Danyo Danev

Complete Characterization of the Pareto Boundary for the MISO Interference Channel

In this correspondence, we study the achievable rate region of the multiple-input single-output (MISO) interference channel, under the assumption that all receivers treat the interference as additive Gaussian noise. Our main result is an explicit parametrization of the Pareto boundary for an arbitrary number of users and antennas. The parametrization describes the boundary in terms of a low-dimensional manifold. For the two-user case we show that a single real-valued parameter per user is sufficient to achieve all points on the Pareto boundary and that any point on the Pareto boundary corresponds to beamforming vectors that are linear combinations of the zero-forcing (ZF) and maximum-ratio transmission (MRT) beamformers. We further specialize the results to the MISO broadcast channel (BC). A numerical example illustrates the result.

Spectrum sensing methods for detection of DVB-T signals in AWGN and fading channels

In this paper, we consider spectrum sensing of DVB-T signals in different fading environments. We compare state-of-the-art detectors including detectors based on pilot subcarriers, as well as detectors for general OFDM signals that exploit the correlation structure incurred by the cyclic prefix. Energy detection is also included for comparison. We show numerically that the choice of detector depends on the scenario, the detector requirements, and on the available prior knowledge. We also show that it is possible to obtain good detection performance by exploiting the correlation, even in a frequency selective channel.

Upper bounds on the minimum distance of spherical codes

We use linear programming techniques to obtain new upper bounds on the maximal squared minimum distance of spherical codes with fixed cardinality. Functions Q/sub j/(n,s) are introduced with the property that Q/sub j/(n,s) m if and only if the Levenshtein bound L/sub m/(n,s) on A(n,s)=max{|W|:W is an (n,|W|,s) code} can be improved by a polynomial of degree at least m+1. General conditions on the existence of new bounds are presented. We prove that for fixed dimension n/spl ges/5 there exists a constant k=k(n) such that all Levenshtein bounds L/sub m/(n, s) for m/spl ges/2k-1 can be improved. An algorithm for obtaining new bounds is proposed and discussed.

Accuracy Comparison of LS and Squared-Range LS for Source Localization

In this correspondence, we compute a closed-form expression for the asymptotic (large-sample) accuracy of the recently proposed squared-range least-squares (SR-LS) method for source localization [A. Beck, P. Stoica, and J. Li, ¿Exact and approximate solutions of source localization problems,¿ IEEE Trans. Signal Process., vol. 56, no. 5, pp. 1770-1778, May 2008]. We compare its accuracy to that of the classical least-squares (LS) method and show that LS and SR-LS perform differently in general. We identify geometries where the performances of the methods are identical but also geometries when the difference in performance is unbounded.

Asymptotically optimal transmit strategies for the multiple antenna interference channel

We consider the interference channel with multiple antennas at the transmitter. We prove that at high signal-to-noise ratio (SNR), the zero-forcing transmit scheme is optimal in the sum-rate sense. Furthermore we prove that at low SNR, maximum-ratio transmission is optimal in the sum-rate sense. We also provide a discussion of the connection to classical results on spectral efficiency in the wideband regime. Finally, we propose a non-convex optimization approach based on monotonic optimization to solve the sum rate maximization problem.

On signal detection techniques for the DVB-T standard

In this paper we discuss some spectrum sensing techniques for detection of DVB-T signals. Their performance is compared in terms of probability of detection and ROC curves. Some simulation results are presented for various scenarios.

Necessary Conditions for Existence of Some Designs in Polynomial Metric Spaces

In this paper we consider designs in polynomial metric spaces with relatively small cardinalities (near to the classical bounds). We obtain restrictions on the distributions of the inner products of points of such designs. These conditions turn out to be strong enough to ensure obtaining nonexistence results already for the first open cases.

Power allocation for OFDM-based cognitive heterogeneous networks

In this paper, the capacity maximization and the spectrum utilization efficiency improvement are investigated for the Pico cells in broadband heterogeneous networks. In frequency-reuse model, the users attached to Macro base station are usually viewed as primary users, and those attached to Pico base station should be regarded as cognitive radio (CR) users. As both the primary users and the CR users communicate in parallel frequency bands, the performance of the system is limited by the mutual inter-carrier interference (ICI). In order to control ICI and maximize the achievable transmission rate of the CR users, an effective power allocation scheme is proposed to maximize the transmission rate of the CR users under a given interference threshold prescribed by the primary users. By transforming this suboptimal solution into an innovative matrix expression, the algorithm is easier to perform in practice. The simulation results demonstrate that the proposed algorithm provides a large performance gain in Pico cell capacity over the non-cooperative and equal power allocation schemes.

Statistically robust resource allocation for distributed multi-carrier cooperative networks

In this paper, we investigate joint subcarrier and power allocation scheme for distributed multicarrier cooperative networks with imperfect channel state information. Using practical channel estimation algorithms, the statistic model of the channel estimation error is first derived. Then based on the channel error model, the resource allocation scheme aims at maximizing the sum rate of the overall network. Specifically, both subcarrier allocation and power allocation are taken into account. In the subcarrier allocation, a realistic problem of the power leakage between neighboring subcarriers is also addressed. Furthermore, based on Lagrange dual-decomposition algorithm, a practical power allocation algorithm is proposed. Finally, the simulation results demonstrate the performance advantages of the proposed robust design.

Subframe allocation for relay networks in the LTE advanced standard

The use of relays is a promising way to extend coverage and increase rates in Long Term Evolution Advanced (LTE Advanced) networks. Performing a transmission in several hops (BS-relay & relay-user) requires more radio resources than a single hop transmission. This paper analyses how the available radio resource should be allocated between relays and users in order to maximize throughput and/or fairness. Time and frequency multiplexed backhaul is investigated under some basic assumptions on the division of the radio resource. It is shown that the system will typically be backhaul limited and that the two ways of multiplexing will perform equally when fairness is taken into account. The analysis results in throughput/fairness suboptimal solutions, dependant on the number of relays per cell, spectral efficiencies and fraction of users served by relays. The analysis is verified by simulations, performed using a MATLA-Bbased network simulator.