Current-mode techniques for UWB frequency synthesizers

A design of a 5.6 GHz frequency synthesizer with switched bias LIT VCO and low noise on‐chip LDO regulator for 5G applications

This paper presents investigation of the impact of electro-absorption modulator integrated laser (EML) on performance of multiband-orthogonal frequency-division-multiplexing (MB-OFDM) ultra wideband (UWB) signal over single-mode fiber transmission by theoretical and experimental analysis, considering various parameters, such as fiber length, bias voltage, modulation power, bias current, and temperature of EML. The effect of the EML modulation nonlinearities on the OFDM subcarriers in MB-OFDM UWB over fiber system is investigated considering intermodulation distortion (IMD) and adjacent channel power ratio. It is shown that MB-OFDM UWB over fiber is limited by SNR for small modulation power and EML modulation nonlinearities induced IMD for high modulation power. Fiber transmission length is mainly degraded by EML phase noise converted relative intensity noise and power fading. The developed theory is verified by experiments.

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.

Multi-band Orthogonal Frequency Division Multiplexing (MB-OFDM) is an efficient approach for Ultra Wideband (UWB) wireless communication applications. However, the high Peak to Average Power Ratio (PAPR) of MB-OFDM UWB signals, limits the power efficiency of the Solid State Power Amplifier (SSPA) due to nonlinear distortion caused by high PAPR. Hence, it is necessary to reduce the PAPR of MB-OFDM UWB signals. In this paper, we used a tunable Pre-Distorter (PD) based on the High Power Amplifier (HPA) characteristics for PAPR reduction of MB-OFDM UWB signals. The PD configuration is self-tuning, i.e., it can automatically readjust itself by tracking changes in the HPA characteristics with very few (typically two) training symbols. Through Computer simulations, the performance of the predistorter is evaluated in comparison with filtering after clipping, and clipping with turbo coding for PAPR reduction. The Bit-Error Rate (BER) is used as performance measure in this evaluation.

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.

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.

As a competitive solution to the short-range high data-rate communication, Multi-Band Orthogonal Frequency Division Multiplexing (MB-OFDM) Ultra-wideband (UWB) technique can obtain further performance improvement with the use of adaptive resource allocation schemes. In this paper, an incremental bit allocation algorithm is proposed for MB-OFDM UWB system, which aims at minimum bit error rate (BER) under constant rate constraint while complying with the spectral mask limit. The BER performance improvement and transmission distance extension due to this algorithm is evaluated by employing a simulation model based on MB-OFDM proposal.

A unified low complexity sign-bit correlation based symbol timing synchronization scheme for Multiband Orthogonal Frequency Division Multiplexing (MB-OFDM) Ultra Wideband (UWB) receiver system is proposed. By using the time domain sequence of the packet/frame synchronization preamble, the proposed scheme is in charge of detecting the upcoming MB-OFDM symbol and it estimates the exact boundary of the start of Fast Fourier Transform (FFT) window. The proposed algorithm is implemented by using an efficient Hardware-Software co-simulation methodology. The effectiveness of the proposed synchronization scheme and the optimization criteria is confirmed by hardware implementation results.

The impact of electromagnetic noises from a PC on the bit error rate (BER) performance of a multiband orthogonal frequency division multiplexing (MB-OFDM) ultra wideband (UWB) communication system equipped on the PC is analyzed. The results of numerical simulation indicate that the PC noise consisting of the harmonic components of the PC clock causes considerable bit error rate (BER) degradation in the UWB system particularly those systems operated in high data-rate communication modes. It is also found that the frequency modulation of a PC clock signal, the so-called spread spectrum clocking (SSC), has no effect on mitigating BER degradation, although SSC techniques are commonly used in PCs for reducing the power spectral density of radiated noise. An interference mitigation scheme using Viterbi decoding with channel state information (CSI) is proposed on the basis of a novel receiver structure in which a reference PC clock signal is fed into the UWB receiver by the PC in order to accurately estimate the instantaneous frequency of interfering clock harmonics.

This paper derives the theoretical bit error rate (BER) of the multiband orthogonal frequency division multiplexing (MB-OFDM) system for ultra wideband (UWB) communication. The proposed derivation takes into account the fading correlation caused by time and frequency spreading, which is one of the most significant factors in MB-OFDM UWB system. Moreover, the proposed formula gives consideration to the frequency characteristics of propagation loss that are not negligible in UWB systems. The theoretical results by the proposed approach are compared with the computer simulation results in order to confirm the validity of the proposed derivation.

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.

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

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.

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.

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.