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Ultra-wideband (UWB) is a useful radio technique for sharing frequency bands between radio systems. It uses very short pulses to spread spectrum. However, there is a potential for interference between systems using the same frequency bands at close range. In some regulatory systems, interference detection and avoidance (DAA) techniques are required to prevent interference with existing radio systems. In this paper, the effect of interference on orthogonal frequency division multiplexing (OFDM) signals from pulsebased UWB is discussed, and an interference mitigation technique is proposed. This technique focuses on the pulse repetition cycle of UWB. The pulse repetition interval is set the same or half the period of the OFDM symbol excluding the guard interval to mitigate interference. These proposals are also made for direct sequence (DS)-UWB. Bit error rate (BER) performance is illustrated through both simulation and theoretical approximations.

The inter-vehicle communication (IVC) systems based on CSMA/OFDM scheme such as IEEE802.11p or ARIB STD-TI09 in Japan are widely developed because autonomous distributed networks are easily made by using the Carrier Sense Multiple Access with Collision Av oidance (CSMA/CA) MAC protocol. However, the hidden terminals in CSMA networks cause the performance degradation. In our previous study, a new IVC scheme using Code Division Multiple Access (CDMA) had been proposed to mitigate the impact of hidden terminals and evaluated the performance in the simple straight road model. However, performances of both IVC schemes are not evaluated in the urban area road model assuming multi path fading. In this paper, performances of the DS-CDMA IVC scheme and CSMAlOFDM IVC scheme are evaluated in urban area road model. As the results of simulations, it was confirmed that the PER (Packet Error Rate) performances of CSMAlOFDM IVC can be made better than the DS-CDMA. On the other hand, DS-CDMA shows the possibility that it is able to achieve a low delay communication as compared with CSMA/OFDM.

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