AMR (Adaptive multi rate)
Adaptive Multi-Rate (AMR) is a codec used for voice compression in modern digital mobile communication networks. It was developed by the 3rd Generation Partnership Project (3GPP) and is used in both GSM and UMTS (Universal Mobile Telecommunications System) networks. The codec is designed to optimize the voice quality and bandwidth efficiency of mobile networks, allowing for clear and reliable voice communication even in areas with poor network coverage.
AMR is a variable bit rate codec, which means that it adjusts the bit rate based on the complexity of the audio signal being compressed. This allows it to allocate more bits to more complex parts of the signal, resulting in higher quality audio. The codec uses a combination of speech coding and channel coding techniques to reduce the amount of data transmitted over the network, while maintaining high quality voice communication.
The codec operates at eight different bit rates, ranging from 4.75 kbps to 12.2 kbps. These bit rates correspond to eight different modes of operation, each with its own set of codec parameters. The mode of operation is selected based on the signal conditions and the available network bandwidth.
AMR uses a combination of several speech coding techniques to compress the voice signal. These techniques include linear predictive coding (LPC), code excited linear prediction (CELP), and algebraic code excited linear prediction (ACELP). LPC is used to model the speech signal as a linear combination of past samples, while CELP and ACELP are used to predict the future speech signal based on the current signal.
In addition to speech coding, AMR also uses channel coding techniques to reduce the amount of data transmitted over the network. These techniques include forward error correction (FEC) and interleaving. FEC adds redundant data to the transmission to allow for error correction, while interleaving rearranges the order of the data to reduce the impact of burst errors.
AMR also includes several features to improve the user experience and optimize network efficiency. These include comfort noise generation (CNG), discontinuous transmission (DTX), and voice activity detection (VAD). CNG generates artificial background noise during periods of silence to prevent the user from experiencing complete silence, which can be unsettling. DTX allows the codec to temporarily suspend transmission during periods of silence to further reduce network traffic. VAD detects when the user is speaking and activates the codec accordingly, further reducing network traffic.
AMR is widely used in modern mobile networks and has proven to be an effective solution for voice communication in areas with poor network coverage. It allows for high quality voice communication while minimizing the amount of data transmitted over the network, resulting in improved network efficiency and reduced operating costs. vantages of AMR is its flexibility. The codec can adjust its bit rate and mode of operation based on the signal conditions, allowing it to adapt to changes in the network environment. This makes it well-suited for mobile networks, where signal conditions can vary widely based on factors such as distance from the tower, interference from other signals, and terrain.
Another advantage of AMR is its low complexity. The codec is designed to be efficient and easy to implement, making it a cost-effective solution for mobile network operators. Its low complexity also allows it to run on a wide range of devices, from low-end feature phones to high-end smartphones.
AMR is also designed to be interoperable with other codecs and network technologies. This allows it to be used in a wide range of mobile networks, making it a versatile solution for voice communication.
Despite its many advantages, AMR does have some limitations. One of the main limitations is its relatively low bit rate compared to other codecs, such as wideband audio codecs. This can result in a loss of audio fidelity, particularly for music and other complex audio signals. However, for voice communication, AMR's bit rate is generally sufficient to provide high-quality audio.
Another limitation of AMR is its reliance on channel coding techniques, which can introduce latency and reduce network efficiency. This can be particularly problematic in areas with poor network coverage, where network resources are limited. However, AMR's low complexity and adaptability help to mitigate these issues, making it a viable solution for mobile networks.
In conclusion, Adaptive Multi-Rate (AMR) is a widely used codec for voice compression in modern digital mobile communication networks. It is designed to optimize the voice quality and bandwidth efficiency of mobile networks, allowing for clear and reliable voice communication even in areas with poor network coverage. AMR is a variable bit rate codec that uses a combination of speech coding and channel coding techniques to reduce the amount of data transmitted over the network, while maintaining high quality voice communication. Its flexibility, low complexity, and interoperability make it a cost-effective and versatile solution for voice communication in mobile networks. While it does have some limitations, AMR's strengths make it a valuable tool for mobile network operators and users alike.