OLATUNDE OLYMPIO
ACSG 525
STUDY GUIDE FOR CHAPTER 6
Chapter 6
High Rate Wireless Personal Area Networks (WPAN)
This chapter focuses on the study of two HR WPAN technologies and standards;
WiMedia (IEEE 802.15.3-2003) and Ultra Wide Band (UWB). Use the following
questions and remarks as a study guide to read and understand the contents of this
chapter:
HR WPAN:
1) What is meant by HR WPAN? What are the applications for HR WPAN?
The IEEE 802.15.3-2003 is a WPAN technology optimized for the transmission
of multimedia voice and video signals. It also defines the specification for HR
WPAN supporting speeds of 11, 22, 33, and up to 55 Mbps in the 2.4GHz ISM
band. It enables multimedia connectivity between portable and fixed consumer
devices within the home and can link more than 200 wireless devices using low
cost and low power radio module.
2) What is the name (number) of the HR WPAN project developed by IEEE to
ensure interoperability and standards among data networking technologies?
IEEE 802.15.3-2003
WiMedia:
3) What is WiMedia ?
Since the IEEE standard defines only the MAC and the PHY layers, the WiMedia
Alliance was formed to support the development of any necessary higher level
protocols and software specifications for 802.15.3
4) What are the two architectures for WiMedia?
The WiMedia group defines two different architectures, called application profile,
for the upper layers of the protocol stack. One is used for multimedia audio/video
applications and the other for data transfer applications. Either or both
architectures can be implemented on a device. The lower two layers of the
stack(MAC and PHY) defines by the 802.15.3 standard are implemented in
hardware.
5) Which part of the spectrum WiMedia operates in?
The current IEEE 802.15.3 operates in the 2.4 GHz of the ISM band and support two
different channel plans: a coexistence channel plan (three non overlapping channel to
enable better coexistence with 802.11b WLANs in homes and businesses) and a high
density channel plan (four non overlapping channels to support higher density
applications such as hotels and conference centers in which large number of
WiMedia devices may be installed and no 802.11b networks are within range).
6) What type of modulation is used in WiMedia?
Since HR WPAN supports five different data rate, different modulation scheme
are used depending on the data rate. QPSK (quadrature phase shift keying) is used
for 11 Mbps, DQPSK for 22 Mbps, 16-QAM (quadrature amplitude modulation)
for 33 Mbps, 32-QAM for 44 Mbps, and 64-QAM for 55Mbps. The 22 Mbps data
rate is not coded with TCM to allow all devices in the WPAN to detect traffic
without having to decode the trellis code first.
7) What is a trellis code modulation and its advantage?
The trellis code modulation encodes the digital signal in such manaer that single
bit error can be detected and corrected. This encoding is also known as the
forward error correction (FEC). Multiple bit errors can be detected but only single
bit errors can be corrected. This technique saves time and system resources
because it avoids retransmission of the data when a single bit error occurs.
8) What are the enhancements to the PHY layer?
To prevent interference with 802.11b a number of enhancements are included in
the PHY layer of 802.15.3: passive scanning (each device scans the channels to
detect an existing piconet before joining or starting a new one. The first device to
be turn on in an area scans the frequencies to find an unused channel.), dynamic
channel selection (once the device locates a channel that is not being used, it
selects the channel to be used in the area), ability to request channel quality
information (802.15.3 devices can request channel quality information from other
devices, the PNC can initiate a channel change if there is interference), link
quality and signal strength indication (devices can request link quality information
between themselves), transmit power control (devices can decrease or increase
signal strength to improve the quality of their links).
9) What is a PNC, child piconets, and neighbor piconets?
The first device in an area assumes the role of piconet coordinator (PNC). The
PNC provides all of the basic communication timing in a piconet. This is done by
sending beacon (a frame containing information about the piconet, such as the
piconet’s unique identification). The beacon also indicates when the devices are
allowed to transmit and for how long. The piconet is peer-to-peer and devices can
transmit data directly to each other based on the timing instruction sent in the
beacon by the PNC. Child piconets are separate piconets in which the child
piconet is a member of the original or parent piconet. The child piconet’s PNC
can exchange data with any member of the parent or child piconet. Neighbor
piconets are separate piconets that have their PNC but that depend on the original
piconet’s PNC to allocate a private block of time when their devices are allowed
to transmit.
10) What are the MAC layers functions?
The IEEE 802.15.3 MAC layer is designed to provide a connection time (fast with
no complicated setup), a short one octet device ID (fast connection and access
time), the ability to obtain other devices capabilities (by request to the PNC or self
capability advertisement), peer-to-peer networking (all devices can communicate
directly to each other), data transport with QoS (voice, music and video),
security, and efficient data transfer (multiple devices can communicate on the
same network).
11) What is a wake superframe?
The wake superframe is the superframe designated by the PNC in which devices
that are in power save mode wake up and listen for the frames addressed to them.
12) What is the general MAC frame format?
Efficient data transmission is accomplished using superframes. A beacon is used
to set allocated time for the device in the piconet and to communicate
management information for the piconet. An optional contention accessperiod
(CAP) is used for association, to communicate commands, or for any
asynchronous data that may be present in the superframe. The channel time
allocation period (CTAP) which include channel time allocations (CTA) and
management channel time allocation (MCTA).
13) What is mesh networking (802.15.5)?
The IEEE 802.15.5 is a proposed standard for mesh networking, in which each
device connects to all devices within range, effectively creating multiple paths for
transmission.
UWB:
14) What is Ultra Wide Band ?
UWB is a communications technology that uses a wide bandwidth (typically
defined as greater than 20% of the center frequency or 500MHz). UWB is usually
used in short-range wireless applications but can be sent over wires. UltraWideband advantages are that it can carry high data rates with low power and
little interference.
15) How does UWB works? What type of modulation is implemented in UWB ?
UWB uses short analog pulses for signaling and does not rely on traditional
modulation methods. UWB uses impulse modulation (amplitude, polarity, or
position of an analog pulse represents either 1 or 0). UWB signals can be
transmitted using simple technique by very simple transmitters. Several
techniques can be used by UWB but the most commonly used is the biphase
modulation (half –cycle positive analog pulse to represent a 1 and half cycle
negative analog pulse to represent a 0). Another method is the multiband
orthogonal frequency division (MB-OFDM). Each frequency band is 528 MHz
wide which is further divided into 128 frequency channels. These channels are
orthogonal and they do not interfere with each other.
16) What does DS-UWB take advantage of?
Direct-sequence UWB takes advantage of the fact that one of the effects of
transmitting pulses are a nanosecond long, or shorter and that the signal naturally
spreads over a very wide frequency band, without using any spreading codes. The
entire pulse falls below the level of the background noise.
17) What is the project P802.15.3a?
The project IEEE P802.15.3a is a proposed enhancement to 802.15.3 that uses
UWB technology to support even higher data rate for multimedia and imaging
applications.
18) Why are 802.15.3 and .3a positioned to compete with Bluetooth for market
share?
802.15.3 and .3a positioned to compete with Bluetooth for market share because
these standards are capable of much higher data rates than Bluetooth.
19) How is IEEE.15.3 HR WPAN security compared to Bluetooth security?
Bluetooth security is becoming an issue because of hackers using Bluetooth to
attack mobile devices (Bluejacking). Bluetooth is also subject to Denial-of-
Service attack, Trojans, viruses and worms attacks. HR WPAN security is based
on the Advance Encryption Standard (AES) which is a symmetric key encryption
mechanism introduces by the NIST in the United States. 801.15.3 also support
message integrity verification at the MAC layer.
20) What is the principal challenge facing 802.15.3 manufacturers?
The principal challenge facing 802.15.3 manufacturers is to ensure that the
technology is incorporated into their product without significantly increasing the
cost for consumers and businesses.
21) What is the protocol functionality limitation of Bluetooth compared to
WiMedia?
The major limitation of the Bluetooth protocol is its lack of hand-off ( the ability
of a device to move from one master or PNC to another without getting
disconnected from the network in a network that extend beyond the
communications range of each device that controls the communications)
capability between piconets.
22) What is the potential effect of 2.4 GHz residential cordless phones, Bluetooth,
or IEEE 802.11b and IEEE 802.11g on HR WPAN transmission?
Using all these technology in close proximity to each other may cause
interference because they all use the 2.4 GHz ISM band. One solution is to move
the Bluetooth device away from 802.11b/g. Devices manufacturers can also
implement the new recommendation of the IEEE15.1 standard that ask the
devices to listen to the channel first before transmissions.