LTE and DL transfer rate
In the continuation of the recent post on LTE in Moscow, a brief explanation of how the width of the spectrum and the “megabits” in LTE are related, as well as what the speed DL can depend on, in addition to the width of the spectrum. On the example of Downlink, FDD.
The picture shows how the base resource allocated to the user is formed in the radio interface - the Scheduling Block (SB). One SB consists of 14 OFDM symbols in a time domain (Time Domain), with a total duration of 1 ms (1 TTI - Time Transmission Interval in LTE, unlike, for example, WCDMA, where 1TTI = 10 ms or now 2 ms) and 12 subcarriers in the frequency domain (Frequency Domain), 12 kHz wide.
One OFDM symbol can transmit, depending on the modulation type, 2, 4 or 6 bits of information (QPSK, 16QAM or 64QAM, respectively). The modulation will be selected from those supported by the mobile terminal (UE) depending on the quality of the radio conditions.
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Suppose we use 64QAM, 6 bits / symbol, for a total of 6 [bits] x 14 [characters] = 84 bits / ms can be transmitted over a duration of one sub-frame on one subcarrier. Further, 12 x 84 [kbps] = 1008 kbps, well, or one megabit roughly, for one SB. The picture shows how SB users can be heard. The 20 MHz wide spectrum contains 100 SB (there are actually 110-20 MHz / 180 kHz there, but 100 are available, 10 are used for isolation between the ranges), so if the user is alone, he can get no more than 1008 kbit / s x 100 = 100.8 Mbps. Or, for example, a spectrum of 1.4 MHz fits 6 blocks, that is, 6.048 Mbit / s in a similar situation.
This is all on one antenna, without using MIMO (Multiple Input - Multiple Output) modes, which by using spatial multiplexing of data streams (Spatial Multiplexing) allow transmitting not one, as in SISO (Single Input - Single Output), but 2 and more data streams, for example, MIMO 2x2 (2 transmitting antennas on a BS, 2 receiving antennas on the terminal) allows to increase these 100 megabits described above to 170. The question is what kind of terminal is it.
The picture shows how the base resource allocated to the user is formed in the radio interface - the Scheduling Block (SB). One SB consists of 14 OFDM symbols in a time domain (Time Domain), with a total duration of 1 ms (1 TTI - Time Transmission Interval in LTE, unlike, for example, WCDMA, where 1TTI = 10 ms or now 2 ms) and 12 subcarriers in the frequency domain (Frequency Domain), 12 kHz wide.
One OFDM symbol can transmit, depending on the modulation type, 2, 4 or 6 bits of information (QPSK, 16QAM or 64QAM, respectively). The modulation will be selected from those supported by the mobile terminal (UE) depending on the quality of the radio conditions.
')
Suppose we use 64QAM, 6 bits / symbol, for a total of 6 [bits] x 14 [characters] = 84 bits / ms can be transmitted over a duration of one sub-frame on one subcarrier. Further, 12 x 84 [kbps] = 1008 kbps, well, or one megabit roughly, for one SB. The picture shows how SB users can be heard. The 20 MHz wide spectrum contains 100 SB (there are actually 110-20 MHz / 180 kHz there, but 100 are available, 10 are used for isolation between the ranges), so if the user is alone, he can get no more than 1008 kbit / s x 100 = 100.8 Mbps. Or, for example, a spectrum of 1.4 MHz fits 6 blocks, that is, 6.048 Mbit / s in a similar situation.
This is all on one antenna, without using MIMO (Multiple Input - Multiple Output) modes, which by using spatial multiplexing of data streams (Spatial Multiplexing) allow transmitting not one, as in SISO (Single Input - Single Output), but 2 and more data streams, for example, MIMO 2x2 (2 transmitting antennas on a BS, 2 receiving antennas on the terminal) allows to increase these 100 megabits described above to 170. The question is what kind of terminal is it.
Source: https://habr.com/ru/post/140302/
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