Communications COMMS (CE )

Transcription

1 Faculty of Computing, Engineering & Technology Multiplexing, (FDM, TDM, CDM) & Communications COMMS (CE ) Alison L Carrington C203 A.L.Carrington@staffs.ac.uk /9

2 2 Overview & Objectives Introduction Multiplexing Schemes FDM, TDM & CDM History/future of Mobile communication systems 1G, 2G, 3G & 4G? Mobile Multiple Access Schemes Advantages and disadvantages FDMA, TDMA, CDMA & Combinations

3 3 Introduction (1) Multiplexing: name given to techniques which allow more than one message to be transferred via the same communication channel. Channel: could be a transmission line Twisted pair Co-axial cable A radio system Fibre optic cable Etc..

4 4 Introduction (2) Channel will offer a specified bandwidth, which is available for a time, t, where t->. With reference to the channel there are 3 degrees of freedom Bandwidth or frequency Time Code B L Channel Bandwidth B H freq

5 5 Introduction (3) freq code Multiplexing are techniques which allow k users to occupy a channel for the duration in time, that the channel is available time

6 6 Multiplexing It costs significant amounts to change a telephone system, not least the cost of the construction Hence the more calls you can pump down a cable the more profitable the cable becomes Telco s (Telephone companies) have developed elaborate multiplexing schemes The schemes can be divided into three categories Frequency Division Multiplexing (FDM) Time Division Multiplexing (TDM) Code Division Multiplexing (CDM)

7 7 Sharing a medium Time division multiplexing brought digital technology to Recall, multiplexing describes how several users can share the same medium with minimum or no interference [Schiller 2003] In multiplexing can be applied in 4 dimensions Space Frequency Time Code

8 8 Space Division Multiplexing (SDM) Premise that if we have entities wishing to communicate using a single channel, then as long as we space them far enough apart interference will not occur To reduce further, the risk of interference place guard space between the frequency spaces

9 9 Frequency Division Multiplexing (FDM) t Divides the available frequency into non-overlapping bands with guard spaces between to avoid overlapping (adjacent channel interference) Receiver only has to know the frequency to tune in to Used in analogue systems Channel f 1 Channel f 2 Channel f 3 Channel f 4 Channel f 5 Channel f 6 f

10 10 Time Division Multiplexing (TDM) Allows access to entire frequency bandwidth but for a limited amount of time All senders use same frequency in at different time If two transmissions overlap known as co-channel interference Precise clock synchronisation required

11 11 Combining FDM/TDM By allowing a channel to use a certain frequency for a certain period of time more efficient use of resource is achieved More robust against interference and tapping This is the scheme used by GSM between the handset and base station

12 12 Combining FDM/TDM Requires coordination between the different senders Two senders will interfere if they select the same frequency To avoid this the senders hop between frequencies: if the hop is fast enough the period of interference may be so small that if the coding of the data signal is sufficient to allow the receiver to recover the data the interference is deemed acceptable

13 13 Code Division Multiplexing (CDM) All channels use the same frequency, however, each channel is given its own unique code Each code must be sufficiently orthogonal to allow appropriate guard spaces Large range of codes provides significant expansion, security, etc

14 14 Code Division Multiplexing (CDM) Highly complex scheme Receiver has to know the code & be able to separate out other traffic on different codes which appear as background noise Receiver & transmitter must be synchronised to provide correct decoding All signals must reach the receiver with relatively equal strength or the receiver will not be able to distinguish between them

15 15 Mobile Introduction Public mobile radio services developed during the 1950 s With a limited coverage area With a service available to a limited number of subscribers. The rapid development of radio and electronic technology made possible the development of cellular systems during the 1980 s. During the 1990 s, digital cellular radio was introduced During the 2000 s truly multimedia tether less communications will be introduced This section provides a review of these developments

16 16 Radio Band Classification Classification Very Low frequency Low frequency Medium frequency High frequency Very high frequency Ultra high frequency Super high frequency Extra high frequency ABB VLF LF MF HF VHF UHF SHF EHF Freq Range 3-30kHz kHz kHz 3-30MHz MHz MHz 3-30GHz GHz λ Range km 10-1km m m 10-1m m 10-1cm 1-0.1cm The frequency & corresponding wavelength may be determined using c = f λ, with c = 3x10 8 m/s, f = frequency in Hz & λ = wavelength in metres.

17 17 Worldwide cellular subscriber growth Subscribers [million] Note that the curve starts to flatten in Prof. Dr.-Ing. Jochen Schiller,

18 18 Cellular subscribers per region (June 2002) Americas (incl. USA/Canada); 22 Middle East; 1,6 Africa; 3,1 Europe; 36,4 Asia Pacific; 36,9 Prof. Dr.-Ing. Jochen Schiller,

19 19 Medium Access Control (MAC) Whilst SDM, FDM, TDM, CDM describe how the medium is accessed at the physical layer, how the selected multiplexing scheme is regulated is called the Medium Access scheme (equivalent to OSI Layer 2 the Data Link Layer) In mobile this layer is divided between the Logical Link Control (2b) and the MAC (2a)

20 20 Medium Access Control (MAC) Why can we not simply use proven data MAC s such ac CSMA/CD used on ethernet? On a fixed wire, the propagation etc, is a known factor, the sender is responsible for detecting collisions, etc. If collision occurs everyone using the medium will be aware In wireless networks attenuation, etc means signal decreases as it propagates out from the transmitter, therefore a collision may occur but will not be detected by the sender

21 21 The role of the Access Scheme Clearly conventional digital access schemes cannot be transferred to mobile Each access scheme has its own solution Mobile networks use a combination of the schemes to overcome the problems Space Division Multiple Access Frequency Division Multiple Access Time Division Multiple Access Code Division Multiple Access

22 22 Telephone Network

23 23 Cellular Communication System Cellular telephones are personally portable devices that may be used in motor vehicles or by pedestrians communicating by radio-wave at MHz band they permit a significant degree of mobility within a defined serving region that may be hundreds of square kilometers in area.

24 24 Cellular Telephone System

25 25 Cellular Coverage The geographic area to be served by a cellular radio system is broken up into smaller geographic areas, or cells. Uniform hexagons most frequently are employed to represent these cells on maps and diagrams; In practice, though, radio-waves do not confine themselves to hexagonal areas, so that the actual cells have irregular shapes. All communication with a mobile or portable instrument within a given cell is made to the base station that serves the cell.

26 26 Cellular Migration Paths First Major Migration Path I Gen, 80 s, ETACS (C-450,NMT-450..), (FDMA), Analogue II Gen 90 s - GSM, II.5 Gen - GPRS, EDGE, (TDMA) Digital III Gen, 00 s, W-CDMA, (CDMA), All Digital Second Major Migration Path I Gen, 80 s, AMPS, (FDMA), Analogue II Gen, 90 s, IS-54 (TDMA), IS-95 (CDMA), Digital III Gen, 00 s, Cdma2000 (CDMA), All Digital

27 27 Mobile Communication #1 Two aspects of mobility: user mobility: users communicate (wireless) anytime, anywhere, with anyone device portability: devices can be connected anytime, anywhere to the network Example Wireless vs Mobile Stationary PC Laptop in a hotel Wireless LAN in historic building Personal Digital Assistant

28 28 Mobile Communication #3 The demand for mobile communication creates the need for integration of wireless networks into existing fixed networks: local area networks: standardization of IEEE ,ETSI (HIPERLAN) Internet: Mobile IP extension of the internet protocol IP wide area networks: e.g., internetworking of GSM and ISDN

29 29 Mobile Communication #4 Started with Mobile phones Which were voice only Limited battery life Limited roaming capability Limited quality Unsecured Advent of Digital phones Allowed for better use of this phone technology Allowed the user to roam and receive calls anywhere Call were encrypted The use of digital communications allowed data calls

30 30 Mobile Communication #5 Roaming capability Brought forward technology Dual/Tri Band phones Satellite phones Expensive about 1.20 a minute for a world phone call This allowed the user to move from the office/home environment and still be connected. Laptops As computers got smaller it was now possible to carry it with you As the computer is available the data was required for it

31 31 Mobile Communication #6 Data Use GSM phones allowed 9.6 Kbps data communications Enough for and simple file transfers SMS messaging is the most popular data use Voice calls are coming to the peak of the popularity Additional avenues of revenue are required Increased data is a obvious choice Charge the user for the packet received Charge for the services they are accessing i.e. Football results service

32 32 Personal Communication Services (PCS) We will soon have the ability for anyone to access digital information like the Internet. Unlike the Internet, there will be value added service from day one Video on Demand Paying your credit card bill Ordering services Value added services will be the primary goal of the PCS This will be needed to pay for the infrastructure and licenses paid for Each user will be able to view the information as they want it Central control will not be put upon on the users Differing levels of hardware capability will effect the end presentation

33 33 Applications Vehicles transmission of news, road condition, weather, music via DAB personal communication using GSM position via GPS local ad-hoc network with vehicles close-by to prevent accidents, guidance system, redundancy vehicle data (e.g., from busses, high-speed trains) can be transmitted in advance for maintenance Emergencies early transmission of patient data to the hospital, current status, first diagnosis replacement of a fixed infrastructure in case of earthquakes, hurricanes, fire etc. crisis, war,...

34 34 Typical Application Road Traffic

35 35 Mobile & Wireless Services: Best Connected GSM 53 kbit/s Bluetooth 500 kbit/s

36 36 Evolution path of cellular communication 1G 2G 2.5G 3G 4G Analogue Digital Multimedia 1980 s 1990 s

37 37 Tutorial - For Each Generation 1-4G define: Technical Specification Reasons to Upgrade?G Strengths Weaknesses

38 38 Solution: 1G Technology #1 Strengths Fairly High Range Up to 50 miles from BS Uses FDMA to increase potential users Cell based network allows for the same frequency to be reused within different cells Weaknesses High Power Usage Required large battery Finite amount of possible phone numbers provided by the service No counteraction for noise, or scanning due to being an analogue signal Interference with radio Limited capacity due to available spectrum Calls disconnected due to handover no priority Voice only traffic Roaming was impossible due to different standards Expansion difficult frequency planning

39 39 Solution: 1G Technology #2 Technical Specifications Range of 50 km AMPS (advanced mobile phone system) base Uses a hexagonal cell based network AMPS Operates on a signal range of 800 MHz Analogue AMPS, TACS, NMT, FDMA TACS uses 900 MHz, 25 khz channels, 1000 channels Reasons to Upgrade High power usage The amount of phones trying to be used exceeded the possible usage Analogue Technology prone to scanning or noise (security) Increased demand Smaller devices Tracking of device Interference limited also improved error checking Ability to expand the network Requirement for standard design rather than many (e.g. tacs, amps)

40 40 Solution: 2G Technology #1 Strengths Voice data can be compressed allowing greater throughput Less power intensive longer battery life, small batteries Digital error checking removes noise Introduction of SMS and availability on mobile handsets (digital data services) Harder to intercept digital signals and reduced scanning Less signal power needed on handset so cells can be made smaller Clearer voice data GSM allows signal roaming Standards based allows roaming Provides security Expanded capacity digital based more efficient

41 41 Solution: 2G Technology #2 Weaknesses Digital signals can produce dropouts rather than a static noise Smaller cells cause some phones to struggle to receive a reasonable signal strength Loss of tone on voice Limited data on control channel Designed for voice Still not one standard throughout the globe Difficult to expand network freq planning required

42 42 Solution: 2G Technology #3 Technical Specifications GSM (European standard) Operates in 4 different signal ranges (900 MHz or 1800 MHz for European and 850 MHZ or 1900 MHZ on the American Continent. 25 MHz bandwidth is divided into 124 carrier frequency channels, each spaced 200 khz apart. Uses TDMA (Time Division Multiplexing) to give 8 full rate or 16 half rate speech channels per radio frequency channel. Transmission power of 2 watt in 850/900 and 1 watt in 1800/ km range on GSM

43 43 Solution: 2G Technology #4 Uses a GMSK (Gaussian minimum-shift keying) a modulation which is a continuous phase frequency shift keying which reduces interference from cross channel Introduced the SIM (Subscriber Identity module) to contain the users subscription information and phone book. Reasons to Upgrade Support more users, higher data rates are required Use of more data centric applications Requirement for a single global standard

44 44 Solution: 2.5G Technology #1 Strengths Frees up control channel Higher data rate then 2G and 1G due to dedicated channels GPRS Added the application of WAP Enabled to work within the GSM technology framework with little in the way of change Data is sent in packets thus lowering the resource requirements Capable of switching between voice and data communications and also providing simultaneous data and voice transfer Packet and voice roaming possible EDGE Improved air interface technology QOS supported Builds on GPRS technology 3 times faster than GPRS Improved forward error checking

45 45 Solution: 2.5G Technology #2 Weaknesses To use GPRS you need a GSM device Still not a global standard Due to backward compatibility system not designed optimally Because channels dedicated to packets there are less voice channel available No 2.5G evolution in USA Uplink and downlink is still symmetrical

46 46 Solution: 2.5G Technology #3 Technical Specifications FDM, FDMA and TDMA Users can access more than 1 channel at a time hence the higher data rates. Data channels are shared. GPRS QPSK modulation 171 kbps theoretical maximum data rate, actual Kbps EDGE 384 kbps theoretical, actual. Increases down to change in coding schemes 8PSK modulation

47 47 Solution: 2.5G Technology #4 Reasons to Upgrade Still not fully compatible globally Voice and data still treated separately require a standard so multimedia can be transmitted and received Higher data rates and increased capacity Higher security measures (CDMA is more difficult to intercept therefore more secure) Dynamically allocated direction of channel (TDM)

48 48 Solution: 3G Technology #1 W-CDMA replaced TDMA to increase the amount of users and allow higher speeds Strengths 3 different data rates based on distance. 2Mbps for fixed in building services (Pico cell), 384 kbps in urban environments (micro cell) and 144 in wide area mobile environments (macro cell) in FDD mode with a modulation of QPSK UMTS Incorporates the developments made for the GPRS and EDGE networks Without the chipping code the data is essentially useless so a moderate level of security (scrambling codes can be used) Ability to extend network easily by adding cells or sectoring existing cells Capacity not limited by bandwidth but other user interference Higher data rate then previously and also is flexible and variable depends on cell size, user mobility and requirements. Dynamic allocation of bandwidth, i.e. direction of flow (TDD) Power control can save battery

49 49 Solution: 3G Technology #2 Weaknesses Still not one single global standard i.e. frequencies, duplex, multiple access technique, nodes in infrastructure due to backward compatibility issues Expensive licences pass cost to user. Not fair competition i.e. not many providers (operators) difficult for new operators Lack of coverage too new hence migration to standard systems Always on = drain of battery Power control requires signalling therefore a drain on resources Technical Specifications Uses 3 main technical implications - UMTS (Europe), CDMA2000(America) and TD-SCDMA (China) UMTS uses ATM (Asynchronous Transfer Method) which allows circuit switched transfer of data using packets UMTS using ATM also allows a high speed of data transfer up to 10Gbps and provides a QOS for the duration of packet transfer.

50 50 Solution: 3G Technology #3 Technical Spec continued. UMTS uses Wideband code division multiple access (W-CDMA) which uses 10x the current processing power of 2G to encode the signal and is done with QPSK W-CDMA supports two modes of operation TDD (time division duplex) and FDD (frequency division duplex) W-CDMA allows multiple users to communicate at the same time over the same frequency. Utilising Chipping Codes which is supplied by the base station to the device. The chipping code is used to identify the signals from the device and it can also be used to adjust the frequency of data transferred during the transfer. UMTS uses 5Mhz for the signal and CDMA uses only 200 KHz

51 51 Solution: 3G Technology #4 Reasons to upgrade 1 standard required 1 device should connect to fixed network best/fast/lowest error rate Reconfigure itself dynamically Software radio

52 52 Solution: Reasons for Future G???? #1 Higher data rates, more secure and more reliable Single Standard OFDM (Orthogonal Frequency division modulation) QAM (Quadrature amplitude modulation) MIMO (Multiple input, multiple output) antenna arrays Killer app What will be the new application that is a must for phone technology Single device that can reconfigure itself dependant on access method I.e. pda phone/laptop, personal organiser in one! Mp3 player

53 53 Solution: Reasons for Future G???? #2 Beheshti, B. Study of the technology migration path of the cellular wireless industry from 3G to 3.5G and beyond ; Long Island Systems, Applications and Technology, IEEE Conference 6 May, 2005 Page(s):15-28 o 3. 5 G a n d b e y o n d B e h e s h t i, B. ; L o n g I s l a n d S y s t e m s, A p p l

54 54 Solution: Development of 4G - Future M 3 Satellite Access Network Mobile Access Network (UTRAN) Wireless Personal Area Net (WPAN) Hierarchical Cell Structure Fixed Network: ATM, IPv4/6, Diff Serv, MPLS PSTN, ISDN xdsl Voice Packet Switched M 3 Circuit Switched Bluetooth, WI-FI, WLAN, Cellular, Satellite Ad-Hoc

55 55 Overlay Networks - the global goal integration of heterogeneous fixed and mobile networks with varying transmission characteristics vertical handover in-house campus-based metropolitan area horizontal handover regional Prof. Dr.-Ing. Jochen Schiller,