2.5 Important definitions for LTE Communication systems

2.5 Important definitions for LTE Communication systems:

2.5.1 Channel estimation:

The radio channels in mobile radio systems are usually multipath fading channels, which are causing inter-symbol interference (ISI) in the received signal.

           

            To remove ISI from the signal, many kinds of equalizers can be used. Detection algorithms based on trellis search (like MLSE or MAP) offer a good receiver performance, but still often not too much computation. Therefore, these algorithms are currently quite popular.

           

            However, these detectors require knowledge on the channel impulse response (CIR), which can be provided by a separate channel estimator. Usually the channel estimation is based on the known sequence of bits, which is unique for a certain transmitter and which is repeated in every transmission burst.

            Thus, the channel estimator is able to estimate CIR for each burst separately by exploiting the known transmitted bits and the corresponding received samples.

Preamble & pilot:

There are two ways to transmit training symbols:

1         1)    Preamble                  2) Pilots tones.

            Channel estimation in MIMO-OFDM systems can be performed in a variety of ways , but it is typical to use the preamble for synchronization & initial channel estimation and the pilot tones for tracking the time varying channel in order to maintain accurate channel estimates.

2.5.2 Channel Coding:

            The engineering problem treated by the subject of error-control codes is that of protecting digital data against the errors that occur during transmission or storage. The storage and transmission of digital data lies at the heart of modern computers and telecommunications.

            If data is corrupted in storage or transmission, the consequences can range from mildly annoying to disastrous. Many error-protection techniques have been developed based on a rich mathematical theory, and the rapid advances in digital integrated circuitry have made possible the implementation of these algorithms.

            The channel coding is considered as an important signal processing operation which provides a reliable transmission of digital information over channel.

            It is used mainly to minimize the effect of NOISE by facilitate two basic operations, Error detection and Error correction.

            Coding is achieved by adding properly designed ―controlled‖ redundant bits to each message or make an operation on the message to get it encoded with some methods.

            These redundant bits (digits) are used for detecting and/or correcting transmission errors, in other words for protecting data against channel impairments (e.g., noise, fading, interference).