PULSE SHAPE, EXCESS BANDWIDTH, AND TIMING ERROR SENSITIVITY IN PRS SYSTEMS - COMMENT

Several non-minimum-bandwidth partial-response-signaling (PRS) techniques were compared in the above paper (ibid., vol.COM-35, p.475-80, April 1987). One of the criteria used for the comparison was the robustness to the timing jitter. The commenter shows that according to this criterion the duobinary signaling technique is superior to the dicode scheme at low values of the roll-off factor, in contradiction to the conclusion in the original study. In reply the author agrees that the comment is correct and that unnormalized and normalized figure-of-merit plots show different aspects of timing jitter sensitivity as a function of excess bandwidth

Capacity improvement by code-hopping in S-CDMA systems

Code-hopping, which is an alternative spreading strategy to the static spreading code assignment of CDMA systems, is evaluated as a method to combat multiuser interference in S-CDMA systems. Uplink capacities of conventional and code-hopping S-CDMA are determined and compared by simulations carried out on a typical S-CDMA system for three nondispersive channels : No-fading, Rayleigh fading and Rician fading. The cellular structure is not composed of regular hexagons, but irregularly shaped natural cells where affiliation of the mobile user depends on the paths to the neighboring base stations. Results are presented for two different values of blocking ratio which is defined as the ratio of the number of rejected call attempts to the number of total call attempts, revealing significant uplink capacity increases provided by code-hopping in both fading and no-fading environments. Furthermore, it is observed that the increase in capacity is greater in fading channels than in no-fading one

Direction finding with a uniform circular array via single snapshot processing

In this work a new algorithm for multiple emitter direction finding by using a uniform circular array is proposed. The algorithm is based on single snapshot processing, and therefore, it has no restriction on the coherency of the sources. The problem formulation is based on the transformation of the snapshot. The transformed sequence is formed by taking the discrete Fourier transform of the snapshot and weighting it suitably. It contains the so-called distortion terms, which are taken into account by using an iterative correction scheme to improve the estimation accuracy. The convergence is achieved in a few steps, and a significant performance improvement is observed when the distortion terms are taken into account. The proposed bearing estimation algorithm is based on the linear prediction method developed in this study, in which the prediction filter coefficients are found by replacing the weighted data matrix by a specified rank approximation, which is obtained by its singular-value decomposition. The direction of arrival estimates are obtained from the angular locations of the prediction-error filter zeros. It is observed through computer simulations that the algorithm performance is improved as compared to that of the forward-backward linear prediction (FBLP) and the modified FBLP methods by choosing an appropriate rank for the approximating matrix. The root-mean-square errors are close to the Cramer-Rao bounds in most cases, where the aforementioned methods fail to work. (C) 1997 Elsevier Science B.V

Code-hopping as a new strategy to improve performance of S-CDMA cellular systems

An alternative coding strategy to the fixed spreading code assignment of code-division multiple-access (CDMA) systems, called code-hopping is proposed for the uplink path of synchronous CDMA (S-CDMA) systems. In code-hopping S-CDMA, mobile users swap their spreading codes according to a predetermined hopping pattern. In this way, mobile channels which are identified by the spreading codes are exchanged. Performance of code-hopping on the uplink path of S-CDMA systems is evaluated numerically on a typical S-CDMA system in the case of random hopping and compared to that of conventional S-CDMA, In performance evaluation, the criterion is the uplink outage probability which is defined as the probability of the uplink interference power exceeding a predetermined threshold. The numerical results show that application of code-hopping to the uplink communication of S-CDMA systems decreases the outage probability significantly

Performance analysis of adaptive loading OFDM under Rayleigh fading

In this paper, we investigate the performance of adaptive loading orthogonal frequency-division multiplexing (OFDM) under Rayleigh fading with maximal ratio-combining (MRC) diversity at the receiver. We assume that channel-state information is available at both the transmitter and the receiver. Closed-form expressions for the lower bound on the average capacity of OFDM transmission under Rayleigh fading are provided for ideal MRC diversity. Simple approximate expressions for the average capacity of the Rayleigh-fading channel are also provided for the high signal-to-noise ratio (SNR) case. In the second part of this paper, a maximum-rate adaptive-loading strategy is derived for uncoded quadrature-amplitude-modulation modulated OFDM. Simple lower bound expressions and high-SNR approximations are provided for the average spectral efficiency of the maximum-rate adaptive-loaded uncoded OFDM under Rayleigh-fading channel conditions. According to the results, the performance of the uncoded adaptive-loading OFDM is about 8.5 dB inferior to the capacity bound at 10(-5) symbol error probability under frequency-selective Rayleigh fading

Direction finding with a circularly rotated antenna

In this work, a new algorithm for multiple emitter direction finding by using a single antenna moving along a circular trajectory is proposed. The problem is formulated by taking the Doppler frequency shift, caused by the movement of the antenna. into account, and by assuming that the information, hidden in the incoming signals, does not change in the observation duration. The proposed direction finding algorithm is, therefore, based on single snapshot processing and also on the linear prediction method developed in [1,2]. It has no restriction on the correlation of the incoming signals since it performs a single snapshot processing. The algorithm performance is investigated through computer simulations and it is observed that the root-mean-square errors of the direction of arrival estimates are less than one degree in most cases. Therefore, it seems reasonable to use the proposed direction finding algorithm in some particular applications, for instance, in identifying the environment for calibration purposes