This document provides an overview of wireless communications. It begins by defining wireless communication as transmitting and receiving voice and data using electromagnetic waves without physical connections. It then discusses the advantages of wireless communication such as mobility and lower installation costs compared to wired systems. The document outlines several challenges in wireless communications including efficient hardware, spectrum usage, and maintaining quality of service over unreliable links. It also describes different multiple access techniques used in wireless systems such as FDMA, TDMA, and CDMA to allow sharing of limited radio spectrum among users. Common existing wireless systems like cellular networks, Bluetooth, and WiFi are also summarized.

1. UNIT-1
Mrs. Chetna Sinha
Assistant Professor
GEC Raipur

2. Outline
 What is Wireless Communications?
 Why Wireless Communications?
 History of Wireless Communications
 The advantages
 The challenges
 The types
 Existing Wireless Systems
 Emerging Wireless Systems

3. WHAT IS WIRELESS COMMUNICATION?
 Transmitting/receiving voice and data using electromagnetic waves in open space.
 The information from sender to receiver is carried over a well defined channel.
 Each channel has a fixed frequency bandwidth & capacity(bit rate).
 Different channels can be used to transmit information in parallel and independently.

4. WHY WIRELESS COMMUNICATION?
 Freedom from wires.
 No bunch of wires running from here and there.
 No cost of installing wires or rewiring
 “Auto Magical” instantaneous communication without physical connection setup e.g.-
Bluetooth, Wi-Fi.
 Global coverage
 Communication can reach where wiring is infeasible or costly
 E.g.- rural areas, buildings, battlefield,outerspace.
 Stay connected, flexiblity to connect multiple devices.

5. TYPICAL FREQUENCIES
 FM RADIO 88 MHZ
 TV BROADCAST 200 MHZ
 GSM PHONES 900 MHZ
 GPS 1.2 GHZ
 PCS PHONES 1.8 GHZ
 BLUETOOTH 2.4 GHZ
 Wi-Fi 2.4 GHZ
 2.4 GHz is a license free band, given to scientific community for experiments

6. Challenges
 Efficient Hardware
 – Low power Transmitters, Receivers
 – Low Power Signal Processing Tools
 Efficient use of finite radio spectrum
 – Cellular frequency reuse, medium access control protocols,...
 Integrated services
 – voice, data, multimedia over a single network
 – service differentiation, priorities, resource sharing,...
 Network support for user mobility (mobile scenarios)
 – location identification, handover,...
 Maintaining quality of service over unreliable links
 Connectivity and coverage (internetworking)
 Cost efficiency

7. Challenges
 Fading
 Multipath
 Higher probability of data corruption
 – Hence, need for stronger channel codes
 Need for stronger Security mechanisms
 – privacy, authentication,…

8. Types of wireless communication
Mobile
Cellular Phones(GSM/ cdma)
Portable
IEEE 802.11b( WiFi)
IEEE 802.15.3 (UWB)
E.g. laptop with wireless n/w is portable
Fixed Wireless
IEEE 802.16 (Wireless MAN)
Take fiber to curb and put up a tower, and solve last mile wiring problem using wireless. This
concept is used in wireless in the local loop scenario, where over short distances we can have
large bandwidth for tx.

9. Wireless vs Mobile
 NOTE : Wireless does not necessarily mean mobile
 Wireless Systems may be
 – Fixed (e.g., Metropolitan Area Network)
 – Portable (e.g., wireless interaction between TV and VCR)
 – Mobile (e.g., mobile phone)

10. TYPES OF WIRELESS COMMUNICATION
 RADIO TRANSMISSION:-
 easily generated, Omnidirectional , travel long distance , easily penetrates buildings.
 PROBLEMS:- frequency dependent , relatively low bandwidth for data communication , tightly licensed by government.
 MICROWAVE TRANSMISSION:-
 widely used for long distance communication , relatively inexpensive.
 tall towers periodically placed with parabolic antennas around the highways are usually the microwave, point to point- line
of sight links.
 PROBLEMS:- don’t pass through buildings , weather and frequency dependent.
 INFRARED AND MILIMETER WAVES:-
 Widely used for short range communication , unable to pass through solid objects , used for indoor wireless LANs , not for
outdoors.
 LIGHT WAVE TRANSMISSION:-
 unguided optical signal such as laser , unidirectional , easy to install , no license required.
 PROBLEMS:- unable to penetrate rain or thick fog , laser beam can be easily diverted by air

11. Wireless Systems : Range Comparison
Satellite
Links
SW
Radio
MW
Radio
FM
Radio
Mobile
Telephony
WLANs
Blueooth
1,000 Km
100 Km
10 Km
1 Km
100 m
10 m
1 m

12.  Propagation characteristics are different in each frequency band, all frequencies can’t be used, since there are h/w
design issues and frequency related issues
 Different frequency gets attenuated differently by air, so air is a frequency selective channel in sense of attenuation.
 To communicate b/w large distances, we can increase power but
 It costs more money
 Equipment is power hungry
 Radiation hazard
 Mobile phones used comply certain max. radiated power constraints-peak power & average power.
 So we can’t increase power of radiation to cover more distance coz it affects ppl near by.
 For same power , if we increase frequency like 2.4 GHz, then attenuation happens, coverage area reduces.

13. Advantages and disadvantages of wireless
communication
 Advantages:
 Working professionals can work and access Internet anywhere and anytime without carrying cables or wires
wherever they go. This also helps to complete the work anywhere on time and improves the productivity.
 A wireless communication network is a solution in areas where cables are impossible to install (e.g.
hazardous areas, long distances etc.)
 Wireless networks are cheaper to install and maintain
 Disadvantages:
 Has security vulnerabilities
 High costs for setting the infrastructure
 Unlike wired communication, wireless communication is influenced by physical obstructions, climatic
conditions, interference from other wireless devices

14. CURRENT WIRELESS SYSTEMS
 CELLULAR SYSTEM
 WIRELESS LANs
 SATELLITE SYSTEM
 PAGING SYSTEM
 PANs(BLUETOOTH

15. What is cellular system?
 Definition
 Wireless communication technology in
which several small exchanges (called
cells) equipped with low-power radio
antennas (strategically located over a
wide geographical area) are
interconnected through a central
exchange. As a receiver (cell phone)
moves from one place to the next, its
identity, location, and radio frequency
is handed-over by one cell to another
without interrupting a call.
 Practical

16. Cellular systems
Reuse channels to maximize capacity
• Geographic region divided into cells
• Frequencies/timeslots/codes reused at spatially separated locations
• Base stations/Mobile Telephone Switching Offices (MTSOs)
coordinate handoff and control functions

17. Cellular concept
 Each cell has a center black point which represents the base station, in real life, the cells are irregular.
 What determines the cell boundaries?
 The first thing is the link budget. Link budget is defined as the total power that is emitted and the total
power that is received. So if we have buildings or foliage or tall towers in the middle which block the
radiation, the received power will be less. Consequently, the cell boundary might get affected.
 The second thing that determines the cell boundary is the number of people in the cell or the capacity.
A cell can only support so many users. For example, if you have an x amount of bandwidth in a cell
and if you can support 100 users, the next user that comes in into the cell will be denied service. The
other way is the cell shrinks its boundary and only accommodates enough number of users that it can
support. In some cases like the CDMA systems, the cell boundaries are not fixed but adaptive.
 The third thing that determines the cell boundaries is the interference. Where does interference come
from? . If you see in the diagrams, there are blue cells which are spaced apart. There are light green
cells and the dark green cells. Cells of one color are using one certain frequency band. The frequency
is being reused assuming that the reuse distance is such that the received power is below a certain
threshold but still it causes co- channel interference.

18. Cellular concept
 An interference which is coming from a cell which is using the same frequency is called the co
channel interference.
 Sometimes we would have a lot of co-channel interference because our user is at the boundary
of the cell and sometimes the co-channel interference can be less. So co- channel interference
itself will also determine what the size of the cell is at the designing stage.
 In real life, cells must be over lapping, when we go from one cell to another, a process called
hand off‟ takes place where one base station hands off the call to the next base station. If there
is no overlap, it is very difficult to make before break the connection. In CDMA systems this
overlap is phenomenon. In GSM systems it is much less.
 In any case at a given time for example, the mobile phone gets good signal from more than one
base station. It maintains a list of good base stations where effective single power is received
and it chooses which base station to talk to. So one can be sitting in a room and the mobile
phone displays to which base station it talks to and after half an hour, the base station may
change even though person have not moved from his chair. This simplifies to the fact that at
the same time, we have good connectivity and good signal strength from more than one base
station and that is simply because there is enough overlap

19. Pagers
 Broad coverage for short messages.
 Message is done in a broadcast mode. So all base stations radiate and pager will
respond to the cell you‟re sitting in.
 It has simple terminals, low complexity and low power consumtion
 Optimized for one way transmission but answer back is hard.
 It has been over taken by cellular communications.

20. Personal area networks (Bluetooth)
 Cable replacement RF technology (low cost)
 Short range( 10m extendable to 100m)
 2.4GHz band
 1 Data(700 kbps) and 3 voice channels
 TDD duplex scheme
 Widely supported by telecommunications, consumer based companies
 At most, seven devices could be connected

22. Emerging wireless system
 Ad hoc wireless networks.
 Wireless sensor networks
 Distributed control networks.
 Ultra Wideband communication (UWB)

23. Ultra Wide Band (UWB)
 UWB or the ultra-wideband communication systems is an emerging technology and can
transmit data at around 100 Mbps (up to a 1000 Mbps)
 UWB essentially transmits low power radio signals with very narrow pulses of the order
of ns or even sub ns.
 The ultra-wideband or the large bandwidth allocated for UWB communications is sub
divided into sub bands and then within each band, a pulse is sent.
 Low power requirements, hence UWB is very difficult to detect. It is almost in the noise
floor and hence inherently secure.
 Generating nanosecond or sub nanosecond broad pulses is a challenge in itself. The
receiver design also poses many challenges.
 UWB earlier was related to defense applications. Today it is being used for commercial
applications.


26. UWB
 The frequency band allocated for the IEEE 802.15.3 starts from 3.1 GHz up to 10.6 GHz. that‟s a total 7.5 GHz of
bandwidth. huge bandwidth
 bandwidth allocated for IEEE 802.11 A is a meager 100 MHz of bandwidth.
 UWB has very low power of transmission. In fact, a dotted line here represents the part 15 limit set by the FCC. This
essentially translates to the noise floor.
 A lot of appliances which work at around 2.4 GHz typically radiate unnecessary power below this dotted line. So
anything below the dotted line is acceptable.
 UWB interestingly has been designed to emit below that level.
 Exceptional multi-path immunity.
 Assuming in a room environment, there is a transmitter and a receiver. There is a direct-path. There is path one through
a reflector. It could be a wall or a table and another reflector in the room. For these three paths, what we receive here are
the direct path which comes in the first, then the path 2 which is a shorter path and then a longer path because of the
distant reflector.
 Each of these pulses are so narrow( nanosecond wide or sub nanosecond) that each pulses can be resolved. Hence they
really do not interfere with each other. The effect of multi-path is gone. It takes care of most of the difficult problems
related to multi-path fading.
 low power consumption
 7.5 GHz of bandwidth. . It is secure because sending noise like emissions which are very hard to detect.
 It has low interference because I transmitting at a level which is below the general interference level of other devices.

28. Multiple Access Scheme
 Multiple access schemes are used to allow many mobile users to share the finite amount of
radio spectrum.
 The radio spectrum is at premium. One of the most important cost comes from the licensing of
the radio spectrum. Even if we have the money to get a big chunk of bandwidth, we have to use
it carefully.
 The sharing of the spectrum is required to achieve high capacity by simultaneously allocating
the bandwidth.
 Constraint:
The constraint is that there should not be severe performance degradation. For every application,
thre is “the quality of service‟. It is different for different applications.
For example, for voice communication we have constraints on the maximum delay allowable or the
packet loss rate or the drop of call rate for data. Again the bit error rate is of importance. So these
constraints do exist and even if we pack in more and more number of users, we must ensure that
there is no severe performance degradation

29. FDMA-Frequency Division Multiple Access
Total bandwidth allocated which is finite is shown on the Y axis
On the x axis is the time. User 1 may be given one sub band followed by the user 2 and so
forth up to user n. these bands are fixed. All of the users are free to use their frequency bands
throughout the time domain.
So if suppose user 1 switches on the mobile phone and have to be allocate one of the sub
bands, we can give them sub band number 1. Suppose user 2 switches on the phone and has to
be allocated a frequency for talking, we can give them another band but not necessarily the
adjacent band.
At this moment in time, we are talking about allocating the sub bands. It‟s clear that the sub
bands have been decided earlier but the allocation has to be done dynamically as and when the
number of users switch on their phones and intend to talk.
For less adjacent channel interference, users should be spaced far apart along the y axis,
PROBLEM: Such closely spaced frequency bands have the problem of energy from one band
spilling over to the other band because of non- ideal filters.
So guard band is necessary. The width of the guard band depends on how sharp the filter cut
offs are. If we have more expensive filters with sharp cut offs, we have narrower guard bands.
Note: Guard bands are not used to communicate data.

32. FDMA, TDMA, and CDMA
 Frequency Division Multiple Access (FDMA) permits individual
allocation of single or multiple frequency bands, or channels to the users.
 Time Division Multiple Access (TDMA) works by dividing a radio
frequency into time slots and then allocating slots to multiple calls. In this
way, a single frequency can support multiple, simultaneous data channels
 Code Division Multiple Access (CDMA) uses spread spectrum
technology with the use of different codes to separate between different
stations or users rather than different frequencies of time slots as in the case
of FDMA and TDMA technologies.
32

33. TDMA
 Time axis is sub divided amongst n users. in effect, we have n times slots where user 1 uses
slot 1, user 2 slot 2 till the slot n.
 each user is speaking or communicating in its own time slot. After n time slots are over, time
slot 1 will repeat followed by 2, 3 and so and so forth.
 When we communicate voice, we sample it first at slightly greater than the Nyquist
sampling frequency. We use these time slots to send the digitized voice. At the receiver end,
we put back these sample points and reconstruct perfectly. So the voice doesnot appear
broken at the receiver end.
 For TDMA also we need time guardband.
 Another important issue in TDMA is synchronization.

34. TDMA

35. Classification
 Simplex- communication is possible in only one direction. Paging systems, in which
messages are received but not acknowledged, are simplex systems.
 Half-duplex- allow two-way communication, but use the same radio channel for both
transmission and reception i.e user can only transmit or receive information. Constraints like
"push-to-talk" and "release-to-listen" are its fundamental features
 Full duplex- allow simultaneous radio transmission and reception between a subscriber and a
base station, by providing two simultaneous but separate channels (frequency division
duplex, FDD) or adjacent time slots on a single radio channel (time division duplex, or TDD)
for communication to and from the user.
NOTE: These full duplex and half duplex systems refer to only the communication between the
mobile and the base station. It is for single user. It should not be confused with the multiple
access schemes where it is decided how the channel is divided amongst several users. So a
mobile system may use a combination of a multiple access scheme and a duplex systems

36. FDD
 Frequency division duplexing (FDD) provides simultaneous radio transmission channels for the subscriber
and the BS, so that they both may constantly transmit while simultaneously receiving signals from one
another.
 At the BS, separate transmit and receive' antennas are used to accommodate the two separate channels. At
the subscriber unit, however, a single antenna is used for both transmission to and reception from the BS,
and a device called a duplexer is used inside the subscriber unit to enable the same antenna to be used for
simultaneous transmission and reception.
 To facilitate FDD, it is necessary to separate the transmit and receive frequencies by about 5% of the
nominal RF frequency, so that the duplexer can provide sufficient isolation while being inexpensively
manufactured.

37. TDD
 Time division duplexing (TDD) : a single radio channel is used in time sharing , so that a portion of the time
is used to transmit from the BS to the mobile, and the remaining time is used to transmit from the mobile to
the BS.
 If the data transmission rate in the channel is much greater than the end-user's data rate, it is possible to store
information bursts and provide the appearance of full duplex operation to a user, even though there are not
two simultaneous radio transmissions at any instant of time.
 TDD is only possible with digital transmission formats and digital modulation, and is very sensitive to
timing.
 So, TDD is used in indoor or small area wireless applications where the physical coverage distances (and
thus the radio propagation time delay) are much smaller than the many kms used in conventional cellular
telephone systems.

38. Cellular Network Generations
 It is useful to think of cellular Network/telephony in terms of generations:
 1G: Analog cellular telephony
 2G: Digital cellular telephony
 3G: High-speed digital cellular telephony (including video telephony)
 4G: IP-based “anytime, anywhere” voice, data, and multimedia telephony
at faster data rates than 3G

39. Cellular Networks-Evolution 1
1G- First Generation
 It was launched in the mid 1980‟s.
 They were purely analog.
 They used analog modulation mostly frequency modulation (FM). They were intended primarily for voice
traffic because at that time phones meant voice.
 They used FDMA multiple access schemes. So they would just chop up the entire frequency band into
sub bands and use analog transmission in each sub band.
 They were confined to national boundaries only. Hence the number of users and customers were limited
 An example is the AMPS or the advanced mobile phones services popular in the US in the mid nineteen
eighty1980‟s.
 As cellular networks evolved, the second generation came into being 150 MHz in Finland and 450 MHz
39

40. Cellular Networks-Evolution 2
 Examples of second generation (2G)
 GSM (Global System for Mobile communication) in July 1991
 900 MHz in 1992
 1800 MHz in 1994
 TDMA/FDMA
 Personal Digital Communication(PDC)
 Popular in japan
 IS-95
 CDMA
 US/ South korea

41. 2G
 Developed for voice communication
 Fully digital
 It uses GMSK- the Gaussian minimum shift keying it’s a digital modulation technique.
 For multiple access they used TDMA FDMA and CDMA.
 Voice is encrypted, SMS, and International roaming
 Limitations
 1. Developed for voice communication and hence unsuitable for data traffic, although data traffic could be
carried out.
 2. The average data rates were the order of only tens of kilobits per second.
 3. It is definitely not suitable for internet because the original GSM phone was a circuit switched system
and not a packet switched service. for internet we need packet switched network.
 4. Multiple standards( No true global coverage). there were too many standards one in the US European
standard, Japanese standard etc.
All these motivated toward the 2.5 G. it resulted as an effort to remove the impediments of the 2G systems. .

42. Difference between Circuit and packet
switching

44. 2.5 G
 The effort to remove impediments of 2G resulted in 2.5G
 Digital system
 voice and low data rate traffic
 Internet access through GPRS (General Packet Radio Service)
 From circuit switched domain to packet switched domain
 Enables data transfers through cellular networks
 It is used for mobile internet, MMS and other data communications
 In theory the speed limit of GPRS is 115 kbps, but in most networks it is around 35
kbps.
 GPRS is based on Global System for Mobile Communication (GSM)
 So it is the first step of going towards 3G and then the step two called „enhanced data
rates for global evolution‟ or the EDGE which uses better digital modulation
techniques to get that EDGE

45. 2.75 G
 EDGE (Enhanced Data rates for GSM Evolution)
 Enhanced GPRS
 EDGE was deployed on GSM in 2003
 Evolution of GSM, & GPRS which used 8PSK modulation
 Transmits data at up to 384 kilobits per second (Kbps).
 Achieves data transfer rates up to 384 kbps

47. 3G
 Digital modulation.
 Simultaneous voice and high speed data.
 Multi-mega bit internet access. So there’s a thrust internet.
 Voice activated calls
 Multi-media transmission
 Up to 2Mbps
 So one can download a movie clip and watch on phone while walking around. So 3G puts constraints on
how fast you go and how fast you can download the traffic. Clearly if you move much faster, the channel
becomes more difficult to handle. The associated problem is fast fading Doppler effects which have to be
taken care of.
 3G is truly a world standard. There are two standards which have been debated. One is the W-CDMA
which is the wide band CDMA and the other is a CDMA 2000 standard.

48. 4G (LTE)
 LTE stands for Long Term Evolution
 Next Generation mobile broadband technology
 Promises data transfer rates of 100 Mbps(individual data rates depends on many factors)
 Based on UMTS 3G technology
 Optimized for All-IP traffic
 4G systems look into the applications point of view. So either it is a mobile phone for voice or high rate data for local area
networks, 4G systems would like to combine all of this. 4G will integrate various networks, functions and applications.
 With 4 G one can walk into the room, configure phone to send the printout to a printer connected to some other network,
may be 802.11 B or an 802.15.3 UWB network and then I should be able to get my printout. The 4 G will truly create the
global information multimedia village.
 The “anywhere” “any time” communication for all the applications is possible. It supports a variety of data rates at variety
of speeds. There will be various sizes of cells.
 The cellular concept had the city divided into cells. Each cell with a base station.in 4G there are not just macro cells but
micro cells, Pico cells, home cells and even body area networks. Each cell for a different application. Each application
with a different quality of service and each application with a different data rate. 4G combines all of these things.

49. LTE
 Uses Orthogonal Frequency Division Multiplexing (OFDM) for downlink
 Uses Single Carrier Frequency Division Multiple Access (SC-FDMA) for uplink
 Uses Multi-input Multi-output(MIMO) for enhanced throughput
 Reduced power consumption
 Higher RF power amplifier efficiency (less battery power used by handsets)
 It focuses on spectral efficiency and interference mitigation

50. Wireless Broadband

51. WiMAX
 The IEEE 802.16, the Air Interface for Fixed Broadband Wireless Access Systems, also
known as the IEEE WirelessMAN air interface, is an emerging suite of standards for fixed,
portable and mobile BWA in MAN.
 These standards are issued by IEEE 802.16 work group that originally covered the wireless
local loop (WLL) technologies in the 10.66 GHz radio spectrum, which were later extended
through amendment projects to include both licensed and unlicensed spectra from 2 to 11
GHz.
 The WiMAX umbrella currently includes 802.16-2004 and 802.16e. 802.16-2004 utilizes
OFDM to serve multiple users in a time division fashion in a sort of a round-robin
technique, but done extremely quickly so that users have the perception that they are always
transmitting/receiving. 802.16e utilizes OFDMA and can serve multiple users
simultaneously by allocating sets of tones to each user.

52.  1. 802.16 :
802.16 is an IEEE standard which defines Wireless Inter-operability for Microwave
Access (WiMAX) technology products. It covers all WiMAX series of products. It is
optimized for 50 km. It provides the service throughout the coverage area to enable
continuous connectivity. This 802.16 standard provides more scalability in usability
point of view.
 2. 802.11 :
802.11 is an IEEE standard which defines Wireless Local Area Network
(WLAN) or WiFi. It covers all WLAN series of products. It is optimized for nearly 100
meters. It does not provide the service throughout the coverage area to enable
continuous connectivity. This 802.11 standard provides less scalability in usability point
of view.


53. WiMAX
 WiMAX broadband technology uses some key technologies to enable it to provide the high speed data rates:
 OFDM (Orthogonal Frequency Division Multiplex): OFDM has been incorporated into WiMAX technology
to enable it to provide high speed data without the selective fading and other issues of other forms of signal
format
 Orthogonal Frequency Division Multiplex, OFDM is a form of signal format that uses a large number of
close spaced carriers that are each modulated with low rate data stream. The close spaced signals would
normally be expected to interfere with each other, but by making the signals orthogonal to each other there is
no mutual interference. The data to be transmitted is shared across all the carriers and this provides resilience
against selective fading from multi-path effects.
 MIMO (Multiple Input Multiple Output): WiMAX technology makes use of multipath propagation using
MIMO. By utilising the multiple signal paths that exist, the use of MIMO either enables operation with lower
signal strength levels, or it allows for higher data rates.
Note on MIMO:
 MIMO is a form of antenna technology that uses multiple antennas to enable signals travelling via different
paths as a result of reflections, etc., to be separated and their capability used to improve the data throughput
and / or the signal to noise ratio, thereby improving system performance.