| 1. |
- Chatzinotas, Symeon, et al.
(författare)
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Joint Precoding with Flexible Power Constraints in Multibeam Satellite Systems
- 2011
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Ingår i: Proceedings Global Communications Conference (GLOBECOM). - 9781424492688
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Konferensbidrag (refereegranskat)abstract
- In conventional multibeam satellite systems, frequencyand polarization orthogonalization have been traditionallyemployed for mitigating interbeam interference. However, theparadigm of multibeam joint precoding allows for full frequencyreuse while assisting beam-edge users. In this paper, the performanceof linear beamforming is investigated in terms of meetingtraffic demands. More importantly, generic linear constraints areconsidered over the transmit covariance matrix in order to modelthe power pooling effect which can be implemented throughflexible traveling wave tube amplifiers (TWTAS) or multiportamplifiers. The performance of this scheme is compared againstconventional spotbeam systems based on the rate-balancingobjective. In this context, it is shown that significantly higherspectral efficiency can be achieved through beamforming, whileflexible power constraint offers better rate-balancing.
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| 2. |
- Haghighi, Kasra, 1978, et al.
(författare)
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An LLR-based Cognitive Transmission Strategy for Higher Spectrum Reutilization
- 2011
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Ingår i: IEEE GLOBECOM 2011 - Cognitive Radio and Networks Symposium. - 9781424492688
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Konferensbidrag (refereegranskat)abstract
- Reutilization of the spectrum licensed to services with low occupancy is of great interest for cognitive radios (CRs). To achieve this goal, we introduce a simple hidden Markov model which captures the primary users activity, signal uncertainties, and noise. For evaluating the performance of any CR, two new criteria are presented entitled spectrum utilization ratio (UR) and interference ratio (IR). Based on this model and new measures, a new a-posterior log-likelihood-ratio based CR is designed and implemented. Its performance is compared with standard energy-detection based spectrum-sensing CR. We demonstrate more than 300% increase in UR for up to 1% allowed interference at the SNR of -5dB.
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| 3. |
- Hussain, Iqbal, et al.
(författare)
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Error floor Analysis of LT Codes over the Additive White Gaussian Noise Channel
- 2011
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Ingår i: 2011 IEEE GLOBAL TELECOMMUNICATIONS CONFERENCE (GLOBECOM 2011)<em> </em>. - : IEEE. - 9781424492688 ; , s. 6133650-
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Konferensbidrag (refereegranskat)abstract
- We investigate the error floor performance of Luby Transform (LT) codes over the additive white Gaussian noise channel. We first derive a lower bound on the bit error rate for an LT code, which we subsequently use to show that the corresponding error floor is predominantly caused by low-degree variable nodes. Based on this observation, we propose a modified encoding scheme for LT codes that provides a lower error floor with no increase in encoding and decoding complexities. The convergence behavior of the proposed scheme is analyzed using extrinsic information transfer charts, and shown to be similar to the original LT code. Numerical examples demonstrate the improvements of the modified LT code as a stand-alone code and as a component code of a Raptor code.
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| 4. |
- Karout, Johnny, 1985, et al.
(författare)
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Designing Power-Efficient Modulation Formats for Noncoherent Optical Systems
- 2011
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Ingår i: GLOBECOM - IEEE Global Telecommunications Conference. - 9781424492688
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Konferensbidrag (refereegranskat)abstract
- We optimize modulation formats for the additive white Gaussian noise channel with a nonnegative input constraint, also known as the intensity-modulated direct detection channel, with and without confining them to a lattice structure. Our optimization criteria are the average electrical and optical power. The nonnegativity input signal constraint is translated into a conical constraint in signal space, and modulation formats are designed by sphere packing inside this cone. Some remarkably dense packings are found, which yield more power-efficient modulation formats than previously known. For example, at a spectral efficiency of 1 bit/s/Hz, the obtained modulation format offers a 0.86 dB average electrical power gain and 0.43 dB average optical power gain over the previously best known modulation formats to achieve a symbol error rate of 10^-6. This modulation turns out to have a lattice-based structure. At a spectral efficiency of 3/2 bits/s/Hz and to achieve a symbol error rate of 10^-6, the modulation format obtained for optimizing the average electrical power offers a 0.58 dB average electrical power gain over the best lattice-based modulation and 2.55 dB gain over the best previously known format. However, the modulation format optimized for average optical power offers a 0.46 dB average optical power gain over the best lattice-based modulation and 1.35 dB gain over the best previously known format.
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| 5. |
- Matthaiou, Michail, 1981, et al.
(författare)
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Two Novel Upper Bounds on the Sum Rate of MIMO ZF Receivers
- 2011
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Ingår i: 54th Annual IEEE Global Telecommunications Conference (GLOBECOM), Houston, DEC 05-09, 2011. - 1930-529X. - 9781424492688
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Konferensbidrag (refereegranskat)abstract
- In this paper, we introduce two novel upper bounds on the achievable sum rate of multiple-input multiple-output (MIMO) systems with Zero-Forcing (ZF) receivers. The presented bounds are given in tractable closed-form and apply for different fading models, like uncorrelated/doubly correlated Rayleigh fading and Ricean fading. In addition, the first bound establishes an interesting relationship between the sum rate and the first negative moment of the unordered eigenvalue of the instantaneous correlation matrix. Based on our analytical expressions, we are able to explore the impact of the model parameters, such as number of antennas, spatial correlation and Ricean-K factor, on the sum rate of MIMO ZF receivers.
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| 6. |
- Mehrpouyan, Hani, 1981, et al.
(författare)
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A New Distributed Approach for Achieving Clock Synchronization in Heterogeneous Networks
- 2011
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Ingår i: IEEE Globecom 2011. - 1930-529X. - 9781424492688 ; , s. 5-
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Konferensbidrag (refereegranskat)abstract
- Heterogeneous networks have the potential to improve coverage, throughput, and energy efficiency of wireless networks through the use of specialized cellular structures, in particular femtocells and macrocells. However, to reduce interference between different cells, ensure smooth hand-offs from cell to cell, and achieve seamless operation the overall network needs to be synchronized. In this paper a new distributed clock synchronization scheme for heterogeneous networks is proposed that employs the clock drift information available at user-equipments (UEs) to achieve synchronization between non-interacting femtocells and macrocells. Simulation results show that the proposed scheme can significantly reduce the clock drift between macrocells and femtocells and result in timing synchronization throughout the network without introducing significant overhead.
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| 7. |
- Möller, Anders, et al.
(författare)
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Congestion-based Rate and Power Control in Wireless Cellular Networks
- 2011
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Ingår i: 2011 IEEE GLOBAL TELECOMMUNICATIONS CONFERENCE (GLOBECOM 2011). - New York : IEEE. - 9781424492688 ; , s. 6133508-
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Konferensbidrag (refereegranskat)abstract
- In a cellular network it is necessary to make a trade-off between congestion and Quality of Service (QoS) of the users. To ensure good system performance in uplink of a WCDMA network, control loops are used to adapt to changing radio and interference conditions. A fast inner power control loop updates the transmission powers of the mobiles based on measurements related to QoS, which are compared to a reference value. The reference value is set dynamically by a slower outer rate control loop that uses measurements of congestion. There is a time-scale difference between the loops, but joint dynamics cannot be neglected. In this paper we derive a high order system model with distributed feedback control based on locally measurable information. We model the time-scale difference between the loops and include this in the model. We give sufficient conditions for stability using control theoretic methods and validate the model and results by simulations.
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| 8. |
- Schwandter, S., et al.
(författare)
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Error probability bounds for decode-and-forward relaying with two correlated sources
- 2011
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Ingår i: GLOBECOM - IEEE Global Telecommunications Conference. - 9781424492688 ; , s. 1-5
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Konferensbidrag (refereegranskat)abstract
- We derive bounds on the error probability of optimal and sub- optimal detectors in an uncoded decode-and-forward relay system with two correlated information sources. This setup is relevant to wireless sensor networks where nearby sensors collect spatially correlated data. We show that taking into account the source correlation at the relay and at the destination leads to significant performance gains. Simulation results corroborate the tightness of our analytical bounds.
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| 9. |
- Sottile, F., et al.
(författare)
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Hybrid GNSS-terrestrial cooperative positioning based on particle filter
- 2011
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Ingår i: GLOBECOM - IEEE Global Telecommunications Conference. - 9781424492688 ; , s. 1-5
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Konferensbidrag (refereegranskat)abstract
- We propose a novel hybrid GNSS-terrestrial localization algorithm based on particle filter that fuses ranging data from both satellites and terrestrial receivers. The proposed positioning approach, named hybrid-cooperative particle filter (HCPF), is fully distributed and allows both increased positioning availability and accuracy compared to GNSS-only localization in challenged scenarios. Moreover, simulation results based on a realistic indoor scenario show that the proposed solution outperforms several state of the art algorithms such as unscented Kalman filter and an approach based on belief propagation.
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| 10. |
- Tavan, M., et al.
(författare)
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Strictly Bandlimited ISI-Free Transmission Over Intensity-Modulated Channels
- 2011
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Ingår i: GLOBECOM - IEEE Global Telecommunications Conference. - 9781424492688
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Konferensbidrag (refereegranskat)abstract
- In this paper, the design and analysis of a new bandwidth-efficient signalling method over the bandlimited intensity-modulated direct-detection (IM/DD) channel is pro- posed. The channel can be modeled as a bandlimited channel with nonnegative input and additive white Gaussian noise. Due to the nonnegativity constraint, the methods previously proposed for conventional bandlimited channels cannot be applied here. We propose a method to transmit without intersymbol interference in a narrower bandwidth compared to previous works, by combining Nyquist pulses with a constant bias. In fact, we can transmit with a bandwidth equal to that of coherent transmission. A trade-off between the required average optical power and the bandwidth is investigated. At low bandwidths, the most power- efficient transmission is obtained by either the parametric linear pulse or the so-called “better than Nyquist” pulse, depending on the exact bandwidth.
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