BER evaluation and rate matching attribute selection for QoS support on the UMTS downlink

In UMTS technology, Coded Composite Transport Channels (CCTrCh-s) are used to carry multiple Transport Channels (TrCh-s) in parallel on (usually) one physical layer connection. Rate Matching Attributes (RMA-s) are used to share the CCTrCh resources among the transport channels. We consider I transport channels on the downlink of a UMTS network, with RMA values RMA ₁,RMA ₂,…,RMA _I . The QoS experienced by the multiplexed connections depends on the RMA values used. We derive analytical expressions for the Bit Error Probabilities (BER-s) seen by each uncoded TrCh in the multiplex when transmitted over an AWGN and a multipath channel. Simulations indicate that the expressions are very accurate. Next, we derive analytical expressions for bounds on the per-channel bit error probabilities seen when convolutional coding is employed by each channel and the multiplex is transmitted over an AWGN and a multipath channel, respectively. The derivation of these analytical expressions is the main contribution of this paper. Further, we use the expressions to obtain simple procedures that provide the RMA values required to achieve a target set of BER-s for a specified signal-to-noise ratio. The results of this paper indicate how differentiated QoS may be provided while maintaining high spectral efficiency. R. M. Karthik is currently a Ph.D. candidate in the Centre for Electronics Design and Technology, Indian Institute of Science, Bangalore, India. He received his B. E. (Electronics and Communication Engineering) from Government College of Technology, Coimbatore, India in 1998 and M. E. (Applied Electronics) from College of Engineering, Guindy, Anna University, India in 2000. His current research interests include communication networks and QoS in UMTS Networks. Joy Kuri has a B.E. in Electronics and Telecommunication engineering from Jadavpur University, Kolkata. After a year in the industry, he joined the M.E. program in the Department of Electrical Communication Engineering at the Indian Institute of Science. He went on to receive a Ph.D. from the same department at IISc in 1995. Subsequently, he spent two years at Ecole Polytechnique, University of Montreal, Canada and one and a half years in INRS-Telecommunications, University of Quebec, Canada as a Research Associate. Since 1999 he has been with the Centre for Electronics Design and Technology, Indian Institute of Science, where he is currently Associate Professor. His research and teaching interests are in the areas of modelling, analysis and control of communication networks and stochastic systems. He is co-author of the book Communication Networking: An Analytical Approach by Kumar, Manjunath and Kuri, published by Morgan Kaufman/Elsevier.     

Application and performance of downlink beamforming techniques in UMTS

The opportunities and constraints for application of beamforming techniques in UMTS are reviewed and compared by means of extensive dynamic network-level simulations. We start by reviewing the physical layer specifications for UMTS in order to clarify which channels are allowed to use beamforming. Second, radio resource management for cells with beamforming capabilities are addressed from a standardization and algorithmic point of view. The exchange of beamforming specific measurement reports between the base station (Node-B) and the radio network controller is discussed as well as beam switching mechanisms, directional power-based admission control, and more. In addition to implementation of beamforming within logical cells, options for exploiting the antenna array to synthesize independent sector beams are also investigated (i.e., higher order sectorization via beamforming). The presented results show that beamforming within logical cells is an effective enabler for higher system capacity, while the use of beamforming for creation of many logical cells is less attractive due to significantly larger soft handover overhead and somewhat reduced capacity gain.     

Approximation of BER performance for adaptive 2-DPSK-RAKE receivers

A statistical model to evaluate the BER performance of an adaptive RAKE receiver in an urban mobile environment is presented. Path delay estimation using the maximum-likelihood estimation (MLE) technique is applied. The theoretical results are compared to computer calculations using the measured complex impulse responses of realistic mobile channels.<>     

Iterative low-complexity receiver for the UMTS downlink

In this paper, an iterative low-complexity receiver is proposed for Code Division Multiple Access (cdma) systems with small spreading factors. Theumts (Universal Mobile Télecommunication System) radio interface based oncdma has been designed to offer a wide range of data rates using variable spreading factors. High data rate services are obtained by using small spreading factors. For such services, the spreading sequences have bad autocor-relation properties causing the degradation of the Rake receiver performance because of the InterSymbol Interférence (isi). In order to improve the receiver performance, we propose to add a Decision Feedback Sequence Estimation (dfse) equalizer at the Rake receiver output. Thedfse is a low complexity equalizer which is able to take into accounta priori probability ratios and to deliver a posteriori probability ratios on bits in order to exchange soft information with the channel decoder, so that the proposed receiver benefits from the turbo-processing gains. Channel estimation is also treated in an iterative fashion. The complete receiver is well suited to theumts downlink system as it drastically reduces theisi while keeping a reasonable computational complexity.     

BER performance evaluation for CPFSK phase and polarizationdiversity coherent optical receivers

The following methods of continuous phase frequency shift keying (CPFSK) signal demodulation are compared for phase and polarization diversity receivers: single filter, dual filter, delay and multiply. Bit error rate (BER) values are obtained in each case showing that for negligible laser linewidths the delay demodulation method outperforms the dual-filter method by approximately 3 dB, and the single-filter method by 6 dB. Since the noise bandwidth for minimum-shift keying (MSK) and delay demodulation is approximately twice as small as for the other methods, one should add another 3 dB to get the gain for that modulation/demodulation method. The influences of nonzero laser linewidth, noise correlation, and the nonGaussian character of the probability density functions of the noise at the sampler are taken into account     

Bit error probability analysis for FRAMES WCDMA downlink receivers

The wide-band code-division multiple-access (WCDMA) concept FMA2 developed in the European Future Radio Wide-Band Multiple-Access Systems (FRAMES) project supports variable-data-rate transmission. The data rate can be altered by changing either the spreading factor or by using multiple spreading codes in parallel. In order to facilitate flexible changing of the data rate, variable-length orthogonal Walsh codes are used for channel separation, followed by the scrambling code. Optional short scrambling codes can be used if interference suppression is used. The downlink performance of the FMA2 system using both the conventional RAKE and LMMSE-RAKE receivers is studied. According to the numerical results, the performance of the conventional RAKE receivers is significantly degraded at the highest data rates, whereas the LMMSE-RAKE performs well in those cases also     

相关Nakagami衰落环境中的2D-Rake接收机的BER性能

分析了最大比合并(MRC)二维Rake(2D-Rake)接收机,在相关频率选择性Nakagarnl衰落环境中的平均误比特率(BER)特性。推导了在任意衰落环境中,存在多个共信道干扰的多天线多Rake抽头接收机的信干噪比(SINR)和BER的闭式表达式。文中还进一步说明了角度扩展、天线间隔、空间和时间分集阶数、平均到达角度、平均路径强度以及衰落程度对2D-Rake接收机BER性能的影响．     

Measurements of the performance degradation of UMTS receivers due to UWB emissions

Results of experimental trials performed to assess the coexistence of the UMTS systems and the UWB emissions are presented. The performance degradation of the UMTS system vs. the in-channel UWB interference power has been measured in terms of the bit error rate and the noise rise.     

Asymptotic analysis of optimum and suboptimum CDMA downlink MMSE receivers

In this paper, we investigate the performance of two linear receivers for code-division multiple-access (CDMA) downlink transmissions over frequency-selective channels, the users having possibly different powers. The optimum minimum mean-square error (MMSE) receiver is first considered. Because this receiver requires the knowledge of the code vectors attributed to all the users within the cell when these vectors are time varying, its use may be unrealistic in the forward link. A classical suboptimum receiver, consisting in a chip rate equalizer followed by a despreading with the code of the user of interest, is therefore studied and compared to the optimum MMSE receiver. Performance of both receivers is assessed through the signal-to-interference-plus-noise ratio (SINR) at their outputs. The analytical expressions of these SINRs depend in a rather nonexplicit way on the codes allocated to the users of the cell, and are therefore not informative. This difficulty is dealt with by modeling the users code matrix by a random matrix. Because the code matrices used in the forward link are usually isometric, the code matrix is assumed to be extracted from a Haar-distributed random unitary matrix. The behavior of the SINRs is studied when the spreading factor and the number of users converge to /spl infin/ at the same rate. Using certain results of the free probability theory, we establish the fact that the SINRs converge almost surely toward quantities that depend only on the complex amplitudes of propagation channel paths. We then use the expressions of these SINR limits to discuss the influence of the various parameters on the performance of the receivers.     

Analysis and optimization of pilot symbol-assisted Rake receivers for DS-CDMA systems

The effect of imperfect channel estimation (CE) on the performance of pilot-symbol-assisted modulation (PSAM) and MRC Rake reception over time- or frequency-selective fading channels with either a uniform power delay profile (UPDP) or a nonuniform power delay profile (NPDP) is investigated. For time-selective channels, a Wiener filter or linear minimum mean square error (LMMSE) filter for CE is considered, and a closed-form asymptotic expression for the mean square error (MSE) when the number of pilots used for CE approaches infinity is derived. In high signal-to-noise ratio (SNR), the MSE becomes independent of the channel Doppler spectrum. A characteristic function method is used to derive new closed-form expressions for the bit error rate (BER) of Rake receivers in UPDP and NPDP channels. The results are extended to two-dimensional (2-D) Rake receivers. The pilot-symbol spacing and pilot-to-data power ratio are optimized by minimizing the BER. For UPDP channels, elegant results are obtained in the asymptotic case. Furthermore, robust spacing design criteria are derived for the maximum Doppler frequency.     

Switched beams versus beam pointing for boosting the downlink capacity of UMTS FDD

In this paper the switched beam method is compared with beam pointing. Using extensive system simulations it is shown that both methods achieve a capacity gain over a 3-sectored reference system of more than 170%. As the capacity achieved with the two systems is nearly the same but the complexity of beam pointing is significantly higher, I conclude that switched beams are the appropriate method for boosting the downlink capacity of UMTS FDD.     

BER performance of 2D-RAKE receivers in DS-CDMA overfrequency-selective, slow Rayleigh fading channels

In this letter, we extend the method that has been proposed in the literature for calculating the bit error probability of two-dimensional (2D) RAKE receivers in asynchronous direct sequence code-division multiple access (DS-CDMA) over flat, slow Rayleigh fading channels to the case of frequency-selective, slow Rayleigh fading channels. We also compute and plot the lower bound on the performance that can be achieved in the above system     

Transmit-preprocessing techniques with simplified receivers for the downlink of MISO TDD-CDMA systems

Time-division-duplex code-division multiple-access (TDD-CDMA) systems have recently gained attention with their inclusion in third-generation mobile systems. In this paper, we introduce two optimized transmit preprocessing techniques to reduce multiple access interference in the downlink of TDD-CDMA systems with multiple transmit antennas that are employed at the base station (BS). In these systems, signal preprocessing is performed at the BS, so that a simplified receiver structure that consists of a one-finger correlator can be utilized at the mobile station. Analytic solutions for both of the optimized transmit preprocessing techniques are derived by minimizing the transmit mean square error. Numerical results are also provided, which demonstrate significant performance improvement when compared to the conventional RAKE system and the pre-RAKE maximum ratio combining transmit diversity system. In particular, transmit antennas can be used to increase the system capacity.     

LTE多用户下行吞吐量性能建模分析

针对LTE系统中多用户下行吞吐量难以预测的问题,从LTE 系统的时域和频域资源出发,结合用户位置、终端类型以及下行MIMO模式等内容,分析了多用户条件下时域和频域调度算法的特点、影响因素和作用过程。并在此基础上建立了多用户下行吞吐量分析和估算模型,进而应用此模型对具体实例进行了预测和分析,从而对多用户性能分析工作起到一定的指导作用。     

Performance analysis of discrete feedback schemes for downlink multiuser diversity in OFDMA systems

This paper analyzes discrete feedback of various feedback schemes for multiuser diversity in a multiple subchannel environment. In these schemes of full feedback, fixed feedback, adaptive feedback, and threshold-based feedback, users report a quantized discrete value to indicate their modulation and coding scheme instead of feeding back the full values of the channel state. A closed-form expression of the sum-rate capacity is developed to evaluate the feedback schemes. By comparing the feedback schemes in terms of the sum-rate capacity and the feedback load, this paper provides guidance for the selection of a feedback scheme. Additionally, a mixed-feedback scheme is proposed to reduce the amount of allocated feedback resources in the threshold-based feedback scheme, where the base station adjusts the capacity-feedback tradeoff by controlling two parameters, namely the number of subchannels and a threshold.     

Adaptive resource allocation for downlink grouped MC-CDMA systems with power and BER constraints

This paper proposes a complete solution to adaptively allocate resource for downlink Multi-Carrier Code Division Multiple Access (MC-CDMA) systems with the power and bit error rate (BER) constraints. Under frequency-selective fading channels, the whole spectrum is divided into several groups and each user is allocated to a group based on its channel state information (CSI). After grouping, the adaptive modulation algorithm assigns the bit loading and allocates the transmission power for each user according to its effective channel response. Simulation results show that the proposed solution can achieve high throughput, guarantee the required BER, and reduce the blocking probability.     

Large-system performance analysis of blind and group-blindmultiuser receivers

We present a large-system performance analysis of blind and group-blind multiuser detection methods. In these methods, the receivers are estimated based on the received signal samples. In particular, we assume binary random spreading, and let the spreading gain N, the number of users K, and the number of received signal samples M all go to infinity, while keeping the ratios K/N and M/N fixed. We characterize the asymptotic performance of the direct-matrix inversion (DMI) blind linear minimum mean-square error (MMSE) receiver, the subspace blind linear MMSE receiver, and the group-blind linear hybrid receiver. We first derive the asymptotic average output signal-to-interference-plus-noise ratio (SINR) for each of these receivers. Our results reveal an interesting "saturation" phenomenon: The output SINR of each of these receivers converges to a finite limit as the signal-to-noise ratio (SNR) of the desired user increases, which is in stark contrast to the fact that the output SINR achieved by the exact linear MMSE receiver can get arbitrarily large. This indicates that the capacity of a wireless system with blind or group-blind multiuser receivers is not only interference-limited, but also estimation-error limited. We then show that for both the blind and group-blind receivers, the output residual interference has an asymptotic Gaussian distribution, independent of the realizations of the spreading sequences. The Gaussianity indicates that in a large system, the bit-error rate (BER) is related to the SINR simply through the Q function     

采用小波变换的OFDMA系统误码性能分析

针对LTE下行链路,建立一种基于小波变换的OFDMA(Wavelet Transform based Orthogonal Frequency Division Multiple Access,W-OFDMA)系统,克服频偏和相位噪声带来的不良影响,提升系统的误码性能.将小波作为系统的正交子载波,利用滤波器组的级联形式实现小波变换,取代原系统的快速傅里叶变换.利用Simulink建立W-OFDMA系统基带模型,分析比较高斯信道下基于不同小波的W-OFDMA系统的误码性能,并与传统的OFDMA系统进行比较.仿真结果表明,sym4小波为W-OFDMA系统的最佳子载波,且基于sym4的W-OFDMA系统的误码性能优于传统的OFDMA系统.     

MQAM-WPM-FH多载波跳频通信系统误码率性能分析

为了分析多进制正交幅度调制(MQAM)映射方式、小波滤波器长度和小波包树结构对小波包跳频通信系统（WPM-FH）的影响,首先利用多进制幅移键控(MASK)和MQAM之间的关系,推导了MQAM-WPM-FH系统在加性高斯白噪声(AWGN)信道中的误码率理论公式,分析了不同小波滤波器长度和小波包树结构对WPM-FH系统的影响。理论分析和仿真结果表明,与正交频分复用跳频（OFDM-FH）系统相比,MQAM-WPM-FH系统具有较高频带利用率和较好的性能;在给定带宽下,通过增大MQAM数据映射中的星座点数M和小波滤波器长度L,可以有效降低多址干扰(MAI)对系统的干扰;AWGN信道下,不同的小波包树结构对跳频系统的性能影响较小,但小波包调制结构的多样性可以提高系统的安全性。     

BER performance analysis of a direct conversion receiver

Direct conversion receivers are increasingly popular for use in mobile terminals. This is due to advantages over other architectures such as heterodyne receivers in terms of cost, electrical current, and physical size. However, a direct conversion receiver often generates a DC-offset that has to be taken care of either by suppressing the DC-offset in the radio-frequency part of the receiver, or by taking care of it during baseband processing. A theoretical analysis of the bit error rate (BER) performance in a direct conversion receiver with different levels of DC-offset suppression is presented. Explicit results are presented on how the BER depends on the signal-to-noise ratio (SNR), the signal-to-DC-level, and the choice of pilot symbols both with M-QAM and M-PSK in a slow, flat Rayleigh fading channel. A design rule, which applies to the design of DC-compensation in direct conversion receivers, is also presented