A Simulation Study of Digital Modulation Methods for Wide-Band Satellite Communications

A computer simulation study has been performed to evaluate the performance of a variety of digital modulation techniques in transmitting high-rate digital data over a satellite channel. Results are presented showing comparative performance of various techniques in the form of error-rate curves and signal-to-noise ratio (SNR) degradation curves.     

Network Control for Multibeam TDMA and SS/TDMA

This paper concentrates on the control of individual burst transmissions of traffic and reference stations in TDMA and SS/ TDMA networks. In a TDMA system, the principal task of a TDMA terminal is to transmit each burst at the proper time to assure that, at the satellite, the burst resides in its assigned location in the TDMA frame. The composite of assigned positions for all bursts in the TDMA frame, or frames if more than one transponder is involved, is called the burst time plan. The paper discusses a specific concept of control used by a station to acquire and synchronize its burst transmission to assigned time slot(s) in the TDMA frame. The concept is applied to single-beam (global or regional) and muitibeam systems. The method used controls the instant of traffic burst transmission by introducing a time delay at each station which causes the round-trip propagation time between the satellite and all earth stations to be equal for burst position control purposes. This time delay is simple to implement in the TDMA terminal's timing circuitry and does not require the storage of traffic to accomplish it. It is also shown that the control method leads to a simple means for accomplishing synchronous burst time plan changes throughout the network. The functions of the reference stations needed to accomplish the burst time plan control are defined and explained. The discussion extends to SS/TDMA, and explains how the satellite switch state time plan change can be synchronized to the overall network burst time plan change.     

卫星TDMA系统的时域逆向解调器

本文介绍了用于中速率ＴＤＭＡ系统中的一种新型解调器ＴＲ－ＭＯＤＥＭ，该方案所需报头短，需８—１６比特，并能以相干方式对各分帧进行解调。在本文中还提出了在ＴＤＭＡ系统中对各分帧分别实现各自的ＡＦＣ与ＡＧＣ算法，而不是对所有的分帧一起处理，它易于采用全数字技术，实现中速率的ＴＤＭＡ解调。该调制解调器可应用在卫星ＴＤＭＡ通信系统中。     

Efficient algorithms for SS/TDMA scheduling

Efficient scheduling algorithms for the slot assignment problem in a satellite-switched time-division multiple-access (SS/TDMA) system are presented. This problem is translated into a modified open-shop scheduling problem, allowing the use of known optimal algorithms. Their complexity is expressed as a function of the following parameters: the number of nonzero entries in the demand matrix, the number of uplinks, and the number of downlinks. According to the values of these parameters, the algorithm with the lowest computational complexity can be adopted. Although the computational complexity of previously published algorithms is drastically reduced, simulation results show that the results are close to previously presented solutions in terms of the assignment duration and the number of switching matrices     

SS/TDMA scheduling for satellite clusters

The authors present a novel approach to the optimal time-slot assignment problem for a general satellite-switched time-division multiple-access (SS/TDMA) satellite cluster with intersatellite links (ISLs) interconnection. The proposed allocation algorithm accounts for the following: systems with any number of satellites; each satellite covers an arbitrary number of zones; no onboard buffering at the satellites; and ISLs with arbitrary capacities. They present an analogy between the satellite cluster scheduling problem and the modified openshop scheduling problem. Using this analogy the authors introduce a heuristic algorithm and an optimal branch-and-bound algorithm. They investigate the performance of the proposed heuristic both by theoretical bounds and by comparing the simulation results produced by the heuristic with the optimal results. In all cases the heuristic algorithm results are within 10% of the optimum     

Burst scheduling algorithms for SS/TDMA systems

Efficient algorithms that generate a detailed operation plan for satellite-switched time-division multiple access (SS/TDMA) systems are proposed. A burst time plan generation problem is analyzed and two algorithms for burst scheduling are presented. The first method is an algorithm based upon a bin pack problem. The other algorithm schedules new bursts while reassigning already scheduled bursts by a single machine scheduling model. These algorithms are shown to be applicable to practical systems operating with transponder hopping and multidestination bursts. Simulation results for a number of example problems are presented     

移动通信平台Ku/C双波段自动切换卫星通信系统设计

本文对双波段车载卫星通信系统的研究背景及气象系统现有的车载卫星通信系统的现状进行了介绍．并对车载Ku／C双波段卫星通信系统的可行性进行了深入的分析,然后对车载卫星通信天线的选型．Ku／C双波段车载卫星通信系统中天线部分、馈源部分和射频部分的设计行了分析和测试．提出卫星链路上几种影响数据传输效率的因素及解决办法．实现了车载卫星通信系统的Ku／C双波段切换．并对卫星通信系统各项性能指标测试的方法进行了介绍。实际测试各项性能指标达到了卫星公司的入网测试要求．验证7Ku／C双波段车载卫星通信系统的设计是可行的。     

一种航天器有效载荷新型高功率微波开关

为了抑制空间高功率器件中微放电击穿,本文提出了一种表面多孔结构。通过在器件表面构造该多孔结构,实现对二次发射电子的禁锢,从而减小器件表面二次电子发射系数,提高微放电阈值。通过模拟分析不同金属材料表面的二次电子发射特性,结合波方程和电子动力学理论建立电磁粒子模拟算法,实现不同微观表面微波器件的数值模拟。使用偏置电流法测量不同条件下金属的二次电子发射数据。模拟计算一定功率电平下典型微波开关微放电的物理图像。测量给出不同银表面处理下的二次电子发射特性,并且模拟给出微放电阈值。模拟结果与实验结果吻合良好,证明了表面多孔结构对微放电的有效抑制。     

A note on efficient SS/TDMA assignment algorithms

A time-slot assignment procedure using the maximum-weight matching algorithm is proposed and investigated. In contrast with previous methods, based on the maximum-cardinality matching, the proposed procedure allows the inclusion of known heuristics in a more direct manner. Computer simulation gives evidence of efficiency improvements by using this approach     

A Wireless Network for Wide-Band Indoor Communications

We propose and analyze a wide-band indoor communication system that uses radio as the transmission medium either on a stand-alone basis or to supplement a hard-wired network for those situations where complete portability is desired. One principal impairment to such a system is intersymbol interference caused by frequencyselective fading. A novel media-access scheme is proposed which permits the use of resource sharing, wherein a small pool of time slots is effectively shared among all users to provide added protection against channel impairments on an as-needed basis. Our results show that the use of resource sharing and diversity provide excellent protection against intersymbol interference caused by frequency-selective fading with negligible impact on throughput. Furthermore, resource sharing plus diversity can permit significantly higher data rates without large queueing delays. For example, a wireless network with a 10 Mbit/s data rate in a 10 MHz bandwidth using four antennas at the base station has a less than 10^-4outage probability at a 10^-4BER in buildings with less than 58 ns rms delay spread. A loading of 75 percent is permitted for a queueing delay of less than 20 packet transmission times all but 0.01 percent of the time.     

A Wide-Band Variable Microwave Coupler

A method is described whereby the coupling value of a TEM quarter-wave coupler can be continuously varied over ranges up to 100 percent of the nominal value. The method employs the change of even- and odd-mode characteristic impedance levels over the coupling region and as such is best suited to stripline and other configurations which use parallel ground planes as outer conductors. Because current lines are crossed only in regions of relatively low current densities and because physical realizations are mechanically simple and compact, reliability is assured. Its major disadvantage is that the voltage standing-wave ratio (VSWR) increases and the isolation decreases as the coupling is tuned away from the nominal value. However, the simple predesign procedures described in Section III can reduce or eliminate this problem. The device can be used as a variable attenuator, a variable sampler, and, in systems with couplers, a trimming device.     

Computer-aided planning of SS/TDMA network operation

A computer-aided approach to the planning of SS/TDMA network operation is proposed. SS/TDMA is a sophisticated satellite communication network based on an onboard switch matrix, whose operation planning is formulated as a large-scale scheduling problem. An overall planning and scheduling model is presented to deal with practical SS/TDMA systems, such as a two-frequency channel network and nondisjoint beam coverage. For systematic planning suitable for a computer-aided approach, the entire scheduling process is divided into several steps, for each of which an efficient mathematical model is proposed. A linear programming model is used for distribution of traffic on a beam-to-beam basis and the generated switching sequence is further refined by a model using the traveling salesman problem. Burst scheduling is carried out by the Bin packing algorithm and scheduling models for practical networks allowing transponder hopping and multidestination bursts. An algorithm called enhanced rescheduling is presented to further improve the scheduling capability of the existing methods. The performance of the proposed methods is demonstrated by simulation results     

A Large 16*16 IF Analog Switch Matrix for Personal Communications Satellites

A 16 input and 16 output channels single chip intermediate frequency range (160 MHz) analog switch matrix for personal communication satellites has been designed and processed by using a commercial 1.2 µm BiCMOS technology. The circuit has low power consumption (,2W) and low insertion loss with maximum output power of 0 dBm.     

A Practical Optimization Approach for QPSK/TDMA Satellite Channel Filtering

This paper reports the results of computer and laboratory hardware simulation studies concerning optimum pulseshaping filter characteristics and configurations to be employed with conventional QPSK signaling in a nonlinear channel. An understanding of the factors and issues contributing to transmission impairments was obtained through an initial hardware simulation which was confirmed and extended with computer simulation. Based on this understanding, the critical characteristics of the channel pulseshaping transmit and receive filters were determined, promising filter candidates were implemented, and a complete system laboratory hardware simulation study was configured to evaluate the candidate filters using an INTELSAT IV satellite. This study emphasizes the performance tradeoff between the nonlinear channel-induced bit-error-rate impairment and the adjacent channel interference levels caused by HPA spectrum regeneration of filtered QPSK as a function of filter configuration. The results show that a more gentle rolloff Nyquist or wider bandwidth non-Nyquist transmit filter produces similar significantly improved performance compared to a conventional sharp rolloff Nyquist transmit filter in nonlinear satellite channels. For the wider non-Nyquist filter case, employing a Nyquist filter at the demodulation also benefits performance.     

System Capacity and Access Control for Multimedia TDMA/SS Networks

In this paper, we study the system capacity and access control for the TDMA/SS (time division multiple access with spread spectrum) cellular networks supporting multimedia services. In the TDMA/SS system, time is divided into frames and each frame is further divided into slots. Only one user is allowed to transmit in a slot and spread spectrum technique is adopted to combat inter-cell interference. A packet can occupy more than one slot, depending on the user's data rate and quality of service requirement. We derive a necessary and sufficient condition for a group of users to be admissible for the TDMA/SS system and prove that its admission region contains that of the TDMA/CDMA system. In the TDMA/CDMA system, time is also divided into frames and each frame consists of several slots. The difference is that every packet occupies exactly one slot and multiple users can transmit their packets in the same slot. Numerical results show that the admission region of the TDMA/SS system can be significantly larger than that of the TDMA/CDMA system. To further increase bandwidth utilization and guarnatee delay bound requirements, several access control schemes are proposed. Simulation results are obtained for these access control schemes.     

Analysis of a switch matrix for an SS/TDMA system

Time slot scheduling problem for a satellite switched/time-division multiple access (SS/TDMA) system is discussed and an algorithm called "Greedy Algorithm" is presented. This algorithm guarantees a most efficient utilization of a frame period with n²- n (n is the number of beams) number of switchings at most. Another problem discussed in this paper is the choice of the type of microwave switch matrix to be put on board the satellite. A switch-matrix structure called rearrangeable multistage matrix is shown to have high reliability and low-insertion-loss characteristics. Also brief discussions are made on the experimental results of an engineering model SS/TDMA system.     

Incremental time-slot assignment in SS/TDMA satellite systems

The heterogeneous traffic in this environment can be categorized into a rapidly changing type composed of packet switched data traffic and a relatively static type composed of circuit switched voice traffic. From the time-slot assignment viewpoint, the problem is to construct an efficient TDMA frame that permits the static voice traffic to be transmitted and, then, on a frame-by-frame basis to attempt to insert the data packets into the slots that are unused by the voice traffic. It is proved that the problem is NP-complete, even for very simple traffic configurations. Several suboptimal fast heuristic algorithms are presented and empirically compared by experiments on randomly generated traffic patterns. The experiments reveal that, on the average, the algorithms give close to the optimal performance     

SS/TDMA time-slot assignment with knowledge-base and prolog implementation

A software production system for the generation of time slot assignment plans for SS/TDMA systems is proposed and implemented. The approach used in this system conveniently combines algorithms derived for ideal configurations with heuristic procedures that are needed to account for conditions present in real systems. Algorithms that produce plans with a minimum number of switchings and minimum traffic transmission duration can now be easily implemented. The assignment plans obtained are as efficient as those previously reported when the assumptions are the same. The proposed production system, however is capable of handling a much larger variety of constraints and heuristic procedures for which no efficient solutions have been reported.     

SS/TDMA Time Slot Assignment with Restricted Switching Modes

The time-slot assignment problem for a satellite-switched time-division multiple access system where only a restricted set of all possible switching modes is to be used is studied. An efficient algorithm for finding an optimal assignment is proposed. Also, methods for selecting restricted sets of switching modes are presented.