Important: Use custom search function to get better results from our thousands of pages

Use " " for compulsory search eg:"electronics seminar" , use -" " for filter something eg: "electronics seminar" -"/tag/" (used for exclude results from tag pages)


 
 
Thread Rating:
  • 0 Votes - 0 Average
  • 1
  • 2
  • 3
  • 4
  • 5
Spread Spectrum ppt
Post: #1

Spread Spectrum


.ppt  Spread Spectrum[.ppt (Size: 223.5 KB / Downloads: 10)

Introduction to Spread Spectrum

Problems such as capacity limits, propagation effects, synchronization occur with wireless systems
Spread spectrum modulation spreads out the modulated signal bandwidth so it is much greater than the message bandwidth
Independent code(PN code) spreads signal at transmitter and dispreads signal at receiver

Frequency multiplex

Separation of spectrum into smaller frequency bands
Channel gets band of the spectrum for the whole time
Advantages:
no dynamic coordination needed
works also for analog signals
Disadvantages:
waste of bandwidth
if traffic distributed unevenly
inflexible
guard spaces

Spread Spectrum Technology

Side effects:
coexistence of several signals without dynamic coordination
tap-proof
Alternatives: Direct Sequence (DS/SS), Frequency Hopping (FH/SS)
Spread spectrum increases BW of message signal by a factor N, Processing Gain

FH/SS (Frequency Hopping Spread Spectrum) I

Discrete changes of carrier frequency
sequence of frequency changes determined via PN sequence
Two versions
Fast Hopping: several frequencies per user bit (FFH)
Slow Hopping: several user bits per frequency (SFH)
Advantages
frequency selective fading and interference limited to short period
uses only small portion of spectrum at any time
Disadvantages
not as robust as DS/SS
simpler to detect

Performance of DS/SS Systems

Pseudonoise (PN) codes
Spread signal at the transmitter
Despread signal at the receiver
Ideal PN sequences should be
Orthogonal (no interference)
Random (security)
Autocorrelation similar to white noise (high at =0 and low for  not equal 0)
Post: #2
In telecommunications and radio communications, spread spectrum techniques are methods by which a signal (eg, an electrical, electromagnetic or acoustic signal) generated with a particular bandwidth is deliberately propagated in the frequency domain, giving result a signal with a wider bandwidth. These techniques are used for a variety of reasons, including establishing secure communications, increasing resistance to natural interference, noise and jamming, to prevent detection, and to limit the power flux-density (e.g. by satellite).

A conventional wireless signal has a frequency, usually specified in megahertz (MHz) or gigahertz (gigahertz), which does not change over time (except for small and rapid fluctuations that occur as a result of modulation). When you hear a signal at 103.1 MHz on an FM stereo receiver, for example, the signal remains at 103.1 MHz. It does not go up to 105.1 MHz or up to 99.1 MHz. The radio frequency dial digits remain the same at all times. The frequency of a conventional wireless signal is kept as constant as the state of the art allows, so the bandwidth can be kept within certain limits, and therefore the signal can be easily located by someone who wants to retrieve the information .

There are at least two problems with conventional wireless communications that may occur under certain circumstances. First, a signal whose frequency is constant is subject to catastrophic interference. This occurs when another signal is transmitted at, or very close to, the desired signal frequency. Catastrophic interference may be accidental (as in amateur radio communications) or may be deliberate (as in times of war). Second, a constant frequency signal is easy to intercept and therefore not suitable for applications where information must be kept confidential between the source (transmitting party) and the destination (receiving party).
 

Marked Categories : spread spectrum technology,

[-]
Quick Reply
Message
Type your reply to this message here.

Image Verification
Image Verification
(case insensitive)
Please enter the text within the image on the left in to the text box below. This process is used to prevent automated posts.

Possibly Related Threads...
Thread: Author Replies: Views: Last Post
  rfid based highway toll tax collection system ppt Guest 1 1,715 06-04-2019 02:28 PM
Last Post: Guest
  smart contact lens ppt Guest 0 0 01-03-2019 08:53 PM
Last Post: Guest
  box shifting machine ppt Guest 0 0 26-01-2019 09:35 PM
Last Post: Guest
Exclamation application of mathematics in digital image processing ppt Guest 0 0 17-12-2018 05:30 PM
Last Post: Guest
  computer hardware and maintenance ppt [email protected] 0 0 16-12-2018 06:48 PM
Last Post: [email protected]
  pdf ppt file of solenoid engine Guest 0 0 05-11-2018 07:04 PM
Last Post: Guest
  ppt about artificial hand using embedded system Guest 0 0 24-10-2018 02:39 PM
Last Post: Guest
  ppt about artificial hand using embedded system Guest 0 0 24-10-2018 02:33 PM
Last Post: Guest
  hydraulic hydrological impacts on bridges ppt Guest 0 0 21-10-2018 12:15 PM
Last Post: Guest
  ultrasonic techniques for hidden corrosion detection ppt Guest 0 0 06-10-2018 06:13 PM
Last Post: Guest
This Page May Contain What is Spread Spectrum ppt And Latest Information/News About Spread Spectrum ppt,If Not ...Use Search to get more info about Spread Spectrum ppt Or Ask Here

Options: