This paper aims to improve the performance of the soft canceller followed by simplified minimum mean-square error (SC/S-MMSE) turbo receiver for multiple-input and multiple-output space-division multiplexing/orthogonal frequency division multiplexing (MIMO-SDM/OFDM) transmission; it performs iterative parallel soft interference cancellation and MMSE filtering, and stream-wise soft-input and soft-output decoding. For this aim, we newly introduce two detection techniques: 1) serial interference cancellation, and 2) cyclic redundancy check (CRC)-assisted interference cancellation and MMSE filter tap computation. Various computer simulations are conducted to evaluate the performance enhancement obtained via the use of the two detection techniques. The computer simulation results show that this paper's proposed serial SC/S-MMSE turbo receiver with CRC achieves frame error rate (FER) performance gain over existing MIMO receivers (MMSE receiver, V-BLAST receiver, parallel SC/MMSE-matched filter (MF) turbo receiver, and parallel SC/S-MMSE turbo receiver) for QPSK, 16QAM and 64QAM modulation while keeping the comparable complexity order.

In this paper an analog-digital signal processing scheme for multichannel signal reception with low-IF receivers is proposed and its performance is investigated. In the low-IF receivers, the signal in the mirror frequency causes interference to the desired signal. In the proposed analog-digital signal processing scheme, the interference signal is extracted with the analog filter and the interference to the desired signal is reconstructed by LMS algorithm.

The noise on power-lines is non-stationary, while the instantaneous noise power in different frequency bands are dependent. Under such noise environments, the instantaneous noise power in a frequency band can be estimated by observing the noise in other frequency bands. In this paper, we propose a receiver structure which uses the estimated instantaneous noise power in the decoding process and show its superiority in BER performance to conventional systems.

In this paper, we improve the performance analysis of the Rake receiver for the DS-CDMA forward link using long random spreading sequences (RSS's) by more accurately evaluating the correlation between the various interference terms. We also extend the analysis to the case of short (periodic) RSS. The accuracy of the expressions obtained in our analysis is verified by computer simulation. We show that for a given normalized spreading factor, the bit error rate (BER) performance of the Rake receiver is the same for BPSK and QPSK data modulation. We also show that when the channel delay spread is smaller than a data symbol duration, the CDMA receiver has similar BER performance for long and short RSS's. However, for large delay spread, the employment of short RSS's may result in severe performance degradation.

A combining method for receiver diversity, followed by a Bayesian decision feedback equalizer, is proposed. This eigenvector based combining maximizes the desired part energy of combined channel, on which the equalizer performance mainly depends. The validity of the proposed method is demonstrated by simulations.

The complete subtree (CS) method is widely accepted for the broadcast encryption. A new method for assigning keys in the CS method is proposed in this paper. The essential idea behind the proposed method is to use two trapdoor permutations. Using the trapdoor information, the key management center computes and assigns a key to each terminal so that the terminal can derive all information necessary in the CS method. A terminal has to keep just one key, while log2 N + 1 keys were needed in the original CS method where N is the number of all terminals. The permutations to be used need to satisfy a certain property which is similar to but slightly different from the claw-free property. The needed property, named strongly semi-claw-free property, is formalized in terms of probabilistic polynomial time algorithm, and its relation to the claw-free property is discussed. It is also shown that if the used permutations fulfill the strongly semi-claw-free property, then the proposed method is secure against attacks of malicious users.

In this paper, we consider a mobile system consisting of a single isolated circular cell with K independent users simultaneously sharing the channel using binary DS-CDMA to establish a full duplex channel with the base station. Both coherent and differential detection RAKE receivers with Maximal Ratio Combining (MRC) techniques are considered. The performance of two uplink/downlink receivers in Nakagami wideband fading channel is studied. Our approach relies on the use of total instantaneous interference power calculations instead of the use of average power approximations. We analyzed and derived new exact formulae for bit error probabilities for the considered system, and presented a set of numerical results both for the exact formulae and Gaussian approximation. The performance comparisons suggest that the exact formulae provide superior performance to Gaussian approximation especially at low number of users and either high fading parameters of the desired user or low fading parameters of the MAIs.

The complete subtree (CS) method is one of the most well-known broadcast encryptions which do not enforce the receivers to keep "online." This paper is to reduce the size of secret information which must be stored in a terminal of the method. In the original CS method, the size of the secret information increases as the number of terminals increases. It is shown in this paper that, by making use of a one-way trapdoor permutation, we can make the size constant regardless of the number of terminals. The security of the proposed scheme is investigated, and detailed comparison with other similar schemes is presented. The proposed scheme is suitable for practical implementations of the CS method.

This paper deals with broadcast encryption schemes, in which a sender can send information securely to a group of receivers excluding some receivers over a broadcast channel. In this paper we propose modifications of the Complete Subtree (CS), the Subset Difference (SD) and the Layered Subset Difference (LSD) methods based on the Master Key Tree (MKT). Our modifications eliminate log N keys or labels from receivers' storage, in exchange for an increase in the computational overhead, where N is the total number of receivers. We also propose modifications of the SD and LSD methods by applying the Trapdoor One-way Permutation Tree (TOPT) which is originally proposed in order to modify the CS method. Our modifications based on TOPT also eliminate log N labels, and the computational cost is much smaller than MKT based methods.

The multiple space-time trellis codes (M-STTC) structure is one of the Multiple Input Multiple output (MIMO) schemes providing high transmission rate and diversity and coding gain without bandwidth expansion. In this paper, an M-STTC system is proposed wherein the transmitter employs a multiple space-time TCM for the fast fading channel and the receiver has a decoding order block, several whitening processors, STTC decoders, and interference cancellers. The proposed layered receiver adopts a whitening process instead of a minimum mean squared error (MMSE) estimator, which is widely used in the BLAST type receiver. An optimum decoding order scheme is also planned since it gives at least a 2 dB gain in the proposed system in the fast flat Rayleigh fading channel of fd Tc = 1/3 at the FER of 10-2. For an M-STTC system employing two STTCs with four transmit and receive antennas, the layered receiver with whitening process obtains a 5 dB gain over the coded layered space-time processing in the fast flat Rayleigh fading channel at the FER of 10-2.

In this paper, the bit error rate (BER) and the outage probability are presented for a maximal ratio combining (MRC) two-dimensional (2D)-RAKE receiver operating in a correlated frequency-selective Nakagami-m fading environment with multiple access interference. A simple approximated probability distribution function of the signal-to-interference-plus-noise ratio (SINR) is derived for the receiver with multiple correlated antennas and RAKE branches in arbitrary fading environments. The combined effects of spatial and temporal diversity order, average received signal-to-noise ratio, the number of multiple access interference, angular spread, antennae spacing and multi-path Nakagami-m fading environment on the system performance are illustrated. Numerical results indicate that the performance of the 2D-RAKE receiver depends highly on the operating environment and antenna array configuration. The performance can be improved by increasing the spatio-temporal diversity gains and antenna spacing.

This paper proposes and theoretically evaluates two different schemes of code acquisition for pulse-position modulation (PPM) and overlapping PPM (OPPM) fiber-optic code-division multiple-access (CDMA) systems, namely threshold-based and demodulator-based code acquisition. Single-dwell detector and serial-search algorithm are employed for both schemes. Theoretical analysis is carried out for shot-noise-limited photon-counting receiver. Discussions upon effects of various parameter settings on the performance of code acquisition for PPM/OPPM fiber-optic CDMA systems, such as index of overlap, PPM/OPPM multiplicity, average photon counts per information nat, and darkcurrents, are presented. It is shown that when the threshold is properly selected, the threshold-based code acquisition system offers better performance, in terms of mean number of training frames, than the demodulator-based one.

While a multicarrier approach of achieving frequency diversity performs well in the presence of partial-band interference, it suffers from the effects of intermodulation distortion (IMD) due to power amplifier (PA) nonlinearity. On the other hand, transmit diversity using multiple transmit antennas has the benefit of no IMD effects, but can suffer from a larger performance degradation due to partial-band interference (e.g., jamming or narrowband signals in a overlay system) compared to the multicarrier approach. Hence, hybrid diversity schemes which use both multicarrier as well as multiple transmit antennas are of interest. Techniques to suppress IMD effects in such hybrid diversity schemes are important. In this paper, we propose and evaluate the performance of a minimum mean square error (MMSE) receiver to suppress the intermodulation distortion in a coded multicarrier multiple transmit antenna (P transmit antennas) DS-CDMA system with M subcarriers on each transmit antenna, for both BPSK and QPSK modulation. The system uses rate-1/M convolutional coding, interleaving and space-time coding. We compare the performance of a (M = 4,P = 2) scheme and a (M = 2,P = 4) scheme, both having the same diversity order. We show that the proposed MMSE receiver effectively suppresses the IMD effects, thus enabling to retain better antijamming capability without much loss in performance due to IMD effects.

An RF front-end using a six-port circuit is a promising technology for realization of a compact software defined radio (SDR) receiver. Such a receiver, called a six-port direct conversion receiver (DCR), consists of analog circuit and digital signal processing components. The six-port DCR itself outputs four different linear combinations of received and local signals. The output powers are measured at each port, and the received signal is recovered by solving a set of linear equations. This receiver can easily cover a wide frequency band unlike the conventional DCR since it does not require the precise orthogonality that the conventional one does. In this paper, we propose a novel calibration method for a six-port system that includes nonlinear circuits such as diode detectors. We demonstrated the demodulation performance of a six-port DCR by computer simulation and experiments at 1.9, 2.45, and 5.85 GHz.

We analyze the performance of multiple input single output (MISO) synchronous downlink CDMA system over Rayleigh fading channels. We propose an upper bound on its bit error rate (BER) assuming maximum likelihood (ML) multiuser detection by extending notion of removable error vector to fading channels. From the upper bound, we discuss the optimality of space-time spreading and its extension to non-orthogonal base sequences. We also give some numerical results.

A simple millimeter-wave quasi-maximal-ratio-combin-ing antenna diversity system based on the millimeter-wave self-heterodyne transmission technique is described. The millimeter-wave self-heterodyne transmission technique is useful for developing millimeter-wave systems with enhanced characteristics in regard to system miniaturization, development and fabrication cost, and the frequency stability of the signal transmission. We also show that applying this technique with an antenna diversity receiver configuration can easily solve a problem peculiar to millimeter-wave systems--the fact that the transmission link always requires a line-of-sight path--without requiring hardware designed with millimeter-scale precision. In this paper, we theoretically analyze the operating principle of a combining antenna diversity system based on the millimeter-wave self-heterodyne transmission technique. We further prove that we can obtain a diversity gain in accordance with that of a maximal-ratio combining diversity system without resorting to any complicated control of the received signal envelope and phase. Our experiments using the simplest two-branch diversity structure have validated the operating principle derived in our theoretical analysis. Our results show that a received CNR improvement of 3 dB is obtained as a diversity gain. We also demonstrate that circuit precision corresponding to the wavelength of the intermediate frequency, rather than to the millimeter wavelength, is sufficient to obtain the diversity effect when we control the signal phase or delay in combining the received signals.

Performance of selective Rake (SRake) receiver is evaluated for direct sequence ultra wideband (DS-UWB) communications considering an independent Rayleigh channel having exponentially decaying power delay profile (PDP). BEP performances are shown. The results obtained are compared with similar results in a channel having flat PDP. Assumption of a flat PDP is found to predict the optimum spreading bandwidth to be lower and sub-optimum operating performance beyond optimum spreading bandwidth to be severely worse than that is achievable in a channel having exponentially decaying PDP by employing an SRake receiver having fixed number of combined paths. Optimum spreading bandwidth for SRake in a channel having exponentially decaying PDP is shown to be much larger than the one in a channel having flat PDP; that is specifically a good-news for UWB communications. Effects of partial band interference are also investigated. Interference is found to be less effective in exponentially decaying PDP.

A fully integrated RF front-end for W-CDMA applications including a low noise amplifier, a down conversion mixer, a digitally programmable gain amplifier, an on-chip VCO, and a fractional-N frequency synthesizer is designed using a 0.35-µm CMOS process. A multi-stage ring shaped on-chip LC-VCO exhibiting bandpass characteristics overcomes the limitation of low-Q components in the tank circuits and improves the phase noise performance. The measured phase noise of the on-chip VCO is -134 dBc/Hz at 1 MHz offset. The receiver RF front-end achieves a NF of 3.5 dB, an IIP3 of -16 dBm, and a maximum gain of 80 dB. The receiver consumes 52 mA with a 3-V supply and occupies only 2 mm2 die area with minimal external components.

A CMOS DFE (decision feedback equalization) receiver with a clock-data skew compensation was implemented for the SSTL (stub-series terminated logic) SDRAM interface. The receiver consists of a 2 way interleaving DFE input buffer for ISI reduction and a X2 over-sampling phase detector for finding the optimum sampling clock position. The measurement results at 1.2 Gbps operation showed the increase of voltage margin by about 20% and the decrease of time jitter in the recovered sampling clock by about 40% by equalization in an SSTL channel with 2 pF 4 stub load. Active chip area and power consumption are 3001000 µm2 and 142 mW, respectively, with a 2.5 V, 0.25 µm CMOS process.

The bit error rate (BER) performance of a fast frequency-hopped frequency division multiple access (FH-FDMA) system is evaluated with diversity combining receivers. The clipper receiver and the normalized envelope detection (NED) receiver which show better performance than other diversity combining receivers under n = 1 band multitone interference (MTI) are chosen as combining alternatives. From simulation results, n = 1 band MTI is the most destructive multitone interference strategy for the FH-FDMA system. As the number of groups increases, eventually becoming a FHMA system, the worst case performance of FH-FDMA with the clipper receiver improves monotonically, while that of the NED receiver hardly improves when the effect of the interference is relatively large. From the viewpoint of BER performance, the FHMA system with the clipper receiver is the most effective solution among the FH-FDMA systems in the presence of the worst case band MTI.