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Future 4G systems require transmission of richer multimedia services which inevitably implies an increase in data rate. Orthogonal frequency and code division multiplexing (OFCDM) technique has shown promising results in achieving a high data rate while simultaneously combating multipath fading. OFCDM is an amalgamation of orthogonal frequency division multiplexing and two-dimensional (2D) spreading. 2D spreading helps to achieve diversity gains in both time and frequency domains. The present OFCDM systems employ 1D orthogonal variable spreading factor (OVSF) codes to achieve the required 2D spreading in code multiplexed channels. However, 2D OVSF codes have better correlation properties in comparison to 1D OVSF codes. Motivated by this principle, the authors propose a spreading scheme for OFCDM systems using 2D OVSF codes. The spreading scheme is designed to increase the system throughput and reduce multi-code interference. Here, the authors study the OFCDM system performance using the proposed spreading scheme in a multipath fast fading channel with varying spreading factors in both time and frequency domains. The results are compared with the existing OFCDM systems using 1D OVSF codes.

Background KCNE1 encodes a 129-residue cardiac potassium channel ( I Ks ) subunit. KCNE1 variants are associated with long QT syndrome and atrial fibrillation. However, most variants have insufficient evidence of clinical consequences and thus limited clinical utility. Methods In this study, we leveraged the power of variant effect mapping, which couples saturation mutagenesis with high-throughput sequencing, to ascertain the function of thousands of protein-coding KCNE1 variants. Results We comprehensively assayed KCNE1 variant cell surface expression (2554/2709 possible single-amino-acid variants) and function (2534 variants). Our study identified 470 loss- or partial loss-of-surface expression and 574 loss- or partial loss-of-function variants. Of the 574 loss- or partial loss-of-function variants, 152 (26.5%) had reduced cell surface expression, indicating that most functionally deleterious variants affect channel gating. Nonsense variants at residues 56–104 generally had WT-like trafficking scores but decreased functional scores, indicating that the latter half of the protein is dispensable for protein trafficking but essential for channel function. 22 of the 30 KCNE1 residues (73%) highly intolerant of variation (with > 70% loss-of-function variants) were in predicted close contact with binding partners KCNQ1 or calmodulin. Our functional assay data were consistent with gold standard electrophysiological data ( ρ  =  − 0.64), population and patient cohorts (32/38 presumed benign or pathogenic variants with consistent scores), and computational predictors ( ρ  =  − 0.62). Our data provide moderate-strength evidence for the American College of Medical Genetics/Association of Molecular Pathology functional criteria for benign and pathogenic variants. Conclusions Comprehensive variant effect maps of KCNE1 can both provide insight into I Ks channel biology and help reclassify variants of uncertain significance.

A novel data-nulling superimposed pilot scheme for orthogonal frequency division multiplexing (OFDM) systems is proposed, where the input data vector is spread over all the subcarriers by a precoding matrix and then nulled at certain subcarriers for the insertion of training pilots. This method avoids the loss of the data rate for frequency-division multiplexed pilots, but results in the distortion of input data. To mitigate the distortion introduced by the nulling operation, a simple iterative reconstruction scheme is used to improve the detection performance.

In this paper, closed form expressions for capacities per unit bandwidth for Spatially Multiplexed Multicarrier-Code Division Multiplexing with Zero Forcing Unified Successive Interference Cancellation detection are derived for optimal power and rate adaptation, optimal rate adaptation with constant transmit power, channel inversion with fixed rate, and truncated channel inversion adaptation policies, taking into account the effect of perfect channel estimation at the receiver. Optimal power and rate adaptation policy provides the highest capacity over other adaptation policies. Truncated channel inversion policy suffers a large capacity penalty relative to the optimal power adaptation policy. However, the capacity penalty for the truncated channel inversion policy is lower compared to channel inversion with fixed rate policy. Furthermore, we derive analytical results for (1) capacity statistics, (2) Complementary Cumulative Distribution Function, and (3) Probability Density Function.

Based on an alternative expression for Q-function, a simple bit error rate expression is derived in this paper for multicarrier code division multiple access systems with maximal ratio combining in correlated Nakagami-q channels. Furthermore, in this paper, we derive bounds on the probability of error and ergodic capacity of spatially multiplexed MC-CDM systems with zero forcing unified successive interference cancellation technique. Closed-form expressions for Capacities per unit bandwidth and Outage probability using optimal power and rate adaptation policy are derived and plotted. Asymptotic approximations and upper bounds on spectrum efficiency are also derived and plotted. Numerical results for Symbol Error Rate are also derived and plotted using MATLAB.

In this work an enhanced semi-blind channel estimator is presented for multicarrier CDMA systems with multiple transmit and receive antennas. The novel scheme is based on embedded pilots that are characterized as virtual users and their number is determined in a dynamic fashion according to the propagation channel conditions. The superimposed code-multiplexed pilots are used initially for channel estimation before the despreading operation, thus achieving per subcarrier estimation using the known unique multi-layer pattern of the virtual users. Afterwards, the estimation is enhanced by using the despread pilots. Furthermore, an iterative scheme is incorporated in channel estimation process minimizing the effect of multiuser interference and operates either in interference cancellation, or in virtual user mode. The proposed architecture is evaluated for spatial diversity systems (space- frequency block coded) with two transmit and up to four receive antennas operating in realistic propagation channels for various modulation and coding schemes. The results demonstrate a significant performance improvement especially as the channel is dominated by its time variant characteristics. The dynamic assignment of spreading codes in the payload and the pilots offers to the system realistic flexibility and adaptivity in demanding channels achieving concurrently maximization of the real overall system throughput, while maintaining low overhead and complexity burden.

Recently, two-way relay network has been taken attention. In this paper, the two-way relayprotocols of ultra-wideband (UWB) network based on code-multiplexed transmitted-reference (CMTR)impulse radio have been studied. Based on code-multiplexed scheme, a new two-way relayingstrategy for two-slots protocol is designed. The corresponding bit error rate (BER) performance isevaluated via simulations and compared with three-slots scheme which can get path diversity gainfrom direct link between terminals. Simulation results reveal that the performance of the two-slotsrelaying scheme is almost same with that of the three-slots scheme. Meanwhile the throughput ispromoted about 33% over three-slots scheme.