I hope you can help me with some questions/doubts I have about the LimeSDR Mini:
Q1: I’ve been wondering if the LimeSDR Mini have less capabilities than the LimeSDR, since in the Comparison Table, it’s shown that the Programmable Logic Gates for the LimeSDR is 40k and for the LimeSDR Mini is 16k and I don’t know if that means that the LimeSDR Mini can not perform some actions that the LimeSDR can.
I have only a very basic knowledge about FPGA and the electronics components and I’d like to know if I will be able to do with the Lime SDR Mini the same projects that I could do with LimeSDR, obviously expect for the bandwith and the number of channels.
Some projects I want to do are related to UMTS, LTE, GSM and Wifi and I also use the GNURadio library, Python and C++.
Q2: Besides, I’d like to know if it is possible to use the LimeSDR Mini with a USB 2.0, I’ve seen some people using it with a raspberry pi. Will I need an special conector/adapter to do that?
A1. This likely doesn’t matter unless you plan to do something with the spare logic gates in the LimeSDR FPGA, e.g. implement your own custom DSP blocks.
A2. LimeSDR Mini has worked fine in testing when I’ve used it with a Raspberry Pi, which as you note is USB 2.0. So far this has been just with transmit or receive. I guess in full duplex use and/or at higher sample rates USB 2.0 may start to become an bottleneck and/or supply insufficient power. In the case of the latter you could probably use an external power supply via a split cable.
Thanks for the responses, however I still have some doubts about the Mini version:
Q3: When you says “implement your own DSP blocks” (from A1) you mean in the firmware for the FPGA (change the FPGA software?) or something like that? or this has to something with the processing blocks that can be implemented in the library gnuradio using C++?
Q4: I’d like to know if the LimeSDR Mini can be used for the same applications than the LimeSDR, as it is shown in this link (website for LimeSDR):
I have this doubt because in the similar website for LimeSDR Mini is not mentioned for what applications can be used and I know that the LimeSDR Mini uses a smaller FPGA, however I don’t know if this could be a limitation. I’d like to use the Mini version for LTE, Wifi, etc and I have doubts if that is possible (specially for LTE)? (website for LimeSDR Mini):
I’ve seen that the Mini version can be use for GSM, but I couldn’t find and LTE example, only for the LimeSDR I’ve seen that this is possible (LTE station).
Sorry if this question is similar to Q1, but I’d like to be sure.
Unless you have spent at least 2 years of your life design FPGA circuits (gateware), I would ignore the number of logic gates as a figure of merit in choosing a SDR device.
A FPGA is an array of low level logic. So if the circuit, which is really what FPGA’s are used to design, can be constructed from a several thousand 4000 series (4–15 V) or 7400 series (5V) integrated circuits then it can be implemented in an FPGA. The four big advantages of a FPGA’s are that you do not need to hardcode your design forever at the time of manufacture (it can be updated, tweaked, and improved after the product has shipped - it is a lot like being able to physically redesign part of the PCB), your power requirements are much much lower that for several thousand individual IC’s (usually they run at 1.0, 1.2 or 1.8 or 3.3 volts, so that will use less power anyhow), the physical space required for several thousand individual IC’s would make products quite heavy and bulky to ship and finally the ability to add new features that were never even concevied of at the time of manufacture. It is only really that last part that will benifit from unused logic inside the FPGA.
A really bad FPGA design can destroy physically hardware, so I would never see using the LimeSDR/mini as a good starting platform to learn gateware design.
So if you step back from the FPGA for now, at a fundamental level an SDR is just:
antenna<->ADC/DAC<->Computer
or
antenna<->filter<->tuner<->filter<->ADC/DAC<->Computer
or
antenna<->galvanic Isolator<->filter<->LNA<->tuner<->filter<->ADC/DAC<->Computer
or
…
That last “<->” in each of the above basic SDR’s designs includes the FPGA (if there is one) and the USB/PCIe data transfer bus. Most people will never implement any custom logic inside of a FPGA to use an SDR.
LTE has scalable carrier bandwidths from 1.4 MHz to 20 MHz.
If you look at the crowdsupply “Comparison Table” the LimeSDR mini supoorts 30.72 MHz of bandwidth, which should be fine. Not finding pre-existing examples for a new device is not uncommon.
If you are fixated on using USB 2.0 High Speed then that would limit your data throughput to a maximum of 280-320 Mbps depending on chiipset. On paper that would be ~11MHz maximum bandwidth in one direction only (with bit packing. So you would get less than half that if you transmitting and receiving at once (USB 2.0 is half-duplex) and if you plan on using RPi hardware half that again. Is LTE possible with RPi hardware, when you factor in minimum RX filter bandwidth of 1.4 MHz and minimum TX filter bandwidth of 5 MHz my gut says:
the RPi would be standing just on the no way side of the maybe.
