Mobile Communications Chapter 7: Wireless LANs

1. Mobile Communications Chapter 7: Wireless LANs • HIPERLAN • HiperLAN2 (pages 257-263) • QoS Prof. Dr.-Ing. Jochen Schiller, http://www.jochenschiller.de/ MC SS02 7.1

2. HiperLAN2 Official name: BRAN HIPERLAN Type 2 • High data rates for users up to 54 Mbps! • 5 GHz band (Europe: 5.15-5.35 GHz and 5.47-5.725 GHz license exempt bands) • Connection oriented: • Prior to data transmission HiperLAN2 networks establish logical connections between sender and receiver. Connection set up is used to negotiate QoS parameters. • All connections are TDMA with TDD for separation of up/downlink. • Point-to-point as well as point-to-multipoint connections are offered. • Additionally, a broadcast channel is available to reach all mobile devices in the transmission range of an access point • Quality of service support: • With the help of connections, support of QoS is much simpler. • Each connection has its own set of QoS parameters (bandwidth, delay, jitter, bit error rate, etc.) Prof. Dr.-Ing. Jochen Schiller, http://www.jochenschiller.de/ MC SS02 7.2

3. HiperLAN2 Official name: BRAN HIPERLAN Type 2 • Dynamic frequency selection: • HiperLAN2 does not require frequency planning like IEEE 802.11. • All access points have built in support which automatically selects an appropriate frequency within their coverage area. • All APs listen to neighboring APs as well as to other radio sources in the environment. • The best frequency is chosen depending on the current interference level and usage of radio channels. • Security support • Authentication as well as encryption are supported by HiperLAN2 • Both, mobile terminal and access point can authenticate each other. • All user traffic can be encrypted to protect against eavesdropping or man-in-the-middle attacks. Prof. Dr.-Ing. Jochen Schiller, http://www.jochenschiller.de/ MC SS02 7.3

4. HiperLAN2 Official name: BRAN HIPERLAN Type 2 • Mobility support • Mobile terminals can move around while transmission always takes place between the terminal and the access point with the best radio signal. • Handover between access points is performed automatically. • If enough resources available, all connections including their QoS parameters will be supported by a new access point after handover. • However, some data may be lost during handover. • Network and application independent • APs can connect to many types of networks like Ethernet, Firewire, etc. • Interoperation with 3G networks, support for many home audio/video devices • Power save modes • Mobile terminals can negotiate certain wake-up patterns to save power. • Either short latency requirements or low power requirements can be supported. • Plug and Play Prof. Dr.-Ing. Jochen Schiller, http://www.jochenschiller.de/ MC SS02 7.4

5. HiperLAN2 architecture - Infrastructure mode AP Core Network (Ethernet, Firewire, ATM, UMTS) APT APC 1 3 AP APT APC 2 APT MT4 MT3 MT2 MT1 • Two access points (AP) are shown • Core network, an Ethernet, Firewire, • ATM, 3G, etc • Each AP: an Access Point Controller • one or more access point tranceivers • An APT can comprise one or more sectors (shown as cells here) • MPs can move around in the cell • The system automatically assigns the APT/APC with the best transmission quality. • No frequency planning is needed. Prof. Dr.-Ing. Jochen Schiller, http://www.jochenschiller.de/ MC SS02 7.5

6. HiperLAN2 – three handover situations may occur AP Core Network (Ethernet, Firewire, ATM, UMTS) APT APC 1 3 AP APT APC 2 APT MT1 MT4 MT3 MT2 • Sector handover – a new cell (See MT1 in the figure below) • Radio handover – different APTs but the same APC (See MT3 in the figure below) • Network handover – different APCs (See MT2 in the figure below) In this case the core network and higher layers are also involved. If not supported by the core network, a new association must take place. Prof. Dr.-Ing. Jochen Schiller, http://www.jochenschiller.de/ MC SS02 7.6

7. Centralized vs. direct mode MT1 MT1 MT2 MT2 MT2 +CC MT1 • Centralized mode: Infrastructure mode • All APs are connected to the core network • MTs are associated with APs • Even if two MTs share the same cell, all data is transferred via the AP. • This mode is mandatory • The AP takes complete control of everything • Direct mode: Ad Hoc mode • Data is directly exchanged between MTs if they can receive each other, but the network still has to be controlled: • This can be done either via an AP that contains a central controller (CC) anyway or via an MT that contains the CC functionality. • There is no difference between an AP and a CC besides the fact that APs are always connected to an infrastructure but here only the CC functionality is needed. AP AP/CC control control data control data control data Prof. Dr.-Ing. Jochen Schiller, http://www.jochenschiller.de/ MC SS02 7.7

8. HiperLAN2 – The physical layer • Many functions and features of HiperLAN2 physical layer served as example for IEEE 802.11a. It is not suprising that both standars offer similar data rates and use identical modulation schemes. • OFDM • BPSK, QPSK, 16-QAM and 64-QAM Prof. Dr.-Ing. Jochen Schiller, http://www.jochenschiller.de/ MC SS02 7.8

9. Operating channels of HiperLAN2 in Europe channel 36 40 44 48 52 56 60 64 5150 5180 5200 5220 5240 5260 5280 5300 5320 5350 [MHz] 16.6 MHz 100 104 108 112 116 120 124 128 132 136 140 channel 5660 5680 5700 5470 5500 5520 5540 5560 5580 5600 5620 5640 5725 [MHz] 16.6 MHz center frequency = 5000 + 5*channel number [MHz] Prof. Dr.-Ing. Jochen Schiller, http://www.jochenschiller.de/ MC SS02 7.9

10. Basic structure of HiperLAN2 MAC frames 2 ms 2 ms 2 ms 2 ms TDD, 500 OFDM symbols per frame MAC frame MAC frame MAC frame MAC frame . . . broadcast phase downlink phase uplink phase random access phase variable variable variable MAC: creates frames of 2 ms duration Each MAC frame is further sub-divided into four phases • broadcast phase: The AP sends inf of the current frame • downlink phase: AP to MTs • uplink phase: MTs to AP • random access phase: for registered MTs – capacity requests • for new MTs access requests (slotted ahloha) Prof. Dr.-Ing. Jochen Schiller, http://www.jochenschiller.de/ MC SS02 7.10

11. HiperLAN2 – Convergence Layer • The physical layer and the data link layer are independent of specific core network protocols. • A special convergence layer (CL) is needed to adapt to the special features of these network protocols. Prof. Dr.-Ing. Jochen Schiller, http://www.jochenschiller.de/ MC SS02 7.11

12. End Prof. Dr.-Ing. Jochen Schiller, http://www.jochenschiller.de/ MC SS02 7.12

13. Connection oriented • Prior to data transmission, HiperLAN2 networks establish a logical connection between a sender and a receiver (e.g. A mobile device and an access point). • Connection set-up is used to negotiate QoS-parameters. • All connections are time-division-multiplexed over the air interface (TDMA with TDD for separation of up/downlinks). Prof. Dr.-Ing. Jochen Schiller, http://www.jochenschiller.de/ MC SS02 7.13

14. QoS support With the help of ”connections”, support of QoS is much simpler! Can handle time sensitive data transfers! Each connection has its own set of QoS parameters: • Bandwidth • Delay • Jitter • Bit error rate • Etc Prof. Dr.-Ing. Jochen Schiller, http://www.jochenschiller.de/ MC SS02 7.14

15. HiperLAN2 protocol stack Higher layers Convergence layer DLC control SAP DLC user SAP Data link control - basic data transport function Radio link control sublayer Radio resource control Assoc. control DLC conn. control Scope of HiperLAN2 standards Error control Radio link control Medium access control Physical layer Prof. Dr.-Ing. Jochen Schiller, http://www.jochenschiller.de/ MC SS02 7.15