This question comes up so frequently that i was surprised we didn't have an area on our site dedicated to answering this in general. I will attempt to do this but caveat this will be a WIP and i will edit/ update as needed. For now the quick and generic answer and if you have any specific questions on variations to this please ask.
The question is if you have a wireless device typically 3G or 4G data card, modem or cellphone etc. what can you do if your the signal keeps dropping or is otherwise too weak not to connect at all.
The simple answer is "It depends". This is not the answer most people want to hear but it really does depend on a variety of factors. For one it depends on the device itself and what data protocol it's using EVDO, HSxPA, WiMax, frequency band 800mhz, 1900mhz, 900mhz ISM, 2.4Ghz ISM, 5.8GHz ISM/UNII, 3.65GHz Wimax, 2.5Ghz WiMax etc etc etc But it also depends on geographic and topographic (spatial) factors etc. But this is not the purpose of this post. This post is what can you do about it:
- Replace the Device: This is usually the simplest and cheapest option. Many people don't realize that not all wireless radios are created equal. Just as in cellphones, different data card modems from different manufacturers have different radio specifications. One important parameter of the radio is the receiver sensitivity which is the minimum signal a receiver can detect while maintaining a certain bit-error-rate (the higher the bit error rate the lower the throughput for data protocols --- for voice this could lead to blocked or dropped calls).
- Relocate the Device: Ok this sounds like a dumb suggestion since i'm sure by now you have tried to move it about However by this i mean completely relocating it up to hundreds of feet which sometimes is enough to pick up a good signal. Well this works really for data devices. Heres how: Convert the data protocol to a wireless protocol that is easier/cheaper to distribute. Typically convert to 802.11a/b/g/n WiFi or 900mhz ISM. For example use something like a Cradlepoint Router to convert cellular 3G EVDO/HSPA and 4G Mobile WiMax to 802.11b/g/n. Then use a long range point-to-point or point-to-multipoint wireless bridge to connect the area where the modem is situated to where the data connection is needed. Sometimes this requires placing the device outside the building which brings up other issues such as protecting against environmental issues or access to power. All these are easily solvable using ruggedized enclosures and remote power devices such as solar PV arrays, Wind power systems and high capacity battery backup systems. It all depends on how much you need to be connected.
- Add high gain antennas: In addition to high gain if you are trying to pick up a weak signal it's often better to get a directional antenna that can focus the radiation field to the direction where the best signal is originating from. One common mistake we encounter though is users not realizing that cable losses can often totally wipe out any benefit the antenna would bring. So keep cables short and more importantly get the correct cable. Radio frequency systems for other than Cable TV typically uses 50 Ohm cables and connectors vs 75 Ohms for CATV systems. Impedance mismatch resulting from using the wrong cable leads to signal loss.
- Add RF bidirectional amplifiers -- two general types exist
- Direct Connect Amplifiers: These directly attach to the device and boost the input signal from the base-station tower as well as the output signal from the data card, modem or phone. By directly attaching the radio to the amplifier we realize the maximum power transfer. We need to take special attention to losses through cables. To attach multiple device you could use a splitter/combiner but the insertion losses are usually large and can be as much as 3dB (recall 3dB loss is halving the power).
- Repeaters: Rather than directly attaching to the device these re-radiate the boosted signal allowing multiple devices to concurrently be boosted. However the coverage area is often limited (often by FCC regulatory limits which would be violated if the manufacturers tried to design repeaters to cover arbitrarily large areas).
- Use a Generic Access Network (GAN) System: This is typically only for cellular data and voice protocols. A simple definition of a GAN is a system that transfers voice and data to an IP system and uses IP (Internet) for backhaul. Two examples of this are Ulicensed Mobile Access Networks (UMAN) such as T-Mobiles Hotspot at Home and femtocells from Sprint, VZW, AT&T. Clearly if your goal is to enable data in a remote location you would not have Internet but this still is useful for a variety of scenarios such as mobile M2M applications that travel to remote sites with weak signals or where you can use a PTP wireless bridge to create the backhaul that the femtocells need. There's also another advantage of GAN where available and this is connection plans are usually highly subsidized by the carrier --- this is partly to encourage users to migrate to this since it eases the load on macrocellular networks.