Non-coherent Scenarios Research Articles

BER Expression of QAM for Symbol-Level Jamming

In wireless communication systems, quadrature amplitude modulation (QAM) schemes are widely used for high-speed data transmission, and recently, symbol-level jamming (SLJ) is being studied as an effective jamming technique. However, bit error rate (BER) expressions of QAM for SLJ have not been presented in previous studies. In this paper, we derive the exact BER expressions of QAM considering phase coherent and noncoherent scenarios under SLJ. Using the derived expressions, we investigate the SLJ order that maximizes BER of QAM for jamming-to-signal ratio (JSR). Further, we present BER of QAM with tone jamming and show that tone jamming is a special case of noncoherent SLJ. In addition, we use a probability density function of the SLJ amplitude to show that the high order noncoherent SLJ is similar to noise jamming. To increase BER in a low JSR region, we present a BER expression of QAM when SLJ exists in a pulse form. Using the derived expression, we investigate the order and pulse duration ratio to maximize BER for JSR. The derived expressions are verified using computer simulations.

Design and analysis of a DCSK-based cognitive radio system using hybrid underlay/overlay transmission

In this paper, we present a hybrid Underlay/Overlay DCSK-based Cognitive Radio (DCR) system using the Cognitive Radio techniques and abilities of a Multi-Carrier DCSK (MC-DCSK) scheme together, which can be extended to many other similar non-coherent scenarios. In this scheme, secondary user (SU) employs the spectrum holes as a dedicated frequency to transmit reference signals in overlay mode and uses remaining common frequencies to transmit data bearing signals by an underlying approach. We derived an analytical BER expression for the DCR scheme over a frequency selective fading channel and adopted it as our optimization criterion. To formulate the optimization problem, we proposed a sub-carrier grouping approach in order to implement our min–max fairness strategy, considering the power budget and interference temperature constraints. The proposed DCR scheme not only employed spectrum holes, but also improved BER performance of the conventional multi-user MC-DCSK system significantly considering the power allocation policy and robustness against frequency selective channel. Finally, simulation results validated the advantages of the proposed scheme.

Successive-Relaying-Aided Decode-and-Forward Coherent Versus Noncoherent Cooperative Multicarrier Space–Time Shift Keying

Successive-relaying-aided (SR) cooperative multicarrier (MC) space-time shift keying (STSK) is proposed for frequency-selective channels. We invoke SR to mitigate the typical 50% throughput loss of conventional half-duplex relaying schemes and MC code-division multiple access (MC-CDMA) to circumvent the dispersive effects of wireless channels and to reduce the SR-induced interference. The distributed relay terminals form two virtual antenna arrays (VAAs), and the source node (SN) successively transmits frequency-domain (FD) spread signals to one of the VAAs, in addition to directly transmitting to the destination node (DN). The constituent relay nodes (RNs) of each VAA activate cyclic-redundancy-checking-based (CRC) selective decode-and-forward (DF) relaying. The DN can jointly detect the signals received via the SN-to-DN and VAA-to-DN links using a low-complexity single-stream-based joint maximum-likelihood (ML) detector. We also propose a differentially encoded cooperative MC-CDMA STSK scheme to facilitate communications over hostile dispersive channels without requiring channel estimation (CE). Dispensing with CE is important since the relays cannot be expected to altruistically estimate the SN-to-RN links for simply supporting the source. Furthermore, we propose soft-decision-aided serially concatenated recursive systematic convolutional (RSC) and unity-rate-coded (URC) cooperative MC STSK and investigate its performance in both coherent and noncoherent scenarios.

Complex-Valued Random Vectors and Channels: Entropy, Divergence, and Capacity

Recent research has demonstrated significant achievable performance gains by exploiting circularity/non-circularity or propeness/improperness of complex-valued signals. In this paper, we investigate the influence of these properties on important information theoretic quantities such as entropy, divergence, and capacity. We prove two maximum entropy theorems that strengthen previously known results. The proof of the former theorem is based on the so-called circular analog of a given complex-valued random vector. Its introduction is supported by a characterization theorem that employs a minimum Kullback-Leibler divergence criterion. In the proof of latter theorem, on the other hand, results about the second-order structure of complex-valued random vectors are exploited. Furthermore, we address the capacity of multiple-input multiple-output (MIMO) channels. Regardless of the specific distribution of the channel parameters (noise vector and channel matrix, if modeled as random), we show that the capacity-achieving input vector is circular for a broad range of MIMO channels (including coherent and noncoherent scenarios). Finally, we investigate the situation of an improper and Gaussian distributed noise vector. We compute both capacity and capacity-achieving input vector and show that improperness increases capacity, provided that the complementary covariance matrix is exploited. Otherwise, a capacity loss occurs, for which we derive an explicit expression.