There are cell amplifiers that work the same way the bullet does but on cellular modes and frequencies. Commonly called cell phone
boosters, they're bi-directional amplifiers that re-broadcast the cellphone network signals through an antenna
typically mounted inside a cabin
or building, or vehicle. They also have a second antenna, usually mounted outside and that is used to connect to the cellsite tower. The consumer grade BDA's ( bi-directional amp) are often crap and more often installed improperly with no separation between the donor and server antennas.
3G & 4G are primarily data rate standards, that can be met using different technologies and on various frequencies. Just in the USA, the different carriers are using CDMA or UMTS for 3G service
. The CDMA carriers are using an enhancement called EV-DO which produces a 1.25MHz wide CDMA channel. UMTS carriers produce a wide band cdma signal that's 5 MHZ wide. They are used on whatever frequencies the carrier has including 850MHz, 1900MHz, 2100MHz, 2400Mhz, etc. Then there's the 4G service
which is also a wide band cdma channel, but can be adjusted from 1.2 to 20 MHZ wide depending on bandwidth the carrier owns. ATT & VZ have most of their LTE on 700MHz and are shiftiing more to the other bands they own as 4G service replaces 3G services. The same occurs around the world and different frequencies are used everywhere. Just in the USA, if you didn't know your carrier, you would need multiple amps to cover all of them. Some of the amps are dual band and cover the traditional cellular 850 band and the common 1900 band, but 700MHz is harder to find, and not likely in the same box as the others. On top of all that, the FCC is clamping down on the manufacturers of the amps because there are some poorly designed one's that easily start oscillating from their own output. This causes major network noise
for the carriers and interferes with everyone in the area. Wilson is a responsible company that makes these devices with anti-oscillation circuitry and has had them approved even for the 700MHz LTE band where the FCC has been much more restrictive in the legal
sales of these devices for consumers.
You might find better support in more places with a MiFi device that converts the 3G/4G cellular signal to standard WiFi. No chance for oscillation and the device is controlled like a regular cellphone so it isn't an uncontrolled noise
source. I have one that I use for mobile computing and it has connections for external antennas which would help, but I've never really had many problems with the internal antennas, and I have no idea if it would work on any asian networks.
Your cellphone carrier can assist and may have other options that would work for you, but several countries will be quite different from each other.