EE 4105 Communication Engg-II Dr. Mostafa Zaman Chowdhury Slide # 1

Transcription

1 EE 4105 Communication Engg-II Dr. Mostafa Zaman Chowdhury Slide # 1 1

2 Circuit-Switched Systems In a circuit-switched system, each traffic channel is dedicated to a user until its cell is terminated. Circuit switching is a methodology of implementing a telecommunications network in which two network nodes establish a dedicated communications channel (circuit) through the network before the nodes may communicate. The circuit guarantees the full bandwidth of the channel and remains connected for the duration of the communication session. The circuit functions as if the nodes were physically connected as with an electrical circuit. Analog system digital system 2

3 Circuit-Switched Systems: Analog Consists of three subsystem a mobile unit : A mobile telephone unit contains a control unit, a transceiver, and an antenna system. a cell site : provides interface between the MTSO and the mobile units. It has a control unit, radio cabinets, antennas, a power plant, and data terminals. mobile telephone switching office (MTSO): The switching office, the central coordinating element for all cell sites, contains the cellular processor and cellular switch. 3

4 Circuit-Switched Systems: Digital (e.g., GSM) (1/3) Consists of four elements: mobile station, base transceiver station (BTS), base station controller (BSC), and switching subsystems, 4

5 GSM Architecture

6 Circuit-Switched Systems: Digital (e.g., GSM) (2/3) MS: consists of two parts, mobile equipment (ME) and subscriber identify module (SIM). SIM contains all subscriber-specific data stored on the MS side. BTS: Besides having the same function as the analog BTS, it has the Transcoder/Rate Adapter Unit(TRAU), which carries out coding and decoding as well as rate adaptation in case data rate varies. BSC: A new element in digital systems that performs the Radio Resource (RR) management for the cells under its control. BSC also handles handovers, power management time and frequency synchronization, and frequency reallocation among BTSs. 6

7 Circuit-Switched Systems: Digital (e.g., GSM) (3/3) Switching subsystems: MSC: The main function of MSC is to coordinate the setup of calls between MS and PSTN users. VLR (Visitor Location Register): A database of all mobiles roaming in the MSC s area of control. HLR(Home Location Register):Acentralized database of all subscribers registered in a Public Land Mobile Network (PLMN). AUC (Authentication Center): Provides HLR with authentication parameters and ciphering keys that are used for security purposes. EIR (Equipment Identity Register): A database for storing all registered mobile equipment numbers. IWF (Interworking function): Provides the subscriber with data services that can access data rate and protocol conversion facilities and interfaces with public and private data networks. EC (Echo Canceller): Used on the PSTN side of the MSC for all voice circuits. XC (Transcoder): Usually installs in each BTS. But for the cost reason, it can be installed in BSC or MSC. OMC(Operational and Maintenance Center): This function resided in analog MSC but became a separated entity in digital systems. 7

8 Packet-Switched Systems: (2.5G+ e.g., UMTS) Packet switching is a digital networking communications method that groups all transmitted data regardless of content, type, or structure into suitably sized blocks, called packets delivery of variable bitrate data streams (sequences of packets) over a shared network which allocates transmission resources as needed using statistical multiplexing or dynamic bandwidth allocation techniques 8

9 SD UMTS Architecture Mobile Station Base Station Subsystem Network Subsystem Other Networks SIM ME BTS BSC MSC/ VLR GMSC PSTN EIR HLR AUC PLMN RNS USIM ME Node B RNC SGSN GGSN Internet + UTRAN Note: Interfaces have been omitted for clarity purposes.

10 Packet-Switched Systems: (2.5G+ e.g., UMTS) There are six elements: MS, Node B, RNC, SGSN, GGSN, and GF MS: Provides the voice and packet data services. It is also called UE (User Equipment). Node B: The name for base station in GSM. RNC (Radio Network Controller): Controls the radio resources of the Node Bs that are connected to it. Its function is similar to BSC. A device PCU (Packet Control Unit) converts the data stream into packet format SGSN (Service GPRS Support Node): Analogous to MSC/VLR in the circuit-switched system. This includes mobility management, security, and access control functions. It interfaces to HLR. GGSN (Gateway GPRS Support Node): The point of interface with external packet data networks such as the Internet. CGF (Changing Gateway Function): Mainly for billing 10

11 LTE Architecture Reff:

12 enode B Functionalities Access Network the enodeb supports a set of legacy features, all related to physical layer procedures for transmission and reception over the radio interface Modulation and de-modulation Channel coding and de-coding Radio Resource Control: this relates to the allocation, modification and release of resources for the transmission over the radio interface between the user terminal and the enodeb Radio Mobility management: this refers to a measurement processing and handover decision. 12

13 Evolved Packet Core (EPC) The MME (Mobility Management Entity) Security procedures Terminal-to-network session handling Idle terminal location management The HSS (Home Subscriber Server) is the concatenation of the HLR (Home Location Register) of GSM User identification and addressing User profile information Mutual network-terminal authentication 13

14 The Serving Gateway Evolved Packet Core (EPC) the Serving GW is the termination point of the packet data interface towards E-UTRAN When terminals move across enodeb in E-UTRAN, the Serving GW serves as a local mobility anchor, meaning that packets are routed through this point for intra E-UTRAN mobility and mobility with other 3GPP technologies, such as 2G/GSM and 3G/UMTS. The PDN (Packet Data Network) Gateway anchor point for sessions towards the external Packet Data Networks, the PDN GW also supports Policy Enforcement features The PCRF (Policy and Charging Rules Function) Server The Policy Decision Function (PDF) The Charging Rules Function (CRF) 14

15 3G Overview 3G is created by ITU-T and is called IMT-2000

16 Evolution from 2G 2G IS-95 GSM- IS-136 & PDC 2.5G IS-95B HSCSD GPRS EDGE 3G Cdma2000-1xRTT Cdma2000-1xEV,DV,DO Cdma2000-3xRTT 3GPP2 W-CDMA EDGE TD-SCDMA 3GPP

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18 LTE vs UMTS Functional changes compared to the current UMTS architecture

19 The Multiple Access Problem The base stations need to serve many mobile terminals at the same time (both downlink and uplink) All mobiles in the cell need to transmit to the base station Interference among different senders and receivers So we need multiple access scheme

20 Multiple Access: Enable many mobile users to share simultaneously radio spectrum. Provide for the sharing of channel capacity between a number of transmitters at different locations. Aim to share a channel between two or more signals in such way that each signal can be received without interference from another. 20

21 Multiple Access Schemes 3 orthogonal Schemes: Frequency Division Multiple Access (FDMA) Time Division Multiple Access (TDMA) Code Division Multiple Access (CDMA)

22 Frequency Division Multiple Access frequency Each mobile is assigned a separate frequency channel for the duration of the call Sufficient guard band is required to prevent adjacent channel interference Usually, mobile terminals will have one downlink frequency band and one uplink frequency band Different cellular network protocols use different frequencies Frequency is a precious and scare resource. We are running out of it Cognitive radio

23 FDMA 23

24 Features of FDMA If an FDMA channel is not in sue, then it sits idle and can t be used by other users. Transmit simultaneously and continuously. FDMA is usually implemented in narrowband systems. Its symbol time is large as compared to the average delay spread. For continuous transmission, fewer bits are needed for overhead purposes (such as synchronization and framing bits) as compared to TDMA. FDMA uses duplexers since both TX and RX operate at the same time. 24

25 Time Division Multiple Access Guard time signal transmitted by mobile terminals at different locations do no arrive at the base station at the same time Time is divided into slots and only one mobile terminal transmits during each slot Like during the lecture, only one can talk, but others may take the floor in turn Each user is given a specific slot. No competition in cellular network Unlike Carrier Sensing Multiple Access (CSMA) in WiFi

26 TDMA Transmitter share a common channel. Only one transmitter is allowed to transmit at a time. Synchronous TDMA: access to the channel is restricted to regular. Asynchronous TDMA: a station may transmit at any time that the channel is free. 26

27 Features of TDMA TDMA systems divide the radio spectrum into time slots. Each user occupies a cyclically repeating time slot. Transmit data in a buffer-and-burst method, thus the transmission for any user is not continuous. TDMA has TDD and FDD modes Share a single carrier frequency with several users. Data transmission is not continuous, but occurs in bursts. No duplexers is required since users employ different time slots for transmission and reception. TDMA can allocate different numbers of time slots per frame to different users, allowing bandwidth be supplied on demand to different users 27

28 Combined used of synchronous TDMA and FDMA 28

29 Code Division Multiple Access Use of orthogonal codes to separate different transmissions Each symbol of bit is transmitted as a larger number of bits using the user specific code Spreading Bandwidth occupied by the signal is much larger than the information transmission rate But all users use the same frequency band together Orthogonal among users

30 CDMA 30

31 Example of CDMA 31

32 Orthogonal Frequency Division Multiplexing(OFDM It is a special kind of FDM The spacing between carriers are such that they are orthogonal to one another Therefore no need of guard band between carriers. Each terminal occupies a subset of sub-carriers Subset is called an OFDMA traffic channel Each traffic channel is assigned exclusively to one user at any time user4 user3 user2 user1 32

33 Multi-user Diversity Advantages of OFDMA broadband signals experience frequency selective fading OFDMA allows different users to transmit over different portions of the broadband spectrum (traffic channel) Different users perceive different channel qualities, a deep faded channel for one user may still be favorable to others 33

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35 History of Mobile Cellular Chapter 1: Wireless and Cellular Telecommunication 35

36 Few Slides from Adv. Wireless Comm 36

37 1G to 5G 1st Generation(1984) Analog cellular (basic voice service) AMPS 2nd Generation(CDMA(1996)) Digital cellular (enhanced voice service) GSM and cdmaone(is-95a, IS-95B(99년)) 3rd Generation(2000(cdma2000), 2002(WCDMA)) Voice, data, and image(384kbps) IMT-2000 (cdma2000 1x, EV-DO, EV-DV and WCDMA, HSDPA, HSUPA, HSPA, 3GPP LTE, LTE-Advanced) WiBro, WiBro Evolution Problems: limited mobility and up to 2Mbps~100Mbps bandwidth 3GPP, 3GPP2, IEEE 802 4th Generation (IMT-Advanced(2010+)) Broadband multimedia applications and virtual reality (VR) applications Full mobility and higher bandwidth (100Mbps, 1Gbps ) ITU-R WP5D and ITU-T SG19 Combination of 3GPP and IEEE m or Dual Mode 5th Generation (2020+) Future Internet and Networks Sense 37

38 Cellular Network Evolution Service System Multiplexi ng Data rate 1G 2 G 2.5 G 3G 4G analog digital PCS IMT-2000 IMT-Advanced FDMA 2.4Kbps TDMA CDMA (14.4Kbps) TDMA CDMA (144Kbps) CDMA OFDMA (384Kbps~14.4Mbps) 100Mbps(이동 시) (mobile) 1Gbps( 정지 시) (stationary) Roaming No Limited Limited Global Global Technolo gy AMPS GSM IS-95(CDMA) PCS-1800 (GSM) IS-95C cdma2000, EVDO WCDMA, HSDPA, LTE, LTE-Advanced, WiBro Evolution Mobile WiMAX, Femtocell, VLC,.. 38

39 4G Evolution Path 39

40 Cellular communication Mobile communication Wireless communication Advantages Disadvantages 40

41 Why Interference Management is Required? Interference is one of the main obstacle for the femtocell network deployment Many femtocells around a small area Huge interference if there is no proper planning Interference causes Reduced throughput Increased outage probability Decreased QoS/QoE Inefficient interference management system Decreased frequency utilization Increased cost

42 Interference Scenarios for Femtocells Overlaid by Macrocells Macrocell downlink Macrocell uplink Femtocell downlink Femtocell uplink

43 QoS What is QoS? Ability of a network to provide a service at an assured service level QoS management Network planning Network dimensioning Number of radio, transmission element and core network Details network planning Requirement of coverage, capacity and QoS QoS provisioning A process that deploys QoS in networks and MT Radio, core and transport QoS QoS monitoring Measure QoS and improve it further QoS optimization A process to improve the overall network quality Performance measurements, analysis of measurement results and update of network quality

44 QoS Requirements for HSDPA Networks QoS Requirements target for audio and video services Medium Application Key performance parameters and target values E2E delay Jitter Loss Audio Audio Audio Video Conversational voice Voice messaging High quality streaming audio Videophone < 150 ms ( preferred) < 400 ms limit < 1 s for play back < 2 s for record < 1 ms < 3% PLR < 1 ms < 3% PLR < 10 s <<1ms < 3% PLR < 150 ms (preferred) < 400 ms limit Lip-synch:<100 ms < 1% PLR Video One-way video <10 s < 1% PLR

45 QoS Requirements for HSDPA Networks QoS requirement target for data services Medium Application Key performance parameters and target values E2E one-way delay Jitter Information loss Data Web-browsing HTML <2 s /page (preferred) < 4 s/page (acceptable) N.A 0 Data Data Bulk data Transfer /retrieval High priority Transaction/services < 15 s (preferred) < 60s acceptable) < 2 s (preferred) < 4 s (acceptable) N.A 0 N.A 0 Data Command/control < 250 ms N.A 0 Data Still image < 15 s (preferred) <60 s acceptable) N.A 0 Data Interactive games < 200 ms N.A 0 Data Telnet < 250 ms N.A 0 Data Data (server access) (server to server transfer) < 2 s (preferred) < 4s (acceptable) Can be several minutes N.A 0 N.A 0

46 Why Mobility Management is Needed? Moving entity? Mobile terminal Mobile user Mobile network Moving scope? Intra/Inter-domain, Micro/Macro-mobility Horizontal, Vertical Active session? Location management (for Paging) Handoff (Session mobility) More network coverage in same area Cost QoS Reliability

47 Handoff Management Requirements Reduction of signaling and processing overhead Minimize packet loss and delay (seamless HO) QoS guarantees during the process and transfer of context Use of any triggers or metrics available to decide when and where (planned HO) Efficient use of network and MT resources Enhanced scalability, reliability and robustness Allow inter-technology handoff (VHO)

48 Soft Handoff Process MS continually scan for pilot signals from neighbor cells When a pilot from a neighbor cell crosses a threshold, MS requests a handoff BS commands MS to perform handoff

49 System Discovery Handover Steps MT must know which wireless networks are reachable Periodic beacons from AP Signal measurements Gathering handoff metrics : bandwidth, cost, delay, SNR, power, etc. Periodic network scanning Handoff Decision MT evaluates the reachable wireless networks to make a decision Price Power consumption Bandwidth availability Handoff Execution If MT decides to perform a HO, it executes the HO procedure required to be associated with the new wireless network Wireless Networks & Communications Lab.

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