Cellular Spectrum Bandwidth: How Much Space is Needed for a Single Call?

[Newtons Apple]

Hi everyone!
In amatuer radio, when we transmit on a specific frequency, we 'use' that frequency and depending on the power you "use' a slice of bandwidth around that frequency. So if two people transmit on the same frequency there's either a pleasant conversation, interference, or they'll just end up talking over each other. Does this same thing apply to cell phone calls? if two people place calls using the same carrier in teh same cell site, can they both use the same exact frequency? Also how "wide" is there call? I suppose this depends on the cellular technology, so let's just assume 3G or LTE... For a pure voice call, how much of the spectrum is used for the single call?

So let's say I have a cell phone belonging to Cell Provider A. They have coverage and license in my area at 700-725MHZ for uplink and 800-825MHZ for downlink. So that's 25MHz total allotted space. How much bandwidth is used then for a single FDD call? How many calls can "fit" into this 25Mhz range? I know each band is then subdivided into channels, but how wide then is each channel and how many calls (average) can fit into a channel?

 

[scottdave]

I suppose this information can be found, perhaps on the FCC website. As for talking over each other, the towers use Code Division Multiplexing, or other Multiplexing techniques to assign each packet of information to a particular phone. I remember that with analog landline phones, the voice is sampled 8000 times per second.

 

[davenn]

So let's say I have a cell phone belonging to Cell Provider A. They have coverage and license in my area at 700-725MHZ for uplink and 800-825MHZ for downlink. So that's 25MHz total allotted space. How much bandwidth is used then for a single FDD call? How many calls can "fit" into this 25Mhz range? I know each band is then subdivided into channels, but how wide then is each channel and how many calls (average) can fit into a channel?

In the case of your example, the one channel is 25MHz in bandwidth ….
in reality most cellular frequency blocks are around 50 - 60 MHz in bandwidth
As scottdave hinted at, there are a number of modulation/multiplexing techniques use

CDMA = code-division multiple access
TDMA = time-division multiple access
FDMA = frequency-division multiple access
OFDMA = orthogonal frequency-division multiple access

to name a few

because the system is digital, it means that these above methods allow 1000's of users access to each small slot within that 25MHz bandwidth

https://en.wikipedia.org/wiki/Cellular_network

https://en.wikipedia.org/wiki/LTE_frequency_bandsthere's tons of info on the net for you to go and do some research yourself …. I have supplied some starting points

 

[EngWiPy]

A governmental entity (FCC in the US) manages the spectrum among the different operators such that each operator takes a portion of the spectrum that doesn't overlap with that of other operators. Within each operator, the assigned spectrum is traditionally further divided between the cells (to a specific frequency reuse factor), and the spectrum assigned to each cell is divided between the uplink and downlink channels (either in frequency in which case it is called Frequency Division Duplex (FDD), or in time in which case it is called Time Division Duplex (TDD)), and the spectrum assigned to each transmission direction is divided between the active users in that cell. All of this spectrum management is done to avoid causing interference between users. But this isn't an efficient way of managing the spectrum, because most of the spectrum will not be fully utilized most of the time. There is a paradigm shift in the wireless communication community about this.

 

[anorlunda]

There is a paradigm shift in the wireless communication community about this.

Tell us more about this shift please.

 

[EngWiPy]

Tell us more about this shift please.

The basic idea is that any unlicensed system can use the spectrum as long as the licensed system is not currently using the spectrum (interweave mode), or the quality of service of the licensed system is not affected by sharing the spectrum (underlay mode). This is called Cognitive Radio technology. It has emerged as a result of a report done by FCC showing that only a small fraction of the spectrum is occupied at any given time, combined with higher demand of the spectrum, but the majority of the spectrum of desirable propagation characteristics is already allocated.

 

[anorlunda]

The basic idea is that any unlicensed system can use the spectrum as long as the licensed system is not currently using the spectrum (interweave mode), or the quality of service of the licensed system is not affected by sharing the spectrum (underlay mode).

That sounds very innovative. But how does either system detect when it is possible to begin transmission without interfering? It reminds me of the carrier-sense-multiple-access packet protocols of Ethernet, including collision detection and handling. Since everything is digital today, perhaps that's exactly what they mean.

 

[EngWiPy]

In Ethernet, all nodes have the same priority in accessing the network. In Cognitive Radio, the licensed system has the priority. The unlicensed system needs to squeeze itself as the current conditions allowed. It needs to adapt its transmission parameters based on the current situation of the spectrum.

In the interweave mode, the unlicensed system uses some white spaces detection and tracking algorithms, called spectrum sensing, like energy detection. Of course these can result in false detection. In the underlay mode, the unlicensed system needs to know what is the interference level allowed at the licensed system, so that it can use that margin for its own transmission.

Many aspects of this technology is still under investigation. I am not sure if it is used in LTE-A, but it is proposed to be used in 5G.

 

[davenn]

The basic idea is that any unlicensed system can use the spectrum as long as the licensed system is not currently using the spectrum

what unlicensed systems ... some examples ?

I don't know about the USA, but in Australia and New Zealand ( at least), cellular providers
have sole use of the sections of spectrum they have purchased. No-one else can operate in those spectrum segments.
Actually, that applies to pretty much the whole RF spectrum, cellular, 2 way radio, various data comms, BC radio and TV where either spectrum segments or spot channel licences are sold.

There are smalls sections of spectrum set aside for non licensed users ... eg 315, 433, ~2400, ~5800 MHz
what we call mere the LIPD (Low Interference Potential Devices) also known as the ISM bands. strictly low power, short range

Dave

 

[Tom.G]

what unlicensed systems ... some examples ?

Following from: https://www.sciencedirect.com/science/article/pii/S2213020916301872

As reported by the survey of FCC (Federal Communications Commission, 2002), most of the assigned spectrums are underutilized. Therefore for the efficient use of the spectrum, FCC opened the licensed spectrums to the unlicensed users/cognitive users (SU) without affecting the performance of primary/licensed user (PU).

Cheers,
Tom

 

[davenn]

Following from: https://www.sciencedirect.com/science/article/pii/S2213020916301872

As reported by the survey of FCC (Federal Communications Commission, 2002), most of the assigned spectrums are underutilized. Therefore for the efficient use of the spectrum, FCC opened the licensed spectrums to the unlicensed users/cognitive users (SU) without affecting the performance of primary/licensed user (PU).

Cheers,
Tom

cool, cheers

it's the opposite over here. cellular providers are always screaming out for more and more bandwidth
Us Australian amateur operators and some others lost access to the 900MHz band when it was sold off to cellular companies
Our 1250 to 1300 MHz amateur band is under threat for same reasons

 

[EngWiPy]

I am not sure Cognitive Radio has been officially standardized. As far as I am aware it is still under study, and proposed to be used.

As for the spectrum, it is auctioned, and large companies are willing to pay billions of dollars for it. Small operators have less chance than other big ones, but the available spectrum with the current cellular structures cannot accommodate the explosion of mobile data. People are talking now about disruptive technologies in 5G: massive MIMO, cognitive radio, mmW radio, heterogeneous networks (multiple networks with different sizes coexist together, which requires sophisticated interference management techniques), Wi-Fi offloading ... etc.

 

[EngWiPy]

what unlicensed systems ... some examples ?

I don't know about the USA, but in Australia and New Zealand ( at least), cellular providers
have sole use of the sections of spectrum they have purchased. No-one else can operate in those spectrum segments.
Actually, that applies to pretty much the whole RF spectrum, cellular, 2 way radio, various data comms, BC radio and TV where either spectrum segments or spot channel licences are sold.

There are smalls sections of spectrum set aside for non licensed users ... eg 315, 433, ~2400, ~5800 MHz
what we call mere the LIPD (Low Interference Potential Devices) also known as the ISM bands. strictly low power, short range

Dave

Unlicensed systems are systems that didn't purchase the spectrum. However, the unlicensed systems can pay to the licensed systems.

What you mentioned is how traditional systems are operated, but other more efficient ways of managing the spectrum is being investigated.

 

[Tom.G]

Here in the US, large pieces of the broadcast TV band have been turned over to cell phone usage. Much of it by purchase and some by government decree. Analog TV broadcast is gone; it's now all digital with appearently denser spectrum usage as shown by High Definition (HD) video and many more channels.

 

[anorlunda]

This topic is news to me. I was unaware of the spectrum sharing developments that could be applied to all bands including the cell phone band. Apparently, it has come far enough to have an IEEE standard.

"https://en.wikipedia.org/wiki/Cognitive_radio#Applications"]
The first cognitive radio wireless regional area network standard, IEEE 802.22, was developed by IEEE 802 LAN/MAN Standard Committee (LMSC)[3] and published in 2011. This standard uses geolocation and spectrum sensing for spectral awareness. Geolocation combines with a database of licensed transmitters in the area to identify available channels for use by the cognitive radio network. Spectrum sensing observes the spectrum and identifies occupied channels. IEEE 802.22 was designed to utilize the unused frequencies or fragments of time in a location. This white space is unused television channels in the geolocated areas. However, cognitive radio cannot occupy the same unused space all the time. As spectrum availability changes, the network adapts to prevent interference with licensed transmissions

A LAN would be the perfect unlicensed application. LAN packets need only short bursts, can be held back a reasonable time before transmission, need only low-power local transmission and thus can avoid wide-area considerations.

 

[berkeman]

Interesting discussion; I didn't know about this either. Thanks.