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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. ; 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. - 0-7803-8280-3
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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. |
- Bilstrup, Katrin, 1972-, 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: Proceedings IEEE Vehicular Technology Conference Fall.
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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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| 6. |
- Bilstrup, Katrin, 1972-, 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: Proceedings of the 15th World Congress on Intelligent Transport Systems.
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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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| 7. |
- Bilstrup, Katrin, 1972-, et al.
(författare)
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On the ability of IEEE 802.11p and STDMA to provide predictable channel access
- 2009
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Ingår i: Proceedings of the 16th World Congress on ITS.
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Konferensbidrag (refereegranskat)abstract
- Emerging traffic safety applications requiring low delay communications will need vehicle ad-hoc networks. The only communication standard currently supporting this is IEEE 802.11p. However, 802.11p uses the medium access method CSMA/CA, which has a major drawback: unbounded worst case channel access delay. We therefore propose an algorithm already in commercial use in the shipping industry: STDMA. With STDMA, nodes always get predictable channel access regardless of the number of competing nodes and the maximum delay is deterministic. In this paper we elaborated with different parameter settings for the two protocols with the aim of improving performance without altering the standards.
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| 8. |
- Davide, Dardari, et al.
(författare)
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Innovative Signal Processing Techniques for Wireless Positioning
- 2012
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Ingår i: Satellite and Terrestrial Radio Positioning Techniques, Davide Dardari, Emanuela Falletti, and Marco Luise, editors. Oxford, Academic Press. - 978-0-12-382084-6 ; s. 207-315
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Bokkapitel (övrigt vetenskapligt)
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| 9. |
- Duran, Mauricio A. Caceres, et al.
(författare)
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Terrestrial Network-Based Positioning and Navigation
- 2012
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Ingår i: Satellite and Terrestrial Radio Positioning Techniques, Davide Dardari, Emanuela Falletti, and Marco Luise, editors. Oxford, Academic Press. - 978-0-12-382084-6 ; s. 75
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Bokkapitel (övrigt vetenskapligt)
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| 10. |
- Gholami, Mohammad Reza, 1976-, et al.
(författare)
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A Concave-Convex Procedure for TDOA Based Positioning
- 2013
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Ingår i: EEE Communications Letters (to appear).
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Tidskriftsartikel (refereegranskat)abstract
- This letter investigates the time-difference- of-arrival based positioning problem in wireless sensor networks. We consider the least-mean absolute, i.e., the l1 norm, minimization of the residual errors and formulate the positioning problem as a difference of convex function (DC) programming. We then employ a concave-convex procedure to solve the corresponding DC programming. Simulation results illustrate the improved performance of the proposed approach compared to existing methods.
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