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Wireless Packet Networking Wireless Packet Networking: an overview (and some novel system ideas) Presented at the University of Alberta, 5.21.2003 by Roland Kempter University of Utah Department of Electrical and Computer Engineering Email: [email protected] Roland Kempter 1 University of Utah, Department of Electrical Engineering, 2003 Preface Purpose of this presentation: • Give you an understanding of the development of Wireless Communication Systems from the very beginning to the present • Give you an overview over the different technologies of Cellular and Wireless LANs • Establish a logical link from today‘s state-of-the-art technology to our current research. Roland Kempter 2 University of Utah, Department of Electrical Engineering, 2003 Organization 1. The history of Packet Based Wireless Networking INTERMEZZO 2. Introduction, technical background of Packet Switched Networks INTERMEZZO 3. State-of-the art in Wireless Packet Networking INTERMEZZO 4. The future of Wireless Packet Based Networking? INTERMEZZO 5. What are „The Others“ doing? Roland Kempter 3 University of Utah, Department of Electrical Engineering, 2003 1. History (overview) • 1971 ALOHANET [21], the first wireless packet-switched network. - established by the University of Hawaii to connect the data centers of 7 campus sites located across 4 islands to the main data center without the use of phone lines. ALOHANET was connected to the ARPAnet on the mainland. • In the 1980's, Amateur Radio Operators or "hams", built terminal node controllers (TNC's) to connect their computers through their radio equipment. • 1G networks - analog, ciruit switched, no „data mode“, Systems like AMPS (Advanced Mobile Phone Service) • Early 1990: Various Kinds of Satellite VSAT systems - capable of transmitting voice, fax and data - MF-TDMA and data packeting, (Frame Relay) [15] [21] Abramson, N. "The ALOHA system, another alternative for computer communications," in Proc. 1970 Fall Jt Computer Conf, AFIPS Press, Arlington, Va., pp 281-285. [15] www.ndsatcom.com, Satellite VSAT Systems, SKYWAN and SKYWAN DVB-IP Roland Kempter 4 University of Utah, Department of Electrical Engineering, 2003 INTERMEZZO Roland Kempter 5 University of Utah, Department of Electrical Engineering, 2003 2. Introduction Two terms joined together: Wireless and Packet (switched) 1) circuit switched: - there exists a switched line from the user to the base station or receiver at all times during the „call“, - permanently allocated network resources 2) packet switched: - splits data into packets and places packets from multiple connections on shared physical circuits, - data is routed on a per-packet basis to its final destination, - bandwidth can be allocated dynamically Basic Modes of Operation of WLANs: 1) infrastructure mode, from nodes to basestation 2) ad hoc mode, from node to node Roland Kempter 6 University of Utah, Department of Electrical Engineering, 2003 2. Introduction Some Types of WLAN architectures • wireless LANS, WLANs • wireless WANs/MANs Wide Area Networks, Metropolitan Area Networks, eg. - CDPD, Cellular Digital Packet Data, Standard for data transmission using GSM, Global System for Mobile Communications, with up to 19.2 kpbs [17], - GPRS, GSM Packet Radio Service [31] • wireless PANs Personal Area Networks, eg. - Bluetooth (IEEE 802.15) lower data rates, low power consumption [17] „What is CDPD?“, http://www.novatelwireless.com/company/cdpd.html [31] „All about GPRS“, http://www.mobilegprs.com/home.htm Roland Kempter 7 University of Utah, Department of Electrical Engineering, 2003 2. Introduction Some Types of WLAN architectures, cont‘d • Satellite networks, - DVB-S(RCS) based networks, -VSatnetworks, up/downstream up to 38Mbps (currently) MF-TDMA, big delays [15] • (mobile) ad hoc networks, - Sensor Networks, - Emergency Relief, multi-hop, infrastructureless, nodes (can also) act as forwarders/routers, network environment can be very difficult since routers can also be mobile! [15] www.ndsatcom.com, Satellite VSAT Systems, SKYWAN and SKYWAN DVB-IP Roland Kempter 8 University of Utah, Department of Electrical Engineering, 2003 2. Introduction We heard about different Wireless LAN Technologies, but how do they work? Understanding Packet Switched Networks: The OSI (Open Systems Interconnect) Layer Model Roland Kempter 9 University of Utah, Department of Electrical Engineering, 2003 2. Introduction, The OSI Layer Model Packet processing acc. to the OSI model Figure 1: OSI Layers Roland Kempter 10 University of Utah, Department of Electrical Engineering, 2003 2. Introduction, The OSI Layer Model Figure 2: OSI Layers and Packeting Roland Kempter 11 University of Utah, Department of Electrical Engineering, 2003 2. Introduction, The OSI Layer Model LAYER 1, PHY: The physical later is concerned with transmitting raw bits over a communication channel. The design issues here deal largely with mechanical, electrical, and procedural interfaces and the physical transmission medium. LAYER 2, MAC: The main task of the data link layer is to take a raw transmission facility and transform it into a line that appears free of transmission errors in the network layer (error correction capabilities). It accomplishes this task by having the sender break the input data up into data frames (typically a few hundred bytes), transmit the frames sequentially, and process the acknowledgment frames sent back by the receiver. Roland Kempter 12 University of Utah, Department of Electrical Engineering, 2003 2. Introduction, The OSI Layer Model LAYER 3: The network layer is concerned with controlling the operation of the subnet. A key design issue is determining how packets are routed from source to destination. The 802.11 Packet: A Sample Message Structure Figure 3: IEEE 802.11 Packet format and Message Structure Roland Kempter 13 University of Utah, Department of Electrical Engineering, 2003 2. Introduction, The IEEE 802.1 Standard and OSI Layers 1 and 2 Figure 4: IEEE 802.11 and the OSI Modell Roland Kempter 14 University of Utah, Department of Electrical Engineering, 2003 2. Introduction So far, we’ve heard a lot about Networking Technology, but how do we use it in a multiple user scenario? Deterministic and Random Channel Access Schemes Roland Kempter 15 University of Utah, Department of Electrical Engineering, 2003 2. Introduction, Deterministic Multiple Access Protocols • General Types of MACs – Multiple Access Protocols: 1) Deterministic channel access, some channel partitioning approaches: -FDMA(and flavors): Frequency Division Multiple Access, every mobile node has its own radio channel, channel is freed when a node finishes communication. Arbiter necessary. -TDMA(and flavors): Time Division Multiple Access, resources (can be) divided into radio channels, further sub-divided into time slots, node is assigned time slot (and radio channel), multiple users can simultaneously share a radio channel. Arbiter necessary. not very flexible, frame structure not easy to change dynamically, control loop over downlink with „channel information table“ necessary Roland Kempter 16 University of Utah, Department of Electrical Engineering, 2003 2. Introduction, Deterministic Multiple Access Protocols 1) Deterministic channel access, some channel partitioning approaches, cont‘d: - Synchronous-CDMA (and flavors): Code Division Multiple Access, Spread Spectrum. Examples of SS: frequency hopping and direct sequenced, tell nodes which code to use → orthogonal codes, global timing → synchronous PROs: - Capacity increases compared to „real world“ TDMA systems, - improved call quality, - simplified system planning (frequency reuse), - better security through scrambling, - improved coverage characteristics, - fewer cells (better diversity characteristics), - lower power consumption, - bandwidth on demand can be accomplished easily by changing the length of the spreading sequence 2) Demand Assignment Protocols: Polling, Token Passing Roland Kempter 17 University of Utah, Department of Electrical Engineering, 2003 2. Introduction, Random Multiple Access Protocols 3) Random Channel Access: - (totally) Asynchronous-CDMA: nodes choose their spreading sequence randomly → PN (pseudo-noise) sequences, no orthogonal user channels but channels separated by a given processing gain N, users can be totally asynchronous → no global network time There are many additional intermediate formats! Roland Kempter 18 University of Utah, Department of Electrical Engineering, 2003 2. Introduction, Random Multiple Access Protocols 4) Random multiple Access Schemes, wireless networks: - (Pure) ALOHA [21], simplest possible protocol, a station with a message simply transmits it to completion. If no collision occurred, message gets through, otherwise wait random time and retransmit. CONTRA: works for when transmissions are rare; quickly degenerates as load increases. Performance analysis based on assumed Poisson distribution shows max throughput of 18%. [20] - Slotted ALOHA: divide time into slots and restrict transmissions to time slots, station waits until next time slot to transmit but slots must be synchronized, max. throughput of 36% [20] - ALOHA with 2 different power levels (transmit either with high or low power), improves max. throughput of pure ALOHA to 26% and slotted to 52% [20] [21] Abramson, N. "The ALOHA system, another alternative for computer communications," in Proc. 1970 Fall Jt Computer Conf, AFIPS Press, Arlington, Va., pp 281-285. [20] www.cs.nps.navy.mil/people/faculty/ baer/N3502/Lans-1.ppt Roland Kempter 19 University of Utah, Department of Electrical
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