11. The speech recognition system of claim 1 , wherein a speech recognition program is installed in the user device and the speech recognition program comprises: a device key transferring part configured to generate the device key with initial installation of the speech recognition program and transmit the device key to the model selector, and transmit the device key to the model selector whenever the speech recognition program is used; and a speech recording part configured to record voice data inputted when speech recognition is performed and transmit the recorded voice data or feature-extracted data to the speech recognizer.
1. A speech recognition system using incremental device-based acoustic model adaptation comprising: a model selector configured to select an acoustic model of a multi-model tree by verifying and categorizing a device key transmitted from a user device; a model manager configured to generate and incrementally adapt the multi-model tree by categorizing voice data based on the device key; and a speech recognizer configured to perform speech recognition based on the selected acoustic model and transmit data of which reliability exceeds a predetermined threshold value to the model manager, wherein the device key represents channel features of the user device, and wherein the model manager comprises: a device-based multi-model tree generating part configured to categorize the voice data based on the device key, extract features therefrom and form the multi-model tree, the multi-model tree being categorized by the device key and comprising hierarchical acoustic models, incremental data and device key trees; a data incrementing part configured to receive data of which the reliability exceeds the predetermined threshold value from the speech recognizer, increment phonetic information and data to the multi-model tree, evaluate a degree of the incremented data of each node, and report a result of the evaluation to a model adaptation generating part when the degree exceeds a predetermined reference value; and the model adaptation generating part configured to incrementally adapt acoustic models corresponding to nodes where newly adapted data from the multi-model tree exceeds the predetermined reference value by using the phonetic information transmitted from the data incrementing part.