Transmit Diversity Gain in LTE
In Long-Term Evolution (LTE) wireless communication systems, transmit diversity gain plays a crucial role in enhancing the reliability and performance of data transmission. Transmit diversity involves the use of multiple antennas at the transmitter to improve the quality of the received signal at the receiver. One common technique employed in LTE for transmit diversity is Space-Time Block Coding (STBC).
Space-Time Block Coding (STBC) in LTE:
STBC is a method used to transmit multiple copies of a data stream over multiple antennas and time intervals. It helps combat fading and improves signal quality by providing diversity in both space and time. In LTE, the most commonly used STBC scheme is Alamouti’s Space-Time Block Code.
- Fading Mitigation: Transmit diversity helps mitigate the effects of signal fading, where the strength of the signal varies due to obstacles and reflections in the transmission environment.
- Improved Signal Quality: By transmitting multiple copies of the same signal through different antennas, the likelihood of receiving a high-quality signal at the receiver is increased.
- Enhanced Reliability: Transmit diversity contributes to the reliability of communication by reducing the probability of errors in the received signal.
- MIMO Technology: Multiple-Input Multiple-Output (MIMO) is a broader concept that includes transmit diversity. MIMO systems use multiple antennas at both the transmitter and receiver to achieve spatial multiplexing and diversity gains.
- Implementation in LTE: LTE supports various MIMO configurations, including Single-Input Single-Output (SISO), Multiple-Input Single-Output (MISO), and Multiple-Input Multiple-Output (MIMO). Transmit diversity is often employed to improve system performance.
In summary, transmit diversity gain in LTE, particularly through techniques like STBC, contributes to a more robust and reliable wireless communication system by addressing signal fading and improving the overall quality of the received signal.
Transmit diversity gain can be used when transmitting broadcast information from multiple antennas. This effectively produces, by design, frequency diversity in the transmitter. The gain obtained from transmit diversity can be approximated with the following equation.
GCC = 10× log(NTx)
Where NTx is the number of transmit antennas.
Thus, a BS that has 2 transmit antennas and transmit diversity will have 3 dB of improvement in its EIRP versus a BS without transmit diversity. Typically, only the BS uses multiple transmit antennas and will benefit from the transmit diversity. The subscriber device using a single transmit antenna would not have this benefit.