Joint Active and Passive Beamforming for RIS-aided MIMO Communications with Low-Resolution Phase Shifts

Practical hardware limitations often impose a reduced number of available phase shifts at the elements of a reconfigurable intelligent surface (RIS). Most works often assume continuous phase-shits at the RIS elements for the transmit and passive beamforming optimization, which can lead to substantial performance loss. Therefore, to harvest the gains of RIS-assisted multi-stream multiple-input multiple-output (MIMO) communications under realistic phase shifts, this letter proposes a problem formulation for the maximization of the achievable rate over the transmit precoder and RIS elements, which avoids an explicit discrete constraint while still incorporating its effect. To efficiently tackle the resulting problem when considering large arrays and RIS panels, an iterative algorithm is derived which comprises a sequence of simple projections. Simulation results demonstrate that the proposed design can be very effective, especially with low-resolution phase-shifts.Comment: 5 pages, 3 figure

A Precoding Aided Space Domain Index Modulation Scheme for Downlink Multiuser MIMO Systems

In this correspondence, we propose a space domain index modulation (IM) scheme for the downlink of multiuser multiple-input multiple-output (MU-MIMO) systems. Instead of the most common approach where spatial bits select active receiver antennas, in the presented scheme the spatial information is mapped onto the transmitter side. This allows IM to better exploit large dimensional antenna settings which are typically easier to deploy at the base station. In order to mitigate inter-user interference and allow single user detection, a precoder is adopted at the BS. Furthermore two alternative enhanced signal construction methods are proposed for minimizing the transmitted power or enable an implementation with a reduced number of RF chains. Simulation results for different scenarios show that the proposed approach can be an attractive alternative to conventional precoded MU-MIMO.Comment: submitted to IEEE Transactions on Vehicular Technolog

Usage of link-level performance indicators for HSDPA network-level simulations in E-UMTS

The paper describes integration of HSDPA (high-speed downlink packet access) link-level simulation results into network-level simulations for enhanced UMTS. The link-level simulations model all physical layer features depicted in the 3GPP standards. These include: generation of transport blocks; turbo coding; rate matching; spreading; scrambling; modulation. At the receiver side, all complementary blocks are designed, with soft-decision demodulation, and a turbo decoder using the MAP (maximum a posteriori) algorithm with 8 iterations. An analytical formula is defined that fits the CQI (channel quality indicator) dependent BLER (block error rate) versus E/sub b//N/sub 0/ results in an AWGN channel. This formula models the physical layer in the network-level simulator. A further extension for frequency selective fading channels has been defined. The network-level simulator includes propagation models that provide SNR values. Based on these SNR values and the simplified physical layer model, an algorithm selects the CQI, and determines the actual BLER at time of reception. The rounding down and delaying of the CQI reporting, which corresponds to the W-CDMA standard, has a significant impact on throughput and transfer delay of the HS-DSCH. Some compensation can be found in a modified transmission. The integration of the link-level and network-level simulators gives accurate and realistic results that can be used in more studies that focus on network layer aspects of packet based services over HSDP

Analytical Matched Filter Bound for M-QAM Hierarchical Constellations with Diversity Reception in Multipath Rayleigh Fading Channels

In this paper, we derive matched filter bound (MFB) expressions for the performance of hierarchical quadrature amplitude modulations (M-HQAM) over time-discrete multipath Rayleigh fading environments with diversity. The expressions are valid for multipath environments where different paths and antennas can be correlated. Since hierarchical constellations are usually employed to achieve unequal bit error protection, the MFB expressions are given in terms of the individual bit error rate (BER) for the different bit streams. Although typically the MFB is obtained assuming slow time varying channels, fast varying channels are also considered in this paper

Atualização em proteções pulpares: uma revisão da literatura

Introdução: A perda de estrutura dentária por lesão de cárie ou traumatismo expõe a dentina o que pode representar uma agressão ao complexo pulpo-dentinário. Assim sendo, por vezes, é necessária a aplicação de agentes protetores quer sobre tecido dentinário, quer sobre tecido pulpar exposto, com o objetivo de obter uma selagem o mais hermética possível, e assim preservar a sua vitalidade. Objetivos: O objetivo desta revisão da literatura foi averiguar, a partir dos estudos existentes, qual o material usado em proteções pulpares diretas, entre o MTA®, Biodentine® e Ca(OH)2, que melhor preserva a vitalidade pulpar. Material e Métodos: Foi realizada uma pesquisa nas bases de dados Pubmed, Cochrane library, Science Direct, e Scielo, compreendida entre 2005 e 2022. As palavras-chave utilizadas foram: “direct pulp capping, “MTA”, “Biodentine” e “Calcium Hydroxide”. Os resultados compreenderam 252 artigos, dos quais, após análise do abstract e leitura integral, incluíram-se 20 artigos. Resultados: Os cimentos de silicato de cálcio revelaram ser superiores ao Ca(OH)2 na preservação da vitalidade pulpar. Estas diferenças foram mais expressivas nas exposições por lesão de cárie. Os resultados do sucesso nas exposições mecânicas foram muito semelhantes em termos de sucesso clínico, mas histologicamente, as pontes dentinárias criadas pelo Ca(OH)2 foram frequentemente menos homogéneas, por vezes incompletas, com a presença de defeitos em túnel, e de menor espessura. Conclusão: Os cimentos de silicato de cálcio, como o MTA® e Biodentine® demonstraram ser clinicamente superiores ao Ca(OH)2.Introduction: The loss of tooth structure due to caries or trauma exposes the dentine, which may represent an aggression to the pulp-dentine complex. Therefore, it is sometimes necessary to apply protective agents to both dentinal tissue and exposed pulp tissue in order to achieve the most hermetic seal possible and thus preserve its vitality. Aim: The aim of this literature review was to investigate, based on existing studies, which material used in direct pulp capping, among MTA®, Biodentine® and Ca(OH)2, best preserves pulp vitality. Methods: A search was conducted in the Pubmed, Cochrane library, Science Direct, and Scielo databases, between 2005 and 2022. The keywords used were: "direct pulp capping, "MTA", "Biodentine" and "Calcium Hydroxide". The results comprised 252 articles, of which, after abstract analysis and full-text reading, 20 articles were included. Results: Calcium silicate cements proved to be superior to Ca(OH)2 in preserving pulp vitality. These differences were more significant in caries lesion exposures. The results of mechanical exposures were very similar in terms of clinical success, but histologically, dentin bridges created by Ca(OH)2 were often less homogeneous, sometimes incomplete, with the presence of tunnel defects, and of lower thickness. Conclusions: Calcium silicate cements such as MTA® and Biodentine® have been shown to be clinically superior to Ca(OH)2

Approaching the matched filter bound with block transmission techniques

Block transmission techniques, with appropriate cyclic prefixes and employing frequency-domain equalisation techniques, have been shown to be suitable for high data rate transmission over severely time-dispersive channels. The most popular techniques based on this concept are orthogonal frequency division multiplexing (OFDM) and single-carrier with frequency-domain equalisation (SC-FDE). In this paper, we consider OFDM and SC-FDE transmission schemes and study the impact of the number of multipath components and the diversity order on their performance. It is shown that when we have a high number of separable multipath components, the asymptotic performance of both schemes approaches the matched filter bound, even without diversity. When we have diversity, the performance approaches the matched filter bound faster, with a small number of separable multipath components. It was also observed that the SC-FDE has an overall performance advantage over the OFDM option, especially when employing the iterative block decision feedback equaliser with turbo equalisation and for high code rates

Coordinated Multi-Point MIMO Processing for 4G

The concept of cooperative Multiple-Input-Multiple-Output (MIMO), also referred to as network MIMO, or as Coordinated Multi-Point Transmission (CoMP), was standardized in 3GPP Release 11. The goal of CoMP is to improve the coverage of high data rates and cell-edge throughput, and also to increase system throughput. In this paper we analyze only the latter scenario, using system level simulations in accordance with 3GPP guidelines. It is shown that the use of joint coordinated multipoint transmission achieves additional throughput gains. However, the gains depend on the scheduling type. This paper also indicates that the criterion of fairness is an important parameter when the number of users is high

Iterative Multipacket Detection for High Throughput Transmissions in OFDM Systems

This paper presents a multipacket detection technique for dealing with packet collisions in OFDM schemes (Orthogonal Frequency Division Multiplexing). Instead of discarding collided packets as it is done in traditional MAC approaches (Medium Access Control) additional packets are transmitted and separated using Multiple Input Multiple Output (MIMO) based techniques. Reliable detection and high throughputs can be achieved as long as different interleavers are used for different retransmissions. We also include a method for estimating the users involved in the collision

On the Multihop Relays with Multiple Antennas for LTE-A

In this paper we analyze cooperative communications for broadcast/multicast wireless communication systems based on the LTE-A standard. Multihop relays utilizing the same frequency bands as the base station are considered. These relays are equipped with multiples antennas (MIMO), at least the double of those employed at the base station side. The simulation results show that multihop relays achieve an improvement of power efficiency, while keeping the average coverage and the overall network throughput unchanged. This can be viewed as an energy-efficient wireless transmission technique, which contributes to the implementation of the green cell networks concept, as it allows a reduction in the carbon emission footprint