Communication Systems 14th lectu by pengxuebo


									Communication Systems
15th lecture

             Chair of Communication Systems
             Department of Applied Sciences
                   University of Freiburg

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    Communication Systems
    Last lecture – UMTS, WCDMA, Wireless LAN

   Last lecture devoted to telephony networks and UMTS
    encoding – WCDMA on the air interface
        WCDMA uses Code Division Multiplexing instead of Time
         Division Multiplexing and Frequency Division Multiplexing
        Per participant a binary channelization code is used thus
         multiple signals on just one frequency
   Switched over then to other mobile technologies, especially
    Wireless LAN
        Standardization of Wireless LAN technology started in1997 the
         IEEE approved 802.11
        The standard specifies the MAC and the physical layers for
         transmissions in the 2.4, 5.0 GHz band (ISM)

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    Communication Systems
    Last lecture – Wireless LAN standards

   Later on the first really popular standard IEEE 802.11b was
    created, which works at additional signal rates of 5.5 and 11
   By the end of the 1990s, the IEEE approved the
    specifications of 802.11a, which uses the 5 GHz band,
    allowing brutto signal rates of 6, 9, 12, 18, 24, 36, 48 up to 54
   In 2003, the IEEE approved 802.11g as a further evolution of
    the 802.11 standard, providing the same performance as
    802.11a, while working in the 2.4 GHz band, compatible with
    802.11b devices
        Most modern devices are equipped with g standard adapters by
        Wireless technology becomes increasingly popular
   In 2007 the 802.11n standard was approved – optimizing
    modulation, using more than one channel and antennas for
    multi-path signal reception                                     3 | 50
    Communication Systems
    This lecture – Wireless LAN and wireless technologies

   Thus we will find more mobile solutions for data
    communication than GSM, UMTS and WLAN
   There are several reasons for the evolution of new wireless
        not all requirements could be met with GSM, UMTS or WLAN
        the data rates of GSM are rather small compared to todays
         multimedia content and demands of modern networked
         applications, delay is an important issue for real time
         applications and communication
        UMTS covers greater areas, but costs are rather high and
         bandwidth is medium compared to WLAN technology
        on the other side GSM and UMTS offer a well established
         framework for user administration, accounting and billing on a
         really world wide scale

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    Communication Systems
    This lecture – Wireless LAN and wireless technologies

   WLANs of the most widely used g and a/h (b/n) standards on
    the other side offer rather high bandwidth and short delay,
    but often
        suboptimal regarding power consumption
        layer 2 security
        every-where access
        user-authentication
        bandwidth compared to classical Ethernet infrastructure
   Therefore we have additional concepts tackling some of the
    issues mentioned above
        Bluetooth for low-power, short-range, low-bandwidth

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    Communication Systems
    This lecture – More on wireless technologies

   Bluetooth is widely established and accepted in small mobile
    devices like mobile phones, PDAs, headsets, ... to replace
   UWB – Ultra Wide Band as an upcoming high bandwidth
    technology which should be able to share bandwidth with
    other users and is authorized to operate in the range of 3.1
    upto 16GHz
   “Wireless DSL” - different wide area network technologies in
    the former band of old analogous mobile phone networks to
    cover rural areas and offer high speed Internet access in
    sparsely populated areas
   WiMaX as a new wireless standard for MANs
   WiMaX and Bluetooth are covered in this lecture

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    Communication Systems
    This lecture – Network fusion

   UWB is a rather new technology and not many products are
    available by now, but you will find some articles on it in the
   In the second part of lecture we will switch over again and
    talk on fusion of telephony and IP networks

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    Communication Systems
    WiMAX - Worldwide Interoperability for Microwave Access

   Broadband Wireless MAN Standard
   Defines wireless service that provide a communications path
    between a subscriber site and a core network such as the public
    telephone network and the Internet.
   "a standards-based technology enabling the delivery of last mile
    wireless broadband access as an alternative to cable and DSL."
   Standards:
        IEEE Std 802.16-2004: addresses fixed and portable systems.
        Amendment 802.16e: Adds mobility components to the standard, called
         “Mobile WiMAX”
   WiMAX Forum coordinates interoperability testing -- “WiMAX Forum

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    Communication Systems
    WiMAX- characteristics

   Frequency ranges 10-66 GHz and 2-11 GHz for the air/physical
    layer interface
   Broad bandwidth
       Up to 134 Mbit/s in 28 MHz channels

   Accommodate either TDD or FDD
   Supports different (higher) layer or transport protocols such as
       ATM

       Ethernet

       IP

   MAC is designed for very high bit rates (up to 268 Mbit/s each
    way), while delivering ATM compatible Quality of Service

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    Communication Systems
    WiMAX- characteristics

   Frame structure allows terminals to be dynamically assigned uplink
    and downlink burst profiles according to their link conditions
   MAC uses variable length PDU and other concepts to increase
   MAC uses a self-correcting bandwidth request/grant scheme that
    eliminates the overhead and delay of acknowledgements, while
    simultaneously allowing better QoS handling
   High security: supports AES and 3DES
   IEEE 802.16e allows full mobility at speeds up to 160 km/h

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Communication Systems
WiMAX - standards

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Communication Systems
WiMAX – architecture and application

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    Communication Systems
    WiMAX – architecture and application

   WiMAX system consists of two parts
            WiMAX Base station (tower): can cover up to 10 km radius
            WiMAX Subscriber station (receiver): sits in your laptop or computer
   Several base stations are connected with one another by high-speed
    backhaul microwave links, allowing for roaming by a WiMAX
    subscriber from one base station to another base station area
   WiMAX has two main topologies
            Point to Point for backhaul
            Point to Multi-Point Base station for Subscriber station
   Typical areas of application of WiMAX
            Residential and SOHO High Speed Internet Access
            Small and Medium Business
            WiFi Hot Spot backhaul

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    Communication Systems
    WiMAX – wireless services

   Line-of-sight
        A fixed dish antenna points straight at the WiMAX tower from a rooftop
         or pole
        11 GHz to 66 GHz frequency range
        At higher frequencies - there is less interference and lots more
        The connection is stronger and more stable, so it is able to send a lot of
         data with fewer errors
   Non-line-of-sight
        A small antenna on the end-users computer connects to the WiMAX
        2 GHz to 11 GHz frequency range
        At lower frequencies – longer wavelength transmissions are not as
         easily disrupted by physical obstructions – they are better able to
         diffract, or bend, around obstacles

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Communication Systems
WiMAX – reference model

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     Communication Systems
     WiMAX – reference model

   Service-Specific Convergence Sublayer (CS):
        provides transformation or mapping of external network data, received
         through the CS service access point (SAP), into MAC SDUs received by
         the MAC Common Part Sublayer (CPS) through the MAC SAP.
   MAC Common Part Sublayer (MAC CPS):
        provides the core MAC functionality of system access, bandwidth
         allocation, connection establishment, and connection maintenance.
        receives data from the various CSs, through the MAC SAP, classified to
         particular MAC connections.
        Data, PHY control, and statistics are transferred between the MAC CPS
         and the PHY via the PHY SAP
   A separate security sublayer provides authentication, secure key
    exchange, and encryption
   Physical Layer (PHY) includes multiple specification, each
    appropriate to a particular frequency range and application

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Communication Systems
Comparison of WiMAX and Wi-Fi

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    Communication Systems
    Bluetooth technology - introduction

   Bluetooth is a radio standard and communications protocol
    primarily designed for low power consumption, with a short range
    (power class dependent: 1 meter, 10 meters, 100 meters) based
    around low-cost transceiver microchips in each device
   Intended to replace the cable(s) connecting portable and/or fixed
    electronic devices
   Designed to operate in noisy frequency environments, the
    Bluetooth radio uses a fast acknowledgment and frequency
    hopping scheme to make the link robust
   Bluetooth radio modules operate in the unlicensed ISM band at
    2.4GHz, use frequency hopping and change freq. every 42 times
    a millisecond, hop is synchronized by cell master

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    Communication Systems
    Bluetooth - characteristics

   Compared with other systems in the same frequency band, the
    Bluetooth radio hops faster and uses shorter packets
   Since March 2002, an IEEE standard, namely IEEE 802.15.1
   Many existing devices support 1.2, newer the 2.0 (defined 2004),
    2.1 (2007, stronger encryption, faster pairing, ...) standards
   Unlicensed 2.4GHz radio band, ISM (industrial, scientific,medical)
    band - available worldwide, also used by Microwave ovens, 802.11,
   Gross data rate of 1 Mbit/s, 3 Mbit/s for 2.X standards
   Basic 10m range extended to 100m with amplifiers/special devices

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    Communication Systems
    Bluetooth - characteristics

   TDMA - TDD - Frequency hopping
   Mixed voice / data paths
   Encryption, low power, low cost
   Extremely small
   Ubiquitous radio link
   Bluetooth technology offers built-in simple networking on layer 2
        thus it attracted the academic world to do research on dynamic networks
         basing on scattered, moving, emerging and disappearing mobile devices
   A Bluetooth device may operate in master mode or in slave mode

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    Communication Systems
    Bluetooth network topology - Piconet

   A maximum of 8 devices (7 active slaves plus 1 master) form a
   A piconet is characterized by the master: frequency hopping scheme,
    access code, timing synchronization, bit rate allocated to each slave
   Only one master: dynamically selected, roles can be switched
   Up to 7 active slaves; up to 255 parked slaves
   No central network structure: “Ad-hoc” network

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    Communication Systems
    Bluetooth network topology -Scatternet

   Interconnected piconets, one master per piconet
   A few devices shared between piconets
   No central network structure: “Ad-hoc” network

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Communication Systems
Bluetooth protocol stack

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    Communication Systems
    Bluetooth protocol stack

   Radio layer: defines the requirements for a Bluetooth transceiver
    operating in the 2.4 GHz ISM band
   Baseband layer: describes the specification of the Bluetooth Link
    Controller (LC) which carries out the baseband protocols and other
    low-level link routines
   Link Manager Protocol (LMP): is used by the Link Managers (on
    either side) for link set-up and control
   Host Controller Interface (HCI): provides a command interface to the
    Baseband Link Controller and Link Manager, and access to
    hardware status and control registers
   Logical Link Control and Adaptation Protocol (L2CAP): supports
    higher level protocol multiplexing, packet segmentation and
    reassembly, and the conveying of quality of service information

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    Communication Systems
    Bluetooth protocol stack

   RFCOMM protocol: provides emulation of serial ports over the
    L2CAP protocol. The protocol is based on the ETSI standard TS
   Service Discovery Protocol (SDP): provides a means for applications
    to discover which services are provided or available
   For experimenting the Linux BT stack ( might be a
    good start
        it is a really good implementation of the standard and supports the
         various Bluetooth profiles offered by the different devices
        it is OpenSource and provides the necessary programming libraries

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      Communication Systems
      Bluetooth profiles and dependencies

   A profile can
    be described
    as a vertical
    slice through
    the protocol

   A profile has
    on the profiles
    in which it is
    directly and

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     Communication Systems
     Bluetooth - applications

   Bluetooth profiles were written to make sure that the
    application level works the same way across
    different manufacturers' products
   Bluetooth applications:
        Wireless control of and communication between a cell
         phone and a hands free headset or car kit.
        Wireless networking between PCs in a confined
         space and where little bandwidth is required
        Wireless communications with PC input devices such
         as mice and keyboards
        Wireless communications to PC output devices such
         as printers

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Communication Systems
Bluetooth – applications, devices

   Built-in in modern laptops or dongles
   Wireless communications with PC
    input devices such as mice and
   Wireless communications to PC
    output devices such as printers
   Transfer of files between devices via
   Replacement of traditional wired serial
    communications in test equipment,
    GPS receivers and medical equipment
   Thus often a serial interface is
    emulated over the BT link as shown
    on the following slides ...
   Remote controls where infrared was
    traditionally used
   ...
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    Communication Systems
    Bluetooth in Linux OS – an example for the rfcomm layer

    Often Bluetooth is the best way to link devices like mobile phones to
     a laptop
mobile linux # hcitool scan
Scanning ...
        00:0E:07:47:93:1B       T610
mobile linux # hcitool cc 00:0E:07:47:93:1B
mobile linux # hcitool dc 00:0E:07:47:93:1B
    Scan for Bluetooth devices within the range of the BT adaptor
         this is much more fun to do on specific fairs like the Cebit, where you
          can compile a list of more then 20 devices within range
         if your are lucky some of the devices use broken firmware and security
          could be overridden – with special tools you can access the mobile
          device, get the phone books, alter entries and so on ...
    hcitool is just a helper to connect, authenticate, disconnect, ...
     to/from a device

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    Communication Systems
    Bluetooth in Linux OS – an example for the rfcomm layer

    hciconfig - show the Bluetooth device and its properties
mobile linux # hciconfig
hci0:    Type: PCCARD
         BD Address: 00:04:76:C8:4A:E8 ACL MTU: 128:8 SCO MTU: 64:8
         RX bytes:1046 acl:0 sco:0 events:58 errors:0
         TX bytes:850 acl:0 sco:0 commands:35 errors:0
mobile linux # hcitool dev
         hci0    00:04:76:C8:4A:E8
mobile linux # l2ping 00:0E:07:47:93:1B
Ping: 00:0E:07:47:93:1B from 00:04:76:C8:4A:E8 (data size 20) ...
0 bytes from 00:0E:07:47:93:1B id 200 time 63.05ms
0 bytes from 00:0E:07:47:93:1B id 201 time 48.13ms
0 bytes from 00:0E:07:47:93:1B id 202 time 45.13ms
3 sent, 3 received, 0% loss
    l2ping is a layer 2 ping utility to check connection on a specific
     linked device
    as you can see, the average trip time is much higher than e.g. in
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    Communication Systems
    Bluetooth in Linux OS

    In next step the emulated serial link could be started
mobile linux # rfcomm connect 1 00:0E:07:47:93:1B 1
Connected /dev/rfcomm1 to 00:0E:07:47:93:1B on channel 1
Press CTRL-C for hangup
mobile linux # pppd call gprs-o2wap
Press CTRL-C to close the connection at any stage!
defining PDP context...
    Which is just used as the lower layer protocol for a PPP connection
     part between the computer and device
    The mobile phone “translates” the data stream for the WAN GSM
     interface, GPRS protocol as explained in earlier lecture
    Of course there are more options for BT protocols between the two
     devices, like OBEX for file transfer (e.g. stored MP3, ...)

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    Communication Systems
    Bluetooth compared to WLAN

   Bluetooth is oriented to connecting close devices, serving as a
    substitute for cables
   Wi-Fi is oriented towards computer-to-computer connections, as an
    extension of or substitution for cable LANs.
   802.11b and Blutooth both utilize the free 2.4GHz band
         no exclusive use
         no guarantees
         special protocol implementations needed to cope with noise, fading, ...
   Bluetooth uses frequency hopping and changes freq. every 42
    times a millisecond, hop is synchronized by cell master
   802.11a/h WLAN standards use the free 5Ghz band
         band is reserved for WLAN only
         range is more restricted than with 802.11b
         bandwidth is increased up to 54Mbit

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Communication Systems
Bluetooth vs WLAN - comparison

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    Communication Systems
    Bluetooth v. Wi-Fi – comparison (cont.)

   Comparison of the older standards ... but only little bit changes for
    the newer ones (BT 2.X, WLAN 802.11n)

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    Communication Systems
    network technologies and network fusion

   By now we have presented a certain range of communication
    networks and their underlying technologies
   The “early” (means standards dating from the 1970s and
    1980s) digital wired and wireless networks were focused on
    the transportation of voice
   The developers of the first drafts on Internet protocols had
    data communication in mind when defining their standards
   The processes of standardization were really different
        Closed “clubs” of telephony providers and equipment
         manufacturers backed up by their states and a rather open
         process in the definition of Internet protocols and applications
        But by now both worlds learn of each other and closing the
         gaps in between ...

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    Communication Systems
    network fusion

   For a rather long time telephone and data networks were
    different entities – remember the network taxonomy
      packet orientated vs. circuit switched

        packet orientation is rather efficient in bandwidth using
         but cannot give any guarantees on packet delivery
        bandwidth growth and optional QoS helped to offer
         service quality near to circuit switching
   Why to provide two completely different infrastructures for
    rather the same services?
      voice is just another piece of data (and not the biggest
       one compared to other applications and services in use)

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    Communication Systems
    real time communication

   Traditional telephony networks are circuit switching networks
        rather centrally operated
        setup of connection in-band or out of band before communication
        no routing delays in transmit
        reserved bandwidth for every connection
        rather homogeneous transport media
   More and more real time services are handled over the Internet,
        hop-by-hop routing without clear hierarchy, principles, protocols
         discussed in the beginning of this lecture
        different media and bandwidth

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    Communication Systems
    real time communication

   Voice-over-IP (VoIP) is a big hype at the moment
      every network equipment vendor has some products in
       its portfolio (even companies like Siemens are able to
       offer products conforming to standards!!)
        many new “telephone companies” evolve to offer
         services, the old providers have to think on new
        all of them hope for reduction of costs and a source for
         roaring profits :-)
   so TCP/IP is just used for another application/service

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    Communication Systems
    delay in communication

   This service has to meet some requirements
   Important issue in communication – delay and packet loss
    (infinite delay)
   Many applications heavily depend on near no delay (e.g. real
    time communication, like VoIP, Video and multi-user online
    gaming ... :-) )
   Routing delay
       High setup delay in virtual circuit networks – no delay if
        path is set up (imagine telephone network)
        No setup delay in datagram networks, but routing
         decision for every packet in every router

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    Communication Systems
    delay in communication

   Other types of delay
      Transmission, nodal processing, queuing, propagation
   Transmission delay (example given with message
      Is L/R (L size of packet in bit, R rate in bit/s)

        e.g. Packet of 1500Byte (standard MTU – max. transfer
         unit in ethernets) on 100MBits LAN travels 0,000015s
         (=15µs) to be transferred completely

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    Communication Systems
    delay in communication

   Ping between two hosts connected via 100Mbits ethernet
        Linux-OS, between 550MHz PII/Cel and P4/2,4GHz, 100Mbits
         interface cards

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    Communication Systems
    delay in communication

   Processing delay is time for
        Evaluating header information
        Check for bit errors
        Decision on outgoing route
   Should be in order of microseconds in high speed routers
    and servers
        Protocols implemented in hardware
        New protocols like Ipv6, implemented in software first, but then
         migrated into the circuits
   Queuing delay – in packet switching networks overbooking
    of resources may occur (no bandwidth reservation as with
        Packets have to wait (a certain time) until sent out

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    Communication Systems
    delay in packet switched networks

   Propagation of signal in physical medium may add to delay
        Normally in order of nanoseconds in LAN and milliseconds in
        We cannot do much on it – but we get some problems:
            Imagine 300km WAN optical link of 10GBit/s (e.g. in GEANT)
            300km/300.000km/s=0.001s (1ms)

            10GBit/s*0.001s = 0.01GBit = 10MBit “on wire” (signal sent

             out but not received by destination)
            => rising “capacity of wire” with rising speed

        Important problem in cluster and parallel computing (!) - you
         need extremely fast connections on very short distances

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    Communication Systems
    delay in packet switched networks

   Propagation and transmission delays are different
        Propagation is the travel time of one signal (single bit)
        Transmission measures time for transferring one packet
         (independent on distance, but dependent on bandwidth and packet
   Processing delay is sum of delays mentioned above
     dnodal = dtrans + dproc + dqueue + dprop
   Contribution of every delay to dnodal may vary heavily

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    Communication Systems
    delay in packet switched networks

   The delay of packets in the output queue dqueue is most important
        Depends on the traffic intensity
        Even when average traffic rate is lower than bandwidth long queues
         may build up with very bursty traffic
        First packet is sent out directly all following can suffer increasing
        Standard problem on routers with different up-link bandwidth
   If outgoing queue is full packets are dropped
   Packet losses increase with traffic intensity

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    Communication Systems
    delay in packet switched networks

   End system to end system delay is sum of all nodal delays along
    the path from source to destination
   Helper program to get an idea on path and delay is traceroute
    (exercises in practical course at the beginning of lecture, see mtr

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    Communication Systems
    requirements towards network

   Voice over IP and Quality of Service:
        Major challenges: delay and delay variation (jitter)
        Delay jitter is the variability of source-to-destination delays of
         packets within the same packet stream
        Voice applications are usually interactive
        Delay requirement for a telephone system: max. 150ms-250ms
   We identified some of the sources of delay in a voice over IP
        OS delay: 10-100 milliseconds (digitization of analogous data,
         compression and inter software data handling) ...
   Special multimedia protocol is introduced next lecture ...

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    Communication Systems
    Information – Job Offer :)

   The professorship of communication systems offers some hiwi
    positions for the upcoming semester!
        up to 3, 4 hiwis (depending on the number of participants) for the
         new “communication systems” lecture next semester (consecutive to
         “Systeme II”)
        tasks: Preparation of new lecture content (exchange of some topics
         to coordinate with “Systeme II”), preparation of the practical
         exercises (prepare the playgrounds, design questions, tasks ...),
         preparation and correction the theoretical exercise sheets
        start 1st October, till 28th February

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    Communication Systems
    End/Literature for this topic

   Bluetooth and WLAN
   802.15.1 2005:

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    Communication Systems
    End/Literature for this topic

   WiMAX
        802.16:
        IEEE 802.16a:
        Telephoy's complete guide to WiMAX:
        Can WiMAX address your application:
   For a generic literature overview – please check the end of last
    exercises (comsys-exercise06.pdf) slides (available from the
    download section of the lectures homepage)

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