Fhss 19 0 1 0 1 1 t t t t b t d f f 3 f 2 f 1 f f 3 f

Info icon This preview shows pages 18–29. Sign up to view the full content.

View Full Document Right Arrow Icon
FHSS
Image of page 18

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
19 0 1 0 1 1 t t t t b t d f f 3 f 2 f 1 f f 3 f 2 f 1 User data Slow hopping (3bit/hop) Fast hopping (3hop/bit) Slow and fast frequency hopping
Image of page 19
20 FHSS hops 79 hops , each 1-MHz wide 2.4 GHz If stations use the same seed of the PN number, they stay synchronized in time. They will hop to the same frequencies simultaneously Dwell time, is an adjustable parameter, but must less than 400 msec. FHSS offers good resistance to multipath fading FHSS advantages for WLAN WLAN systems can overlap without interference • Immunity from noise and interference • Resistance to radio reflections (multipath transmission) • High data transfer capacity • Low price for TR and R P FHSS provides a security since an intruder, who does not know the hopping sequence or dwell time cannot overhear on transmissions. 2.483 23 for Japan
Image of page 20

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
21 Example: Bluetooth Frequency Hopping frequency hopping spread spectrum 2.402 GHz + k MHz, k=0, …, 78 1,600 hops per second GFSK modulation 1 Mb/s symbol rate transmit power 0 dBm (up to 20 dBm with power control) . . . 1Mhz 1 2 3 79 83.5 Mhz
Image of page 21
22 Mobile Radio Propagation Free space loss Two ray model Slow fading Fast fading Delay spread Ground, Space, Sky, and Satellite waves
Image of page 22

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
23 Radio Transmission (a) In the LF ( hertz), and MF ( hertz) bands, radio waves follow the curvature of the earth ( ground ). (b) In the HF ( hertz) band, they bounce off the ionosphere ( space ). 5 10 6 10 7 10 troposphere CELLULAR Sky
Image of page 23
24 Example 1 Example 1 What is the period of the moon according to Kepler’s law? Solution Solution The moon is located approximately 384,000 km above the earth. The radius of the earth is 6378 km. Applying the formula, we get Period = (1/100) (384,000 + 6378) 1.5 = 2,439,090 s = 1 month According to Kepler’s law, what is the period of a satellite that is located at an orbit approximately 35,786 km above the earth? Example 2 Example 2 Applying the formula, we get Period = (1/100) ( 35,786 + 6378) 1.5 = 86,579 s = 24 h A satellite like this is said to be stationary to the earth. The orbit, as we will see, is called a geosynchronous orbit. Solution Solution
Image of page 24

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
25 Reflection and diffraction of radio signals Scatterin g
Image of page 25
26 Propagation mechanisms Reflection: propagation wave reflected by object larger than wavelength results Large-scale fading. Diffraction: wave obstructed by surface with sharp, irregular edges. Scattering: wave hits loose objects smaller than wavelength; signal scattered in bunch of outgoing weaker signals are result Small-scale fading.
Image of page 26

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
27 multipath signals, Intersymbol interference In a time-dispersive medium the transmission rate R for a digital transmission is limited by the delay spread d R τ 2 1 =
Image of page 27
28 Basics of Antenna Theory Antenna reciprocity -A transmitting antenna will transfer energy to the atmosphere with the same efficiency with which it transfers energy from the atmosphere to its terminals.
Image of page 28

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Image of page 29
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern