Help my TP-LINK router

I bought a TP-LINK wifi router (TP-LINK) 3MIMO 2.4G 450Mbps Wireless Router CNP-147541 - TinyDeal in March. The transfer rate is 450Mps. I used wifi in my own room while the router is set in living room and there are 3 walls between. The signal sense is strong and it worked perfectly at the first 2 months.
But a trouble started after 2 months. Network speed is unstable as first period and it even cut down at last. I had to reboot the router but it still went wrong.
I kept the warranty so i'm gonna change a new one but i'd really like to solve the problem, at least i need to know the reason. Some people might say TP-LINK's quality had been lower since this year.
So guys what's the problem?

 

This is not CNP-147541 as the retailer states (there is no such router as far as I am aware although it's possible that it is a Chinese naming scheme). This router is known as TL-WR941N v6 and is only offered domestically in China.

Apparently the most recent firmware for this device is TL-WR941N_V6_130318 ans it can be found here but I don't feel comfortable recommending a firmware update for a router that I can't be sure is what I think and an upgrade sourced from a Chinese website (seeing as I don't speak the language).

Check signal strength using inSSIDer (version two preferably as it's available for free). See if there are other networks on the same channel you are using and/or neighboring channels - that can lead to problems on an already overcrowded 2.4GHz band.

So it's either interference (which can't be helped but you can change a wireless channel to avoid the most congested ones) or a hardware issue in which case the warranty replacement is the only possibility.

 

Oh, sorry for that. That's just a model named by wholesaler itself. I post it that way just because i bought it there. And thanks for your answer. I did change a new one but still unaware of the reason. Don't make sure that if it will happen again at this second one.