1. expanded by Jozef Goetz, 2014 The McGraw-Hill Companies, Inc., 2007
Lesson 7 - 8
Wireless
LANs
Part I
September 15, 2018
expanded by Jozef Goetz, 2014
The McGraw-Hill Companies, Inc., 2007

2. Topics discussed in this section:
IEEE
IEEE has defined the specifications for a wireless LAN, called IEEE , which covers the physical and data link layers.
Topics discussed in this section:
Architecture MAC Sublayer
Physical Layer

3. LANs
Wireless LANs are found on college campuses, office buildings, and public areas.
At home, a wireless LAN can connect roaming devices to the Internet.
In this chapter, we concentrate on two promising wireless technologies for LANs:
IEEE wireless LANs, sometimes called wireless Ethernet, and
Bluetooth, a complex technology for small wireless LANs.

4. LANs IEEE 802.11, which covers the physical and data link layers.
The Industrial, Scientific and Medical (ISM) radio bands were originally reserved internationally for the use of RF electromagnetic fields for Industrial, Scientific and Medical purposes other than communications.

5. WIRELESS LANs
A set of wireless LAN standards has been developed by the IEEE committee.
Three transmission schemes are defined in the current standard:
[1] Infrared: at 1 Mbps & 2 Mbps.
[2] Direct-sequence spread spectrum: 2.4GHz ISM band
[3] Frequency-hopping spread spectrum: 2.4GHz ISM band
802.11b - 11 Mbps
802.11g - 54 Mbps

6. Basic Service Set BSS (Cell)
IEEE defines the Basic Service Set (BSS) or Cell as the building block of a wireless LAN.
The Basic Service Set (BSS) is made of stationary or mobile wireless stations and a possible central Base Station (BS), known as the Access Point (AP).
BSS without an AP is a stand-alone network and cannot send data to other BSSs.

7. a BSS without an AP is called an ad hoc network;
Note
a BSS without an AP is called an ad hoc network;
a BSS with an AP is called an infrastructure network.

8. Extended Service Set (ESS)
An Extended Service Set (ESS) is made up of two or more BSSs with APs.
In this case, the BSSs are connected through a distribution system, which is usually a wired LAN.
The distribution system connects the APs in the BSSs.
IEEE does not restrict the distribution system;
it can be any IEEE LAN such as an Ethernet.
Note that the extended service set uses two types of stations: mobile and stationary.
The mobile stations are normal stations inside a BSS.
The stationary stations are AP stations that are part of a wired LAN.
When BSSs are connected, we have what is called an infrastructure network.

9. Extended Service Set (ESS)
In this infrastructure network, the stations within reach of one another can communicate without the use of an AP.
However, communication between two stations in two different BSSs usually occurs via two APs.
The idea is similar to communication in a cellular network
if we consider each BSS to be a cell and each AP to be a base station.
Note that a mobile station can belong to more than one BSS at the same time.

10. WIRELESS LANs
ESS
Wired Backbone LAN
functions as a bridge
BSS
BSS

11. Wireless LAN
A multicell network (WiFi).
The connection between the system and the outside world is called a portal
All the base stations are wired together using copper or fiber
Unlike cellular tel. systems, each cell has only one channel, covering the entire available bandwidth ( 11 – 54 Mbps) and covering all the stations in its cell

12. Station Types
IEEE defines 3 types of stations based on their mobility in a wireless LAN: no-transition, BSS-transition, and ESS-transition.
No-Transition Mobility
A station with no-transition mobility is either stationary (not moving) or moving only inside a BSS.
BSS-Transition Mobility
A station with BSS-transition mobility can move from one BSS to another, but the movement is confined inside one ESS.
ESS-Transition Mobility
A station with ESS-transition mobility can move from one ESS to another.
However, IEEE does not guarantee that communication is continuous during the move.

13. The Protocol Stack
ISM: Abbreviation for Industrial, Scientific, and Medical applications (of radio frequency energy).
range is 7 times greater

14. MAC layers in IEEE 802.11 standard

15. Reminder: IEEE standard for wired LANs
Note: there is one LLC sublayer for all IEEE LANs
Reminder: IEEE standard for wired LANs

16. Modulation
In analog transmission, the sending device produces a high-frequency signal that acts as a base for the information signal.
This base signal is called the carrier signal or carrier frequency.
The receiving device is tuned to the frequency of the carrier signal that it expects from the sender.
This kind of modification is called modulation (shift keying).

17. Modulation
Modulation - is the process of encoding source data onto a carrier signal with frequency carrier fc
i.e. process of modulating the carrier signal by modifying one or more of parameters:
amplitude,
frequency, &
phase
of a sine wave.

18. Modulation of Digital Data
Basic Digital-to-Analog conversion or modulation or encoding
Amplitude Shift Keying (ASK)
Frequency Shift Keying (FSK)
Phase Shift Keying (PSK)
Quadrature Amplitude Modulation
(QAM)

19. The digital data must be modulated on an analog signal
Digital-to-analog modulation
The digital data must be modulated on an analog signal
Modulation of binary data or (digital-to-analog modulation)
is the process of changing one of the characteristics
of an analog signal
a sine wave is defined by 3 characteristics:
amplitude,
frequency, and
phase
based on the information in a digital signal (0s and 1 s).

20. Digital-to-analog conversion

21. Types of digital-to-analog modulation
Amplitude Shift Keying (ASK)
Frequency Shift Keying (FSK)
Phase Shift Keying (PSK)
Quadrature Amplitude Modulation (QAM)

22. Note:
Bit rate is the number of bits per second [bps]
Baud rate is the number of signal elements (or impulses or symbols or signal units) per second [baud]
Baud rate <= Bit rate.

23. Bit rate N is the # of bits (passengers by analogy) per second.
Note
Bit rate N is the # of bits (passengers by analogy) per second.
Baud rate S is the # of signal
elements (vehicles by analogy) per second.
In the analog and digital transmission of digital data,
S <= N

24. In data transmission:
a signal element as the smallest unit of a signal that is constant
The baud rate determines the bandwidth required to send the signal.

25. In analog transmission:
We can define the data rate (bit rate) and the S signal rate (baud rate)
baud rate: S = N / r [baud] = N / r [signal/sec] = N / r [paulse/sec]
where N is the data rate (bps) and
r is the # of data elements (bits) carried in one signal element.
The value of r in analog transmission is
r = log2 L
where L is the # of signal elements (pulses), not the level
e.g. for FSK is # of different frequencies
S = N / r => N = S r

26. Example
An analog signal carries 4 bits in each signal element (unit).
If 1000 signal elements (units or pulses) are sent per second, find the baud rate and the bit rate
Solution
Given: r = 4 [bit/pulse] , S = 1000 [pulse/sec]
Find N = ?
S = N / r => N = S r
S = Signal rate =Baud rate = 1000 pulse/sec
N = Data rate = Bit rate = S r = [pulse/sec] 4 [bit/pulse] =
4000 bps

27. Example
The bit rate of a signal is If each signal element carries 6 bits, what is the baud rate?
Solution
Baud rate S = N / r = 3000 [bit/sec] / 6 [bit/pulse] =
500 [pulse/sec] = 500 baud

28. DIGITAL DATA, ANALOG SIGNALS AMPLITUDE-SHIFT KEYING (ASK)
In ASK, the two binary values are represented by two different amplitudes A1 and A0 of the carrier frequency f sub c; t is a time .

29. DIGITAL DATA, ANALOG SIGNALS FREQUENCY-SHIFT KEYING (FSK)
In FSK, the two binary values are represented by two different frequencies. The frequencies of the modulated signal is constant for the duration of one signal element.

30. DIGITAL DATA, ANALOG SIGNALS PHASE-SHIFT KEYING (PSK)
In PSK, the phase of the carrier signal is shifted to represent data.

31. Analog-to-analog modulation
needed when the medium has a band-pass nature or if only band-pass bandwidth is available
and e.g. a radio produced by each station is a low-pass signal.
So a low-pass signal need to be shifted.

32. ANALOG DATA, ANALOG SIGNALS
There are two principal reasons for analog modulation of analog signals:
A higher frequency may be needed for effective transmission.
Modulation permits frequency-division multiplexing.
Three techniques:
Amplitude Modulation (AM)
Frequency Modulation (FM)
Phase Modulation (PM)

33. Amplitude modulation
AM works by varying the strength (amplitude) of the carrier in proportion to the waveform being sent
while the frequency remains constant

34. ANALOG DATA, ANALOG SIGNALS
AM - MODULATION
Amplitude modulation (AM) is the simplest form of modulation.
Mathematically, the process can be expressed as
Carrier
Input signal
Modulation index

35. Figure Amplitude modulation

36. ANALOG DATA, ANALOG SIGNALS
FM - MODULATION
In frequency modulation (FM) we modulate the instantaneous frequency fi(t), with the signal s(t) - he frequency of the carrier signal is varied.
Mathematically, the process can be expressed as
Carrier
Input signal
Modulation index

37. ANALOG DATA, ANALOG SIGNALS
PM - MODULATION
For phase modulation (PM), the phase is proportional to the modulating signal s(t).
Mathematically, the process can be expressed as
Carrier
Input signal

38. Industrial, Scientific, and Medical (ISM) band
3 unlicensed bands in the 3 ranges