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The fundamental problem of our interest is soft MIMO detection for the case of block fading, i.e., when the transmitted codeword spans over several independent channel realizations. We develop methods that adaptively allocate computational resources to the detection problems of each channel realization, under a total per-codeword complexity constraint. The new results consist of a new algorithm, a...
In the context of spectrum sensing, we investigate the performance of detectors equipped with M antennas (co-located or distributed) under Rayleigh fading, in terms of detection diversity. Rather than the high-SNR concept of diversity order common in the communications literature, we adopt the notion recently advocated by Daher and Adve in the radar community: the slope of the average probability...
In this paper, a new successive interference cancellation (SIC) strategy for multiple-input multiple output (MIMO) spatial multiplexing systems is developed to combat the error propagation (EP) in decision feedback systems. The proposed scheme employs a parallel multi-branch (MB) structure. Each branch employs a SIC with multi-feedback (MF) strategy to detects the signals according to their respective...
Cooperative sensing based on energy detection in distributed antenna systems is considered in this letter. We investigate soft combination of the observed energies from different cognitive radio users. Based on the Neyman-Pearson criterion, an optimal soft combination scheme which can maximize the detection probability for the constant false alarm rate is obtained. Closed-form expressions for the...
In this paper, we develop a centralized spectrum sensing and Dynamic Spectrum Access (DSA) scheme for secondary users (SUs) in a Cognitive Radio (CR) network. Assuming that the primary channel occupancy follows a Markovian evolution, the channel sensing problem is modeled as a Partially Observable Markov Decision Process (POMDP). We assume that each SU can sense only one channel at a time by using...
In this work, a reduced complexity wideband linear SIC multi-user detector that is suitable for large-dimension wireless/wired systems in which the multi-access interference is varying rapidly (i.e. current long-code CDMA systems) is introduced. The proposed scheme exhibits low computational complexity and can converge to either the decorrelator or the LMMSE detectors. It uses a set of weighting factors...
this paper is focused on simulation of stochastic adaptive detectors of a direct sequence (DS) spread spectrum signals as a member of code-division multiplex access (CDMA). The kalman filter (KF) algorithm has shown better performance in compare of the other LMS and RLS algorithm which can be used for channel estimation and data detection. KF acted more stable in different ranges of SNR and represented...
In this paper, different energy combining schemes for non-coherent UWB impulse radio systems are analysed. Closed form expressions for the Symbol Error Rate (SER) of Pulse Amplitude Modulation (PAM) using a non-coherent energy detection receiver with energy combining in the AWGN and fading channels are presented. The principle of energy combining is based on the fact that the symbol energy is combined...
This paper considers cooperative spectrum sensing in Cognitive Radios. In our previous work we have developed DualSPRT, a distributed algorithm for cooperative spectrum sensing using Sequential Probability Ratio Test (SPRT) at the Cognitive Radios as well as at the fusion center. This algorithm works well, but is not optimal. In this paper we propose an improved algorithm- SPRT-CSPRT, which is motivated...
This paper considers the detection problem for fading channels in the presence of interference when both the transmitter of interest and the interferers employ practical modulation schemes. It is shown that, for Rayleigh fading, it is possible to obtain symbol error rates that have the same dependence on the received signal-to-noise ratio as when transmission is interference-free. This is achieved...
This paper considers the problem of how to quickly and accurately identify spectrum holes from downlink orthogonal frequency division multiple access (OFDMA) signals in frequency selective fading environment. We assume that the subcarrier assignment of primary users (PUs) in an OFDMA system is a priori known to the detector. Under this assumption, we formulate the original problem as the problem of...
It is known that, energy detector for spectrum sensing in cognitive system is simple in implementation, fast, and standards independent. However, it is known that energy detector suffers from its dependency over the noise level of detected signal. Different techniques have been proposed in order to combat that dependency. Among those techniques: antenna diversity, collaborative sensing, and double...
A serious threat to cognitive radio networks which sense the spectrum in a cooperative manner is the transmission of false spectrum sensing data by malicious secondary nodes. This enforces the system to acquire authentication. Actually, the decision maker needs to determine the reliability or trustworthiness of the shared data. In this paper, the evaluation process is considered as an estimation dilemma...
This paper develops a cooperative scheme among cognitive radios (CRs) to increase the spectrum sensing performance. CRs adaptively transmit local binary decisions to a fusion center (FC), which in turn uses a simple maximum-likelihood detector to decide the presence of absence of the primary user (PU). The diversity order of the probability of false alarm and miss-detection is studied under both Neyman-Pearson...
Cognitive radio (CR) networks require reliable spectrum sensing techniques in order to avoid interference to the primary users of the spectrum. Most existing spectrum sensing techniques are based on simple energy detection. However, in practice, the signals transmitted by primary users usually also contain known symbol such as pilots and preambles for synchronization and channel estimation purposes...
This paper investigates detection capability of energy detectors. With the help of receiver operating characteristics (ROC) curve and area under the ROC curve (AUC), a new measure, Complementary AUC (CAUC), is introduced as a proxy for the overall detection capability. When relays are available to help forward the target signal, the upper bound of the CAUC under Rayleigh fading channels is derived...
Cyclostationarity based sensing methods are appealing for OFDM signals under low SNR areas. However, such methods are sensitive to doubly-selective fading channels. In this paper we develop a new sensing method by exploiting the cyclostationarity incurred by the spread of autocorrelation due to the Doppler effect in doubly-selective fading channels. First, we model the doubly-selective fading channel...
In this paper, the expectation-maximization (EM) algorithm for maximum a posteriori (MAP) estimation is employed to derive an iterative soft-in soft-out (SISO) detection scheme for differential unitary space-time modulation (DUSTM) system employing cyclic group codes. The data sequence produced by conventional differential detection is differentially recoded and used to estimate the channel state...
In this paper, we propose an iteration scheme for the virtual layered space frequency communication architecture. The architecture enables the decoding of the transmitted orthogonal frequency division multiplexing (OFDM)-QPSK signals even if the number of spatial multiplexed layers is twice that of receiving antennas over multipath fading channels. In the proposed iteration scheme, the MAP decoder...
Spatial Modulation (SM) is a recently proposed joint coding and modulation scheme for Multiple-Input-Multiple-Output (MIMO) wireless systems, which is receiving a growing interest. SM offers a low-complexity alternative to the design of MIMO wireless systems, which avoids multiple Radio Frequency (RF) chains at the transmitter and high-complexity interference cancellation algorithms at the receiver,...
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