How the selected network affects the Internet speed of the phone, or the problems of LTE networks in the CIS region

    Kcell and tele2

    For wired internet, the speed promised by the provider is the bandwidth of the “last mile” channel. Usually, the real speed for wired Internet providers is close to the declared one. With regard to mobile networks, the “last mile” is a radio channel, and the speed does not always correspond to that stated in the 3GPP standard (100 - 150 Mbit / s). Below is information on factors affecting the speed of mobile Internet in an LTE network.

    1. Category of mobile device.
    CategoryDL speedNumber of antennasUL speed
    Category 110.3 Mbit / s15.2 Mbit / s
    Category 251.0 Mbit / s225.5 Mbit / s
    Category 3102.0 Mbit / s251.0 Mbit / s
    Category 4150.8 Mbit / s251.0 Mbit / s
    Category 5299.6 Mbit / s475.4 Mbit / s
    Category 6301.5 Mbit / s2 or 451.0 Mbit / s
    At the time LTE technologies were launched in the CIS, mobile devices were sold with Category 4. support. If an Internet provider acts as a data channel, then the width of this channel at the telephone input is 150.8 Mbit / s.

    2. Bandwidth. Each of the antennas of the mobile device can receive a signal with a frequency bandwidth of 20 Mhz. The tower can highlight frequency bands 1.4 MHz, 3 MHz, 5 MHz, 10 MHz, 15 MHz and 20 MHz wide. To separate the bands among themselves, 10% of the bandwidth (except for the band with a width of 1.4 MHz) act as a boundary zone, information is not transmitted over them. Thus, the maximum width of the frequency channel of a mobile device is 2 * (20Mhz * 90%) = 36 Mhz.

    3.Resource block ( RB )- unit of the transmission resource in the LTE channel, consisting of 12 sub-frequency intervals occupied during the time interval ( TS - 0.5 ms). The total frequency band RB is 180 kHz. Therefore, the number of RBs in the maximum frequency range is 36Mhz / 180kHz = 200.

    4. The resource element ( RE ) is the smallest data transmission unit in DL and UL mode. The required frequency band is 15 kHz. During TS - 0.5 ms, the antenna can transmit 7 REs in the range of 15 kHz (in case of poor conditions, this number is 6). 1 RB = 12 * 7 = 84 RE. At the maximum channel width, 200RB * 84RE = 16800RE can be transmitted for a TS time of 0.5 ms.

    5. Modulation. Depending on the type of modulation, a different amount of information can be transmitted in one RE . With QPSK modulation type - 2bit; 16QAM - 4bit; 64QAM - 6 bit. The choice of modulation depends on the signal level of the coverage. At 64QAM speed: 16800RE * 6 * 2000TS = 201600000 bit / s = 201.6 Mbit / s. 25% of all transmitted information is used to control the physical level and data transfer level. Therefore, the resulting speed is 201.6Mbit / s * 75% ~ 150Mbit / s

    RB, RE

    BUT, in the CIS there is no operator who can simultaneously allocate 2 bands of 20 MHz and the signal quality is poor. Additional overhead from IP packets, temporary interference in the radio channel, the influence of other subscribers nearby only worsen the speed declared in the standard. If the operator has a spectrum of 15 MHz available, then only three people can simultaneously download (be in the RRC_CONNECTED state ) at a speed of 18.3Mbit / s within the same tower, and this with an ideal signal.

    throughput
    (the graph shows the data transfer rate of one antenna depending on the selected range and type of modulation).

    Technologies such as carrier aggregation ( CA) allow the subscriber to select several spaced frequency bands from the available operator, while (the amount of information) / Hz remains constant. Features of economic trends and rules in the post-Soviet space are forcing LTE network owners to increase the number of subscribers by expanding coverage. In developed countries, operators have similar frequency bands, but when planning, they use microcell, picocell, femtocell to improve signal quality. Now in the CIS countries, existing LTE networks do not have much better performance than HSDPA networks. The only mechanism to increase the speed of the Internet is to improve coverage and optimize the use of radio resources.

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