Short-Range Wireless Technologies
Bluetooth: short-range wireless (up to 10m for Class 2; 100m for Class 1). Used for: headphones, keyboards, mice, speakers, wearables. Bluetooth versions: 4.0 (Bluetooth Low Energy / BLE introduced), 5.0 (4× range, 2× speed of 4.0). Pairing process: both devices in discoverable mode, enter PIN or confirm pairing code. Troubleshooting: unpair and re-pair, ensure both devices support the same Bluetooth profile (A2DP for audio, HID for keyboard/mouse, AVRCP for media control).
NFC (Near Field Communication): extremely short range (4 cm or less). Used for: contactless payments (Apple Pay, Google Pay), Bluetooth pairing (tap-to-pair), building access cards, transit cards, NFC tags (scan with phone to trigger action). NFC operates at 13.56 MHz. Security: the very short range limits passive eavesdropping risk, but relay attacks are theoretically possible.
Infrared (IR): line-of-sight, very short range. Used in older devices and TV remote controls. Limited use in modern mobile devices (some Android phones include IR blaster for TV remote app). Not used for data transfer in modern mobile computing.
Wi-Fi Direct: peer-to-peer Wi-Fi connection between two devices without an access point — used for screen mirroring (Miracast), printer connectivity, file transfer. Higher bandwidth than Bluetooth. One device acts as a soft AP.
Cellular and Long-Range Connectivity
Cellular standards: 4G LTE — current standard for voice and data. 5G: sub-6 GHz (moderate speed improvement, wide coverage) and mmWave (extremely high speed, very short range — indoor coverage challenges). Phones use SIM cards (Subscriber Identity Module) to store carrier credentials. Physical SIM sizes: standard, micro-SIM, nano-SIM. eSIM: embedded SIM — software-programmable, no physical card. Allows carrier switching without physical swap.
Hotspot / tethering: sharing a smartphone's cellular internet connection with other devices. Personal hotspot creates a Wi-Fi network from the cellular connection. USB tethering: connects phone to PC via USB, phone provides internet. Bluetooth tethering: phone shares internet via Bluetooth. Carrier plans typically include or separately charge for hotspot data.
Airplane mode: disables all wireless radios (cellular, Wi-Fi, Bluetooth, NFC, GPS) simultaneously. Required by FAA during takeoff and landing. After enabling airplane mode, Wi-Fi and Bluetooth can be re-enabled individually on modern devices — useful for international flights.
Wired Mobile Connections
USB types for mobile: USB-C: current standard — reversible, supports USB 3.x, Thunderbolt 3/4, Power Delivery charging, video output. Micro-USB: older Android standard — directional connector. Lightning: Apple proprietary (older iPhones/iPads) — being replaced by USB-C (iPhone 15+ uses USB-C). USB-A: host port (chargers, computers) — receives devices. USB-B: square connector on older printers.
USB speeds: USB 2.0 (480 Mbps), USB 3.0/3.1 Gen 1 (5 Gbps — blue ports), USB 3.1 Gen 2 (10 Gbps), USB 3.2 Gen 2×2 (20 Gbps), USB4 (40 Gbps). USB-C connector does not indicate speed — must verify protocol supported.