| 1. |
- Agrell, Erik, 1965, et al.
(författare)
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Gray coding for multilevel constellations in Gaussian noise
- 2007
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Ingår i: IEEE Transactions on Information Theory. - 0018-9448 .- 1557-9654. ; 53:1, s. 224-235
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Tidskriftsartikel (refereegranskat)abstract
- The problem of finding the optimal labeling (bit-to-symbol mapping) of multilevel coherent phase shift keying (PSK), pulse amplitude modulation (PAM), and quadrature amplitude modulation (QAM) constellations with respect to minimizing the bit-error probability (BEP) over a Gaussian channel is addressed. We show that using the binary reflected Gray code (BRGC) to label the signal constellation results in the lowest possible BEP for high enough signal energy-to-noise ratios and analyze what is "high enough"in this sense. It turns out that the BRGC is optimal for PSK and PAM systems whenever the target BEP is at most a few percent, which covers most systems of practical interest. New and simple closed-form expressions are presented for the BEP of PSK, PAM, and QAM using the BRGC. © 2007 IEEE.
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| 2. |
- Agrell, Erik, 1965, et al.
(författare)
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On the optimality of the binary reflected Gray code
- 2004
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Ingår i: IEEE Transactions on Information Theory. - 0018-9448 .- 1557-9654. ; 50:12, s. 3170-3182
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Tidskriftsartikel (refereegranskat)abstract
- This paper concerns the problem of selecting a binary labeling for the signal constellation in M-PSK, M-PAM, and M-QAM communication systems. Gray labelings are discussed and the original work by Frank Gray is analyzed. As is noted, the number of distinct Gray labelings that result in different bit-error probability grows rapidly with increasing constellation size. By introducing a recursive Gray labeling construction method called expansion, the paper answers the natural question of what labeling, among all possible constellation labelings, will give the lowest possible average probability of bit errors for the considered constellations. Under certain assumptions on the channel, the answer is that the labeling proposed by Gray, the binary reflected Gray code, is the optimal labeling for all three constellations, which has, surprisingly, never been proved before.
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| 3. |
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| 4. |
- Agrell, Erik, 1965, et al.
(författare)
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The binary reflected Gray code is optimal for M-PSK
- 2004
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Ingår i: Proc. IEEE International Symposium on Information Theory, Chicago, Illinois, USA. - 0780382803 ; , s. 164-
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Konferensbidrag (refereegranskat)abstract
- This paper is concerned with the problem of selecting a binary labeling for the signal constellation in an M-PSK communication system. A good starting point is labelings having the Gray property, but this is not altogether enough, since the number of distinct Gray labelings that result in different bit error probability grows rapidly with increasing constellation size. By introducing a recursive Gray labeling construction method called expansion, the paper answers the natural question of what labeling, among all possible constellation labelings (not only Gray), that will give the lowest possible average probability of bit errors. Under certain assumptions on the channel, the answer is that the labeling originally proposed by Gray, the binary reflected Gray code, is the optimal labeling for M-PSK systems, which has, surprisingly, never been proved before.
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| 5. |
- 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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| 6. |
- Haghighi, Kasra, 1978, et al.
(författare)
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On Optimum Causal Cognitive Spectrum Reutilization Strategy
- 2012
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Ingår i: IEEE Journal on Selected Areas in Communications. - 0733-8716 .- 1558-0008. ; 30:10, s. 1911-1921
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we study opportunistic transmission strategies for cognitive radios (CR) in which causal noisy observation from a primary user(s) (PU) state is available. PU is assumed to be operating in a slotted manner, according to a two-state Markov model. The objective is to maximize utilization ratio (UR), i.e., relative number of the PU-idle slots that are used by CR, subject to interference ratio (IR), i.e., relative number of the PU-active slots that are used by CR, below a certain level. We introduce an a-posteriori LLR-based cognitive transmission strategy and show that this strategy is optimum in the sense of maximizing UR given a certain maximum allowed IR. Two methods for calculating threshold for this strategy in practical situations are presented. One of them performs well in higher SNRs but might have too large IR at low SNRs and low PU activity levels, and the other is proven to never violate the allowed IR at the price of a reduced UR. In addition, an upper-bound for the UR of any CR strategy operating in the presence of Markovian PU is presented. Simulation results have shown a more than 116% improvement in UR at SNR of -3dB and IR level of 10% with PU state estimation. Thus, this opportunistic CR mechanism possesses a high potential in practical scenarios in which there exists no information about true states of PU.
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| 7. |
- Haghighi, Kasra, 1978, et al.
(författare)
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Sensing or Transmission: Causal Cognitive Radio Strategies with Censorship
- 2014
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Ingår i: IEEE Transactions on Wireless Communications. - 1558-2248 .- 1536-1276. ; 13:6, s. 3031-3041
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Tidskriftsartikel (refereegranskat)abstract
- This paper introduces a novel opportunistic transmission strategy for cognitive radios (CRs). The primary user (PU) is assumed to transmit in a time-slotted manner according to a two-state Markov model, and the CR is either sensing, that is, obtaining a causal, noisy observation of a primary user (PU) state, or transmitting, but not both at the same time. In other words, the CR observations of the PU are censored whenever the CR is transmitting. The objective of the CR transmission strategy is to maximize the utilization ratio (UR), i.e., the relative number of the PU-idle slots that are used by the CR, subject to that the interference ratio (IR), i.e., the relative number of the PU-active slots that are used by the CR, is below a certain level. We introduce an a-posteriori LLR-based CR transmission strategy, called CLAPP, and evaluate this strategy in terms of the achievable UR for different PU model parameters and received signal-to-noise ratios (SNRs). The performance of CLAPP is compared with a simple censored energy detection scheme. Simulation results show that CLAPP has 52% gain in UR over the best censored energy detection scheme for a maximum IR level of 10% and an SNR of -2dB. © 2002-2012 IEEE.
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| 8. |
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| 9. |
- Lassing, Johan, 1973, et al.
(författare)
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Computation of the Exact Bit-Error Rate of Coherent M-ary PSK With Gray Code Bit Mapping
- 2003
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Ingår i: IEEE Transactions on Communications. - 0090-6778 .- 1558-0857. ; 51:11, s. 1758-1760
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Tidskriftsartikel (refereegranskat)abstract
- The problem of calculating the average bit-error probability (BEP) of coherent M-ary phase-shift keying (PSK) over a Gaussian channel has been studied previously in the literature. A solution to the problem for systems using a binary reflected Gray code (BRGC) to map bits to symbols was first presented by Lee. In this letter, we show that the results obtained by Lee are incorrect for M greater than or equal to 16. We show that the reason for this is an invalid assumption that the bit-error rate (BER) is independent of the transmitted symbols, an assumption which has also propagated to textbooks. We give a new expression for the BER of M-PSK systems using the BRGC and compare this with Lee's results.
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| 10. |
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| 11. |
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| 12. |
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| 13. |
- Lassing, Johan, 1973, et al.
(författare)
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Unequal Bit-Error Protection in Coherent M-ary PSK
- 2003
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Ingår i: Proceedings IEEE Vehicular Technology Conference Fall, Orlando, Florida, USA. ; 1, s. 251-256
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Konferensbidrag (refereegranskat)abstract
- This paper addresses the problem of evaluating the bit-error probability of the individual bits of a symbol in a communication system using coherent M-ary phase shift keying. Exact expressions are provided, and these are evaluated for seven different mappings from bits to symbols, including five Gray mappings, for a 32-PSK system. It is shown that the highly varying error performance obtained with a common binary reflected Gray mapping can be restored by using a balanced Gray mapping.
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| 14. |
- Esmaily, Mohsen, 1987, et al.
(författare)
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Corrosion behavior of alloy AM50 in semi-solid cast and high pressure die cast states in cyclic conditions
- 2015
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Ingår i: Corrosion. - : Association for Materials Protection and Performance (AMPP). - 0010-9312 .- 1938-159X. ; 71:6, s. 737-748
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Tidskriftsartikel (refereegranskat)abstract
- The atmospheric corrosion behavior of the Mg-Al alloy AM50 produced by high pressure die casting (HPDC) and a semi-solid metal (SSM) technique was studied under alternating wet-dry conditions for up to 672 hours. The alloy AM50 in the SSC state was fabricated using rheocasting (RC) technique in which the slurry was prepared by the newly developed RheoMetal process. To simulate the real-world atmospheric environment, the exposure program included a 6 hour wet phase (including rain with 0.5 % NaCl), a 2.5 hours transition phase followed by a 15.5 hours dry phase at 50°C and 70% relative humidity (RH). The results showed that the RC alloy was substantially less prone to corrosion than the HPDC material in the cyclic wet/dry atmosphere. Based on the gravimetric results and microstructural characterization studies, this was attributed to a lower fraction of porosity and to the barrier role of β phase particles in the RC.
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| 15. |
- Antonakoglou, Konstantinos, et al.
(författare)
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On the needs and requirements arising from connected and automated driving
- 2020
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Ingår i: Journal of Sensor and Actuator Networks. - : MDPI AG. - 2224-2708. ; 9:2
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Tidskriftsartikel (refereegranskat)abstract
- Future 5G systems have set a goal to support mission-critical Vehicle-to-Everything (V2X) communications and they contribute to an important step towards connected and automated driving. To achieve this goal, the communication technologies should be designed based on a solid understanding of the new V2X applications and the related requirements and challenges. In this regard, we provide a description of the main V2X application categories and their representative use cases selected based on an analysis of the future needs of cooperative and automated driving. We also present a methodology on how to derive the network related requirements from the automotive specific requirements. The methodology can be used to analyze the key requirements of both existing and future V2X use cases.
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| 16. |
- Aydin, Osman, et al.
(författare)
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EU FP7 INFSO-ICT-317669 METIS, D4.2 Final report on trade-off investigations
- 2014
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Research activities in METIS WP4 include several aspects related to the network-level of future wireless communication networks. Thereby, a large variety of scenarios is considered and solutions are proposed to serve the needs envisioned for the year 2020 and beyond. This document provides vital findings about several trade-offs that need to be leveraged when designing future network-level solutions. In more detail, it elaborates on the following trade-offs:• Complexity vs. Performance improvement• Centralized vs. Decentralized• Long time-scale vs. Short time-scale• Information Interflow vs. Throughput/Mobility enhancement• Energy Efficiency vs. Network Coverage and CapacityOutlining the advantages and disadvantages in each trade-off, this document serves as a guideline for the application of different network-level solutions in different situations and therefore greatly assists in the design of future communication network architectures.
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| 17. |
- Bencheikh Lehocine, Chouaib, 1993, et al.
(författare)
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Antenna Combiner for Periodic Broadcast V2V Communication Under Relaxed Worst-Case Propagation
- 2023
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Ingår i: IEEE Transactions on Intelligent Transportation Systems. - 1524-9050 .- 1558-0016. ; 24:9, s. 9817-9834
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Tidskriftsartikel (refereegranskat)abstract
- The performance of a previously developed analog combining network (ACN) of phase shifters for periodic broadcast vehicle-to-vehicle (V2V) communication is investigated. The original ACN was designed to maximize the sum of signal-to-noise ratios (SNRs) for $K$ consecutive cooperative awareness messages (CAMs). The design was based on the assumption of a dominant propagation path with an angle of arrival (AOA) that is constant for $K$ messages. In this work, we relax this assumption by allowing the AOA and path-loss (PL) of the dominant path to be time-variant. Assuming a highway scenario with a line of sight (LOS) propagation between vehicles, we use affine approximations to model the time variation of different path quantities, including the PL, the relative distance-dependent phase shift between antennas, and the AOA-dependent far-field function of the antennas. By leveraging these approximations, we analytically derive the ACN sum-SNR as each one of these quantities varies over $K$ CAMs. Moreover, we suggest a design rule for a phase slope that is robust against time variation of the dominant path and optimal under time-invariant conditions. Finally, we validate this design rule using numerical computations and an example of vehicular communication antenna elements.
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| 18. |
- Bencheikh Lehocine, Chouaib, 1993, et al.
(författare)
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Hybrid Combining of Directional Antennas for Periodic Broadcast V2V Communication
- 2022
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Ingår i: IEEE Transactions on Intelligent Transportation Systems. - 1524-9050 .- 1558-0016. ; 23:4, s. 3226-3243
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Tidskriftsartikel (refereegranskat)abstract
- A hybrid analog-digital combiner for broadcast vehicular communication is proposed. It has an analog part that does not require any channel state information or feedback from the receiver, and a digital part that uses maximal ratio combining (MRC). We focus on designing the analog part of the combiner to optimize the received signal strength along all azimuth angles for robust periodic vehicle-to-vehicle (V2V) communication, in a scenario of one dominant component between the communicating vehicles (e.g., highway scenario). We show that the parameters of a previously suggested fully analog combiner solves the optimization problem of the analog part of the proposed hybrid combiner. Assuming L directional antennas with uniform angular separation together with the special case of a two-port receiver, we show that it is optimal to combine groups of ⌈L/2⌉ and ⌊L/2⌋ antennas in analog domain and feed the output of each group to one digital port. This is shown to be optimal under a sufficient condition on the sidelobes level of the directional antennas. Moreover, we derive a performance bound for the hybrid combiner to guide the choice of antennas needed to meet the reliability requirements of the V2V communication links.
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| 19. |
- Bencheikh Lehocine, Chouaib, 1993, et al.
(författare)
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Robust Analog Beamforming for Periodic Broadcast V2V Communication
- 2022
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Ingår i: IEEE Transactions on Intelligent Transportation Systems. - 1524-9050 .- 1558-0016. ; 23:10, s. 18404-18422
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Tidskriftsartikel (refereegranskat)abstract
- We generalize an existing low-cost analog signal processing concept that takes advantage of the periodicity of vehicle-to-vehicle broadcast service to the transmitter side. In particular, we propose to process multiple antennas using either an analog beamforming network (ABN) of phase shifters, or an antenna switching network (ASN) that periodically alternates between the available antennas, to transmit periodic messages to receivers that have an analog combining network (ACN) of phase shifters, which has been proposed in earlier work. To guarantee robustness, we aim to minimize the burst error probability for the worst receiving vehicular user, in a scenario of bad propagation condition that is modeled by a single dominant path between the communicating vehicles. In absence of any form of channel knowledge, we analytically derive the optimal parameters of both ABN and ASN. The ABN beamforming vector is found to be optimal for all users and not only for the worst receiving user. Further, we demonstrate that Alamouti scheme for the special case of two transmit antennas yields similar performance to ABN and ASN. At last, we show that the derived parameters of the two proposed transmission strategies are also optimal when hybrid ACN-maximal ratio combining is used at the receiver.
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| 20. |
- Bencheikh Lehocine, Chouaib, 1993, et al.
(författare)
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Sensitivity analysis of beamforming techniques for periodic broadcast V2V communication
- 2021
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Ingår i: Conference Record - Asilomar Conference on Signals, Systems and Computers. - 1058-6393. ; Volume 2021-October, s. 61-66
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Konferensbidrag (refereegranskat)abstract
- In this work, we extend the results of two previously proposed transmit beamforming techniques for periodic, broadcast, vehicle-to-vehicle communication with a common fixed broadcast period, to the scenario where vehicular users (VUs) use different, and potentially varying broadcast periods. The two techniques, analog beamforming network (ABN) of phase shifters and antenna switching network (ASN), were previously developed in accordance with a multiple antenna receiver that employs an analog combining network (ACN) of phase shifters. To accommodate the use of multiple broadcast periods, we propose the design of phase shifter parameters of ABN-ACN and ASN-ACN systems using a design period Td. Then, we analytically derive sets of broadcast periods that sustain optimality, in the sense that the sum signal-to-noise ratio (SNR) of Kconsecutive packets for any receiving VU is maximized. Next, we provide guidelines on how to set Td to ensure a sufficient granularity of the sets of optimal broadcast periods. Finally, we investigate using numerical computations the effect of certain design choices on the sensitivity of ABN/ASN-ACN systems to small variations of the broadcast period.
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| 21. |
- Beygi, Sajjad, et al.
(författare)
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Geometry-Based Stochastic Modeling and Estimation of Vehicle to Vehicle Channels
- 2014
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Ingår i: ICASSP, IEEE International Conference on Acoustics, Speech and Signal Processing - Proceedings. - 1520-6149. - 9781479928927 ; , s. 4289-4293
-
Konferensbidrag (refereegranskat)abstract
- In this paper, a geometry-based stochastic channel model (GSCM) for vehicle-to-vehicle (V2V) wireless communica- tion is developed. The channel model reveals that the channel representation in delay-Doppler domain can be divided into four regions. In each region, the V2V channel can be modeled using a hybrid sparse/diffuse (HSD) model. Prior art on hybrid channel estimation for linear time-invariant channels is extended to the time-varying case. Furthermore, the effects of pulse shape leakage are explicitly determined and compensated. Simulation results shows that exploiting the V2V channel properties in the delay-Doppler domain, yields significantly improved channel estimates over unstructured approaches (more than 10 dB gain in SNR).
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| 22. |
- Beygi, Sajjad, et al.
(författare)
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Nested Sparse Approximation: Structured Estimation of V2V Channels Using Geometry-Based Stochastic Channel Model
- 2015
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Ingår i: IEEE Transactions on Signal Processing. - 1941-0476 .- 1053-587X. ; 63:18, s. 4940-4955
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Tidskriftsartikel (refereegranskat)abstract
- Future intelligent transportation systems promise increased safety and energy efficiency. Realization of such systems will require vehicle-to-vehicle (V2V) communication technology. High fidelity V2V communication is, in turn, dependent on accurate V2V channel estimation. V2V channels have characteristics differing from classical cellular communication channels. Herein, geometry-based stochastic modeling is employed to develop a characterization of V2V channel channels. The resultant model exhibits significant structure; specifically, the V2V channel is characterized by three distinct regions within the delay-Doppler plane. Each region has a unique combination of specular reflections and diffuse components resulting in a particular element- wise and group-wise sparsity. This joint sparsity structure is exploited to develop a novel channel estimation algorithm. A general machinery is provided to solve the jointly element/group sparse channel (signal) estimation problem using proximity operators of a broad class of regularizers. The alternating direction method of multipliers using the proximity operator is adapted to optimize the mixed objective function. Key properties of the proposed objective functions are proven which ensure that the optimal solution is found by the new algorithm. The effects of pulse shape leakage are explicitly characterized and compensated, resulting in measurably improved performance. Numerical simulation and real V2V channel measurement data are used to evaluate the performance of the proposed method. Results show that the new method can achieve significant gains over previously proposed methods.
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| 23. |
- Beygi, Sajjad, et al.
(författare)
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Structured Sparse Approximation via Generalized Regularizers: With Application to V2V Channel Estimation
- 2014
-
Ingår i: Proceedings - IEEE Global Communications Conference, GLOBECOM. - 2334-0983 .- 2576-6813. - 9781479935116 ; , s. 3013-3018
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Konferensbidrag (refereegranskat)abstract
- In this paper, we consider the estimation of a signal that has both group- and element-wise sparsity (joint sparsity); motivated by channel estimation in vehicle-to-vehicle channels. A general approach for the design of separable regularizing functions is proposed to adaptively induce sparsity in the estimation. A joint sparse signal estimation problem is formulated via these regularizers and its optimal solution is computed based on proximity operations. Our optimization results are quite general and they can be applied in the context of hierarchical sparsity models as well. The proposed recovery algorithm is a nested iterative method based on the alternating direction method of multipliers (ADMM). Due to regularizer separability, key operations can be performed in parallel. V2V channels are estimated by exploiting the joint sparsity (group/element-wise) exhibited in the delay-Doppler domain. Simulation results reveal that the proposed method can achieve as much as a 10 dB gain over previously examined methods.
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| 24. |
- Bilstrup, Katrin, et al.
(författare)
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Evaluation of the IEEE 802.11p MAC method for vehicle-to-vehicle communication
- 2008
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Ingår i: 68th IEEE Vehicular Technology Conference, 2008. VTC 2008-Fall. - Piscataway, N.J. : IEEE Press. - 9781424417216 ; , s. 1-5
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Konferensbidrag (refereegranskat)abstract
- In this paper the medium access control (MAC) method of the upcoming vehicular communication standard IEEE 802.11p has been simulated in a highway scenario with periodic broadcast of time-critical packets (so-called heartbeat messages) in a vehicle-to-vehicle situation. The 802.11p MAC method is based on carrier sense multiple access (CSMA) where nodes listen to the wireless channel before sending. If the channel is busy, the node must defer its access and during high utilization periods this could lead to unbounded delays. This well-known property of CSMA is undesirable for time critical communications. The simulation results reveal that a specific node/vehicle is forced to drop over 80% of its heartbeat messages because no channel access was possible before the next message was generated. To overcome this problem, we propose to use self-organizing time division multiple access (STDMA) for real-time data traffic between vehicles. This MAC method is already successfully applied in commercial surveillance applications for ships (AIS) and airplanes (VDL mode 4). Our initial results indicate that STDMA outperforms CSMA for time-critical traffic safety applications in ad hoc vehicular networks.
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| 25. |
- Bilstrup, Katrin, et al.
(författare)
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Medium access control in vehicular networks based on the upcoming IEEE 802.11p standard
- 2008
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Ingår i: 15th World Congress on Intelligent Transport Systems and ITS America Annual Meeting 2008. - : World Congress on ITS. - 9781615677566 ; , s. 4155-4167, s. 12-
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Konferensbidrag (refereegranskat)abstract
- In this paper, initial simulations are presented showing that the upcoming IEEE 802.11p standard is not suitable for traffic safety applications requiring reliable, low delay communication between vehicles. The medium access control procedure is one of the most important parts in the design of delay-constrained communication systems, and emerging vehicle safety applications put new stringent demands on timely and reliable delivery of data packets. The medium access procedure used in 802.11p is carrier sense multiple access, which is inherently unsuitable for time-critical data traffic since it is contention-based and cannot provide a finite upper bound on the time to channel access. The simulation results indicate that with IEEE 802.11p, channel access cannot be granted in a manner that is sufficiently predictable to support reliable, low-delay communications between vehicles on a highway.
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