Antenna - Theory .com: The Antenna Site

Antenna Basics Antenna Types Smith Charts Antenna Measurements

antenna-theory.com :: View topic - Friis Transmission Formula in the Media
antenna-theory.com Forum Index antenna-theory.com
Antenna Theory
 
 FAQFAQ   SearchSearch   MemberlistMemberlist   UsergroupsUsergroups   RegisterRegister 
 ProfileProfile   Log in to check your private messagesLog in to check your private messages   Log inLog in 

Friis Transmission Formula in the Media

 
Post new topic   Reply to topic    antenna-theory.com Forum Index -> News
View previous topic :: View next topic  
Author Message
bigSteve
Antenna Wizard


Joined: 14 Mar 2009
Posts: 265

PostPosted: Mon Mar 28, 2011 11:03 am    Post subject: Friis Transmission Formula in the Media Reply with quote

Here is an article, by The Financial Times. It discusses the "US spectrum crunch", or lack of bandwidth available for mobile communications (ipads, smartphones, etc).

http://www.ft.com/cms/s/0/46eab1de-58a9-11e0-9b8a-00144feab49a.html?referrer_id=yahoofinance&ft_ref=yahoo1&segid=03058#axzz1HtAnmu9a

Interestingly, there is a statement in the article:
"Mr Ahuja says the airwaves he plans to use are more attractive because they are at a lower frequency where wireless signals travel further. This means it should cost LightSquared less than Clearwire to build a network."

Now, recall the Friis Transmission Formula, which does state that pathloss increases with higher frequency (that is, the transmitted power dies off quicker at higher frequencies):
http://www.antenna-theory.com/basics/friis.php

Now, in regards to Mr Ahuja's statement, it is true that the pathloss is less at LTE (700 MHz band) as opposed to WiMax (2 GHz and up). However,
the difference in path loss between 700 MHz and 2100 MHz (3 times higher in frequency) is 3^2 = 9 = 9.5 dB. This does sound like a large gain.

The statement is true, but note that cell phones transmit less than a watt of power (1/60th of what comes out of a small crappy light bulb). Hence, to achieve the same "expected receive power at a mobile phone", the power from a cell station simply be increased from 1 W to 9W, which is insignificant.

However, the mobile phone power is regulated (primarily by SAR), so the uplink (data from mobile device to base station) will be improved for a given distance at lower frequency.

One extra advantage of lower frequencies is that low frequency energy "spreads out" more than high frequency energy. That is, light beams (very high frequency) tend to travel in a straight lines, whereas the lower the frequency the more uniform or spread out in space the signal will be.
Back to top
View user's profile Send private message
Display posts from previous:   
Post new topic   Reply to topic    antenna-theory.com Forum Index -> News All times are GMT
Page 1 of 1

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum


Powered by phpBB © 2001, 2005 phpBB Group