Publications

A modified CLPDI for code acquisition in multipath channel

Analytical results are presented for a direct sequence spread spectrum system code acquisition in a static multipath channel. The performance measure is the mean acquisition time. The constant false alarm rate criterion is used as threshold setting rule for comparator. The energies of the multipath components are combined already in the acquisition process by using a modified chip level post detection integration. Therefore, diversity combining in the acquisition is used. The method increases the probability of detection of the burst of multipath components, ie, it decreases the mean acquisition time for finding the existence of a multipath profile. The numerical results indicate that the method improves the acquisition performance significantly. Also total acquisition time, ie, time to acquire all the multipaths can be decreased by the proposed method.

On the Performance of Cognitive Full-Duplex Relaying Systems under Spectrum Sharing Constraints

No abstract is provided for this article.

Robustness of NOMA in HetNets: Impact of Hardware Impairments and Imperfect CSI

Network Slicing for eMBB and mMTC with NOMA and Space Diversity Reception

In this work, we study the coexistence in the same Radio Access Network (RAN) of two use cases present in the Fifth Generation (5G) of wireless communication systems: enhanced Mobile BroadBand (eMBB) and massive Machine-Type Communications (mMTC). eMBB services are requested for applications that demand extremely high data rates and moderate requirements on latency and reliability, whereas mMTC enables applications for connecting a massive number of low-power and low-complexity devices. The coexistence of both services is enabled by means of network slicing and Non-Orthogonal Multiple Access (NOMA) with Successive Interference Cancellation (SIC) decoding. Under the orthogonal slicing, the radio resources are exclusively allocated to each service, while in the non-orthogonal slicing the traffics from both services overlap in the same radio resources. We evaluate the uplink performance of both services in a scenario with a multi-antenna Base Station (BS). Our simulation results show that the performance gains obtained through multiple receive antennas are more accentuated for the non-orthogonal slicing than for the orthogonal allocation of resources, such that the non-orthogonal slicing outperforms its orthogonal counterpart in terms of achievable data rates or number of connected devices as the number of receive antennas increases.

Performance Evaluation of Interleaved MC-CDMA Systems with Correlated Nakagami-m Fading Channels

Multicarrier code division multiple access (MC-CDMA) has emerged as a promising air interface candidate for future wireless communication systems. With the help of the characteristic function of correlated Nakagami-m variables, the performance of an interleaved MC-CDMA with a maximal-ratio combining (MRC) receiver and frequency selective Nakagami-m fading channels is studied. Computer simulations demonstrate the accuracy of the analysis. Based on the analytical results, with an exhaustive search of different subcarrier interleaving schemes, the optimal subcarrier interleaver which provides the minimum bit error rate (BER) can be achieved. Compared to a random interleaver, the optimal subcarrier interleaver offers considerable performance improvement.

Conditional Denoising Diffusion Probabilistic Models for Data Reconstruction Enhancement in Wireless Communications

No abstract is provided for this article.

Low Latency Decoder for Short Blocklength Polar Codes

Polar codes have been gaining a lot of interest due to it being the first coding scheme to provably achieve the symmetric capacity of a binary memoryless channel with an explicit construction. However, the main drawback of polar codes is the low throughput of its successive cancellation (SC) decoding. Simplified SC decoding algorithms of polar codes can be used to reduce the latency of the polar decode by faster processing of specific sub-codes in the polar code. By combining simplified SC with a list decoding technique, such as SC list (SCL) decoding, polar codes can cater to the two conflicting requirements of high reliability and low latency in ultra-reliable low-latency (URLLC) communication systems. Simplified SC algorithm recognizes some special nodes in the SC decoding tree, corresponding to the specific subcodes in the polar code construction, and efficiently prunes the SC decoding tree, without traversing the sub-trees and computing log-likelihood ratios (LLRs) for each child node. However, this decoding process still suffers from the latency associated with the serial nature of SC decoding. We propose some new algorithms to process new types of node patterns that appear within multiple levels of pruned sub-trees and it enables to process of certain nodes in parallel. In short blocklength polar codes, our proposed algorithm can achieve up to $13\%$ latency reduction from fast-simplified SC \cite{Sarkis2013} without any performance degradation. Furthermore, it can achieve up to $27\%$ latency reduction if small error-correcting performance degradation is allowed.

BER performance evaluation for MC-CDMA systems in Nakagami-m fading

Based on the approximation of the sum of several Nakagami-m variables and an alternative expression of Q-function, an efficient bit error rate (BER) expression is described. The closed BER form is applicable to multicarrier code-division multiple-access (MC-CDMA) systems with equal gain combining (EGC) in frequency selective Nakagami fading channels.

Distributed resource allocation for MISO downlink systems via the alternating direction method of multipliers

We provide a distributed algorithm for the radio resource allocation problem in multicell downlink multi-input single-output systems, subject to satisfying quality of service requirements of each user. Specifically, the problem of minimizing total transmit power subject to signal-to-interference-plus-noise ratio constraints of each user is considered. We propose a consensus-based distributed algorithm based on alternating direction method of multipliers. Numerical results show that the proposed distributed algorithm can achieve the optimal centralized solution.

CSI-free vs CSI-based multi-antenna WET for massive low-power Internet of Things

Wireless Energy Transfer (WET) is a promising solution for powering massive Internet of Things deployments. An important question is whether the costly Channel State Information (CSI) acquisition procedure is necessary for optimum performance. In this paper, we shed some light into this matter by evaluating CSI-based and CSI-free multi-antenna WET schemes in a setup with WET in the downlink, and periodic or Poisson-traffic Wireless Information Transfer (WIT) in the uplink. When CSI is available, we show that a maximum ratio transmission beamformer is close to optimum whenever the farthest node experiences at least 3 dB of power attenuation more than the remaining devices. On the other hand, although the adopted CSI-free mechanism is not capable of providing average harvesting gains, it does provide greater WET/WIT diversity with lower energy requirements when compared with the CSI-based scheme. Our numerical results evidence that the CSI-free scheme performs favorably under periodic traffic conditions, but it may be deficient in case of Poisson traffic, specially if the setup is not optimally configured. Finally, we show the prominent performance results when the uplink transmissions are periodic, while highlighting the need of a minimum mean square error equalizer rather than zero-forcing for information decoding.

Quasi-coherent delay-locked loops for fading channels

The most widely used delay estimators in DS-CDMA receivers are based on the delay-locked loops (DLL). In a coherent RAKE receiver the complex channel coefficient estimate can be used to attain the phase coherency in DLL and the effect of data modulation can be removed via decision feedback. The resulting algorithms are called quasi-coherent delay-locked loops (QCDLL). The performance of four variations for QCDLLs based on lead-lag phase-locked loops has been analyzed by computer simulations. All the loops performed satisfactorily in a fading channel, but the quasi-coherent sample-correlate-choose-largest (QCSCCL) loop had 5-6 dB better performance than the other schemes.

Throughput maximization in multi-hop wireless networks under a secrecy constraint

This paper analyzes the achievable throughput of multi-hop sensor networks for industrial applications under a secrecy constraint and malicious jamming. The evaluation scenario comprises sensors that measure some relevant information of the plant that is first processed by an aggregator node and then sent to the control unit. To reach the control unit, a message may travel through relay nodes, which form a multi-hop wireless link. At every hop, eavesdropper nodes attempt to acquire the messages transmitted through the legitimate link. The communication design problem posed here is how to maximize the multi-hop throughput from the aggregator to the control unit by finding the best combination of relay positions (i.e. hop length: short or long) and coding rates (i.e. high or low spectral efficiency) so that the secrecy constraint is satisfied. Using a stochastic-geometry formulation, we show that the optimal choice of coding rate is normally high and depends on the path-loss exponent only, while a greater number of shorter hops are preferable to smaller number of longer hops in any situation. For the investigated scenarios, we prove that the optimal throughput subject to the secrecy constraint achieves the unconstrained optimal performance – if a feasible solution exists.

Optimum Transmission Rate in Fading Channels with Markovian Sources and QoS Constraints

This paper evaluates the performance of reliability and latency in machine type communication networks, which composed of single transmitter and receiver in the presence of Rayleigh fading channel. The source's traffic arrivals are modeled as Markovian processes namely Discrete-Time Markov process, Fluid Markov process, and Markov Modulated Poisson process, and delay/buffer overflow constraints are imposed. Our approach is based on the reliability and latency outage probability, where transmitter not knowing the channel condition, therefore the transmitter would be transmitting information over the fixed rate. The fixed rate transmission is modeled as a two state Discrete time Markov process, which identifies the reliability level of wireless transmission. Using effective bandwidth and effective capacity theories, we evaluate the trade-off between reliability-latency and identify QoS requirement. The impact of different source traffic originated from MTC devices under QoS constraints on the effective transmission rate are investigated.

CSI-free vs CSI-based multi-antenna WET for massive low-power Internet of Things

Wireless Energy Transfer (WET) is a promising solution for powering massive Internet of Things deployments. An important question is whether the costly Channel State Information (CSI) acquisition procedure is necessary for optimum performance. In this paper, we shed some light into this matter by evaluating CSI-based and CSI-free multi-antenna WET schemes in a setup with WET in the downlink, and periodic or Poisson-traffic Wireless Information Transfer (WIT) in the uplink. When CSI is available, we show that a maximum ratio transmission beamformer is close to optimum whenever the farthest node experiences at least 3 dB of power attenuation more than the remaining devices. On the other hand, although the adopted CSI-free mechanism is not capable of providing average harvesting gains, it does provide greater WET/WIT diversity with lower energy requirements when compared with the CSI-based scheme. Our numerical results evidence that the CSI-free scheme performs favorably under periodic traffic conditions, but it may be deficient in case of Poisson traffic, specially if the setup is not optimally configured. Finally, we show the prominent performance results when the uplink transmissions are periodic, while highlighting the need of a minimum mean square error equalizer rather than zero-forcing for information decoding.

Untrained DNN for Channel Estimation of RIS-Assisted Multi-User OFDM System with Hardware Impairments

Reconfigurable intelligent surface (RIS) is an emerging technology for improving performance in fifth-generation (5G) and beyond networks. Practically channel estimation of RIS-assisted systems is challenging due to the passive nature of the RIS. The purpose of this paper is to introduce a deep learning-based, low complexity channel estimator for the RIS-assisted multi-user single-input-multiple-output (SIMO) orthogonal frequency division multiplexing (OFDM) system with hardware impairments. We propose an untrained deep neural network (DNN) based on the deep image prior (DIP) network to denoise the effective channel of the system obtained from the conventional pilot-based least-square (LS) estimation and acquire a more accurate estimation. We have shown that our proposed method has high performance in terms of accuracy and low complexity compared to conventional methods. Further, we have shown that the proposed estimator is robust to interference caused by the hardware impairments at the transceiver and RIS.

A Bayesian Framework of Deep Reinforcement Learning for Joint O-RAN/MEC Orchestration

No abstract is provided for this article.

Low-Complexity Iterative Algorithm for Finding the MIMO-OFDM Broadcast Channel Sum Capacity

A novel low-complexity and provably convergent algorithm is proposed to find the sum capacity for vector Gaussian broadcast channels. Unlike the recently proposed sum-power constraint iterative waterfilling (SPC-IWF) algorithms, it has lower complexity and requires no additional precautions to ensure the convergence. We have proved analytically the convergence with probability one, and the computer simulations show that the proposed algorithm converges faster than the earlier variants of SPC-IWF algorithms. We formulate the problem in the context of a multiple-input multiple-output orthogonal frequency-division multiplexing system and discuss the simplifications provided by the block-diagonal channel structure

On frequency domain equalization for MC‐CDMA in Nakagami fading channels

In this letter, we evaluate the performance of multicarrier code division multiple access (MC‐CDMA) in terms of average bit error probability (BEP) in Nakagami fading channels. The results are applicable to MC‐CDMA systems employing coherent demodulation with maximal‐ratio combining (MRC) or equal gain combining (EGC) reception. The effects of fading parameters and number of users are presented. The accuracy of the proposed analysis is demonstrated by computer simulations. The BEP performance of the EGC receiver in the uplink is highly influenced by the fading parameter compared with that of the MRC receiver. The EGC receiver outperforms the MRC receiver in the downlink, but the MRC receiver gives almost the same performance as the EGC in the uplink. Copyright © 2004 AEI