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 21ECO101T
SHORT RANGE WIRELESS COMMUNICATION

Dr. D. Tharani
ECE
https://lotusarise.com/qna/upsc/q-consider-the-following-communication- tharanid@srmist.edu.in
technologies
 SHORT RANGE WIRELESS COMMUNICATION

•Unit-1: Wireless systems

•Unit-2: Antennas and Baseband coding basics
•Unit-3: RF transceivers
•Unit-4: Wireless standards
•Unit-5: Optical wireless technologies

References

1. Alan Bensky, “Short range Wireless Communications-Fundamentals of

RF system design and Applications”, Elsevier Inc, 2004
3. Rolf Kraemer and Marcos Katz, “Short-range wireless communications
emerging technologies and applications”, Wiley WWRF series, March
2009
 Unit 1-Wireless systems
• Introduction to wireless systems
• Reasons for the Spread of Wireless Applications
• Characteristics of Short-range Radio Wireless Applications
• Elements of Wireless Communication Systems-Transmitter,
Elements of Wireless Communication Systems-Receiver
• Wireless Local Area Networks (WLAN)- WiFi, Network
Architecture
• Bluetooth Transceiver, Bluetooth Modes
• Zigbee Architecture, Frame Structure, Applications and conflicts
• Ultra-wideband Technology-Bit Sequence detection, UWB Block
Diagram
• Case study: Design and analyze the WLAN hardware module
 What is Wireless Communication?

•Transmitting/receiving voice and data using electromagnetic waves in

free space.

•The information from sender to receiver is carried over a well defined

frequency band (channel).

• Each channel has a fixed frequency bandwidth and capacity (bit rate).

• Different channels can be used to transmit information in parallel and

independently.
 Types of Wireless Communication
• Mobile
Cellular Phones (GSM( Global System for Mobile)/ CDMA(Code
Division Multiple Access))
• Portable
IEEE 802.11b (Wi-Fi-Wireless Fidelity)
IEEE 802.15.3 (UWB-Ultra-Wideband)
• Fixed
IEEE 802.16 (Wireless Metropolitan Area Network-WMAN)

*GSM- describe the protocols for second-generation digital cellular networks used
by mobile devices such as mobile phones and tablets.
*CDMA-method of encoding several sources of data so they may all be transmitted
over a single RF carrier by one transmitter, or by using a single RF carrier
frequency with multiple transmitters.
 Typical Frequencies

• FM Radio ~ 88 MHz
• TV Broadcast ~ 200 MHz
• GSM Phones ~ 900 MHz
• GPS ~ 1.2 GHz
• Bluetooth ~ 2.4 GHz
• WiFi ~ 2.4 GHz
 Why Wireless?
• Benefits
• Mobility: Ability to communicate anywhere!!
• Easier configuration, set up and lower installation cost

• Difficulties
• Communication medium: Free space
• Noisy and unpredictable channel
• Broadcast channel, more user ->less BW per user
• Higher equipment cost
• Usually regulated spectrum and limited BW
• Need backbone systems in order to function properly
 Challenges
• Efficient Hardware
• Low power transmitters, receivers
• Low power signal processing tools
• Efficient use of finite radio spectrum
• Cellular frequency reuse, medium access control (MAC) protocols
• Integrated Services
• Voice, data, multimedia over the same network
• Service differentiation, priorities, resource sharing
• Network support for user mobility (mobile scenarios)
• Location identification, Handoffs,..
• Maintaining quality of service over unreliable links.
• Connectivity and coverage (internetworking)
• Cost efficiency
 Challenges
• Fading-variation of signal attenuation over variables like time,
geographical position, and radio frequency.
• Multipath-
the propagation phenomenon that
results in radio signals reaching the
receiving antenna by two or more
paths.
• Higher probability of data
corruption
• Hence, need for stronger
channel codes
• Need for stronger security
mechanisms
• Privacy, Authentication.
 Introduction to Wireless Systems
•A wireless system refers to a network or communication system
that transmits and receives data or information without the use
of physical cables or wired connections.
•It utilizes electromagnetic waves or radio frequencies to
transmit signals between devices, allowing for convenient and
flexible communication and connectivity.
•Wireless systems have become an integral part of modern life,
enabling various technologies such as mobile phones, Wi-Fi
networks, Bluetooth devices, wireless sensors, and many other
applications.
•These systems have revolutionized the way we communicate,
access information, and interact with our environment.
Advantages of Wireless system:-
1. Mobility: Users can access and communicate wirelessly from
virtually anywhere within the coverage area, providing freedom
of movement and flexibility.
2. Convenience: Wireless systems eliminate the need for physical
cables, reducing clutter and simplifying device connectivity.
3. Scalability: Wireless networks can be easily expanded or
modified to accommodate new devices or users without the
need for additional infrastructure.
4. Cost-Effectiveness: In many cases, deploying wireless systems
can be more cost-effective than laying physical cables or wiring.

Online Quiz 1
https://quizizz.com/admin/quiz/665c029803e0dab0e5ae9fa9?source=admin
&trigger=quizPage
 SHORT RANGE WIRELESS COMMUNICATION

Overview
•Short-range wireless communications typically refers to a wide variety
of technologies with communication ranges from a few centimeters to
several hundreds of meters.
•While the last three decades of the wireless industry have been
mostly dominated by cellular systems, short-range wireless devices
have gradually become a more integrated part of our everyday lives
over the last decade.
•The Wireless World Research Forum (WWRF) envisions that this trend
will accelerate in the upcoming years: by the year 2017, it is expected
that seven billion people in the world will be using seven trillion
wireless devices.
•The majority of these devices will be short-range wireless devices
that interconnect people with each other and their environments.
 SHORT RANGE WIRELESS COMMUNICATION

Reasons for spread of Wireless Applications

• Employment of higher and higher frequencies in spectrum
which was expensive previously
• SSD (solid state devices) amplify at mm(millimeter)
wavelengths or 10’s of GHz
• Efficient and compact antennas (planar antennas) are available
used in short-range devices.
• Development of SAW(Surface Acoustic Wave) frequency
determining components allows generation of UHF with very
simple circuits
• Digital modulation techniques permits multiplication of
number of communication channels
• Progress in circuit miniaturization Hybrid IC (integrated
circuits) combining analog and digital functions on one chip and
RFIC (radio frequency IC) responsible for compact size of
cellular handsets.
 SHORT RANGE WIRELESS COMMUNICATION

Characteristic of Short Range Radio

• RF output  several microWatts up to 100 milliWatts
• Communication range several cm up to several 100 m
• Indoor operation
• Omnidirectional built-in antennas
• Simple construction and low price  consumer applications
• Unlicensed operation
• Non critical bandwidth specifications
• UHF operation
• Battery operated Tx/Rx

Omnidirectional antenna which radiates equal radio power in all directions

perpendicular to an axis, with power varying with angle to the axis,
Short range radio applications
Elements of Wireless Communication Systems

1. Data source
2. RF generating
section
3. RF conduction and
radiation
4. Radio channel
5. Receivers
6. Power supply
 Elements of Wireless Communication Systems
1. Data source:
• Analog/ Digital
• Simple on/off info security intrusion detector, panic button, manual
remote control unit
• Change of state of data cause message frame modulated on RF carrier

• Address field  identifies unit that is transmitting

• Data field conveys specific info (on/off form)
• Parity bit  detect false messages
• Computer accessories and WLAN send continuous digital data over
short –range link
– Data are organized protocol including sophisticated error
detection and correction technique
• Audio devices wireless microphone and headsets send analog data to
modulator.
– These data specially processed for better pefromance over wireless
channel
Elements of Wireless Communication Systems-Data source-cont…
• FM transmission: pre-emphasis filter increases HF before txion
– Receiver : De-emphasis filter will also reduce HF noise
– Dynamic range is increased by use of compander
– Txer: weak sounds are amplified more and strong signals are amplified less
– Rxer: Opposite procedure reduces background noise while retaining weak sounds
to their proper relative level
• RFID: different aspect of data source
– Data not available in Txer but added to RF signal in an intermediate receptor
called Transducer ( may be active/passive)

COMPANDER:
combination of a
COMPressor and
an exPANDer.

– Txed RF is modified by transducer and detected by Rxer that deciphers data

added and passes to host computer
Elements of Wireless Communication Systems
2. Radio frequency (RF) generating section:
• Part of Txer consists of RF source (oscillator), modulator, and
amplifier.
• Simplest short range devices  all 3 functions included in a
single circuit of only one transistor.
• RFID is different from other applications modulation is
carried out remotely from RF source

3. RF conduction and radiation:

• Built-in antennas transmission lines are relatively short &
simple
• Antennas of short range devices must be small fraction of
wavelength and omnidirectional mostly
Elements of Wireless Communication Systems
4. Radio channel
• Range channel is short and equipment is used indoors
• RF power is relatively low and regulated by telecom authorities
• Devices often operated close to or attached to human bodyaffects
communication performance
• Reliable operating range difficult to predict
• Lack of knowledge of special propagation characteristics by manufactures,
sellers and users  dominant reason for unreliable
• Short range devices often used to replace hard wiring when similar
performance is expected, limitations of radio propagation compared to wires
must be accounted for each application
5. Receivers
• Similar blocks to Txer but operation is reversed antenna, Txion line, RF
amplifiers and oscillators
• Weak signals intercepted by antenna amplified above the circuit noise by
low noise amplifier(LNA)
Elements of Wireless Communication Systems-Rxer-cont…
• Desired signal is separated from all others and shifted lower in frequency in
downconverter more effectively amplified to level required for demodulation or
detection
• Demodulator conversion of data source implanted on RF wave in Txer back to
original form
• Txer power is limited by authorities, Rxer sensitivity is not
• To improve system performance improve sensitivity and selectivity to reduce
interference from unwanted sources must be done under constraints of physics,
cost, size and power consumption
• Important factor in Low Power system design and controversial one type of
modulation
• Simpler systems security and medical alarms choice is between amplitude
shift keying (ASK), parallel to amplitude modulation (AM) in analog system and
frequency shift keying (FSK) analogous to frequency modulation (FM)
•Downconverter takes a radio frequency (RF) signal and converts it to a lower,
intermediate frequency (IF) signal that is suitable for digital processing.
•Selectivity is the ability of radio receiver to reject signals close to desired frequency.
•Sensitivity of a radio receiver is its ability to amplify the desired weak signal.
AM and FM

AM and FM modulation video link

https://www.youtube.com/watch?v=QEubAxBfqKU
Elements of Wireless Communication Systems-Power supply
6. Power supply
• Short range devices, @least one side of wireless link must be completely
untethered( unattached to any data or power source by wire or fiber)
• When size limited, in hand-operated remote control Txers and security
detectors, battery size and energy is limited
• Need to change batteries not only highly inconvenient but also expensive
• Low current consumption is important design aim for wireless devices 
harder to achieve for Rxer than Txers
• Many short range app.  intermittent Txer operation …
• Eg. security systems : Txers  kept in very low current standby status
until data needs to be send.. …Rxer  doesn’t know when data will be sent
 must be alert all the time
• Techniques to reduce Rxer duty cycle doesn’t draw full current all time
• Another way for reducing Rxer power consumption to operate in reduced
power standby mode, operation goes to normal when beginning of signal is
detected reduced sensitivity
Wireless Local Area Networks (WLAN)
•Three Wi-Fi network configurations are shown in Figs. 11.1–11.3.
•Fig. 11.1 shows two unattached basic service sets (BSS), each with two
stations (STA).
•The BSS is the basic building block of an 802.11 WLAN. A station can make
adhoc connections with other stations within its wireless communication
range but not with those in another BSS that is outside of this range.
•In order to interconnect terminals that are not in direct range one with the
other, the distributed system shown in Fig. 11.2 is needed.

WLAN and WiFi:

WLAN https://www.youtube.com/watch?v=RBc7MyE9RTQ https://www.youtube.com/watch?v=xt0YqqbvSFQ
Wireless Local Area Networks (WLAN)
•Here, terminals that are in range of a station designated as an AP can
communicate with other terminals not in direct range but who are
associated with the same or another AP.
•Two or more such APs communicate between themselves either by a
wireless or wired medium, and therefore data exchange between all
terminals in the network is supported.
•Important thing media connecting the STAs with the APs, and connecting
the APs among themselves are totally independent.
Wireless Local Area Networks (WLAN)
•STA is an addressable destination, not necessarily at a fixed location. STA’s
may have varied characteristics and functions.
•A STA AP terminal, a mobile terminal, or it may have another specified
function.
•A network of arbitrary size and complexity can be maintained through the
architecture of the extended service set (ESS), shown in Fig. 11.3.
•STAs have full mobility and may move from one BSS to another while
remaining in the network.
Wireless Local Area Networks (WLAN)
•Fig. 11.3 shows another element type—a portal. The portal is a gateway
between the WLAN and a wired LAN.
•It connects the medium over which the APs communicate to the medium of the
wired LAN—coaxial cable or twisted pair lines.
•In addition to the functions Wi-Fi provides for distributing data throughout the
network, two other important services, although optionally used, are provided.
•They are authentication and encryption.
•Authentication is the procedure used to establish the identity of a station as a
member of the set of stations authorized to associate with another station.
•Encryption applies coding to data to prevent an eavesdropper from
intercepting it.
•802.11 details the implementation of these services in the MAC(Media Access
Control).
•Further protection of confidentiality provided by higher software layers in the
network that are not part of 802.11.
 Wireless Fidelity Wi-Fi
• IEEE 802.11g
– Data Rate: Maximum 54 Mbps
– Range: up to 100 meters
– Operating Frequency: 2.4 GHz
– Security: Password Encryption
• How It works?
• Data Transmission/Acquisition
• Wired Ethernet connection
• OFDM
• Closely spaced orthogonal sub-carriers.
• Reduction of attenuation with high frequencies.
• Facilitates single-frequency networking.
• Broadcasting
• Decoding of the Signal
• Wireless Card
In telecommunications, orthogonal frequency-division multiplexing is a type of digital
transmission used in digital modulation for encoding digital data on multiple carrier
frequencies.
WiFi :https://www.youtube.com/watch?v=St0V1yYxpv4
 Wi-Fi
Applications
• Modem for internet
– Cable
– DSL
• Device to device communication
Advantages:
– Comparatively higher data
transfer rates than other similar
technologies.
– Low infrastructure
– Wide availability
Disadvantages:
– Cost
– Limited range: Restricted to “Hot
Spots”

DSL(Digital subscriber
line)used to transmit digital
data over telephone lines.
 Bluetooth
• Open Wireless Protocol, WPAN standard
• Operates ISM (industrial, scientific, and
medical) band at 2.4-2.4835 GHz
• Uses radio technology called frequency-
hopping spread spectrum (FHSS)
• Modulation - Gaussian Frequency-Shift Key
Modulation
• Frequency- Hopping Spread Spectrum
 Chunks of data transmitted
 Spread-spectrum signals are highly
resistant to narrowband interference
 Difficult to intercept
 Transmissions share a frequency band
with minimal interference
Bluetooth: https://www.youtube.com/watch?v=jzxZUJmOu3o
Quiz2:
https://www.mentimeter.com/app/presentation/almanmn3acz3d2brcis8o1e4vb1h3c4p/pq9jjpingi
wh
 Bluetooth
• Data rate up to 1Mb/s – 3 Mb/s
• Use in mobile phones, laptops,
telephones, printers, GPS, video game
consoles
• Bluetooth USB dongle – must use if
computer is not Bluetooth enabled
• Advantages:
– Wireless, Inexpensive, Automatic
– Low energy and power consumption
• Disadvantages:
– Security
– Viruses over the years
– Bluejacking
– Health Concerns (same as mobile
phones)
Bluejacking is when an attacker sends
unsolicited messages to a victim's Bluetooth-
enabled device.
Bluetooth Architecture

• Bluetooth is an example of a WPAN. (wireless personal area networks

(WPAN), which typically serve a communication range of 10 m).
• It’s based on the creation of ad hoc, or temporary, on-the-fly connections
between digital devices associated with an individual person and located in
the vicinity of around 10 m from him.
• Bluetooth devices in a network have the function of a master or a slave,
and all communication is between a master and one or more slaves, never
directly between slaves.
• The basic Bluetooth network is called a piconet. It has one master and
from one to seven slaves.
• A scatternet is an interrelated network of piconets where any member of
a piconet may also belong to an adjacent piconet.
• Conceptually, a Bluetooth network is infinitely expandable.
Bluetooth Architecture

• Fig. 12.2 shows a scatternet made up of three piconets.

• A node may be a slave in one piconet and a master in another.
• A device may be a master in one piconet only.
Bluetooth Transceiver
•Three basic parts: RF, baseband, and application software
•A Bluetooth chip set will usually include the RF and baseband parts, with the
application software being contained in the system’s computer or controller.
Bluetooth Transceiver
•The user data stream originates and terminates in the application software.
•The baseband section manipulates the data and forms frames or data bursts for
transmission. It also controls the frequency synthesizer according to the
Bluetooth frequency-hopping protocol.
•The Gaussian low-pass filter block before the modulatorimplemented digitally
as part of a complex signal I/Q modulation unit or it may be a discrete element
filter whose output is applied to the frequency control line of a VCO(Voltage-
controlled oscillator electronic oscillator whose oscillation frequency is
controlled by a voltage input)
•Receiver may be one of several types.
•If a superheterodyne configuration is chosen, the filter at the output of the
downconverter will be a bandpass type.
•A direct conversion receiver will use low pass filters in complex I and Q
outputs of the downconverter.

IQ modulation
https://www.youtube.com/watch?v=zNbWTiKEl30
Bluetooth modes
•Bluetooth has three modes for achieving different degrees of power consumption during
operation: sniff, hold, and park.
•Even in the normal active mode, some power saving can be achieved.
1. Active mode:
•During normal operation, a slave can transmit in a particular time slot only if it is
specifically addressed by the master in the proceeding slot.
• As soon as it sees that its address is not contained in the header of the master’s
message, it can “go to sleep,” or enter a low-power state until it’s time for the next
master transmission.
•The master also indicates the length of its transmission (one, three, or five slots) in its
messageheader, so the slave can extend its sleep time during a multiple slot interval.
2. Sniff mode:
•In this mode, sleep time is increased because the slave knows in advance the time
interval between slots during which the master may address the slave.
•If it’s not addressed during the agreed slot, it returns to its low-power state for the
same period and then wakes up and listens again.
•When it is addressed, the slave continues listening during subsequent master
transmission slots as long as it is addressed, or for an agreed time-out period.
Bluetooth modes
3. Hold mode:
•The master can put a slave in the hold mode when data transfer between
them is being suspended for a given period of time.
•The slave is then free to enter a low-power state, or do something else, like
participate in another piconet.
• It still maintains its membership in the original piconet, however.
•At the end of the agreed time interval, the slave resynchronizes with the
traffic on the piconet and waits for instructions from the master.
4. Park mode:
•Park has the greatest potential for power conservation, but as opposed to hold
and sniff, it is not a directly addressable member of the piconet.
•While it is outside of direct calling, a slave in park mode can continue to be
synchronized with the piconet and can rejoin it later, either on its own initiative
or that of the master, in a manner that is faster than if it had to join the piconet
from scratch.
•In addition to saving power, park mode can also be considered a way to virtually
increase the network’s capacity from eight devices to 255, or even more.
Bluetooth modes
4. Park mode:
•When entering park mode, a slave gives up its active piconet address and
receives an 8-bit parked member address.
•It goes into low-power mode but wakes up from time to time to listen to
the traffic and maintain synchronization.
• The master sends beacon transmissions periodically to keep the network
active. (Beacon kind of like a lighthouse: it repeatedly transmits a constant
signal that other devices can see)
•Broadcast transmissions to all parked devices can be used to invite any of
them to rejoin the network.
•Parked units themselves can request reassociation with the active network
by way of messages sent during an access window that occurs a set time
after what is called a “beacon instant”
•A polling technique is used to prevent collisions.
•Park mode was removed in Version 5 of the Bluetooth specification.
Parameters that affect interference between Bluetooth and Wi-Fi:
Parameters that affect interference between Bluetooth and Wi-Fi
•Frequency and time overlap:
•A collision occurs when the interferer transmits at the same time as the
desired transmitter and is strong enough to cause a bit or symbol error in
the received packet.
•Packet length:
:
• The longer the packet length of the Wi-Fi system, relative to a constant
packet length and hop rate of Bluetooth, the longer the victim may be
exposed to interference from one or more collisions and the greater the
probability of a packet error.
•Bit rate:
•Higher the bit rate, the lower the receiver sensitivity and therefore the
more susceptible the victim will be to packet error for given desired and
interfering signal strengths.
•Higher bit rates usually result in reduced packet length, with the opposite
effect.
Parameters that affect interference between Bluetooth and Wi-Fi
•Use factor:
•More often the interferer transmits, the higher the probability of packet error.
•When both communicating terminals of the interferer are in the interfering
vicinity of the victim, the use factor is higher than if the terminals are further
apart and one of them does not have adequate strength to interfere with the
victim.
:
• Relative distances and powers:
•The received power depends on the power of the transmitter and its distance.
•Generally, Wi-Fi systems use more power than Bluetooth, typically 20 mW
compared to 1 mW.
•Bluetooth Class 1 systems may transmit up to 100 mW, but their output is
controlled to have only enough power to give a required signal level at the
receiving terminal.
• Signal-to-interference ratio of the victim receiver, SIR, for a specified symbol or
frame error ratio.
• Type of modulation, and whether error-correction coding is used.
 ZigBee
• High-level communication protocol
• The Name
– Zig-zagging of bees from flower to flower
– Analogous to mesh networking

https://youtu.be/QXV_HgGO--g?si=-YOB-22gOHflQv2B
 Zigbee
•IEEE specification 802.15.4 associated with Zigbee, but it should be seen as a separate
entity.
•Low data rate WPAN which describes the physical and data link layers that typically
address remote monitoring and control applications.
•An association of committed companies, the Zigbee Alliance, has defined the network,
security, and application layers above the 802.15.4 physical and medium access control
(MAC) layers, and deals with interoperability certification and testing
•Distinguishing features are:
•Low data rates—raw rates between 20 and 250 kbps
•Low power consumption—several months up to two years on standard primary
batteries
• Network topology appropriate for multisensor monitoring and control applications
•Low complexity for low cost and ease of use
• Very high reliability and security
 Zigbee
•Applications:
•consumer electronics
•Home and building
automation and
security systems
•industrial controls
• PC peripherals
•medical and industrial
sensor applications
•toys and games

Source: http://www.zigbee.org/imwp/idms/popups/pop_download.asp?ContentID=7092
Zigbee Architecture
Zigbee Architecture
•Similar to that of other IEEE standards, Wi-Fi and Bluetooth
•On the bottom are the physical layers, showing two alternative options for the
RF transceiver functions of the specification.
• Both of these options are not expected to exist in a single device, and indeed
their transmission characteristics—frequencies, data rates, modulation system—
are quite different.
•Embedded firmware and software layers above them will be essentially the
same no matter what physical layer is applied.
• Just above the physical layers (PHY) is the MAC layer which is responsible for
management of the physical layer and delivering data to and from the applications
through the layer above it.
•MAC layer functions channel access, keeping track of slot times, and
message delivery acknowledgement.
•The higher layers are not part of IEEE 802.15.4.
Zigbee Architecture
•Functions of the network layer forming a network, managing
association with the network and disassociation from it, and routing.
• Its functions and the application services above it are defined by the
Zigbee Alliance.
•Application software is not a part of the IEEE 802.15.4 specification.
•Zigbee Alliance prepares profiles, or programming guidelines and
requirements for various functional classes in order to assure product
interoperability and vendor independence.
These profiles define network formation, security, and application
requirements while keeping in mind the basic Zigbee features of low
power and high reliability.
Zigbee Frame structure
•Purpose of the preamble permit acquisition of chip and symbol timing.

•PHY header, PHR, which is signaled by a delimiter byte SFD (Start-of-frame

deliminator), notifies the baseband software in the receiver of the length of the
subsequent data.
• PSDU (PHY service data unit) is the message that has been passed down through the
higher protocol layers.
•can have a maximum of 127 bytes although monitoring and control applications will
typically be much shorter.
Each of the new coded bits is called a chip. The complete group of chips
representing a data bit is called a symbol
Zigbee Frame structure
• Included in the PSDU are information on the format of the message frame, a sequence
number, address information, the data payload itself, and at the end, two bytes that serve
as a frame check sequence.
• Reliability is assured since the receiver performs an independent calculation of this frame
check sequence and compares it with the value received.
•If any bits have been changed by interference or noise, the numbers will not match.
•Only when a match occurs, the receiving side returns an acknowledgement to the
originator of the message.
•Lacking an acknowledgement, the transmission will be repeated until it is successfully
received.
•In order to avoid two or more stations trying to transmit at the same time, a carrier sense
multiple access with collision avoidance (CSMA-CA) routine is employed, similar to that
used in Wi-Fi, IEEE 802.11.
• The 802.15.4 receiver monitors the channel and if it is idle it may initiate a transmission. If
the channel is occupied, the terminal must wait a random back off period before it can
again attempt access.
•Acknowledgement messages are sent without using the collision avoidance mechanism.
Zigbee Applications
• Promoters of Zigbee aim to cover a very large market for those applications that require
relatively low data rates.
•open specification and a recognized certification of conformity are an advantage in many
situations.
Eg. home burglar alarm system would accept wireless sensors produced by different
manufacturers, which will facilitate future expansion or allow installers to add sensors of
types not available from the original system manufacturer.
•Use of devices approved according to a recognized standard gives the consumer some
security against obsolescence.
•Although Zigbee claims to be appropriate for most control applications, its declared
maximum range of some 50–75m will fall short of the requirements of many systems.
•Under the constraint of low power output for low power consumption, greater range
means reduced bandwidth and reduced data rate.
•In fact, a great many of the applications envisaged by Zigbee can get by very well with data
rates of hundreds or a few thousand bits per second, and by matching receiver bandwidth
to these rates for maximum sensitivity, ranges of hundreds of meters can be achieved.
Zigbee Applications and conflicts

• One partial answer to the range question is the deployment of the Zigbee
network in a cluster-tree configuration.
•Adjacent nodes serve as repeaters so that large areas can be covered, as long
as the greatest distance between any two directly communicating nodes does
not exceed IEEE 802.15.4 basic range capability.
•For Eg, in a multi-floor building, sensors on the top floor can send alarms to
the control box in the basement by passing messages through sensors located
on every floor and operating as relay stations.
•There is competition between Bluetooth and Zigbee for use in certain
applications, but the overall extent of deployment and the reliability of
wireless control systems are higher because of it.
•The proportion of wireless security and automation systems has increased
because adherence to the 802.15.4 standard provides high reliability, security,
and reduced development costs compared to many proprietary solutions.
Ultra-wideband Technology
•Ultra-wideband :
•UWB is a radio technology use a very low energy level for short-range,
high-bandwidth communications over a large portion of the radio
spectrum.
•UWB has traditional applications in non-cooperative radar imaging. Most
recent applications target sensor data collection, precise locating, and
tracking.
•Ultra-wideband Technology:
•Creates a radio spectrum that is spread over a very wide bandwidth—
much wider than the bandwidth used in the spread-spectrum systems.
• UWB transmissions are virtually undetectable by ordinary radio
receivers and therefore can exist concurrently with existing wireless
communications without demanding additional spectrum or exclusive
frequency bands.
•Advantages of UWB technology:
•Very low spectral density—very low probability of interference with
other radio signals over its wide bandwidth
• High immunity to interference from other radio systems
•Low probability of interception/detection by other than the desired
communication link terminals
•LP consumption
•Ultra fast 1000X fatser, seamless user interface
https://youtu.be/pE-WbKLMElI?si=7xsJpiM1_hoWKySN
Ultra-wideband Technology
Advantages of UWB technology—Cont…
• High multipath immunity
• Many high data rate UWB channels can operate
concurrently
• Fine range-resolution capability
• Relatively simple, low-cost construction, based on nearly
all-digital architectures.
•Transmission and reception methods are unique
•UWB “carrier” is a Gaussian monopulse

Applications
• Air tags  get accurate location
•Smart car access
•Wearable health sensors
•Wireless printers to contactless payments
Ultra-wideband Technology- Bit Sequence detection
•A “1” monopulse is represented by a negative line followed by a positive line, and a
“0” monopulse by the inverse—a positive line and a negative line.
•The synchronized sequence generated in the receiver is drawn on the second line and
below it the result of the correlation operation
•∫f(t)g(t)dt
•where f(t) is the received signal and g(t) is the locally generated sequence.
•By sampling this output at the end of each bit period and then resetting the correlator,
the transmitted sequence is reconstructed in the receiver.
•This is shown as the “Logic Output” which is delayed by one symbol period.
Ultra-wideband Technology- Bit Sequence detection

•Individual bit can be represented by more than one sequential monopulse.

•Doing so increases the processing gain by the number of monopulses per bit.
Ultra-wideband block diagram
Ultra-wideband block diagram
•The pulse generator block creates short impulse or step functions with rise times on
the order of tens or at the most hundreds of picoseconds which are conditioned in the
shaping network to produce the required output spectrum.
•High speed integrated circuits or special circuit elements such as tunnel diodes or
step recovery diodes, can be employed in the pulse generator.
•The receiver produces a replica of the known transmitted pulse sequence which is
synchronized with the incoming pulse stream in the acquisition and tracking block.
•The baseband mixer (multiplier), integrator and sample and hold blocks perform the
correlation function and data are output as demonstrated in Fig. 12.24.

Quiz 3: https://quizizz.com/admin/quiz/6662a5a3590eea703e28c2b8
Comparison between various short range wireless technologies