Companding Systems Research Articles

Multilevel Delta Modulation with Switched First-Order Prediction for Wideband Speech Coding

In this paper a delta modulation speech coding scheme based on the ITU-T G.711 standard and the switched first-order predictor is presented. The forward adaptive scheme is used, where the adaptation to the signal variance is performed on frame-by-frame basis. The classification of the frames into weakly and highly correlated was done based on the correlation coefficient calculated for each frame, providing a basis for choosing the appropriate predictor coefficient. The obtained results indicate that the proposed model significantly outperforms the scalar companding system based on the G.711 standard. The obtained experimental results were verified using the theoretical model in the wide dynamic range of the input variance. DOI: http://dx.doi.org/10.5755/j01.eie.24.1.20156

MC CDMA Papr Reduction Techniques Using Discrete Transforms And Companding

High Peak to Average Power Ratio (PAPR) of the transmitted signal is a serious problem in multicarrier modulation systems. In this paper a new technique for reduction in PAPR of the Multicarrier Code Division Multiple Access (MC CDMA) signals based on combining the Discrete Transform either Discrete Cosine Transform (DCT) or multi-resolution Discrete Wavelet Transform (DWT) with companding is proposed. It is analyzed and implemented using MATLAB. Simulation results of reduction in PAPR and power Spectral Density (PSD) of the MC CDMA with companding and without companding are compared with the MC CDMA with DCT and companding, DWT and companding systems. The new technique proposed is to make use of multi-resolution DWT in combination with companding in order to achieve a very substantial reduction in PAPR of the MC CDMA signal.

Performance enhancement of SC-FDMA systems using a companding technique

In this paper, a companding technique is proposed to effectively reduce the peak-to-average power ratio (PAPR) in single-carrier frequency division multiple access (SC-FDMA) systems. By companding the samples with large amplitudes, while enhancing those with small amplitudes, a significant reduction in the PAPR can be achieved. The performance of the proposed SC-FDMA with companding system is studied and compared with that of the standard SC-FDMA system. Simulation results show that the SC-FDMA with companding system has a lower PAPR when compared with the conventional SC-FDMA system, while the complexity of the system slightly increases. Results also reveal that the companding coefficient must be chosen carefully in order to limit the PAPR without introducing degradations into the bit error rate performance.

Companding System Based on Time Clustering for Reducing Peak Power of OFDM Symbol in Wireless Communications

This paper proposes a novel compressing and expanding (companding) system for OFDM wireless communications that minimizes the compression distortion and so reduces the peak power of OFDM symbols. OFDM systems suffer from large variations in instantaneous peak power. Such transients distort the signals when they are passed through a nonlinear high power amplifier (HPA) prior to transmission. Existing companding systems are far from perfect since the receiver can not accurately estimate the degree of compression applied by the transmitter and thus can not regenerate the original signal by expansion; the key problems are the band pass filter (BPF), HPA, and the noise component enhanced by the channel compensation filter. In the proposed companding system, each symbol is divided into segments, and series of consecutive segments are grouped into clusters. Each cluster is multiplied by a weight equal to the inverse of the largest instantaneous power within the cluster. The receiver estimates the weight used for each time cluster. The weights for all clusters are averaged to mitigate the weight estimation error. As a result, the proposed expander can accurately estimate the weights used and thus well suppress the compression distortion.

Systematic Design of Companding Systems by Component Substitution

A design method for externally linear, internally nonlinear systems is presented which allows them to be derived from externally equivalent systems in a systematic way and with a minimum synthesis effort, just performing a simple component-to-component substitution. As a particular case, the synthesis of the most popular versions of voltage companding systems from externally equivalent Gm-C systems is addressed. The practical design of companding systems based on the MOS square law (Square-Root Domain systems) is fully illustrated along the complete design flow, from the Gm-C prototype to silicon. These systems, feasible in CMOS technologies and formerly difficult to obtain due to the inherent complexity of existing synthesis methods, particularly benefit from the simplicity of the proposed approach. Experimental results for two versions of tunable Square-Root Domain biquadratic filters and oscillators thus obtained and fabricated in a 2.4-μm CMOS process are presented, featuring favorable tunability and low THD.

A 1.2-V low-power BiCMOS class AB log-domain filter

A third-order class AB current-mode Chebyshev filter based on the log-domain instantaneous companding principle and integrated in a 1-/spl mu/m BiCMOS process is presented. It has a nominal cutoff frequency of 320 kHz corresponding to a bias current of 1 /spl mu/A and can be frequency tuned over almost three decades up to about 10 MHz. It operates with a nominal supply voltage of 1.2 V maintaining a dynamic range at 1% total harmonic distortion (THD) of 65 dB. For cutoff frequencies in the range of 10 kHz, the supply voltage can be reduced down to 0.9 V. Typical to companding systems, the class AB filter shows a measured SNR versus input signal that saturates to a maximum value which for this particular realization is 52.5 dB. It has an active area of 0.55 mm/sup 2/ and dissipates 65 /spl mu/W, leading to a power consumption per pole and edge frequency of 67.7 pJ. These results demonstrate the potential of instantaneous companding filters for very low-voltage and low-power applications with moderate linearity and SNR requirements.

Piecewise uniform vector quantizers

The companding model for quantizer design and analysis has been widely applied in the scalar quantization case. However, if the signal to be quantized is a vector, then the optimum companding system can be designed for only a limited number of distributions. On the other hand, multidimensional piecewise linear companders can be designed for any signal density, generating quantizers that are uniform on each region of the compander. These systems, while not optimal, can have asymptotic performance arbitrarily close to the optimum. Their analysis and implementation can be simpler than those of optimal systems. Piecewise linear companders for asymptotic multidimensional quantization are analyzed, and a method for their design is suggested. >

A Companding System for Multichannel TV Sound

The US Federal Communications Commission recently authorized the broadcast of multichannel sound for television. A five-year industrywide effort sponsored by the Electronics Industries Association resulted in a new standard for transmission of stereo information with the simultaneous opportunity for broadcasting a separate Second Audio Program (SAP) channel. This standard includes a unique three-part companded noise-reduction system intended to allow broadcasters to increase their programing options without reducing present coverage area.

Adaptive Delta Modulation

In this paper, design principles of a delta modulator are discussed to arrive at the design parameters. For a sampling rate of 25 K/bits and reference frequency of speech at 1·12 KHz, the maximum signal to quantization noise ratio is found to be around 24 db. The concept of reference frequency of speech spectrum is explained while deriving the design parameters. The parameter S/K, which is the ratio of signal amplitude to quantizing step, is then, used for discussing the principles of companding, keeping the signal to quantizing noise power ratio constant. Syllabic compandor and instantaneous compander are then discussed. Performance characteristics of a companded system is also given.