Diversity Evaluation of Two-Port Antenna System for a Mobile Terminal

Next-generation mobile communication systems require high data transmission rate and low bit error rate, but multi-path fading still stands as a major problem. Antenna diversity techniques can overcome the problem. In this paper, we thoroughly study the antenna diversity performance on a mobile terminal through theoretical analysis, computer simulations, and practical prototype measurements. Specifically, a genetic methodology is developed to accurately evaluate the diversity gain achieved in the mobile terminal from both power level approach and correlation approach. Throughout the simulations and measurements, we demonstrate that it is beneficial to implement antenna diversity on mobile terminal side, and high diversity gain can be achieved when the antennas are placed in the terminals properly. Moreover, further improvement of the diversity gain can be obtained from the implementation of the matching networks.     

Two-antenna receive diversity performance in indoor environment

Receive diversity gain performance of a two-antenna setup in an office environment is reported. The terminal is handheld in front of the user simulating a data mode scenario while walking around. The dual polarised base station sector antenna is placed at the end of a corridor. The results indicate that experimentally achieved diversity performance is similar to previously predicted theoretical data.     

Coupling Element-Based Dual-Antenna Structures for Mobile Terminal with Hand Effects

This paper presents a comprehensive simulation study on the performance of coupling element-based dual-antenna structures on a mobile terminal at the 2,000 MHz Universal Mobile Telecommunications System (UMTS) frequency band with varying two significant hand effects; vertical position of hand along terminal chassis, and distance between hand palm and terminal chassis. The results reveal that in uniformly distributed isotropic environment, there exists a gain imbalance between antenna elements due to hand effects and it is shown that a gain imbalance of 3.7 dB lead to a reduction of 1.9 dB in diversity gain at 99% reliability level using maximal ratio combining (MRC) technique. For a dual-antenna configuration, the impact of gain imbalance on diversity gain is more significant when only one antenna element is in close proximity to the hand, compared to when both antenna elements are in the presence of the hand. It is also shown that a dual-antenna structure with elements vertically oriented along the edges of a small 100 mm × 40 mm mobile terminal chassis achieves better performance in port-to-port isolation, gain imbalance and diversity gain compared to other studied dual-antenna configurations when the user’s hand is present.     

Orbital and site diversity systems in rain environment: Radar-derived results

During the summers of 1981 and 1982, an experiment was carried out in the Po River Valley with the scope of evaluating the statistical performance of diversity systems for earth to satellite links experiencing rain attenuation. The data were collected by anS-band meteorological radar scanning a32deginclined plane having the SIRIO path as its highest radial. Attenuation values directly measured through the satellite beacon at 11.6 GHz were used to "calibrate" the radar on event basis, in order to properly convert reflectivity into specific attenuation. In a previous paper the performance of site diversity (SD) systems was presented for earth terminals spaced from 1 to 20 km. In this paper, the same set of data is processed to simulate orbital diversity (OD) systems, which employ two satellites angularly spaced and one earth terminal. Aperture anglesthetaup to95deghave been considered. The results show that this diversity scheme already has a significant gain withtheta = 30degwhere at 10 dB single link attentuation the gain (as defined by Hodge) is 2.5 dB and it increases steadily asthetaincreases. The comparison between orbital diversity and site diversity performances shows that the site separation is linearly related to the orbital diversity aperture angle for any single link attenuation of the site diversity configuration.     

基于信道编码及空时编码级联的两用户协同分集

传统协同分集通过使网络中各单天线用户共享彼此天线,形成虚拟多天线阵列来实现空间分集,使得体积和功耗受限的网络终端也能获得分集增益,然而这并没有将信道编码和空时编码结合起来以使系统得到编码增益。为了能够获得编码增益来进一步改善系统性能,本文提出了一种基于信道编码和分布式空时分组码级联方式下的两用户协同分集方案,并且在准静态的瑞利衰落信道下对系统误码性能进行了理论推导和系统仿真,给出了误比特率的上限解析表达式。在协同用户间信道存在噪声的情况下,我们分别对CRC-DSTBC和CC-DSTBC级联下的发射方案进行了性能分析和系统仿真。仿真结果表明:即使协同用户间的信道存在噪声,本文所提出的协同分集方案与传统协同分集相比,不但获得了分集增益,同时也得到了编码增益,系统误比特率大大降低,从而显著提高了系统性能,并且这也和理论分析相吻合。     

基于网络编码的分布式天线系统性能分析

文章针对多输入多输出（MIMO）系统在移动终端实现上的限制,提出分布式天线系统（DAS）的解决方案来获得空间分集增益。采用DAS模型,通过使用一个具有网络编码解码运算能力的辅助天线增强用户与基站间的通信,探讨基于网络编码的天线分集增益。分析比较无辅助天线系统、简单DAS和基于网络编码的DAS中断概率性能后,理论分析和计算机仿真结果表明,相比简单DAS,基于网络编码的DAS节约硬件成本并提高了频谱利用率;系统中断概率平均降低0．0164,可获得更大的分集增益。     

Space and frequency diversity measurements of the 1.7 GHz indoorradio channel using a four-branch receiver

The practical space and frequency diversity performance achievable inside a building at 1.75 GHz under fading conditions due to the motion of a portable terminal and due to the movement of people are investigated. Data are collected using a four-branch dual-frequency envelope receiver positioned throughout one floor of a university building of common construction type. The measurement environment is characterized for large-scale path loss and wall transmission loss. Envelope cross correlations are calculated, and performance of diversity is measured for various frequency separations and antenna spacings which would be applicable given the physical size of portable telephones and data terminals. Two-branch space diversity is directly compared to two-branch frequency diversity and to four-branch hybrid diversity based on simultaneous measurements of each using selection combining. The distributions of correlations and diversity gain at different locations are also investigated. Results indicate that two- and four-branch diversity can be a very effective way to combat signal fading for portable terminals in an indoor radio environment     

Asymptotic analysis of amplify-and-forward relaying in Nakagami-fading environments

Amplify-and-forward (AF) relaying strategies are studied for Nakagami-fading channels in an (N + 2)-terminal wireless cooperative system where a source terminal transmits information to a destination terminal with the assistance of N relay terminals. The asymptotic outage behavior is investigated in terms of coding and diversity gains for channel-state information (CSI)-assisted AF relaying and semi-blind AF relaying in various channel profiles. It is shown that semi-blind AF relaying system achieves strictly higher average SNRs. Further, when there exists fading severity difference between the source-to-relay and relay-to-destination links, both AF strategies achieve the same diversity gain whereas semi-blind AF achieves strictly lower coding.     

Design and Implementation of a Baseband WCDMA Dual-Antenna Mobile Terminal

The design and implementation of a baseband wide-band code-division multiple access (WCDMA) dual-antenna mobile terminal system-on-a-chip (SoC) is presented in this paper. Spatial diversity processing mitigates wireless channel impairments and is a key enabling technology for WCDMA to support high quality of service at high data rates and capacity. The SoC integrates the baseband transceiver, coding and decoding functions, microcontrollers to implement the radio access protocols, and external interfaces to communicate with the application layer. The receiver design, which takes advantage of diversity benefits in several blocks, is described in detail. The SoC was fabricated in a 0.18-mum 1.8-V CMOS technology and requires a total area of 72mm² consuming 532 mW at the maximum data rates. The application-specific integrated circuit was used in lab testing where a gain of up to 9 dB was observed for the dual-antenna receiver, which demonstrates the tremendous improvement provided by spatial diversity. The results presented in this paper provide a base architecture and a performance benchmark for commercial implementations of WCDMA mobile terminals     

Collaborative space-time spreading scheme for higher than unity rate CDMA downlink

A novel scheme referred to as collaborative space-time spreading is proposed to provide a higher than unity rate with spatial diversity gain for the downlink of a CDMA system operating in a fading channel. This is achieved by performing collaborative coding and spreading over groups of T users, each of which is assigned a single orthogonal spreading sequence and followed by space-time encoding on the total composite signal of all groups. A user terminal simply despreads the incoming signal to recover the composite T-user group data and then extracts its intended data after space-time and collaborative decoding. Extensive comparisons with other relevant schemes are provided to show the superiority of this approach.     

一种基于LDPC编码的协作通信方式

采用空间分集的方法可以有效地对抗无线信道中的衰落.由于受到体积、重量、成本等因素的限制,在无线通信系统的用户终端上实现多天线技术较为困难.而在单天线的无线用户间通过协作,共享天线,可以实现虚拟的多天线.低密度奇偶校验(LDPC)编码是一种性能优良的线性分组码,利用其码字内码元间固有的相关性,通过不同的用户发送码字的不同部分,可以实现虚拟的多发送天线,获得发送分集增益,在不增加系统带宽和发射功率、系统复杂度也不会明显增加的情况下能显著地提高系统性能.     

Site diversity gain at the equator: radar‐derived results modeling in Singapore

Site diversity is an effective rain attenuation mitigation technique, especially in the tropical region where high rainfall rates are common. According to our previous study, site diversity gain is found to be dependent on the site separation distance and path elevation angle while it is independent of signal frequency, baseline angle and polarization angle. Therefore, using 28 months of radar data, a simple site diversity gain prediction model is proposed. The proposed model is compared with the existing ITU‐R models. The seasonal wind direction, another factor that might affect the site diversity gain prediction model, is shown to have negligible effect on site diversity gain. Triple‐site diversity is also investigated, and although it is found to provide gain improvement over dual‐site diversity, this gain improvement is too little to justify for the cost of setting up an additional site. This study is useful for the implementation of site diversity as a rain attenuation mitigation technique in the tropical region. Copyright © 2014 John Wiley & Sons, Ltd.     

Satellite path diversity reception at 11.4 GHz: directmeasurements, radar observations, and model predictions

Two-site diversity gain measurements made with a pair of 11.4 GHz satellite beacon receivers are compared to predictions based on dual-polarized radar reflectivity data and to values calculated from the Hodge model. All three agree closely. Examinations of data for a third path synthesized from radar data alone indicate that baseline orientation has a negligible effect on diversity gain     

Finite-SNR Diversity–Multiplexing Tradeoff for Correlated Rayleigh and Rician MIMO Channels

A nonasymptotic framework is presented to analyze the diversity-multiplexing tradeoff of a multiple-input-multiple-output (MIMO) wireless system at finite signal-to-noise ratios (SNRs). The target data rate at each SNR is proportional to the capacity of an additive white Gaussian noise (AWGN) channel with an array gain. The proportionality constant, which can be interpreted as a finite-SNR spatial multiplexing gain, dictates the sensitivity of the rate adaptation policy to SNR. The diversity gain as a function of SNR for a fixed multiplexing gain is defined by the negative slope of the outage probability versus SNR curve on a log-log scale. The finite-SNR diversity gain provides an estimate of the additional power required to decrease the outage probability by a target amount. For general MIMO systems, lower bounds on the outage probabilities in correlated Rayleigh fading and Rician fading are used to estimate the diversity gain as a function of multiplexing gain and SNR. In addition, exact diversity gain expressions are determined for orthogonal space-time block codes (OSTBC). Spatial correlation significantly lowers the achievable diversity gain at finite SNR when compared to high-SNR asymptotic values. The presence of line-of-sight (LOS) components in Rician fading yields diversity gains higher than high-SNR asymptotic values at some SNRs and multiplexing gains while resulting in diversity gains near zero for multiplexing gains larger than unity. Furthermore, as the multiplexing gain approaches zero, the normalized limiting diversity gain, which can be interpreted in terms of the wideband slope and the high-SNR slope of spectral efficiency, exhibits slow convergence with SNR to the high-SNR asymptotic value. This finite-SNR framework for the diversity-multiplexing tradeoff is useful in MIMO system design for realistic SNRs and propagation environments     

Differential Distributed Space-Time Modulation for Cooperative Networks

In this paper, we develop a protocol for the construction of cooperative networks when the channel state information is not available at the transmitters and the receivers. In the proposed protocol, differential space-time codewords are generated at the source terminal. In the broadcast phase, each row of the differential space-time codeword is transmitted to a different relay, whereas in the relay phase, the relaying terminals retransmit the codeword through simple amplify-and-forward algorithm. The performance of the cooperative diversity system is analyzed for a two-user case for different channel environments in. terms of the diversity gain and the diversity product. The optimization of the power allocation between source and relay terminals is considered for the maximization of the diversity product. When the same modulation scheme is used, the performance of differential detection is degraded by 3 dB noise enhancement compared with coherent detection     

Cooperative ARQ protocol for correlated wireless channels

A novel Automatic repeat ReQuest （ARQ） protocol called cooperative ARQ is presented in this letter, where a relay terminal is requested to retransmit an erroneously received packet, instead of the source terminal. The data link layer Packet Error Rate （PER） performance of cooperative ARQ is derived in correlated wireless channel. The results show that even though the relay-destination channel is worse than the sourcedestination channel, the new protocol outperforms the traditional one as long as the average SNR of the relaydestination channel is better than a certain threshold. It is also demonstrated that a second order diversity gain can be achieved with the cooperative ARQ protocol.     

Space-Time Cooperation Diversity Using High-Rate Codes

In a multi-user communication system, cooperative diversity allows single-antenna mobile sets to achieve transmit diversity. Cooperative diversity improves the communication capacity and enhances the robustness of a wireless link when a single channel alone is not reliable. In this paper, a novel cooperative diversity scheme is introduced that enables simultaneous transmission of non-redundant data from all cooperative terminals. By taking advantages of both high-rate full-diversity space-time codes and the cooperative diversity, the proposed method provides high diversity gain beyond the number of physical transmit antennas without compromising the data rates. In essence, the proposed system aims at higher data rates over the non-cooperative counterpart, while maintaining the full diversity gain.     

非对称协作分集通信中网络编码的应用

该文提出了网络编码在非对称三点协作传输系统中的应用。通过协作分集技术和网络编码技术的联合运用,不但可得到无线通信传输系统的分集增益,也可得到系统的编码增益。该文设计的方案,充分考虑无线通信环境的差异性,利用非对称调制方式,在保证较差通信环境中取得通信可靠性的同时,在较优链路采取较高速率进行传输,利用较优链路传输更多的信息,实现系统资源的充分利用。在方案的具体实现中,通过在中继链路的中继节点加入已知信息实现网络编码,使得系统的译码性能得到增加。仿真结果表明,将网络编码技术应用于非对称协作分集通信中,相对比非协作传输方案可增加分集增益,降低系统的误比特率。跟传统对称传输系统相比,可充分利用系统资源,提升了系统传输容量。     

中继卫星系统用户终端关键技术分析

用户终端在跟踪与数据中继卫星系统(TDRSS)中具有重要作用.介绍了中继卫星系统用户终端的分类、功能和组成,重点对用户终端采用的全数字化可编程综合基带、自动增益控制(AGC)、相参转发和小型化等关键技术进行了总结和分析,已工程实现的用户终端功能和性能满足系统要求.最后,提出了用户终端技术的发展趋势.     

Analysis and design of short block OFDM spreading matrices for use on multipath fading channels

We consider the use of block spreading in a multicarrier system to gain diversity advantage when employed over multipath fading channels. The main idea is to split the full set of subcarriers into smaller blocks and spread the data symbols across these blocks via unitary spreading matrices in order to gain multipath diversity across each block at the receiver. We pose the problem of designing the spreading matrix as a finite dimensional optimization problem in which the asymptotic error is minimized. This formulation allows us to find explicit solutions for the optimal spreading matrices. The performance is validated for the uncoded channel as well as for the coded channel employing turbo-iterative decoding. We further demonstrate that suboptimal linear complexity equalization strategies for spread orthogonal frequency division multiplexing (OFDM) do not gain any diversity advantage over traditional diagonal OFDM.