Mobile Communications Chapter 7: Wireless LANs

Prof. Dr.-Ing. Jochen Schiller, http://www.jochenschiller.de/ MC SS02 7.1

Mobile Communications Chapter 7: Wireless LANs

HIPERLANHiperLAN2 (pages 257-263) QoS


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.)


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.


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


HiperLAN2 architecture - Infrastructure mode

2

3

1

AP

APT APC CoreNetwork

(Ethernet,Firewire,

ATM,UMTS)APT

APT

APC

AP

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.


HiperLAN2 – three handover situations may occur

2

3

1

AP

APT APC CoreNetwork

(Ethernet,Firewire,

ATM,UMTS)APT

APT

APC

AP

MT4

MT3

MT2

MT1

• 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.


Centralized vs. direct mode

MT1

AP/CCAP

MT2

data

control control

MT1 MT2

data

control

Centralized mode: Infrastructure modeAll APs are connected to the core networkMTs are associated with APsEven if two MTs share the same cell, all data is transferred via the AP.This mode is mandatoryThe AP takes complete control of everything

Direct mode: Ad Hoc modeData 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.

MT1 MT2 +CCdata

control

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


Operating channels of HiperLAN2 in Europe

5150 [MHz]5180 53505200

36 44

16.6 MHz

center frequency = 5000 + 5*channel number [MHz]

channel40 48 52 56 60 64

5220 5240 5260 5280 5300 5320

5470

[MHz]

5500 57255520

100 108

16.6 MHz

channel104 112 116 120 124 128

5540 5560 5580 5600 5620 5640

132 136 140

5660 5680 5700


Basic structure of HiperLAN2 MAC frames

MAC frame MAC frame MAC frame MAC frame

2 ms 2 ms 2 ms 2 ms

broadcast phase downlink phase uplink phaserandom

access phase

. . .

TDD, 500 OFDMsymbolsper frame

variable variable variable

MAC: creates frames of 2 ms durationEach 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)

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.

End


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).


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



HiperLAN2 protocol stack

Higher layers

Convergence layer

Data link control - basic data

transport functionScope of HiperLAN2standards

DLC controlSAP

DLC userSAP

Radio link control sublayer

Physical layer

Radioresourcecontrol

Assoc.control

DLCconn.

controlError

controlRadio link control

Medium access control

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Mobile Communications Chapter 7: Wireless LANs