Kohei Ohno

Interference mitigation study for UWB radio using template waveform processing

Ultra-wideband (UWB) is an effective technique that enables coexistence with other radio systems using very short pulses and spread spectrum. However, there are potential interferences among those using the same frequency bands. This paper discusses the effects of interference between pulse-based UWB (p-UWB) and other systems: continuous wave, binary phase-shift keying signal, IEEE802.11a wireless LAN using a 5-GHz band, and multiband orthogonal frequency-division multiplexing (MB-OFDM). The MB-OFDM is inferentially proposed for personal area networks, as is p-UWB. The FCC has stated that both p-UWB and MB-OFDM systems will use the same band from 3.1 to 10.6 GHz. The bit-error-rate performance is shown assuming that p-UWB and the other systems are utilized at close range. To mitigate the effects of interference to p-UWB from other radio systems, a multicarrier template wave technique is proposed. The multicarrier template wave is approximated with an ordinary pulse waveform by Gabor transform formula and is composed of several subband pulses without interfering bands. The proposed UWB receiver for MB-OFDM interferences can detect their hopping pattern without a priori knowledge from the MB-OFDM transmitter. These techniques are shown to be effective for the systems to coexist.

A proposal for an interference mitigation technique facilitating the coexistence of biphase UWB and other wideband systems

The paper discusses the effects on biphase UWB radio systems of interference from other systems. Various systems, such as IEEE 802.11a wireless local area network (LAN) and multiband orthogonal frequency division multiplexing (OFDM), are assumed to interfere and the bit error rate performances of a UWB system are evaluated. To reduce the effects of interference, we propose using multicarrier type transmission pulse and template waveforms. We show that the proposed interference mitigation technique is effective, allowing for the coexistence of different wideband systems.

Interference mitigation study for UWB impulse radio

This paper discusses the reduction of interference from coexisting narrowband signal to UWB impulse radio. Two countermeasure techniques are proposed to reduce interference from narrowband signals on only the receiver side. One is to use a filter that rejects the interference signals. The second is to use modified template waveform at the receiver correlation. We propose to use multi-carrier type template waveform that has 11-sub-carrier pulses. When there are some interferers, it is possible to reduce the effect of the interferers by using a modified template waveform that is constructed with the multi-carrier type template removing some sub-carrier pulses that are close to the interfering spectrum. We show that the bit error rate performance is improved by the multi-carrier template.

Interference DAA Technique for Coexisting UWB Radio

Ultra Wideband (UWB) is an attractive technique that enable coexistence with other radio systems to spread spectrum. However, there are potential interferences among those using the same frequency bands and close range. In some country regulations, the interference DAA (detect and avoidance) techniques are required to utilize UWB devices. This paper discusses the interference DAA technique. To utilize multi-carrier pulses made from several narrower sub-band pulses, that is possible to detect and mitigate the interference. The multi-carrier pulses are also suited for the transmitted pulse waveform, since they have advantages for adaptive wave forming. The proposal system is evaluated by the bit error rate performance and signal detection error rate to show their effectiveness. The WiMAX (world interoperability for microwave access) system is considered as an example of the interferer.

Interference mitigation study for the coexistence of bi-phase UWB and multi-band OFDM

Ultra wideband (UWB) is an effective technique that enables coexistence with other radio systems using very short pulses and spread spectrum. Multi band orthogonal frequency division multiplexing (MB-OFDM) is inferentially proposed for personal area networks as well as pulse-based UWB. According to the FCC, both systems is used in same band from 3.1 GHz to 10.6 GHz. This paper discusses the effects of interference between pulse-based UWB (p-UWB) and MB-OFDM. The bit-error rate performance is shown assuming that p-UWB and MB-OFDM are utilized at close range. To mitigate the effects of interference from MB-OFDM to p-UWB, multi-carrier template wave techniques and MB-OFDM band sensing in the p-UWB are proposed. These techniques are found effective for the coexistence of both systems.

Interference mitigation technique for coexistence of pulse-based UWB and OFDM

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 pulse-based 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.

Reducing impulsive noise in OFDM transmission using higher order modulation

One of the major factors of performance degradation in OFDM systems is influence of additive impulsive noise. Especially, reception characteristic is extremely degraded under multi-path channel. Many efficient impulsive noise reduction schemes are proposed for low order modulation such as QPSK, 16QAM. However, in higher order modulation as 64QAM, reception characteristics are degraded because constellation is dense. In this paper, efficient impulsive noise reduction scheme is proposed for OFDM transmission using higher order modulation such as 64QAM.

An Interference Mitigation Study for Coexistence of DS-UWB and OFDM

This paper discusses an interference DAA (detection and avoidance) technique for the ultra wideband (UWB) to share frequency bands with other radio systems. The effect of interference on DS (direct sequence) -UWB system to OFDM (multi band orthogonal frequency division multiplexing) modulated signal is evaluated. The proposed interference mitigation technique focuses on the symbol repetition cycle of DS-UWB. The effective symbol repetition interval is investigated to mitigate the effect of interference. The proposal DAA technique is aimed to the simple hardware structure only to control the symbol repetition cycle.

A study on channel estimation using pilot symbols under impulsive PLC channel

In order to improve performance of high-speed power line communication (PLC) using OFDM (Orthogonal Frequency Division Multiplexing), compensation of the influence of additive impulsive noise is required. In this paper, the scheme to make precise channel estimation under impulsive power line channel is proposed. Although many schemes to improve influence of the additive impulsive noise are proposed, they usually require precise estimation of the PLC channel transfer function. We have already proposed the scheme for channel estimation under these situations using the pilot symbols inserted in two successive OFDM symbols. However, data transmission performance slightly degrades because two successive pilot symbols are inserted. In this paper, the scheme to estimate channel transfer function using only one OFDM symbol is proposed. As the result of computer simulation, possibility of precise channel estimation was confirmed under existence of class A impulsive noise.

Performance evaluation of DS-CDMA IVC scheme and CSMA/OFDM IVC scheme

The inter-vehicle communication (IVC) systems based on CSMA/OFDM scheme such as IEEE802.11p or ARIB STD-T109 in Japan are widely developed because autonomous distributed networks are easily made by using the Carrier Sense Multiple Access with Collision Avoidance (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 multipath fading. In this paper, performances of the DS-CDMA IVC scheme and CSMA/OFDM 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 CSMA/OFDM 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.