ANALYSIS OF A RAIN COMPENSATION ALGORITHM FOR K/Ka-BAND COMMUNICATIONS

A rain compensation algorithm (RCA) has been developed for use in the advanced communications technology satellite (ACTS) mobile terminal (AMT) system. The basic goal of the RCA is to control the transmitted data rates (9·6, 4·8 or 2·4 kbps) in the forward and return links so that a 3 dB link margin is maintained at the highest possible transmitted data rate. In this paper, analyses of both theoretical and practical issues relating to the RCA are presented. In addition, sample simulations of a one-dimensional version of the RCA at the MT are presented which illustrate typical RCA performance using both simulated and recorded pilot fade field data. It is found that with suitable post-processing, the RCA can provide reasonable (conservative) data rate estimates without making excessive data rate changes, i.e., data rate change fluctuations. It is anticipated that the results presented here will not only be useful for the eventual operation of the RCA, but more generally will be useful in the design and operation of other rain compensation techniques for K/Ka-band communication systems.     

降雨对于CAPS微小卫星终端通信的影响

中国区域卫星定位系统（CAPS）是卫星导航通信一体化的系统。当利用CAPS微小卫星终端系统进行卫星通信时,所用的天线口径极小,增益低,终端的有效全向辐射功率EIRP。较小,整个通信链路的余量较小。虽然C波段的降雨衰减远没有Ku波段大,但是相对于微小卫星终端的整个卫星通信链路来说,降雨带来的信号衰减、地球站接收天线G／T值的变化以及对卫星通信上、下行链路载噪比的影响也是不可忽视的。文章对这些影响进行了分析,并利用ITU—R给出的降雨衰减预报模式,给出了C波段的降雨衰减的计算方法及结果,并且分析了降雨对CAPS微小卫星通信系统的整个链路余量的影响。     

Joint Turbo Equalization and Multiuser Detection of MC-CDMA Signals With Low Envelope Fluctuations

In this paper, we consider the uplink transmission in multicarrier code-division multiple-access (MC-CDMA) systems. As other multicarrier signals, MC-CDMA signals have high envelope fluctuations and a high peak-to-mean envelope power ratio (PMEPR), which leads to amplification difficulties. This is particularly important for the uplink transmission, since an efficient low-cost power amplification is desirable at the mobile terminals (MTs). Moreover, the transmission over time-dispersive channels destroys the orthogonality between spreading codes, which might lead to significant multiple-access interference levels. To reduce the envelope fluctuations of the transmitted signals, while maintaining the spectral efficiency, the MC-CDMA signal associated to each MT is submitted to a clipping device, followed by a frequency-domain filtering operation. However, the nonlinear distortion effects can be high when an MC-CDMA transmitter with reduced envelope fluctuations is intended (e.g., a small clipping level and/or when successive clipping and filtering operations are employed). In this paper, we define an iterative receiver that jointly performs a turbo multiuser detection and the estimation and cancellation of the nonlinear distortion effects. Our performance results show that the proposed receiver structure allows good performances, very close to the linear receiver ones, even for high system load and/or when a PMEPR as low as 1.7 dB is intended for each MT.      

Fuzzy-Based Uplink Power Control in Forward Broadband Satellite Links

End-to-end performance of broadband satellite links operating at Ku band and above is studied in this paper. The problem of power control in terms of optimal power allocation and maximization of the total carrier-to-interference-and-noise ratio is considered. More specifically, the paper proposes the use of Fuzzy Inference Systems (FIS) to optimize power allocation in a dual-hop (end-to-end) satellite system, considering the general case of dual-polarized satellite links with transparent satellite transponder. The quality of the link is assessed through the FIS based on the predicted values of rain attenuation induced on the corresponding links and the interference-to-noise ratios. According to this estimation, the satellite hub-station increases or reduces the allocated uplink power. The proposed scheme’s effectiveness is investigated in terms of carrier-to-noise plus depolarization plus interference ratio and power consumption for 30/20 GHz frequency in the uplink and the downlink respectively. A variety of conditions is considered regarding the rain attenuation values from 0 (no rain) to 30 dB and interference-to-noise ratio from ?15 to 15 dB to both links. Finally, the scheme is compared to step-based power control algorithms, showing that it can significantly reduce the total consumed power.     

小仰角下移动卫星通信性能的改善及仿真

移动卫星通信系统为功率受限系统,相对地面移动通信而言,其链路余量较小,而且由于多径及遮蔽效应,当系统工作在小仰角时,其信号衰落可达到30dB,这对系统的设计提出了严峻的挑战。本文研究了信道编码和交织技术在移动卫星通信系统中的应用。通过仿真,得到了应用该技术对不同仰角特别是小仰角条件下系统性能的改善程度。同时,在研究信道相关的基础上,给出了交织相关参数的设计准则。     

Transmit beamforming and power control for cellular wirelesssystems

Joint power control and beamforming schemes are proposed for cellular systems where adaptive arrays are used only at base stations. In the uplink, mobile power and receiver diversity combining vectors at the base stations are calculated jointly. The mobile transmitted power is minimized, while the signal-to-interference-and-noise ratio (SINR) at each link is maintained above a threshold. A transmit diversity scheme for the downlink is also proposed where the transmit weight vectors and downlink power allocations are jointly calculated such that the SINR at each mobile is above a target value. The proposed algorithm achieves a feasible solution for the downlink if there is one and minimizes the total transmitted power in the network. In a reciprocal network it can be implemented in a decentralized system, and it does not require global channel response measurements. In a nonreciprocal network, where the uplink and downlink channel responses are different, the proposed transmit beamforming algorithm needs to be implemented in a centralized system, and it requires a knowledge of the downlink channel responses. The performances of these algorithms are compared with previously proposed algorithms through numerical studies     

无人蜂群分布式相干协作通信系统

为了解决无人（UAV）蜂群数据链系统受机载端发射功率及天线口径限制，空地通信距离受限的问题，提出了一种分布式相干协作通信系统的设计方法。基于信道反馈的校正补偿信息，蜂群节点可同时发送通信信号，在地面节点处实现相干协作信号增强。在实验室内搭建原型测试系统，通过理论分析和实测对比，验证了多节点相干协作传输的通信能力。4节点协作时，相干协作能力实测可增加10.58 dB。该方法使得在保持无人蜂群数据链端机及全向天线不变基础上，实现通信距离扩展、抗干扰能力提升变得可行。     

Partial compensation signal-level-based up-link power control toextend terminal battery duration

Power control (PC) techniques have been studied for years with the aim of reducing interference and allowing efficient battery energy management. Among PC algorithms, those based on the signal-level (not on cochannel interference) show good characteristics in terms of network stability and provide optimum downlink performance when a half-compensation scheme is used instead of a full-compensation algorithm. This work is concerned with partial (including the full and half cases) compensation signal-level-based PC algorithms and their impact on battery duration of mobile terminals, i.e., the uplink is investigated. A time division multiple access (TDMA)-based cellular system is considered. The effect of a slow PC, i.e., following only slow channel fluctuations, on the average transmitted power of mobile terminals is evaluated through a completely analytical model; both ideal and nonideal PC are considered. Starting from suitable requirements on radio coverage, we show that a half-compensation PC scheme is often a good choice for extending terminal battery life (thus, also reducing health risks)     

Power control for an asynchronous multirate decorrelator

For code-division multiple-access (CDMA) wireless systems employing multiuser detection, the varied bit-error rate (BER) requirements of multimedia traffic dictate the use of transmitted power control. Using a decorrelator in an asynchronous multirate direct-sequence CDMA system, it may be necessary for different users to combat the noise enhancement and the propagation losses to varying degrees depending on individual requirements. In this context, we propose a power control algorithm for a multirate decorrelator that is suitable for a class of BER-based link quality objectives. If the uplink channel gain of the desired user is known, then it is straightforward for each user to choose the transmitted power needed to meet its target BER objective. In practice, however, the uplink channel gain is often difficult to measure. To avoid this measurement, we employ stochastic approximation methods to develop a simple iterative power control algorithm. In this algorithm, each mobile uses the output of its own decorrelator to update its transmitted power in order to achieve its BER objective. We show that when a user's bits have nonzero asymptotic efficiencies, the power control algorithm converges quickly in the mean square sense to the minimum power at which a user achieves its quality-of-service objective     

COCHANNEL INTERFERENCE IN SATELLITE COMMUNICATION SYSTEMS DERIVED FROM RAIN ATTENUATION MEASUREMENTS AT 20 GHz

This paper reports experimental results on cochannel interference during rain, derived from measurements of simultaneous and copolar rain attenuations, in the 20 GHz band, in two convergent slant paths to fixed receivers at Spino d'Adda (Northern Italy), from the geostationary satellites Olympus (19°W) and Italsat (13°E). The results show that during rain the interference can be larger than that in clear sky, with probability 0.5 and that, in this case, the interfering level I = A_C − A_n (dB), i.e. the difference between the simultaneous rain attenuations (dB) in the interfered path, A_C (dB), and in the interfering path, A_n (dB), increases as the system power margin increases. For system design, the paper reports the cumulative distributions of I, conditioned to the maximum value of the attenuation not exceeded (i.e. system power margin) in the interfered link. It is shown how the results could be used in systems with regenerative or transparent transponders on board.     

衰落余量对cdma2000 1x前向链路发射功率和容量的影响

衰落余量决定链路可靠性并影响信道发射功率和用户容量的数值。本就衰落余量对cdma2000lx系统前向链路发射功率和渐近容量的影响进行了深入分析，首先介绍衰落余量概念，提出了cdma2000lx系统前向链路的发射功率和渐近容量表达式，然后通过仿真实验和数值计算给出一定条件下cdma2000lx系统前向链路的业务与导频SNR之间存在的对应关系，最后利用公式与仿真数据研究了衰落余量对前向总发射功率和渐近容量的影响。研究结果表明，cdma2000lx系统的前向总发射功率和渐近容量对衰落余量的大小十分敏感，衰落余量每增加ldB，都会引起总发射功率大幅上升，而渐近容量则迅速下降。     

A FREQUENCY OFFSET ESTIMATION AND COMPENSATION ALGORITHM FOR K/Ka-BAND COMMUNICATIONS

This paper presents a new open-loop technique for estimating and correcting Doppler frequency shift in K/Ka-band communication systems with special reference to the advanced communications technology satellite (ACTS) mobile terminal (AMT) modem, which utilizes square-wave pulse-shaped, binary differential phase shift-keyed (DPSK) modulation. The novelty of this estimation scheme is that it exploits the Doppler-induced phase shift over a fraction of a symbol interval to provide an estimate of the Doppler offset, without requiring symbol synchronization. Furthermore, by utilizing time-differential detection (delay-and-multiply), the proposed technique can tolerate much larger frequency offsets than existing open- or closed-loop techniques. Analytical results are provided for the variance of the above estimator and the error probability performance of the AMT is evaluated in the presence of the Doppler correction. Practical design considerations are also discussed, including a method for modifying the front end, digital bandlimiting filter in such a way that Doppler bias effects in the new estimator are eliminated. Simulation results reveal that, in general, performance improves with increasing data rates, i.e., the new frequency offset estimation/compensation algorithm induces a degradation from ideal of approximately 1 dB at a 6 dB energy per data symbol (bit) and a 2⋅4 kbps data rate. However, there is no appreciable degradation when the data rate is increased to 9⋅6 or 19⋅2 kbps.     

NSA架构语音解决方案及优化策略研究

NSA网络架构模式下，5G语音业务承载于4G锚点网络上。4/5G双连接模式的网络架构，使得终端语音业务上行功率较传统4G语音业务上行功率损失3dB，从而影响小区边缘NSA用户语音业务体验。本文研究了几种基于NSA终端上行功率分配的策略及其特点，以提升NSA终端上行覆盖性能和用户感知体验。     

An Integrated Design Approach to 30/20 GHz Trunking Systems

A design procedure for 30/20 GHz trunking systems is presented which permits the joint optimization of the satellite links and the terrestrial links between diversity terminals of individual earth stations. This process involves the generation of uplink and downlink power control functions (PCF's), which depend on 1) the rapidity with which power control can be exercised, relative to the rate of variation of atmospheric attenuation, and 2) the available uplink and downlink HPA power. The PCF's combine to produce a link availability curve (LAC), which describes the uplink/downlink fade combinations for which a specified bit error rate (BER) can be maintained. The set of required terminal separation distances (TSD's) can generally be computed from the LAC, together with the marginal uplink and downlink attenuation distributions. Methods of implementing uplink and downlink power control are discussed. In particular, several alternatives for determination of uplink attenuation and selection of the appropriate transmit terminal are contrasted.     

Extending optical transmission distance in fiber wireless links using passive filtering in conjunction with optimized modulation

The authors demonstrate a simple passive technique for increasing the transmission distance in fiber wireless links through the application of a narrowband fiber Bragg grating (FBG) with high reflectivity (90-99%). They are applied in a conventional downstream link and also for the upstream in a wavelength-reused scheme. In the conventional nonwavelength-reused system, the grating is used to optimize the optical modulation depth and, hence, the receiver sensitivity in the downstream transmitted signal by reducing the power of the optical carrier before fiber transmission. In the wavelength-reused systems, the highly reflective FBGs can be effectively used at the base stations to recover a major portion of the optical carrier (as high as 99% of the downlink carrier) for uplink transmission from a weakly modulated downstream signal. In the latter case, the penalty in the downstream signal due to the large extraction of carrier power is partially offset by the sensitivity enhancement obtained in the filtering process. The authors present experimental results for the increased transmission performance for both the nonwavelength-reused and wavelength-reused scenarios. The increase in the sensitivity (at biterrorrate=10/sup -9/) in the nonwavelength-reused scheme for a given launch channel power that facilitates the increased transmission distance can be as large as 7 dB. The relative increase in the power margin for the upstream signal can be up to 4 dB in the wavelength-reused scheme. This would more than double the currently demonstrated transmission distances in such wavelength-reused systems without any optical amplification. The scheme is applicable to a wide range of radio frequencies and modulation depths.     

Frequency division multiplexed microwave and baseband digitaloptical fiber link for phased array antennas

A frequency-division multiplexed optical fiber link is described in which microwave (1-8 GHz) and baseband digital (1-10 Mb/s) signals are combined electrically and transmitted through a direct-modulation microwave optical link. The microwave signal does not affect bit error rate (BER) performance of the Manchester-coded baseband digital data link. The baseband digital signal affects microwave signal quality by generating second-order intermodulation noise. The intermodulation noise power density is found to be proportional to both the microwave input power and the digital input power, enabling the system to be modeled as a mixer (AM modulator). The conversion loss for the digital signal is approximately 68 dB for a 1-GHz microwave signal and is highly dependent on the microwave frequency, reaching a minimum value of 41 dB at 4.5 GHz corresponding to the laser diode relaxation oscillation frequency. It is shown that Manchester coding on the digital link places the intermodulation noise peak away from microwave signal, preventing degradation of close-carrier phase noise (<1 kHz offset). A direct trade-off between intermodulation noise and digital link margin is developed to project system performance     

LTE系统上行链路质量提升的方法研究

随着VoLTE业务的商用以及4G用户大规模增加,4G网络不仅承担数据业务,还承担着语音业务,这对上行链路质量提出了更高的要求.本文利用功率余量值表征LTE上行链路质量,通过挖掘并调整上行性能参数对其进行快速地提升.结合核心城区低功率余量TOP小区的实际情况,探究低功率余量报告小区占比高的主要原因,并提出一套区别于传统优...     

CDMA网络规划的上行功率迭代算法

该文提出了一种用于CDMA网络规划的的上行功率迭代算法。在迭代的过程中,移动台根据各个基站的负载情况,动态地选择所连接的基站,使发射功率最小,最终使移动台的发射功率和基站处的干扰功率收敛。对算法的收敛性给出了理论分析,仿真结果验证了理论分析的正确性。该算法便于计算机实现,可用于实际的网络规划。