Advances in Vehicular Networking Technologies Part 9 pdf

0 10 20 30 40 50 60 70 80 0 5 10 15 20 25 30 35 Positions separated each other 75 cm Distance [m] Actual distance scale−W scale−W with PNMC (a) Correction of severe NLOS measurements with PNMC 0 2 4 6 8 10 12 14 16 18 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Error [m] Probability scale−W scale−W with PNMC (b) CDF Fig. 12. NLOS error mitigation from a record of distance estimates using a window size of 5 m walking. (a)scale-W distance estimates before and after applying PNMC method. (b) Comparison of CDFs errors in distance estimate before and after applying PNMC method. Fig. 12(b) the improvement of applying the PNMC method can be observed through the CDF of errors in distance estimates. Generally speaking, the distance estimate can be improved on approximately 2 m for cumulative probabilities higher than 30% when applying the PNMC method. 6. Conclusions The achievable positioning accuracy of traditional wireless localization systems is limited when harsh radio propagation conditions like rich multipath indoor environments are present. In this chapter a novel RTT-based ranging method is proposed over a PCB that performs RTT measurements. The effect of hardware errors has been minimized by choosing the scale-W parameter as RTT estimator. A coefficient of determination value of 0.96 achieved with this estimator in LOS justified the simple linear regression function as the model that relates distance estimates to R TT measurements in LOS. As LOS is not guaranteed in an indoor environment, the accuracy of the proposed localization algorithm has been tested in a rich multipath environment without any NLOS error mitigation technique achieving an error lower than 4 m on average. However, this error is improved after having implemented the PNMC technique to correct NLOS errors. Once reliable RTT-based ranging estimates are obtained, simple geometrical triangulation methods can be used to find the location of the MS (Pahlavan & Krishnamurthy, 2002). Indoor localization schemes have experienced a flurry of research in recent years. However, there still remain multiple areas of open research that will help systems to meet the requirements of applications that have to operate in indoor propagation environments where GNSS typically fails. These are: i) Interference mitigation: To date, the majority of research effort ignores the effects of interference on time estimation accuracy, and few papers propose robust interference mitigation techniques. ii) Inertial Measurements Units (IMU): the integration of traditional localization metrics, such as TOA, RSS or AOA with IMU information, such as the one reported by accelerometers, gyroscopes and magnetometers, could provide location estimations more precisely and continuously, since IMU-based 232 Advances in Vehicular Networking Technologies localization is a beacon-free methodology. iii) Secure ranging: In certain scenarios the localization process m ay be subject to hostile attacks. While some works have presented secure localization algorithms (see, e.g., (Li et al., 2005; Zhang et al., 2006)), less attention has been paid to secure ranging. 7. Acknowledgment This research is partially supported by the General Board of Telecommunications of the Council of Public Works from Castilla-León (Spain) and by the spanish national project LEMUR (TIN2009-14114-C04-03). 8. Appendix 8.1 Maximum likelihood estimator of the scale parameter of the Weibull distribution The scale-W parameter is estimated by using the MLE method and assuming that the shape parameter is known. The probability density function of a Weibull (two-parameter) random variable x is f (x; k, λ)= k λ  x λ  k−1 ·e − ( x λ ) k x ≥ 0 = k λ k · x k−1 ·e − ( x λ ) k x ≥ 0 where k > 0 is the shape parameter and λ > 0 is the scale-W parameter. Let X 1 , X 2 , X n be a random sample of random variables with two-parameter Weibull distribution, k and λ. The likelihood function is L (x 1 , x n ; k, λ)= n ∏ i=1 f (x i ; k, λ) Therefore, lnL (x 1 , , x n ; k, λ)= n ∑ i=1 ln f(x 1 , x n ; k, λ) = n ∑ i=1  ln  k λ  +(k −1) ·ln  x i λ  −  x i λ  k  = n · ln  k λ  +(k −1) · n ∑ i=1 ln  x i λ  − n ∑ i=1  x i λ  k = n · (ln(k) − ln(λ)) + (k −1) ·  −n ·ln(λ)+ n ∑ i=1 ln(x i )  − n ∑ i=1  x i λ  k = n · ln(k)+(k −1) · n ∑ i=1 ln(x i ) −n · k ·ln(λ) −λ −k · n ∑ i=1 x k i thus, ∂lnL ∂λ = −n ·k · 1 λ + k · 1 λ k+1 · n ∑ i=1 x k i 233 Distance Estimation based on 802.11 RTS/CTS Mechanism for Indoor Localization in order to find the maximum, ∂lnL ∂λ = 0 then, 0 = −n · k · 1 λ + k · 1 λ k+1 · n ∑ i=1 x k i = ∑ n i =1 x k i −n ·λ k λ k+1 = n ∑ i=1 x k i −n · λ k hence, the MLE of the scale-W parameter  λ =  1 n n ∑ i=1 x k i  1 k this expression is known as the generalized mean or Hölder mean. The Hölder mean is a generalized mean of the form, M p (x 1 , x 2 , , x n )=  1 n n ∑ i=1 x p i  1/p (6) where the parameter p is an affinely extended real number, n is the number of samples and x i are the samples with x i ≥ 0. The Hölder mean is an abstraction of the Pythagorean means which for example includes minimum (M −∞ ), harmonic mean (M −1 ), geometric mean (M 0 ), arithmetic mean (M 1 ), quadratic mean (M 2 ), maximum (M ∞ ), and the MLE of the scale-W parameter (M k )wherek is the shape parameter of Weibull distribution. 9. References Bahillo, A., Mazuelas, S., Lorenzo, R.M., Fernández, P., Prieto, J. & Abril, E.J. (2009a). Indoor location based on IEEE 802.11 round-trip time measurements with two-step NLOS mitigation. Progress In Electromagnetics Research B, PIERB, Vol.2009, No.15, (September 2009) 285-306, ISSN: 1937-6472. Bahillo, A., Prieto, J., Mazuelas, S., Lorenzo, R.M., Blas, J. & Fernández, P. (2009b). 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Allen, B., Dohler, M., Okon, E., Malik, W., Brown, A. & Edwards, D., (2007), Ultra Wideband Antennas and Propagation for Communications, Radar, and Imaging, John Wiley & Sons, Inc., ISBN: 0-470-03255-3, West Sussex, UK. Tang, H., Park, Y. & Qui, T., (2008). NLOS mitigation for T OA location based on a modified deterministic model. Research Letters in Signal Processing, Vol.8, No.1, (April 2008) 1-4, ISSN: 1687-6911. Wylie, M. P. & Holtzman, J., (1996). The non-line of sight problem in mobile location estimation. Proceedings of the 5th IEEE International Conference on Universal Personal Communications, Vol.2, pp. 827-831, ISBN: 0-7803-3300-4, Cambridge, October 1996, Mass, USA. Güvenç I., Chong, C C., Watanabe, F. & Inamura, H., (2008). NLOS identification and weighted least-squares localization for UWB systems using multipath channel 235 Distance Estimation based on 802.11 RTS/CTS Mechanism for Indoor Localization statistics, EURASIP Journal on Advances in Signal Processing, Vol. 2008, (April 2008) 1-14, ISSN: 1110-8657. Yarkoni, N. & Blaunstein, N., (2006). Prediction of propagation characteristics in indoor radio communication environment. Progress In Electromagnetics Research, PIER 59, (2006) 151-174, ISSN: 1070-4698. Cong, L. & Zhuang, W., (2005). Non-line-of-sight error mitigation in mobile location. INFOCOM 2004, 23th Annual Joint Conference of the IEEE Computer and Communications Societies, Vol. 4, pp. 560-572, ISBN: 0-7803-8355-9, Hong-Kong, March 2004. Urrela, A., Sala, J. & Riba, J., (2006). Average performance analysis of circular and hyperbolic geolocation. IEEE Transactions on Vehicular Technology, Vol. 55, (January 2006) 52-66, ISSN: 0018-9545. Chen, P C., (1999). A non-line-of-sight error mitigation algorithm in location estimation. Proceedings of Wireless Communications and Networking Conference, Vol. 1, pp. 316-320, ISBN: 0-7803-5668-3, New Orleans, La, USA, September 1999. Li, Z., Trappe, W., Zhang, Y. & Nath, B., (2005). Robust statistical methods for securing wireless localization in sensor networks, Proceedings of IEEE Information Processing Sensor Networks, pp. 91-98, ISBN: 0-7803-9202-7, Los Angeles, California, USA, April 2005. Zhang, Y., Liu, W., Lou, W. & Fang, Y. , (2006). Location-based compromise-tolerant security mechanisms for wireless sensor networks, IEEE Journal on Selected Areas in Communications, Vol. 24, (February 2006) 247-260, ISSN: 0733-8716. 236 Advances in Vehicular Networking Technologies Advances in Vehicular Networking Technologies 238 the relaying, RS shall forward data as simple as possible to prevent wasting processing power and storage. This study proposes a burst-switch concept aiming to tackle the issues and provides a simple and efficient data forwarding for wireless relay networks. The rest of the chapter is organized as follows. First, wireless relaying and a conventional relay system are overviewed in section 2. The proposed new forwarding mechanism is then elaborated in section 3; section 4 presents the evaluation and simulation results for the mentioned issues. At last, conclusions are given in section 5. 2. Background and related works Relay technology has been investigated for years, and a realistic relay system will be deployed in few years to enhance legacy wireless networks. This section overviews IEEE 802.16 communication system and introduces the relay enhancements. The data forwarding mechanisms adopted in the system are also discussed to address the issues. 2.1 Overview of wireless relay networks A wireless relay network consists of a BS, one or more RSs, and numbers of SSs. In the network, directly or through the assistances of RSs. BS forwards the downstream data coming from outside network to SS while RSs relay upstream data generated by SSs to BS. Since all the data transmissions within the network are arranged by BS and there are no communications between RSs, the relay network is usually constructed as a tree topology, which is illustrated in figure 1. Fig. 1. Wireless Relay Network There are two types of radio links in this network: relay link and access link. The radio link between a BS and a RS and between two RSs are called relay links, and BS constructs a relay path by multiple relay links. The access link is the radio communication between a SS and its access station, which can be a BS or an access RS. The access RS is a RS attached by a SS and can helps BS for relaying data to the SS. For the example in figure 1, RS 2 is an access RS of SS u and assists BS 0 to provide relay services for SS u . BS 0 allocates resources Data Forwarding in Wireless Relay Networks 239 along the relay path between SS u and itself so that the help on data relay in corresponding relay links. 2.2 IEEE 802.16 and multi-hop relay network IEEE Std 802.16e TM -2005 is one of the most popular wireless broadband networks nowadays, and figure 2 shows the reference model for that system. The system consists of two layers, Medium Access Control (MAC) and Physical (PHY) layers, to handle wireless communications. Packets from TCP/IP layer are translated into MAC Protocol Data Units (MPDUs) and then encoded into a PHY burst. The burst is associated with a MAP Information Element (MAP-IE) that indicates a station for receiving and decoding the burst. After the data process, BS transforms both the burst and the associated MAP-IE into a radio frame and pumps it into wireless medium. Fig. 2. Data Processing in IEEE 802.16 The overview of 802.16e frame structure is depicted in figure 3. The frame composes two subframes: downlink and uplink subframes, and starts with a synchronization part of preamble and Frame Control Header (FCH). The first part is used for each receiving station synchronize with BS and abstracting the frame. Following the synchronization part, the frame header further includes a downlink MAP (DL-MAP) and an uplink MAP (UL-MAP), which consists of MAP-IEs to indicate the stations where and how to access data bursts. As stated before, each data burst is associated with an MAP-IE, and one or more MPDUs destining to a destination can be concatenated or packed into the burst. With a connection identity (CID) in the MAP-IE, every receiving station locates and receives MPDUs in the desired PHY burst, and has no need to check all the bursts in the frame. Advances in Vehicular Networking Technologies 240 Fig. 3. IEEE 802.16e Frame Structure The system further specifies an option for disabling MAP to save overheads so that more data can be allocated. In this case, receiving stations should put more efforts to process entire frame since there are no indications in frame header any more. Without MAP indication, the receiving station cannot but store the whole frame to check if there are any desired MPDUs. However, it is inefficient for buffering and checking all the MPDUs in a frame. Although, the operations brought overheads but the problem should not be as serious as that in multi-hop communications. Because of redundant processing and transmissions during relay, multi-hop data forwarding makes the overhead become a severe problem. 2.3 Data forwarding and issues in 802.16j MR network IEEE working group specifies Multi-hop Relay (MR) support for 802.16e system in IEEE Std 802.16j TM -2009. The specification aims to solve the capacity problem and reduce development cost with advanced relay technologies. Efficiency during data relay is also a major concern for implementing RSs. Two data forwarding schemes are specified to facilitate relay functionalities and reduce overheads. The first forwarding scheme is CID-based transmission, in which RS forwards MPDUs based on the CIDs contained in the MAP-IE or MPDU headers. For saving signalling overheads, relayed MPDUs do not carrier any extra routing information, and are transmitted as in 802.16e conventional system. When MPDUs are relayed, each receiving RS gets CIDs from MAP-IEs and checks associating bursts if there are any data required for further forwarding. The RS discards the burst that is not indicated by the recorded CIDs in its forwarding list. When the CID of the burst is in the forwarding list, the receiving RS forwards the burst to the station in next hop. Besides, there is another implementation that RSs forward MPDUs by identifying CIDs containing in MPDU headers. As mentioned, each RS has to process all the MPDU in receiving frame, and determines the MPDUs for relay. Figure 4 depicts the example for this forwarding scheme based on the relay network in [...]... middle level of security In automotive ECUs, sensors, anti-skid-systems, etc are connected using CAN with bit rates up to 1 Mbps However, in today’s car, CAN is used as an SAE (Society of Automotive Engineers) class C (classification defined in J2056/2 Survey, 199 4)) network for real time control in the powertrain and 258 Advances in Vehicular Networking Technologies chassis domains (at 250 or 500 kbps)... without checking the MPDU so as to eliminate the processing in MPDU level Moreover, checking CIDs in MAP also saves unnecessary processing for the data destining to other destinations Before relaying data, BS identifies the access RS and sets up the forwarding path for a SS As the legacy schemes, a data burst binding a relay path aggregates multiple MPDUs and is transmitted in frames Since each relay... When initializing a relay transmission, BS first identifies a receiving SS and the associating access RS from the table Then, radio resources are allocated for relay links in the relay path By the MAP indications, intermediate RSs switch burst by checking the CIDs within MAP when receiving a frame Only when the received burst CID matches the recorded CID, the binding burst is switched to next hop Intermediate... four mechanisms obtain more stable performance in overhead saving when relay hop count increases Regarding tunnel-based solutions, it is found that enabling MAP does not increase as much overheads as applying tunnel headers because it is tunnel header to dominate the overhead in heavy load conditions The forwarding schemes without introducing any extra MPDU headers perform better in the simulation The... Tunnel_w/o_MAP as basics to show following observations (1) Without MAP indications, CID-based forwarding scheme performs worst in saving processing and storage overheads, no matter in 2-hop or 5-hop cases (2) In tunnel-based schemes, enabling MAP indication can reduce the amount of cached data with some penalty from extra MAP-IE processing (3) Comparing the benefits coming from applying MAP and tunnel headers,... the automotive industry to face a great challenge in its transition from mechanical engineering towards mechatronical products The X-by-wire and X-tainment applications involve efficient networks that allow bus sharing while reducing both cabling costs, number of wires and connectors This chapter deals with the embedded in- vehicle networks and the use of emerging technologies combining different communication... MPDUs destining to same access RS However, the 242 Advances in Vehicular Networking Technologies extra overhead brought from the tunnel header should be considered Furthermore, the impact caused by adopting MAP and tunnel headers at the same time shall be also investigated Fig 5 Tunnel-based Transmission Comparing these two forwarding schemes, RSs applying tunnels forward data efficiently since RS identifies... burst CID, the proposed forwarding scheme is so called burst switch 244 Advances in Vehicular Networking Technologies Fig 6 Burst Switch Transmission Figure 6 shows the proposed scheme in detail In the figure, BS establishes a path for switching the burst for SSw, SSx, and SSy, and assigns an end-to-end burst CID for the relay destination, RS3 When receiving the MAP in first hop, RS1 and RS2 check... Processing Overhead (bits) 70000 60000 50000 40000 30000 20000 10000 0 20 40 60 80 100 120 200 Number of Traffic Flows Fig 9 Processing Overhead in 5-hop Scenario As the relay hop count increases, RSs shall handle more and more control information in the relaying process, and figure 9 depicts the results in multi-hop relay environments Generally speaking, the processing overheads of all the schemes increase... channels The sending slots are used deterministically (pre-defined TDMA strategy) in the static part In the dynamic part there can be differences in the phase on the two channels Nodes that are connected to both channels send their frames in the static part simultaneously on both channels An interesting feature of FlexRay is that it can provide scalable dependability i.e., the “ability to operate in configurations . Areas in Communications, Vol. 24, (February 2006) 247-260, ISSN: 0733-8716. 236 Advances in Vehicular Networking Technologies Advances in Vehicular Networking Technologies 238 the relaying,. more precisely and continuously, since IMU-based 232 Advances in Vehicular Networking Technologies localization is a beacon-free methodology. iii) Secure ranging: In certain scenarios the localization. checking the MPDU so as to eliminate the processing in MPDU level. Moreover, checking CIDs in MAP also saves unnecessary processing for the data destining to other destinations. Before relaying