With the growing demand for mobile communications, multicarrier (MC) schemes are receiving an increasing amount of attention, primarily because they handle frequency selective channels better than ordinary single-carrier schemes. However, despite offering several advantages, MC systems have certain weak points. One is their high sensitivity to interchannel interference (ICI). The influence of Doppler shift and ICI are the focus of this paper. Newly proposed B3G/4G systems are developed for data transmission rates higher than those of the IEEE 801.11. It is then necessary that the bandwidth of the subcarrier be small. Moreover, for a higher carrier frequency and mobile speed, the influence of the Doppler shift will be large; therefore, the influence of ICI becomes severer. Using a Markov chain approach, we synthesized a turbo equalizer (TE) that minimizes ICI when interference affects the arbitrary number M of adjacent subchannels. This approach shows the complexity of the proposed algorithm exhibits linear growth with respect to M and independence with respect to the total number of subchannels in the multicarrier system. The proposed ICI cancellation scheme can also be effective in the case of multiple Doppler frequency offsets. This makes the proposed approach attractive for practical implementations.

This paper addresses several relevant issues in detection process of a reverse link multicarrier code division multiple access system with frequency offset. Due to the presence of frequency offsets, power of a group of subcarriers is spread to all the available subcarriers. In order to collect all the scattered signal power, we propose a two stages receiver. First stage of the proposed receiver performs maximum ratio combining. Following from the first stage, multiple access interference is suppressed in the second stage. We propose various multiple access interference suppression techniques, having different complexity and performance. Simulation results demonstrate the advantage of the proposed receiver. We also investigate the performance of 2 major subcarrier assignment schemes, namely continuous subcarrier assignment scheme and interleaved subcarrier assignment scheme, in both ideal independent fading channel and practical correlated fading channel.

This paper presents a new blind symbol timing recovery technique for OFDM systems. The proposed technique is based on modifying the conventional early-late loop used for single carrier systems. The new topology exploits the interference introduced by the loss of orthogonality due to symbol timing offsets. The new structure is completely non data-aided and is independent of the OFDM symbol structure. The new technique can extract symbol timing with carrier frequency offset up to 94% of the OFDM spectrum.

A new channel estimator that does not require a separate frequency offset estimator is proposed. The new algorithm has low complexity and low latency compared to the well-known weighted multi-slot averaging algorithm. The simulation results demonstrate the improved resistance to high Doppler frequency and high frequency offset.

Orthogonal frequency division multiplexing (OFDM) has been adopted in the physical layer of IEEE802.11a WLAN standard. In this Letter, a high-resolution frequency-offset estimation scheme is presented for the OFDM-based WLAN. The scheme efficiently exploits the features of the 802.11a preamble for high-resolution estimation of frequency-offset. Simulation results indicate that the algorithm is much superior to the conventional scheme for frequency-offset estimation in the 802.11a WLAN.

In this letter, a joint estimation algorithm of Doppler spread and frequency offset for OFDM systems in Rayleigh fading channels is proposed based on the autocorrelation function between the last part of the received OFDM signal and its copy in guard interval. It is shown by computer simulations that the proposed algorithm performs well for different Doppler spread values and carrier frequency offsets.

A robust joint symbol timing and fractional frequency offset estimator for OFDM systems in multipath fading channels is proposed based on cyclic shifting and autocorrelation properties of PN codes. A new timing metric is also introduced by considering the delay spread to improve the robustness of the estimator in the multipath fading channels.

In this paper, we present a new all-digital carrier recovery loop for high-order quadrature amplitude modulation (QAM) signal constellations. The proposed approach is a blind phase-frequency detector structure that consists of a phase detector, a phase offset estimator, a frequency offset estimator, and a digital control oscillator. Compared to previous related approaches, the proposed algorithm provides a wider acquisition range and a more accurate estimation of frequency and phase offsets. These features are demonstrated by simulation results of the DOCSIS (Data-Over-Cable Service Interface Specifications) cable modem system.

A sampling frequency offset estimation scheme for MB-OFDM UWB systems is proposed based on technical specification and multi-band utilization of the MB-OFDM. An estimation scheme using simple weighting factor based on the received signal power of each sub-channel is also introduced to efficiently combine estimates obtained from all the sub-carriers and to improve the estimation performance.

In order to simultaneously combat both of the inter-carrier interferences (ICIs) and multiple access interferences (MAIs) to achieve reliable performance in multi-carrier code division multiple access (MC-CDMA) systems, this letter proposes a maximum likelihood based scheme for joint frequency offset estimation and multiuser symbol detection. To reduce the computational complexity called for by the joint decision statistic without extra mechanisms, the genetic algorithm (GA) is employed to solve the nonlinear optimization involved. Due to the robustness of the GA, the joint decision statistic can be efficiently solved, and, as shown by furnished simulation results, the proposed approach can offer satisfactory performance in various scenarios.

We propose a DOA-Matrix based blind CFO estimation method for a MIMO-OFDM system with Virtual Carriers. The method estimates CFO in closed-form by jointly exploiting the shift-invariant structure of time-domain signal received on multiple receive antennas. In contrast to previous training-based methods, the proposed method is bandwidth efficiency. We also present numerical simulation results for different transmit and receive antenna configurations and for different record lengths.

The recent Internet needs a network structure and traffic engineering that can support various applications requiring differentiated traffic processing and a high quality of service. The extension of the Internet from wired to wireless systems that generate location-dependent and burst errors has made the support of good services more difficult with existing packet scheduling algorithms. Accordingly, this paper proposes a wireless differentiated service packet scheduling (WDSPS) algorithm that can provide reliable and fair services in differentiated wireless internet service networks. As such, the proposed scheduling algorithm solves the HOL blocking problem within a class packet queue that occurs in a wireless network, supports differentiated services for each class defined in a differentiated service network, and facilitates gradual and efficient service compensation not only among classes but also among flows within a class, thereby preventing a monopoly by one class or one flow. Simulations confirmed that the proposed WDSPS scheduling algorithm could provide the required QoS differentiation between classes and enhanced the service throughput under various wireless network conditions.

This paper presents a low-complexity equalization for M-ary biorthogonal keying based direct sequence ultra wideband (MBOK DS-UWB) systems. We focus on a Viterbi equalizer, which is based on maximum likelihood sequence estimation (MLSE). To reduce the computational complexity of MLSE-based equalizer, we use two strategies. One is the use of delayed-decision feedback sequence estimation (DDFSE), which is a hybrid estimation between MLSE and decision feedback estimation (DFE). And the other is the truncation of state transition in MLSE by considering MBOK pulse mapping. The reduced complexity sequence estimation is named as reduced state (RS)-DDFSE. By the use of RS-DDFSE, the complexity of Viterbi equalizer for MBOK DS-UWB is significantly reduced, by comparison with that of MLSE. The performance of RS-DDFSE based equalizer is evaluated on multipath fading channel models provided by IEEE802.15.3a. An analysis on trellis diagram of RS-DDFSE and simulation results show that the impact on error rate performance generated by the complexity lower is slight.

With the occurrence of new applications such as Voice over IP (VoIP) and multimedia conference, there is an ongoing discussion about realizing QoS in the Internet today. Because of its potential scalability in support of QoS guarantees, the Differentiated Service (DiffServ) architecture with aggregate packet scheduling has recently attracted much attention in the networking community as a feasible solution for providing Internet QoS. Thus, it is important to understand delay bound of an individual flow in the DiffServ architecture in order to provide delay-sensitive applications. In this paper, we study, via both analysis and simulation, the deterministic bound on edge-to-edge delay of a flow in a DiffServ network domain with FIFO aggregation and a class-based Latency Rate (LR) server that provides guaranteed performance with rate reservation for a traffic class. We derive edge-to-edge delay bound for a single flow as a function of allocated service rate for a traffic class, token bucket parameters adopted for flows at the network ingress, and information about joining and leaving flows. We compare the obtained delay bound with previous works using analytic results, and then conduct simulation to confirm the results. The derived bound is less than that of previous studies in all cases.

A robust time and frequency synchronization scheme is proposed for the high rate OFDM-based wireless local area networks (WLANs). The IEEE 802.11a standardized preamble is efficiently utilized and makes the proposed scheme practical. Simulation results under different channel environments are presented to illustrate the effectiveness of the proposed scheme.

A DC offset caused by self-mixing is a serious problem for direct-conversion receivers. Local oscillation (LO) leakage via quadrature demodulators (QDEMOD) must be suppressed in order to achieve a low DC offset. An LO buffer which drives QDEMOD mainly causes the LO leakage. We proposed an LO buffer which has a high-pass frequency response with small occupied area and low current consumption. A QDEMOD using the proposed LO buffer is fabricated using a SiGe BiCMOS process. Measured low LO leakage of -70 dBm is achieved, which is 10 dB lower than that of a QDEMOD with a conventional LO buffer. This measured result indicates that the proposed LO buffer is suitable for QDEMODs for direct-conversion receivers.

Screen pattern used in offset-printed documents has been one of great obstacles in developing document recognition systems that handle color documents. This paper proposes a selective smoothing method for filtering the screen patterns/noise in high-resolution color document images. Experimental results show that the method yields significant improvements in character pattern extraction.

In this letter, the problem of attaining frequency synchronization for high rate WPANs is considered. An estimation of the frequency offset is essential step at the receiver because the frequency offset means that the phase of transmitted signal is corrupted. The proposed algorithm utilizes the difference in phase between received preamble and estimated preamble. It turns out that the proposed algorithm has low complexity and good performance. To enhance the capability, we use peak phase detector. The performance of the proposed algorithm is assessed by computer simulation, and the frequency offset variance is compared to Cramer Rao Bound.

An even-harmonic mixer using a bipolar differential pair (bipolar harmonic mixer;BHMIX) is theoretically analyzed from the direct conversion point of view; i.e, conversion gain, third-order input intercept point (IIP3), self-mixing induced dc offset level, and second-order input intercept point (IIP2). Also, noise are analyzed based on nonlinear large-signal model, and numerical results are given. Noises are treated as cyclostationary noises, thus all the folding effects are taken into account. Factors determining IIP3, IIP2, dc offset, and noise are identified and estimation procedures for these characteristics are obtained. For example, design guidelines for the optimal noise performance are given. Measured results support all the analysis results, and they are very useful in the practical BHMIX design.

High-Speed High-Resolution Comparators are integral parts of very high-speed high-resolution Analog-to-Digital Converters (ADC). Parallel successive-approximation and flash ADCS can boost conversion rates while providing high resolution, provided that accurate and fast offset-cancelled comparators could be implemented. Moreover, accurate offset cancellation is needed in accurate gain stages of other types of high speed ADCs as well. This has never been easy and creates a bottle neck for high-speed high-resolution ADCs. The reason is that conventional offset cancellation methods, suffer either from inaccurate cancellation or from slow operation. Hence, either speed or accuracy is compromised. This is due to the trade off of gain (accuracy) for bandwidth (speed) in conventional methods. Here, we introduce a new offset cancellation method which satisfies the need for both high-speed and accurate offset cancellation simultaneously.