Why do we use the 60 GHz band?

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Pushhead

Joined: 19 Jan 2005
Posts: 195
Helped: 8

28 Sep 2009 21:41 Why do we use the 60 GHz band?

Hi All,

I'd like your good answers about this topic.
In fact, i'm not asking only about the 60 GHz band, but generally the "tens of gigahertz" bands.
1. I know that cellular service providers use microwave links @ ~30 GHz to transmit data with high capacity. Why can't they use their own GSM/WCDMA/etc. frequency bands for the same purpose?

2. Given that they have a physically larger bandwidth at those microwave bands, what is their transmission modulation? Is it different than the one they use for regular broadcast?

Thanks and have a good week,
P.

kspalla

Joined: 19 Aug 2008
Posts: 848
Helped: 140

29 Sep 2009 7:27 Why do we use the 60 GHz band?

These are bands at low atmosphere loss

radiohead

Joined: 13 May 2004
Posts: 412
Helped: 34
Location: Heart of Europe

29 Sep 2009 10:19 Re: Why do we use the 60 GHz band?

1. This is because you need much more bandwidth. It's a historical thing: The mobile phone antenna towers needed to be deployed very fast at the most exotic places and the operators required a high-bandwidth (aggregated from all GSM traffic) backhaul network for interconnecting all towers. Optical fiber would have been an option but deployment time would have been much longer. Hence the microwave links.

2. Deeper modulation requires good phase noise and frequency stability of the LO. Also reaching linearity in the PA is much more difficult at these multidecade GHz bands. This is why it is doubtful whether OFDM is possible at 60GHz (ie at an affordable price) and things like CPM and GMSK are considered. So yes you have more bandwidth but you cannot increase modulation depth a lot when having a good link budget.

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Pushhead

Joined: 19 Jan 2005
Posts: 195
Helped: 8

29 Sep 2009 17:13 Why do we use the 60 GHz band?

Thanks guys.
What i'm actually trying to understand is how those backhaul RF front-ends actually process a large bandwidth signal, when it is down converted back to their "regular" network processors with the slower clock rates?
Is it uncompressed data that is compressed later, is it being multiplexed?

Thanks again,
P.