A new computationally efficient discrete bit-loading algorithm for DMT applications

This letter presents a new bit-loading algorithm for discrete multitone systems that converges faster to the same bit allocation as the optimal discrete bit-filling and bit-removal methods. The algorithm exploits the differences between the subchannel gain-to-noise ratios in order to determine an initial bit allocation and then performs a multiple-bits loading procedure for achieving the requested target rate. Numerical results using asymmetric digital subscriber test loops demonstrate the computational efficiency of the proposed algorithm.     

Multiuser bit loading for multicarrier systems

A multiuser bit-loading problem is investigated in multicarrier communication systems. Assuming knowledge of all the channel gains, we propose a multiuser bit-loading algorithm that attempts to minimize the total power to transmit a target rate-sum of all users. It is shown that this algorithm is optimal when the interference among users is nonexistent or strong. The simulation results show that the proposed algorithm finds a near-optimal solution for very-high-speed digital subscriber line systems.     

A multi-user power control algorithm for digital subscriber lines

The paper investigates the power control problem in a frequency-selective interference channel. A centralized power control algorithm is developed with the objective of maximizing the achievable rate region given an average power constraint for each user. The proposed algorithm is based on the multi-user discrete bit-loading algorithm that considers the power allocation over frequency and users simultaneously. Simulation results for very high-speed digital subscriber line (VDSL) systems show that the proposed algorithm achieves a larger rate region than that achieved by a power control algorithm based on iterative waterfilling.     

Optimal Discrete Bit Loading for DMT-Based DSL Systems With Equal-Length Loops

This letter examines a discrete bit-loading problem of upstream and downstream for discrete multitone digital subscriber lines with echo cancellation. Both far-end crosstalk and near-end crosstalk are taken into account. An optimal discrete bit-loading algorithm is developed when the loop lengths of all same-service users in a common binder are the same. Simulation results show that the optimal algorithm achieves a substantially higher data rate than existing suboptimal schemes.     

下行多用户CoMP系统资源分配算法

针对下行多用户多点协作传输系统(MU-CoMP)边值自适应(MA)的问题,提出了一种快速资源分配算法。该算法首先根据用户的速率要求及平均信道增益估计出每个用户需要的子载波数目,在此基础上设计合理的子载波分配算法进行子载波分配,通过预判并且剔除不适合传输数据的较差空间子信道实现快速比特加载。仿真结果表明,所提算法在满足用户最低速率和误码率要求的前提下有效地降低了总发射功率,以较低的复杂度获得了接近最优算法的性能。     

Overhead reduction in rate-adaptive MAC over OFDM-based wireless networks

While many researchers have focused on bit-loading algorithm itself, proposed here is an implementation method of the bit-allocation in terms of layer-2 protocol. A novel protocol is presented to implement a bit-allocation over time-varying wireless channels by using as small an overhead as only one OFDM symbol.     

基于天线阵元功率限制MIMO系统的自适应调制

本文研究了天线阵元的发射功率受限MIMO系统。在信道准静态和系统发端已知信道信息的假设下,我们研究了该受限MIMO系统性能。在系统优化分析基础上,设计了一种简单的Bit分配方案进行系统自适应调制逼近系统容量。仿真结果表明该系统能更好接近真实环境,调制方案有较好性能。     

Ordered subcarrier selection algorithm for OFDM-based high-speed WLANs

In this letter, a low-complexity and low-overhead adaptive bit-loading algorithm for wireless multicarrier schemes is proposed and analyzed. It is based on the diversity gain obtained through the ordering and selection of the more reliable subcarriers. Higher order modulations are used to compensate for the reduced subcarrier utilization. On the contrary to other bit-loading algorithms, it does not require nonuniform bit and power level allocation among subcarriers, thus drastically reducing the modem hardware complexity and making it attractive as a possible extension of existing high-speed wireless local-area network standards. System performance is analyzed in different configurations and conditions, including a realistic 5-GHz propagation scenario. Comparison with optimal adapted and unadapted solutions is also made. Finally, the effect of unideal feedback of the channel state information is analyzed showing the robustness and the low overhead required of the new scheme.     

Bit- and power-allocation algorithm for symmetric operation ofDMT-based DSL modems

Discrete multi-tone (DMT) based digital subscriber loop (DSL) modems must allocate power and information bits to the discrete tones for quadrature amplitude modulation. The bit allocation (also referred to as bit-loading) algorithms in the literature are designed for modems that operate in the simplex mode in which the upstream and downstream signals use nonoverlapping frequency bands. However, greater data transmission capacity can be achieved by using overlapping frequency bands and echo cancelled duplex operation. The conventional bit-loading algorithms are not well suited for the allocation of data bits for transmission in the duplex mode, and the problem of bit loading for duplex operation has not yet been considered in the literature. This article introduces an algorithm suitable for echo-canceled duplex DMT modems that use overlapping frequency bands for upstream and downstream transmissions for the purpose of transmitting equal data rates in both directions. Moreover, the algorithm performs the bit loading while jointly minimizing a weighted sum of the power used by the central office and the customer premise transmitters. Simulation results are included to show the higher data rates that are possible with the duplex operation as a function of varying levels of echo return loss enhancement     

Fast bit-loading algorithm for DMT systems

In this paper, a novel solution to bit-loading algorithm for Discrete MultiTone modulation (DMT) systems is proposed. Simulation results, using the carrier serving area (CSA) loops in an ADSL environment impaired by crosstalk, show that the proposed algorithm converges more rapidly than the Campello algorithm, which is the fast algorithm that can be efficiently implemented in practice among those proposed in the past.     

基于循环相关的扩展空间解相关算法及其模式检测中的应用

针对空域扩展空间解相关(spatial extended spatial decorrelation;SESD)算法对参数选择鲁棒性差的缺点,使用一维循环相关操作代替原二维平移相关操作,提出了一种基于循环相关的扩展空间解相关(extended spatial decorrelation based- on cycle correlation;ESDBCC)算法。在无噪和有噪环境下,研究了SESD算法与ESDBCC算法对参数选择的鲁棒性,结果表明ESDBCC算法有以下两个显著优点:1)与二维平移相关操作相比,一维循环相关操作更适合计算机计算,从而降低了计算量;2)在有噪和无噪环境下,ESDBCC算法对参数选择的鲁棒性都要明显好于SESD算法。     

Symbol-error rate analysis of Fischer's bit-loading algorithm

We obtain an analytical result for the symbol-error rate of a wireless orthogonal frequency-division multiplexing system employing Fischer's bit-loading algorithm. First we assume that the subchannel coefficients are statistically independent, then we extend the results to the case with dependent subchannel coefficients. Throughout the analysis, we assume that the number of subchannels is large, and that subchannels have Rayleigh-distributed coefficients. The comparison of analytical and simulated results shows that the approximation error is small, especially at low noise and high bit rate.     

Adaptive Loading Algorithm Implemented in AMOOFDM for NG-PON System Integrating Cost-Effective and Low-Bandwidth Optical Devices

We experimentally investigate the transmission performance of a novel modulation based on a recently proposed technique of adaptively modulated optical orthogonal frequency- division multiplexing (AMOOFDM) for next-generation passive optical network (NG-PON). This signal was generated by direct modulation of cost-effective and low-bandwidth commercially available distributed-feedback and vertical-cavity surface-emitting lasers. Using the Levin–Campello adaptive bit-loading algorithm for channel capacity optimization over AMOOFDM modulation to reach maximum transmission performance, we experimentally demonstrated that high bit rate can be transmitted in optical access network without the need for chromatic dispersion compensation and optical amplification on the link.      

基于时延分数阶相关函数时空处理的子空间测向算法

本文定义了一种时延分数阶相关函数和阵列输出信号的时延分数阶相关矩阵,在此基础上,提出了一种新的基于时延分数阶相关函数时空处理的了空间测向算法一时延分数阶相关MUSIC(TLFOC-MUSIC)算法。该算法在进行空域处理的同时,引入了时域处理,弥补了空域信息的不足,更充分地开发了空间信号中的有用信息,提高了算法的稳健性和测向的性能,对SαS噪声和干扰有较强的抑制作用。计算机仿真实验结果验证了该算法的有效性和稳健性。     

Fractal image compression based on spatial correlation and hybrid genetic algorithm

In order to solve the high complexity of the conventional encoding scheme for fractal image compression, a spatial correlation hybrid genetic algorithm based on the characteristics of fractal and partitioned iterated function system (PIFS) is proposed in this paper. There are two stages for the algorithm: (1) Make use of spatial correlation in images for both range and domain pool to exploit local optima. (2) Adopt simulated annealing genetic algorithm (SAGA) to explore the global optima if the local optima are not satisfied. In order to avoid premature convergence, the algorithm adopt dyadic mutation operator to take place of the traditional one. Experiment results show that the algorithm convergent rapidly. At the premise of good quality of the reconstructed image, the algorithm saved the encoding time and obtained high compression ratio.     

Reductions of peak-to-average power ratio and optical beat interference in cost-effective OFDMA-PONs

The peak-to-average power ratio (PAPR) and optical beat interference (OBI) effects are examined thoroughly in orthogonal frequency-division multiplexing access (OFDMA)-passive optical networks (PONs) at a signal bit rate up to $\sim 20\,\mathrm{{Gb}}/{\hbox {s}}$ per channel using cost-effective intensity-modulation and direct-detection (IM/DD). Single-channel OOFDM and upstream multichannel OFDM-PONs are investigated for up to six users. A number of techniques for mitigating the PAPR and OBI effects are presented and evaluated including adaptive-loading algorithms such as bit/power-loading, clipping for PAPR reduction, and thermal detuning (TD) for the OBI suppression. It is shown that the bit-loading algorithm is a very efficient PAPR reduction technique by reducing it at about 1.2 dB over 100 Km of transmission. It is also revealed that the optimum method for suppressing the OBI is the TD + bit-loading. For a targeted BER of $1 \times 10 ^{-3}$ , the minimum allowed channel spacing is 11 GHz when employing six users.     

Spatial scales of tropical precipitation inferred from TRMM microwave imager data

The local spatial scales of tropical precipitating systems were studied using Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) rain rate imagery from the TRMM satellite. Rain rates were determined from TMI data using the Goddard Profiling (GPROF) Version 5 algorithm. Following the analysis of Ricciardulli and Sardeshmukh (RS), who studied local spatial scales of tropical deep convection using global cloud imagery (GCI) data, active precipitating months were defined alternatively as those having greater than either 0.1 mm/h or 1 mm/h of rain for more than 5% of the time. Spatial autocorrelation values of rain rate were subsequently computed on a 55/spl times/55 km grid for convectively active months from 1998 to 2002. The results were fitted to an exponential correlation model using a nonlinear least squares routine to estimate a spatial correlation length at each grid cell. The mean spatial scale over land was 90.5 km and over oceans was 122.3 km for a threshold of 0.1 mm/h of rain with slightly higher values for a threshold of 1 mm/h of rain. An error analysis was performed which showed that the error in these determinations was of order 2% to 10%. The results of this study should be useful in the design of convective schemes for general circulation models and for precipitation error covariance models for use in numerical weather prediction and associated data assimilation schemes. The results of the TMI study also largely concur with those of RS, although the more direct relationship between the TMI data and rain rate relative to the GCI imagery provide more accurate correlation length estimates. The results also confirm the strong impact of land in producing short spatial scale convective rain.     

Optimal precoding for orthogonalized spatial multiplexing in closed-loop MIMO systems

In this paper, we propose a new precoding algorithm for orthogonalized spatial multiplexing (OSM) systems over flat-fading multiple-input multiple-output (MIMO) channels. The OSM scheme was recently introduced for closed-loop MIMO systems which allows single symbol decodable maximum likelihood detection. To further improve the performance of the OSM system, we propose a new precoding method by maximizing the minimum Euclidean distance between constellation points in the effective channel. In order to efficiently identify the parameters of a precoder which maximizes the minimum distance, we introduce a partitioning approach. Through analysis, it is shown that one real value parameter and two bits are required for feedback information for precoding in 16-QAM systems. Simulation results demonstrate that our algorithm provides 9 dB and 7.5 dB gains at a bit error rate (BER) of 10^-4 over the conventional OSM systems for 4-QAM and 16-QAM, respectively. We also confirm that the performance of the proposed scheme is the same as that of the optimum closed-loop MIMO systems in terms of the minimum distance. Consequently, our precoding algorithm significantly improves the system performance with a small increase of feedback amount.     

A new parallel greedy bit-loading algorithm with fairness for multiple users in a DMT system

This letter first reviews the multiuser bit-loading algorithms for discrete multitone systems. Then an improved algorithm is proposed, which allows several users to get additional bits in parallel. It reduces the number of iterations dramatically. A new fairness coefficient is also introduced to reduce the variance of the data rate among users.     

Improving power efficiency of coded OFDM with feedback

Coding with diversity is one of the keys to reliable wireless communication over fading channels. Adaptive modulation can provide additional performance improvement which may be significant when the channel diversity orders are small. In this letter, we propose adaptation algorithms for improving the power efficiency of coded orthogonal frequency division multiplexing (OFDM) on fading channels. We derive simple power-loading and bit-loading algorithms for achieving a fixed throughput and reliability with minimal transmitter power. We illustrate the performance of our schemes using simulations.