Rodger E. Ziemer

Conversion and Matched Filter Approximations for Serial Minimum-Shift Keyed Modulation

Serial minimum-shift keyed (MSK) modulation, a technique for generating and detecting MSK using series filtering, is ideally suited for high data rate applications provided the required conversion and matched filters can be closely approximated. Lowpass implementations of these filters as parallel inphase- and quadrature-mixer structures are characterized in this paper in terms of signal-to-noise ratio (SNR) degradation from ideal and envelope deviation. Several hardware implementation techniques utilizing microwave devices or lumped elements are presented. Optimization of parameter values results in realizations whose SNR degradation is less than 0.5 dB at error probabilities of 10-6.

Effect of correlation between subcarriers of an MCM/DSSS communication system

The analysis of a combined multicarrier modulation/direct-sequence spread-spectrum (DSSS) modem carried out by Kondo and Milstein (see IEEE Trans. on Commun., 1995) in delay spread multipath is extended to include the effect of correlation between the DSSS subcarriers due to an exponential power delay profile. Analytical and simulation results show that additional diversity gain can be achieved with more subcarriers, but at the expense of multiple access capability. Eventually, an irreducible bit error probability (BEP) is approached as more subcarriers are used.

Computationally efficient bounds for the performance of direct-sequence spread-spectrum multiple-access communications systems in jamming environments

An approach for calculating upper and lower bounds for the probability of error for asynchronous multiple-access spread-spectrum communication systems using deterministic codes is presented. The techniques is then generalized to include multiple-tone jamming. The approach utilizes the cumulative distribution function of individual interference terms. The computational complexity of the technique is calculated to the polynomial-like. Results showing the multiple-access performance of gold codes of lengths 31 and 127 in the presence of jamming are shown. The fact that this computational technique gives upper and lower bounds is rigorously proved using the Riemann-Stieltjes integral. >

Orthogonal frequency division multiplexing performance in delay and Doppler spread channels

Orthogonal frequency division multiplexing (OFDM) is examined via digital computer simulation. Bit error performance of OFDM in a doubly spread channel is examined, and the effects of varying the guard interval and the number of carriers are demonstrated. The use of simulation as a design tool when doubly spread channel performance cannot be modeled mathematically is demonstrated. Simulations reveal that the designer has to strike a balance between the number of carriers and the guard interval in order to optimize performance and resource utilization.

Comments on "Carrier tracking in RAKE reception of wide-band DSSS in Ricean fading"

An analysis is given of the effect of phase tracking error in the fingers of a coherent RAKE receiver. Results for constant and exponentially decaying power delay profiles indicate that, for sufficiently low tracking loop signal-to-noise ratio, a point is eventually reached where performance does not improve with the use of an increased number of fingers. This suggests that the expected performance improvement due to finer multipath resolution in the very wideband personal communications systems anticipated for third generation will be negated by parameter estimation error unless special care is taken to minimize these errors, such as jointly optimum detection and estimation procedures.

Joint maximum-likelihood parameter estimation for burst DS spread-spectrum transmission

We first derive the joint optimal maximum-likelihood (ML) estimator of the carrier phase, both Doppler shift and Doppler rate, and the spreading code delay for a short burst direct sequence/spread spectrum (DS/SS) transmission in the absence of the data modulation. The typical burst duration is three data bit periods (60 ms). The performance of the joint estimator is analytically derived separately for high and low carrier-to-noise ratio (CNR) values. A suboptimal ML estimator based on the method of averaged periodogram is proposed for the data modulation present case, allowing the joint estimation of the data bit values. Then the above parameters are assumed correctly estimated and a segmentation approach is adopted, deriving the optimal joint ML estimator for the bit synchronization epoch and data. Simulations show the joint estimators perform reliable down to a CNR of approximately 30 dB/spl middot/Hz.

The Cholesky-iterative detector: a new multiuser detector for synchronous CDMA systems

The decorrelating decision-feedback (DDF) multiuser detector based on Cholesky factorization has been shown to alleviate the performance degradation of the users in the detection process, especially for relatively low cross-correlation values between user signals. A new detection concept for multiple users described in this paper employs two triangular matrices (upper and lower) and soft output information to improve the data estimates. Simulation results show that significant performance gains can be achieved over the DDF. Also, the users tend to have their bit error probabilities clustered. Thus, the performance of a given user is less dependent on its position in the detection process than for the DDF detector.

Multicarrier spread spectrum performance in fading channels with serial concatenated convolutional coding

We study a multicarrier direct sequence code division multiple access (CDMA) system combined with interleaved serial concatenated convolutional codes. This combination of modulation method and coding scheme provides great flexibility in obtaining a particular bit error rate performance. With interleaved serial concatenated convolutional codes, in which an interleaver is situated between two convolutional codes connected in series, coding gain can be altered by changing the size of the interleaver, or by changing the rate or constraint length of either of the two constituent codes. With a multicarrier direct sequence CDMA system, frequency diversity can be obtained by spreading the code symbols across the carriers, and by using repetition coding. The number of carriers and the processing gain can be altered as well to achieve a particular performance goal. In addition, frequency diversity can be traded for data rate by parallel transmission of information symbols. This paper characterizes system performance so that intelligent tradeoffs can be made in system design. Emphasis is on terrestrial communication in fading for a personal communication system.

Biorthogonal multicode modulation for high-rate high-reliability personal communications requiring controlled peak-to-average transmit power ratio

A modulation scheme is proposed for high-information-rate high-reliability personal communications where controlled peak-to-average transmit power ratio is an issue. The scheme is a hybrid of classical biorthogonal modulation and code division multiple access multicode modulation. Analytical and simulation results are presented for static AWGN channels and simulation results are presented for flat fading channels.

Equal-gain combining of multichannel DPSK in Doppler-spread Ricean fading

A method for computing the bit error probability (BEP) of multichannel differentially coherent phase-shift keying (DPSK) with equal gain combining in Doppler spread Ricean fading is given. It is based on Gauss-Chebyshev quadrature integration of the moment generating function of the decision statistic at the combiner output. The method allows nonuniform power delay profiles for the received multipath rays. Applications to multicarrier spread spectrum modulation and spread spectrum with RAKE reception systems are discussed. It is found that for moderate values of the Ricean K-factor (ratio of specular to diffuse fading signal power) an optimum order of diversity exists whereas, for large K-factors, diversity does not improve performance.