One of the key issues in the next generation Internet is end-to-end Quality of Service (QoS) provisioning for real-time applications. The Differentiated Services (DiffServ) architecture offers a scalable alternative to provide QoS in the Internet. However, within this architecture, an efficient scheduling mechanism is still needed to ensure such QoS guarantees. In this paper, scheduling mechanism for supporting QoS differentiation among multiple traffic classes in IP differentiated services networks is studied. A scheduling algorithm called Multiclass Efficient Packet Fair Queueing (MEPFQ) is proposed that enables fair bandwidth sharing while supporting better bounds on end-to-end network delay for QoS-sensitive applications such as voice over IP (VoIP) within the DiffServ framework. The mechanism allows to create service classes and assign proportional weights to such classes efficiently according to their resource requirements. Besides, MEPFQ tries to ensure that packets from low priority class will not be starved even under extreme congestion cases. The results from the simulation studies show that the mechanism is able to ensure both the required end-to-end network delay bounds and bandwidth fairness for QoS-sensitive applications based on the specified service weights under various traffic and network conditions. Another important aspect of the MEPFQ algorithm is that the scheme has lower implementation complexity, along with scalability to accommodate the growing traffic flows at the core routers of high-speed Internet backbone.

This paper presents a blind frequency offset estimation method for Polynomial Cancellation Coded Orthogonal Frequency Division Multiplexing (PCC-OFDM) systems. We have theoretically derived the frequency offset estimator. The estimation exploits the Subcarrier Pair Imbalance (SPI) which is presented in terms of the power difference between two demodulated subcarriers in a PCC-OFDM subcarrier pair. The estimator can be used for high order QAM modulation schemes. In all cases, the estimator has an approximately linear relationship with the frequency offset. The potential application of the estimator in conventional OFDM systems is also investigated in this paper.

In this letter, a concise formula for the SNR degradation of OFDM caused by carrier frequency offset is derived by approximations over a shadowed two-path channel, which explicitly shows the sensitivity of SNR degradation to various parameters including the frequency offset. It is shown that, for small frequency offset, the SNR degradation is proportional to the square of the frequency offset and the square of the number of subcarriers. It is also shown that, if Es/N0 is reasonably large, the SNR degradation becomes insensitive to Es/N0, which is contrary to the case of the AWGN channel.

The detection performance of coherent OFDM receivers significantly depends on the accuracy of channel estimation. The accuracy of channel estimation can be improved by properly post-processing the channel estimate using a so-called channel estimation filter (CEF). Minimum mean-squared error (MMSE) filter is known optimum as the CEF, but it may not be practical due to its implementation complexity. We consider the use of a reduced-complexity CEF whose tap coefficient is real-valued and symmetrically weighted (RSW). The optimum RSW CEF is analytically designed using the SNR and multi-path intensity profile of the channel. For further improvement, we also propose a method to adapt the coefficient of the RSW CEF to the channel condition. Numerical results show that the proposed RSW CEF can provide channel estimation performance comparable to that of linear MMSE filter, while significantly reducing the computational complexity. In addition, the proposed RSW CEF can provide performance robust to unknown timing offset with a fractional dB loss compared to the optimum one.

In this paper, a novel algorithm is presented for blind estimation of the symbol timing and frequency offset for OFDM systems. Time-varying frequency-selective Rayleigh fading multipath channel is considered, which is characterized by the power delay profile and time-varying scattering function and has high reliability for real-world mobile environment. The estimators exploit the intrinsic structures of OFDM signals and rely on the second-order moment rather than the probability distribution function of the received signals. They are totally optimum in sense of minimum mean-square-error and can be implemented easily. In addition, we have presented an improved approach which not only preserves the merits of previously proposed method, but also makes the estimation range of the frequency offset cover the entire subcarrier spacing of OFDM signals and the timing estimator be independent of the frequency offset.

In order to investigate the sensitivity of fast frequency hopping-multiple access (FFH-MA) systems due to the frequency offset under Rician fading, we evaluate the bit error rate (BER) performance of the FFH-MA system using noncoherent M-ary frequency shift keying (FSK) with the hard decision decoding and the majority logic decision. Numerical results show that for satisfying the BER performance of 10-5 at a given normalized frequency offset of 0.2, the additional signal to noise ratio (SNR) of about 4 dB is required with the 8-ary FSK signaling compared to the case of the perfect frequency synchronization. While the frequency offset increases at a given SNR, the BER is more severely degraded, and subsequently, the BER performance is saturated at the normalized frequency offset of 0.5 regardless of fading environments. For the SNRs of more than 15 dB, the threshold level of the receiver suffering from normalized frequency offsets of less than 0.4 should be larger than that of the perfectly frequency synchronized receiver.

This letter addresses the performance degradation due to carrier frequency offset in an orthogonal frequency and code division multiplexing (OFCDM) systems with multiple transmit antennas. For the performance evaluation, the average bit error rate (BER) expression is derived taking account of the effect of a carrier frequency offset. Derived results show that the BER performance of the space-time coded OFCDM system is less sensitive to a frequency offset, compared to the normal OFCDM system.

In this letter, we present a normalized least-mean-square algorithm of blind estimator for carrier frequency offset estimation of orthogonal frequency division multiplexing systems. In conjunction with the closed-loop estimate structure, the proposed efficient algorithm eliminates the inter-carrier interference for time varying carrier frequency offset. The proposed algorithm offers faster convergence speed and more accuracy to the carrier frequency offset estimate. Several computer simulation examples are presented for illustrating and effectiveness of the proposed algorithm.

In this letter, the effect of an imperfect channel estimation and carrier frequency offset on the performance of transmit diversity OFDM systems is investigated. For the performance evaluation, the average bit error rate (BER) expression is derived in the presence of the imperfect channel information including both the inherent estimation error and the imperfect windowing error derived in a mismatched channel separation.

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 a high sensitivity to interchannel interference (ICI). Using a Markov chain approach, we synthesized an optimal receiver for a situation where interference affects three adjacent subchannels. Simulation results showed that the proposed 'turbo scheme' provided better BER performance than a conventional receiver, especially at higher signal-to-noise ratios. The implementation of the turbo algorithm is independent of the transmitted signal, providing complete OFDM reception compatibility.

The coarse frequency offset estimation algorithm has to provide an initial frequency error estimate, which is sufficiently accurate in order to operate reliably for the subsequent fine frequency synchronization algorithm. In this letter, we deal with a coarse frequency offset estimation for digital audio broadcasting. We propose an improved frequency synchronization scheme which uses the minimum energy detection scheme. We compare the performance of proposed scheme with that of conventional schemes under AWGN and Rayleigh channel. It has been shown that the proposed algorithm has high robustness against a large range of symbol timing offset with a low complexity.

This paper proposes the IMADF (improved multiplication-free adaptive digital filter) algorithm to cancel the background noise that spans nearly all frequency bandwidths in biomedical signals. Under conditions of zero-mean, wide-sense stationary and white Gaussian noise, we analyze the convergence characteristics of the IMADF with a FSE (fractionally-spaced equalizer). In the experimental results, the IMADF algorithm has the advantage in which has superior to a condition of low-frequency and slow data speed. This application gives an important significance in ensuring the objectivity of clinical information and in promoting the representation and the disease diagnosis.

We describe a low-cost and extremely stable millimeter-wave transmission system that uses a double-side-band (DSB) millimeter-wave self-heterodyne transmission technique. This technique allows us to use a comparatively low-cost and unstable millimeter-wave oscillator regardless of the modulation format. Furthermore, a transmission band-pass-filter (BPF) is not needed in the millimeter-wave band. The system cost can therefore be substantially reduced. We have theoretically and experimentally evaluated the carrier-to-noise power ratio (CNR) performance that can be obtained when using this technique relative to that attainable through a conventional millimeter-wave self-heterodyne technique where a single-side-band signal is transmitted. Our results show that the DSB self-heterodyne transmission technique can improve CNR by more than 3 dB.

The OFDM technique has recently received considerable attention in the fields of wireless LAN communication systems. It is accompanied with many practical issues and one major issue is synchronization. In this letter, we propose a frequency offset estimation technique for OFDM system. The proposed frequency offset estimator employing interpolation technique in the frequency domain has a simple structure and good performance.

This paper proposes a wireless scheduling algorithm that can provide the Internet with delay proportional differentiated services in wireless networks. When considering wireless network environments that include burst and location-dependent channel errors, the proposed WDPS (Wireless Delay Proportional Service) scheduling algorithm can adaptively serve packets in class queues based on the delivered delay performance for each class. The significant characteristics of the WDPS scheduler include support for a fair relative delay service, the provision of graceful throughput and delay compensations, and the avoidance of class queue-blocking problems. Simulations show that the proposed algorithm can achieve the desirable properties for providing delay proportional services in wireless networks.

Beaulieu has proposed four signal-to-noise ratio (SNR) estimators for quadrature phase shift keying (QPSK) signaling in time domain. In this letter, we propose SNR estimators for QPSK signaling in frequency domain. A discrete Fourier transform (DFT) algorithm is used for the frequency domain analysis of the received signal. The frequency spectrum enables biased SNR estimation in the frequency domain. Circular convolution is used for robust and fast SNR estimation when the received signal exhibits a frequency offset. Simulation results show that the new estimators present good performance even when the received signal exhibits a large frequency offset.

A parallel current-mode multilevel identifying circuit for flash memories is proposed. The sensing scheme based on the CMOS cross-coupled structure modified from the clamped bit-line sense amplifier achieves high speed and low power dissipation. The offset of the proposed sense amplifier due to mismatch is also reduced significantly. The circuit has been fabricated using 0.6 µm CMOS technology. The simulation and measurement indicate the sensing speed reaches 1 ns at 3 V supply voltage with average power consumption about 2 mW at 50 MHz.

This paper describes a low-power-supply 2-GHz CMOS up-converter. A current-mode mixing method using current adding and self-switching mixers is proposed for 1-V operation. The current-mode up-converter achieves conversion gain of 6.7 dB and linearity of 6.5-dBm OIP3 at 1 V. Balanced configuration and DC offset canceller reduce LO leakage below -40 dBc even with 20-mV Vth mismatches. The bias circuit of the IC is designed to maintain constant conversion gain for variation of temperature for practical usage. The measurement results indicate the proposed up-converter is applicable for future wireless systems.

This paper proposes a novel synchronization method of jointly estimating symbol frame timing and carrier frequency-offset for Orthogonal Frequency Division Multiplexing (OFDM) signal operating in the burst mode which is usually employed in the wireless LAN communications systems. The proposed method enables a fast and accurate synchronization for the burst mode OFDM signal even under the presence of large frequency-offset, very low C/N and frequency selective fading environments by using only two preamble symbols inserted at the start of every burst frame. This paper presents the various computer simulation results to verify the performance of proposed synchronization methods both for symbol timing and carrier frequency.

This paper presents a cell search scheme embedded with carrier frequency synchronization for inter-cell asynchronous orthogonal frequency-division multiplexing code-division multiplexing (OFDM-CDM) systems. Several subcarriers are dedicated to a differentially encoded synchronization channel (SCH). In the other subcarriers, data symbols and pilot symbols are two-dimensionally spread in the time-frequency domain. The cell search scheme consists of a three-stage cell search and a two-stage carrier-frequency synchronization, that is, coarse carrier-frequency acquisition, fast Fourier transform window-timing detection, SCH frame-timing detection, fine carrier-frequency synchronization, and cell-specific scrambling code (CSSC) identification. Simulation demonstrated that this scheme can identify the CSSC with high detection probability while precisely synchronizing the carrier frequency in severe frequency-selective fading channels.