I have a very popular device (a smartphone) which works on 3G: TD-SCDMA 1880/2010 standards and 4G: LTE 1900/2300/2600. I want to turn it compatible with 3G: UMTS 900/2100 or, if not possible, with 4G: LTE 1800/2100.
To solve that two things came to my mind.
The first one consists in the fact that there is already another device which is absolutely identical to mine but with the antenna that I desire. Then, I suppose I can try to buy the other's model antenna and try to solder it by myself, but I have no experience dealing with such small circuits. If I could do that, I think I would also need to reprogram the device, to recognize its new antenna.
The later is to try to design a board to successful read and then transcripts and generates a signal on a standard that my device can read. Since, relative to 3G, the devices use not only different frequencies but also standards, is it hard to transcript the signals? It would be a lot easier to deal with the 4G possibility? Are only the frequencies different in 4G and is it possible to convert them without problems?
Sorry if the question seems a little abstract. I think is very probably that either ideas are not cost efficient and would demand tons of work. So I wanted to check with all of you if that worth further researches on those possibilities and which one seems better. Also, where can I learn technical parameters about those telecommunications standards?