In this letter, we study a scenario based on decoupled RF energy harvesting networks (DRF-EHNs) that separate energy sources from information sources to overcome the doubly near-far problem and improve harvesting efficiency. We propose an algorithm to maximize energy efficiency (EE) while satisfying constraints on the maximum transmit power of the hybrid access point (H-AP) and power beacon (PB), while further satisfying constraints on the minimum quality of service and minimum amount of harvested power in multi-user Rayleigh fading channel. Using nonlinear fractional programming and Lagrangian dual decomposition, we optimize EE with four optimization arguments: the transmit power from the H-AP and PB, time-splitting ratio, and power-splitting ratio. Numerical results show that the proposed algorithm is more energy-efficient compared to baseline schemes.

This paper firstly analysis the coherent correlation, non-coherent accumulation detector used in weak satellite signal detection mathematically and statistically, and derives its single threshold based on the CFAR (constant false alarm rate). And then the paper improved the detector under the situation of more than one satellite existing with different signal power. Based on this new type of detector, a threshold calculation method is introduced considering the effect of near-far problem in the weak signal detection. Finally the method is verified and compared to the traditional single threshold with simulated data and collected intermediate frequency real data. The results show that this new threshold method can detect signal efficiently with lower false alarm possibility and larger detection possibility.

In this paper, performance of a novel interference cancellation technique for the single user detection in a direct-sequence code-division multiple access (DS-CDMA) system has been investigated. This new algorithm is based on the Cycle-and-Add property of PN (Pseudorandom Noise) sequences and can be applied for both synchronous and asynchronous systems. The proposed strategy provides a simple method that can delete interference signals one by one in spite of the power levels of interferences. Therefore, it is possible to overcome the near-far problem (NFP) in a successive manner without using transmit power control (TPC) techniques. The validity of the proposed procedure is corroborated by computer simulations in additive white Gaussian noise (AWGN) and frequency-nonselective fading channels. Performance results indicate that the proposed receiver outperforms the conventional receiver and, in many cases, it does so with a considerable gain.

This paper presents a novel interference cancellation (IC) scheme for both synchronous and asynchronous direct-sequence code-division multiple-access (DS-CDMA) wireless channels. In the DS-CDMA system, the multiple access interference (MAI) and the near-far problem (NFP) are the two factors which reduce the capacity of the system. In this paper, we propose a new algorithm that is able to detect all interference signals as an individual MAI signal by maximum correlation detection. It is based on the discovery of all the unknowing spreading codes of the interference signals. Then, all possible MAI patterns so called replicas are generated as a summation of interference signals. And the true MAI pattern is found by taking correlation between the received signal and the replicas. Moreover, the receiver executes MAI cancellation in a successive manner, removing all interference signals by single-stage. Numerical results will show that the proposed IC strategy, which alleviates the detrimental effect of the MAI and the near-far problem, can significantly improve the system performance. Especially, we can obtain almost the same receiving characteristics as in the absense of interference for asynchrnous system when received powers are equal. Also, the same performances can be seen under any received power state for synchronous system.

A new dimension-reduced interference suppression scheme is proposed for DS-CDMA systems over multipath channels. The proposed receiver resolves the problems of interference and multipath effects without needing to estimate the channel and training sequences. The minimum mean squared error (MMSE) criterion is used to obtain an algorithm to cancel the interference of each path. The MMSE filter is composed of two stages based on multipath effects. The proposed receiver has low complexity without great degradation of performance compared with the full dimension MMSE receiver with known channel information. Simulation results show that the proposed receiver converges to the optimal value rapidly because of its reduced dimension.

In this paper, the sequence interference suppression characteristics of code-diversity DS/CDMA over multipath fading channels are presented. In a code-diversity system, the data signal is modulated with several PN sequences, and using these sequences at the receiver, diversity reception of the signal is carried out to suppress the influence of multiple access interference (MAI) or sequence interference (SI) especially under a near-far problem. First, in a sequence interference and AWGN environment, the basic performance of code-diversity system is presented. Next, in single-path (flat-fading) and multipath fading channels, the average BER performance of the code-diversity system is shown and the observation that the performance of code-diversity system (combined with RAKE reception) is more effective over a multipath fading channel is clarified. Finally, it is presented that by implementing adaptive weight control (AWC) for the code-diversity system over fading channels, the BER performance can further be improved.

This paper proposes a novel DS/CDMA system with code-diversity techniques constituted by a simple system to suppress multiple access interference (MAI) without estimating the PN sequence of interference at the receiver. In the transmitter, the data signal is modulated with a sum of several PN sequences, and, two types of code- diversity reception are proposed, (1) maximal-ratio combining (MRC) code-diversity by autocorrelation, and (2) MRC code-diversity by anti-crosscorrelation. By computer simulations, it is shown that MRC code-diversity by anti-crosscorrelation is superior to the other one. It is also shown that MRC code-diversity by anti-crosscorrelation can improve BER more effectively for the interference which takes the phase to degrade BER at the worst. Next, to design the optimum number of branches for code-diversity, average BERs are calculated for several combinations of codes in code-diversity. As a result, the optimum number of branches varies for each combination of codes, however, it is decided from 3 to 7 branches. Finally, the effectivity of the proposed system in a near-far problem is presented.

In this letter, we propose a blind adaptive receiver with nonlinear structure for DS/CDMA communication systems. The proposed receiver requires the signature waveform and timing for only the desired user. It is shown that the blind adaptation is equivalent to the adaptation with the training signal and the function to be minimized has no local minima.

In this letter, we propose an adaptive multiuser receiver using a Hopfield network for code-division multiple-access communications and its performance is compared with that of the other types of multiuser receiver via computer simulation. The proposed adaptive receiver estimates both the signal amplitudes and spreading sequences for all the users using training data.

In this paper performance of M-stage detection for DS/CDMA is considered in terms of near-far resistance. Asymptotic multiuser efficiency (AME) of M stage detection over fading multipath channel is calculated and it is shown that even in the fading case the detector is near-far resistant i.e., insensitive to the relative energies of the users. The idea is extended to cellular environment. The effect of power control imperfection is investigated. It is shown that capacity can be increased if near-far resistant technique is employed in conjunction with limited power control.

In this paper we consider multiuser detection using a neural network in a synchronous code-division multiple-access channel. In a code-division multiple-access channel, a matched filter is widely used as a receiver. However, when the relative powers of the interfering signals are large, i.e. the near-far problem, the performances of the matched filter receiver degrade. Although the optimum receiver for multiuser detection is superior to the matched filter receiver in such situations, the optimum receiver is too complex to be implemented. A simple technique to implement the optimum multiuser detection is required. Recurrent neural networks which consist of a number of simple processing units can rapidly provide a collectively-computed solution. Moreover, the network can seek out a minimum in the energy function. On the other hand, the optimum multiuser detection in a synchronous channel is carried out by the maximization of a likelihood function. In this paper, it is shown that the energy function of the neural network is identical to the likelihood function of the optimum multiuser detection and the neural network can be used to implement the optimum multiuser detection. Performance comparisons among the optimum receiver, the matched filter one and the neural network one are carried out by computer simulations. It is shown that the neural network receiver has a capability to achieve near-optimum performance in several situations and local minimum problems are few serious.