A new technique based on the auto-correlation function is described for the estimation of the Doppler spread in mobile communication systems. We first propose to divide a uncertainty region of Doppler spread into multiple frequency bins. Based on the given multiple bins the correlator compares the estimated value at a certain time index to the theoretical exact value and then decides which bin the Doppler spread is estimated in. The certain time index can be optimized to give the largest decision region among multiple bins. We derive the optimum time index algorithm to give the largest decision region for each bin based on Rayleigh fading channel. We also apply the same Doppler spread estimator to the Rician case with the slight transformation of the received signal. We show that the proposed technique is not affected significantly by the Rician factor and the SNR degradation with the reasonable number of samples for estimation which is not the case of other estimators given in the literature.

This paper investigates a random-interleaver-based approach to space-time coding. The basic principle is to employ a good forward error correction (FEC) code and transmit randomly interleaved codewords over an antenna array. A low-cost estimation technique is considered. The complexity involved grows only linearly with the number of transmit antennas. Near-capacity performance can be achieved with moderate complexity.

This paper is concerned with the signal processing aspects of the recently proposed interleave-division multiple-access (IDMA) scheme. We propose several low-cost detection algorithms to solve the problems of multiple-access, cross-antenna and intersymbol interference (ISI). The complexities (per user) of these algorithms are very low and increase either linearly or quadratically with the number of paths. It is shown that an IDMA system with a rate- 16-state convolutional code and a length-8 spreading sequence can support more than 100 users in a multipath fading channel with two receive antennas. This clearly indicates the great potential of IDMA systems.

This paper presents a novel decoding strategy called combined iterative demapping/decoding (CIDD), for coded M-ary biorthogonal keying-based direct sequence ultra-wideband (MBOK DS-UWB) systems. A coded MBOK DS-UWB system consists of a convolutional encoder, an interleaver, and an MBOK DS-UWB pulse mapper. CIDD improves the error rate performance of MBOK DS-UWB systems by applying the turbo principle to the demapping and decoding processes at the receiver side. To develop the CIDD, a soft-in/soft-out MBOK demapping algorithm, based on the max-log-MAP algorithm, was derived. Simulation results showed that using CIDD siginificantly improved the error rate performance of both static and multipath fading channels. It was also shown that the computational complexity of CIDD is comparable to that of the Viterbi decoding used in [133,171]8 conventional convolutional coding.

One of the categories of decoding techniques for DFT codes in erasure channels is the class of iterative algorithms. Iterative algorithms can be considered as kind of alternating mapping methods using the given information in a repetitive way. In this paper, we propose a new iterative method for decoding DFT codes. It will be shown that the proposed method outperforms the well-known methods such as Wiley/Marvasti, and ADPW methods in the decoding of DFT codes in erasure channels.

Unlike most of the previous work for smart antennas that covered each area individually (antenna-array design, signal processing and communications algorithms and network throughput), this paper may be considered as a review of comprehensive effort on smart antennas that examines and integrates antenna array design, the development of signal processing algorithms (for angle of arrival estimation and adaptive beamforming), strategies for combating fading, and the impact on the network throughput. In particular, this study considers problems dealing with the impact of the antenna design on the network throughput. In addition, fading channels and tradeoffs between diversity combining and adaptive beamforming are examined as well as channel coding to improve the system performance.

We propose a neural-sensing LSI with a bi-directional wireless interface, which is capable of detecting 5-channel neural signals in a living animal. The proposed sensing LSI consists of a multiplexer with 5-channels selectable from 10 channels, a chopper amplifier using a new direct-chopper-input scheme, a programmable multi-mode analog-to-digital converter (ADC), and a wireless-transmitter/receiver with BPSK modulation signals. The test-chip was implemented by mixed-signal 0.35-µm CMOS technology. We measured the test chip and confirmed basic operations of these blocks. The chopper-amplifier achieved 66-dB DC gain, bandwidth of 400 kHz, and 4-µV noise with power dissipation of 6-mW with a 3-V supply. We observed real nerve signals in a living cricket using the proposed chopper amplifier. ADC achieved 52-ksps operation with power dissipation of 0.43-mW at 3-V supply. The wireless transmitter achieved 1-Mbps data transmission at a distance of 1-m with 1.5-mW power dissipation at 3-V supply.

Channel estimation is one of the key technologies in mobile communications. Channel estimation is critical in providing high data rate services and to overcome fast fading in very high-speed mobile communications. This paper presents a novel channel estimation based on hybrid spreading of I and Q signals (CEHS). Simulation results show that it can effectively mitigate the influence of fast fading and enable to provide high data rates for very high speed mobile systems.

In this paper, we present a new closed-form formula for the ergodic capacity of multiple-input multiple-output (MIMO) wireless channels. Assuming independent and identically distributed (i.i.d.) Rayleigh flat-fading between antenna pairs and equal power allocation to each of the transmit antennas, the ergodic capacity of such channels is expressed in closed form as finite sums of the exponential integrals which are the special cases of the complementary incomplete gamma function. Using the asymptotic capacity rate of MIMO channels, which is defined as the asymptotic growth rate of the ergodic capacity, we also give simple approximate expressions for the MIMO capacity. Numerical results show that the approximations are quite accurate for the entire range of average signal-to-noise ratios.

A neural-signal sensing system with multi-input-channels was designed utilizing a new chopper amplifier with direct connected to a multiplexer. The proposed system consists of multiplexers, chopper amplifiers, a multi-mode analog-to-digital converter (ADC), and a wireless transmitter. It enables to measure 50-channel signals at the same time, which are selected out of 100 channels to detect useful information. The test chip including 10-channel-inputs chopper-amplifier and multi-mode ADC, that was designed and fabricated with a mixed signal 0.35-µm CMOS technology. Utilizing the proposed direct chopper input scheme and the shared chopper amplifier, the circuits was designed with a small area of 9.4 mm2. High accuracy channel selecting and multiplexing operations were confirmed, and an equivalent input noise of 10-nV/root-Hz was obtained with test chip measurements. Power dissipation of the chopper amplifier and the ADC were 6.0-mW and 2.5-mW at a 3-V supply voltage, respectively.

We analytically investigate combinatorial effects of timer control and backoff algorithms on performance of bulk data transfer over two-state Markovian packet error channels. Numerical results for throughput, energy efficiency, and the probabilities of packet loss and loss of bulk data indicate that linear backoff algorithms outperform binary exponential ones as a whole when they are employed at the logical link sublayer with timer control.

The design criteria for space-time trellis codes (STTC's) in fast fading channels have been proposed: the Distance Criterion and the Product Criterion. The design criteria in [1] are based on optimizing the pairwise error probability (PWEP). However, the frame error rate (FER) of STTC's depends on the distance spectrum. In this paper, we propose a new design criterion for STTC's based on the distance spectrum in fast fading channels. The proposed design criterion is based on the product distance distribution for the large signal-to-noise ratio (SNR) and the trace distribution for the small SNR, respectively. Moreover, we propose new STTC's by the computer search based on the proposed design criterion in fast fading channels. By computer simulation, we show that the proposed design criterion is more useful than the Product Criterion in [1] in fast fading channels. We also show that the proposed STTC's achieve better FER than the conventional STTC's in fast fading channels.

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, an online SNR estimator is proposed for parallel combinatorial SS (PC/SS) systems in Nakagami fading channels. The PC/SS systems are called as partial-code-parallel multicode DS/SS systems, which have the higher-speed data transmission capability comparing with conventional multicode DS/SS systems referred to as all-code-parallel systems. We propose an SNR estimator based on a statistical ratio of correlator outputs at the receiver. The SNR at the correlator output is estimated through a simple polynomial from the statistical ratio. We investigate the SNR estimation accuracy in Nakagami fading channels through computer simulations. In addition, we apply it to the convolutional coded PC/SS systems with iterative demodulation and decoding to evaluate the estimation performance from the viewpoint of error rate. Numerical results show that the PC/SS systems with the proposed SNR estimator have superior estimation performance to conventional DS/SS systems. It is also shown that the bit error rate performance using our SNR estimation method is close to the performance with perfect knowledge of channel state information in Nakagami fading channels and correlated Rayleigh fading channels.

Let us introduce n ( 2) mappings fi (i=1,2,,n) defined on complete linear metric spaces (Xi-1, ρ) (i=1,2,,n), respectively, and let fi:Xi-1 Xi be completely continuous on bounded convex closed subsets Xi-1(0) Xi-1, (i=1,2,,n 0), such that fi(Xi-1(0)) Xi(0). Moreover, let us introduce n set-valued mappings Fi : Xi-1 Xi (Xi)(the family of all non-empty closed compact subsets of Xi), (i=1,2,,n 0). Here, we have a fixed point theorem on the successively recurrent system of set-valued mapping equations: xi Fi(xi-1, fi(xi-1)), (i=1,2,,n 0). This theorem can be applied immediately to analysis of the availability of system of circular networks of channels undergone by uncertain fluctuations and to evaluation of the tolerability of behaviors of those systems. In this paper, mathematical situation and detailed proof are discussed, about this theorem.

In this paper, we propose an efficient dual-tree-based multicasting scheme with three destination-switch partition strategies on irregular switch-based networks. The dual-tree-based routing scheme supports adaptive, distributed, and deadlock-free multicast on irregular networks with double channels. We first describe a dual-tree structure constructed from the irregular networks and prove that the multicasting based on such a structure is deadlock-free. Then, an efficient multicast routing algorithm with three destination-switch partition strategies: source-switch-based partition, destination-switch-based partition, and all-switches-based partition, is proposed. Finally, we perform simulations to evaluate our proposed algorithm under various impact parameters: system size, message length, and startup time. The experimental results show that the improved tree-based multicasting scheme outperforms the usual tree-based multicasting scheme. The dual-tree-based multicasting scheme with destination-switch-based partition is shown to be the best for all situations.

Since components faults occurring at arbitrary places (primarily on the links) affect seriously network performance and reliability, the multicomputers operating in harsh environments should be designed to guarantee normal network-missions in presence of those faults. One solution to the end is a fault-tolerant routing scheme, which enables messages to safely reach their destinations avoiding failed links when transmission of messages is blocked by certain faults. In the paper, we develop a fault-tolerant routing algorithm with deadlock freedom in an n-dimensional meshed network, and validate its efficiency and effectiveness through proper simulations. The aspects of fault-tolerance is adopted by appending partial-adaptiveness and detouring to the e-cube algorithm, while using a wormhole routing for the backbone routing method. The phenomenon of deadlock incurred due to its adaptiveness is eliminated by classifying a physical channel into a couple of virtual channels.

Near-optimality of subcodes of the cyclic Hamming codes is demonstrated on the binary additive channel whose noise process is the two-state homogeneous Markov chain, which is a model of bursty communication channels.

We propose a new structure of decision feedback adaptive equalizer (DFE) suitable for use in mobile radio systems. The proposed structure named Commutating Decision Feedback Equalizer (CDFE) has two DFEs that operate in a commutating fashion; the two DFEs commutate between training and equalization. Such a commutating operation effectively lengthens the equalizer tracking period over time variant channels. Thus, the CDFE has a superior performance over the conventional DFE in fading channels. Simulation results are presented in the paper.

A simplified analysis is presented for the reverse link maximum capacity trade-offs between each layer, spectrum efficiency and its multi-rate features of TDMA/W-CDMA and N-CDMA/W-CDMA overlaid systems with the perfect power control based on the measurement of signal-to-interference ratio (CIR). In order to suppress the multi-cross interference, the other important techniques used in the analysis are the ideal notch filtering and the signal level clipper for W-CDMA system transmitters and receivers. We firstly propose the concepts of the notch filtering depth and signal level clipping depth in the paper. The numerical results can be adopted as a guideline in designing the overlaid systems in the various cases as well as a means to investigate the flexibility of sharing of the spread spectrum and their feasibility in the future mobile communication system.