A practical implementation and the maximum likelihood detection analysis of the blind cyclic‐feature detection (BCD) in cognitive radios is presented in this study. The sum of the magnitude squared of the cyclic spectral density (SCSD) is the merit criterion for the maximum likelihood detection. The authors show that the SCSD can be conveniently obtained from the autocorrelation of the power spectral density for a cyclostationary process. Unfortunately, this is not true for a stationary process. For a white Gaussian noise process, the SCSD exhibits non‐zero values for all cyclic frequencies although the noise process does not have any cyclic features. To ameliorate the challenge, the authors introduce noise elimination methods in the BCD. The simulation results show that the receiver operating characteristics of the BCD are considerably superior to the energy detection especially in signal‐to‐noise ratio fluctuation. With a moderately increased computational complexity, the BCD can be very beneficial for millimeter‐wave cognitive radios with fast fading.

Self‐encoded spread spectrum (SESS) incorporated with binary‐offset‐carrier modulation can significantly improve the navigation accuracy exploiting the inherent temporal diversity of iterative detection (ID). ID is the natural realisation of the detection scheme based on the unique SESS spreading sequence that comes from the data source itself. The enhanced precision is presented in terms of multipath error envelope, running average error and root‐mean‐square error for early‐minus‐late and elary/late slope. SESS is a promising technology that can substantially mitigate detrimental effects of multipath on tracking error for position location or navigation. The accuracy of SESS with ID is superior to other conventional correlation detection schemes with a similar or minimally increased computational complexity.

In this paper, we demonstrate that the sampling property of a delta function can be used to quantify integration dynamically. The proposed approach reduces integration to a sampling. The sampling point is obtained in terms of a constant or fading parameter. We illustrate an example using Rayleigh fading channel. We investigate the dynamic behavior of the sampling error probability, relative error and sampling point error of the proposed integration. We extend the result to the general order rectangular QAM with Nakagami-n fading. The significance of the proposed method is that the dynamic integration can be used to find integrals with no available antiderivative.

In this paper, we present a simple approach to evaluating the performance of amplify-and-forward cooperative diversity. The Q-function can be asymptotically reduced to a delta (impulse) function. We extend the result to cooperative networks in fading channels. The proposed approach introduces a simple technique to evaluate the performance of complex networks by sampling.

Self-encoded spread spectrum (SESS) is a novel modulation technique that acquires its spreading sequence from the randomness of an input data stream rather than through the use of the traditional pseudo-random (PN) code generator. The statistical properties of random codes in SESS offer a number of advantages over the deterministic PN codes. In this paper we propose a multiple-input multiple-output (MIMO) SESS system that employs iterative detection to exploit the inherent time diversity in SESS modulation. Alamouti scheme-based spacetime block coded MIMO technique is used to exploit the spatial diversity. The simulation results demonstrate that the proposed system can completely mitigate the fading effect to achieve about 7.5 dB of gain over a PN-coded spread spectrum MIMO system in Rayleigh fading channels.

We analyze the performance of code division multiple access (CDMA) systems with multicarrier (MC) that employ random spreading sequences in downlink frequency selective fading channels. We obtain the probability density function (pdf) of the multiple access interference (MAI) of CDMA systems and extend the results to MC-CDMA systems to determine the pdf of MAI, inter-carrier interference (ICI) and noise in terms of the number of users, the spreading factor, the number of sub-carriers and frequency offset. The results show that the effects of frequency offset vary with system loading. We consider the synchronous downlink of cellular MC-CDMA and derive a Gaussian approximation of the MAI and ICI to reduce the computational complexity in calculating the bit error rate (BER). The accuracy of the Gaussian approximation is examined by computer simulations.

In this letter, we have analyzed and compared two different multiuser detection receiver structures that are appropriate for code-division multiple-access systems with multiple antennas. We compare the distributed decorrelator (where signal decorrelation is performed at each receiving antenna) and the centralized decorrelator (where decorrelation is performed once collectively). We show that they provide the same performance in additive Gaussian noise channels. The distributed decorrelator provides better performance in flat fading channels.

In this paper, we compare the asymptotic performance of the decorrelator approaches to multiuser detection in code-division multiple-access (CDMA). Precoding is the decorrelation which is performed at a common transmitter such as the base station or satellite that allows single-user detection at the handset receiver. Receiver-based decorrelator decorrelates multiple user signals at the receiver side. We analyze the performance of the aforementioned decorrelation approaches with time-varying random spreading sequences in additive white Gaussian noise channels. The results demonstrate that the performance of precoding and that of receiver-based decorrelator are asymptotically equivalent.

Transmitter optimization, in addition to receiver optimization, contributes significantly to efficient interference suppression in multiple access and multipath channels. The system design is based on the joint optimization of the transmitter and the receiver in a synchronous multiuser channel characterized by multipath propagation. Joint optimization is represented by a linear transformation of the transmitted signals at the transmitter and a linear transformation of received signals at each receiving site that minimize the effect of multiple access and multipath interference. The minimum mean squared error between the true bit value and its estimate at the output of the receiver is taken as the cost function, subject to average and peak transmit power constraints. It is shown that joint transmitter-receiver optimization outperforms significantly either transmitter optimization or receiver-based techniques. The crucial assumption, in the case of multipath channels, is that the transmitter knows the multipath characteristics of all channels and that the channel dynamics are sufficiently slow so that multipath profiles remain essentially constant over a block of preceded bits. The practical applications can be found in indoor and cellular communications, satellite communications, or military communications where nonorthogonal signature waveforms are employed.

A synchronous multiuser system operating in an additive white Gaussian noise channel, with or without multipath fading, is considered. It is shown that when either a conventional single user receiver or the RAKE receiver is employed, both multiple access and intersymbol interference can be eliminated by means of a suitable transmitter precoding scheme. Transmitter precoding represents a linear transformation of transmitted signals, such that the mean squared errors at all receivers are minimized. Precoding, with both conventional single user receiver and with the RAKE receiver, results in near-far resistant performance and outperforms considerably the respective schemes without precoding. The crucial assumption, in the multipath case, is that the transmitter knows the multipath characteristics of all channels and that channel dynamics are sufficiently slow so that multipath profiles remain essentially constant over the block of precoded bits.