What are the key features of time-division multiple access (TDMA) in wireless communication systems?

1 TDMA basics

TDMA is a digital multiple access technique that allows multiple users to transmit and receive data over the same channel by using different time slots. Each user is assigned a specific time slot in each cycle or frame, and only transmits or receives data during that time slot. The other users are silent or listen during that time slot. The duration of each time slot depends on the data rate, the number of users, and the channel bandwidth. The time slots are synchronized by using a common reference signal or clock.

2 TDMA operation

To implement TDMA, the wireless communication system requires a central controller or base station that manages the channel allocation and synchronization among the users. The controller assigns each user a unique time slot and informs them about the timing and duration of their time slot. The users then transmit or receive data according to their assigned time slot, using the same frequency and modulation scheme. The controller also monitors the channel quality and adjusts the time slot allocation and power control as needed.

3 TDMA advantages

TDMA offers several advantages over other multiple access techniques, such as frequency-division multiple access (FDMA) or code-division multiple access (CDMA). It is efficient in using the channel bandwidth, as it allows multiple users to share the same frequency without causing interference. It is also compatible with digital data and voice transmission, as it can easily accommodate different data rates and modulation schemes. Furthermore, TDMA is flexible and scalable, as it can dynamically adjust the number of users and time slots according to the traffic demand and channel conditions. Additionally, TDMA is simple and cost-effective, as it does not require complex signal processing or filtering at the transmitter or receiver.

4 TDMA disadvantages

TDMA has some disadvantages or challenges that need to be addressed, such as the need for precise synchronization and coordination among users and the controller which can be affected by propagation delays, clock drifts, or channel errors. Additionally, TDMA introduces time gaps or guard intervals between the time slots to avoid overlapping or interference, reducing the effective data rate and channel utilization. Furthermore, TDMA is vulnerable to multipath fading and interference as it uses the same frequency for all users, which can degrade the signal quality and require more power or error correction. Lastly, TDMA is susceptible to near-far problem when a user with a stronger signal or closer distance to the controller dominates the channel and interferes with other users with weaker signals or farther distances.

5 TDMA applications

TDMA is a widely used technique in various wireless communication systems and standards, such as Global System for Mobile Communications (GSM). GSM is the most popular cellular network standard, which uses TDMA to divide the 200 kHz channel into eight time slots, each with a data rate of 270.833 kbps. In addition, Enhanced Data Rates for GSM Evolution (EDGE) is an extension of GSM that uses TDMA with higher-order modulation and coding schemes to achieve data rates up to 473.6 kbps per time slot. Digital Enhanced Cordless Telecommunications (DECT) is another standard for cordless phones that divides the 1.728 MHz channel into 24 time slots, each with a data rate of 32 kbps. Lastly, Integrated Services Digital Broadcasting-Terrestrial (ISDB-T) is a standard for digital television broadcasting that uses TDMA to divide the 6 MHz channel into 13 segments, each with a data rate of 5.57 Mbps.