Reducing the large sidelobes of multicarrier signals is crucial to prevent adjacent channel interference. Spectral precoding is an effective approach toward this goal, at the expense of throughput loss due to precoder redundancy; thus, it is of interest to explore alternative precoder designs with improved performance at lower redundancies. We present a novel precoder which minimizes radiated power within a user-selectable frequency region. The structure of the precoding matrix is chosen to allow efficient mitigation of in-band distortion at the receiver by means of iterative and successive interference cancellation, while completely avoiding distortion to protected and pilot subcarriers. By exploiting the low-rank properties of constituent blocks, computational complexity can be significantly reduced with little impact on sidelobe reduction. Simulation results show the benefits of the proposed design, which is particularly effective in redundancy-limited settings targeting high spectral efficiency.

In this paper we present a method for estimating the height of the nocturnal stable boundary layer by using lidar measurements and a single radiosonde for unambiguous initial guess. The method relies on the correlation between aerosol stratifications in the stable boundary layer and minimum variance levels in the attenuated backscatter profile. The method is based on calculating either temporal or spatial variance vertical profiles of the attenuated backscatter and threshold-limited decision. A radiosonde temperature-based estimation is used to provide an initial guess if several minimum variance regions are detected. Two study cases using ceilometer data are shown. Comparison with temperature-based estimations from a collocated microwave radiometer have been used for validation. The method can be useful for estimating the stable boundary layer height in sites with a ceilometer but without any available temperature profiler.

A multiple access (MA) optimization technique for massive low-rate direct-sequence spread spectrum communications is analyzed in this work. A dense network of users transmitting at the same rate to a common central node under channel-aware energy allocation is evaluated. At reception, successive interference cancellation (SIC) aided by channel decoding is adopted. Our contribution focuses on wireless scenarios involving a vast number of users for which the provided user-asymptotic model holds. Variational calculus (VC) is employed to derive the energy allocation function that, via user-power imbalance, maximizes the network spectral efficiency (SE) when perfect channel state information at transmission (CSIT) is available and both average and maximum per-user energy constraints are set. Monte Carlo simulations at chip-level of a SIC receiver using a real decoder assess the proposed optimization method.

This paper studies the throughput maximization of a dense multiple access network of low-rate subscribers that share the same practical Forward Error Correction (FEC) code and modulation scheme, and transmit to a central node that implements a Successive Soft Interference Cancellation (soft SIC) strategy in order to mitigate Multiple Access Interference (MAI). In the user-asymptotic case, we make use of Variational Calculus (VC) tools to derive, in terms of the Packet Error Rate (PER) of the shared encoder and the Residual Energy (RE) from imperfect cancellation, the optimum energy profile that maximizes the network spectral efficiency, when a sum power constraint at the SIC input is enforced. Comparative performance analyses using a representative encoder are carried out. Simulation results show the benefit of the adopted soft SIC scheme in front of other SIC strategies, obtaining relevant throughput gains under high traffic loads.

A two-scale ad hoc wireless network is envisaged in which the interference power generated in long-range connections is recycled by the surrounding wireless nodes in order to support their own short-range communications. We prove that the network energy efficiency is independent of the transmitters range and, therefore, that long-range transmitters can supply the power required for short-range connectivity without degrading the overall network energy efficiency. As an example, we have studied the feasibility of a short-range multiple-access return-link powered by the interference harvested from neighboring long-range connections.

This letter focuses on the design of an adaptive bit-interleaved coded modulation (BICM) scheme for frequency selective slow fading channels where the transmitter has certain knowledge of the channel response. In particular, we consider the design of the interleaver stage for a specific convolutional code operating with OFDM modulation. The adaptive interleaver uses the puncturing tables of the rate-compatible punctured convolutional codes (RCPC codes) to rearrange the bits as a function of the fading values and the specific constellation. The performance of different interleavers are compared, revealing that the adaptive RCPC-based interleaver produces larger Euclidean distances between the received codewords and reduces the packet error rate (PER), specially when the number of deep-faded subcarriers increases. Numerical results also evidence the importance of the interleaver choice when comparing the performance of different power allocation strategies.

A beamforming for OFDM modulation is proposed that allocates power over subchannels and subcarriers. The design follows a minimum BER criterion taking into account the different reliability of CSI estimates at both ends of the transmitter link. The transmitter design is based on a generalized exponential BER bound that is tighter than the Chernoff bound, whereas the receiver that minimizes the BER is implemented by the MAP detector. The resulting design reconfigures itself, from the known solution, when perfect CSI is available to the open-loop solution depending on the channel uncertainty.

This paper deals with closed-loop schemes in OFDM modulation systems. A Bayesian approach is presented to design minimum BER prefiltering matrices in the presence of channel uncertainties. This formulation leads to a robust algorithm that exhibits lower sensitivity to channel estimation errors than classical schemes. The proposed design encompasses the single antenna transmission, the beamforming schemes and the frequency flat fading channels as particular cases.

The design of accurate equalization schemes, optimizing the transmission strategy, can be achieved if channel status information is available not only at the receiver but also at the transmitter side. Accordingly, we propose a feasible scheme to track the channel response by the transmitter based on channel prediction, becoming a suitable solution in time-varying channels. Moreover, to follow faithfully the channel variability, the receiver can estimate the channel prediction error and next update the transmitter predictor through a return link. This paper provides an accurate study of the predictor design, and analyzes the way to minimize the amount of information exchanged through the feedback channel concerning the differential entropy of channel evolution. Furthermore, the prediction error is quantified focusing on the rate-distortion function, and it is shown that a low throughput is enough for tracking the channel coefficients even in the presence of fast time-varying channels.

Linear block codes in the complex field can be applied in spatial and/or temporal diversity receivers in order to develop high performance schemes for (almost-) blind equalization in mobile communications. The proposed technique uses the structure of the encoded transmitted information (with redundancy) to achieve equalization schemes based on a deterministic criterion. Simulations show that the proposed technique is more efficient than other schemes that follow similar equalizer structures. The result is an algorithm that provides the design of channel equalizers in low EbNo scenarios.

Linear block codes can be applied in spatial and/or temporal diversity receivers in order to develop high performance schemes for blind equalization in mobile communications. The proposed technique uses the structure of the encoded transmitted information (with redundancy) to achieve equalization schemes based on a deterministic criterion. Simulations show that the proposed technique is more efficient than other schemes that follow similar equalizer structures. The result is an algorithm that provides the design of blind channel equalizers in low EbNo scenarios.