Time-spread multiple-access (TSMA) protocols for multihop mobileradio networks

This paper introduces a novel technique called protocol threading, yielding a deterministic protocol that gives a guaranteed upper bound on the transmission delay of each packet at every node in a multihop mobile network. By eliminating the maximum degree constraint, the new method improves upon existing time-spread multiple-access (TSMA)-type protocols while preserving the advantages of the deterministic operation and topology transparency. We introduce the protocol threading solution, derive the maximum delay bound in a mobile topology, and analyze the performance of the protocol     

Delay bounds for packet satellite protocols

Two simple and tight delay lower bounds are derived for packet satellite protocols with memoryless packet arrival process and single copy transmission. One bound is for protocols with contention‐free reservation and the other is for protocols with contention‐based reservation. The derivation indicates that for minimum delay, a protocol should strive to maintain a balance between transmitting packets immediately and making reservations before transmissions. This revised version was published online in June 2006 with corrections to the Cover Date.     

Multiple-access protocols for satellite packet communication networks: A performance comparison

This paper considers satellite packet communication networks with a large population of bursty users and presents an analytic comparison of the throughput versus average message delay trade-off characteristics of multiple-access protocols. The following six multiple-access protocols are examined: 1) slotted ALOHA, 2) reservation-ALOHA, 3) a reservation protocol with a slotted ALOHA reservation channel, 4) a reservation protocol with a TDMA reservation channel, 5) SRUC (Split Reservation Upon Collision), and 6) fixed assigned TDMA. All the protocols are required to ensure that all packets of a message are correctly received in the proper order at the destination. Then, a unified presentation of the delay-throughput performance of the protocols is given by means of an analytical technique called equilibrium point analysis. The throughput versus average message delay tradeoff characteristics are compared taking into account the system stability.     

A bit-map-assisted dynamic queue protocol for multiaccess wireless networks with multiple packet reception

A novel network-assisted (signal processing based) medium access control (MAC) protocol known as the bit-map-assisted dynamic queue (BMDQ) is presented. The protocol is explicitly designed for a wireless slotted system with multiple packet reception (MPR) capability. In the proposed protocol, the traffic in the channel is viewed as a flow of transmission periods (TPs). Each TP has a bit-map (BM) slot at the beginning followed by a data transmission period (DP). The BM slot is reserved for user detection so that accurate knowledge of the active user set (AUS) can be obtained. Then, given the knowledge of the AUS and the channel MPR matrix, the number of users that can access the channel simultaneously in each packet slot in the DP is chosen to maximize the conditional throughput of every packet slot. Compared with other conventional and network-assisted MAC protocols, the proposed BMDQ protocol yields better performance. Its maximum steady-state throughput is close to the channel MPR capacity, and it can achieve the same throughput with lower traffic load and smaller delay. Performance issues are investigated analytically and via simulations.     

The scheduled-retransmission multiaccess (SRMA) protocol for packetsatellite communication

An improvement of the announced retransmission random access (ARRA) protocol for packet satellite communication, called the scheduled retransmission multiaccess protocol, is introduced. Besides avoiding collision between new and retransmitted packets, the improved protocol eliminates reservation conflicts between different slots. Explicit acknowledgement is used, so that traffic to other zones served by the same satellite can also be accommodated. Assuming that 3% of the channel capacity is used for retransmission reservation, fixed frame and dynamic-frame SRMAs achieve effective maximum throughputs of 0.65 and 0.89, respectively. Both protocols give average delays considerably lower than slotted ALOHA, even when the throughput is as low as 0.2     

Idle-signal casting multiple access with data slot reservation(ICMA-DR) for packet radio communications

A population of terminals communicating with a central station over a packet-switched multiple access radio channel is investigated with regard to multiple access control schemes. The authors describe the ICMA-DR, which is an advanced idle-signal casting multiple access (ICMA) scheme characterized by data slot reservation. This improved central controlled multiple-access scheme for packet transmission in terrestrial radio communications is evaluated in terms of throughput traffic, throughput delay characteristics, and handling capacity. It is shown that the throughput characteristics of ICMA-DR are superior than those of ICMA or slotted ALOHA when a packet for data slot reservation is relatively short in comparison to that for upward data. Thus, it is shown that ICMA-DR is suitable for the packet radio multiple-access scheme, especially in the case where fading packet error occurs frequently and ordered traffic is heavy. The ICMA-DR scheme has been utilized for the access control channel of NTT's new 800-MHz-band high-capacity land mobile communication system since the Spring of 1988     

Network protocols for frequency-hop packet radios with decoder sideinformation

Reliable data distribution within spread-spectrum packet radio networks requires high performance from the network protocols. This paper describes research in forwarding and routing protocols that are designed specifically for slow-frequency hop (SFH) packet radio networks in which some of the radios are subjected to excessive interference. It is shown that information extracted from the decoder can be used to aid the network protocols. New metrics are introduced that use this information to give a quantitative assessment of the interference environment experienced by the receiver in an SFH radio. Forwarding protocols are developed that can react quickly to local sources of interference, and the metrics that are introduced permit the routing algorithm to react to changes in the interference conditions in the network     

SS/FDMA router for flexible satellite communications networks

The subchannel switched frequency-division multiple-access (SS/FDMA) system improve the routing flexibility of transponder banks in channelized multibeam satellites. This system can efficiently be utilised to construct a VSAT (very small aperture terminal) network and/or a business satellite communications network using small aperture terminals. The authors address the application of the SS/FDMA system to such networks. A proof-of-concept (POC) model of SS/FDMA onboard equipment called the SS/FDMA router is described in terms of its configuration and measured electrical performance. Results of transmission experiments using the POC model as well as computer simulations are presented. In addition, a redundant SS/FDMA router configuration is proposed, and its reliability is calculated for a 15-year satellite mission time. Finally, estimated values of volume, mass, and DC power consumption of the redundant SS/FDMA router are presented     

Visible light communications heterogeneous network (VLC-HetNet): new model and protocols for mobile scenario

Wireless Networks - In order to resolve the crowded radio spectrum of wireless communication systems, visible light communications (VLC), which uses a vast unregulated and free light spectrum, has...     

A model for the handover traffic in low earth-orbiting (LEO) satellite networks for personal communications

The spectacular growth of cellular telephone networks has demonstrated the demand for personal communications. Communication systems based on low earth orbit (LEO) constellations of satellites seem to be an adequate approach to achieve a world-wide network. When defining the capacity in terms of satellite circuits, the network designer has to take into account the handover traffic. Unfortunately, in a LEO communication network where handover is most often due to the network nodes motion, handover traffic models for terrestrial cellular networks cannot be used. Hence specific models must be developed. This paper proposes an analytical model for the handover in LEO satellite networks. This model is applied to different network configurations and compared to discrete-time simulations. Simulation results agree with those obtained from the analytical model.     

Adaptive resource allocation for multiaccess MIMO/OFDM systems with matched filtering

In this letter, we propose an adaptive resource-allocation algorithm for multiaccess multiple-input multiple-output/orthogonal frequency-division multiplexing systems. The proposed algorithm endeavors to maximize the system power efficiency, given that the users' quality of service (QoS) requirements, specified by bit-error rate and data rate, are satisfied. Subcarrier allocation, power distribution, and modulation for multiple users are jointly optimized according to users' channel states and QoS requirements. To avoid the joint optimization of resource allocation and beamforming, matched-filter-based receivers are employed at the base station, with cochannel interference being mitigated through dynamic subchannel allocation. A neighborhood search scheme is further developed to obtain a good allocation solution with reasonable computational efforts. Our results show that the proposed algorithm is able to achieve significant enhancement in the system power efficiency due to the successful exploitation of multiuser diversity, as well as channel variations in the time, frequency, and space domains.     

低轮廓车载卫星通信天线的跟踪设计

针对低轮廓车载卫星通信天线由于受载体的扰动,在无航向和跟踪器的指引下,将很难保证天线稳定的指向目标的情况,提出一种新型的低轮廓车载通信天线控制系统和跟踪策略,使用倾角仪,补偿车体在天线俯仰波束正交的两个方向的倾斜,使用速率陀螺,通过软件实现了车体扰动的隔离以及航向隔离,解决了车体运动中实时准确跟踪的关键问题,提高了车载卫星通信天线的性价比.并用工程实例验证该方法的正确性.在城市路面,卫星不被遮挡的情况下,车载卫星跟踪系统可稳定接收卫星数字电视节目.     

Standardized testing conditions for satellite communications on‐the‐move (SOTM) terminals

Performance validation of Satcom on‐the‐move (SOTM) terminals is becoming more important as the satellite operators continue to recognize the negative influence of suboptimal terminals on their satellite networks. Traditionally, SOTM testing is performed with actual operational satellites in field tests, which lack repeatability. The capability to repeat the conditions in which SOTM terminals are tested is important, especially when the performance of multiple terminals is compared. This contribution describes how the qualification test of SOTM terminals can be conducted in a laboratory environment so that repeatability can be ensured. A major advantage of a laboratory environment is the ability to test the complete terminal as if it was in the field of operation, yet without the involvement of real satellites effectively reducing the costs of testing. The main contributions of this paper are motion and shadowing profiles suitable for standardization of SOTM testing. Standardization of such profiles is necessary to guarantee a fair comparison of the performance of different terminals. Moreover, the paper presents the methodology for testing SOTM terminals at the Fraunhofer Facility for Over‐the‐air Research and Testing, * * * https://www.iis.fraunhofer.de/en/profil/standorte/forte.html the procedure used to obtain the proposed profiles and results of testing a Ka‐band SOTM terminal, taken as an example.     

A congestion control middleware layer with dynamic bandwidth management for satellite communications

Historically, satellites have been set aside for what regards Internet connectivity; however, the interest in their usage to provide Internet connectivity is now rising again. Because of the growing demand for Internet services around the world, satellites can be an effective medium to serve scarcely populated areas as well as mission‐critical communications. While the standard transmission control protocol (TCP) performs badly when employed on satellite links for the high propagation delay, when a number of client hosts are wirelessly connected to a gateway that forwards and receives traffic across such links, the major limit is represented by the channel condition estimation performed by the TCP through loss detection and/or acknowledgement‐based timing information. This paper proposes congestion control middleware layer (C²ML+), a centralized and collaborative middleware with dynamic bandwidth management, that aims to improve performance and QoS for TCP flows in the aforementioned scenarios. Results of ns‐3 simulations show an improvement in aggregate throughput, a significant reduction of latencies because of low queues occupancy levels, and higher fairness and friendliness guarantees among flows. They also confirm that C²ML+ allows a dynamic and efficient usage of the bottleneck link, avoiding a waste of resources when some client nodes are unable to fully exploit their transmission potential. Copyright © 2015 John Wiley & Sons, Ltd.     

Performance of DS/CDMA systems with differential M-ary orthogonal modulation and RS-coding for LEO satellite communications

This paper presents a coded modulation scheme based on M-ary orthogonal modulation by means of Walsh–Hadamard (WH) sequences, suitable for low-earth-orbit (LEO) direct sequence/code division multiple access (DS/CDMA) satellite communication systems. Based on the IS-95 scheme, we consider Reed–Solomon (RS)-coded M-ary orthogonal modulation with error or erasures decoding, which presents good performance enhancement with low complexity. LEO satellite links are characterized by large Doppler frequency shifts caused by the difference in velocity between the satellite and the earth mobile terminal, which make conventional non-coherent detection ineffective. In order to overcome the phase shift variations during the symbol period, which result in orthogonality loss of the WH sequences, we applied a differential encoding process to the spreading sequences or the WH chips prior to transmission. A special diversity process suitable for the environment under consideration is also applied. Simulation results show that the proposed diversity/coding/modulation scheme attains very good performance at low transmitter/receiver complexity. © 1998 John Wiley & Sons, Ltd.     

Antenna and receiver system with digital beamforming for satellite navigation and communications

To demonstrate and investigate the possibilities of active antennas with digital beamforming, a compact breadboard model operating in C-band with planar patches as radiators is fabricated and measured. It was originally designed as a technology demonstrator for navigation purposes, but will be extended for future use in combined navigation and communication systems. Several parameters for beam position, sidelobe reduction, and ing are set and controlled by a suitable user interface. A special calibration and error-correction procedure is developed to compensate for drift of active elements, mutual coupling of the patches, and finite-ground plane effects. The excellent results demonstrate the versatile features of digital beamforming for satellite navigation and communication systems.     

Trellis coded modulations with improved non-coherent detection for personal and mobile satellite communications

In this work, the performance of trellis coded modulations with improved non-coherent receivers is examined for application to personal and mobile satellite communications. The schemes are analysed and evaluated in additive white Gaussian noise, Rayleigh, Rician and shadowed faded channels. Evaluations have shown that the improved non-coherent receivers are capable of providing considerable gains in performance as compared to the conventional differential receivers.     

Signal-detection and signal-processing algorithms for code-division multiple-access satellite mobile communications systems employed simultaneously with satellite radio navigation systems

The Markovian theory of random process estimation is applied to synthesize optimal (and close to optimal) algorithms with discrete-parameter feedbacks. The problem is solved in the case when it is necessary to provide for detection and complex nonlinear processing of discrete-continuous noiselike signals used in code-division multiple-access satellite mobile communications systems employed simultaneously with satellite radio navigation systems. It is assumed that the discrete part of a discrete-continuous state vector to be estimated contains two components, each being characterized by a multiposition simple Markovian chain and that desired signals are observed in the presence of additive partially colored (correlated) Gaussian noises.     

A Ku-band T-shaped gate GaAs power MESFET with high breakdownvoltage for satellite communications

^GaAs power MESFET's with 0.5-μm T-shaped gate for Ku-band power applications have been developed using a new self-aligned and optical lithography. It displays a maximum current density of 350 mA/mm, an uniform transconductance of 150 mS/mm and a high gate-to-drain breakdown voltage of 35 V. Both the high breakdown voltage and the uniform transconductance were achieved by the new MESFET design incorporating an undoped GaAs cap and a thick lightly doped active layers. The breakdown voltage is the highest one among the values reported on the power devices. The device exhibits 0.61 W/mm power density and 47% power added efficiency with 9.0 dB associated gain at a drain bias of 12 V and an operation frequency of 12 GHz