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We consider cooperative communications where nodes forward information for each other to achieve reliable communication. Cooperative communication is realized through various protocols such as Decode-and-Forward which are primarily designed with the assumption that nodes are always willing to cooperate. However, in practical systems nodes may violate the rules of cooperation with the selfish intention...
In this paper, we propose a novel method to generate the cyclostationary signature for Orthogonal Frequency Division Multiplexing (OFDM) signals with a low overhead of signature (i.e. number of signature subcarriers) and a good performance of the signature detection under frequency-selective fading channel, for dynamic spectrum access (DSA) networks. Moreover, we also present how to employ the proposed...
In this work we present a theoretical formulation for the performance of a constant false alarm ratio (CFAR) detector for GNSS signals based on an FFT fully parallel acquisition scheme. The performance is measured in terms of receiver operating characteristic (ROC) and analytical expressions for the false alarm probability and the detection probability are derived. A detailed analysis is carried out...
Initial ranging (IR) involves detecting the binary phase shift keying (BPSK) code transmitted by the new subscriber station (SS). In this paper, we formulate a simple detector using the Neyman-Pearson theorem (NPT) for single-code detection in IEEE 802.16-compliant time division duplex (TDD) orthogonal frequency division multiple access (OFDMA) systems. Exploiting the BPSK structure in the ranging...
This paper deals with detection algorithms for impulse-radio ultrawideband transmitted-reference systems. For binary modulation schemes, we propose a novel detector that operates on the partial autocorrelations of the received signal as computed over time intervals (bins) of size less than the symbol period. Assuming that the receiver has knowledge of the partial autocorrelations of the channel response...
As the value of reputation systems is widely recognized, the incentive to manipulate such systems is rapidly growing. We propose TAUCA, a scheme that identifies malicious users and recovers reputation scores from a novel angle: combination of temporal analysis and user correlation analysis. Benefiting from the rich information in the time-domain, TAUCA identifies the products under attack, the time...
Many acquisition schemes have been proposed and investigated for Ultra-Wideband (UWB) systems, however, most of them setup for low duty-cycle Impulse Radio UWB (IR-UWB) signals, with the assumption that the pulse repetition time is greater than the maximum excess delay of channels, so that intra- and inter-frame interference can be bypassed. This assumption limits the transmission rate and cannot...
Conventional intercept receivers based on second order signal processing are generally ineffective in detecting direct sequence spread spectrum signals if the spreading sequences are unavailable. Also the capacity of direct sequence code division multiple access is limited by multiple access interference. Previous work has shown that the triple correlation function is used to implement triple correlation...
Cognitive radio is an emerging technology in communication systems. Cognitive radios aim to relief the shortage of spectral resources by identifying and exploiting underutilized radio spectrum. A key task of the cognitive radio is spectrum sensing in order to find free spectrum and detect licensed spectrum user transmissions. In this paper, an FPGA implementation of a feature detector for OFDM-based...
Self-encoded spread spectrum (SESS) employs non-deterministic spreading codes that have been generated from the random information source and provide unique advantages over traditional pseudo-random codes. In previous work we have shown that the memory in SESS-modulated signals not only can deliver a 3dB gain in AWGN channels, but also can be exploited to achieve time diversity and robust bit-error...
This paper presents a novel synchronization scheme that base on Baker Codes autocorrelation property for UWB impulse radio system. Simple threshold detection circuit is used to perform early quantization. An asynchronous pulse capture block is introduced to perform a direct down conversion of the UWB pulses from RF band to baseband. The new scheme provides run time synchronization tracking and resynchronization...
Direct sequence code division multiple access (DSCDMA) is mainly an interference limited channel. When several users are accessed in a common channel and since signature sequences assigned to users are not perfectly orthogonal, so interference is introduced in each user's desired signal. Several interference cancellation methods were proposed to reduce multi-access interference. In this paper, we...
The man-induced cyclostationary signatures can provide a robust mechanism for the self-coordination of cognitive radio networks. However, such artificial signatures incur signaling overhead and come at the bandwidth cost. In this paper, we show intrinsic cyclostationary signatures in the Orthogonal Frequency Division Multiplexing (OFDM) system with Cyclic Delay Diversity (CDD). The standard conformable...
Based on the requirement of improving the detection capability of laser detector, the pseudorandom code may be adopted as the transmitting code of a laser detector. The auto correlation and the anti-jamming characteristics of the pseudorandom code are analyzed at first. Because the emitting power of a laser is reduced greatly where the journey of the pseudorandom code is longer than one, the pseudorandom...
Mobile WiMAX is a wireless protocol for broadband wireless access that utilizes TDD OFDMA. The WiMAX frame begins with a preamble symbol that establishes frame timing and initial symbol timing for the mobile. In a mobile, the preamble symbol detection is often accomplished by a delay correlation detector. Delay correlation detectors take advantage of the preamble symbols redundancy. Previous detection...
Multiple peaks in autocorrelation functions of Binary Offset Carrier (BOC) modulation in the Galileo signals cause ambiguities during signal acquisition. Some techniques address this problem by compromising receiver sensitivity or acquisition time. The delay and add method addresses this problem by combining delayed versions of the correlator outputs. Types of detectors and the effect of signal filtering...
Communication signals are appropriately to be modeled as cyclostationary stochastic processes. The most significant advantage of cyclostationarity is its suppression on the stationary noise and interference. Therefore, cyclostationary theory has been a powerful tool in LPI (Low Probability of interception) signal processing. In non-cooperative condition, blind detection and parameter estimation of...
In the widely used traditional control system, traffic coordination and control between regions are neglected. Regional boundarypsilas traffic control effect has direct influence on the input traffic flow control and output traffic flow control of the regions. In this paper, a traffic coordination and control model of regional boundary based on fuzzy control is proposed. Two fuzzy controllers are...
In a slot-synchronized wireless communication system, a set of signature sequences can be derived by circularly shifting a base sequence with good auto correlation properties. In a time-dispersive channel, the sequences with different circular time shifts can be uniquely identified as long as their minimum separation in time is greater than the channelpsilas maximum delay spread. In this paper, we...
A high bandwidth critical path monitor (1 sample/ cycle at 4-5 GHz) capable of providing real-time timing margin information to a variable voltage/frequency scaling control loop is described. The critical path monitor tracks the critical path delay to within 1 FO2 inverter delay with a standard deviation less than 3 FO2 delays over process, voltage, temperature, and workload. The CPM is sensitive...
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