HiperLAN or more recently, HiperLAN2 are standards
approved by the European Telecommunications Standards
Institute (ETSI). HiperLAN2 is the most recent version. It is
an interoperable standard providing high-speed, broadband
connectivity for wireless LANs in corporate environments,
public “hot spots” and home environments
HiperLAN2 provides a 54 Mbps data rate on the globally
allocated 5.15–5.3 GHz band. It also may be used in the
17.1–17.3 GHz band in certain geographic locations. It surpasses
the IEEE 802.11a standard with both greater security
and traffic prioritization capabilities. HiperLAN2 also
includes mechanisms for handoffs between WLANs and 3G
mobile systems.
Currently several European manufacturers are implementing
solutions that provide a wireless Virtual Private Network
(VPN) solution for HiperLAN 2 which includes authentication
and encryption. This will enable wireless mobile users to have
a secure connection to their corporate networks when traveling
through so called “hot spots,” such as airports, hotels and conference
centers.
HiperLAN2 achieves its high data rate by using a frequency
multiplexing method called Orthogonal Frequency Digital
Multiplexing (OFDM) with various physical layer modulation
schemes as shown in Table 2-2.
OFDM is particularly efficient in time-dispersive environments,
i.e. where the radio signals are reflected from many points
such as in offices. The basic idea of OFDM is to transmit broadband,
high data rate information by dividing the data into several
interleaved, parallel bit streams, and let each bit stream
modulate a separate subcarrier. HiperLAN2 is time-division multiplexed
and connection-oriented. It can be used for point-topoint
or point-to-multipoint connections. A dedicated broadcast
channel is also included. Each connection can be assigned either
a simple relative priority level or a specific QoS in terms of bandwidth,
delay, jitter, bit error rate, etc. Hiperlan2 uses an approach
for the Access Channel that differs from the OSI model but is
very similar to the IEEE 802-11 standard as seen in Figure 2-15.
HiperLAN2 was designed for short range communications,
about 150 feet maximum. It is primarily meant to be used in a
stationary environment but does support mobility up to 4.3
feet/second. It may be used on networks with or without infrastructure
to support isochronous traffic such as audio or video
with minimum latency. It can support asynchronous traffic
data of 10Mbps with immediate access. HiperLAN2 is also
compatible with ATM.
Radio-based wireless LANs tend to exhibit randomized
“bursty” traffic patterns which can result in performance
issues. Many factors have to be taken into consideration, when
quality of service is to be measured. Among these are:
• Landscape topography
• Elevations that might cause shadows
• Multi-path from signal-reflection surfaces
• Signal loss through absorbing surfaces
• Quality and placement of the wireless equipment
• Number of stations
• Interference
• Etc.
These and other factors have been figured into the
HiperLAN2 specification to allow for a certain level of Quality
of Service guarantee.
Figure 2-16 depicts a typical topology of a HiperLAN2 network.
The Mobile Terminals (MTs) communicate with one
Access Point (AP) at a time over an air interface. As a user
moves from one AP to the next, handoffs can take place. In an
ad hoc networks, the MTs communicate directly., can also be
created, but their development is still in early phase. The
HIPERLAN/2 is planned to be finalized by the end of 1999.