Communication

WIRED

• Low mobility
• Unlimited capacity
• More reliable ink
• Low chance of inteferance
• More secure

WIRELESS

• High mobilty
• Restricted capacity
• Links condition variable
• High chance of interferance
• less secure

Dual-Band

Phones are Designed to operate in two different frequency band's

Dual-Mode

Phones can work with two different types of technology.A phone that works with both GSM and UMTS

Frequency Division Multiple Access(FDMA) allocates a different part of the frequency spectrum to each link.

This is the multiple access technique used in the first generation (analogue) mobile telephone networks.

FDMA can be used with both analogue and digital systems. It is used in GSM to separate the up-link and the down-link.

Time Division Multiple Access(TDMA)  serves different users on the same frequency band by allocating resources to each user for a small part of the total available time.

The time is divided into equally sized time slots and the slots are allocated to all the users  in turns .

multiplexing in optical fibres is a form of TDMA

Code Division Multiple Access(CDMA) uses codes to separate the required signal from other signals.

Each link has a different spreading code , known by both the transmitter and receiver.

Each digit in the spreading code is called a chip.