We launched LTE-Advanced: 100 Mbit / s barrier per subscriber has been overcome

Areas where you can start YouTube parties. At least I have no other ideas for recycling the channel. The whole territory of Moscow and a little near Moscow region.

The developers of LTE-Advanced set out to provide speeds of up to 1 Gbps . It is clear that such speeds are achievable so far only in ideal laboratory conditions. But the 110 Mbit / s we received in our commercial 4G network in Moscow is impressive. Moreover, it did not require any special efforts on our part - we simply combined the resources of two frequency bands.


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One of the most important additional advantages is the redistribution of mobile network load between the ranges. You will feel it as the acceleration of the mobile Internet, even in difficult areas, in particular, in the premises, as well as in loaded cells, for example, in traffic jams.

Increase bandwidth

The 3GPP LTE 8 standard allows the subscriber to get speeds of only up to 150 Mbps with a bandwidth of 20 MHz. There are two methods to achieve the required bandwidth. The first is the complication of antenna systems and the inclusion of Multiple Input Multiple Output (MIMO) mode. Usually, the MIMO order is indicated, for example, MIMO 4x4 means that 4 independent streams of information are transmitted from four transmit antennas to four receive antennas. This is roughly the same as if you had 4 SIM cards connected in a bridge.


Figure 1. MIMO 4x4.

The second method is the expansion of the spectrum by combining several frequency bands (Carrier aggregation):

So, we have two options:

• MIMO (multiple independent streams)
• Carrier Aggregation

In current networks, MIMO 2x2 is predominantly used. Using higher MIMO modes, for example, MIMO 4x4 or 8x8, is currently not possible, because Mobile terminals with high-order support MIMO exist so far only as prototypes and look like big routers with remote antennas. For this reason, it is not possible to receive 1 Gb / s at 20 MHz by complicating antenna systems in existing LTE networks. In theory - yes, in practice - unreal. Naturally, we immediately refused this bright thought.

Now expanding the spectrum. The 3GPP standard defines the following LTE bandwidth options: 1.4, 3, 5, 10, 15, and 20 MHz. Unfortunately, the maximum bandwidth is limited to 20 MHz.

Does this mean that it is impossible to use the frequency resource in more than 20 MHz? No, does not mean. Channel aggregation - Carrier Aggregation (CA) helps to extend the frequency resource. The functionality works for both LTE frequency division (FDD) and time division (TDD). Since most networks in Russia are FDD, consider the CA using this example as an example:


Channel aggregation in LTE FDD

Suppose a base station (eNodeB) uses two frequency channels of 20 MHz each. For subscribers with phones of R8 / R9 releases, these cells will look like 2 separate cells and they can use only one of them. For the subscriber, the owner of the LTE-Advance device, the picture will be somewhat different.

Suppose we are registered on a cell and download a very heavy file. For us, this cell (frequency channel) will be Primary. The base station determines that we need more resources and assigns a second cell, called the secondary cell. The phone, combining the resources of both cells, can receive up to 300 Mbit / s (2 frequency channels transmitting at 150 Mbit / s).

Different LTE frequency bands can be aggregated, starting at 1.4 MHz and ending at 20 MHz, but only 5 carriers and up to 100 MHz with a total spectrum width. The number of aggregated channels in UL and DL may differ, but the number of aggregated UL channels will always be less than or equal to the total number of carriers in DL.

Spectrum aggregation options

There are several options for aggregation of the spectrum:

• Intra-band, contiguous or aggregation of adjacent ranges. The easiest option, but it is only suitable for operators who have more than 20 MHz of continuous spectrum, which is not often.
• Intra-band, non-contiguous or aggregation of non-contiguous spectra. A more interesting option, because allows you to combine small pieces of the spectrum, divided among themselves.
• Inter-band, non-contiguous or aggregation of spectrum from different ranges. This type of channel aggregation will allow Russian operators to combine the frequencies issued to them in the 800 and 2600 bands, thereby increasing their maximum speeds.

However, not all LTE frequencies can be aggregated with each other. Due to the fact that a lot of combinations can be invented, a large number of possible frequency combinations are defined in the 11th 3GPP release. The tables below show the frequency ranges and their possible combinations for Russian reality.

Table 1. LTE frequency ranges for the RF.

Range number	Range name	Uplink frequency range (MHz)	Downlink Frequency Range (MHz)	Bandwidth (MHz)	Duplex Spacing (MHz)
3	DCS 1800	1710-1785	1805-1880	75	95
7	2.6 GHz	2500–2570	2620-2690	70	120
20	Europe 800 EDD	832–862	791–821	thirty	-41

Table 2. LTE frequency band combinations for CA

Type of CA and duplex type	CA configuration	Maximum aggregated bandwidth (MHz)	Max number of CC
Intra-band contiguous Fdd	CA_7C	40	2
Inter-band Fdd	CA_3A_7A	40	1 + 1
	CA_7A_20A	thirty	1 + 1

These are the aggregation of two bands in the 2600 MHz band (Band 7 + Band 7), the aggregation of two bands in the 1800 MHz and 2600 MHz bands (Band 3 + Band 7) and the band aggregation in the 800 MHz and 2600 MHz bands (Band 20 + Band 7) . The list of possible configurations is extended from release to release, for example, in release 12, it becomes possible to aggregate UL. In the future, Russian operators will be able to aggregate bands from 3 ranges, thus obtaining Band 20 + Band 3 + Band 7 combinations.

Russia

Consider the actual question for Russian operators: is it possible to use the Carrier Aggregation for the 800 MHz band to use a completely non-standard 7.5 MHz band?

The answer is no. There are several reasons for this. First, despite the fact that the standard sets the bands at 1.4 and 3 MHz, they are not defined for Band 20 (LTE800). Secondly, the aggregation of two bands in Band 20 is also not possible.

Thus, at the moment, operators can not fully use the 7.5 MHz, issued by the regulator. It may be available in the future, but now there are no plans to standardize the 7.5 MHz band.

UPD: In Russia, according to the licenses obtained for LTE networks, operators can use the 10 MHz band in the 2600 band and 5 MHz in the 800 band

Carrier Aggregation has a lot of potential, but the main deterrent is the need for mobile terminals to support this functionality. Moreover, in addition to simple support, the phone should also be able to aggregate precisely our ranges. It is expected that in Russia such phones will begin to appear in late 2014 - early 2015.

What does all of this mean?

• Unloading base stations. Now, for example, a very common situation occurs when the same base station operates on transmitters in the 800 and 2,600 MHz bands. All subscribers with new devices are sitting at 2600. 800 is almost empty. This idle power can be distributed to subscribers, as an additional band to their already open connection.
• Acceleration of the mobile Internet. Given the expansion of the band and the emergence of a secondary-cell for the subscriber, the connection speed and its stability will increase. Especially - in difficult conditions when loading the cell.
• Increased signal penetration. The range of 800 MHz is physically the best penetrating power compared to the 2600 MHz range. So now, inside the premises where you previously saw only the GSM 900 signal, there is a chance to catch the LTE 800 network.
• Increased compound stability. Now subscribers will be distributed between the cells only in case of overload of a specific range. In LTE-A distribution will be done immediately, which will significantly optimize the load. A very rough example: there were two physical cells with their interfaces, now they are combined into one virtual one with a common interface.

What's up with the launch?

The launch took place in Moscow. At the moment, you will not be able to enjoy all the pleasures of high speed due to the fact that you need devices that support LTE-A. Moreover, in our supporting Carrier Aggregation for specific Russian bands Band 20 (800 MHz) and Band 7 (2600 MHz). Fortunately, our frequencies meet European standards, so next year we can expect the appearance of the necessary terminals.

To launch LTE-A on the basis of the LTE network, we updated the equipment of some base stations (reducing the transmitters 800 and 2600 ranges into one digital module). In other cases, the case was limited to installing new firmware and updating configurations.

Now only one phone with LTE-A support in the required standard is known - this is the Samsung Galaxy Alpha, and by September 18 it should be on sale. According to forecasts, in 2015, most of the new phones will have this functionality out of the box.