About the TDMA technology:
TDMA stand for (Time Division Multiple
Access )is also digital wireless telephony transmission technique. TDMA
allocates each user a different time slot on a given frequency. TDMA divides
each cellular channel into three time slots in order to increase the amount of
data that can be carried.
TDMA technology was more popular in Europe, Japan and Asian countries, where as CDMA is widely used in North and South America. But now a days both techologies are very popular throughtout in the world.
Advantages of TDMA:
TDMA can easily adapt to transmission of data as well as voice communication.
TDMA has an ability to carry 64 kbps to 120 Mbps of data rates.
TDMA allows the operator to do services like fax, voice band data, and SMS as well as bandwidth-intensive application such as multimedia and videoconferencing.
Since TDMA technology separates users according to time, it ensures that there will be no interference from simultaneous transmissions.
TDMA provides users with an extended battery life, since it transmits only portion of the time during conversations.
TDMA is the most cost effective technology to convert an analog system to digital.
Disadvantages of TDMA:
using TDMA technology is that the users has a predefined time slot.
When moving from one cell site to other, if all the time slots in this cell are full the user might be disconnected.
Another problem in TDMA is that it is subjected to multipath distortion.
To overcome this distortion, a time limit can be used on the system. Once the time limit is expired the signal is ignored.
About the FDMA technology:
The signal multiplexing technology used
in the Advanced Mobile Phone Service (AMPS) analog version of cellular
phone technology. Frequency Division Multiple Access (FDMA) is one of
three methods used for allocating channels to users over the shared wireless
communications medium in cellular phone communication; the others are Time
Division Multiple Access (TDMA) and Code Division Multiple Access (CDMA).
FDMA is implemented at the media access control (MAC) layer of the data-link layer in the Open Systems Interconnection (OSI) reference model for networking protocol stacks. FDMA is based on the frequency-division multiplexing (FDM) technique used in wireless networking. In FDMA, the user is assigned a specific frequency band in the electromagnetic spectrum, and during a call that user is the only one who has the right to access the specific band. In the AMPS cellular phone system, these frequency bands are allocated from the electromagnetic spectrum as follows:
a)Transmission by mobile station:
824 MHz to 849 MHz
b)Transmission by base station:
869 MHz to 894 MHz
FDMA Two different frequency bands are used to allow full-duplex communication between base and mobile stations. Both of these bands are then divided into discrete channels that are 30 kHz wide in bandwidth.