The Carpcomm ground station network natively supports software-defined radios (SDR). Indeed our Ground Station 1 product is based on an SDR. SDR provides much more flexibility than hardware-only radios because their functionality can be extended by software updates. In this blog post, I'll give a quick introduction to how SDRs work.

I'll assume you are familiar with complex numbers. If not, take a look at the wikipedia page. The most important result we need is Euler's identity:

exp(iθ) = cos(θ) + i sin(θ)

Suppose a satellite transmits a continuous carrier signal at frequency

where ω=2πf and

This is written in complex notation as

Many cubesats uses frequencies near 437 MHz. Digitizing this directly isn't feasible because the sample rate required would be too high. Instead, the signal is first downconverted using a quadrature mixer which produces a new signal

~ exp[i(ω - ω

This is sent through a low-pass filter which removes the ω+ω

Now that the frequency is more manageable, it is sampled by an analogue-to-digital converter (ADC) at a certain sampling frequency (typically 100k to 1M samples/second). Both the real and imaginary parts are converted so that we get complex number samples. The sampling frequency must be greater than or equal to the low-pass filter cutoff frequency to avoid aliasing.

Graphically, the procedure looks like this:

On the software side, the output of the ADC is received as an array of complex numbers. Algorithms can then be used to extract information from the raw samples. At Carpcomm, we have implemented various algorithms for the popular modes used by cubesats: morse code, 1200 baud AFSK (AX.25) and 9600 baud FSK (AX.25). Combined with algorithms for doppler correction, these processors take the raw samples and extract data packets, which are then stored in a database.

The great advantage of SDR compared to hardware-only radios is flexibility. If a new satellite uses an innovative new method such as forward-error correction, all that is needed is to write a new processor algorithm, which can be deployed on the Carpcomm network very quickly because we run all the signal processing in the cloud.

I'll assume you are familiar with complex numbers. If not, take a look at the wikipedia page. The most important result we need is Euler's identity:

exp(iθ) = cos(θ) + i sin(θ)

Suppose a satellite transmits a continuous carrier signal at frequency

*f*. When the electromagnetic wave reaches our antenna, we see a time-varying electric field*E*(t) ~ cos(ω*t*),where ω=2πf and

*t*is time. This field produces a proportional voltage at the input of the radio receiver:*V*(t) ~ cos(ω*t*).This is written in complex notation as

*V*(t) ~ Re[exp(iω*t*)] ~ exp(iω*t*) + i exp(-iω*t*).Many cubesats uses frequencies near 437 MHz. Digitizing this directly isn't feasible because the sample rate required would be too high. Instead, the signal is first downconverted using a quadrature mixer which produces a new signal

*IQ*(*t*) ~ exp(-iω_{tune}*t*)*V*(*t*)~ exp[i(ω - ω

_{tune})*t*] + i exp[-i(ω + ω_{tune})*t*]This is sent through a low-pass filter which removes the ω+ω

_{tune}component. We are left with:*IQ*(*t*) ~ exp[i(ω - ω_{tune})*t*].Now that the frequency is more manageable, it is sampled by an analogue-to-digital converter (ADC) at a certain sampling frequency (typically 100k to 1M samples/second). Both the real and imaginary parts are converted so that we get complex number samples. The sampling frequency must be greater than or equal to the low-pass filter cutoff frequency to avoid aliasing.

Graphically, the procedure looks like this:

On the software side, the output of the ADC is received as an array of complex numbers. Algorithms can then be used to extract information from the raw samples. At Carpcomm, we have implemented various algorithms for the popular modes used by cubesats: morse code, 1200 baud AFSK (AX.25) and 9600 baud FSK (AX.25). Combined with algorithms for doppler correction, these processors take the raw samples and extract data packets, which are then stored in a database.

The great advantage of SDR compared to hardware-only radios is flexibility. If a new satellite uses an innovative new method such as forward-error correction, all that is needed is to write a new processor algorithm, which can be deployed on the Carpcomm network very quickly because we run all the signal processing in the cloud.

Excellent commentsb are placed here grosirtasbrandedwanita!

ReplyDeleteArticles are very nice…Nice comments too.

konteynershop

Articles are very nice

ReplyDeletelduv-wx

ReplyDeleteThank you for this guidance.its really informative for all..

lsxgjg

Excellent comments are placed here gecpx!

ReplyDeleteExcellent comments are placed here imobiliarianiteroi

ReplyDeleteTechnically very well above you said.

ReplyDeletemrstexasamerica

Nice work,keep going. wjdkj

ReplyDeleteEveryone can easily understand the comments junkinyourtrunkshop

ReplyDeleteThe information's are really good and peoples are given superb comments

ReplyDeletelyon-agenda

Nice to read all post and more innovative

ReplyDeleteonlyasiansforme

ReplyDeleteArticles are very nice…Nice comments too.

bobmehrpharmacies

Thanks for the comments which the peoples are give here michaelkorsoutletq

ReplyDeleteIt is very nice and thanks for sharing it mircenbiotech

ReplyDeleteThose post in the blog are very useful….. ofthedarkness

ReplyDeleteAll the information's are more innovative

ReplyDeletepikkukaupunkilainen

The information's are useful for all the people

ReplyDeleteoceanlawpublishing

Technically very well above you said.

ReplyDeleteiteratesolutions

Nice Post and all information's are used to everybody

ReplyDeletebognarrudolf

All the post are good and the people nice comments to giving all post

ReplyDeletehzsdxc

Thank your for your great post thegreattequilashootout

ReplyDeleteI am so excited while I read all the comments.

ReplyDeleteIkzhiBo

Thank your for your great post solnejeskyne

ReplyDeleteI am so excited while I read all the comments.

ReplyDeleteAishopeacademy

Really nice,everybody like All the Post

ReplyDeletealkinserver

This comment has been removed by the author.

ReplyDeletetantovincoio super comments are posted here

ReplyDeleteMust be appreciated for this article

ReplyDeletencaafootballclinics

ReplyDeleteits really informative tutorial. Thank you for this tutorial . artchartrons

event-safari We can use this in our blog

ReplyDeleteSimply super comments are posted here.

ReplyDeletebabblein

All this comments are wonderful and we can implement in our life nagasaki-npo

ReplyDeletePeoples are giving really nice comments for this article

ReplyDeleteyeyige

Its very useful if every one should follow this

ReplyDeleteaaa-stone

Simply super comments are posted here.

ReplyDeletedsn027

All of them can easily understand this comments sundoz

ReplyDeleteThank you for this tutorial.its really informative tutorial. gxshangsi

ReplyDeleteAfter read all the comments gets so excited xhdeutz

ReplyDeleteReally nice,every should like this

ReplyDeletegemofive

Thank you for this guidance.its really informative for all.. nigerianmusicfactory

ReplyDeleteiias2013 Its good one,every should like this

ReplyDeletePeoples are giving the wonderful thoughts for all comments

ReplyDeleteredhouselanescotland