In this letter, we study the problem of designing an efficient power and bit allocation scheme in the context of a hierarchical image transmission system based on an embedded multi-carrier modulation (EMCM) scheme over digital subscriber line. Authors describe a novel algorithm that performs power minimization under bit rate constraint and QoS requirement. It is based on the Hughes-Hartogs algorithm, and successively allocates the bits of the high, then low priority data streams. Simulations that assess the performance of the proposed algorithm are also provided and discussed; they demonstrate the interest of the proposed scheme.

In this letter two noise-predictive equalization schemes, which are based on zero-forcing (ZF) and minimum mean square error (MMSE) criteria, are presented for unique-word (UW) based single-carrier systems. The correlation properties of the noises in the outputs of the frequency domain equalizer are exploited to predict and cancel the noise contained in the estimation of data. Theoretical analyses show that both of the proposed techniques perform better than the conventional frequency domain equalizers. Simulation results have confirmed the significant performance improvement they could achieve.

In this paper, we introduce a Parallel Interference Canceller (PIC) based on a sorting method to improve the performance in the MC-DS/CDMA environment. A conventional PIC estimates and cancels out all of the MAI (Multiple Access Interference) for each user in parallel. The parallel process ensures a limited delay for the detection of all users. Since the performance of PIC is strongly related to the correct MAI estimation, we introduce an interference cancellation scheme to estimate accurately the MAI of the weaker interferers than the desired signal. The principle of proposed IC (Interference cancellation) scheme is to sort in descending order from the strength of the signal and subtracted by the MAI of the strong interferer from the weak signal. Therefore, the signal of the weak interferer becomes a better estimation. Following this, the output of the front processing is achieved by a rank operation of the signals in an ascending order of strength. Then the strong signal eliminates the improved weak interferer. Resulting from this, the proposed scheme obtains a better BER performance than the conventional PIC, because the accuracy of the strong signal has been improved. However, a disadvantage exists in that the processing time has a slightly longer delay than the PIC-1stage owing to a two step processing, including the sorting one.

We have developed an open-architecture router (OAR) prototype using industrial standard hardware, software components, and interfaces. The prototype is built with Advanced Telecom Computing Architecture (ATCA)-compliant hardware. Carrier-grade Linux (CGL) is used as the operating system. A new OAR configuration method is described where industrial standard hardware and software interfaces are used. Basic forwarding functions with routing protocol processing are demonstrated for the first time.

We propose optical wireless multiple-input multiple-output (OMIMO) communications to achieve high speed transmission with a compact transmitter and receiver. In OMIMO, by using zero forcing (ZF), minimum mean square error (MMSE) or other detection techniques, we can eliminate the interference from the other optical transmit antennas. In this paper, we employ ZF as the detection technique. We analyze the signal-to-interference-plus-noise ratio (SINR) and the bit error rate (BER) of the proposed OMIMO with a linear array and a square array of optical transmit and receive antennas, where we employ subcarrier multiplexing (SCM) for each optical transmit antenna. Note that the proposed OMIMO is applicable to other arrangements of optical transmit and receive antennas. We show that the proposed OMIMO system can realize MIMO multiplexing and achieve high speed transmission by correctly aligning the optical transmit and receive antennas and the transmitter semiangle.

This letter evaluates the performance of an uplink multicarrier-code division multiple access (MC-CDMA) system when the frequency offsets of all users are random variables and the frequency offset for the desired user is compensated. The analysis confirms that performance degradation due to frequency offset is negligible if the estimation error of normalized frequency offset for the desired user is less than 10-1.

This paper examines the bit and power allocation problem for orthogonal frequency division multiplexing systems in which the overall transmission power is minimized by constraining the fixed data rate and bit error rate. To provide the optimal allocation with less computational complexity, we propose new bit and power allocation schemes based on the Lagrangian method. Firstly, we propose an initial search range of the bisection search method to find the optimal Lagrangian multiplier efficiently. The simulation results verify that the proposed initial search range guarantees the optimal solution with less computational complexity. Secondly, a new iterative search method for the optimal Lagrangian multiplier is proposed using Newton's search method. The simulation results demonstrate that the proposed scheme has significant computational advantages over the conventional algorithms while providing optimal performance.

We have proposed two space division multiple access (SDMA) approaches for OFDM signals: "Virtual Subcarrier Assignment (VISA)" and "Preamble Subcarrier Assignment (PASA)," both of which can enhance the system capacity without significant change of transmitter/receiver structures for already-existing OFDM-based standards such as IEEE802.11a. In order to investigate the performance of the proposed approaches in real wireless scenarios, we conducted a measurement campaign to obtain real channel state data at 5-GHz band in an indoor environment. Using the measured channel data, we can make the performance evaluation realistic. In this paper, after the brief overview of the two proposed SDMA approaches, we describe our measurement campaign in detail. Furthermore, we evaluate the performance of VISA-based system and PASA-based system by computer simulations using the measured channel state data and present a comparative study on the performance of the two proposed SDMA approaches in the realistic wireless environment.

In this letter, a novel pilot-aided inter-carrier interference (ICI) self-cancellation scheme is proposed for use in orthogonal frequency division multiplexing (OFDM) systems. The proposed scheme maps both modulated data symbols and pre-defined pilot symbols onto non-neighboring sub-carriers with weighting coefficients of +1 and -1. With the aid of pilot symbols, a more accurate estimation of frequency offsets can be obtained, and the ICI self-cancellation demodulation can be operated properly.

In this letter, we propose a partial minimum mean-squared error (MMSE) with successive interference cancellation (PMMSESIC) method in frequency domain to mitigate ICI caused by channel variation. Each detection, the proposed method detects the symbol with the largest received signal-to-interference-plus-noise ratio (SINR) among all the undetected symbols, using an MMSE detector that considers only the interference of several neithborhood subcarriers. Analysis and simulations show that it outperforms the MMSE method at relatively high Eb/N0 and its performance is close to the MMSE with successive detection (MMSESD) method in relatively low Doppler frequency region.

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 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.

In OFDM systems, employing a cyclic prefix (CP) as the guard interval is a simple way to combat the inter-symbol interference (ISI) and the inter-carrier interference (ICI), however it reduces the transmission efficiency of the system, especially for some channels with a very long delay spread. In this paper, we consider the OFDM system with insufficient CP, much more efficient than conventional OFDM systems. First, we present the system mathematical model and give the ISI and ICI analysis. Then the signal-to-interference power ratio (SIR) performance is presented. To reduce the ISI and ICI due to the insufficient CP, we develop a minimum-mean-square-error decision feedback equalizer (MMSE_DFE). Based on the MMSE criterion, the optimum feedforward and feedback filter coefficients are derived. For time-varying channel, to avoid brute force matrix inversion in conventional schemes, we propose an adaptive LMS based solution to update the filtering coefficients by tracing the channel variation. Since the high complexity of MMSE_DFE, a reduced complexity scheme, ordered successive partial interference cancellation DFE (OSPIC_DFE), is developed. From the performance comparison between the MMSE_DFE and the OSPIC_DFE, we see that the latter is very near to the former. Finally the simulation shows these proposed methods are highly effective in combating ISI and ICI with low complexity.

In this letter, new results on the BER performance of multitone DS-CDMA systems for transmissions over Nakagami-m fading channels with exponentially decaying multipath intensity profile are presented. The results show that, in viewpoint of the BER performance, there is a critical relation between the number of resolvable paths and the effect of the rate of average power decay.

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.

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.

OFDM-based networks utilizing the frequency reuse factor of 1 may produce the severe ICI (intercell interference) at the cell boundary even though overall cell capacity is increased and network deployment is facilitated. In the forward-link, the ICI may rise above a QoS (quality of service) threshold beyond some distance from BSs (base stations). In this paper, we analyze the forward-link capacity of an MC-CDMA system as a function of the ICI according to the distance from a cell. To achieve this goal, a closed form of the outage probability is derived and utilized to obtain the accommodated number of users and system parameters.

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.

In this paper, downlink performance of multicarrier CDMA (MC-CDMA) systems under correlated fading channels is analytically investigated. Under code hopping, a signal to interference plus noise ratio (SINR) and bit error rate (BER) performance are derived in multi-cell environments. In addition, specific conditions to validate the commonly used Gaussian approximation of an interference plus noise distribution in MC-CDMA systems are discussed. It is proved that the approximation is adequate in case of low correlation between subcarriers and a large spreading factor (SF). The proposition is confirmed through comparison between analytical and simulation results.

One of the drawbacks of multicarrier transmission schemes is that the transmitted signals have high peak-to-average power ratio (PAPR). When PAPR of the signal is larger than the input-back off (IBO) of the high power amplifier (HPA), signal powers larger than the saturation threshold of the HPA cause the saturation events so that the error rate performance is degraded. To improve the error-rate performance degraded by the nonlinear distortion, not only the signal power above the saturation threshold but also the interval of the signals causing the saturation events at HPA should be reduced. In this paper, we propose the total exceeding power (TEP) as a new criterion for improving the error rate performance degraded by the nonlinear amplifier for multicarrier transmission.