In this paper, a simple subcarrier selection combining technique is proposed for orthogonal frequency-division multiplexing (OFDM) systems with multiple receive antennas. The subcarrier-based selection algorithm is developed in the frequency domain to achieve an optimal selection combining gain for OFDM systems, instead of the antenna-based selection algorithms in the time domain or frequency domain. The proposed technique selects an optimal subcarrier with a maximum channel gain among all the receive antennas with the same subcarrier position, based on the estimated channel frequency response during the training period. Hardware complexity for the proposed technique is minimal since it requires single front-end with multiple receive antennas and single baseband demodulator. It is shown by computer simulation that a significant gain can be achieved by the proposed technique over the conventional selection combining technique for OFDM systems in practical situations.

This paper considers a wireless coherent system that enables high-speed-data transmission in the presence of carrier phase error over an additive white Gaussian noise (AWGN) channel. Carrier phase noise is caused by imperfect carrier tracking of the coherent demodulation. The channel characteristics of the system were modeled using phase noise whose stochastic process followed the Tikhonov distribution. For this model, we first propose an optimum detector that produces the most suitable decoding metric for a soft-input/soft-output (SISO) decoder, and then develop some simpler forms of the optimum detector to obtain efficient implementation at close to optimal performance. Those simple detectors that have a wide range of performance/complexity tradeoffs are promising in various applications. To evaluate the effectiveness of the proposed detectors, we have applied them to a bandwidth-efficient turbo-coded modulation scheme in which a component decoder based on SISO principles necessitates more exact channel measurement than is possible with a conventional decoder based on Viterbi decoding. Simulation results have demonstrated that the optimum detector enables excellent bit error rate (BER) performance that exceeds that with a normal detector designed for AWGN channels by more than 1 dB at a BER of 10-6 under a severe phase noise environment.

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 compares the radio link capacity between multi-carrier/DS-CDMA (MC/DS-CDMA) and multi-carrier CDMA (MC-CDMA) for reverse-link broadband packet wireless access taking into consideration: the asynchronous signal reception at the receiver; the path timing or symbol timing detection of all major subject factors; and the channel estimation error. Simulation results show that although the influence of the asynchronous signal reception on the packet error rate (PER) performance in MC-CDMA is slight, the degradation caused by the channel estimation error in MC-CDMA is severe compared to that caused by the path timing detection error in MC/DS-CDMA. Consequently, the required average received signal energy per bit-to-background noise spectrum density ratio (Eb/N0) at the average PER of 10-2 in MC/DS-CDMA is reduced by approximately 4.5 dB compared to that in MC-CDMA assuming a 12-path exponential decayed Rayleigh fading channel. Furthermore, the number of accommodated users in MC/DS-CDMA is 2.5 fold greater than that in MC-CDMA employing two-branch antenna diversity reception. Therefore, we conclude that MC/DS-CDMA is more appropriate than MC-CDMA for the reverse link broadband packet wireless access, and that it has advantageous features such as an inherently much lower peak-to-average power ratio compared to MC-CDMA, which accompanies a high peak-to-average power ratio causing an increase in the back-off of the power amplifier.

This paper proposes an efficient random access channel (RACH) transmission method that utilizes soft-combined consecutively retransmitted message data packets according to the Quality of Service (QoS) requirements for broadband multi-carrier/DS-CDMA (MC/DS-CDMA) in the reverse link. In the proposed scheme, the relative transmission power of a message from that of a successfully detected preamble for non-real time (NRT) type traffic data is significantly reduced by soft-combining several retransmitted message data packets thanks to time diversity since the delay requirement is relaxed. Meanwhile, for real time (RT) type traffic data, the relative transmission power of the message from that of the detected preamble is increased in order to reduce the packet error rate with a limited number of retransmissions. Simulation results elucidate that the total required average received signal energy per bit-to-background noise power spectrum density ratio (Eb/N0) for error-free transmission with time diversity for NRT type traffic data is reduced by more than 2 dB compared to that for conventional RACH without the relative transmission power control for a wide rage of fading maximum Doppler frequencies.

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.

A simple configuration for millimeter-wave fiber-wireless transmission, with remote local-oscillator (LO) delivery from the central office, both for the uplink and for the downlink, and a simple, cost-effective, base-station solution is proposed. Under the assumption of using commercially available components and a conventional single-mode fiber (with dispersion of 17 ps/nm/km at 1.55 µm), our numerical results show that, with a laser linewidth of 150 MHz, a laser power of 0 dBm and an optical gain of only 6 dB, it is possible to transmit, without repeaters, data rates of 622 Mbit/s across about 18 km at a bit-error-rate of 10-9. By increasing the optical gain to 24 dB, the link length can be increased to approximately 67 km for a laser linewidth of 75 MHz and to 78 km for a laser linewidth 1 MHz.

In this paper, we propose a new transmitter diversity. We propose a combined system with path diversity gain of the distributed antennas and frequency diversity gain of the multi-carrier. The proposed system transmits different data using several sub-carriers which are correlated, while, transmitting the same data using several sub-carriers which are decorrelated. It can achieve combined path and frequency diversity in a variable frequency selective fading channel. It provides high data rate services by transmitting the different data using each correlated carrier, and supports good quality by transmitting the same data on decorrelated carriers using multiple antennas. The proposed system is applicable to multimedia service and can achieve high quality according to channel condition. Thus, the proposed system is sufficiently flexible enough to very support a variety of video, image, voice and data services at a high level of quality.

This paper presents an efficient application of hot-carrier reliability simulation to delay libraries of 0.18µm and 0.14µm gate length logic products. Using analysis of simple primitive inverter cells, a design rule was developed in restricting signal rise time, and delay libraries of actual products were screened to check whether the rise time restrictions were met. At 200MHz, maximum rise time (0-100%) triseMAX was 0.8nsec (17% of duty) under Δtd/td = 5%. For a 800,000 net product, only 25 simulations were done (each less than one minute CPU time) for the internal devices with screening done for this logic process. 30 nets were caught, but judged reliable due to their reduced duty.

The power dissipation tolerances for InP/ InGaAs uni-travelling-carrier photodiodes (UTC-PDs) and pin-PDs under high power optical inputs are compared. Catastrophic failures occur at constant power dissipations of 240 and 160mW for the UTC-PDs and pin-PDs, respectively. Scanning electron microscope observations confirm that the areas of destruction are located in the high electric-field region in the depletion layer.

An 80 Gbit/s conventional and carrier-suppressed return-to-zero optical time-division multiplexing signal transmission over a 208 km standard single-mode fiber was experimentally demonstrated. This was achieved by using mid-span optical phase conjugation based on four-wave mixing in semiconductor optical amplifiers. In addition, it was confirmed that the transmitted carrier-suppressed return-to-zero optical signal's carrier phase-relation was held.

Time variations of the wireless channel cause Inter-Carrier Interference (ICI) between different subcarriers in an OFDM system. In a highly mobile environment this interference may become so high that it degrades up to unacceptable levels the communication channel. In this paper, firstly we obtain a simplified expression for the total ICI experienced by every subcarrier in an OFDMA system. Unlike other previous works, the result establishes an explicit and useful relation between the ICI on each subcarrier and the speed of the rest of the terminals in the system. Then, by means of a mathematical analysis we extend the scope of that expression to a hybrid system in which OFDMA and CDMA are combined. Using the good autocorrelation and cross-correlation properties provided by Gold-sequences we propose a Gold-Code-based CDMA-OFDMA transmission technique for the asynchronous uplink channel. We show that the proposed method can reduce the total ICI and potentially increase the capacity of the system in comparison to a conventional OFDMA system.

A new bandwidth-efficient asynchronous multicarrier DS CDMA scheme is proposed for the uplink. In this new scheme, each user employs a set of FIR filters whose impulse responses are a mutually orthogonal (MO) complementary set of sequences. The intentional inter-symbol interference (ISI) and multiple access interference (MAI) are eliminated by the properties of these sequences. We also propose applying this new scheme in a DS CDMA packet network in which slotted ALOHA or pure ALOHA protocol is used. Packet throughput figures are obtained for the new ALOHA/bandwidth-efficient asynchronous MC DS CDMA packet network. Numerical results are given for both slotted and pure ALOHA cases. With the same bandwidth and number of simultaneous users, the throughput is compared favorably to similar figures for single-carrier DS CDMA with random spreading sequences.

In this paper, we propose a TCAD driven hot carrier reduction methodology of 3.3 V I/O pMOSFETs design. The hot carrier reliability of surface channel I/O pMOSFET having drain structure in common with core devices has a critical issue. It is substantially important for the high-reliability devices to reduce both drain avalanche and channel hot hole components. The drain structures are successfully optimized in short time by applications of TCAD local models. Considering tradeoffs between hot carrier injection (HCI) and drive current (ION), SDE/HALO of both core and I/O transistors can be totally optimized for reduction of process-steps and/or photo-masks.

This paper presents a cell search scheme embedded with carrier frequency synchronization for inter-cell asynchronous orthogonal frequency-division multiplexing code-division multiplexing (OFDM-CDM) systems. Several subcarriers are dedicated to a differentially encoded synchronization channel (SCH). In the other subcarriers, data symbols and pilot symbols are two-dimensionally spread in the time-frequency domain. The cell search scheme consists of a three-stage cell search and a two-stage carrier-frequency synchronization, that is, coarse carrier-frequency acquisition, fast Fourier transform window-timing detection, SCH frame-timing detection, fine carrier-frequency synchronization, and cell-specific scrambling code (CSSC) identification. Simulation demonstrated that this scheme can identify the CSSC with high detection probability while precisely synchronizing the carrier frequency in severe frequency-selective fading channels.

This paper proposes a novel synchronization method of jointly estimating symbol frame timing and carrier frequency-offset for Orthogonal Frequency Division Multiplexing (OFDM) signal operating in the burst mode which is usually employed in the wireless LAN communications systems. The proposed method enables a fast and accurate synchronization for the burst mode OFDM signal even under the presence of large frequency-offset, very low C/N and frequency selective fading environments by using only two preamble symbols inserted at the start of every burst frame. This paper presents the various computer simulation results to verify the performance of proposed synchronization methods both for symbol timing and carrier frequency.

The adaptive phase tracking scheme for orthogonal frequency division multiplexing (OFDM) signals can provide superior PER performance in channels with varying phase noise power. It is an effective technique for achieving high-rate and high quality wireless transmission. This paper proposes a new simple adaptive phase tracking scheme for OFDM signals in order to realize high-rate wireless local area networks (LANs). The proposed scheme measures the integrated phase rotation in order to appropriately set the properties of the FIR filter in the phase tracking circuits. This scheme uses the fact that the integrated phase rotation is correlated to the phase noise power. Assuming an RMS delay spread of 100 ns, computer simulations show that the proposed scheme offers superior required Eb/N0 performance (with regard to the phase noise power) compared to the conventional fixed-tap scheme, where the phase noise to signal power ratios are below -18 dB. It also offers excellent PER performance at the packet length of 1000 bytes unlike the conventional schemes, which suffer degraded PER performance.

OFDM transmission performance in mobile communications suffers severe degradation caused by multipath delay difference greater than the Guard Interval (GI). This is because the excess delay results in considerable Inter-Symbol Interference (ISI) between temporally adjacent symbols and Inter-Carrier Interference (ICI) among subcarriers in the same symbol. This paper proposes a robust OFDM receiver for the scattered pilot OFDM signal that can effectively suppress both ISI and ICI by using two types of equalization and a smoothed FFT-window. In order to verify the performance of the proposed receiver, computer simulations are conducted in accordance with the scattered pilot OFDM signal format of the Digital Terrestrial Television Broadcasting (DTTB). The simulation results demonstrate that the proposed receiver shows much better performance than the conventional receiver in multipath fading environments with the delay difference greater than GI duration.

In this paper, a new approach is proposed to improve the channel estimation accuracy with channel tracking capability for adaptive multicarrier equalization systems under time-variant multipath fading channel. The improvement is carried out based on the assumption that the channel is static over a transmitted block period, and slowly linearly changing over several block periods. By applying IFFT to the concatenated channel transfer function derived from different blocks, the noise-averaging improvement is achieved, and a better estimation of the channel coefficients with some delay can be obtained. A multi-step channel predictor and a smoothing filter is utilized to compensate for the delay and make the system more robust in terms of channel tracking performance. Adaptive time domain equalization is jointly performed with this approach to avoid the channel invertibility problem found in the frequency domain approach. A short period of training sequences is utilized resulting in more efficient use of available communication capacity. The effectiveness of the proposed approach is evaluated through simulation for multicarrier systems in time-variant multipath fading channels. Results show improvement over previous channel estimation schemes.

In this paper, we propose and describe a new synchronizer for the FFT timing applicable to multi-carrier spread-spectrum (MC-SS) communication systems. The performance of the synchronizer is evaluated in terms of false- and miss-detection probabilities in the presence of additive white Gaussian noise (AWGN) and Rayleigh fading.