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.     

Smart antenna arrays with oscillating beam patterns: characterization of transmit diversity in semi-elliptic coverage

By applying carefully selected time-varying delays to the array elements of a smart antenna located at the base station (BS), small oscillations are generated in the beam pattern. These oscillations create a time-varying channel demonstrating intra-symbol time variation and characterized by coherence time T/sub C/. At a single-antenna mobile station (MS), the time-varying channel (with coherence time T/sub C/) creates a time diversity which is exploited to enhance the mobile's performance (by introducing oversampling to the mobile receiver). We present a channel model which characterizes the time-varying channel that results from beam pattern oscillation. We then use our channel model to evaluate the coherence time, T/sub C/, at the mobile station (MS). The channel model presented corresponds to the so-called geometric-based stochastic channel model (GSCM), with a semi-elliptic coverage area. This geometric approach allows us to stochastically model the parameters of the time-varying channel impulse response. Simulations based on the GSCM show that 7-fold time diversity can be exploited at the MS (when beam pattern movement is small), which significantly improves the MS receiver probability-of-error performance.     

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.     

The diversity gain of transmit diversity in wireless systems withRayleigh fading

In this paper, we study the ability of transmit diversity to provide diversity benefit to a receiver in a Rayleigh fading environment. With transmit diversity, multiple antennas transmit delayed versions of a signal to create frequency-selective fading at a single antenna at the receiver, which uses equalization to obtain diversity gain against fading. We use Monte Carlo simulation to study transmit diversity for the case of independent Rayleigh fading from each transmit antenna to the receive antenna and maximum likelihood sequence estimation for equalization at the receiver. Our results show that transmit diversity with M transmit antennas provides a diversity gain within 0.1 dB of that with M receive antennas for any number of antennas. Thus, we can obtain the same diversity benefit at the remotes and base stations using multiple base-station antennas only     

Achieving high-capacity wireless by merging multicarrier CDMA systems and oscillating-beam smart antenna arrays

We establish the network capacity (measured in terms of number of users) of a wireless system merging multicarrier code-division multiple-access (MC-CDMA) and smart antennas with oscillating-beam patterns. The MC-CDMA component supports high performance (in a probability-of-error sense) via frequency diversity and high network capacity via code division. The smart antenna with oscillating-beam pattern further enhances performance via transmit diversity (in the form of an induced time diversity) and further enhances network capacity via spatial division. The proposed merger has been shown to achieve a very high performance by exploiting a two-dimensional time-frequency diversity. We demonstrate the impressive network capacity gains achieved by this merger.     

Smart versus dumb antennas-capacities and FEC performance

We compare two approaches to use multiple transmit antennas in an FEC coded wireless system: smart antennas use an antenna array to direct a beam in the direction of the dominant transmission path in order to obtain an antenna gain. Another approach is to use multiple transmit antennas for diversity using space-time block codes. Since no knowledge of the channel is required at the transmitter we denote this approach as dumb antennas. Using equivalent single-input channel models we compare smart and dumb antennas in terms of the BER performance and channel capacity and discuss under which conditions it is preferable to use multiple transmit antennas for transmit diversity or for beamforming     

Performance analysis of space-time transmitter diversity techniques for WCDMA using long range prediction

Transmitter diversity in the downlink of code-division multiple-access (CDMA) systems achieves similar performance gains to the mobile-station receiver diversity without the complexity of a mobile-station receiver antenna array. Pre-RAKE precoding at the transmitter can be employed to achieve the multipath diversity without the need of the RAKE receiver at the mobile station. We examine feasibility of several transmitter diversity techniques and precoding for the third-generation wideband CDMA (WCDMA) systems. In particular, selective transmit diversity, transmit adaptive array and space-time pre-RAKE (STPR) techniques are compared. It is demonstrated that the STPR method is the optimal method to combine antenna diversity and temporal precoding. This method achieves the gain of maximum ratio combining of all space and frequency diversity branches when perfect channel state information is available at the transmitter. We employ the long range fading prediction algorithm to enable transmitter diversity techniques for rapidly time varying multipath fading channels.     

Performance of a cellular hybrid C/TDMA mobile radio systemapplying joint detection and coherent receiver antenna diversity

For future mobile radio systems, an appropriately chosen multiple access technique is a critical issue. Multiple access techniques presently under discussion are code division multiple access (CDMA), time division multiple access (TDMA), and hybrids of both. In the paper, a hybrid C/TDMA system using joint detection (JD-C/TDMA) with coherent receiver antenna diversity (CRAD) at the base station (BS) receiver is proposed. Some attractive features of the JD-C/TDMA system are the possibility to flexibly offer voice and data services with different bit rates, soft capacity, inherent frequency and interferer diversity, and high system capacity due to JD. Furthermore, due to JD, a cluster size equal to 1 can be realized without needing soft handover. The single cell E_b/N₀ performance and the interference situation in a cellular environment of the uplink of a JD-C/TDMA mobile radio system with CRAD is investigated in detail. It is shown that the cellular spectrum efficiency is remarkably high, taking values up to 0.2 bit/s/Hz/BS in the uplink, depending on the actual transmission conditions     

Outage and ergodic sum‐rate performance of cooperative MIMO‐NOMA with imperfect CSI and SIC

In this paper, we examine a half‐duplex cooperative multiple‐input multiple‐output non‐orthogonal multiple access system with imperfect channel state information (CSI) and successive interference cancelation. The base station (BS) and mobile users with multi‐antenna communicate by the assistance of a CSI based or fixed gain amplify‐and‐forward (AF) relay with a single antenna. The diversity schemes, transmit antenna selection, and maximal ratio combining are applied at the BS and mobile users, respectively. We study the system performance in terms of outage probability (OP) and ergodic sum‐rate. Accordingly, the exact OP expressions are first derived jointly for the CSI based and fixed gain AF relay cases in Nakagami‐m fading channels. Next, the corresponding lower and upper bound expressions of the OP are obtained. The high signal‐to‐noise ratio analyses are also carried out to demonstrate the error floor value resulted in the practical case and achievable diversity order and array gain in the ideal case. Moreover, the lower and upper bounds of the ergodic sum‐rate expressions are derived together for the CSI based and fixed gain AF relay cases. Finally, the Monte‐Carlo simulations are used to verify the correctness of the analytical results.     

Transmission Strategies for MISO Downlink MC-CDMA Mobile Systems

This paper proposes two space-frequency schemes with a multi-user pre-filtering technique for downlink (DL) multicarrier code division multiple access (MC-CDMA) systems. We consider the use of antenna arrays at the base station (BS) and a single antenna at the mobile terminal (MT) and derive the proposed multi-user pre-filtering technique that modulates the transmitted signal to eliminate the effects of multiple access interference (MAI) and channel distortions at the mobile terminals, while maintaining low MT complexity. Two types of detectors are considered at the MT: simple despreading and single user equalizers. The performances of the proposed schemes are compared to those of other transmit signal design approaches that have been recently proposed for DL MC-CDMA, considering both typical indoor and pedestrian scenarios, and channel coding based on UMTS specifications.     

The Downlink Capacity of Single-User SA-MIMO System

In this paper, a novel multiple antenna system framework, which combines smart antennas (SA) with multiple-input-multiple-output (MIMO) at the transmitter, is proposed. The downlink capacity of the single-user SA-MIMO wireless systems is investigated. The joint optimization problem corresponding to the capacity is deduced. After that, upper bounds of the capacity are given in general case and in the case of equal power allocation, respectively. Furthermore, in the case of equal power allocation and the same direction of departure from one transmit smart antenna to all antenna arrays at the receiver the closed-form expression of the capacity is obtained. Some numerical results are given to show that smart antennas can bring significant capacity gain for the MIMO systems due to the smart antennas gain, without additional spatial degrees of freedom, especially at high SNR with strong correlation among the MIMO channel links or at low SNR.     

Tradeoff between diversity gain and interference suppression in a MIMO MC-CDMA system

In this paper, the uplink of an asynchronous multi-carrier direct-sequence code-division multiple-access (MC-DS-CDMA) system with multiple antennas at both the transmitter and the receiver is considered. We analyze the system performance over a spatially correlated Rayleigh fading channel with multiple-access interference (MAI), and evaluate the antenna array performance with joint fading reduction and MAI suppression. Assuming perfect channel knowledge available at the transmitter, maximal ratio transmission is employed to weight the transmitted signal optimally in terms of combating signal fading. At the receiver, adaptive beamforming reception is adopted to both suppress MAI and combat the fading. Note that while correlations among the fades of the antennas in the receive array reduce the diversity gain against fading, the array still has the capability for interference suppression. We examine the effect of varying the number of transmit and receive antennas on both the diversity gain and the interference suppression.     

Intelligent antenna system for cdma2000

Third-generation (3G) cellular code division multiple access (CDMA,) systems can provide an increase in capacity for system operators over existing second-generation (CDMA) systems. The gain in capacity for the base station to mobile (forward) link can be attributed to improvements in coding techniques, fast power control, and transmit diversity techniques. Additional gains in the mobile to base station (reverse) link can be attributed to the use of coherent quadrature phase shift keyed (QPSK) modulation and better coding techniques. While these enhancements can improve the performance of the system, system operators expect that with increased demand for data services, even greater capacity enhancements may be desired. There are essentially three methods, which we describe, based on diversity, spatial beamforming, and a combination of diversity and beamforming, to improve the performance of system through the use of additional antennas at the base station transmitter and receiver. The performance improvements are a function of the antenna spacings and the algorithms used to weight the antenna signals. We focus on the possibilities for the cdma2000 3G system that do not require standards changes. We highlight the performance enhancements that can be obtained on both the reverse and forward links through use of an antenna array architecture that supports a combination of beamforming and transmit diversity. We focus on the performance enhancements for the forward link     

多天线无线数据通信系统中多用户分集的研究

研究当接收天线不少于发送天线时多输入多输出(MIMO)系统的多用户分集能力。首先从理论上分析了发送天线个数等于1和2时最大似然接收和迫零接收系统的平均吞吐量和调度增益,以及仿真分析了发送天线个数大于2时系统性能。理论分析和仿真表明：在多用户的MIMO系统中,接收的平均信噪比、用户个数、收发天线个数、接收机的结构等对于多用户分集有很大的影响。当发送天线个数为1时,接收天线较少(1,2,3)和平均信噪比为．10dB时调度增益很大,但调度增益随着天线个数和发送功率增大急剧下降。和最大似然接收相比,迫零接收具有更大的多用户分集增益,因此迫零接收机的吞吐量可以很容易超过最大似然接收机。     

Experiments on coherent adaptive antenna array diversity forwideband DS-CDMA mobile radio

In wideband direct sequence code division multiple access (W-CDMA), employing an adaptive antenna array is a very promising technique to reduce severe multiple access interference (MAI) from high rate users. A four-antenna pilot symbol-assisted coherent adaptive antenna array diversity (PSA-CAAAD) receiver comprising an adaptive antenna array based on a minimum mean squared error (MMSE) criterion and a RAKE combiner is implemented in preliminary laboratory and field experiments. There are two important design concepts of the PSA-CAAAD receiver. The first is that the adaptive antenna array forms an antenna beam for each resolved propagation path and tracks only slow changes in the directions of arrival (DOAs) and average powers of the desired and interfering user signals. The second is that the RAKE combiner tracks the instantaneous changes in channel conditions and coherently combines the signals of the desired user propagating along the resolved paths to maximize the instantaneous signal-to-interference plus background noise power ratio (SINR). This paper presents, both by laboratory and field experiments, the effectiveness of PSA-CAAAD receiver as a powerful means to reduce severe MAI from high rate users, and that it is more effective than using a space diversity receiver with the same number of antennas in the W-CDMA reverse link     

Blind Signal Reception and Channel Estimation in Downlink MC-CDMA Communication System with Transmit Diversity

In this paper, we exploit transmit diversity in downlink multicarrier CDMA (MC-CDMA) system to provide a solution to a high data rate, high capacity, yet reliable and robust to fading channel network. Our first emphasis is on designing a blind (without knowing the undesired users' signatures and channel parameters) MC-CDMA receiver in the mobile station that can suppress the multiple access interference (MAI) and combine the desired signal stemmed from all the transmitting antennas. Two blind signal reception algorithms are proposed and the performances in terms of signal-to-interference-and-noise-ratio (SINR) are comprehensively analyzed. One is based on the decorrelating RAKE (DRAKE) scheme proposed in [IEEE Trans. Communs. 47(7), 1036–1045, 1999] and the other is designed to meet the minimum output energy (MOE) criterion [IEEE Trans. on Information Theory 41(4), 944–996, 1995]. The MOE receiver, though optimum in ideal situation, is semi-blind that the vector channel impulse responses (VCIR) should be explicitly known. While the proposed modified DRAKE receiver is completely blind that it does not require any information of VCIR. Furthermore, we demonstrate that in practical scenario, the modified DRAKE scheme substantially outperforms the MOE receiver. The second part of this paper is to develop an efficient and blind (without requiring training sequences) algorithm to estimate the VCIR of downlink antenna array MC-CDMA system. Simulation results show that both the channel estimation algorithm and the blind reception schemes are reliable and near-far resistant. Wei-Chiang Wu received the M.S. and Ph.D. degrees both in electrical engineering from the National Tsing Hua University, Hsin-chu, Taiwan, R.O.C., in 1992 and 1998, respectively. From 1992 to 1994, he was an assistant researcher in the Communication Department at Chung Shan Institute of Science and Technology (CSIST), Taiwan, R.O.C.. From 1998 to 2000, hewas in the Army of Taiwan, where he conducted the research of Integrated Logistic Support (ILS). Since 2000, he has been an assistant Professor at the Department of Electrical Engineering, Da Yeh University, Changhua, Taiwan. His current research interests are in multiuser detection, smart antenna technology, multi-carrier CDMA and ultra-wideband (UWB) impulse radio (IR) technology.     

MISO CDMA transmission with simplified receiver for wirelesscommunication handsets

The next-generation wireless personal and mobile communication systems are expected to accommodate not only high-quality voice services, but also a broad range of other multirate services. Of the various multiaccess techniques, wide-band code-division multiple access (CDMA) has been regarded as an important part of the third-generation wireless communication systems because of its high frequency utilization efficiency and suitability for handling multimedia and multirate services. In this paper, we consider a system with a simplified receiver structure for direct-sequence CDMA (DS/CDMA) wireless communication handsets, in which improved performance is demonstrated when compared to a conventional DS/CDMA system with a RAKE receiver at the mobile station. We arrive at this system by finding the optimal solution to a general multiple-input single-output (MISO) DS/CDMA smart antenna system. We find that this solution reduces to a pre-RAKE with space transmit diversity system under the assumption that a simple one-finger matched filter is used at the receiver. This system combines the advantages of pre-RAKE diversity and transmit antenna diversity. It is shown that significant system performance and capacity improvements are possible. The numerical results also reveal that this system is not too sensitive to channel estimation errors     

On Multicarrier Detection and Coherent CDMA Mobile Receiver Radio Systems with Joint Antenna Diversity

The combination of code division multiple access(CDMA) and multicarrier (MC) transmission techniques,termed MC-CDMA, is considered a promising alternative toconventional DS (direct sequence)-CDMA. For this reason, recent research activities haveconcentrated on the application of MC-CDMA to mobileradio systems. In this paper an MC-CDMA concept which iswell suited for mobile radio applications is described. The described MC-CDMA concept overcomesdisadvantages of previously proposed concepts. InMC-CDMA mobile radio systems, signal reception isimpaired by time-varying multipath propagation. Theimpairments can be reduced by applying diversitytechniques. Coherent receiver antenna diversity (CRAD)is especially attractive because only the signalprocessing at the receivers must be modified. In thiscommunication, the application of CRAD in combination withjoint detection (JD) techniques to the more criticaluplink of MC-CDMA mobile radio systems is investigated.It is explained that the deployment of JD techniques for CRAD is an effective countermeasure againstthe influence of the mobile radio channel on the systemperformance. Four JD techniques for CRAD which areapplicable to MC-CDMA are presented. Their performances are studied in bad urban, typical urban, andtypical macrocellular environments. It is shown thatMC-CDMA allows a favorable performance compared to otherCDMA concepts.     

Simulation,implementation and performance evaluation of a diversity enabled WCDMA mobile terminal

Smart antenna array technology has been shown to greatly improve the performance of wireless communication systems. In this article, we describe the impact of smart antenna array processing at the mobile terminal for Wideband Code Division Multiple Access (WCDMA) cellular networks. Using system simulations we demonstrate the quality of service, network coverage, and network capacity improvement provided by a WCDMA dual antenna receiver and we establish a relationship between this improvement and the link level performance. We then describe a receiver architecture for a dual antenna WCDMA mobile receiver. The proposed receiver was implemented, as part of a complete mobile terminal solution, in an ASIC using a 0.18 μm, 1.8 V CMOS technology. The ASIC was integrated with RF, analog and digital components in a PCMCIA card form factor. The PCMCIA is a 3GPP compliant user equipment and has been submitted to standardized performance and conformance tests. Experimental measurements gathered with the PCMCIA card illustrate the impact of a diversity enabled mobile data terminal on the link level performance. For various propagation environments and transmission data rates, improvements in the range of 2.7 – 10 dB in the required DPCH I _c/I _or for a 1% Block Error Rate (BLER) were observed. These measurements are within 1.4 dB of the ideal link level simulations which indicates that the predicted improvement at the network level should also materialize. The results presented in this paper show the tremendous potential of smart antenna arrays in 3G WCDMA cellular networks and establish diversity as a viable solution for high-speed cellular communications.     

MIMO系统中简单的扩展空时块编码分集技术研究

本文提出一种多输入多输出（MIMO）天线系统中简单的扩展空时块编码（SSTBC）分集技术，采用沃尔什码来区分各天线发送数据子流。采用这种方法，在系统带宽一定时，不降低发送信息速率，同时接收机简单。不同天线的发送信息经过了所有收一发天线对之间的空间子信道，获得了所有路径的部分空间分集增益，仿真结果表明，这种增益的获得不受限于接收分集阶数，并且随发射天线的增加以一定的线性关系增加。