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
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
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-inthe-middle attacks.
Prof. Dr.-Ing. Jochen Schiller, http://www.jochenschiller.de/
MC SS02
7.3
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
HiperLAN2 architecture - Infrastructure mode
• 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.
AP
MT1
1
APT
APC
MT2
3
MT3
APT
APC
2
MT4
AP
Core
Network
(Ethernet,
Firewire,
ATM,
UMTS)
APT
Prof. Dr.-Ing. Jochen Schiller, http://www.jochenschiller.de/
MC SS02
7.5
HiperLAN2 – three handover situations may occur
• 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.
AP
MT1
1
APT
APC
MT2
3
MT3
APT
APC
2
MT4
AP
Core
Network
(Ethernet,
Firewire,
ATM,
UMTS)
APT
Prof. Dr.-Ing. Jochen Schiller, http://www.jochenschiller.de/
MC SS02
7.6
Centralized vs. direct mode
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
control
MT1
data
MT1
MT2
MT1
Prof. Dr.-Ing. Jochen Schiller, http://www.jochenschiller.de/
data
MT2
MC SS02
7.7
data
control
MT2 +CC
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
Operating channels of HiperLAN2 in Europe
36
5150
40
44
48
52
56
60
64
channel
5180 5200 5220 5240 5260 5280 5300 5320
5350 [MHz]
16.6 MHz
100
5470
140
channel
5500 5520 5540 5560 5580 5600 5620 5640 5660 5680 5700
5725
[MHz]
16.6 MHz
104
108
112
116
120
124
128
132
136
center frequency =
5000 + 5*channel number [MHz]
Prof. Dr.-Ing. Jochen Schiller, http://www.jochenschiller.de/
MC SS02
7.9
Basic structure of HiperLAN2 MAC frames
2 ms
2 ms
MAC frame
2 ms
MAC frame
broadcast phase
MAC frame
downlink phase
variable
2 ms
MAC frame
uplink phase
variable
...
TDD,
500 OFDM
symbols
per frame
random
access phase
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
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
End
Prof. Dr.-Ing. Jochen Schiller, http://www.jochenschiller.de/
MC SS02
7.12
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
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
HiperLAN2 protocol stack
Higher layers
DLC control
SAP
Radio link control sublayer
Radio
resource
control
DLC user
SAP
Convergence layer
DLC
conn.
control
Assoc.
control
Data link control basic data
transport function
Error
control
Radio link control
Scope of
HiperLAN2
standards
Medium access control
Physical layer
Prof. Dr.-Ing. Jochen Schiller, http://www.jochenschiller.de/
MC SS02
7.15