L21 - Wireless LANs Increasing in popularity. Some LANs use...

Info iconThis preview shows pages 1–5. Sign up to view the full content.

View Full Document Right Arrow Icon
Wireless LANs Increasing in popularity. Some LANs use base station, some don’t. 802.11is the standard number for wireless LANs. It allows for different physical layer methods . Show Fig. 4-25
Background image of page 1

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

View Full DocumentRight Arrow Icon
Physical layer alternatives for 802.11: 1. Infrared - Diffused, 1 or 2 Megabits/second, isolated to a room. 2. Frequency Hopping Spread Spectrum (FHSS) 79 channels, 1 Mhz each. Hop by a pseudorandom hopping pattern known to sender and receiver. Dwell time at one frequency - adjustable up to 400 milliseconds per hop.
Background image of page 2
Some thoughts on 79 - channel frequency hopping : If only one is sending, the data rate is slow compared to 79 mhz total bandwidth. Data rate only about 1 mb/s But if there are two or more simultaneous senders, they may occasionally collide in one or more hops. If there is one hop per packet, each collision is a packet loss. If there are multiple hops per packet, there is a high probability part of a packet will be lost. Redundancy in the packet could recover some partial loss. Extra packets could recover some lost packets. But extra packets add to the traffic.
Background image of page 3

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

View Full DocumentRight Arrow Icon
Physical layer alternatives for 802.11, continued: 3. Direct Sequence Spread Spectrum - 11 chips/bit, for 1 mb/s for 11 mbaud pulse rate. Also a 2 mb/s version available. 4. 802.11a - Orthogonal Frequency Division Multiplexing (OFDM) - Up to 54 megabits/second, sending simultaneously on multiple frequencies. (Operates in 5 Ghz band) 52 different frequencies, 48 for data. With fading, some frequencies could be avoided, or redundancy used to recover lost bits. Something like the ADSL idea in telephone
Background image of page 4
Image of page 5
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 09/23/2009 for the course CMPEN 362 taught by Professor Johnmetzner during the Spring '09 term at Penn State.

Page1 / 19

L21 - Wireless LANs Increasing in popularity. Some LANs use...

This preview shows document pages 1 - 5. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online