Why UMTS can have 5MHz Band only?

[khurrambilal01]

Hi experts,
Whats the reason behind the fact that UMTS can have 5Mhz (For some vendors 4.4Mhz minimun) for operating?
Chip rate for UMTS is 3.84Mcps which corresponds to 3.84Mhz rest is guard band, So this chip rate is the only reason for UMTS to be 5Mhz or some other technical reason as well?

[dmitry28]

The UARFCN (UTRA Absolute Radio Frequency Channel Number) is the channel number representing the full 5 MHz UMTS carrier. Only 3.84MHz is used for transmission, while the 116 kHz acts as a built-in guard-band to adjacent UARFCN's (580kHz + 3840kHz + 580kHz = 5MHz). If an operator owns the adjacent frequency bands, it is possible to reduce the size of the UMTS carrier from 5MHz to 4.4 or 4.2 MHZ, but this is not recommended.

[khurrambilal01]

But question is why only 5Mhz? Why not 6Mhz or 3Mhz etc? Like LTE?


The UARFCN (UTRA Absolute Radio Frequency Channel Number) is the channel number representing the full 5 MHz UMTS carrier. Only 3.84MHz is used for transmission, while the 116 kHz acts as a built-in guard-band to adjacent UARFCN's (580kHz + 3840kHz + 580kHz = 5MHz). If an operator owns the adjacent frequency bands, it is possible to reduce the size of the UMTS carrier from 5MHz to 4.4 or 4.2 MHZ, but this is not recommended.

[dmitry28]

But question is why only 5Mhz? Why not 6Mhz or 3Mhz etc? Like LTE?

See document for more information http://books.google.ru/books?id=aq0g934064wC&pg=PA114&lpg=PA114&dq=UMTS+guard&source=bl&ots=P6nf6zO6OL&sig=oLPNt-xorBNsAsWJvfl47vBxSzo&hl=ru#v=onepage&q=UMTS%20guard&f=false

(http://books.google.ru/books?id=aq0g934064wC&pg=PA114&lpg=PA114&dq=UMTS+guard&source=bl&ots=P6nf6zO6OL&sig=oLPNt-xorBNsAsWJvfl47vBxSzo&hl=ru#v=onepage&q=UMTS%20guard&f=false)

[RF-SYR]

But question is why only 5Mhz? Why not 6Mhz or 3Mhz etc? Like LTE?There is DC-HSPA on UMTS, it is used 5MHz + 5MHz = 10MHz and for sure with high throughput rate.

[khurrambilal01]

There is DC-HSPA on UMTS, it is used 5MHz + 5MHz = 10MHz and for sure with high throughput rate.

RF-SYR,
That's still another carrier of 5Mhz :) Question is why can't it be 7Mhz or 3Mhz?? :confused:

[bilalahmed002]

Can any one tell me which frequency used as RF and Which one is used as Microwave in GSM Communications????

[khurrambilal01]

Can any one tell me which frequency used as RF and Which one is used as Microwave in GSM Communications????

Please follow the below link for answer.

http://www.finetopix.com/showthread.php?31725-GSM-Frequencies!!!!!!!

[cterms]

Hey bilalahmed ... actually UHF freq range 300 MHz to 1 GHz is used for RF range it has the capability of Multi path propagation maxi 64 QAM .... and MW freq range is from 1GHz to 30 Ghz it actually follows the LOS propagation and support more tham 128 QAM modulation ... eg. if ch spacing is 28 MHz then 2^7 (128) then 28 * 7 is 196 Mbps in general..which is on further allocation reduced to 155 Mbps for STM-1 capacity , hence for more than STM-1 we go for OFC ....

hope u find it ... any query PLS...

[baha]

Can any one tell me which frequency used as RF and Which one is used as Microwave in GSM Communications????

In theory, any frequency above 3 kHz and below 300 GHz is RF (radio frequency). In practice, you can use any RF (even optical frequencies too) for any type of wireless communication. The only problem is that lower frequencies (below 30 MHz) have less capacity but they are able to propagate longer, even able to propagate in water media (some spotted freq.). Higher frequencies (above 3 GHz) have good capacity, but cannot penetrate the buildings, overcome obstacles and attenuate more in rain and gases. Therefore these frequencies are ideal to establish communication over line-of-site paths. Frequencies between 30 MHz and 3 GHz are good compromise in terms of penetration and capacity. Therefore they are used (even most demanded) for mobile communication.
I hope this short intro will help to understand basic elements why various type of communication systems predominantly use certain frequencies only.

BR

[wernfried]

RF-SYR,
That's still another carrier of 5Mhz :) Question is why can't it be 7Mhz or 3Mhz?? :confused:

I would assume technically it would be possible but 3GPP simply defined 5MHz - that's it.
You could also ask: "Why does a (classic) CD contains max. 74 Minutes of music?" - Because that was defined by the standard.

I don't think there was a certain reason to take 5MHz, it was just the choice.

Kind Regards

[scorpion]

The UARFCN (UTRA Absolute Radio Frequency Channel Number) is the channel number representing the full 5 MHz UMTS carrier. Only 3.84MHz is used for transmission, while the 116 kHz acts as a built-in guard-band to adjacent UARFCN's (580kHz + 3840kHz + 580kHz = 5MHz). If an operator owns the adjacent frequency bands, it is possible to reduce the size of the UMTS carrier from 5MHz to 4.4 or 4.2 MHZ, but this is not recommended.

It is good explanation, but still why they choose 3.84 Mhz ? Why they haven't gone for double of that ?

[sabila]

The UTRAN radio technology is direct-sequence CDMA. Each 10 ms radio frame is divided into 15 slots, with 2560 chips/slot
If we count
(2560 chips *15slot)* (1000ms/10ms)=3.84 Mc/s.
So for channel spacing using 3.84Mhz with guardband total to be 5Mhz.

There's another bandwith

The specifications cater for Frequency Division Duplex (FDD) and Time Division Duplex (TDD) forms, with high (3.84 Mc/s) and low (1.28 Mc/s) chip rate flavours. (Low chip rate TDD was developed in China, but may well be deployed elsewhere.) Other chip rates (e.g. 7.68 Mc/s) were subsequently added.

For 1.28Mc/s using bw 1.6Mhz
For 7.68 Mc/s usinv bw 10Mhz


Sent from my GT-N7000

[babak1349]

Hello,
i saw this post it is a good questions If you look at the Shannon theory, it tells you more bandwidth gives you more capacity Like LTE, you can use a range of bandwidth from 3 to 20 MHZ. Depending allocated bandwidth the capacity will increase
In the contrary if you look IM2000, you can use up to 3 carriers each with 1.25 MHZ (based on classic CDMA)
So I think 5 MHZ has been chosen because the designers of standard had specific capacity and data rate in mind comparing with GSM targeting to achieve higher rate and capacity
If you look at the chips they are not pure sinusoid and therefore more bandwidth is required to guarantee adjacent carrier interference is not happening
Thre is no reason to not have WCDMA with 10 MHZ bandwidth but is it efficient ? I meant from bit/HZ point of view of data tansferring Anyway there is DC-HSPA which is using 2 carriers to achieve higher data rate and it means 10 MHz bandwidth is used practically



Cheers

[elkador]

Remember that at the 3G introduction, having a full 5MHz span of empty frequencies was thought as a challenge, compared to cdma2k and its 1.25MHz. So much simpler for operator to deploy 5MHz (especially in low frequency bands), and eventually add some other 5MHz when GSM was becoming less and less busy, hence freeing some space.



It is good explanation, but still why they choose 3.84 Mhz ? Why they haven't gone for double of that ?