David Vargas

Rate-splitting multiple access (RSMA) has been recognized as a promising multiple access technique for future wireless communication systems. Recent research demonstrates that RSMA can maintain its superiority without relying on successive interference cancellation (SIC) receivers. In practical systems, SIC-free receivers are more attractive than SIC receivers because of their low complexity and latency. This paper evaluates the theoretical limits of RSMA with and without SIC receivers under finite constellations. We first derive the constellation-constrained rate expressions for RSMA. We then design algorithms based on projected subgradient ascent to optimize the precoders and maximize the weighted sum-rate or max-min fairness among users. To apply the proposed optimization algorithms to large-scale systems, one challenge lies in the exponentially increasing computational complexity brought about by the constellation-constrained rate expressions. In light of this, we propose methods to avoid such computational burden. Numerical results show that, under optimized precoders, SIC-free RSMA leads to minor losses in both weighted sum-rate and max-min fairness in comparison to RSMA with SIC receivers, making it a viable option for future implementations.

Rate-Splitting Multiple Access (RSMA) is a powerful and versatile physical layer multiple access technique that generalizes and has better interference management capabilities than 5G-based Space Division Multiple Access (SDMA). It is also a rapidly maturing technology, all of which makes it a natural successor to SDMA in 6G. In this article, we describe RSMA’s suitability for 6G by presenting: i) link and system level simulations of RSMA’s performance gains over SDMA in realistic environments, and (ii) pioneering experimental results that demonstrate RSMA’s gains over SDMA for key use cases like enhanced Mobile Broadband (eMBB), and Integrated Sensing and Communications (ISAC). We also comment on the status of standardization activities for RSMA.

Rate-Splitting Multiple Access (RSMA) has emerged as a novel multiple access technique that enlarges the achievable rate region of Multiple-Input Multiple-Output (MIMO) broadcast channels with linear precoding. In this work, we jointly address three practical but fundamental questions: (1) How to exploit the benefit of RSMA under finite constellations? (2) What are the potential and promising ways to implement RSMA receivers? (3) Can RSMA still retain its superiority in the absence of successive interference cancellers (SIC)? To address these concerns, we first propose low-complexity precoder designs by taking finite constellations into account and show that the potential of RSMA is better achieved with such designs than those assuming Gaussian signalling. We then consider some practical receiver designs that can be applied to RSMA. We notice that these receiver designs follow one of two principles: (1) SIC: cancelling upper layer signals before decoding the lower layer and (2) non-SIC: treating upper layer signals as noise when decoding the lower layer. In light of this, we propose to alter the system design according to the receiver category. Through link-level simulations, the effectiveness of the proposed power allocation and receiver designs are verified. More importantly, we show that it is possible to preserve the superiority of RSMA over Spatial Domain Multiple Access (SDMA), including SDMA with advanced receivers, even without SIC at the receivers. Those results therefore open the door to competitive implementable RSMA strategies for 6G and beyond communications.

We consider a downlink multicast and unicast superposition transmission in multi-layer Multiple-Input Multiple-Output (MIMO) Orthogonal Frequency Division Multiple Access (OFDMA) systems when only the statistical channel state information is available at the transmitter (CSIT). Multiple users can be scheduled by using the time/frequency resources in OFDMA, while for each scheduled user MIMO spatial multiplexing is used to transmit multiple information layers, i.e., single user (SU)-MIMO. The users only need to feedback to the base-station the rank-indicator and the long-term average channel signal-to-noise ratio (SNR), i.e., statistical CSIT, to indicate a suitable number of transmission layers, a suitable modulation and coding scheme and allow the base-station to perform user scheduling. This approach is especially relevant for the delivery of common (e.g., popular live event) and independent (e.g., user personalized) content to a high number of users in deployments in the lower frequency bands operating in Frequency-Division-Duplex (FDD) mode, e.g., sub-1 GHz. We show that the optimal resource allocation that maximizes the ergodic sum-rate involves greedy user selection per OFDM subchannel and superposition transmission of one multicast signal across all subchannels and single unicast signal per subchannel. The optimal resource allocation dynamically chooses between sending unicast only, multicast only, or their superposition in each subchannel based on the disparity between the best and the worst user channel conditions and minimum multicast rate target. Degree-of-freedom (DoF) analysis shows that while the lack of instantaneous CSI limits DoF of unicast messages to the minimum number of transmit antennas and receiver antennas, the multicast message obtains full DoF that increases linearly with the number of users. We present resource allocation algorithms consisting of user selection and power allocation between multicast and unicast signals in each OFDM subchannel. System level simulations in 5G rural macro-cell scenarios show overall network throughput gains in realistic network environments by superposition transmission of multicast and unicast signals.

As part of a biochemical systematic investigation of the tribe Helianteae (Compositae) for their secondary metabolites, Calea deltophylla Cowan from the subtribe Galinsoginae, Squamopappus skutchii (S. F. Blake) Jansen, Harriman and Urbatsch, from the Ecliptinae, and Podachaenium eminens (Lagasca) Shultz-Bip. from the Verbesininae were chemically investigated. Calea deltophylla provided the known compounds ageratochromene and eupatarone and three new compounds, 3-methoxy-4-hydroxyseneciophenone, caldeltophyllide and deltophyllin. Squamopappus skutchii yielded the known sesquiterpenoid (beta)-eudesmol, two new guaianolides, skutchiolides A and B, and the new eudesmanolide chapinolin. P. eminens provided three known guaianolides. The structures of the compounds were established by chemical and spectroscopic methods including MS, IR, CD, ('1)H NMR and ('13)C NMR techniques and single crystal X-ray diffraction analysis. The chemical data support the taxonomical classification of C. deltophylla and P. eminens and justify the removal of S. skutchii from the genera Calea and Podachaenium, and its placement into the subtribe Ecliptinae. Terpenoid extracts of thirty plants from the Composite family were tested for their molluscicidal activity against Biomphalaria glabrata snails. Nearly 50% of the extracts exhibited molluscicidal activity, the most active being those of Podachaenium eminens from Mexico and Ambrosia confertiflora from Nuevo Leon, Mexico, and Texas, with LC(,100) (24 hrs) of 50, 100 and 100ppm, respectively. Confertiflorin from A. confertiflora DC provided upon treatment with p-toluensulfonic acid a mixture of desacetylconfertiflorin and allodesacetylconfertiflorin. Treatment of confertiflorin with phenylselenyl chloride followed by hydrogen peroxide oxidation yielded a mixture of 8(alpha)-acetoxyambrosin and 2,3-dehydro-8(alpha)-acetoxypsilostachin C. The structures of the new compounds were inferred from spectral data. Forty sesquiterpene lactones were tested for their molluscicidal activity against B. glabrata snails. The most active of the compounds was 7(alpha)-hydroxy-3-desoxyzaluzanin C with an LC(,100) (24 hrs) = 1.0 ppm. Ten sesquiterpene lactones, four guaianolides and six pseudoguaianolides, were tested for their inhibitory activity toward the enzyme phosphofructokinase. All compounds were found to be active as inhibitors. The most active of the guaianolides was 7(alpha)-hydroxy-3-desoxyzaluzanin C and allodesacetylconfertiflorin the most active pseudoguaianolide with apparent K(,i) values of 0.07 and 3.24 mM, respectively.

La búsqueda de potenciales soluciones para tratar aguas residuales y brindarles un valor agregado motivan el objetivo de este estudio que fue evaluar la eficiencia y desempeño de las bioceldas en generar bioelectricidad a partir del tratamiento de los efluentes de una granja de cerdos; teniendo en cuenta su desempeño con y sin el uso de inóculo. Se construyeron 03 bioceldas de doble cámara y se implementaron dos tratamientos por 13 días bajo monitoreo horario del voltaje. En el primer tratamiento se emplearon los microorganismos autóctonos del agua residual y en el segundo, se empleó estiércol vacuno como fuente de inóculo. El efluente presentó baja biodegradabilidad (DBO₅/DQO=0,22), además se alcanzó remociones mayores al 80% y 67% para la DQO y DBO₅ respectivamente, atribuido en primera instancia a la sedimentación de los sólidos del efluente. Los parámetros eléctricos fueron muy bajos comparados a otras investigaciones, alcanzando un voltaje promedio menor a 200 mV y la eficiencia coulómbica menor a 0,1%. Estadísticamente los tratamientos no tuvieron diferencias significativas en la remoción de DQO y DBO₅, el voltaje medio y eficiencia coulómbica. Finalmente, fue posible generar bioelectricidad, pero a una eficiencia muy baja, lo que hace importante investigar sobre cómo optimizar el proceso.

We study optimal delivery strategies of one common and K independent messages from a source to multiple users in wireless environments. In particular, two-layered superposition of broadcast/multicast and unicast signals is considered in a downlink multiuser OFDMA system. In the literature and industry, the two-layer superposition is often considered as a pragmatic approach to make a compromise between the simple but suboptimal orthogonal multiplexing (OM) and the optimal but complex fully-layered non-orthogonal multiplexing. In this work, we show that only two-layers are necessary to achieve the maximum sum-rate when the common message has higher priority than the K individual unicast messages, and OM cannot be sum-rate optimal in general. We develop an algorithm that finds the optimal power allocation over the two-layers and across the OFDMA radio resources in static channels and a class of fading channels. Two main use-cases are considered: i) Multicast and unicast multiplexing when K users with uplink capabilities request both common and independent messages, and ii) broadcast and unicast multiplexing when the common message targets receive-only devices and K users with uplink capabilities additionally request independent messages. Finally, we develop a transceiver design for broadcast/multicast and unicast superposition transmission based on LTE-A-Pro physical layer and show with numerical evaluations in mobile environments with multipath propagation that the capacity improvements can be translated into significant practical performance gains compared to the orthogonal schemes in the 3GPP specifications. The impact of real channel estimation is also analyzed and it is shown that significant gains in terms of spectral efficiency or increased coverage area are still available even in the presence of estimation errors and imperfect interference cancellation for the two-layered superposition system.

3GPP LTE eMBMS release (Rel-) 14, also referred to as further evolved multimedia broadcast multicast service (FeMBMS) or enhanced TV (EnTV), is the first mobile broadband technology standard to incorporate a transmission mode designed to deliver terrestrial broadcast services from conventional high power high tower (HPHT) broadcast infrastructure. With respect to the physical layer, the main improvements in FeMBMS are the support of larger inter-site distance for single frequency networks (SFNs) and the ability to allocate 100% of a carrier's resources to the broadcast payload, with self-contained signaling in the downlink. From the system architecture perspective, a receive-only mode enables free-to-air (FTA) reception with no need for an uplink or SIM card, thus receiving content without user equipment registration with a network. These functionalities are only available in the LTE advanced pro specifications as 5G new radio (NR), standardized in 3GPP from Rel-15, has so far focused entirely on unicast. This paper outlines a physical layer design for NR-MBMS, a system derived, with minor modifications, from the 5G-NR specifications, and suitable for the transmission of linear TV and radio services in either single-cell or SFN operation. This paper evaluates the NR-MBMS proposition and compares it to LTE-based FeMBMS in terms of flexibility, performance, capacity, and coverage.