1. Wireless Networking Spread Spectrum Technologies Module-05
Jerry Bernardini
Community College of Rhode Island
4/17/2017
Wireless Networking J. Bernardini

2. Presentation Reference Material
CWNA Certified Wireless Network Administration Official Study Guide
(PWO-104), David Coleman, David Westcott, 2009, Chapter-6
The California Regional Consortium for Engineering Advances in Technological Education (CREATE) project
Spread Spectrum Scene
4/17/2017
Wireless Networking J. Bernardini

3. Wireless Networking J. Bernardini
OSI Model
4/17/2017
Wireless Networking J. Bernardini

4. Telecommunication Channel
Channel - a path along which information in the form of an electrical signal passes. Usually a range of contiguous frequencies involved in supporting information transmission.
Center
Channel Frequency
Amplitude
Bandwidth
Frequency
Channel

5. RF Bands for Wireless Networks
ISM- Industrial Scientific and Medical – Three Bands
900 MHz band
2.4 GHz band
5 GHz Band
UNII- Unlicensed National Information Infrastructure
5 GHz band
UNII-1 (Lower)
UNII-2 (middle)
UNII2 Extended
UNII-3 (Upper)
4/17/2017
Wireless Networking J. Bernardini

6. ISM Bands Summary Band Frequency MHz Band-width MHz Channels
Applications
900 MHz 26 1
GSM, baby monitors, cordless phone, headsets
Foliage penetration
2.4 GHz
83.5 14
Wireless LAN , microwaves, cordless phone
5.8 GHz
150 23
WLANs, Monitors, cordless phones, outdoor Point to point I
4/17/2017
Wireless Networking J. Bernardini

7. 5 GHz UNII Bands Summary UNII Band Category GHz Band-width Channels
FCC max Power -mW
Applications
UNII-1
Lower
100 4 50
Indoor
UNII-2
Middle
250
Indoor/outdoor
UNII-2 Extended
Extended
255 11
UNII-3
Upper
1000
Indoor/outdoor Point to point
4/17/2017
Wireless Networking J. Bernardini

8. Wireless Networking J. Bernardini
UNII or U-NII Bands
4/17/2017
Wireless Networking J. Bernardini

9. Narrow and Wide Band
Narrow and Wide Band – a relative comparison of a group or range of frequencies used in a telecommunications system. Narrow Band would describe a small range of frequencies as compared to a larger Wide Band range.
Amplitude NB WB
Frequency
Freq. Range fL fH

10. Noise Floor
Noise –A disturbance, especially a random and persistent disturbance, that obscures or reduces the clarity of a signal. Anything you don’t want.
Amplitude
Channel
The noise floor is the level caused by the environment surrounding a wireless LAN.
Thermal and shot noise usually set the noise floor in a quite RF environment.
Thermal Noise is the fluctuating voltage across a resistance due to the random motion of free charge caused by thermal agitation.
Shot Noise is caused by the quantized and random nature of current flow. Think of it as noisy current.
Signal
Noise Floor
Thermal
Shot
Freq.

11. Signal to Noise Ratio dBm. VRMS 100 V -60 dBm Signal SNR-1 SNR-2
SRX
-95 dBm
SNR-1 shows an example of signal and noise levels measured in rms voltages. SNR-2 is a second example showing signal and noise measured in dBm. Notice at the time SNR-1 was measured a noticeable peak in noise level occurred which might indicate an interference source. Also an example of a drop in signal level is shown between the two SNR measurements. This could indicate a phenomenon that has interfered with the signal path or possible one of the end points are in motion.
RX S = receiver sensitive for threshold. For example: SRX = -91 dB
Noise
Time
SNRdB = 20 log (100 V/ 10 V) = 20 dB
SNRdB = -60 dBm – (-95 dBm) = 35 dB

12. Signal to Noise Ratio
Orinoco Client
NetStumbler
AirMagnet

13. Windows XP Wireless 802.11b Windows Signal Level Signal to Noise Ratio
Data Rates
Excellent
26 dBm and above
11Mpbs
Very Good
25dBm to 21dBm
Good
20dBm to 16dBm
Low
15dBm to 11dBm
Very Low
10dBm to 8dBm
5.5Mbps
8dBm to 6dBm
2Mbps
6 dBm and under
1Mbps

14. Introduction to Spread Spectrum
Spread Spectrum – a telecommunications technique in which a signal is transmitted in a bandwidth considerably greater than the frequency content of the original information.
Narrowband
Amplitude
Wideband
Frequency

15. 4-Types Spread Spectrum
Time Hopping, (THSS)
Frequency Hopping, (FHSS)
Direct Sequence Spread Spectrum, (DSSS)
Hybrid, DSSS/FHSS

16. Uses of Spread Spectrum
Military - For low probability of interception of telecommunications.
Civil/Military - Range and positioning measurements. GPS – satellites.
Civil Cellular Telephony.
Civil Wireless Networks – and Bluetooth.

17. Frequency Hopping
Hedy Lamarr and composer George Antheil, patent number 2,292,387
circa 1942
The concept of frequency hopping was invented in 1942 during World War II by actress Hedy Lamarr and composer George Antheil, who received patent number 2,292,387 for their "Secret Communications System". This early version of frequency hopping used a piano-roll to change between 88 frequencies, and was intended to make radio-guided torpedoes harder for enemies to detect or to jam. The patent was little-known until recently because Lamarr applied for it under her married name of Hedy Keisler Markey. Neither Lamarr nor Antheil made any money from the patent.

18. FHSS
FHSS - Acronym for frequency-hopping spread spectrum , Bluetooth, & HomeRF.
Amp.
Acronym for frequency-hopping spread spectrum. FHSS is one of two types of spread spectrum radio, the other being direct-sequence spread spectrum. FHSS is a transmission technology used in WLAN transmissions where the data signal is modulated with a narrowband carrier signal that "hops" in a random but predictable sequence from frequency to frequency as a function of time over a wide band of frequencies. The signal energy is spread in time domain rather than chopping each bit into small pieces in the frequency domain. This technique reduces interference because a signal from a narrowband system will only affect the spread spectrum signal if both are transmitting at the same frequency at the same time. If synchronized properly, a single logical channel is maintained.
The transmission frequencies are determined by a spreading, or hopping, code. The receiver must be set to the same hopping code and must listen to the incoming signal at the right time and correct frequency in order to properly receive the signal. Current FCC regulations require manufacturers to use 75 or more frequencies per transmission channel with a maximum dwell time (the time spent at a particular frequency during any single hop) of 400 ms. 1 2 3 4
Freq.
Channel
Wide Band
Frequency Hop Sequence: 1, 3, 2, 4

19. Frequency Hopping Spread Spectrum – Simplistic View
CWNA Guide to Wireless LANs, Second Edition

20. FHSS Timing Time Amplitude Data Hop Time Dwell Time Hop Sequence 1 2 34
Channels
Frequency

21. FHSS System Block Diagram
Antenna
FHSS
Data
Buffer
Mixer
Mod 1 3 2 4
Carrier
Frequency
Sequence
Generator 1 3 2 4
Frequency Synthesizer

22. FHSS Channel Allocation
2.403 GHz
2.480 GHz
2.402 GHz
2.479 GHz CH 2 CH 3 CH 79 CH 80
Amplitude
1 MHz
1 MHz
GHz
GHz
GHz
GHz
Freq.
GHz
2.400 GHz

23. DSSS DSSS - Acronym for direct-sequence spread spectrum. WLAN, 802.11.
Amp.
Signal 1
Acronym for direct-sequence spread spectrum. DSSS is one of two types of spread spectrum radio, the other being frequency-hopping spread spectrum. DSSS is a transmission technology used in WLAN transmissions where a data signal at the sending station is combined with a higher data rate bit sequence, or chipping code, that divides the user data according to a spreading ratio. The chipping code is a redundant bit pattern for each bit that is transmitted, which increases the signal's resistance to interference. If one or more bits in the pattern are damaged during transmission, the original data can be recovered due to the redundancy of the transmission. 1 2 3 4
Freq.
Channel
DSSS Band

24. DSSS USA Channel Allocation
Amplitude
Channels 1 2 3 4 5 6 7 8 9 10 11
There are only three non-overlapping channels: 1, 6, and 11. However there are several two non-overlapping channels: 1, 5; 2, 7; 7, 11; etc.
Freq.
2.401 GHz
2.473 GHz

25. DSSS 3 Non-overlap Channels
Amplitude
Ch 1
Ch 6
Ch 11
(2.412 GHz)
(2.437GHz)
(2.462 GHz)
Freq.
22 MHz
3MHz
2.473 GHz
These are the only three that do not overlap as a group. The 3-MHz gaps are sometimes called guard bands because the isolate the channels from one another. There are other pairs that do not overlap for example channel 2 and 7.
2.401 GHz
2401 MHz
2423 MHz
2426 MHz

26. CCRI J. Bernardini

27. CCRI J. Bernardini

28. Channel Bonding
CCRI J. Bernardini

29. 2.4 GHz ISM Band Spectrum Mask
CCRI J. Bernardini

30. Spectrum Mask –Channel-3
CCRI J. Bernardini

31. DSSS System Block Diagram
Carrier
Frequency
Antenna
DSSS
Mixer
Carrier
Generator
Mod
11-bit Barker Code
Pseudo –
Noise
Generator
Data
Buffer
Barker Code =
Encoder
Chipping Code

32. Comparing FHSS & DSSS Frequency Hopping Spread Spectrum, FHSS 802.11
Direct Sequence
Spread Spectrum, DSSS
802.11b
Dwell Time
400 mS
Higher Cost No
Lower Cost
Lower
Throughput (2 or 3 Mbps)
Interoperability
Higher
Throughput (11 Mbps)
Better Immunity to Interference
More User Density (79)
Poorer Immunity to Interference
Less User Density (3)
Cost of FHSS is greater than DSSS. Sample of throughput of , b. FHHS has slow radio sync up while DSSS is very fast. FHHS long latency time.

33. OFDM Orthogonal Frequency Division Multiplexing
Frequency division multiplexing (FDM) is a technology that transmits multiple signals simultaneously over a single transmission path, such as a cable or wireless system.
Orthogonal means to establish right angle relationships between frequencies
OFDM spread spectrum technique distributes the data over a large number of carriers that are spaced apart at precise frequencies and null out of channel sidebands f2 f3 f1 f4
4/17/2017
Wireless Networking J. Bernardini

34. IEEE 802.11n Draft Modulation
Uses three modes of OFDM
20MHz and 40 MHz bands
Data rates up to 600 Mbps
Non-HT mode
OFDM
Backward compatibility to a, b, g
HT mixed mode
Supports OFDM and ERP-OFDM
Greenfield mode
Only ERP-OFDM
Highest data rates
4/17/2017
Wireless Networking J. Bernardini

35. Encoding and Modulation
Encoding - To change or translate one bit stream into another.
Barker Code, Complementary Code Keying
Modulation – Appling information on a carrier signal by varying one or more of the signal's basic characteristics - frequency, amplitude and phase.
DBPSK (Differential Binary Phase Shift Keying) DQPSK (Differential Quaternary PSK)

36. Convolution Coding
Convolution coding is a method of channel coding by adding additional redundant information to provide error correction. Convolution codes operate on serial data, one or a few bits at a time and may use Exclusive-Or logic and shift registers. This type of error correction is used in wireless OFDM schemes.
Remember this coding is used for error detection and correction.

37. FCC Rules for FHSS Prior to 8-31-00 After 8-31-00
Use 75 of the 79 channels
Output Powermax = 1 Watt
Bandwidthmax = 1 MHz
Data Ratemax = 2 Mbps
After
Only 15 of the 79 channels required
Output Powermax = 125 mW
Bandwidthmax = 5 MHz
Data Ratemax = 10 Mbps

38. Co-location
Co-location is the ability to place multiple devices in a frequency space minimal interference
FHSS has many more frequencies / channels then DSSS which only has 3 co-location channels.
However 3 DSSS access points co-located at 11 Mbps each would result in a maximum throughput of 33 Mbps. It would require 16 access points co-located for FHSS to achieve a throughput of 32 Mbps.
DSSS 3 AP X 11 Mbps = 33 Mbps.
FHSS 16 AP X 2 Mbps = 32 Mbps

39. CWNA Guide to Wireless LANs, Second EditionCCRI J. Bernardini
Modulation
Carrier signal is a continuous electrical signal
Carries no information
Three types of modulations enable carrier signals to carry information
Height of signal
Frequency of signal
Relative starting point
Modulation can be done on analog or digital transmissions
CWNA Guide to Wireless LANs, Second EditionCCRI J. Bernardini

40. Analog vs. Digital Transmissions
Analog Signal = A signal that has continuously varying voltages, frequencies, or phases. All amplitude values are present from minimum to maximum signal levels.
Digital Signal = A signal in which information is carried in a limited number of different discrete states or levels; High/Low, One/Zero, 1/0
CWNA Guide to Wireless LANs, Second EditionCCRI J. Bernardini

41. Analog and Digital Modulation
Analog Transmission use analog carrier signals and analog modulation.
Digital Transmission use analog carrier signals and digital modulation.
Modem (MOdulator/DEModulator): Used when digital signals must be transmitted over analog medium
On originating end, converts distinct digital signals into continuous analog signal for transmission
On receiving end, reverse process performed
WLANs use digital modulation of analog signals (carrier signal)
CWNA Guide to Wireless LANs, Second EditionCCRI J. Bernardini

42. CWNA Guide to Wireless LANs, Second EditionCCRI J. Bernardini
Frequency and Period
CWNA Guide to Wireless LANs, Second EditionCCRI J. Bernardini

43. CWNA Guide to Wireless LANs, Second EditionCCRI J. Bernardini
Analog Modulation
Amplitude: Height of carrier wave
Amplitude modulation (AM): Changes amplitude so that highest peaks of carrier wave represent 1 bit while lower waves represent 0 bit
Frequency modulation (FM): Changes number of waves representing one cycle
Number of waves to represent 1 bit more than number of waves to represent 0 bit
Phase modulation (PM): Changes starting point of cycle
When bits change from 1 to 0 bit or vice versa
CWNA Guide to Wireless LANs, Second EditionCCRI J. Bernardini

44. CWNA Guide to Wireless LANs, Second EditionCCRI J. Bernardini
Analog Modulation
Amplitude modulation (AM) – Carrier frequency varies in amplitude
Frequency modulation (FM) – Carrier frequency varies in frequency
Phase modulation (PM) – Carrier varies in phase
CWNA Guide to Wireless LANs, Second EditionCCRI J. Bernardini

45. CWNA Guide to Wireless LANs, Second EditionCCRI J. Bernardini
Digital Modulation
Advantages over analog modulation:
Better use of bandwidth
Requires less power
Better handling of interference from other signals
Error-correcting techniques more compatible with other digital systems
Unlike analog modulation, changes occur in discrete steps using binary signals
Uses same three basic types of modulation as analog
Amplitude shift keying (ASK)
CWNA Guide to Wireless LANs, Second EditionCCRI J. Bernardini

46. CWNA Guide to Wireless LANs, Second EditionCCRI J. Bernardini
Digital Modulation
Frequency shift keying (FSK)
Phase shift keying (PSK)
CWNA Guide to Wireless LANs, Second EditionCCRI J. Bernardini

47. Quadrature phase shift keying (QPSK)
CWNA Guide to Wireless LANs, Second Edition

48. 16-QAM Modulation
CWNA Guide to Wireless LANs, Second Edition

49. 64-QAM - 64-level Quadrature Amplitude Modulation
CWNA Guide to Wireless LANs, Second Edition

50. Max Total Service Area Data Rate
Summary
PHY
Data Rates
Frequency Band
Standards
Max Colocated WLANs
Max Total Service Area Data Rate
FHSS
1 or 2 Mbps
2.4 GHz ISM
IEEE
79 max,
12 practical
24 Mbps
practical
DSSS
2 or 3
6 Mbps
HR/
1, 2, 5.5, or
11 Mbps
IEEE802.11b1999 3
33 Mbps
ERP
1-54 Mbps
IEEE g 2003
162 Mbps
OFDM
6-54 Mbps
5 GHz U-NII
IEEE a 1999 23
648 Mbps
4/17/2017
Wireless Networking J. Bernardini

51. Throughput vs. Data Rate
Data Rate = Total Data Rate through system
Throughput = Data Payload Rate
Data Rate = Data Payload Rate + Overhead
Overhead = Coding + Modulation+ Bandwidth Hardware + Software + Retransmission(errors)
5 Mbps Throughput
11 Mbps Data Rate
5 Mbps Throughput
4/17/2017
Wireless Networking J. Bernardini

52. Data Rates and Throughput Estimates
PHY
Standards
Data Rate
Throughput
FHSS
IEEE
1–2 Mbps
0.7–1 Mbps
DSSS
HR/DSSS
IEEE b-1999
1, 2, 5.5, and 11 Mbps
3–6 Mbps
ERP
IEEE g-2003
1, 2, 5.5, 11, 6, 9, 12, 18, 24, 36, 48, 54 Mbps
3–29 Mbps
OFDM
IEEE a-1999
6, 9, 12, 18, 24, 36, 48, 54 Mbps HT
IEEE n-2009
1–600 Mbps (with 4 spatial streams)
~ 100 Mbps
4/17/2017
Wireless Networking J. Bernardini

53. Wireless Networking J. Bernardini
Bandwidths
Analog Bandwidth – Frequency in Khz,Mhz (1 Mhz)
Digital Bandwidth – bits per second (11 Mbps)
Wireless Bandwidth – Frequency Space made available to network devices (22 Mhz)
Digital Bandwidth (Average Bit Rate)
Frequency
Amplitude
Bandwidth
4/17/2017
Wireless Networking J. Bernardini

54. Communication Resilience
Resistance to interference
FHSS best resilience but lowest throughput
OFDM next best resilience and higher throughput
HT-OFDM in IEEE n will provide the best resilience and the best throughput
4/17/2017
Wireless Networking J. Bernardini

55. Modulation Technique (DSSS)
Orinoco Gold b
Frequency Channels
11, MHz
Modulation Technique (DSSS)
CCK,DQPSK, DBPSK
Encoding (Spreading)
11 - chip Barker Sequence
Nominal Output Power
15 dBm (31.6 mW)
11 Mbps
5.5 Mbps
2 Mbps
1 Mbps
25m (80ft)
35m (115 ft)
40m (130 ft)
50m (165 ft)
-82 dBm
-86 dBm
-91 dBm
-94 dBm
Note: The second table’s first row shows data rates at the second row distances for a closed system. The last row shows the receiver sensitivity in dBm.

56. Orinoco 802.11 abg Frequency Channels Modulation Technique Data Speeds
FCC (26 Channels) ; ; ; MHz
ETSI (32 Channels) ; ; ; MHz
TELEC (18 Channels) ; MHz
IDA (22 Channels) ; ; MHz
Modulation Technique
802.11a, g Orthogonal Frequency Division Modulation (64 QAM, 16 QAM, QPSK, BPSK)
802.11b Direct Sequence Spread Spectrum (CCK, DQPSK, DBPSK)
Data Speeds
802.11a, g modes: 54, 48, 36, 24, 18, 12, 9, 6 Mbps
802.11b mode: 11, 5.5, 2, 1 Mbps
2X mode: 108, 96, 72, 48, 36, 24, 18, 12 Mbps
Max Output Power
802.11a, g: 60 mW EIRP
802.11b: 85 mW EIRP
Note: g has fall back to b data speeds, ie: 11 and 5.5 Mbps.

57. Wireless Networking J. Bernardini
Key Terms and Concepts
bandwidth
coding
colocation
data rate
DSSS
ERP
FHSS
HR/DSSS
modulation
OFDM
throughput
4/17/2017
Wireless Networking J. Bernardini