A Random Access Protocol incorporating Multi-Packet Reception, Retransmission Diversity and Successive Interference Cancellation

8th International Workshop on Multiple Access Communications (MACOM2015), Helsinki, Finland.This 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

Throughput, stability and fairness of carrier-sense multiple access with cooperative diversity

Cooperative diversity has been identified as a potential candidate for boosting the physical (PHY) layer performance of future wireless networks. However, several issues remain open today in the design of an appropriate medium access control (MAC) layer for this type of system. This paper attempts to partially fill this gap by addressing the MAC-PHY cross-layer design of a class of carrier-sense multiple access protocols where collision-free transmissions are assisted by the potential cooperative retransmission of the remaining silent terminals in the network. Unlike previous works, the analysis is focused on full asymmetrical settings, where terminals experience different channel and queuing statistics. To achieve this goal, a packet reception model is here proposed for cooperative schemes where the relaying phase is activated only when the reception of previous (re)transmissions has failed. Closed-form expressions of correct reception probability are derived for Rayleigh fading channels assuming that correct reception occurs only when the instantaneous signal-to-noise ratio (SNR) exceeds a reception threshold. This reception model allows for a MAC-layer design aware of PHY-layer information, and vice versa, PHY-layer enhancement and activation using MAC-layer information. The boundary of the throughput region (i.e., the set of all achievable throughput values) is derived in a parametric closed-form expression using a multi-objective optimization approach. A method for deriving a non-parametric form was further proposed, which allows for a geometric interpretation of the two-user case. Stability features such as backlog user distribution and backlog delay are evaluated by using a novel Markov model for asymmetrical systems. Fairness is evaluated by means of the Gini index, which is a metric commonly used in the field of economics to measure income inequality. The protocol is shown to outperform its non-cooperative counterparts under diverse network conditions that are here discussed

Trade-Off Performance Regions of Slotted ALOHA Protocol using Multi-Objective Optimization

10th Conference on Telecommunications (Conftele 2015), Aveiro, Portugal.This 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

System Level Simulation and Radio Resource Management for Distributed Antenna Systems with Cognitive Radio and Multi-Cell Cooperation

4th International Conference on Future Generation Communication Technologies (FGCT 2015), Luton, United Kingdom.The 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

An RFID Anti-Collision Algorithm Assisted by Multi-Packet Reception and Retransmission Diversity

RFID provides a way to connect the real world to the virtual world. An RFID tag can link a physical entity like a location, an object, a plant, an animal, or a human being to its avatar which belongs to a global information system. For instance, let's consider the case of an RFID tag attached to a tree. The tree is the physical entity. Its avatar can contain the type of the tree, the size of its trunk, and the list of actions a gardener took on it

Stability and Delay of NDMA-MPR Protocol in Rice-Correlated Channels with Co-Channel Interference

This paper investigates backlog retransmission strategies for a class of random access protocols with retransmission diversity (i.e., network diversity multiple access or NDMA) combined with multiple-antenna-based multi-packet reception (MPR). This paper proposes NDMA-MPR as a candidate for 5G contention-based and ultra-low latency multiple access. This proposal is based on the following known features of NDMA-MPR: (1) near collision-free performance, (2) very low latency values, and (3) reduced feedback complexity (binary feedback). These features match the machine-type traffic, real-time, and dense object connectivity requirements in 5G. This work is an extension of previous works using a multiple antenna receiver with correlated Rice channels and co-channel interference modelled as a Rayleigh fading variable. Two backlog retransmission strategies are implemented: persistent and randomized. Boundaries and extended analysis of the system are here obtained for different network and channel conditions. Average delay is evaluated using the M/G/1 queue model with statistically independent vacations. The results suggest that NDMA-MPR can achieve very low values of latency that can guarantee real- or near-real-time performance for multiple access in 5G, even in scenarios with high correlation and moderate co-channel interference

A Space-Time Correlation Model for MRC Receivers in Rayleigh Fading Channels

This paper presents a statistical model for maximum ratio combining (MRC) receivers in Rayleigh fading channels enabled with a temporal combining process. This means that the receiver effectively combines spatial and temporal branch components. Therefore, the signals that will be processed by the MRC receiver are collected not only across different antennas (space), but also at different instants of time. This suggests the use of a retransmission, repetition or space-time coding algorithm that forces the receiver to store signals in memory at different instants of time. Eventually, these stored signals are combined after a predefined or dynamically optimized number of time-slots or retransmissions. The model includes temporal correlation features in addition to the space correlation between the signals of the different components or branches of the MRC receiver. The derivation uses a frequency domain approach (using the characteristic function of the random variables) to obtain closed-form expressions of the statistics of the post-processing signal-to-noise ratio (SNR) under the assumption of equivalent correlation in time and equivalent correlation in space. The described methodology paves the way for the reformulation of other statistical functions as a frequency-domain polynomial root analysis problem. This is opposed to the infinite series approach that is used in the conventional methodology using directly the probability density function (PDF). The results suggest that temporal diversity is a good complement to receivers with limited spatial diversity capabilities. It is also shown that this additional operation could be maximized when the temporal diversity is adaptive (i.e., activated by thresholds of SNR), thus leading to a better resource utilization

MAC-PHY Cross-layer design for Secure Wireless Avionics Intra-Communications

This paper presents a framework for medium access control (MAC) and physical (PRY) cross-layer security design of wireless avionics intra-communications (WAICs). The paper explores the different options based on the latest results of MAC-PRY cross-layer design and the available standard technologies for WAICs. Particular emphasis is given to solutions based on multiple-input multiple-output (MIMO) systems and recent developments towards a wireless technology with ultra-low latency and high reliability in the context of 5G and machine-type traffic support. One major objective is to improve WAICs technology and thus match the real-time, reliability and safety critical performance of the internal aeronautics bus technologies (e.g., ARINC 664). The main identified vulnerabilities and potential solutions are explored, as well as their impact on system design complexity and feasibility for wireless networks on-board aircraft. The solutions are presented in the context of the European project SCOTT (secure connected trustable things) using the recently released reference architecture for trusted IoT systems. Other aspects of SCOTT such as trust, privacy, security classes, and safety are also discussed here for the aeronautics domain.info:eu-repo/semantics/publishedVersio

Network and Economic Trade-Off Performance Regions of Cognitive Radio Systems with Power Control

Abstract: Cognitive radio will enable terminals with access to licensed and unlicensed portions of the spectrum. This feature is expected to solve bandwidth scarcity problems in future wireless networks. However, different parts of the spectrum will be subject not only to different propagation conditions, but also to different licensing and billing agreements. Therefore, in order to obtain the major profit and spectrum efficiency, resource allocation algorithms must now target both network and economic performance metrics. This problem can be conveniently expressed as a multi-objective portfolio optimization problem, which has been studied in detail in the field of economics. This paper addresses the study of network and economic Pareto optimal trade-off performance regions of cognitive radio systems under average transmit power control policies. Each packet transmission in primary and secondary mode is regarded as a financial asset whose average transmit power is optimized so as to simultaneously maximize return and minimize risk, where risk is the variance of the return. This paper studies three types of Pareto optimal trade-off regions: primary vs. secondary throughput, return vs. risk, and sum-throughput vs. fairness, where fairness is evaluated by means of the Gini index. The boundaries of these trade-off regions are derived in parametric closed-form expressions. A power control policy is further proposed that maximizes return while simultaneously controlling risk and ensuring a level of quality of service for primary and secondary users. This means that operators can maximize revenue and network efficiency, while simultaneously minimizing risk and also ensuring fairness between primary and secondary users

Performance Model for MRC Receivers with Adaptive Modulation and Coding in Rayleigh Fading Correlated Channels with Imperfect CSIT Performance Model for MRC Receivers with Adaptive Modulation and Coding in Rayleigh Fading Correlated Channels with Imperfec

Abstract This paper presents a performance model of the packet reception process in a wireless link with one antenna transmitter and a multiple-antenna maximum-ratio combining (MRC) receiver. The objective is to address the performance evaluation of multiple antenna systems enabled with adaptive modulation and coding (AMC). Two main assumptions are used: 1) Rayleigh fading correlated channels, and 2) imperfect (outdated) channel state information at the transmitter side (CSIT). The results presented here suggest that spatial correlation not always affects the performance of the MRC receiver: at low signal-to-noise ratio (SNR), correlation can improve performance rather than degrading it. By contrast, at high SNR, correlation is found to always degrade performance. At high SNR, correlation tends to worse the degrading effects of imperfect CSIT, particularly when the number of antennas increases. Imperfect CSIT causes errors in the assignment of MCSs, thus reducing throughput performance. These errors become more evident at high SNR, particularly when the values of branch correlation and the number of antennas increase. Abstract-This paper presents a performance model of the reception process in a wireless link with one antenna transmitter and a multiple-antenna maximum-ratio combining (MRC) receiver. The objective is to address the performance evaluation of multiple antenna systems enabled with adaptive modulation and coding (AMC). Two main assumptions are used: 1) Rayleigh fading correlated channels, and 2) imperfect (outdated) channel state information at the transmitter side (CSIT). The results presented here suggest that spatial correlation not always affects the performance of the MRC receiver: at low signal-to-noise ratio (SNR), correlation can improve performance rather than degrading it. By contrast, at high SNR, correlation is found to always degrade performance. At high SNR, correlation tends to worse the degrading effects of imperfect CSIT, particularly when the number of antennas increases. Imperfect CSIT causes errors in the assignment of modulation and coding schemes (MCSs), thus reducing throughput performance. These errors become more evident at high SNR, particularly when the values of branch correlation and the number of antennas increase