Introduction to Mobile Data (3G/4G)3G

 


Ofcom's Mobile Coverage Checker provides a single-stop for consumers and businesses across the UK to discover the quality of the mobile coverage in areas where they live, work, or intend to move.

The Mobile Mast Finder by Ofcom is an application that will let you search for mobile masts in your locality and includes information about operators, mast height, as well as the frequencies and mobile standards used.

 

3G Spectrum
The bandwidth of a radio signal is defined as being the difference between the upper and lower frequencies of the signal. The amount of bandwidth needed for 3G services is typically as much as 15-20 MHz. Compare this with the bandwidth of 30-200 KHz used for current 2G communication and you can see that there is as much as a 500-fold increase in the amount of bandwidth required. The UK telecoms operators have had to buy 3G spectrum from Ofcom and the UK government in an auction arranged to achieve the highest possible price. The radio spectrum is organised (and sold) as a paired spectrum - a bit of spectrum in a lower frequency band, and a bit of spectrum in an upper frequency band. Paired spectrum is often specified in a form like "2x15MHz" meaning 15MHz in a lower band and 15MHz in an upper band. This technique of two users talking to each other on two separate frequencies is called Frequency Division Duplex. The spectrum system used by 3G applications is called UMTS (Universal Mobile Telephone System).

Frequency Bands Used
UMTS is quite specific about its spectrum requirements which has resulted in bidding wars for UMTS spectrum. In Europe UMTS specifies the bands 1900-2025 MHz and 2110-2200 MHz for 3G transmission. Satellite UMTS service uses the bands 1980-2010 MHz (uplink), and 2170-2200 MHz (downlink). This leaves the 1900-1980 MHz, 2010-2025 MHz, and 2110-2170 MHz bands for terrestrial UMTS (see the diagram below):

3G Europe Spectrum
As can be seen from the diagram, UMTS FDD is designed to operate in paired frequency bands, with uplink in the 1920-1980 MHz band, and downlink in the 2110-2170 MHz band. UMTS TDD is left with the unpaired frequency bands 1900-1920 MHz, and 2010-2025 MHz.
The UK Government auctioned five licenses for UMTS:
Licence Name Frequencies Winner Final Amount Bid
Licence A (reserved for
a new entrant to the industry)
2x15 MHz paired spectrum plus
5 MHz unpaired spectrum
Hutchison 3G (now simply called Three) £4,384,700,000
Licence B 2x15 MHz paired spectrum Vodafone £5,964,000,000
Licence C 2x10 MHz paired spectrum plus 5 MHz unpaired spectrum BT(O2) £4,030,100,000
Licence D 2x10 MHz paired spectrum plus 5 MHz unpaired spectrum One2One (now T-Mobile) £4,003,600,000
Licence E 2x10 MHz paired spectrum plus 5 MHz unpaired spectrum Orange £4,095,000,000

Below shows the position of these licenses (A, B, C, D, and E) in the paired spectrum diagram (you can see that some licenses were for 10 MHz and some licenses were for 15 MHz):

3G Europe Spectrum

In Europe the choice of frequency band for implementing UMTS was clear, however these frequency bands were not available in the U.S., so alternative frequency bands are used consisting of 45MHz of space in the 1710-1755 MHz band and 45 MHz of space in the 2110-2170 band.

Using Antenna to improve reception

Indoor Antennas
It’s critical to consider the distance from the transmission tower and any obstacles that lie between the antenna and the tower. These factors also affect outdoor antennas, but it is more critical to pay attention to these details since indoor antennas are usually having top cope with trying to receive the signal through the walls of your property which will obviously have a considerable effect on the signal strength and signal quality (the amount of noise on the signal).

Distance From Transmission Tower
There isn’t a specific distance that determines if an indoor antenna will work for you. If you live within a built up area then you will likely be able to use an indoor antenna. If you are in a rural area where the mobile phone cell density is lower then you might have to resort to an outdoor antenna (which is generally higher gain and can be mounted in an outdoor position which gives better clear line of site to the nearest transmission mast).

Obstacles Between Antenna and Transmission Tower

Obstacles can be mountains, hills, buildings, walls, doors, people walking in front of the antenna, etc. These create havoc with all wireless signals and impact the reliability in signal reception. The effects of obstacles in the signal path are impossible to predict. You might notice that if you configure the antenna direction just right, get the right atmospheric conditions and open the front door or blinds then it comes in without issue. The door and blinds can be considered obstacles to your reception. Also, reception cuts in and out when someone walks in front of the antenna. These are all factors which can effect indoor reception. Therefore, when comparing indoor to outdoor antennas, indoor antennas typically have a shorter reception range, easier to install and cost less BUT the outdoor antenna will generally allow much better signal reception.

Directional vs. Omni Antenna

The first thing to note is that an antenna does not BOOST a signal. An antenna simply concentrates a signal i.e. it takes signal from an unused direction and concentrates it into a useful direction. Generally there are two main types of antenna: Directional and Omni. A directional antenna typically concentrates the signal into a cone which you aim at the signal source. If you have a clear line of site between your receiver and the transmission tower then a directional antenna is generally the best type. An omni antenna concentrates the signal into a horizontal disc: It’s taken signal that would normally be directed upward or downward and sent into a thin disc. An omni antenna is generally your best choice where you are unsure where the signal is coming from or the signal is being received after reflection or scatter due to obstructions in the way.  

Antenna Gain

dBi is the measuring unit for the gain of an antenna. The reference level or dBi is the strength of the signal that would be transmitted by a non-directional isotropic antenna i.e. radiates equally in all directions. This antenna exists as a mathematical concept used only as a known reference to measure antenna gain per dBi. In electronics, the term "gain" is often repeated but misunderstood. Gain implies increase e.g 20 dBi but without respect to where the increase originated.

An antenna transmits and receives radio waves. Antenna gain is used to indicate the increase in power of one antenna (transmitting or receiving) as compared to another antenna. Gain is actually a ratio of power levels and is stated in decibels dBi. The dipole or basic antenna concentrates it signals in two directions. The isotropic antenna doesn't favour any particular direction so its dBi gain equals 0. The dipole has a 2.1 dBi measurement gain over an isotropic radiator. Therefore a 6 dBi antenna gain over an isotropic radiator computes to a 3.9 dBi gain over a dipole. For every 3 dBi of improvement added to your antenna, results in a noticeable effect on the receiving station. Any dBi gain less than 3 dBi leads to an undetectable dBi improvement, however don't discount improvements under 3 dBi. Sometimes even a antenna gain of .5 dBi can make the difference between receiving and not receiving a wireless signal!

The important point to remember though is the extra gain of an antenna has been achieved by concentrating the signal and hence, narrowing the useable reception beamwidth. Typically, if you double the power (gain) of an antenna then you’ve halved the area of beam coverage. This is an important consideration when you consider how easy or difficult it’s going to be to aim the antenna at the signal source: Obviously it will be easier with a low gain antenna with a wider beamwidth than it will with a much higher gain with a much tighter beam angle. Deciding on which antenna gain to use is often a compromise between signal strength and signal coverage.

4G (LTE) Spectrum

In the years since we first wrote our 3G introduction, 4G (actually LTE) has come along. LTE is a multi-stream radio MiMo technology. This is like 11n WiFi (which is also MiMo). One of the ways that LTE gets its performance improvements is to use multiple radio data streams to and from the end client. Just like 11n WiFi, the more streams of data the client can take then the faster the effective broadband.

Like 11n WiFi, the terminology which denotes the number of streams is expressed as TxR where T is the number of transmit radio streams and R is the number of receive streams the connection can support. So, if a client supports 2×2 streams then it can generally support twice the upload and download speed of a 1×1 device. In the world of LTE you can have anything from 1×1 right up to 8×8 stream capability with all the possible mixes in between.

In simple terms a client device needs to have an antenna for each radio stream. For a 1×1 service then the client just needs a single antenna. For a 2×2 service the client needs two antenna, and so on. So the number of streams a connection can support depends upon the capabilities of the service providers masts and also the radio capabilities of the client device.

If your client device (dongle, router, whatever) only has a single antenna connector then there’s just no point in getting an LTE antenna with dual connections; you’re just wasting your money. On the other hand if you do have a dual connection device then you must use either two single connection antenna or one dual connection antenna.

Frequency Bands

In some countries there is just a single frequency band used for their 4G service. In the UK LTE is spread across three widely different bands. i.e. 791-862MHz, 1710-1880MHz, and 2570-2620MHz.

In the Ofcom LTE auctions in early 2013 the following allocations were awarded:

4g-lte-allocations-table-ofcom-2013

In addition to the above, Everything Everywhere, also have use in the 1800MHz (this was decided before the auction). As you can see the allocations are all over the place.

The implications for the end user are you need to ensure your antenna suits the providers service. So, if you get an antenna suitable for EE on their 800MHz band and then change to a service that uses 2.6GHz then the antenna may or may not be suitable; it just depends if you were sensible in the first place and picked an antenna that can cover 800MHz and also 2.6GHz. All of the LTE antenna from Solwise clearly state the frequency bands they support. In fact we’ve made a conscious decision to only stock LTE antenna that are suitable to all three UK LTE bands so you don’t have to worry about choosing which band antenna for which supplier.

Omni or Directional?

The arguments about using omni or directional antenna for LTE are the same as those applicable to 3G. So, use an omni where you DON'T have line of sight where you're relying upon scattering and reflection. Only consider a directional antenna when you can aim directly at the transmitting mast.


Antenna Considerations for 4G/LTE



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