signal bandwidth

[feras]

hello everybody ,
i am working on lte over fiber simulation , and i have a question if anybody can help me
how can i set the lte signal bandwidth ( 5 to 20 MHz )

[Dr. Dhiman Kakati]

Hi feras,
in case of LTE, greater the bandwidth, the greater the channel capacity. There are different channel bandwidths LTE are: 1.4 MHz, 3 MHz, 5 MHz, 10 MHz, 15 MHz, 20 MHz. If the subcarriers spacing is 15 kHz, i.e. the LTE subcarriers are spaced 15 kHz apart from each other. To maintain orthogonality, this gives a symbol rate of 1 / 15 kHz = of 66.7 µs.
Each subcarrier is able to carry data at a maximum rate of 15 ksps (kilosymbols per second). This gives a 20 MHz bandwidth system a raw symbol rate of 18 Msps. In turn this is able to provide a raw data rate of 108 Mbps as each symbol using 64QAM is able to represent six bits.
accordingly you can choose as per the design.

Regards,
Dhiman

[feras]

hi Dhiman Kakati
thank you for ur reply but please i didn’t understand the last section of ur answer and how can i translate that in optisystem

[alistu]

Hi Fera,

Signal bandwidth is very much dependent on the bit rate of the system you use and the modulation scheme you adopt. However, you can use filters at transmitter set at the desired bandwidth, but if the signal bandwidth is far more than the filter bandwidth, the signal may be degraded.

Regards

[feras]

hi alistu
thank you for ur reply but i want to set the bandwidth for the signal without using filter in the transmitter , i am using 16QAM and 64QAM and QPSK modulation in my simulation < so how can i do that

[alistu]

i think the signal bandwidth pretty much depends on the modulation scheme. If you have already chosen the scheme and still you are not getting the bandwidth you expect, then I can only think of reducing the bit rate. If you are trying to reproduce a paper results, can you please introduce the it to me?

[Gokul Boro .]

Hi everybody, to the extent I know (may be I am wrong, I am not sure) if the number of subcarriers is increased then the width of each subcarrier will be narrower, i.e., there will be no increase in the bandwidth of the overall system bandwidth. The number of subcarriers does not affect the system bandwith. If it is ok, then now how can the bandwidth be changed? As stated aove in the comments, it can be changed by changing the data rate. But I didn’t understand how changing the data rate can change the bandwidth.

[alistu]

Hi Gokul,

As we all know, Hz is inverse of ‘second’, which means if we have more changes in one second, then we have a higher frequency. On the other hand, when the bit rate is increased, it means more bits are being transmitted in one second, so there are more changes in time unit and therefore, the frequency is higher.

Regards

[feras]

thank you all for ur interested ,
i also think that the signal bandwidth depend on modulation scheme and data rate but how can we set that in the simulation? that is the question

[alistu]

You’re welcome Feras. However, I have given my suggestion at reply #27956. A part of this signal bandwidth cannot certainly be reduced (there is nothing to be done about it) and a part may be reduced with modulation scheme (For example, using multilevel modulations such as 64-QAM instead of 4-QAM; even though error might increase sometimes).

Regards

[Author]

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