Abstract
In mobile communication systems bit-rate reductions while maintaining an acceptable voice quality are necessary to achieve efficiency in channel bandwidth utilization and users satisfaction. As Long-Term Evolution(LTE) converging towards all-IP solutions and supporting VOIP service, the voice signals are converted into coded digital bit-stream and sent over the network. This paper proposes the implementation of codebook excited linear prediction (CELP) voice codec algorithm based on two source-rates of low 9.6Kbps and medium 16Kbps for achieving a perceptible level of voice quality, while efficiently using available bandwidth during the transmission over advanced LTE. The architecture of proposed CELP codec model is implemented to decompose the voice signal into a set of parameters that characterize each particular frame at the encoder part, these parameters are quantized and encoded for transmission to the decoder. The investigation showed that the configuration of the link and the applied CELP codec mode mainly influence on the obtained voice capacity and quality. The quantifying also shows that the voice quality can be traded for the enhanced capacity, since the low rate codec will produce lower voice quality than higher rate codec. Also, this paper is achieved, during theconfiguration of the system with higher channel quality indicator (CQI) index, increasing in the capacity gain to a saturated value of about 500 and 1000 users per cell over 5MHz bandwidth for transmit diversity (TD) and Open-Loop Spatial Multiplexing (OLSM) respectively and up to 1000 and 2000 users per cell over 10MHz channel bandwidth for TD and OLSM respectively.
Highlights
In Global mobile networks, voice service has been always considered as the essential revenue generator for mobile operators as it is the main required service by subscribers
VOICE CAPACITY EVALUATION This scenario is motivated to study the aspects of downlink Long-Term Evolution (LTE) voice capacity for various channel quality indicator (CQI) corresponding to the 9.6 Kbps and 16 Kbps codebook excited linear prediction (CELP) codec modes over various link configuration approach
The voice quality to voice capacity relation revealed that such a low rate codec of 9.6kbps provide better voice capacity at the cost of inferior voice quality compared to high rate codecs which show the conflicting result
Summary
In Global mobile networks, voice service has been always considered as the essential revenue generator for mobile operators as it is the main required service by subscribers. The most important driving forces that enable CELP for increasing system capacity and preserve a certain quality is the hybrid process, analysis by synthesis and voice signal parameterization based codec [9] , [11]. Another attractive approach in CELP is the use of a codebook that incorporates all the excitation sequences that are to be searched for the selection of the optimum sequence for encoding short voice segments in the encoder and only the selected sequence index is to be transmitted [9]. The work in this paper is routed towards the area of the application layer and physical layers processing to study and evaluate: The impact of implementing CELP voice codec, with 9.6kbps and 16kbps codec rate over LTE downlink PHY layer, to obtain the encoded voice bit-stream
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