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Private Line covers what has occurred, is occurring, and will ocurr in telecommunications. Since communication technology constantly changes, you can expect new content posted regularly.

Consider this site an authoritative resource. Its moderators have successful careers in the telecommunications industry. Utilize the content and send comments. As a site about communicating, conversation is encouraged.

Writers

Thomas Farely

Tom has produced privateline.com since 1995. He is now a freelance technology writer who contributes regularly to the site.

His knowledge of telecommunications has served, most notably, the American Heritage Invention and Technology Magazine and The History Channel.
His interview on Alexander Graham Bell will air on the History Channel the end of 2006.

Ken Schmidt

Ken is a licensed attorney who has worked in the tower industry for seven years. He has managed the development of broadcast towers nationwide and developed and built cell towers.

He has been quoted in newspapers and magazines on issues regarding cell towers and has spoke at industry and non-industry conferences on cell tower related issues.

He is recognized as an expert on cell tower leases and due diligence processes for tower acquisitions.

« WISPCON | | Marconi's 1901 trans-Atlantic radio transmission questioned »

October 28, 2003

Posted by Tom Farley & Mark van der Hoek at 03:11 AM

Tech time! Always more on modulation . . .

A privateline.com/TelecomWriting.com reader asks:

I'm confused. How in GSM can we fit a gross bit rate of 270 Kbps in the 200 KHz channel on the air interface? GSM uses Gaussian-filtered Minimum Shift Keying or GMSK. That technology has a spectral efficiency of 1 bit/symbol/Hz. Does that mean we use1 bit per symbol and not more?

Professor R.C. Levine responds:

I am writing this quickly and may not remember all the numbers exactly, so if you find other numbers in other source documents, I may have the numbers wrong.

GMSK modulation has a "spectral efficiency" of APPROXIMATELY 1 bit per symbol or 1 bit per hertz of bandwidth. The word "approximately" is used because there are several different ways to measure the bandwidth of a signal.

The method used for GMSK signals in GSM is to find the bandwidth that contains about 99% of the radio signal power. GMSK was developed specifically for GSM by the COST (Council on Science and Technology, a scientific advisory group funded by CCITT and later ETSI). GMSK is a type of minimum frequency shift (MFS) modulation that achieves an approximately optimum compromise . . . .---> (continues here within the GSM article)

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