Comparison of TDD and FDD duplex technology of mobile communication technology

Duplex is a process of implementing two-way communication on a single communication channel, including two types, half-duplex and full-duplex.

In a half-duplex system, the communicating parties use a single shared channel to transmit data in turn. This method is used for two-way broadcasting. When one party sends data, the other party can only listen. The sender of the data usually sends an "Over" signal indicating that the data transmission is finished and the other party can start sending data. In an actual network, two computers can use a single communication cable to send and receive data in turn.

Full duplex refers to simultaneous two-way communication. Both parties can send and receive data at the same time. This method is used for the communication between landline and mobile phones. Other types of networks also support data transmission and reception at the same time. This is a more practical duplexing technique, but more complex and costly than half-duplex. Full-duplex technology is divided into two types: time division duplex (TDD) and frequency division duplex (FDD).

FDD requires the system to have two separate communication channels. There will be two communication cables in the network. Full-duplex Ethernet uses CAT5 twisted-pair cable for simultaneous data transmission and reception.

Mobile communication systems require two different frequency bands or channels. Sufficient spacing between the two channels is required to ensure that the transceivers do not interfere with each other. Such systems must filter or mask the signal to ensure that the transmitter does not affect adjacent receivers.

In mobile phones, the transmitter and receiver work simultaneously at very close distances. The receiver must filter as much of the signal as possible from the transmitter. The better the spectrum separation, the higher the filter efficiency.

FDD usually requires more spectrum resources, which is twice as large as TDD. In addition, proper spectral separation must be performed for the transmit and receive channels. This so-called "safe frequency band" will be unusable and therefore wasteful. Considering the scarcity and expensive cost of spectrum resources, this is a major drawback of FDD.

However, FDD is widely used in mobile communication systems, such as GSM networks that have been deployed in large numbers. In some systems, the 25 MHz bandwidth spectrum from 869 MHz to 894 MHz is used for base station to handset downlink communication, while the 824 MHz to 849 MHz 25 MHz bandwidth spectrum is used for handset to base station uplink communication.

Another disadvantage of FDD is that it is difficult to apply multiple input multiple output (MIMO) antenna technology and beamforming techniques. These technologies are at the heart of current 4G LTE networks and can dramatically increase data transfer rates. A single antenna is often difficult to have enough bandwidth to cover the full frequency used by the FDD, which also requires more complex dynamic adjustment circuitry.

FDD systems can also be implemented with a single cable. In this case, the transceiving channels use different frequency bands respectively. This is the case with cable television systems. Similarly, filters are also required in such systems to separate channels.

The TDD system uses a single frequency for transceiving. By allocating different time slots, the TDD system can utilize a single frequency band for transceiving operations. The information sent in the TDD system, whether it is voice, video or computer data, is serial binary data. Each time slot may be 1 byte in length, and multiple bytes can be assembled into a frame.

Due to the fast data transfer rate, it is difficult for the communication parties to distinguish that the data transmission is intermittent. Therefore, instead of using the term "simultaneously" to describe such transmission, the term "concurrent" may be more appropriate. For example, in the process of converting digital speech to analog format, no one would think that this process is not full duplex.

In some TDD systems, the uplink and downlink can be assigned equal time slots. However, the system does not actually require such a symmetric allocation, and in some cases the system can be asymmetrical up and down.

For example, in an Internet access application, the data download time is usually much larger than the upload time, so fewer time slots can be allocated for data upload. Some TDD systems support dynamic bandwidth allocation, where the number of time slots can be allocated on demand.

The real advantage of TDD is that the system only needs to use one channel of the spectrum. In addition, there is no need to waste spectrum resources to set "safe frequency bands" or to adopt channel isolation measures. However, the main problem with TDD is that the system requires very precise time synchronization between the transmitter and the receiver to ensure that the time slots do not overlap and interact.

Usually, the time in the TDD system is synchronized by the atomic clock and the GPS system. It is also necessary to set a "safe time" between different time slots to prevent time slot overlap. This time is usually equivalent to the loopback time from the transmission to the reception, and the delay over the entire communication link.

Currently, most mobile phone systems use FDD technology. 4G LTE technology also initially chose FDD, while cable TV systems are based entirely on FDD.

However, most wireless data transmission systems use TDD technology. Both WiMax and WiFi are TDD technologies, as are Bluetooth and ZigBee systems. Cordless phones also use TDD. Due to the scarcity of spectrum and high cost, TDD is also used in some mobile communication systems, such as China's TD-SCDMA and TD-LTE. In the event of spectrum tension, other countries may also deploy TD-LTE networks.

in conclusion

Overall, TDD may be a better choice, but FDD is now more widely used. This is mainly due to historical reasons for spectrum allocation and the fact that FDD technology appeared earlier. At present, FDD will still dominate the mobile communication system. However, as spectrum resources become more tense and costs increase, TDD is expected to gain more applications in the redistribution of spectrum.

POWER UNITS FOR DOUBLE-SCISSORS LIFT

Hydraulic Power Unit For Warehousing,Closed Center Hydraulic Valve,Energy Hydraulic Valve Parts,Air Operated Hydraulic Valve

CHANGZHOU ROHN HYDRAULIC SCI-TECH CO.,LTD , https://www.rohnhydraulic.com