Mobile Radio Transmission System -5.Error Control
Digital mobile radio transmissions are subject to both burst errors and random errors. Burst errors occur partly on a concentrated basis and are mainly caused by fading. Random errors, which are mainly caused by thermal noise in the receiver, occur independently in individual bits that are transmitted. Error control technology is used to detect and reduce such errors in order to realize high-quality and highly reliable digital mobile radio transmissions.
Error control technology includes both the FEC and ARQ systems. In FEC, error correction codes are added on the transmission side and used on the reception side. While this permits transmissions on a real-time basis with few transmission delays, a powerful error correction capability is required as a lot of information can be lost if all errors are not corrected. Because of this, the decoding circuitry becomes complex. ARQ actually involves three systems, SAW, GBN and SR. Systems using these technologies are widely employed to meet the needs in the field of mobile communications including portable and automobile telephones. NTT DOCOMO's high-speed mobile data communication uses an error control technology called WORM-ARQ, which combines the GBN and SR systems.