Perfectly Secure Index Coding

In this paper, we investigate the index coding problem in the presence of an eavesdropper. Messages are to be sent from one transmitter to a number of legitimate receivers who have side information about the messages, and share a set of secret keys with the transmitter. We assume perfect secrecy, meaning that the eavesdropper should not be able to retrieve any information about the message set. We study the minimum key lengths for zero-error and perfectly secure index coding problem. On one hand, this problem is a generalization of the index coding problem (and thus a difficult one). On the other hand, it is a generalization of the Shannon's cipher system. We show that a generalization of Shannon's one-time pad strategy is optimal up to a multiplicative constant, meaning that it obtains the entire boundary of the cone formed by looking at the secure rate region from the origin. Finally, we consider relaxation of the perfect secrecy and zero-error constraints to weak secrecy and asymptotically vanishing probability of error, and provide a secure version of the result, obtained by Langberg and Effros, on the equivalence of zero-error and $\epsilon$-error regions in the conventional index coding problem.Comment: 25 pages, 5 figures, submitted to the IEEE Transactions on Information Theor

Subset regularized zero-forcing precoders for cell-free C-RANs

Comunicació presentada a: 29th European Signal Processing Conference (EUSIPCO) celebrat del 23 al 27 d'agost de 2021 a Dublin, Irlanda.This paper formulates regularized zero-forcing (RZF) precoders that are both network- and user-centric for the downlink of centralized radio-access networks operating in a cell-free fashion. The transmission to every user involves a distinct subset of access points (APs), and every AP participates in the transmission to a distinct subset of users, hence the moniker subset precoders. These subsets, defined on the basis of the large-scale channel gains between users and APs, capture the most relevant signal and interference contributions while disregarding those whose processing is cost-ineffective and whose associated channel estimations would incur unnecessary overheads. With that, subset precoding approaches the performance of network-wide RZF, for the power allocation strategies of interest, while being scalable.Work supported by the European Research Council under H2020 Framework/ERC grant 694974, by MINECO's Projects RTI2018-102112 and RTI2018-101040, and by ICREA

Comparison of the Cost-utility Analysis of Electroacupuncture and Nonsteroidal Antiinflammatory Drugs in the Treatment of Chronic Low Back Pain

Introduction and objective: Chronic low back pain (CLBP) is among the most common and important reasons for visiting a spine surgeon by patients; it is the second cause of visiting a doctor. Low back pain can cause considerable suffering and is a major financial burden in the society. There are many different methods available for the treatment of CLBP. This study aimed to compare the cost-utility of electroacupuncture (EA) and nonsteroidal antiinflammatory drugs (NSAIDs), as two common treatment methods for patients with CLBP. Methods: This study was conducted on 100 patients suffering from CLBP. Cases were randomly selected from patients referring to two hospitals and four acupuncture clinics in Tehran. Forty-one patients received EA, and 59 patients were prescribed NSAIDs. The EuroQol five dimensions questionnaire was used to calculate quality-adjusted life-year. For calculating the total cost of the two treatment methods, face to face interview with patients was conducted by the researchers (using specific basic literature questionnaire), neurologists, and spine surgeons. The study perspective was social (direct and indirect costs calculated). Results: The mean age for EA group was 41 ± 2.3 years, and for NSAIDs group, it was 38.0 ± 4.4 years. The average of the utility of patients under treatment by EA and NSAIDs was estimated as 0.70 and 0.627, respectively. The difference in utility between the two groups was significant (p ≤ 0.05). The total cost of EA and NSAIDs was estimated as 461.48 ± 57.8$and 497.77 ± 85.2$ for one year (2016), respectively, which was also significant (p ≤ 0.05). Conclusion: The results indicate a significant difference between EA and NSAIDs in cases of both utility and total cost. The findings demonstrate that EA is more cost-effective than NSAIDs, as therefore can be considered as an alternative treatment for CLBP, with reasonable cost-utility. Keywords: chronic low back pain, cost-utility, electroacupuncture, nonsteroidal antiinflammatory drug

Parallel interference cancellation for Cell-Free C-RANs

Comunicació presentada al 54th Asilomar Conference on Signals, Systems and Computers, celebrat de l'1 al 4 de novembre de 2020 a California, Estats Units.This paper formulates a linear receiver for the uplink of centralized, possibly cloud-based, radio access networks operating in a cell-free fashion. This receiver, which draws on the notion of soft parallel interference cancellation, exhibits substantial interference rejection abilities, yet it does not involve any matrix inversions. Its computational cost is hence decidedly inferior to that of an MMSE receiver, but its performance is markedly superior to that of matched-filter beamforming. And, with an adequate sparsification of the channel matrix that it derives from, the proposed receiver can be rendered scalable in the sense of its computational cost per access point not growing with size of the network.Work supported by the European Research Council grant agreement 694974 and by the ICREA Academia program

Pseudo-Inverse vs generalized inverse for C-RAN downlink precoding

Comunicació presentada a: GLOBECOM 2020 celebrat del 17 a l'11 de desembre de 2020 a Taipei, Taiwan.This paper tackles the problem of zero-forcing (ZF) precoding for the downlink of centralized radio-access networks operating in a cell-free fashion. While the customary workhorse of ZF precoding is the channel pseudo-inverse, because of the separate power constraint at each participating access point, the pseudo-inverse is not optimum. Rather, it can be improved upon by other inverses that allow conveying stronger signals (or, equivalently, consuming less power) while respecting the same ZF conditions. Motivated by the enormous disparity in computational cost between simple pseudo-inversion and general inversion, we ascertain the performance disadvantage of the former in a wide range of conditions. The welcome conclusion is that pseudo-inversion is close-to-optimum for all operational regimes of interest.Work supported by the European Research Council under the H2020 Framework Programme/ERC grant 694974, and by MINECO's Projects RTI2018-102112 and RTI2018-101040

Spatial-wideband effect in line-of-sight MIMO communication

Comunicació presentada a IEEE International Conference on Communications (ICC 2022), celebrat del 16 al 20 de maig de 2022 a Seül, Corea del Sud.This paper addresses the spatial-wideband effect in line-of-sight multiple-input multiple-output channels. This effect arises once the bandwidth is large enough that the differences in propagation delays for distinct transmit-receive antenna pairs cease to be negligible relative to the symbol period; this, in turn, gives rise to intersymbol interference. The impact of this effect is quantified as a function of the relevant geometric parameters (range, array orientations, antenna spacings) and a family of scalable solutions is proposed to counter it. In particular, a solution based on per-antenna delay lines at transmitter and receiver is shown to be highly effective, and a criterion is derived to set those delay lines as a function of the channel.This work was supported by the European Research Council under the H2020 Framework Programme/ERC grant agreement 694974, by the ICREA Academia program, and by the UPF-Fractus Chair on Tech Transfer and 6G

Linear interference cancellation for the cell-free C-RAN uplink

Drawing on the notion of parallel interference cancellation, this paper formulates a one-shot linear receiver for the uplink of centralized, possibly cloud-based, radio access networks (C-RANs) operating in a cell-free fashion. This receiver exhibits substantial interference rejection abilities, yet it does not involve any matrix inversions; rather, its structure hinges on the pairwise projections of the users' channel vectors. Its performance is markedly superior to that of matched-filter beamforming, while the computational cost is decidedly inferior to that of an MMSE filter, altogether constituting an attractive alternative in terms of performance vs cost. Furthermore, with a proper sparsification of the channel matrix that it estimates and processes, the proposed receiver can be rendered scalable in the sense of its computational cost per access point not growing with size of the network. Uplink power control is also readily accommodated.The authors are with Univ. Pompeu Fabra, 08018 Barcelona and their work is supported by the European Research Council under the H2020 Framework Programme/ERC grant agreement 694974, by MINECO’s Projects RTI2018-102112 and RTI2018-101040, and by the ICREA academia program