A few of the suggestions involve higher gain antennas, more power, larger coverage area. Beware of such solution.
While they seem intuitively as good solutions, but there are inherent problems.
The reason these devices have simple antennas is to assure that the area near the wireless device is flooded with signal. The higher the gain of an antenna, the more concentrated the signal is in some directions, at the expense of signal strength (coverage) in other directions. A high gain antenna doesn't add overall power, it changes the way coverage is distributed. If the gain is high enough, the only coverage would be in the plane created perpendicular to the antenna (for vertical antennas). High gain antennas do not increase overall power, they simply change the way power is delivered spacially, which may or may not produce desired results.
Higher overall power is also problematic. It will create higher signal levels at greater distances, not necessarily improving the reception of the device, but increasing it's impact on other wireless coverage areas.
The best design to achieve wireless coverage over a broad area is to use multiple CELLULAR coverage access points, without creating a lot of overlap. The simplest way to achieve this is to use a wired 'backbone' or wired network to interconnect wireless access points. There is a reason for this.
The way wireless works is simple to understand. A node in the wireless coverage area transmits, other nodes decode a signal and do NOT transmit simultaneously. Ideally, all nodes should be able to detect transmissions from other nodes, to avoid trashing packets by transmitting simultaneously. This is 'carrier sense' and a node will NOT begin transmitting if it senses a carrier.
The second principle is 'multiple access' which is basically that several nodes can access the channels to achieve connectivity, but they use random wait times after sensing a carrier, and hopefully reduce the probability of two stations starting to transmit at the same time, which trashes packets. After such interference, and with no handshake response, a node will again wait some random time before attempting again. Combined with 'carrier sense' the theory is that several stations can use a single channel, to connect to an access point, because they can hear (sense) each other and reduce the chance of simultaneous transmissions (and interference).
Now, increase the coverage of some access point with higher power, and a bigger antenna. Here's what happens.
1. When the access point transmits, all stations that can sense the carrier and with higher power and a bigger coverage area, more stations or nodes are affected and refrain from transmitting. Yes, the frequency hopping nature of 802.11b/g helps in channel sharing, but if nodes are all trying to access the same access point, they are all going to follow the same frequency hopping sequence. Only nodes accessing different access points will be using a different sequence.
2. When a user node transmits back to the access point, if other nodes are also using that same access point, but cannot detect each other (like an AP in the middle of an area, with big signal and antenna, but nodes are at different ends of the coverage area). The nodes that cannot detect (hear) other nodes using the same higher power, higher coverage AP, they will very likely start transmitting while another node is also transmitting, creating interference, and REDUCING the effectiveness of the wireless coverage area.
Hidden nodes is the term used to describe this, it means Node A cannot hear Node B, but the AP node can hear both. Expand this to multiple nodes that cannnot detect each other, but can detect this overpowered, high coverage AP, and you can create a situation where throughput is radically compromised.
This is why cellular telephones use cell sites, instead of putting their antennas on mountain tops or tall towers where many cell phones could potentially access the cell site, but can't detect each other, and the cell site will hear (detect) numerous cell phones, and may quickly overlead it's capacity to handle calls.
The whole idea of cellular design is to avoid overlap, provide good coverage IN the cell, but avoid overlapping coverage between cells (reduce it) and interconnect the cell sites on a backbone (wired or wireless between cells).
You can achieve this cellular design in a home, or business, by using multiple APs with cellular coverage, that service nodes (users) that are in closer proximity, so they can all work together to avoid interference. This is the CSMA part of CSMA/CD that is used on ethernet networks. The /CD part means 'carrier detect' while transmitting, and this is only possible with devices that can HEAR packets at the SAME time as they are transmitting. 802.11b/g systems are half duplex, that is, they are either transmitting or receiving, but not both, hence the best we can do is Carrier Sense, and Multiple Access, but not Carrier Detect while transmitting.
Large antennas do not really solve coverage problems in a 3-D world. They work okay on a flat plane (an office floor, or one story house) but the antenna pattern will create problems of poor coverage in some areas, and extended coverage in areas that you really don't need or want in your wireless network.
Large power also just increases the cell overlap, introducing a potential problem with other nearby wireless coverage area.
If you really want more coverage, create additional coverage areas with added access points interconnected by wire. This is the ONLY way to assure good service to a smaller area, avoid the hidden node problem, and overall, increase the service to any node accessing your wireless system (a system of access points).
Do not waste your money on higher gain antennas unless you are solving a problem on a flat plane of coverage. And consider other wireless networks that may be nearby, and avoid overlapping your coverage into their converage area, it just creates more interference.
Maybe this will make sense to some, without offending anyone who is trying to create a super access point with higher power and higher gain (a misnomer) antennas. (The misnomer: Higher gain means higher gain in some directions, but lower gain in others. It does not mean higher gain everywhere).