Interference mitigation study for UWB radio using template waveform processing

Ultra Wideband (UWB) is an attractive technique that enables coexistence with other radio systems using very short pulses and spread spectrum. However there are potential interferences each other if UWB and other radio system are used same frequency band at close range. This paper discusses interference detection and mitigation techniques for pulse based UWB (p-UWB). A multi-carrier template wave is proposed to mitigate effect of interference with by other radio systems and also to detect the interfering bands. Multi-Band Orthogonal Frequency Division Multiplexing (MB-OFDM) is also proposed for Personal Area Network (PAN) and is utilized same frequency band as p-UWB. MB-OFDM is adopted frequency hopping, thus it is necessary to know the interfering band to reduce the effect of interference. In this paper, MB-OFDM hopping band is estimated by using sub-band pulses of multi-carrier template waveform and the template wave composed adaptively to mitigate the interference. Those techniques are found effective for coexistence of both systems.

Ultra wideband (UWB) systems transmit signals across a much wider frequency than conventional systems and are usually very difficult to detect. UWB systems tend to be useful for short‐range indoor applications. However, because of the short duration of UWB pulses, it is easier to engineer extremely high data rates. In multi‐band orthogonal frequency division multiplexing (MB‐OFDM) architecture, designers gain flexibility, reduction in power consumption, high spectrum efficiency and cost. In the earlier study, people shadowing has been considered to model attenuation in a packet‐level UWB channel model. However, in dense short‐range indoor applications, the effect of scatterers, diffractors and reflectors cannot be ignored. This happens mostly when the transmit antenna is omni‐directional. Compared with the earlier work which incorporated only shadowing effects, this study discusses a packet‐level UWB channel model subject to both multipath fading and people shadowing, which can arise even in an indoor channel (e.g. inside a hall of dimensions ∼ 10 m), and is incorporated in an MB‐OFDM system. The performance analysis of the link is made based on link throughput and delay in servicing packets. The numerical results show the relative effects of various fading distributions, viz., Rayleigh, Rician, Weibull and Nakagami, together with people shadowing on the MB‐OFDM system.

UWB(Ultra-Wideband)는 낮은 전력으로 초고속 통신을 실현하는 근거리 무선 통신 기술로서 주파수 부족 현상을 넘어서서 신규 기술을 도입할 수 있는 획기적인 기술 방식이다. UWB 전송방식 중의 하나인 MB-OFDM(Multiband Orthogonal Frequency Division Multiplexing) 시스템은 다양한 무선 통신 서비스에 적용이 가능하다. 본 논문에서는 협력 전송에서 전송률이 감소하는 문제를 해결하기 위한 UWB 시스템에서 계층 변조(HM : Hierarchical Modulation)와 순환 중복 검사를 통해 중계기에서 적응적으로 변조방식을 변경하는 새로운 중계 기법을 제시한다. 이는 기존 방법에 비해 비트 에러율은 비슷하며 처리량을 33%까지 증가시키는 장점이 있다. Recently, various transmission techniques for communication and broadcasting systems have been developed to meet the dramatically increasing requirement of consumers. Because UWB (Ultra-Wideband) is a wireless communication technique that supports high data rate with low power, it can satisfy the requirement and can be applied to various wireless communication services. The multi-band orthogonal frequency division multiplexing (MB-OFDM) system, one of UWB system, is the wireless communication system that satisfies the transmission characteristic for UWB and so it can be used for various wireless communication services. In this paper, we propose a scheme that uses hierarchical modulation which is applied in digital video broadcasting system at the source and adaptive modulation based on the channel quality at the relays. The simulation results have shown that the proposed scheme has both the advantages of the increased throughput by 33% and similar BER performance to conventional scheme.

This paper studies the performance differences of three low data rate ultra wideband (UWB) systems in interfered AWGN and multipath channels. The studied systems are based on ultra wideband frequency modulation (UWB-FM), direct sequence UWB (DS-UWB) and multiband orthogonal frequency division multiplexing (MB-OFDM). The systems are studied in very high and ultra high frequency bands (VHF/UHF), i.e. 230 - 390 MHz, and 6.336 - 7.920 GHz. The VHF/UHF channel model is based on the measurements carried out in typical Finnish forest, whereas channel model for 6.336 - 7.920 GHz band is based on the modified Saleh-Valenzuela model. The intentional interference locates at the centre of the studied band having a 20 MHz bandwidth. In the literature, the comparison of the different low data rate UWB systems is rather insignificant. Therefore, the results of this paper are filling up this evident gap. The same spectral allocation and data rate are used as a starting point for a study. In the lower band, DS-UWB seems to tolerate more interference than UWB-FM in AWGN and multipath channels. The interference power can be higher for UWB-FM than MB-OFDM without performance degradation in AWGN channel in the upper band. The system performance starts to decrease with the same interference power in the case of MB- OFDM and UWB-FM in the interfered multipath channels in the upper band.

Several recent standards such as IEEE 802.11a/g, IEEE 802.16, and ECMA multiband orthogonal frequency division multiplexing (MB-OFDM) for high data-rate ultra-wideband (UWB), employ bit-interleaved convolutionally-coded multicarrier modulation over quasi-static fading channels. Motivated by the lack of appropriate error rate analysis techniques for this popular type of system and channel model, we present two novel analytical methods for bit error rate (BER) estimation of coded multicarrier systems operating over frequency-selective quasi-static channels with non-ideal interleaving. In the first method, the approximate performance of the system is calculated for each realization of the channel, which is suitable for obtaining the outage BER performance (a common performance measure for e.g. MB-OFDM systems). The second method assumes Rayleigh distributed frequency-domain subcarrier channel gains and knowledge of their correlation matrix, and can be used to directly obtain the average BER performance. Both methods are applicable to convolutionally-coded interleaved multicarrier systems employing quadrature amplitude modulation (QAM). To illustrate the application of the proposed analysis, both methods are used to study the performance of the MB-OFDM system.

In this paper, we describe a novel approach for reducing the power consumption and complexity of a multiband orthogonal frequency-division multiplexing (MB-OFDM) ultrawideband (UWB) system by applying ideas from pulsed UWB systems. The approach is quite general and applicable to many other systems. Unlike the MB-OFDM system, the enhancement that we propose uses pulses with duty cycles of less than 1 as the amplitude shaping pulse of orthogonal frequency-division multiplexing (OFDM) modulation. Pulsating OFDM symbols spread the spectrum of the modulated signals in the frequency domain, leading to a spreading gain that is equal to the inverse of the duty cycle of the pulsed subcarriers. We study the spectral characteristics of pulsed OFDM and the added degrees of diversity that it provides. We show that pulsed-OFDM signals can easily be generated by either upsampling an equivalent OFDM baseband signal with a reduced number of carriers or by replacing the digital-to-analog converter (DAC) of a normal MB-OFDM transmitter with a low-duty-cycle DAC. We establish that a pulsed-OFDM receiver can fully exploit the added diversity without using Rake receivers. It is shown that, while pulsed OFDM has superior or comparable performance to MB-OFDM in multipath fading channels, it also has intrinsic low-complexity and power consumption advantages compared with MB-OFDM. To establish this fact, we describe an example design for the IEEE 802.15.3a Standard and present full simulation results for the UWB indoor propagation channels provided by the IEEE 802.15.3a Standard activity committee.

The correct modeling and measurement of ultra-wideband (UWB) radio signal are a critical issue to evaluate the electromagnetic (EM) emission of any communication system based on this technology. In this paper (Part I), UWB radio communication systems based on impulse radio (IR) and multiband orthogonal frequency division multiplex (MB-OFDM) technologies are characterized by simulations and experiments in both frequency and time domains. The EM characteristics of UWB radio are measured by different methods (conducted and radiative) and in different environments (anechoic and reverberation chambers).

In this paper, a closed form expression for the bit error rate performance of the multi-band orthogonal frequency division multiplexing (MB-OFDM) ultra wideband (UWB) communication system in the presence of interference is analytically analysed. The considered channel is the Saleh-Valenzuela multipath fading channel model. The interference is modelled as the OFDM-based IEEE802.11n wireless local area networks (WLANs). The dependence of the bit error rate performance of the MB-OFDM UWB communication system on the transmission range along with the impact of interference is also analytically investigated. Numerical results are validated with the aid of simulations. It is shown that the range performance of the MB-OFDM UWB communication system is severely deteriorated due to the presence of such interference.

Ultra-WideBand (UWB) systems have recently gained popularity for short range high rate communications. UWB system may cause serious interference to the other wireless systems whose spectra overlap the UWB band because it makes use of huge bandwidth. Therefore, we have to implement detect-and-avoid (DAA) techniques in order to detect the other systems and control the transmit signal of the UWB devices not to interfere with the other systems. In this paper, we propose a new method to suppress interference for UWB multi-band orthogonal frequency division multiplexing (MB-OFDM) system. Our proposed method determines weighting factors on several subcarriers based on a criterion to minimize the interference energy in the interference band. By computer simulations, we show performances of the proposed method in comparison with the conventional one.

Ultra-wideband (UWB) is an alternative wireless communications technology that offers high bandwidth wireless communications without the constraints of spectrum allocation. Fundamentally different from conventional radio frequency communications, UWB relies on a series of narrow, precisely timed pulses to transmit digital data. Transmitters and receivers that use UWB can be much simpler to build than their conventional counterparts, resulting in lower cost and higher power efficiency. Moreover, the inherent properties of UWB emissions allow them to potentially coexist with conventional wireless systems on a noninterfering basis. In April 2002, the Federal Communications Commission (FCC) released UWB emission masks and introduced the concept of coexistence with traditional and protected radio services in the frequency spectrum, which allows the operation of UWB systems mainly in the 3.1 to 10.6 GHz band, limiting the power level emission to -41dBm/MHz. Within the power limit allowed under the current FCC regulations, Ultra-wideband can not only carry huge amounts of data over a shortto- medium distance at very low power (this range can be extended by using ad-hoc or mesh networks), but it also has the ability to carry signals through doors and other obstacles that tend to reflect signals at more limited bandwidths and a higher power (Reed, 2005). At higher power levels, UWB signals can travel to significantly greater ranges. In March 2005, the FCC granted the waiver request, filed by the multiband Orthogonal Frequency Division Multiplexing (OFDM) alliance (MBOA), in which it approved the change in measurement for the all UWB technologies (neutral approach) (Barret, 2005). The FCC’s waiver grants effectively removes the previous transmit power penalties for both frequency-hopping (OFDM) and gated UWB technologies (TH and DS). Hence, they are allowed to transmit at higher power levels and then become idle for some time, as long as they meet the limits for average power density. This new rules allow those technologies to achieve up to four times better performance and double the range.

An ultra wideband (UWB) technology is a potential candidate for implant body area networks (BANs), where wireless communications are established between inside and outside of a human body. The UWB can accomplish higher data rate than the other frequency band for the implant communication. However, due to its high frequencies, the UWB signals suffer from quite large attenuation in the implant communication link, which makes it difficult to achieve reliable communications. For achieving reliable communication, it is well known that a spatial diversity technique is efficient without any frequency extension. In our previous works, we developed a transmit polarization diversity antenna for the UWB implant communication. However, optimal UWB modulation scheme for transmit diversity were rarely discussed. In this paper, in order to investigate the optimal UWB modulation schemes for implant communication with transmit diversity, we compare the communication performances of UWB-impulse radio (UWB-IR) and multiband-orthogonal frequency division multiplexing (MB-OFDM). For this purpose, we first analyze the propagation characteristics in the implant UWB channel, which ranges from 3.4 GHz to 4.8 GHz, using a finite difference time domain (FDTD) numerical analysis technique. Then, we evaluate and discuss the communication performances of both modulation schemes for the transmit polarization diversity from the viewpoint of the BER and the required transmit power.

A frequency domain multiple-antenna and channel estimation approach for facilitation of UWB technologies coexistence in heterogeneous WPANs

This paper presents an analysis of the performance of the multiband orthogonal frequency division multiplexing (MB-OFDM) system for ultra wideband (UWB) communication in the presence of interference from a single-carrier IEEE 802.16 WiMAX system operating in the 3.5 GHz band. The intent of our analysis is to provide theoretical justification for the commonly-used bandlimited Gaussian noise model for this type of interference. We present an exact analysis of the uncoded bit error rate (BER) of the MB-OFDM system, based on Laplace transform techniques. We also present a simple and relatively accurate Gaussian approximation for the WiMAX interference.

In this literature, we present a new method for estimating the coarse frequency offset in multi-band orthogonal frequency division multiplexing (MB-OFDM) based ultra-wideband (UWB) communication systems. The proposed training based coarse frequency offset (CFO) estimator performs an averaging of initial estimate over the multiple bands of transmission during estimation process. The proposed multi-band averaging provides an improved estimation of approximately three times for band group 1 (BG1) compared to our earlier proposed scheme. To prove the efficiency of the proposed scheme, the Cramer Rao lower bound (CRLB) of the estimation error is calculated and compared with the simulation results. We illustrate the performance of MB-OFDM system in terms of bit-error rate (BER) with multi-band averaged frequency synchronization (MBAFS) and compare with earlier reported results for 100,000 noisy realizations in UWB channel model 2 (CM2).

This A multi-band orthogonal frequency division multiplexing (OFDM) UWB system is the new proposal for the IEEE 802.15.3a standard for wireless high bit-rate personal area networks. Pulsed OFDM is an enhancement to the multi-band OFDM system that offers better performance with lower complexity and correspondingly reduced power consumption. In this paper, the implementation issues and pipeline structures of a pulsed OFDM transmitter are presented. In particular, architectural features of the system and its components are described and analyzed.