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3G TD-SCDMA Tutorial
- overview or tutorial of the basics of TD-SCDMA, the 3G UMTS TDD system that has been widely deployed in China.
UMTS WCDMA tutorial includes:
• UMTS WCDMA Tutorial• UMTS 3G history
• UMTS WCDMA network architecture
• UMTS / WCDMA radio or air interface
• CDMA multiple access technology
• UMTS / WCDMA modulation schemes
• UMTS WCDMA channels
• UMTS TDD
• TD-SCDMA
• UMTS WCDMA handover / handoff
TD-SCDMA is an additional TDD version of UMTS. Devised in China, the system provides a number of advantages in several applications. TD-SCDMA has been adopted as a 3G standard by the International Telecommunications Union (ITU), and it is part of the 3GPP UMTS system being defined in the 3GPP standards.
Much of the initial work for the system was undertaken by the China Academy of Telecommunications Technology (CATT). Apart from the advantages of the basoc TDD approach, TD-SCDMA is able to support IP services, and it has been designed to incorporate new technologies such as joint detection, adaptive antennas, and dynamic channel allocation
While similar in many was to UMTS TDD, TD-SCDMA is has a number of differences and handsets for the two systems would not be compatible unless the capability for both systems was specifically built in to them.
TD-SCDMA basics
One of the key elements of TD-SCDMA is the fact that it uses a TDD, Time Division Duplex approach. As seen with UMTS TDD this has advantages in a number of areas, enabling the balance to be changed between uplink and downlink to accommodate the different levels of data transfer. It also has advantages in terms of using unpaired spectrum, spectrum efficiency for certain loads and it does not require expensive diplexers in the handsets to enable simultaneous transmission on the uplink and downlink, although transmit / receive switching times must be accommodated and can reduce the efficiency of the system.
Note on TDD and FDD duplex schemes:
In order for radio communications systems to be able to communicate in both directions it is necessary to have what is termed a duplex scheme. A duplex scheme provides a way of organizing the transmitter and receiver so that they can transmit and receive. There are several methods that can be adopted. For applications including wireless and cellular telecommunications, where it is required that the transmitter and receiver are able to operate simultaneously, two schemes are in use. One known as FDD or frequency division duplex uses two channels, one for transmit and the other for receiver. Another scheme known as TDD, time division duplex uses one frequency, but allocates different time slots for transmission and reception.
Click on the link for more information on TDD FDD duplex schemes
As a further advantage, TD-SCDMA uses the same RAN as that used for UMTS. In this way it is possible to run TD-SCDMA alongside UMTS, and thereby simplifying multi-system designs.
Although UMTS (W-CDMA) and cdma2000 are widely recognized as 3G cellular standards, TD-SCDMA is equally valid. In fact it has been adopted as the low chip rate (LCR) version of the 3GPP TDD standard.
TD-SDCMA specification overview
The TD-SCDMA standard provides many advantages. As already mentioned it has many similarities to W-CDMA, although a summary of the basic features and specification is given below:
| Characteristic | Figure |
|---|---|
| Bandwidth | 1.6 MHz |
| Chip rate per carrier | 1.28 Mcps |
| Spectrum spreading mode | DS SF=1/2/4/8/16 |
| Modulation | QPSK |
| Channel coding | Convolutional codes: R=1/2,1/3 Turbo implemented |
| Interleaving | 10/20/40/80 ms |
| Frame structure | Super frame 720ms,Radio frame 10ms Subframe 5 ms |
| Uplink synchronisation | 1/2 chip |
| Number of voice channels per carrier | 48 |
| Spectrum Efficiency | 25Erl./MHz |
| Total transmission rate provided by each carrier | 1.971Mbps |
Other popular cellular tutorials . . . . . |
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| • 3G LTE | • LTE Advanced | • UMTS / W-CDMA | • GSM |
| • 3G HSPA | • CDMA2000 | • GPRS | • EDGE |
| • Femtocells | |||