Browsing by Author "Robles, Ramiro Sámano"
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- DEWI - Wirelessly into the FuturePublication . Rom, Werner; Robles, Ramiro Sámano; Priller, Peter; Dominguez, Luis; Rivilla, Javier; Koivusaari, Jani; Komi, Marjaana; Van Driel, WillemThe ARTEMIS/ECSEL project DEWI (Dependable Embedded Wireless Infrastructure) focusses on the area of wireless sensor / actuator networks and wireless com-munication. With its four industrial domains (Aero-nautics, Automotive, Rail, and Building) and 21 clearly industry-driven use cases / applications, DEWI will pro-vide and demonstrate key solutions for wireless seamless connectivity and interoperability in smart cities and infra-structures, by considering everyday physical environ-ments of citizens in buildings, cars, trains and aeroplanes. It will add clear cross-domain benefits in terms of re-usability of technological building bricks and architecture, processes and methods. DEWI currently is one of the largest funded European R&D projects, comprising 58 renowned industrial and research partners from 11 Euro-pean countries. (For further details see www.dewi-project.eu)
- Distributed Linear Precoding and User Selection in Coordinated Multicell SystemsPublication . Castañeda, Eduardo; Silva, Adão; Robles, Ramiro Sámano; Gameiro, AtílioIn this manuscript we tackle the problem of semidistributed user selection with distributed linear precoding for sum rate maximization in multiuser multicell systems. A set of adjacent base stations (BS) form a cluster in order to perform coordinated transmission to cell-edge users, and coordination is carried out through a central processing unit (CU). However, the message exchange between BSs and the CU is limited to scheduling control signaling and no user data or channel state information (CSI) exchange is allowed. In the considered multicell coordinated approach, each BS has its own set of cell-edge users and transmits only to one intended user while interference to non-intended users at other BSs is suppressed by signal steering (precoding). We use two distributed linear precoding schemes, Distributed Zero Forcing (DZF) and Distributed Virtual Signalto-Interference-plus-Noise Ratio (DVSINR). Considering multiple users per cell and the backhaul limitations, the BSs rely on local CSI to solve the user selection problem. First we investigate how the signal-to-noise-ratio (SNR) regime and the number of antennas at the BSs impact the effective channel gain (the magnitude of the channels after precoding) and its relationship with multiuser diversity. Considering that user selection must be based on the type of implemented precoding, we develop metrics of compatibility (estimations of the effective channel gains) that can be computed from local CSI at each BS and reported to the CU for scheduling decisions. Based on such metrics, we design user selection algorithms that can find a set of users that potentially maximizes the sum rate. Numerical results show the effectiveness of the proposed metrics and algorithms for different configurations of users and antennas at the base stations.
- Multi-Objective and Financial Portfolio Optimization of Carrier-Sense Multiple Access Protocols with Cooperative DiversityPublication . Robles, Ramiro Sámano; Gameiro, AtílioThis paper presents a trade-off design and optimization of a class of wireless carrier-sense multiple access protocols where collision-free transmissions are assisted by the potential cooperative retransmissions of inactive terminals with a correct copy of the original transmission. Terminals are enabled with a decode-and-forward relaying protocol. The analysis is focused on asymmetrical settings, where terminals experience different channel and queuing statistics. This work is based on multi-objective and financial portfolio optimization tools. Each packet transmission is thus regarded not only as a network resource, but also as a financial asset with different values of return and risk (or variance of the return). The objective of this financial optimization is to find the transmission policy that simultaneously maximizes return and minimizes risk in the network. The work is focused on the characterization of the boundaries (envelope) of different types of trade-off performance regions: the conventional throughput region, sum-throughput vs. fairness, sum-throughput vs. power, and return vs. risk regions. Fairness is evaluated by means of the Gini-index, which is a metric commonly used in economics to measure income inequality. Transmit power is directly linked to the global transmission rate. The protocol is shown to outperform non-cooperative solutions under different network conditions that are here discussed.
- A Random Access Protocol incorporating Multi-Packet Reception, Retransmission Diversity and Successive Interference CancellationPublication . Robles, Ramiro SámanoThis paper presents a random access protocol assisted by a set of signal processing tools that significantly improve the multi-packet reception (MPR) capabilities of the system. A receiver with M antennas is used to resolve collisions with multiplicity K _ M. The remaining unresolved conflicts (with multiplicity K > M) are processed by means of protocol-induced retransmissions that create an adaptive multiple-input multiple-output (MIMO) system. This scheme, also known as NDMA (network diversity multiple access) with MPR, can achieve in ideal conditions a maximum throughput of M packets/time-slot. A further improvement is proposed here, where the receiver attempts to recover the information immediately after the reception of each (re)transmission. This is different from conventional NDMA, where this decoding process only occurs once the adaptive MIMO channel is assumed to become full-rank (i.e., once the estimated number of required retransmissions has been collected). The signals that are correctly decoded at every step of the proposed algorithm are used to mitigate interference upon the remaining contending signals by means of successive interference cancellation (SIC). This allows for improved reception as well as for the reduction of the number of retransmissions required to resolve a collision. Significantly high throughput figures that surpass the nominal rate of the system (T > M) are here reported. To the best of our knowledge this is the first random access protocol that achieves this figure. Correlation between antennas and between retransmissions, as well as imperfections of SIC are also considered. In ideal conditions, the effects of SIC are equivalent to a splitting tree operation. The inclusion of SIC in NDMA-MPR also opens the possibility of backwards compatibility with legacy terminals. The protocol achieves the highest throughput in the literature of single-hop wireless random access with minimum feedback complexity. This is a significant result for future highly dense 5G networks.
- System Level Simulation and Radio Resource Management for Distributed Antenna Systems with Cognitive Radio and Multi-Cell CooperationPublication . Robles, Ramiro Sámano; Gameiro, Atilio; Pereira, NunoThe performance of wireless networks will experience a considerable improvement by the use of novel technologies such as distributed antenna systems (DASs), multi-cell cooperation (MCC), and cognitive radio (CR). These solutions have shown considerable gains at the physical-layer (PHY). However, several issues remain open in the system-level evaluation, radio resource management (RRM), and particularly in the design of billing/licensing schemes for this type of system. This paper proposes a system-level simulator (SLS) that will help in addressing these issues. The paper focuses on the description of the modules of a generic SLS that need a modification to cope with the new transmission/economic paradigms. An advanced RRM solution is proposed for a multi-cell DAS with two levels of cooperation: inside the cell (intra-cell) to coordinate the transmission of distributed nodes within the cell, and between cells (inter-cell or MCC) to adapt cell transmissions according to the collected inter-cell interference measurements. The RRM solution blends network and financial metrics using the theory of multiobjective portfolio optimization. The core of the RRM solution is an iterative weighted least squares (WLS) optimization algorithm that aims to schedule in a fair manner as many terminals as possible across all the radio resources of the available frequency bands (licensed and non-licensed), while considering different economic metrics. The RRM algorithm includes joint terminal scheduling, link adaptation, space division multiplexing, spectrum selection, and resource allocation.
- Trade-Off Performance Regions of Slotted ALOHA Protocol using Multi-Objective OptimizationPublication . Robles, Ramiro Sámano; Gameiro, AtilioThis paper revisits the study of the Slotted ALOHA protocol with J = 2 terminals. Unlike previous approaches, this work employs multi-objective optimization tools. The work is focused on the characterization of the boundary (envelope) or Pareto optimal front curve of different types of trade-off region: the conventional throughput region, sum-throughput vs. fairness, and sum-throughput vs. transmit power. When possible, parametric and non-parametric expressions of these envelopes are here provided. Fairness is evaluated by means of the Gini-index, which is a metric used in economics to measure income inequality. Transmit power is directly linked to the global transmission rate. The approach presented in this paper generalizes previous works and provides more insights into the operation of random access protocols.