This letter presents a buck converter for the dynamic voltage scaling systems where the supply voltage is dynamically adjusted to the minimum value required by the applications. A voltage controlled delay line based PWM controller is designed to simplify the structure for the purpose of energy saving. In order to speed up the transient response, the pseudo-continuous conduction mode and the pulse division technique are used. When the switching frequency ƒ is 800kHz and the input voltage is 3.3V, the output voltage of the converter is dynamically modulated from 1.7V to 2.8V according to a changeable reference clock ƒref from 70MHz to 140MHz. A fast transient response of 5.27µs for a step voltage change from standby to the maximum operation is obtained. The output voltage ripple is less than 2mV.
The H.264/AVC coding standard only specifies the decoding process and the bitstream syntax to allow considerable flexibility for the designers to optimize the encoder for coding performance improvement and complexity reduction. This paper proposes the use of redundant Predicted (Marionette) frames to prevent temporal error propagation in H.264/AVC streaming over error prone wireless channels. Compared with the H.264/AVC conventional redundant slices technique, our proposed approach can effectively enhance the smoothness of the video. A visual quality comparative study has been also carried out in order to validate the proposed approach.
In this paper, we propose a novel sub-optimum detection technique for asynchronous multicarrier code-division multiple-access (MC-CDMA) systems. The proposed technique extracts desired user's bits by means of expectation-maximization (EM) algorithm considering outputs of subcarriers demodulators as observation data. Our presented numerical results demonstrate the efficiency of the proposed detection algorithm both in bit error rate performance and computational complexity points of view.
A fully reconfigurable architecture of a LDPC (low-density parity check) decoder for IEEE 802.11n system is proposed in this paper. This architecture can be operated in 12 kinds of modes specified in IEEE 802.11 system. Under the proposed architecture, memory usage and hardware complexity obviously improved, as compared with the other research works. Furthermore, the proposed decoder also able to support multi-rate and multi-size LDPC codes decoding. The proposed decoder was implemented in UMC 0.18µm CMOS technology. The maximum operating frequency is measured 200MHz and the corresponding power dissipation is 691.23mW and total area is 4.61mm2.
This paper proposes an amplitude-modulated and phase-inverted (AMPI) ultrasonic driving signal for accurate distance measurements. Undesirable part of the ultrasonic wave was canceled using the phase-inverted wave and its active canceling effect was enhanced by the amplitude-modulation, so that a unique ultrasonic waveform having a sharp envelope could be generated even with a narrow-band transducer of frequency 40kHz (wavelength λ ≅ 9mm). The sharp envelope generated by the AMPI signal determined a zero-crossing time without any uncertainty. As a result, an accuracy better than 0.02mm was achieved in the range of 0.1 - 0.5m.
A cooperative communication in a two-way relay channel is a bidirectional communication between two terminals with the aid of a common relay. In order to improve the performance of the cooperative communication in a two-way relay channel, a network coding can be used to exploit the broadcasting nature of wireless transmission. In , it was shown that each individual link can achieve its own capacity when the length of the codewords is the same. However, the length of the codewords can be different in practical systems since the two-way relay channel is naturally asymmetric. Thus, in this paper, we show a practical network coding scheme with a given modulation and coding set by employing a rate-compatible puncturing technique. Simulation results show that the proposed scheme can provide at least as good performance as that obtained in individual link without using special encoder/decoder.
In this paper a reduced size microstrip log periodic dipole antenna with top loading of elements is presented. In many situations, the lateral size of the LPDA antenna has to be reduced to fit the antenna into the installation space. In this work, top loaded element structure is adopted to reduce the size of the dipole elements. Each straight dipole element of the LPDA antenna is turned into a T-shaped element whose total length is equal to that of the original straight dipole element length, resulting in a dipole length that is half that of the original dipole element, i.e. lateral size of the LPDA has been reduced by more than half. This procedure can be repeated to reduce the dipole element length even further, by placing a double T-shaped element on top of each other, resulting in an overall length that is almost 46% of the original dipole element length. Comparison of the reduced sized LPDA with that of the original LPDA shows that the VSWR (≤ 2.0) results of the reduced size LPDA are lower than those of the straight elements over the 2.3-8GHz frequency band. For the three LPDA structures results of peak gain shows that on average over the frequency band, 2-8GHz, gain varies between 5-6dBi. Simulation and measured results on VSWR, radiation pattern and gain at the various frequencies are provided.