Capacity analysis of macro/microcellular CDMA with power ratiocontrol and tilted antenna

The reverse link capacity is obtained analytically for macro/microcellular code-division multiple-access (CDMA) systems operating in the same frequency band. The focuses are on the ratio of required receive power of the macrocell base station (BS) to that of the microcell BS and the tilt angle of the microcell antenna to increase the system capacity. The microcell-to-macrocell interference is derived in closed form by geometric approximation, and the macrocell-to-microcell interference is calculated on the divided regions of macrocell. The optimal tilt angle is obtained by defining the minimum interference tradeoff factor that maximizes the system capacity. It is shown that the system capacity increases remarkably with power ratio control in macro/microcellular environments. Also, the properly chosen antenna tilt angle adds more capacity, and enables the microcell users to save on the transmit power     

A novel single base station location technique for microcellular wireless networks: description and validation by a deterministic propagation model

Positioning algorithms in cellular networks has become increasingly important as a means of supporting emerging services that require a sufficiently precise estimation of the position of the mobile terminal (MT) associated with a given base station (BS). Currently, even the most sophisticated positioning algorithms require at least three BSs to achieve satisfactory precision. This paper presents a novel algorithm that makes use of a single-BS antenna array to locate MTs in cellular networks. A triangulation technique is utilized and supported by some minimal information about the environment in the BS neighborhood. This algorithm is shown to perform well when operating in a microcellular environment with perfect channel-parameter estimation. The effect of finite resolution of the input parameters is also investigated. The performance is analyzed for a universal mobile telecommunications system microcellular scenario through a three-dimensional deterministic channel model. Finally, the performance of the proposed positioning technique is compared to the well-known location method based on the time-of-arrival measurements at three different BSs.     

Oscillating-beam smart antenna arrays and multicarrier systems: achieving transmit diversity, frequency diversity, and directionality

We introduce a novel merger of smart antenna arrays and multicarrier code-division multiple-access (MC-CDMA) systems. Here, each group of Q carriers in the MC-CDMA system is applied to its own M-element smart antenna at the base station (BS). The smart antennas are separated by a distance that ensures that signals generated by each smart antenna are independent. Applying proper time-varying phases to array elements of each smart antenna array, the beam pattern is carefully controlled to generate a mainlobe at the position of the intended user and small oscillations in the beam pattern. This beam-pattern oscillation creates a time-varying channel with a controllable coherence time and a time diversity benefit at the receiver. Employing MC-CDMA with the proposed antenna array at the BS, we achieve: 1) directionality, which supports space-division multiple access (SDMA); 2) a time diversity gain; 3) increased capacity and performance via MC-CDMA's ability to support both CDMA and frequency diversity benefits. Hence, merging MC-CDMA and BS antenna arrays in an innovative fashion, we achieve high performance at the mobile via joint frequency-time diversity, and high network capacity via joint space-code division multiple access.     

Transmit diversity via oscillating-beam-pattern adaptive antennas: an evaluation using geometric-based stochastic circular-scenario channel modeling

Applying carefully-selected time-varying phases (delays) to array elements of an adaptive antenna, the beam pattern oscillates in a controlled manner. This creates a time varying channel with a controllable coherence time. With an adaptive antenna at the base station (BS) and a single omnidirectional antenna at the mobile, the controllable coherence time is used by the mobile to exploit time diversity and enhance performance. In this work, assuming an oscillating-beam-pattern antenna array at the BS, the channel is properly modeled and the coherence time is evaluated. A so-called geometric-based stochastic channel model is presented, assuming a circular coverage area, and the channel is simulated in an urban environment. We demonstrate the relationship between coherence time and the antenna array control parameters and show that seven-fold-diversity can be created via small beam pattern oscillation.     

Downlink channel covariance matrix (DCCM) estimation and itsapplications in wireless DS-CDMA systems

The downlink channel covariance matrix (DCCM) is of vital importance in determining downlink beamforming weights for base station (BS) antenna array systems. For the frequency-division-duplex (FDD) mode, DCCM is difficult to obtain due to a lack of direct measurement of downlink channel responses. In this paper, a novel technique is proposed for estimating DCCM using uplink channel responses only, which does not need direction-of-arrival (DOA) estimation and its association. The downlink beamforming scheme is then proposed for wireless DS-CDMA systems, using the obtained DCCM information together with the so-called virtual uplink beamforming and power control technique. Computer simulations show that using the BS antenna array together with this new beamforming technique can provide larger system capacity than traditional DOA-based approaches, which just direct the main beam toward the desired user     

Transmission Scheme for 2D Antenna Array MIMO Systems with Limited Feedback

Three-dimensional (3D) multiple-input multiple-output (MIMO) systems exploit spatial richness and provide another degree of freedom to transmit signals and eliminate spatial interference. Currently, however, there is no 3D codebook for two-dimensional (2D) antenna array MIMO systems with limited feedback. In this paper, based on the existing 2D codebook, we present a limited feedback and transmission scheme for 2D antenna array MIMO systems. In this scheme, the mobile station (MS) has imperfect channel knowledge, and the base station (BS) only acquires partial information relating the channel instantiation. MS must feed back two channel state information (CSI) instances, i.e., the horizontal and vertical CSIs. After receiving the two CSI instances, the BS interpolates a new vertical precoding vector using the vertical CSI. Then, the BS re-constructs a 3D beamforming vector using horizontal and vertical precoding vectors and compensates the reported horizontal channel quality indicator. System level simulation is employed, and the simulation results show that the proposed method improves the system spectral efficiency and the cell-edge SE significantly.     

A flexibly configurable spatial model for mobile radio channels

The application of multiple directive antennas, i.e., directional diversity, may lead to significant capacity benefits in cellular mobile radio systems. A flexibly configurable statistical channel model for mobile radio systems using directional diversity is presented. The parameters of this model, which is available as a FORTRAN77 program, can be easily adjusted to various propagation areas such as, for example, rural, urban, microcellular, and picocellular environments. Therefore, the model is well suited to perform simulations, evaluations, and comparisons of mobile radio systems. Simulation results concerning a code-division multiple-access (CDMA) mobile radio system which uses multiple directive base station (BS) antennas in combination with joint detection illustrate the application of the presented channel model     

Merging multicarrier CDMA and oscillating-beam smart antenna arrays: exploiting directionality, transmit diversity, and frequency diversity

In this paper, a novel merger of multicarrier code-division multiple access (MC-CDMA) and smart antenna arrays is introduced. Here, a group of Q carriers in the MC-CDMA system is applied to its own M-element smart antenna array at the base station (BS). The smart antennas are located in close proximity to one another. We generate a transmit diversity gain at the receiver by carefully moving (oscillating) the antenna array's pattern. The pattern oscillation is achieved by applying appropriate time-varying phases to array elements of each smart antenna. The beam pattern oscillation ensures a mainlobe at the position of the intended user and small oscillations in the beam pattern. This beam pattern oscillation leads to a time-varying channel with a controllable coherence time; hence, a transmit diversity benefit, in the form of a time diversity benefit, is available at the receiver. Employing MC-CDMA with the proposed smart antenna at the BS, we achieve: 1) directionality which creates high network capacity via space-division multiple access; 2) a transmit diversity gain which supports high performance at the receiver in the mobile unit; and 3) increased capacity and performance via MC-CDMA's ability to support both CDMA and frequency diversity benefits, respectively.     

Performance evaluation of directive handset antenna inmicrocellular environment

The effect of a directive handset antenna on the performance of mobile radio systems has been studied by comparing the simulated relative received power of a directive antenna with the received power of an omnidirectional antenna in a microcellular environment at 1.8 GHz. Different radiation patterns have been used to find out the effect of pattern shape, nulls and the general level of the backlobe     

A novel wideband space‐time channel simulator based on the geometrical one‐ring model with applications in MIMO‐OFDM systems

In this paper, we extend the geometrical one‐ring multiple‐input multiple‐output (MIMO) channel model with respect to frequency selectivity. Our approach enables the design of efficient and accurate simulation models for wideband space‐time MIMO channels under isotropic scattering conditions. Two methods will be provided to compute the parameters of the simulation model. Especially, the temporal, frequency and spatial correlation properties of the proposed wideband space‐time MIMO channel simulator are studied analytically. It is shown that any given specified or measured discrete power delay profile (PDP) can be incorporated into the simulation model. The high accuracy of the simulation model is demonstrated by comparing its statistical properties with those of the underlying reference model with specified correlation properties in the time, frequency and spatial domain. As an application example of the new MIMO frequency‐selective fading channel model, we study the influence of various channel model parameters on the system performance of a space‐time coded orthogonal frequency division multiplexing (OFDM) system. For example, we investigate the influence of the antenna element spacings of the base station (BS) antenna as well as the mobile station (MS) antenna. It turns out that an increasing of the antenna element spacing at the BS side results in a higher diversity gain than an increasing of the antenna element spacing at the MS side. Furthermore, the diversity gain brought in by space‐time block coding schemes is investigated by simulation. Our results show that transmitter diversity can significantly reduce the symbol error rate (SER) of multiple antenna systems. Finally, the influence of the Doppler effect and the impact of imperfect channel state information (CSI) on the system performance is also investigated. Copyright © 2009 John Wiley & Sons, Ltd.     

A performance comparison of the SCM and the Onering channel modeling method for MIMO‐OFDMA systems

This paper compares two types of channel modeling methods, which are the spatial channel modeling (SCM) and the Onering channel modeling method. These two well‐known channel models are proposed for 4G wideband mobile communication networks. To compare the performance of these channel modeling methods, we analyze the properties of the spatial, temporal, frequency correlation functions simulated by using these methods. The correlation functions of the two channel models are compared in the same conditions of antenna arrangements. The simulation and calculation results show that the correlation functions of Onering and SCM channel models are very close to each other if the BS and the MS antenna arrays are parallel and perpendicular to the broadside of MS‐BS. In other cases, the correlation functions of the two models are slightly different; however, their shapes are similar. These differences can be explained that the Onering model hardly fully describes all the characteristics of 4G channels as the performance SCM model does. The performance of these channel modeling methods is compared in system simulation level—MIMO‐OFDMA systems. The combination SFBC‐MMSE is used for spatial channel coding and the signal detection. The simulation results show that the system performance obtained by using these two channel models are comparable, given that the both modeled channels have same parameters and antenna directions. Copyright © 2016 John Wiley & Sons, Ltd.     

Adaptive Channel Estimation for Multiple Antenna OFDM Systems

We propose a simple adaptive algorithm for channel estimation of multiple antenna OFDM systems to provide competitive performance with low computational complexity and tracking ability. The derivation of the mean-squared error (MSE) for the proposed scheme is presented and the optimum selection of the parameter in the scheme is analyzed by utilizing the derived MSE expression.     

基于微蜂窝基站应用的小型化多频段内置天线

一种应用于微蜂窝基站的覆盖5个频段的新型多频段小型化内置天线被提出。该天线的体积为26×16×25mm3,可以工作于以下无线通信系统:GSM850/GSM900/DCS/PCS/UMTS。将该天线与微蜂窝基站模型安装在一起之后的测试结果和仿真结果都已给出并予以讨论。     

Capacity Enhancement Using MIMO Antenna Arrays in Realistic Macro-Cellular Urban Environment

In MIMO systems the antenna array configuration in the BS and MS has a large influence on the available channel capacity. In this paper, we first introduce a new Frequency Selective (FS) MIMO framework for macro-cells in a realistic urban environment. The MIMO channel is built over a previously developed directional channel model, which considers the terrain and clutter information in the cluster, line-of-sight and link loss calculations. Next, MIMO configuration characteristics are investigated in order to maximize capacity, mainly the number of antennas, inter-antenna spacing and SNR impact. Channel and capacity simulation results are presented for the city of Lisbon, Portugal, using different antenna configurations. Two power allocations schemes are considered, uniform distribution and FS spatial water-filling. The results suggest optimized MIMO configurations, considering the antenna array size limitations, specially at the MS side.     

Channel estimation for multi-panel millimeter waveMIMO based on joint compressed sensing

Channel state information (CSI) is essential for downlink transmission in millimeter wave( mmWave) multipleinput multiple output (MIMO) systems. Multi-panel antenna array is exploited in mmWave MIMO system due to itssuperior performance. Two channel estimation algorithms are proposed in this paper, named as generalized jointorthogonal matching pursuit (G-JOMP) and optimized joint orthogonal matching pursuit (O-JOMP) for multi-panelmmWave MIMO system based on the compressed sensing (CS) theory. G-JOMP exploits common sparsity structureamong channel response between antenna panels of base station ( BS) and users to reduce the computationalcomplexity in channel estimation. O-JOMP algorithm is then developed to further improve the accuracy of channelestimation by optimal panel selection based on the power of the received signal. Simulation results show that theperformance of the proposed algorithms is better than that of the conventional orthogonal matching pursuit (OMP)based algorithm in multi-panel mmWave MIMO system.     

Interference analysis and capacity for forward link 3G CDMA network with adaptive antennas

In code division multiple access (CDMA) systems, the capacity of forward link (FL) communication to mobile receivers is limited primarily by co‐channel interference (CCI). Adaptive antenna arrays (AAAs) that use antenna arrays along with advanced signal processing at the base station (BS) have been proposed to mitigate this limitation. For a 3G CDMA cellular network, where each BS equipped with an AAA serves mixture of voice and data users within its coverage, we study FL capacity and investigate the effects of different factors (array topology, multipath angle spread, data rate, and beamforming algorithm) on this capacity under Rayleigh fading channel. By modeling the instantaneous signal‐to‐interference power ratio received at the mobile, we derive the system outage equation that considers blocking of either desired voice or data user. Simulation results show that for the same element spacing and number of antenna elements per cell, the uniform circular array (UCA) topology results in larger capacity than the sectorized uniform linear array (ULA) topology does, and that a larger angle spread or data user rate reduces FL capacity. Copyright © 2007 John Wiley & Sons, Ltd.     

基于大规模天线的多用户 MISO 下行链路频谱效率分析简

在大规模天线时分双工通信系统中,分析了多用户MISO下行链路的频谱效率。假定用户数固定且基站天线数M无限增大,通过理论推导分析发现,当基站发送功率减小到单天线基站的1/M时,随着M的增加系统频谱效率趋于一个恒值;并且简单的预处理即可消除用户间干扰和快衰落的影响。虽然多小区系统会受导频污染的影响,致使小区间干扰不能被完全消除,但是降低后的发送功率可使系统由干扰受限转变为噪声受限。采用迫零单位预编码与采用最大比发送单位预编码的系统频谱效率极限表达式相同。最后给出采用空时分组码的多用户下行链路的频谱效率下限值,并通过仿真分析证实了以上结论的正确性。     

Generalized multiuser orthogonal space-division multiplexing

This paper addresses the problem of performing orthogonal space-division multiplexing (OSDM) for downlink, point-to-multipoint communications when multiple antennas are utilized at the base station (BS) and (optionally) all mobile stations (MS). Based on a closed-form antenna weight solution for single-user multiple-input multiple-output communications in the presence of other receiver points, we devise an iterative algorithm that finds the multiuser antenna weights for OSDM in downlink or broadcast channels. Upon convergence, each mobile user will receive only the desired activated spatial modes with no cochannel interference. Necessary and sufficient conditions for the existence of OSDM among the number of mobile users, the number of transmit antennas at the BS, and the number of receive antennas at the MS, are also derived. The assumption for the proposed method is that the BS knows the channels for all MS's and that the channel dynamics are quasi-stationary.     

A back-to-back rectangular-patch antenna fed by a CPW

The configuration of a back-to-back rectangular-patch antenna fed by a coplanar waveguide (CPW) is proposed. The characteristics of the proposed antenna element were clarified by experiments. The radiation patterns and input impedances were measured as parameters of the widths of the rectangular patch and the substrate. Experimental results for an array antenna using the proposed back-to-back rectangular-patch antenna element are described. Good omnidirectional radiation patterns and input impedance characteristics were obtained. The proposed array antenna is suitable for microcellular, wireless LAN, and indoor radio systems     

微蜂窝多径色散信道电波损耗预测的建模与仿真

本文在深入分析微蜂窝移动无线信道特性及其传播机理的基础上，研究和提出了微蜂窝多径色散信道电波传播损耗的一般性 预测模型，其特点是用附加路径衰减因子来表征三维多径色散信道特性对电波传播的影响，以及用传播信道第一菲涅耳区的最上拐点距离作为统一反映天线高度和频率影响的特征参量；最后根据该预测模型对不同情况下的电波损耗特性进行了仿真分析。