Iuwne10 S01 L05
Upcoming SlideShare
Loading in...5
×
 

Iuwne10 S01 L05

on

  • 876 views

 

Statistics

Views

Total Views
876
Views on SlideShare
876
Embed Views
0

Actions

Likes
0
Downloads
63
Comments
0

0 Embeds 0

No embeds

Accessibility

Categories

Upload Details

Uploaded via as Microsoft PowerPoint

Usage Rights

© All Rights Reserved

Report content

Flagged as inappropriate Flag as inappropriate
Flag as inappropriate

Select your reason for flagging this presentation as inappropriate.

Cancel
  • Full Name Full Name Comment goes here.
    Are you sure you want to
    Your message goes here
    Processing…
Post Comment
Edit your comment

    Iuwne10 S01 L05 Iuwne10 S01 L05 Presentation Transcript

    • Wireless Fundamentals Understanding Spread Spectrum Technologies
    • Spread Spectrum
        • Narrowband and spread spectrum are the two main ways of sending a signal.
        • Spread spectrum uses less energy at peak.
        • The bandwidth required depends on the amount of information to be sent.
        • FHSS is a time-based narrowband hopping of frequencies.
        • DSSS is a broadband use of frequencies.
      FHSS Versus DSSS
    • DSSS: Encoding
        • Each bit is transformed into a sequence, called “chip” or “symbol.”
        • In this example, the chipping code is called Barker 11.
        • Up to 9 bits can be lost.
        • When using DBPSK, the phase shifts with 180 ° angles; each shift represents 1 bit.
        • When using DQPSK, shifts are 90 ° ; each shift represents 2 bits.
        • DBPSK allows 1 Mb/s.
        • DQPSK allows 2 Mb/s.
      DSSS Modulations: DBPSK and DQPSK
        • With CCK, each symbol of 6 bits is associated to a unique code sequence as shown on the example here .
        • Coding 4 bits per symbol allows 5.5 Mb / s, coding 8 bits per symbol allows 11 Mb / s .
      DSSS Modulation: CCK
    • Orthogonal Frequency-Division Multiplexing
        • Of 64 subcarriers:
        • 12 zero subcarriers (in black) on sides and in center
        • Sides function as frequency guard band, leaving 16.5-MHz occupied bandwidth
        • Center subcarrier zero for DC offset/carrier leak rejection
        • 48 data subcarriers (in green) per symbol
        • 4 pilot subcarriers (in red) per symbol for synchronization and tracking
        • Uses the same principles as DBPSK and DQPSK: BPSK shifts 180 º; QPSK shifts 90º.
        • Speed depends on density of signal per tone.
      OFDM Modulations: BPSK and QPSK 18 375 QPSK 12 250 QPSK 9 187.5 BPSK 6 125 BPSK Total Data Rate (Mb/s) Data Rate per Subchannel (kb/s) Modulation
        • With QAM, 90 º shifts are associated with amplitude modulation.
        • With four amplitude positions, 16 values are possible.
        • OFDM for wireless uses 16-QAM and 64-QAM, with speeds up to 54 Mbps.
      OFDM Modulation: QAM
    • Channels and Overlap Issues
        • With channels built for 5-MHz interchannel space, each DSSS channel uses more than one channel.
        • Only three or four nonoverlapping channels are available in the 2.4-GHz ISM band.
        • Channel overlap can be co-channel interference or adjacent channel interference.
    • Summary
        • Spread spectrum technologies offer better resistance to narrowband interferences.
        • Wireless networks use DSSS.
        • DBPSK allows 1 Mb/s, DQPSK 2 Mb/s.
        • Using CCK increases the speed to 11 Mb/s.
        • OFDM uses subcarriers to carry the signal.
        • BPSK allows 9 Mb/s, QPSK 18 Mb/s.
        • Using QAM increases the speed to 54 Mb/s.
        • Larger channels imply interference and channel collocation planning.
    •