Capacity unbalance between uplink and downlink in spectrallyoverlaid narrow-band and wide-band CDMA mobile systems

In this paper, we discuss capacity unbalance between uplink (mobile-to-base) and downlink (base-to-mobile) in future code division multiple access (CDMA) radio networks where both narrow-band and wide-band CDMA systems are coexisted. Since the two links are not operated in an identical condition, their capacities are unequal and either of the links determines the whole system capacity. The purpose of this paper is to examine which link limits the system capacity and what are the limiting factors. To facilitate the examination, “transmission capacity” and “connection capacity” are defined, and simplified formulas are presented to compute those capacities, respectively for uplink and downlink. Signal quality required for each link, effectiveness of power control, spatial distribution of mobile users and other-cell as well as same-cell user interference are usually determining the limiting link. Besides, the traffic unbalance between the links imposed by specific service applications and the network evolution scenarios are also shown to be very influencing factors     

Capacities of spectrally overlaid single-code and multicode CDMA systems

This paper is concerned with the capacities of spectrally overlaid narrowband and wideband systems using two code-division multiple-access (CDMA) techniques - single-code and multicode. The capacity is defined here as the maximum achievable total throughput in the narrowband and wideband subsystems. User signal power in the overlay systems affects the performance of the systems. The signal power is characterized as the relative power level of wideband and narrowband users according to the spreading bandwidth, spectral overlay ratio, and the number of spreading codes assigned to a user in single-cell and multiple-cell environments. The capacities of the overlay systems are then analyzed. The results of the analysis show that the single-code technique yields better performance than the multicode scheme in terms of the capacities of the overlay systems. Furthermore, the use of a multicode technique for wideband subsystems and a single-code scheme for narrowband subsystems is desirable for enhancing the performance of CDMA overlay systems.     

Adaptive nonlinear filters for narrow-band interference suppressionin spread-spectrum CDMA systems

This paper presents a novel nonlinear filter and parameter estimator for narrow band interference suppression in code division multiple access spread-spectrum systems. As in the article by Rusch and Poor (1994), the received sampled signal is modeled as the sum of the spread-spectrum signal (modeled as a finite state independently identically distributed (i.i.d.) process-here we generalize to a finite state Markov chain), narrow-band interference (modeled as a Gaussian autoregressive process), and observation noise (modeled as a zero-mean white Gaussian process). The proposed algorithm combines a recursive hidden Markov model (HMM) estimator, Kalman filter (KF), and the recursive expectation maximization algorithm. The nonlinear filtering techniques for narrow-band interference suppression presented in Rusch and Poor and our proposed HMM-KF algorithm have the same computational cost. Detailed simulation studies show that the HMM-KF algorithm outperforms the filtering techniques in Rusch and Poor. In particular, significant improvements in the bit error rate and signal-to-noise ratio (SNR) enhancement are obtained in low to medium SNR. Furthermore, in simulation studies we investigate the effect on the performance of the HMM-KF and the approximate conditional mean (ACM) filter in the paper by Rusch and Poor, when the observation noise variance is increased. As expected, the performance of the HMM-KF and ACM algorithms worsen with increasing observation noise and number of users. However, HMM-KF significantly outperforms ACM in medium to high observation noise     

Capacity analysis of spectrally overlaid multiband CDMA mobilenetworks

The future (third-generation) mobile communications system will provide not only voice and low-speed data services, but also video and high-speed data services. It will eventually have the capability for wireless multimedia communications. As a radio-access technique for such a system, the code-division multiple access (CDMA) has been considered in many potential third-generation systems including CODIT and the proposal of Ohno, Sawahashi and Adachi (see Proc. IEEF VTC'95, Chicago, IL, p.779-83, 1995). We model those CDMA systems as the spectrally overlaid multiband CDMA (SOM-CDMA) system. In an SOM-CDMA system, several CDMA (sub)systems with different spreading bandwidths are spectrally overlaid with each other. The reverse-link capacity of an SOM-CDMA system is calculated, and some numerical results are presented with discussion. As a result, we demonstrate how much capacity the SOM-CDMA has and how we can achieve an optimal allocation of frequency and power between (sub)systems. The results can be used as a guideline in designing the radio network of SOM-CDMA systems as well as a means to assess the performance of given systems. The results can be applied to any CDMA system with an SOM-CDMA concept, including CODIT and the proposal of Ohno et. al     

Combined multiresolution (wide-band/narrow-band) spectrogram

Existing speech spectrograms-the wideband spectrogram and the narrowband spectrogram-are either deficient in time or frequency resolution. The authors present a method to combine the two spectrograms by evaluating the geometric mean of the corresponding short-time Fourier transform magnitudes. The combined spectrogram preserves the desirable visual features of the originals     

Capacity analysis of spectrally overlaid macro/microcellular CDMA systems supporting multiple types of traffic

The reverse link capacity of a spectrally overlaid macrocell/microcell cellular code-division multiple-access system supporting various types of traffic is analyzed. Several narrowband subsystems are overlaid with a wideband subsystem in macrocells, while in a microcell, a single narrowband subsystem is operated with the same spectrum as one of the macrocell narrowband subsystems. Using a typical propagation model, the reverse link signal power and interference are characterized as the relative user signal power and the cross-tier interference factors between the macrocell and the microcell, considering various system parameters. The reverse link capacity of the overlay system is then analyzed. Results show that the dominant parameters affecting the system performance are the spectral overlay ratio and the distance between the microcell and macrocell base stations. In particular, when the distance equals half of the macrocell radius, optimum performance can be achieved by minimizing the cross-tier interference factors. These results can be applied to network planning for future wireless communication services.     

Approximate analysis of narrow-band interference rejectiontechnique in CDMA spread spectrum systems using nonlinear predictionfilters

The performance of code-division multiple access (CDMA) spread spectrum systems using nonlinear prediction filters in the presence of narrow-band interference is approximately analyzed. Closed-form approximate analytical expressions for the performance improvement are derived. Also, the closed-form approximate analytical results are compared with simulated results by numerical examples. The comparison results show that the analytical results are valid when the interference bandwidth is small     

Time-varying narrow-band interference rejection in asynchronousmultiuser DS/CDMA systems over frequency-selective fading channels

In this paper, we handle the problem of joint suppression of multiple-access interference (MAI) and narrowband interference (NBI) in fading, dispersive channels. The detectors we consider are linear, one-shot structures, which allow for possible window enlargement and signal-space oversampling to improve performance. We focus on both zero-forcing and minimum-mean square-error design strategies, showing that the presence of NBI generally requires a time-varying processing of the observables, no matter what the optimization criterion. A thorough performance assessment of the proposed detectors is also presented, either through analytical formulas or through computer simulations. We finally deal with the problem of blind suppression of both MAI and NBI, introducing batch-estimation procedures to be implemented offline, which require very little and sometimes no prior knowledge as to the interference structure     

Combined multidimensional signaling and transmit diversity forhigh-rate wide-band CDMA

Multidimensional signaling is newly designed to provide a diversity gain of order 2 using two transmit antennas in uplink transmission of wide-band CDMA (W-CDMA) while achieving high and multiple data rates at the same time. The rate can be easily changed on the slot basis in a frame transmission by adapting the order of multidimensional signaling to the incoming traffic. The multidimensional signaling of order zero simply reduces to conventional multicode scheme, so there exists a tradeoff between rate and complexity. Also, the use of multidimensional signaling results in far reduced envelope variations at the maximum rate. With the transmit diversity, the uplink signal-to-interference ratio (SIR) will be further stabilized to meet the requirements of multimedia traffic. Statistics of interferences are characterized in terms of their second- and fourth-order moments from which diversity gain is theoretically verified. For realistic multipath fading channels, considering both equal and unequal average path powers, the average probability of symbol error is obtained in compact form, in which the two schemes, multidimensional signaling with and without transmit diversity are compared, and then with nonmulticode scheme in view of the bit error rate (BER). Numerical and simulation results show that the multidimensional signal with transmit diversity provides a significant gain over that with no diversity, and furthermore outperforms nonmulticode scheme subject to the same signal energy per bit and chip rate     

Accurate computation of wide-band response of electromagneticsystems utilizing narrow-band information

Cauchy's technique for interpolating a rational function from samples of frequency responses and/or their derivatives is investigated. This technique can be used to speed up the numerical computations of parameters, including input impedance and RCS of any linear time-invariant electromagnetic system. This technique is utilized to find the far field of a slit conducting cylinder (TM incidence) over a bandwidth utilizing the information about the current and its derivatives at a few sample points. The numerical results are presented are in good agreement with exact computational data. This technique is a true interpolation/extrapolation technique as it provides the same defective result as the original electric field integral equation at a frequency which corresponds to the internal resonance of the closed structure     

Analysis of time-frequency duality of MC and DS CDMA for multiantenna systems on highly time-varying and wide-band channels

Direct sequence (DS) and multicarrier (MC) are code-division multiple-access (CDMA) schemes based on single-carrier and MC modulations, respectively. While in DS CDMA, spreading is performed by increasing the transmission rate, or in the time domain, in MC CDMA, spreading is performed using several subcarriers, or in the frequency domain. In this paper, it is shown that MC and DS CDMA are time-frequency dual systems. Their analysis in time- and frequency-dispersive multiple-input multiple-output channels revealed that they can be described equally in terms of dual-channel functions, therefore exhibiting the same performance on dual channels. Furthermore, the duality property is used to derive matched filters for highly time-variant and wide-band channels. Finally, other issues involved in the comparison of DS and MC, namely spreading-sequence design and multiuser detection, are addressed.     

Analytical investigation on sharing band overlaid high altitude platform station-terrestrial CDMA system

Uplink inter-system interference factor for sharing band overlaid high altitude platform stations (HAPS) and terrestrial CDMA system has been investigated. A simple model is proposed and key parameters affecting the interference factor are identified. The results suggest that appropriate design of the system could provide reasonable sharing capacity.     

宽带CDMA信道中的智能天线测试平台的设计与分析

在宽带CDMA WLL的环境中，使用波束形成模块(BFM)设计智能天线系统，并分析了其性能。波束形成模块是由DSP(TMS320C6701)电板实现的。首先，给出计算机仿真的结果，这些结果通过由基带信号处理设备组成的测试平台系统产生的模拟接收(RX)信号获得，包括模拟接收(RX)信号生成的PC、计算最优化加权矢量的BFM及接口模块。然后，用基站测试平台系统去评估实际信号的自适应波束形成功能。测试平台包括多用户、RF模块，以及其他相关设备。     

宽带变多通道窄带信号检测高速目标算法

高速目标的宽带信号回波产生的目标距离走动会导致传统动目标检测相参积累信噪比损失较大. Keystone变换以及相关改进算法虽然能够校正目标距离走动, 但该类算法需要预先估计目标较为精确的多普勒速度, 难于应用到实际工程中.文中采用一种宽带线性调频信号变多通道窄带信号处理方法, 在没有目标速度先验知识的情况下, 能够对高速目标回波信号能量进行有效积累, 从而提高目标检测性能.给出了算法框图, 经仿真验证该方法有效.     

GSM-CDMA双模系统设计

目前的大多数的双模系统都是由两个CPU组成,为了保证整个系统的稳定性,那么两个CPU的通信就尤其重要。详细地讨论了一种GSM/CDMA的双模系统的交互和开关机流程的解决方案。这种方案能够使GSM和CDMA两个模块在稳定工作的前提下,实现稳定的通信和协同。     

Spectrally efficient MSK scheme for SCPC communication systems

A spectrally efficient scheme is described, for SCPC (single channel per carrier) communication systems, in which slightly modified MSK (minimum shift keyed) channels can be allowed to overlap spectrally, with a channel spacing equal to half the individual channel bit rate, without causing any crosschannel interference     

密集光码分多址系统

基于一种新型光码分多址(OCDMA)的混合(DS/FH)编解码器,提出了多用户公用同一跳频(FH)码字但使用不同的直扩(DS)码字的密集光码分多址系统方案。在忽略噪声的情况下,采用随机过程理论对系统误码率进行了上线分析。分析表明,混合系统适于密集光码分多址通信,从而克服了单一(DS或FH)系统可用码字较少,不能承载多用户的问题。另外,还有效地解决了单一系统中存在的失配和群速度色散等问题。     

Mobile frequency-hopping CDMA systems

Through analysis and simulation, a unified evaluation of the potential performance of both mobile peer-to-peer and sectorized cellular frequency-hopping code-division multiple-access (CDMA) systems is presented. The equivalent number of frequency channels and the minimum area-mean signal-to-noise ratio are defined and shown to be important parameters in understanding and predicting network capacity. The effects of spectral splatter are analyzed. Separated orthogonality is defined and shown to be useful in completely eliminating intracell or intrasector interference. Spatial diversity by postdetection rather than predetection combining is proposed and shown to be invaluable. Noncoherent demodulation by a frequency discriminator rather than parallel matched filters and envelope detectors is proposed and shown to be effective. It is shown that even without exploiting either its natural bandwidth advantage or power control, frequency-hopping CDMA provides a reverse-link capacity nearly the same as direct-sequence CDMA with realistic power-control imperfections     

Integrated selectivity for narrow-band FM IF systems

An 18th-order all-pole continuous-time bandpass filter for IF (intermediate frequency) filtering purposes has been designed and integrated in a 3-μm CMOS process. Implemented using nine fully balanced, transconductor-capacitor coupled resonators, the filter features a 20-kHz bandwidth at 200-kHz center frequency and 54-dB dynamic range (IM3<-40 dB) and consumes 300 μA from a single 4-V supply. With the use of conventional phase-locked loop techniques for automatic tuning, the accuracy of the filter response is comparable to that of ceramic filters. As expected, the fundamental limitations of such an active implementation compared to a passive realization are noise and distortion     

A novel 3-D indoor ray-tracing propagation model: the pathgenerator and evaluation of narrow-band and wide-band predictions

A novel three-dimensional (3-D) ray-tracing model capable of supporting detailed representation of the indoor environment, as well as external building structures, is presented in this paper. The developed algorithm uses a hybrid imaging technique where the two-dimensional (2-D) image generations in vertical and horizontal planes are combined to produce 3-D paths. It also employs the concept of “illumination zones” of the images which greatly simplifies the image map and allows the evaluation of complex indoor scenarios. In order to investigate the accuracy of the presented model, comparisons of predictions with narrow-band and wide-band measurements are performed in line-of-sight (LOS), non-LOS (NLOS), and deep shadow areas, both for co- and cross-polarized antennas. The analysis shows that accurate power predictions can be achieved for both antenna polarizations with rms errors less than 7 dB, even when long sections of the test route are in deep shadow areas. There is a trend agreement between the simulated and measured channel impulse responses, while the rms delay spread in NLOS areas is predicted with less than 5-ns rms error (or better than 13% normalized mean error). The paper provides an insight into the real and the modeled radio channel