We propose a multiple-subcarrier (MS) optical communication system using intensity modulation with direct detection (IM/DD) with peak reduction carriers (PRCs) to improve the power efficiency of IM/DD MS systems. The proposed system transmits L subcarriers referred to as PRCs among N subcarriers for the d.c. bias reduction so that the optical power is reduced. Since information bits are mapped onto each subcarrier other than PRCs independently, the information bits of each subcarrier can be detected independently and the error rate of the proposed system is unaffected by PRCs.

Orthogonal frequency division multiplexing (OFDM) is a possible candidate for the modulation used in mobile multimedia communications because of its robustness to fading and flexibility of transmission rate. Partial transmit sequence (PTS) is an effective technique for reducing the peak power of OFDM signals by means of phase rotation. In PTS, side information (SI) is transmitted to correct the effects of the phase rotation. We propose a new method based on rotationally invariant trellis coded modulation for coded OFDM with PTS. In this method, no SI is required and the few information bits affected by the phase rotation are not used as data. (They are regarded as dummy bits). It is shown that the proposed method yields better bit error rate (BER) performance than other methods using side information under the condition of almost the same transmission rate.

This paper addresses bitwidth optimization focusing on leakage power reduction for system-level low-power design. By means of tuning the design parameter, bitwidth tailored to a given application requirements, the datapath width of processors and size of memories are optimized resulting in significant leakage power reduction besides dynamic power reduction. Experimental results for several real embedded applications, show power reduction without performance penalty range from about 21.5% to 66.2% of leakage power, and 14.5% to 59.2% of dynamic power.

A peak power reduction technique is proposed for subcarrier transmit power control applied orthogonal frequency division multiplexing (OFDM) system. In the proposed system, carrier-holes are created by applying a partial non-power allocation (PNPA) technique in which no transmit power is allocated to subcarriers with lower received Eb/N0, and the amplitude and phase adjusted peak reduction subcarrier (PRS) is iteratively inserted in the non-power allocated subcarrier so as to suppress peak power. Computer simulation confirms that the proposed scheme can reduce peak power by 3.6 dB while keeping the same information bit-rate with conventional subcarrier transmit power control applied OFDM systems.

This paper proposes a new signal peak power reduction technique, Peak Reduction based on Control Signal Insertion (PRCSI), for broadband mobile communications based on multi-channel signaling schemes. PRCSI reduces the peak power with a peak control signal that is generated symbol-by-symbol; no signal band expansion is incurred because the peak control signal is inserted into the transmission signal band. PRCSI can achieve 4 dB peak power reduction for 8-carrier signaling, while the Eb/N0 value required to achieve 10-3 average BER is 1 dB larger with PRCSI than without it. This BER performance degradation can effectively be compensated by the proper use of Trellis coding. The proposed technique is applied to OFDM transmission systems with large carrier number. The proposed technique can achieve 3-dB peak power ratio for 128-carrier OFDM signals with less than 1-dB performance degradation at the BER of 10-3.

This paper presents a test vector modification method for reducing average power dissipation during test application for a full-scan circuit. The method first identifies a set of don't care (X) inputs of given test vectors, to which either logic value 0 or 1 can be assigned without losing fault coverage. Then, the method reassigns logic values to the X inputs so as to decrease switching activity of the circuit during scan shifting. Experimental results for benchmark circuits show the proposed method could decrease switching activity of a given test set to 45% of the original test sets in average.