Proposed modification in ETSI GSM 06.10 full rate speech codec for high rate data hiding and its objective evaluation of performance using Simulink Ninad Bhatt Research Scholar, Veer Narmad South Gujarat University, Surat, Gujarat, India bhattninad@gmail.com Yogeshwar Kosta Principal, Marwadi Education Foundat`ion, Rajkot, Gujarat, India ypkosta@yahoo.com Vishal Tank Research Scholar, L.D. Engg. College, Amdavad, Gujarat, India tankvishal@gmail.com Abstract—Today, the primary constrain in wireless communication system is limited bandwidth and power. Wireless systems involved in transmission of speech envisage that efficient and effective methods be developed (bandwidth usage & power) to transmit and receive the same while maintaining quality-of- speech, especially at the receiving end. Speech coding is a technique, since the era of digitization (digital) and computerization (computational and processing horsepower - DSP) that has been a material- of- research for quite some time amongst the scientific and academic community. This paper proposes modifications in grid selection strategy in Regular Pulse Excitation section of ETSI GSM 06.10 Full Rate 13 kbps coder [6] so that there is an overall 1.8 kbps (36bits / each 20ms frame) reduction in bit-rate which can be utilized for high bit rate data hiding. These steganographic 36bits are appended in class 1B (bit d146-d181) as per 05.03[7] to finally produce bitstream of 260 bits for each frame. So, proposed modifications in GSM FR allow joint data hiding and speech coding. Watermark data like text, audio and image can be reliably transmitted at a rate of 1.8 kbps with a small effect on Objective speech quality (as can be witnessed from the obtained results with text file chosen in our analysis) and with reasonable computational complexity [1]. Here, both ETSI GSM 06.10 FR coder and proposed steganographic GSM FR coders are implemented using Simulink model in MATLAB and then Objective analysis comparison between both coders are carried out using set of tables and graphs. Apart from hiding data, the proposed modifications in GSM FR is useful for overall reduction in codec bit-rate and provides room for better error concealment at channel coding. Keywords- Speech Coding, data hiding, steganography, ETSI, GSM, RPE-LTP coder, MATLAB, simulink I. INTRODUCTION In GSM network, “data hiding” or “digital watermarking” techniques can be used which allow secret data transmission by establishing virtual communication channel embedded within the transmitted host signal. The steganographic data embedded into host (cover) signals can be text, audio, image or multimedia signals. Data hiding for speech signal is mostly performed directly on digital speech signal or in a transformed domain but in later case the goal is to reduce audibility of embedded watermark [4]. In data hiding over speech signal, bit-rate of embedded watermark data and the speech quality of modified host signal are important factors. The good ‘data hiding’ scheme has to be designed such that (1) hidden data can successfully be extracted at receiver even in presence of possible deliberate attacks (2) The minimum data-rates should be guaranteed and (3) The modified host signal should not (or hardly) be subjectively distinguishable from original signal [4]. In contrast with potential applications of ‘data hiding’ in authentication and digital rights management, here in this research, the aim is hidden transmission of steganographic data over wireless channel as a part of host signal. Hence, robustness against deliberate attacks can be considered to be less relevant in comparison with other factors like higher hidden data-rates, constant (minimum) data-rate and robustness against transmission errors [2]. In our research, robustness against deliberate attacks is not investigated and studied rather the focus is given to the other important factors like higher hidden data-rates and constant (minimum) data-rates. In comparison with classical data hiding approaches, here, steganographic data can be embedded into compressed or encoded digital speech bitstream. So, this method is called as “bitstream watermarking” or “compressed domain watermarking” as steganographic data which is added to host signal where host signal is already compressed. This happens because the transmission system itself implements signal compression. Now the data embedding can either take place by content itself by overwriting least significant bits of respective parameters or by modifying partially decoded parameters by means of requantization [4]. In our research, we have partially modified the parameters and they have been requantized to provide room for embedding steganographic data into the bitstream of host signal. II. ETSI GSM 06.10 FULL RATE STRUCTURE Full Rate GSM 06.10 Speech Coder basically belongs to Hybrid coder (Analysis by Synthesis coder) which provides attractive tradeoff between waveform coders and vocoders, both in terms of speech quality and transmission bit rate, although generally at the price of higher complexity [1]. The speech encoder takes its input as a 13 bit uniform PCM signal either from the audio part of the mobile station or on the network side, from the PSTN via an 8bit / A-law to 13 (13bit* 8KHz=104Kbps) bit uniform PCM as specified in GSM 06.01 [6]. The encoded speech at the output of the speech encoder is delivered to a channel encoder unit which is specified in GSM 05.03 [6]. In the receive direction, inverse operations take place. GSM 06.10 describes the detailed mapping between input blocks of 160 speech samples in 13 bit 2011 International Conference on Communication Systems and Network Technologies 978-0-7695-4437-3/11 $26.00 © 2011 IEEE DOI 10.1109/CSNT.2011.13 27