TDD vs TDMA
TDD and TDMA are two technologies that are used to maximize the available bandwidth. TDD stands for Time Division Duplexing while TDMA stands for Time Division Multiple Access. Both technologies use time division to partition the available bandwidth. The difference between TDD and TDMA is their main goal. TDD is a duplexing technology that aims to use the same frequency to provide continuous flow of information in both directions. TDMA, on the other hand, is a multiplexing technology. Its main goal is to combine multiple signals into a single channel. This is used in cellular applications where hundreds of cellphone units may be connecting to a single base station.
One discriminating factor between TDD and TDMA is the length of the frames that they use. TDMA uses a fixed length of frames that are then assigned to the individual signals that are going to use the channel. Each frame can only contain specific amount of data, thus a signal may require more than one frame for its data. In contrast, TDD doesn’t use a fixed frame length and it can be varied depending on the circumstance. If the downlink traffic is considerably more than the uplink traffic, then the former would be assigned a larger time frame and the latter would have its time frame reduced. In TDMA, if the signal requires more than one time frame, it can acquire as many as it needs. But the time frames may not be sequential in nature as other signals may grab the following frames.
TDMA is a technology that is still being used nowadays, predominantly in the cellular communication industry where multiple phones utilize a very limited bandwidth. TDD is a rather old concept that is still quite applicable today. Even though it is no longer used, TDD is the basis of some other technologies that are used in modern technologies like UMTS and WiMax.
Time division is a very wide concept that is employed by many technologies. It provides the best level of partitioning when the frequency range available is not really appropriate for the number of users to be accommodated. Time division is also used in conjunction with technologies like frequency division to further enhance partitioning.
Summary:
- TDD focuses on the return signal while TDMA is concerned about mixing multiple signals
- TDMA has a fixed frame length while TDD does not
- TDMA is still in use today while TDD is just being used as a basis for other technologies