GPRS Support Nodes): It is responsible for the delivery of data packets from and to the mobile stations within its geographical service area. SGSN performs the following functions: authentication and authorization. SGSN

32 GGSN (Gateway GPRS Support Nodes). It acts as interface between the GPRS backbone and the external PLMN (Public Land Mobile Network) or Internet It interfaces to external data networks (basically it is a network router) GGSN

33 CGF (The Charging Gateway Function) It provides the mechanism of transfer of charging information from the GPRS Support Nodes (GSNs) to the billing system The CGF can be a separate centralized element or it can be distributed among GPRS Support Nodes GPRS networks derive charging information for each user transaction into Call Detail Records (CDRs) from SGSNs and GGSNs. Billing is typically based on the amount of data transferred

34 Public Switched Telephone Network (PSTN)

35 Call set-up scenario from PSTN to the MS 1. From PSTN, the call is requested to the GMSC for the mobile station. 2. GMSC transfers the call to the HLR for verification and possible location of the mobile station. 3. HLR searches the assigned mobile station in MSC/VLR, where currently it is located. 4. VLR gives the requested mobile station current location (base station) to the HLR. 5. HLR transfers that message to the GMSC for possible connection with the current base station where the mobile station is located. GMSC (Gateway Mobile Switching Center) is a special kind of MSC that is used to route calls outside the mobile network

36 Call set-up scenario from PSTN to the MS (Contd..) 6. GMSC connects to the MSC. 7. MSC in-turn connects to the base station. 8. Base station establishes the connection with the mobile station until the end of the call. 9. When the call is completed, the mobile station releases the channel by informing to the base station. 10. Base station releases the channel and updates in HLR and VLR.

37 Satellite networks A satellite is an object that orbits or revolves around another object. Satellite communication systems differ from terrestrial systems in that the transmitter is not based on the ground but in the sky. A satellite system consisting of one or more satellites and the cooperating earth stations is referred as a satellite network.

38 Satellite and Orbits An orbit is the path that a satellite follows as it revolves around Earth. LEO: 1.5 2h, min MEO: 5h -10 h, 2-8h GEO: 24h, permanent Round trip propagation LEO: several ms MEO: tens of ms GEO: 250 ms Basically there are three main categories of orbits, They are Low Earth Orbit (LEO), Medium Earth Orbit (MEO), and Geostationary Earth Orbit (GEO) authors of the textbook: Wireless and Mobile Networks, concepts and protocols. See slide number one.

39 Architecture

40 Salient features A satellite network communicates using earth stations and satellites Communication from earth station to satellite is called uplink channel whereas communication from satellite to earth station is called downlink channel.

41 Architecture (Contd..) Satellite A satellite is a type of satellite network component that orbits the earth in space as a wireless receiver/transmitter. Ground stations Many satellites are moving in their respective orbits over the earth, thus it is idealistic that we can freely communicate with a satellite by a radio frequency whenever we want to monitor its status or send a command. Users A satellite network user may be a satellite telephone (sat phone), or a communication unit in the ship, a type of mobile phone that connects to orbiting satellites instead of terrestrial cell sites.

42 Salient features of satellite networks are as follows Coverage Speed Security Service types Usage Repeater Packet switched Frequency band

43 Satellite networks Coverage A satellite may cover global, regional, or national geographical

44 Satellite networks Speed All services include simplex or duplex, balanced or asymmetric links from 64 kbps-45 Mbps. Higher rate services are also possible in selected coverage area. Wireless WAN speeds differ depending on the technology used GPRS networks offer a maximum user data rate of over 115 kbps if all eight timeslots in a cell are allocated for data transmission. Data speeds on CDMA networks were initially available at speeds of 14.4 kbps, but have increased to a maximum throughput of 153 kbps as carriers have implemented CDMA2000 1X (1xRTT) networks

45 Satellite networks Security Encryption Hotspots are wireless LANs available to the public in a location like an airport, coffee shop, or city neighborhood.

46 Satellite networks Service types - Fixed Service Satellite (FSS) - Broadcast Service Satellite (BSS) - Mobile Service Satellite (MSS)

47 Satellite networks Usage Commercial Military Amateur Experimental Mobile Services Direct broadcast Private networks High speed hybrid networks (satellite-fiber)

48 Satellite networks Repeater Overhead wireless repeater station that provides a microwave communication link between two geographically remote sites

49 Satellite networks Packet switched TV broadcasts Voice telephony

50 Frequency band Satellite networks ISM : Unlicensed 2.4 GHz or 900 MHz Industrial, Scientific, and Medical radio bands L/S: L for long wave GHz S for short wave 2 4 GHz

51 WLAN Vs. WWAN Coverage Wireless local area networks by definition operate over a small, local coverage area, normally about 100 m in range. Wireless wide area networks cover a much wider area, such as wherever the cellular network provider has wireless coverage. Nationwide, Regional, or even global scale (access to data wherever you are)

52 WLAN Vs. WWAN Speed LAN b 11 Mbps a 54 Mbps. WWAN: Differs depending on the used technology Kbps-Mbps

53 Data security One of the most important issues when using wireless networks WLAN Vs. WWAN MAC Address Filtering SSID (Service Set Identifier) Broadcast Wired Equivalent Privacy (WEP) WWAN: extremely secure Military technology Sophisticated encryption methodologies

54 WLAN Vs. WWAN Cost LANs Since wireless LANs operate in the unlicensed frequency range, there is no service cost for using a private wireless LAN. The main cost involved is the cost of purchasing and installing the wireless LAN equipment and devices, and the cost of maintaining the network and the users. WWANs Fee for the time or volume of data transferred

55 Interworking of WLAN and WWAN Although WLANs and WWANs may appear to be competing technologies, they are far more useful as complementary technologies. These are used together, a user would have the best of both technologies, offering high-speed wireless access in a campus area, and access to all their data and applications with high-speed cellular access from anywhere with wireless WAN network coverage.

56 WWAN applications Cost effective backup for data applications Quick deployment Disaster recovery Mobile workers Lower bandwidth applications Connectivity in locations such as branch offices Point of sale locations Vehicles Remote measurment

57 WWAN applications (cont) Wireless Internet can be accessed through the following: Global Satellite Networks. Cellular Networks: GSM, GPRS Personal Area Networks: IEEE Bluetooth

58 Wireless Internet access Service types for Internet access are as follows: Fixed Portable Mobile Terminal/User Mobility UMTS: Universal Mobile Telecommunications System 3 rd generation, based on GSM

59 Other applications of WWAN