The 2.4 GHz wireless frequency bandwidth used by the 3DS for wireless communication continues to become an extremely crowded bandwidth, as it is used for a wide variety of wireless devices, first and foremost among them, Wi-Fi devices. In addition, worsening wireless conditions sometimes result in instability for 3DS wireless communication—a problem that cannot be solved with technology. Ideally, development would use wireless communication features and prepare conditions to remove interference from other devices. The unique characteristics of wireless communication mean that it is not easy to create these conditions. In addition, a lack of understanding of wireless conditions can mistakenly lead people to believe that an environment is clear when it is not. This misunderstanding can add development time in many instances when trying to isolate the causes of a bug in communication.
This appendix describes several types of information related to interference between wireless devices, to further your understanding of wireless environments. It describes how to prepare a wireless environment free from the effects of other devices.
8.1. Cautions When Preparing a Wireless Communication Environment
The following section describes what you need to know to avoid interference between two wireless devices, and includes cautions to help you confirm whether you have set up a good wireless environment.
8.1.1. Setting Channels for Other Wi-Fi Devices
Figure 8-1 shows an example of assigning frequency channels in the 2.4 GHz bandwidth used by for 3DS wireless communication. As shown in the figure, 3DS wireless communication, and Wi-Fi communication in general, uses a wider amount of bandwidth than is assigned to a single channel. As a result, when devices are set with channels close to another, it results in interference in the communication of both devices. When you set channels to avoid interfering with other devices, we recommend a separation between devices of at least five channels.
The channels available for use differ by country.
However, even when devices are separated by at least five channels, it is impossible to completely eliminate mutual interference during communications. For example, even when two devices use channels 1 and 13 for communication, but are physically close to one another, they can both interfere with each other. To eliminate the effect on both devices, set them to channels that are at least five channels apart and at a distance of at least two meters.
The necessary distance varies depending on amplification, signal strength, receive frequency, and device send output.
8.1.2. Interference From Devices Other Than Wi-Fi Devices
In addition to 3DS wireless communication and other general Wi-Fi communication under the IEEE 802.11 standard, the 2.4 GHz bandwidth is host to a wide variety of other communication methods and electronic devices. Such devices include microwave ovens, cordless phones, and Bluetooth devices (including peripherals for PCs and smartphones). There is no feature allowing for their efficient co-existence with IEEE 802.11, so interference from their signals can make communication unstable.
For a clear wireless environment, you must halt these other devices. Of particular concern is the smartphone, which now comes standard with Bluetooth. You must be cautious when bringing smartphones into the testing environment.
8.1.3. Caution Using Packet Capture
A wireless packet can be captured using packet capture tools available on the market, such as AirPcap (a wireless LAN protocol analyzer made by Riverbed Technology). While there are probably developers using packet capture tools to facilitate communication testing, the use of these tools does nothing to help determine how good or bad a wireless environment is, so take caution. In other words, even when the captured wireless packets are few in number or in an "empty state," communication may be unstable.
Packet capture tools do not capture packets using communication methods other than those set forth in IEEE 802.11. In addition, even when a wireless packet is IEEE 802.11-compliant, large portions of data might not be captured because they could not be decoded correctly due to weak signal reception. Note that even when a wireless packet is not captured, it can still be strong enough to have an effect on low-level processing such as the physical and MAC layers. In that case, such wireless packets indicate unstable communication.
When reception strength is weak, the protocol of the MAC layer sometimes does not operate correctly. A wireless packet that cannot be captured can have a more serious effect on communication than a wireless packet that can be captured.
8.2. Preparing a Wireless Communication Environment Unaffected by Other Devices
Given the intense pace at which wireless devices that use the 2.4 GHz bandwidth are spreading, it is likely to be difficult to yield a truly clear wireless environment, short of using an advanced electromagnetic black box or black room. Although it will not be completely clear, a comparatively clear wireless environment can be implemented through the use of commercially available electromagnetic shielding and coaxial cables.
Even with the wireless environment prepared using the methods introduced below, perform development and testing with the understanding that you cannot completely eliminate interference from other wireless devices. Being aware of the potential problems can help avoid unnecessary confusion and foster more efficient work.
8.2.1. Using an Electromagnetic Shield
One way to yield a clear wireless environment is to use a shield that blocks out electromagnetic field signals. There are a wide variety of shielding products on the market, ranging from the simple bag and box types to larger tent types. These products possess a degree of ability to shield electrical devices from external interference, so that more stable communication can be expected. However, take caution, as the majority of shielding products on the market reduce external interference, but cannot completely block it out.
As a general guideline, if the dampening capacity (attenuation capacity) of the shielding product is 40 dB or less, it cannot block, at a minimum, a wireless signal that is in the same room. To yield a clear wireless environment, use a shield with a dampening capacity of at least 60 dB, and avoid placing wireless devices near the shield.
Caution is needed because the shield can foster the harmful effects from dampened wireless packets.
8.2.2. Using Coaxial Cables
With a debugger, devices can be connected by coaxial cable instead of the wireless antenna, and communication can occur using the coaxial cable. As with the electromagnetic shield, this has the benefit of controlling the effect of other wireless communication. However, because the signal that is exchanged via the cable is the same as the signal exchanged in wireless communication, there is no way to completely eliminate all external interference. When you use a coaxial cable, you must assume that there will be interference from wireless devices within a radius of a few meters.