【 Weak current College 】 LTE LTE TDD and FDD technology comparison 】

LTE systems also defines the frequency division duplex (FDD) and time division duplex (TDD) in two ways, but because of the differences between wireless technology, using different frequency bands, as well as the interests of the various manufacturers and other factors, more powerful LTEFDD support camp, standardization and industry developments are leading to LTETDD. November 2007, 3GPPRAN1 meeting adopted 27 companies jointly signed by LTETDD fusion frame structure, unifies the two frame LTETDD structure. Fusion of LTETDD frame structure is to the frame structure TD-SCDMA, this evolution to success for TD-SCDMA LTE and even 4G standards laid the Foundation. TDD frame structure of fusion that more firms to participate in the standardization process in TDD, LTETDD technology was widespread, and its industrialization process also has a significant development.
FDD and TDD works
Frequency division duplex (FDD) and time division duplex (TDD) are two different duplex mode. FDD is the separation of two symmetrical frequency channels for receiving and sending, isolation with protection band to receive and transmit channels. FDD must be paired frequency, depending on the frequency to distinguish between upper and lower lines link, its resources in a single direction is continuous. FDD in support symmetric business can make full use of upper and lower lines of the spectrum, but support asymmetric business, spectrum utilization will be greatly reduced.
TDD with time to receive and send channel separation. In TDD mode of mobile communication systems, and use the same frequency carrier of different time slots as host of the channel, its resources in a single direction is not continuous, time resources in both directions has been assigned. A time period by base stations send a signal to the mobile station, another time by the mobile station to send signals to the base station, base stations and mobile stations must be coherent to work smoothly.
TDD duplex mode of work characteristics make TDD has the following advantages: flexibility to configure the frequency, use the FDD system difficult to use the scattered band; you can adjust the top and bottom line, improve timeslot slot ratio in the downlink, very good support for non-symmetrical business; with top and bottom line channel consistency, the base station and can share part of the radio unit, reducing equipment costs; receive downlink data, do not need to send and receive isolator, just a switch to reduce the complexity of the device; with top and bottom line channel reciprocal, ability to make better use of transport preprocessing techniques such as pre-rake technology, joint transmission technology, smart antenna technology, etc., can effectively reduce the complexity of mobile terminal for processing.
LTETDD advantages
LTETDD in frame structure, physical layer technology, radio resource allocation with its own unique technology features, and have unique compared to LTEFDD advantage.
(1) frequency allocation
Band wireless communication resources are the most valuable resource, along with the development of mobile communication, multimedia services for increasing spectrum demand. Existing communications system GSM900 and GSM1800 are made of duplex FDD, FDD duplex occupied a large number of frequency resources, at the same time, some scattered spectrum resources as FDD cannot use and idle, resulted in the spectrum. Because LTETDD system does not need to be paired frequency, can be easily configured in the system is not easy to use LTEFDD of scattered band, has certain spectrum flexibility, can effectively improve spectrum utilization.
In addition, China has been divided for TDD 155MHz band application for LTETDD. Therefore, in the frequency resources, LTETDD system and LTEFDD system has more advantages. China Mobile for different frequency bands respectively deployment LTETDD system and LTEFDD system, making full use of the spectrum resource.
(2) support for non-symmetrical business
In the third generation mobile communications system, as well as the future of mobile communication system, in addition to providing voice, data and multimedia services will become the primary content, and Internet access, file transfer, and multimedia businesses usually have the bottom line asymmetric characteristics. LTETDD systems in support of asymmetric operations have a certain flexibility. According to the characteristics of frame structures LTETDD, LTETDD system can be configured according to your business type flexible LTETDD frame ratio of up and down. If the browse page, video-on-demand, and downlink data rate significantly greater than the amount of data uplink, the system can be based on traffic analysis, configuration downlink frames than uplink frames, such as 6DL: 3UL, 7DL: 2UL, 8DL: 1UL, 3DL: 1UL, etc. Whereas in traditional voice services, the system can configure downlink frames equal to the upper frame, such as 2DL: 2UL.
In LTEFDD system, implementation of non-symmetrical business on uplink channel resources exist for certain waste, must be in the high speed packet access (HSPA), EV-DO and broadcast/multicast technology. Relative to LTEFDD system, LTETDD system to better support different types of business, it will not cause a waste of resources.
(3) the use of a smart antenna
Smart antenna technology is the future direction of development of wireless technology, it can reduce multiple access interference, increase system throughput. In LTETDD system, and down-link uses the same frequency and interval time shorter, less than coherent time, channel link wireless communication environment differences are not large, when in use, the arrow shaped algorithm uplink can use the same weight. In contrast, because of the FDD system up and down link environmental transmission of wireless signals from different frequency selective fading effect, according to the uplink calculated weights cannot be directly appliedto downlink. Thus, LTETDD system can effectively reduce the complexity of mobile terminal for processing.
In addition, in the system, because LTETDD downlink channels, the base station and can share part of RF modules, thus to some extent reduces the base station systemCause this.
(4) and TD-SCDMA coexistence
LTETDD system also has an incomparable advantage LTEFDD is LTETDD systems can coexist with TD-SCDMA System. On existing communication systems, the current data transfer rates have been unable to meet the growing needs of users, operators must plan ahead to existing communications system B3G/4G smooth evolution of the system. Because LTETDD frame structure is based on the frame structure in China TD-SCDMA, the ability to easily implement TD-LTE system and TD-SCDMA System coexistence and integration.
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TDD-duplex mode with spectrum configuration flexibility, spectrum utilization is high, the top and bottom line channel reciprocal, ability to meet next-generation mobile communications system bandwidth requirements as well as the frequency distribution of scattered, B3G/4 g mobile communication system with a strong advantage. The spectrum utilization LTETDD, asymmetric business support, smart antenna technology support, and coexistence, TD-SCDMA system, there are great advantages in future communication systems with strong competitiveness. With in-depth technical research LTETDD and international marketing, will become the future wireless communication system of mainstream technologies.