Multiband Orthogonal Frequency Division Multiplexing Research Articles

Cross-layer multiple-access optimization scheme for linear precoded OFDM UWB systems

With the growing demand for new wireless applications accompanied with high expectations for better QoS fulfillment especially for multimedia and real-time applications, the performance of the radio resource management in a multiuser context is ensured by the ability to provide an efficient and optimized spectrum sharing scheme that should respect the wireless channel conditions and satisfy the different users’ demands. From the physical layer perspective, metrics such as spectrum efficiency and minimum BER are the most important criteria to be considered. On the other hand, from a user perspective, QoS as well as fairness among the competing users are the main metrics because they determine how much end-users are satisfied and how efficient the available resources are shared among the existing users. Based on the use of the linear precoded orthogonal frequency division multiplexing (LP-OFDM) solution proposed as an evolution of the well-known multiband OFDM (MB-OFDM) solution supported by the WiMedia Alliance for future high-rate ultra-wideband (UWB) systems, the objective of this paper is twofold. First, we study a multiuser optimization spectrum sharing scheme for LP-OFDM systems. Second, based on the optimization study, we define a novel multiple-access solution which jointly considers the frequency resource allocation and the time scheduling for the high-rate LP-OFDM UWB systems. Simulation results demonstrate the efficiency of the use of the LP-OFDM transmission technique in the multiuser spectrum sharing scheme. Besides, the novel multiuser time–frequency sharing scheme shows its capacity to provide a high performance level for high-priority users.

Performance Analysis of Multiband OFDM System Over Ultra Wide Band Channels Using Kalman Filter

In this paper a modified version of Saleh-Valenzuela (S-V) channel model has been proposed for Ultra Wide Band (UWB) Orthogonal Frequency Division Multiplexing (OFDM) system and the performance has been estimated. In the proposed model, Poisson process has been modified for ray arrival rate and found that the proposed model is optimum for modeling ray arrival rate as compared to S-V model. Also Nakagami fading distribution has been considered in UWB channel model which suits for time varying multipath radio environment. The performance of the proposed channel model has been statistically analyzed over multiband OFDM by considering frequency domain channel estimation technique. The estimated coefficients have been tracked using Kalman filter technique and found that it gives more accurate prediction of channel coefficients as compared with Least Squares and Minimum Mean Square Estimation channel estimation techniques.

Peak to Average Power Ratio Reduction in ECMA-368 Ultra wideband Communication Systems Using Active Constellation Extension

Multiband Orthogonal Frequency Division Multiplexing (MB-OFDM) is an efficient approach for The ECMA-368 Ultra Wideband (UWB) wireless communication Standard. However, the high Peak to Average Power Ratio (PAPR) of MB-OFDM UWB signals, limits the power efficiency of the High Power Amplifier (HPA) due to nonlinear distortion. Hence the need to reduce the PAPR of MB-OFDM UWB signals. In this paper, the efficiency of some recently proposed methods including the Active Constellation Extension Approximate Gradient-Project technique (ACE-AGP) is evaluated in real ECMA-368 communication system, with the use of typical HPA models and the UWB channel models defined in IEEE 802.15.3a standard. The PAPR measure and the bit error rate (BER) are used as performance measures in this evaluation.The results indicate that the ACE-AGP algorithm introduces a significant reduction of PAPR about 6.7 dB and reduces the BER degradation in all UWB channel models with different data rates.

On the Perfomance of Multiband OFDM under Log-normal Channel Fading

On the Perfomance of Multiband OFDM under Log-normal Channel Fading

A polarity comparison timing synchronization estimation for MB-OFDM-based UWB systems

Abstract We propose a new approach for timing synchronization estimation with polarity comparison for multi-band orthogonal frequency division multiplexing (MB-OFDM)-based UWB systems. We attempt to locate the start sample of frame sequences by calculating difference of the two cross-correlation functions, between received symbols, the successive received symbols, and predefined preamble sequence. It makes sense to propose polarity comparison and identification ideas to the scenario, the cross-correlation difference exceeding predefined threshold is not unique. If polarities of selected symbols are not all the same, the estimator is put forward to find out a peak of correlation summation to figure out the unique timing point and promote synchronization accuracy. Uniqueness and accuracy of timing synchronization, therefore, could be guaranteed. The performance of the proposed estimator is evaluated by mean square error (MSE) and synchronization probability. The proposed estimator could carry out timing synchronization for MB-OFDM-based UWB systems and make the uniqueness of timing index for sure. The MSEs of the proposed estimator are evidently lower than the reference method for a great deal. Total and exact synchronization probability could get as much as 100 and 96%.

Iterative Sampling Frequency Offset Estimation for MB-OFDM UWB Systems With Long Transmission Packet

A multiband orthogonal frequency-division multiplexing (MB-OFDM) system, which is one of the effective modulation techniques that have been adopted for high-speed ultrawideband (UWB) systems, is very sensitive to sampling frequency offset (SFO) due to the mismatch between local oscillators at the transmitter and the receiver. In this paper, we propose an iterative SFO estimation method for a high-data-rate MB-OFDM UWB system to improve its SFO estimation accuracy in the case of a long transmission packet. The proposed method is an iterative process of 2-D SFO estimation across pilot subcarriers and consecutive OFDM symbols, together with joint channel estimation. Furthermore, we derive the Cramer-Rao lower bound (CRLB) for the proposed SFO estimation method. This CRLB can be used as a guide for algorithm design and to explore the theoretical limit. Our performance analysis and simulation results show that the proposed iterative SFO estimation method is both practical and effective.

Symbol Timing Estimation in Multiband Orthogonal Frequency Division Multiplexing based Ultrawide band System

Problem statement: The Multiband Orthogonal Frequency Division Multiplexing (MB-OFDM) Based Ultra Wideband system (UWB) is highly susceptible to symbol timing error. Symbol timing estimation in MB-OFDM based UWB is difficult due to the presence of strongest path at delayed instant. Approach: Symbol timing estimation has two steps namely a coarse estimation and a fine estimation. In this study, a maximum likelihood framework for the fine timing estimation is proposed. It utilizes the delay embedded in the estimated Channel Impulse Response (CIR) obtained from the cross correlation of training sequence with the received sequence. Results: The performance of the proposed method is analyzed in terms of probability of correct timing detection. It is observed that the proposed technique has better probability of correct timing detection performance compared to the existing algorithm, in all the UWB channel models proposed by IEEE 802.15.3a working group for UWB systems. Conclusion: A novel method to estimate fine symbol timing error for MB-OFDM based UWB system is proposed. This method will be suitable for MB-OFDM receivers for UWB positioning and UWB communication.

Multi-band OFDM for underwater acoustic communications

For underwater acoustic communications (UAC), the bandwidth is wide compared with the carrier frequency. Because of this fact, the advantages of using multiband OFDM (MB-OFDM) for ultra-wideband communications in terrestrial environments may also apply to UAC scenarios. In this paper, a comparison is made between the use of single-band OFDM and MB-OFDM for UAC. The complexity of each method is shown and experimental results from the WHOI09 undersea trial are presented for both single-band and multiband schemes. From the analysis and experimental results, the validity of treating UAC as ultra-wideband can be determined and the comparative advantages and disadvantages of MB-OFDM versus single-band OFDM for UAC discovered.

A Frequency Offset Estimation and Compensation Scheme for MB-OFDM UWB Modem

We present a carrier and sampling frequency offset estimation and compensation scheme for a multi-band orthogonal frequency division multiplexing (MB-OFDM) ultra-wideband (UWB) modem. We first perform initial carrier frequency offset (CFO) estimation and compensation during the preamble period, and then conduct the estimation and compensation of the residual CFO and sampling frequency offset (SFO) during the payload period. The proposed design scheme reduces the logic gate count of the frequency offset compensation block by about 10%, while it gives almost the same performance at the packet error rate (PER) of 10-4 in the CM1 channel. The frequency offset estimation and compensation block is implemented using 90nm CMOS technology and tested.

Performance analysis of High Speed ADC using SR F/F

This paper present a new design of comparator for flash ADC . The flash ADC is the fastest Application ADC that requires the high speed comparator. The new design consist of sense amplifier and SR Latch ,the combining configuration of design have the considerable stable output which helps in high speed and resolution. The use of SR symmetric latch makes stable output as compared to the conventional SR latch moreover the design has high resolution. This paper has been done in 180 nm and 90nm gpdk in CADENCE VIRTUOSO. For low power application. There are many issues in the design of the comparator, we will discuss those design issues in this paper. I. Introduction The design of comparator is the most critical part in the flash ADC, since the speed and the resolution is determined by the comparator. The dual tail current sense amplifier based comparator can run faster with lower supply voltage than the normal one, and the kick back effect is also better than the normal one. The symmetric S-R latch provides shorter delay time and stable time than the normal S-R latch. Combing the sense amplifier based comparator and the symmetric S-R latch, the whole block can run faster and the output signal is more stable than the normal structure. This design of comparator is for 2GSample/sec flash ADC. Based on IEEE 802.15.3a WPAN UWB applications, the signals using multi-band orthogonal frequency division multiplexing (MB-OFDM) occupy a bandwidth of 528MHz for every band. It requires the conversion rate at least higher than 1.06GSample/sec. 1.1. The Analysis Of The Traditional Sense Amplifier Based Comparator And Sr Latch: In the analysis of any comparator there are 2 stages in which operation is divided, one is reset phase and other is regeneration phase. In this sense amplifier based comparator sense amplifier connects positive feedback with the resistive input as shown in fig.1.Now during reset phase when clock is low, the nodes of inverters (M1-M4) are charged to Vdd, through transistor M7 and M8. Again on regeneration phase when clock is high Nmos transistor M9 is turned on which is a part of differential pair M5 and M6. Current flowing through this pair controls the latch circuit and small changes between differential pair cause large output change. And this differential pair discharge the node Ni, and later difference of the input voltage will built charge it. When Ni come to Vth voltage then inverter M1,M3 turns on and this wil start the positive feedback. After Ni comes to 2Vth below Vdd transistor M2,M4 are turn on. Now with the help of strong positive feedback small input converted to full differential output. For the generation of output there is very short period of time in sense amplifier when its gain is good.so switch M11 ,M12 is added to increase the integration time. In the conventional sense amplifier, it is better to add a reset switch (M11, M12) connecting the Vdd and the Di so as to increase the integration time . In the sense amplifier there is only a very short time in which the differential pair actually have the gain. Actually the differential pair comes to triode region during Ni drop to Vth. This reset transistor also increase the active time of differential pair and decrease the offset effect in coming signals.

Combined Time Synchronization And Channel Estimation For MB-OFDM UWB Systems

Symbol timing error amounts to a major degradation in the system performance. Conventionally, timing error is estimated by predefined preamble on both transmitter and receiver. The maximum of the correlation result is considered the start of the OFDM symbol. Problem arises when the prime path is not the strongest one. In this paper, we propose a new combined time and channel estimation method for multi-band OFDM ultra wide-band (MB-OFDM UWB) systems. It is assumed that a coarse timing has been obtained at a stage before the proposed scheme. Based on the coarse timing, search interval is set (or time candidates). Exploiting channel statistics that are assumed to be known by the receiver, we derive a maximum a posteriori estimate (MAP) of the channel impulse response. Based on this estimate, we discern for the timing error. Timing estimation performance is compared with the least squares (LS) channel estimate in terms of mean squared error (MSE). It is shown that the proposed timing scheme is lower in MSE than the LS method.

Throughput enhancement using synchronization and three-dimensional resource allocation

Emerging multimedia applications require more bandwidth and strict QoS requirements. To meet these in wireless personal area networks, WiMedia multiband-orthogonal frequency division multiplexing (MB-OFDM) has been designed while consuming low-transmission power. In this article, we increase the wireless bandwidth of the standard MB-OFDM scheme three times using device synchronization, and consider resource allocation policies to deal with the increased bandwidth. Then, we apply the proposed allocation policies with some operation rules to support prioritized QoS traffic. Extensive simulations verify that the synchronized MB-OFDM triples the throughput of the standard MB-OFDM, and the considered allocation policies with the considered operation rules run effectively as desired.

Adaptive low-rank channel estimation for multi-band OFDM ultra-wideband communications

In this paper, an adaptive channel estimation scheme based on the reduced-rank (RR) Wiener filtering (WF) technique is proposed for multi-band (MB) orthogonal frequency division multiplexing (OFDM) ultra-wideband (UWB) communication systems in multipath fading channels. This RR-WF-based algorithm employs an adaptive fuzzy-inference-controlled (FIC) filter rank. Additionally, a comparative investigation into various channel estimation schemes is presented as well for MB-OFDM UWB communication systems. As a consequence, the FIC RR-WF channel estimation algorithm is capable of producing the bit-error-rate (BER) performance similar to that of the full-rank WF channel estimator and superior than those of other interpolation-based channel estimation schemes.

Channel estimation in ECMA-368-based UWB systems with unknown interference

Ultra-wideband (UWB) is one of the fledging paradigms that the next generation of wireless personal area network (WPAN) is developing towards. With its appealing dimensions, UWB communication comes with a set of challenges of which channel estimation is prominent. In this article, we explore the problem of channel estimation in ECMA-368-based multiband orthogonal frequency division multiplexing (MB-OFDM) UWB system affected by unknown narrowband interference (NBI). We analytically show that the unknown NBI causes larger variance of a channel estimator. Thus, MB-OFDM UWB systems are supposed to experience significant performance degradation. To reduce this effect, we follow a new preamble-based channel estimation approach, where the interference power on each subcarrier is treated as a nuisance parameter which is averaged out from the corresponding likelihood function. The later is then optimized in an iterative manner according to the quasi-Newton algorithm. Furthermore, we address highly-accurate channel estimation in a time-variant channel and propose an iterative interpolation method. Simulation results indicate that our proposed approaches provide more precise estimation performances than those offered by conventional channel estimation methods.

Outage and BER Analysis for Ultrawideband-Based WPAN in Nakagami- $m$ Fading Channels

This paper presents a performance analysis of multiband orthogonal frequency-division multiplexing (MB-OFDM) in ultra wideband (UWB)-based personal area networks (UPANs). A UPAN consists of devices with different UWB technologies at the physical layer. Approximate expressions for the outage probability and average bit error rate (BER) are derived in closed form for the MB-OFDM target receiver, taking into account multi-user interference (MUI), as well as external interference in the form of time-hopping (TH) and direct-sequence (DS) UWB signals.

Cost-effective 33-Gbps intensity modulation direct detection multi-band OFDM LR-PON system employing a 10-GHz-based transceiver

We develop a dynamic multi-band OFDM subcarrier allocation scheme to fully utilize the available bandwidth under the restriction of dispersion- and chirp-related power fading. The experimental results successfully demonstrate an intensity-modulation-direct-detection 34.78-Gbps OFDM signal transmissions over 100-km long-reach (LR) passive-optical networks (PONs) based on a cost-effective 10-GHz EAM and a 10-GHz PIN. Considering 0-100-km transmission bandwidth of a 10-GHz EAM, the narrowest bandwidth is theoretically evaluated to occur at ~40 km, instead of 100 km. Consequently, the performances of 20-100-km PONs are experimentally investigated, and at least 33-Gbps capacity is achieved to support LR-PONs of all possible 20-100-km radii.

A multi-band OFDM ultra-wideband SoC in 90 nm CMOS technology

We present a multi-band orthogonal frequency division multiplexing (MB-OFDM) ultrawideband (UWB) system on chip (SoC) for high speed wireless communications. The UWB SoC has a power management scheme to minimize the average power consumption and adopts hardware-efficient parallel processing architecture to reduce the logic gate count of the modem. Specifically, symbol synchronization block is implemented with the signed algorithm; automatic gain control (AGC), carrier frequency offset (CFO) estimation, and preamble delimitation check block share the eight complex multipliers during preamble transmission; and AGC, fast Fourier transform (FFT), symbol synchronization, CFO estimation, and preamble delimitation check blocks share the buffer which contains received symbols. This SoC adopts a 32-bit reduced instruction set computer (RISC) processor for high speed data transaction and supports universal serial bus (USB) 2.0 and secure digital input/output (SDIO) for host interface. The designed SoC is implemented with 90 nm CMOS technology with a core voltage of 1.2 V. The implemented chip size is about 5 mm x 5 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sup> .

초광대역 시스템의 계층변조 기반 적응적 듀얼 홉 전송 기법

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.

Blind frequency-offset tracking scheme for multiband orthogonal frequency division multiplexing using time-domain spreading

A blind scheme for estimating the residual carrier-frequency offset of multiband orthogonal frequency division multiplexing (MB-OFDM)-based ultra-wideband (UWB) systems is proposed. In the MB-OFDM UWB system, time-domain spreading (TDS) is used by transmitting the same information across two adjacent OFDM symbols. By using the TDS structure, the proposed frequency estimation scheme does not require the use of pilot symbols. To demonstrate the usefulness of the proposed estimator, analytical expression of the mean square error is derived and the performance is compared with a conventional pilot-assisted estimator.

Preamble-based improved channel estimation for multiband UWB system in presence of interferences

Interferences reduce the performance of a correct data signal detection and decoding. This problem becomes severe when interferences exist during the period of channel estimation. This will destroy the accuracy of channel estimation and will eventually result severe degradation in the performance of signal detection and decoding in the entire data packet/frame. In this article, we propose an improved channel estimation technique for multiband orthogonal frequency division multiplexing (MB-OFDM) ultra-wideband (UWB) system in presence of interferences. In particular, we work towards a preamble-based channel estimation technique in multi-access and narrowband interfering environments. We construct two preamble symbols with opposite, both in amplitude and phase, sequences in frequency-domain. Time-domain redundancy (TR) is introduced into these preamble symbols before transmission. Based on this time-domain redundancy property, we eliminate multi-access interference (MAI) through an adaptive select and replace (ASR) scheme. We show that the use of opposite sequences in preambles leads a simple addition, subtraction and compare (ASC) scheme to cancel narrowband interference (NBI). In addition, we apply a frequency-domain filter, driven by channel's power delay profile (PDP), to get a further enhancement in the estimation accuracy. Simulation results urge that our proposed technique outperforms the conventional channel estimation methods.