History, Basic concepts of wireless communication, challenges in wireless communication, cellular communication, performance criteria, wireless communication standars, how call is made?

1. R. S. Anande

2. • Transmitting/Receiving VOICE & DATA using
electromagnetic waves in open space.
• The information from sender to receiver is carried over
a well-defined frequency band.

3. • Freedom from Wires (Cost Minimized) –
No cost of installing wires,
Instantaneous communications without physical connection setup e.g.
Bluetooth, Wi-Fi.
• Global Coverage –
Communications can reach where wiring is infeasible or costly e.g.
rural areas, old buildings, etc.

4. • Stay Connected (Mobility)–
Roaming allows flexibility to stay connected anywhere and any time.

5. • Multipath
• Fading
• Efficient Hardware
- Low Power Consumption
- Low Power Signal processing Tools

6. • Efficient use of finite radio spectrum –
- Frequency reuse
• Network Support for user mobility -
- Handoff
• Maintaining quality of service –
• Connectivity & Coverage -

7. • First Generation –
- Launched in the mid-1980s.
- Analog Systems
- Analog Modulation(FM)
- Voice Traffic Only
` - FDMA multiple access

8. • Second Generation (2G) –
- Developed for voice communications
- Digital systems, Digital Modulation
- TDMA & CDMA multiple Access
- Data rate ~ 9.6 Kbps
• Most popular 2G standards
• Global System for Mobile (GSM)
• IS-136 or North American Digital Cellular (NADC)
• Pacific Digital Cellular (PDC) – Japan
• IS-95 or cdmaOne

9. • 2.5 G –
- 2G Limitations
Uses circuit-switched data modem
Data rate – 10 kbps – too slow for email and internet browsing
Limited support to internet browsing
- Digital Systems
- GPRS(General Packet Radio Service)
- EDGE(Enhanced data rates for global Evolution)

10. • 3 G –
- Digital Modulation
- Simultaneous voice + High speed data
- Multimedia Transmission
- Uses ITU approved IMT-2000 standard in 2000 MHz
frequency band
• - G standards for GSM and IS-136
W-CDMA (Wideband CDMA)
TD-SCDMA (Time Division-SynchronousCDMA)

11. • Definition: A cellular mobile communication system uses a large
number of low power wireless transmitters to create cells :- the
basic geographical service area of a wireless communication
system.
Cell-1
Cell-7
Cell-6
Cell-5
Cell-4
Cell-3
Cell-2

12. • Partition the region into smaller regions called cells.
• Each cell gets at least one base station or tower.
• Users within a cell talks to the tower.

13. • GSM allocated the bands 890-915 MHz for the uplink (mobile
station to base station) and 935-960 MHz for the downlink
(base station to mobile station) for mobile networks.
• Thus provides total 25 MHz bandwidth.
f
t
124
1
124
1
20 MHz
200 kHz
890.2 MHz
935.2 MHz
915 MHz
960 MHz
Uplink
Downlink

15. • Cellular system provide a wireless connection to the PSTN for
any user location within the radio range of the system.
• Cellular system accommodate a large number of users over a
large geographic area, within a limited frequency spectrum.
• Basic cellular system consists of
1. Mobile Stations
2. Base Stations
3. Mobile Switching Center(MSC) / Mobile telephone
switching office

16. • Mobile Station –
- It contains a transceiver, an antenna & Control circuitry.
- Each mobile communicates via radio with one of the
base stations may be handed-off to any number of base
stations throughout the duration of call.
• Base Station –
- Consists of several transmitters and receivers which
simultaneously handle full duplex communications and
generally have towers which support several transmitting
& receiving antennas.
- It serves as bridge between all mobile users in the cell &
connects simultaneous mobile calls to MSC.

17. • MSC/ MTSO –
- It coordinates the activities of all of the base stations &
connects the entire cellular system to the PSTN.
- A typical MSC handles 1,00,000 cellular subscribers &
5000 simultaneous conversations at a time &
accommodates all billing & system maintenance functions,
as well.

18. • Communication between base station and cell phones
• Common air interface (CAI) standard specifies four channels
• Forward voice channels (FVC)- Channel used for voice transmission
from the base station to mobiles.
• Reverse voice channels (RVC)- Channel used for voice transmission from
the mobiles to base station.
• Forward control channels (FCC) – Responsible for initiating mobile calls
• Reverse control channels (RCC) - Responsiblefor initiating mobile calls
• Control channels often called as setup channels because they
are only involved in setting up a call & moving it to an unused
voice channels.
• Control channels transmit & receive data messages that carry
call initiation & service requests.
• Control channels are monitored by mobiles when they don’t
have a call in progress.

19. • When cell phone is ON (idle)
• Scans group of FCC to determine the one with the strongest signal,
and then monitors that channel.
• Call from landline to cell phone
• When telephone call is placed to a mobile user, MSC dispatches
request to all BS
• BS broadcast MIN (Mobile Identification Number) as a message
over all FCC
• Mobile receives this message, and responds by identifying itself
over RCC

20. • The BS receives the acknowledgement and informs the MSC of the
handshake
• MSC instruct BS to move the call to an unused voice channel pair
(FVC & RVC)
• BS signals mobile to change frequencies to an unused voice channel
pair
• Another data message (alert) is transmitted over FVC to instruct the
mobile to ring instructing the mobile user to answer the call
• Call from cell phone to Landline
• When a mobile originates a call, a request is sent on the RCC to
the BS
• In this request the mobile transmits its MIN, ESN (Electronic Serial
Number), and MIN of the called party.

21. • BS receives this data and sends it to the MSC
• MSC validates the request and makes connection to the called
party through the PSTN
• MSC instructs BS and mobile user to move to an unused voice
channel pair

24. • Voice Quality -
- Voice quality is very hard to judge without subjective
test from users opinions.
- In this technical area engineers can not decide how to
build a system without knowing the voice quality that will
satisfy the users.
- Voice quality is decided on the basis of customers rating.

25. • Service quality –
1. Coverage –
- System should serve an area as large as possible,
however because of irregular terrain configurations, it is
not practical to cover 100 % of the area for two reasons:
a) Transmitted power should be very high to illuminate
weak spots, this significantly add cost factor.
b) The higher transmitted power, the harder it becomes to
control interference.
Therefore systems usually try to cover 90% of an area in
flat terrain & 75% of an area in hilly terrain.

26. 2. Required Grade of Service -
- Grade of service-> Measure of the ability of the user to
access trunked system during the busiest hour.
- GOS of 2% blocking means 2 out of 100 calls will be
blocked due to channel occupancy during the busiest hour
- To decrease the blocking probability requires a good
system plan and a sufficient number of radio channels.
3. Number of Dropped Calls –
- During Q calls in an hour, if a call is dropped and Q-1
calls are completed, then the call drop rate is 1/Q.
- This drop rate must be kept low.
- A high drop rate is caused by either coverage problems
or handoff problems related to inadequate channel
availability.

27. • Special Features –
- A system would like to provide as many features as
possible, such as call forwarding, call waiting, navigation
services, etc.

28. • IEEE 802.11- (Wireless LAN)
• IEEE 802.15 – (PAN – Bluetooth)
• IEEE 802.16 – (Wireless MAN)
• IEEE 802.20 – (WAN)

29. • A wireless LAN or WLAN is a wireless Local Area Network,
which is the linking of two or more computers without using
wires.
• This gives users the mobility to move around within a broad
coverage area and still be connected to the network.
• IEEE 802.11, the Wi-Fi standard, denotes a set of Wireless
LAN/WLAN standards developed by working group 11 of the
IEEE LAN/MAN Standards Committee.
• The most popular (and prolific) techniques are those defined
by the b, a, and g amendments to the original standard.

31. • Wireless Personal Area Network (WPAN) is made possible with
network technologies such as Infrared (IrDA) and Bluetooth.
• Bluetooth - Bluetooth is an industrial specification for wireless
personal area networks (PANs), also known as IEEE 802.15.1.
• Bluetooth provides a way to connect and exchange information
between devices such as personal digital assistants (PDAs),
mobile phones, laptops, PCs, printers, digital cameras and video
game consoles via a secure, globally unlicensed short-range
radio frequency.
• Bluetooth is a radio standard and communications protocol
primarily designed for low power consumption, with a short
range (1m, 10m, 100m) based around low-cost transceiver
microchips in each device.

32. • Infrared (IrDA): The Infrared Data Association (IrDA) defines
physical specifications communications protocol standards for
the short range exchange of data over infrared light, for
typical use in Personal Area Networks.

33. • Wireless Metropolitan Area Network (MAN) is the name
trademarked by the IEEE 802.16 Working Group on
Broadband Wireless Access Standards for its wireless
metropolitan area network standard (commercially known as
WiMAX), which defines broadband Internet access from fixed
or mobile devices via antennas.
• The average ranges for most WiMAX networks will likely boost
4-5 mile range (in NLOS capable frequencies) even through
tree cover and building walls.
• WiMAX (Worldwide Interoperability for Microwave Access) is
a wireless communications standard designed to provide 30 to
40 megabit-per-second data rates, with the 2011 update
providing up to 1 Gbps for fixed stations.

34. • A Wide Area Network or WAN is a computer network covering
a broad geographical area. Contrast with (PAN’s), (LAN’s) or
(MAN’s) that are usually limited to a room, building or campus.
• WAN’s are used to connect local area networks (LAN’s)
together, so that users and computers in one location can
communicate with users and computers in other locations.

35. • TDMA –
• FDMA –
• CDMA –
• SDMA –

36. • FDMA assigns individual channels to individual users.
• These channels are assigned on demand to users who request
service.
• Available frequency band is divided into N non-overlapping
channels.
• During the period of the call, no other user can share the same
channel.

38. • The FDMA channel carries only one phone circuit at a time.
• If channel is not in use, it sits idle.
• After assignment of a voice channel, base station & mobile
transmit simultaneously & continuously.
• Channel bandwidth is relatively narrow (30kHz)
• Complexity is lower compared to TDMA systems.
• No need for network timing
• No restriction regarding the type of baseband or type of
modulation

39. • The presence of guard bands.
• Requires right RF filtering to minimize adjacent channel
interference.
• Maximum bit rate per channel is fixed .

40. • In TDMA radio spectrum is divided into time slots, and in each
slot only one user is allowed to either transmit or receive.
• Each user occupies a cyclically repeating time slot, so particular
timeslot reoccurs every frame, where N time slots comprise a
frame.
• Each frame is made up of a preamble, an information message
and tail bits.

42. • Flexible bit rate
• No frequency guard band required
• No need for precise narrowband filters
• Extended battery life.
• The most cost-effective technology for upgrading a current
analog system to digital

43. • Requires timing synchronization
• Demand high peak power on uplink
• High synchronization overhead is required.

44. • In traditional mobile cellular network systems, the base
station has no information on the position of the mobile units
within the cell and radiates the signal in all directions within the
cell in order to provide radio coverage.
• This results in wasting power on transmissions when there are no
mobile units to reach.
• SDMA controls the radiated energy for each user in space.
• SDMA serves different users by using spot beam antennas.

46. • The reverse link presents the most difficulty in cellular systems
for several reasons.
• First, Because of different radio propagation paths between
each user & the base station, the transmitted power from each
subscriber unit must be dynamically controlled to prevent any
single user from driving up the interference level for all other
users.
• Second, transmit power is limited by battery consumption at the
subscriber unit , therefore there are limits on the degree to
which power may be controlled on the reverse link.

47. • With SDMA, all users within the system would be able to
communicate at the same time using the same channel.

48. • In CDMA, the narrowband message signal is multiplied by a
very large bandwidth signal called the spreading signal.
• The spreading signal is a pseudo noise code sequence that has
a chip rate which is greater than data rate of the message.
• Each user has its own pseudorandom code word which is
approximately orthogonal to all other codewords.