Hi, On Sunday 08 January 2006 14:19, you wrote: > As you said, I have just found that, in NS2, the bandwidth can be set by > "Phy/WirelessPhy set bandwidth_ 2e6" and it will be constant, even though > the transmission power is changed. I am not sure why bandwidth is not > related to transmission power. According to my understand, when the > transmission power is decreased, the communication range will be decreased. > It is logical true. However, decreasing of transmission power should > increase SNR. Once SNR increases, the bandwidth or data rate should be > decreased somehow. Do you think so? Could you give me an explaination if i > am wrong?
You have to keep in mind that the received signal strength is not only defined by the sender. You can increase the transmission range just by attaching an external antenna with positive gain to the receiver. So the signal strength is defined by the transmission power, the antenna gains, and the distance. Above this you have the modulation (with a maximum possible bandwidth) that requires a certain SNR. This does not mean that the bandwidth will automatically increase with an increasing SNR because the sender does not know about the SNR at the receiver side. The current 802.11 implementation does not has multi-rate support. There is a new implementation (s. wiki for more information) that has, but I cannot tell you exactly how it works. If you use the current implementation you have to decide for a bandwidth, set it in the PHY layer and set the RXThresh accordingly. Just as an example what you can do with antennas (and an unamplified 802.11b card) lock here: http://www.unwiredadventures.com/unwire/2005/12/defcon_wifi_sho.html They reached more than 125 miles! Daniel. -- +-[Dipl.-Inf. Daniel Mahrenholz / Otto-von-Guericke Universität Magdeburg]-+ | http://ivs.cs.uni-magdeburg.de/~mahrenho Geb. 29 Raum 407 | | mailto:[EMAIL PROTECTED] Tel. +49-391-67-12788 | +--------------------------------------------------------------------------+
