1 / 7

Wireless Communication Fundamentals II

Wireless Communication Fundamentals II. David Holmer dholmer@jhu.edu. Review. Wireless = electro-magnetic waves Path-loss over distance Multi-path reflections Modulation. Symbol Rate & Bandwidth. Modulation allows transmission of one of several possible symbols (two or more)

trish
Télécharger la présentation

Wireless Communication Fundamentals II

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Wireless Communication Fundamentals II David Holmer dholmer@jhu.edu

  2. Review • Wireless = electro-magnetic waves • Path-loss over distance • Multi-path reflections • Modulation

  3. Symbol Rate & Bandwidth • Modulation allows transmission of one of several possible symbols (two or more) • Data stream is encoded by transmitting several symbols in succession • Symbol rate ≈ bandwidth • Throughput (bits/sec) • Spectrum usage (Hz) • Inter-symbol interference (ISI) occurs unless delay spread << symbol time

  4. Thermal Noise • Ever-present thermal noise in wireless medium • Sums with any wireless transmission • Potentially causes errors in reception (digital) or degradation of quality (analog) • Effectively limits transmission range when transmitting signal strength falls below noise floor • -174 dBm/Hz

  5. Thermal Noise Calculation • Depends on channel bandwidth • About 25 MHz for 802.11b or 802.11a channel • = -174dBm/Hz + 10log(bandwidth in Hz) • So for 802.11 • Noise Floor is about -100 dBm • -100 dBm = 10log( .0000000000001 Watts )

  6. Noise Limits Transmitting Distance Signal to Noise Ratio (SNR) Short range transmission (low path loss) + = High Long range transmission (high path loss) = + Low

  7. Physical Channel Properties Review • Wireless signal strength • Transmit power • Loss over distance (falls off by d2) • Shadowing (e.g. absorption by walls) • Multi-path (e.g. bouncing off of metal objects) • Noise • Thermal noise floor • Environmental noise (e.g. microwave ovens) • Channel quality • Related to signal to noise ratio

More Related