On Girth Conditioning for Low-Density Parity-Check Codes

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Techniques for radio network optimization

none1Packet-switching communication is gaining an ever increasing relevance for wireless networks. On one hand, releasing radio resources to single communication units, i.e. the packets, is much more efficient than releasing resources to entire connection; on the other hand, IP is becoming the predominant technology in the backbone network for integration and transport of heterogeneous multimedia and data traffic. Two important radio resource optimization problem have to be considered, within this framework, for the design of MAC and RRM functionalities in a wireless packet network. The first problem is to look for the best way (as a tradeoff between capacity and complexity) to dynamically assign radio resources to a set of users having packets to transmit. The second problem is to look for the best way (as a tradeoff among capacity, user satisfaction, fairness and complexity) to schedule packet transmission in time over the available radio resources for a set of users with one or more packet traffic sources with possible QoS constraint.noneV. TRALLITralli, Veli

Distortion-Fair Cross-Layer Resource Allocation for Scalable Video Transmission in OFDMA Wireless Networks

The design of optimized video delivery to multiple users over a wireless channel is a challenging task, especially when the objectives of maximizing the spectral efficiency and providing a fair video quality have to be jointly considered. In this paper we propose a novel cross-layer optimization framework for scalable video delivery over OFDMA wireless networks. It jointly addresses rate adaptation and resource allocation with the aim of maximizing the sum of the achievable rates while minimizing the distortion difference among multiple videos. After having discussed the feasibility of the optimization problem, we consider a 'vertical' decomposition of it and propose the iterative local approximation (ILA) algorithm to derive the optimal solution. The ILA algorithm requires a limited information exchange between the application and the MAC layers, which independently run algorithms that handle parameters and constraints characteristic of a single layer. In order to reduce the overall complexity and the latency of the optimal algorithm, we also propose suboptimal strategies based on the first-step of the ILA algorithm and on the use of stochastic approximations at the MAC layer. Our numerical evaluations show the fast convergence of the ILA algorithm and the resulting small gap in terms of efficiency and video quality fairness between optimal and suboptimal strategies. Moreover, significant individual PSNR gains, up to 7 dB for high-complexity videos in the investigated scenario, are obtained with respect to other state-of-the-art frameworks with similar complexity

IRSA-based Unsourced Random Access over the Gaussian Channel

A framework for the analysis of synchronous grant-free massive multiple access schemes based on the irregular repetition slotted ALOHA (IRSA) protocol and operating over the Gaussian multiple access channel is presented. IRSA-based schemes are considered here as an instance of the class of unsourced slotted random access codes, operating over a frame partitioned in time slots, and are obtained by concatenation of a medium access control layer code over the entire frame and a physical layer code over each slot. In this framework, an asymptotic analysis is carried out in presence of both collisions and slot decoding errors due to channel noise, which allows the derivation of density-evolution equations, asymptotic limits for minimum packet loss probability and average load threshold, and a converse bound for threshold values. This analysis is exploited as a tool for the evaluation of performance limits in terms of minimum signal-to-noise ratio required to achieve a given packet loss probability, and also provides convergence boundary limits that hold for any IRSA scheme with given physical layer coding scheme. The tradeoff between energy efficiency and spectrum efficiency is numerically evaluated comparing some known coding options, including those achieving random coding bounds at slot level. It is shown that IRSA-based schemes have a convergence boundary limit within few dB from the random coding bound when the number of active transmitters is sufficiently large

Performance Characterization of Digital Transmission Systems with Cochannel Interference

none2This paper presents a general methodology for performance characterization of digital transmission systems in the presence of cochannel interference, as a function of the actual number of interferers (ranging from zero to infinity). The bit error probability in time-invariant channels and outage probability in time-varying quasi-stationary channels are discussed. More precisely, a general approach to an outage probability definition based on the concept of the outage domain is introduced. This allows the discussion of the relation to the other definitions which have appeared in the literature and the proposal of some new more accurate methods for the evaluation of outage probability. A suitable comparison between exact evaluation, the well-known Gaussian approximation, and the other new approaches proposed in this paper, is carried out to evaluate performance, bit error probability is suitably obtained for linearly modulated signals by adopting a semianalytical approach, and for nonlinear (e.g., continuous phase) modulation signals, by means of simulation. Finally, as an example, the different approaches to derive performance discussed in the paper have been applied to a linear microcellular scenariononeTRALLI V.; VERDONE R.Tralli, Velio; Verdone, R

Fair resource allocation with QoS support for the uplink of LTE systems

Resource allocators that maximize ergodic sum-rate under proportional rate constraints have been recently introduced and analysed for both OFDMA and SC-FDMA wireless systems. They are able to provide long-term fairness by assigning to users, on average, a predefined share of the available system capacity. However, the short-term fairness of these schedulers with its effect on the delays, and their efficiency in presence of bursty traffic may be open issues for a possible application in 4G wireless networks. In this paper we address these issues by proposing some solutions that make such resource allocators able to support both GBR and best effort traffic. We consider the uplink of a LTE single cell scenario with some realistic conditions (e.g., discrete rate assignment, power control) and evaluate the performance of the proposed solutions in presence of heterogeneous traffic by using QoS-aware proportional fairness based schedulers as benchmark. The results show that the proposed resource allocator is able to achieve an high number of satisfied GBR users with a significant reduction of the packet delay without starving non-GBR users

MIMO systems outage capacity based on minors moments of Wishart matrices

Complex Wishart matrices represent a class of random matrices exploited in a number of wireless communication problems. This paper analyzes the first and second order statistical moments of complex Wishart matrices' minors. This enables to derive new closed-form approximations for the outage capacity of multiple input multiple output (MIMO) systems operating in Rayleigh fading channels at any signal-to-noise ratio (SNR) regime and with any number of inputs and outputs. The derived expressions are compared with bounds known in the literature as well as with simulations. Results show the tightness of the proposed approximations to simulations for a broad range of MIMO settings

Joint admission control and resource allocation for D2D communications with QoS constraints

The use of Device-to-Device (D2D) communications underlaying a cellular network is an efficient way to improve cell capacity and resource utilization. When the D2D links are allowed to share the same physical resources with traditional cellular links, efficient admission control (AC) and radio resource allocation (RRA) strategies play a key-role to control the co-channel interference and to provide QoS support. In this paper, we propose a novel joint AC and RRA strategy that provides QoS support in the long-term to cellular and D2D communications. The AC algorithm derives the best set of cellular and D2D links in order to maximize the total revenue under QoS and resource constraints. Then, given the set of admitted links, the low-complexity short-term RRA maximizes the average weighted sum-rate under QoS constraints. Numerical results show that the proposed strategy increases the number of satisfied communication links up to 50 %, compared to other state-of-the- art frameworks

Bit error and outage probability for digital cellular systems with a small number of interferers

This paper proposes a semi-analytical approach to characterise the performance of digital cellular systems when cochannel interference is determined by a small number of interferers. Linearly modulated signals (such as BPSK, QPSK, M-ASK, M-QAM, MSK, O-QPSK, etc.) with linear receivers are investigated by considering the probability density function of the interference at the input of the decision device. Non-linear (Continuous Phase) modulation signals (such as GMSK) and non coherent detection are also investigated by means of simulation. As a consequence, a general approach to outage probability definition considering the protection ratio as a function of the interferers number and useful signal-to-noise ratio is introduced