Article

A Measurement Study of Time-Scaled 802.11a Waveforms Over The Mobile-to-Mobile Vehicular Channel at 5.9 GHz

Carnegie Mellon Univ., Pittsburgh, PA, USA
IEEE Communications Magazine (Impact Factor: 4.46). 06/2008; 46(5):84 - 91. DOI: 10.1109/MCOM.2008.4511654
Source: IEEE Xplore

ABSTRACT We have studied the effects of the mobile vehicle-to-vehicle (V2V) channel on scaled versions of the current IEEE 802.11 a standard to investigate how readily they can be applied to vehicular networks. In particular, measured parameters for the V2V channel at 5.9 GHz in suburban, highway, and rural environments are studied in the context of critical parameters for OFDM. Actual performance of scaled OFDM waveforms with bandwidths of 20 MHz (bandwidth of IEEE 802.11 a), 10 MHz (bandwidth of the draft IEEE 802.11 p), and 5 MHz (halved bandwidth of IEEE 802.11 p) are described and interpreted in light of the channel parameters. At 20 MHz the guard interval is not long enough, while at 5 MHz errors increase from lack of channel stationarity over the packet duration. For these choices of the scaled 802.11 a OFDM waveform, 10 MHz appears to be the best choice.

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    • "The physical layer is based on the 802.11a standard and uses OFDM (Orthogonal Frequency-Division Multiplexing) modulation . The bandwidth was changed from 20 MHz to 10 MHz [9] in order to reduce the spreading delay (Root Mean Square delay spread) in VANETs. Optionally, the bandwidth can be set at 5 MHz. "
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    ABSTRACT: The IEEE 802.11 working group proposed a standard for the physical and medium access control layers of vehicular networks called 802.11p. In this paper we report experimental results obtained from communication between vehicles using 802.11p in a real scenario. The main motivation is the lack of studies in the literature with performance data obtained from off-the-shelf 801.11p devices. Our study characterizes the typical conditions of an 802.11p point-to-point communication. Such a study serves as a reference for more refined simulation models or to motivate enhancements in the PHY/MAC layers. Field tests were carried out varying the vehicle's speed between 20 and 60 km/h and the packet length between 150 and 1460 bytes, in order to characterize the range, throughput, latency, jitter and packet delivery rates of 802.11p links. It was observed that communication with vehicles in motion is unstable sometimes. However, it was possible to transfer data at distances over 300 m, with data rates sometimes exceeding 8 Mbit/s.
    04/2014; 1. DOI:10.1016/j.vehcom.2014.04.001
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    • "It is found that the fading statistics change from near Rician to Rayleigh as the vehicle separation increases. Furthermore, Cheng et al. [4] provided analysis of Doppler spread and coherence time and their dependence on the vehicular environment. For example, it was found that, for a highway environment, the coherence bandwidth and the coherence time can be on the order of 400 kHz and 0.3 ms, respectively. "
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    ABSTRACT: Space–frequency block coding with orthogonal frequency-division multiplexing (SFBC-OFDM) suffers from the effect of intercarrier interference (ICI) in doubly selective channels. In this paper, a scheme is proposed in which windowing is applied to the received signal to reduce the effect of ICI to a limited number of neighboring subcarriers. The subcarriers holding the SFBC components of each codeword are separated by a number of subcarriers larger than the ICI range, and hence, they do not interfere with each other. To preserve the structure of the SFBC, the separation between the codeword components is also selected within the coherence bandwidth of the channel. As a result, the diversity gain of the SFBC is preserved. By proper selection of the pilot locations, each OFDM symbol can be divided into subsymbols that can be decoded independently. We show that the proposed windowing technique allows the use of decision feedback equalization to estimate the data transmitted in each subsymbol with low complexity. Simulation results are presented showing the ability of the proposed scheme to significantly improve the performance of SFBC-OFDM and preserve its diversity gain.
    IEEE Transactions on Vehicular Technology 04/2014; 63(5):2197-2207. DOI:10.1109/TVT.2013.2291872 · 2.64 Impact Factor
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    • "However, we may require additional channel information in high mobility to support reliable communication links. In [8], four criterions for channel characteristics are measured with vehicle-to-vehicle (V2V) environments at 5.9GHz, and Table 1 represents the worst value of four criterions. To provide reliable communication links, four criterions have to satisfy the following conditions: Fig. 2 OFDM Packet structure with midamble 1. Guard interval > Maximum excess delay 2. Coherence bandwidth > Carrier spacing >> Doppler spread 3. Interval between channel estimates < Coherence time Table 1 represents the measured data of vehicular communication channel, and the data indicates that the signal satisfies first two conditions. "
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    ABSTRACT: Orthogonal Frequency Division Multiplexing (OFDM) based IEEE 802.11 a/g systems which are widely used in wireless LAN carry out channel estimation in one time per packet since the systems use only preamble. Whereas, midamble based channel estimation supports continuous channel estimation by tracking the channel state information periodically. Using IEEE 802.11p Wireless Access in Vehicular Environments (WAVE) system, we analyze the performance of the proposed system via practical measurements. Based on these results, practical issues on midamble based channel estimation are investigated.
    05/2013; 8(5). DOI:10.13067/JKIECS.2013.8.5.733
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