Wednesday, January 19, 2011

Turbo Code Applications 1


Mobile radio: 
 
     Few environments require more immunity to fading than those found in mobile communications. For applications where delay vs performance is crucial, turbo codes Offer a wide trade-off space at decoder complexities equal to or better than conventional concatenated code performance. The major benefit is that such systems can work with smaller constraint-length convolutional encoders. The major drawback is decoder latency. Turbo codes with short delay are being heavily researched. Turbo codes generally outperform convolutional and block codes when interleavers exceed 200 bits in length. 

Digital video: 
 
     Turbo codes are used as part of the Digital Video Broadcasting (DVB) standards, ComAtlas, a French subsidiary of VLSI Inc, has developed a single-chip turbo code Codec that operates at rates to 40M bps. The device integrates a 32x32-bit interleaver and performance is reportedly at least as good as with conventional concatenated Codes using a Reed-Solomon outer code and convolutional inner code. 

Long-haul terrestrial wireless: 
 
     Microwave towers are spread across and communications between them is subjected to weather induced fading. Since these links utilize high data rates, turbo codes with large interleavers effectively combat fading, while adding only insignificant delay. Furthermore, power savings could be important for towers in especially remote areas, where turbo codes are used. 

Satellite communications and Deep space communication: 
 
     Turbo codes are used for deep-space applications. Low power design is important for many communication satellites that orbit closer to earth. Turbo codes can be used in such applications. Many of these satellites are equipped with programmable FECs using turbo codes. Turbo codes can include serial as well as parallel concatenations and NASA group has also proposed hybrid structures. Turbo encoders are used in spacecrafts. 

Military applications: 
 
     The natural applicability of turbo codes to spread-spectrum systems provides increase opportunity for anti-jam and low probability of intercept (LPI) communications. In particular, very steep BER vs. curves lead to a sharp demarcation between geographic locations that can receive communication with just sufficient and 30 those where is insufficient. Turbo codes are used in a number of military and defense application.

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