Which type of handsets utilizes a code to modulate signals for subscriber traffic extraction?

CDMA, or Code Division Multiple Access, utilizes a unique code assigned to each user to modulate signals, allowing for simultaneous transmission of multiple signals over a single communication channel. This method enables each user to occupy the same frequency band at the same time without interference, as the unique codes act as the "keys" that unlock the intended signals for each subscriber.

In CDMA, the modulation process involves spreading the signal using these unique codes, resulting in a high level of security and the ability to accommodate many users efficiently. This technique is crucial for managing subscriber traffic extraction effectively, as it allows the network to distinguish between various users transmitting simultaneously.

The other options represent different multiplexing techniques that do not primarily rely on unique codes for signal extraction. TDMA (Time Division Multiple Access) segments the channel into time slots, while GSM (Global System for Mobile Communications) employs a combination of TDMA and FDMA (Frequency Division Multiple Access), which divides the frequency spectrum into distinct channels. FDMA, on the other hand, assigns separate frequency bands to each user. These methods do not utilize a coding technique for signal modulation, which is a defining characteristic of CDMA.