How to combine signals with different sampling times?

Question

Glo 2015-1-2

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https://ww2.mathworks.cn/matlabcentral/answers/168723-how-to-combine-signals-with-different-sampling-times

回答： Asfand Haroon 2022-7-26

Hello all,

I am designing a communication system, in which two channels must be combined and sent over the same AWGN channel, and then received at the receiver. I am using BPSK mod/demodulator block from Comm. sys. Toolbox.

Both channels have same Bandwidth (100 kHz), but different carrier frequencies (one sided local oscillator of fc_1 = 22.4 MHz and fc_2 = 23.9 MHz respectively). Moreover, my carrier frequencies are sampled sinusoidal signals at 4*fc:

T_sample_fc_1 = 1/(22.4 MHz *4) = 11.16071429 e-9; T_sample_fc_2 = 1/(23.9 MHz *4) = 10.46025105 e-9;

So, I have to up sample/interpolate the base-band signals with a different up sampling factor, i.e

T_sample_baseband = 1/(100e3); For 100 kHz base-band signal

Upsampling factor for signal 1 = [1/100e3]/[1/(4*22.4e6)] = 896; Upsampling factor for signal 2 = [1/100e3]/[1/(4*23.9e6)] = 956;

Now, the problem starts when I try to combine these two channels to be sent over the same channel.

I have tried using the following blocks to combine them:

- Add - Merge - Create Bus

Simulink returns an error stating that the sample time of both signals are different so they cannot be combined.

I cannot use a rate transition block (without losing deterministic behavior of one of the signals) to make the two sample times equal, because the two sample times are not a rational multiple of each other (like 0.1 s and 0.2 s for example).

I have been stuck at this problem for about 3 weeks, and cannot find the solution to it. Any guidance/recommendation will be highly appreciated. Thanks!