1. Duplex mode
TDD: Time Division Duplex. The transceiver shares one RF frequency point, and the uplink and downlink use different time slots for communication.
FDD: Frequency Division Duplex, which uses different RF frequency points for communication.
Theoretically, under the same bandwidth conditions, such as 10m + 10m allocated by FDD and 20m allocated by TDD, the rate of TDD will be lower than that of FDD. The main reason is that there is a frame called special subframe in the frame structure of TDD. Some of these frames will be wasted (such as the protection time slot) and will not transmit any data, and there is no such complete waste of FDD frames.
TDD-LTE is suitable for hot area coverage, and FDD is suitable for wide area coverage
An early Qualcomm report showed that under the condition of the same frequency and power, FDD can provide better coverage than TDD. TDD coverage is 80% (DL / UL = 2:1) / 40% (DL / UL = 1:1) less than FDD. One of the main reasons is that the transmission time of uplink power (TDD) is shorter than that of uplink power (TDD).
4. Moving speed of mobile station
FDD is a continuous control system and TDD is a time separated control system. When moving at high speed, Doppler effect will lead to fast fading. The higher the speed, the higher the fading transform frequency and the deeper the fading depth.
Based on the current chip processing speed and algorithm, when the data rate is 144KB / s, the maximum moving speed of TDD can reach 250km / h, which is still a certain gap compared with FDD system. Generally, the moving speed of TDD mobile station can only reach half or even lower than that of FDD mobile station.