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Space communications urgently need an effective transmission control mechanism. This paper presents an experimental, comparative analysis of window-based transmission control, rate-based transmission control, and a hybrid of the two over error-prone, congestion-free, high-latency, point-to-point space communication links simulated using the space-to-ground link simulation (SGLS) test-bed. The results revealed that the traffic shaping mechanism of rate-based transmission protocol is more effective than the bursting flow of window-based protocol over simulated space communication links with a high error rate and a long link delay. The window-based transmission mechanisms show performance degradation due to traffic bursts and frequent packet retransmissions caused by their acknowledgment (ACK)-clocked transmission control algorithms. Pure rate-control is always preferable to other mechanisms in the simulated congestion-free, error-prone, point-to-point, geostationary-Earth orbit (GEO)-space communication channels, and its advantages become more pronounced when the channel rates are asymmetric. The performance differences come from their different behavior in controlling data transmission.

We present a general framework for the computation of the optimal scheduling policies for delay and overflowconstrained joint rate and power adaptations for type-I hybrid automatic-repeat-request systems. This framework can be applied to adaptive resource-allocation problems on correlated flat-fading or frequency-selective fading channels for bursty nonconstant packet arrivals. It is shown that the optimal-rate and powercontrol laws can be obtained by solving the formulated Markov decision process problems. We consider two cases for packet scheduling over wireless channels that are of significant practical importance. In the first case, we assume that the transmitter perfectly knows the channel-state information (CSI) at the beginning of the transmission. The transmitter is also provided with the decoding result for the previous transmission in terms of observation feedback at the end of the transmission. Second, we consider the scheduling problem when the transmitter does not know the CSI at the time of transmission, but it makes the transmission decision based on the history of previous transmissions and corresponding outcomes. In both cases, our objective is to minimize transmission power, and the optimal policies are computed under two different buffer-cost constraints, namely, the average buffer delay and the average packet overflow rate. The results of this paper are of importance for the development of modern wireless standards that support heterogeneous multimedia and Internet traffic with certain application-dependent-delay and packet-dropping requirements. Index Terms--Adaptive type-I hybrid automatic repeat request (ARQ), finite-state Markov channel (FSMC), joint transmission rate and power adaptation, Markov decision process (MDP), nonconstant bursty traffic, packet scheduling, partial channel-state information (CSI).

In this paper, we study the performance of a channeladaptive packet transmission system over fading channels with a finite transmit buffer. This transmission scheme combines the essential features of two popular communication techniques, namely adaptive modulation and coding (AMC) and automatic repeat request. Our joint design takes into consideration the size limitation and the dynamic variation of the transmit buffer. Specifically, we introduce a novel buffer-assisted mode selection strategy for AMC in addition to the traditional channel-quality-based strategy. We also developed three buffer management schemes. Moreover, we develop a Markov-ehain-based analytical framework to investigate the performance, efficiency, and complexity of this transmission system with different mode selection strategies and buffer management schemes. This general framework allows us to derive the accurate analytical expressions for the packet loss, average delay, spectral/power efficiency, and average feedback load of this system over general fading channel. The selected numerical results, together with the related discussion, illustrate the various design tradeoffs. Index Terms--Adaptive modulation, automatic repeat request (ARQ), cross-layer design, Markov chain.

A novel adaptive transmission scheme is proposed to improve the computational efficiency of conventional adaptive algorithms for multiple-input multiple-output orthogonal frequency-division multiplexing systems. By exploiting the stationary ergodicity of subchannel amplitudes, the proposed scheme can reduce the complexity of any existing adaptive algorithms to a considerably low level that is linear in the number of subchannels, while it causes little performance degradation. Index Terms--Adaptive transmission, fading channels, multiple-input multiple-output (MIMO) systems, orthogonal frequency-division multiplexing (OFDM).

The problem of retrieving information by a mobile access point from a sensor network where sensors cooperatively transmit messages using a common codebook is considered. It is assumed that there is a probability that a sensor is misinformed with a wrong message, which complicates the information retrieval process. The access point uses the capacity achieving stay-k scheduler that schedules a sensor to transmit for k consecutive code-letters before switching to a new sensor. The random coding exponent is derived as a function of k, and it is shown that there is an optimal k that gives the largest error exponent. The application of low-definition parity-check (LDPC) codes is considered next. It is shown in simulations that the optimal k of the stay-k scheduler for LDPC codes can be inferred from that for the random coding exponent. Index Terms--Cooperative transmission, error exponent, low-density parity-check (LDPC) codes, sensor networks.

The VME data acquisition system is described for a new tomographic diagnostic currently under development at the RFX nuclear fusion experiment. The system architecture, and its integration into the existing Control and Data Acquisition System of RFX is presented. A modelling approach in the definition and analysis of the distributed software architecture is then discussed. Finally the user interface requirements of the system and the implemented solutions are presented.

In the following a new data acquisition architecture is proposed allowing high sampling rates along with a large memory data buffer. The modular design allows up to four 250 MHz, 8-bit acquisition channels to operate in an interleaved way, achieving 1 GSPS. Each channel can acquire continuously up to 3 MBytes of data (or 12 MBytes when interleaved). Since several modules can coexist in an acquisition system, provision was made for several parallel operations, including trigger distribution and download of digital signal processing programs. The module will be used in a dedicated acquisition system for the reflectometry diagnostic on the Asdex-Upgrade tokamak[1].

We have designed and built a modified Positron Emission Tomography (PET) imaging system for monitoring the dose delivered by proton and [Gamma]-ray radiotherapy beams. By measuring the amount and ratio of the beam-induced positron-emitting activity, the dose distribution and tissue composition may be determined. The system utilizes fast LeCroy ECLine electronics and a VME multinode transputer based frontend. Utilizing a transputer based filter, positron annihilation events containing timing, energy, and position information will be filtered in real-time at event rates of up to 40 kHz. This will result in only valid events being transmitted back to the host for further analysis and display, reducing both storage media requirements and image reconstruction time. At these rates proton radiotherapy beams may be monitored between beam pulses for on-line range verification. It will also be possible to perform bloodflow studies on tumors using the activity induced by a [Gamma]-ray radiotherapy beam. Future electronic developments will allow event rates up to roughly 80 kHz. For both treatment modalities, determination of the composition of tumors will directly affect treatment planning through compensation for oxygen enhancement effects to the dose.

A multichannel TDC subsystem was designed and built at the Institute for Nuclear Physics at Mainz University. The system is based on a TDC ASIC chip called TDC 2001 and consists of several TDC modules housed in a VME-type crate. The TDC modules are controlled and read out by a transputer. The transputer can deliver the data through the transputer links to VME-systems, workstations, or PCs as data acquisition master. The subsystem, as it was developed for the A1 experiment at the MAMI accelerator in Mainz, is described, and first results from the operation at the experiment are given.

A modular system to determine correlations among many detectors in radiation measurements is described. It is based on PC computer and supports several types of CAMAC crate controllers. Besides standard techniques and procedures such as data taking, event building, event sorting, also sophisticated data visualization, processing, and a new efficient method of multidimensional data analysis with on-line compression have been implemented in the system.

The new general purpose data acquisition system developed at GSI is currently installed at about 30 experiments at GSI and other sites. It is based on the LynxOS operating system [1]. Several CPUs, i.e. GSI developed CAMAC computer boards, VME processor boards, and Aleph Event Builders, are connected by a memory mapped bus, i.e. a VSB or VME bus. It can be configured easily for various hardware setups and is highly optimized for fast trigger rates and data throughput. The first and successful experiment taking data with the system was the SHIP production run for elements 110 and 111.

A field portable data acquisition system has been developed around a VMEbus based micro-processor and standard TCP/IP network protocols. The hardware consists of a compact VME crate and a single CAMAC crate containing the signal processing electronics. The component processes of the data acquisition system transfer control and event data over a set of TCP/IP socket connections. The use of network sockets for the interprocess communications allows the data acquisition system to be operated transparently on one workstation or on a number of workstations distributed around a local network.

The capacity of data acquisition systems will improve by an order of magnitude with the advent of the new high-bandwidth network technology. Data acquisition systems will really be scalable. To be in the front line of the application of this new technology, we participate in the Dutch national asynchronous transfer mode (ATM) pilot project SURFnet4. In this framework we have initiated a project: 'Remote data acquisition and analysis'. The aim is to have an ATM network between remote VME front-ends and controlling and monitoring workstations.

A new data acquisition system has been developed at the Hahn-Meitner-Institut to handle almost 550 parameters of nuclear physics experiments. The system combines a UNIX host running a portable data buffer router [1] and a VME frontend based on the OS9 real time operating system. Different kinds of pulse analyzers are located in several CAMAC crates which are controlled by the VME system via a VICbus connection. Data readout is performed by means of an ECL daisy chain. Besides controlling CAMAC the main purpose of the VME front-end is event data formatting and histogramming. Using TCP/IP services, the UNIX host receives formatted data packages for data storage and display. During a beam time at the antiproton accelerator LEAR/CERN, the PS208 experiment has accumulated about 100 Gbyte of event data [2].

Asynchronous Transfer Mode (ATM) is a candidate technology to implement the high performance network in the data collection system for the ATLAS experiment. This work presents the results of modelling and simulation studies which aim at integrating the detailed organization of the detector read-out, the trigger requirements and the capabilities of ATM switching networks. The status of hardware development of small scale demonstrators is outlined.

H1 is a high energy physics experiment at the electron proton collider HERA at DESY, routinely taking data since 1.992. Calorimetric and tracking systems record the properties of the particles produced in the collisions in a total of 270,000 electronic channels. The collision frequency of 10.4 MHz necessitates pipelining of all data in the centrally clocked trigger and front end readout systems. This report outlines the architecture of the trigger and data acquisition system and describes the experience gained in the first years of running the experiment. A crucial aspect is the clock phase adjustment and stability of all trigger signals.

Lightwave links are being developed for volume application in the transfer of analog signals from the tracking detector front-ends to the readout electronics. The links are based on electro-optic intensity modulators which are mounted on detectors and connected by optical fibers to remotely located transceivers (lasers and photoreceivers). The modulators are III-V semiconductor reflective devices based on multi-quantum well structures. The transceivers will be integrated devices of a novel design. Modulator prototypes have been fabricated and tested. Neutron and [Gamma]-ray irradiation studies have been performed on modulators and fibers. The main results achieved so far are reported and key system issues are reviewed. This work is part of the CERN DRDC project RD23 ([1]- [3]).

During 1992-1993 the Nuclear Structure Facility at Daresbury Laboratory hosted phase one of the EUROGAM[1] experimental programme. These were the first nuclear physics experiments to make large scale use of the VXIbus standard for electronics and data acquisition. EUROGAM phase 1 was made up of an array of 45 escape suppressed Germanium (Ge) detectors. It was used for gamma-ray spectroscopy both stand-alone and in conjunction with external detectors including the Daresbury Recoil Separator (RS)[2], isomer detectors and various particle detectors. An overview of the system, details of special VXI cards, the readout and trigger systems for EUROGAM have been previously reported at the 1991 IEEENSS. Here we report on how they worked in real experiments.

A High Voltage system has been designed to allow multiple users (clients) access to the database of measured values and settings. This database is actively maintained in real time for a given mainframe containing multiple modules each having their own database. With limited CPU and memory resources the mainframe system provides a data coherency scheme for multiple clients which 1) allows the client to determine when and what values need to be updated, 2) allows for changes from one client to be detected by another client, and 3) does not depend on the mainframe system tracking client accesses.

This paper proposes a design of a trigger and data acquisition system for a detector at the PEP-II B Factory. The system is asynchronous, data-driven, and scalable. Design goals include orthogonal tracking and calorimetric triggers, minimal dead time, graceful degradation, high efficiency, and useful performance in the face of backgrounds so high as to overwhelm reconstruction. Also described are instrumentation of the Drift Chamber, based on 8-bit FADCs, and of the Calorimeter, based on a new custom integrated circuit, the Charge Amplifier with Range Encoding (CARE), and 10-bit ADCs. This design employs commercial embedded CPUs in VME and VXI crates.

This paper presents a fibre optic link (FOL) that has been developed for the NA48 experiment at CERN [1]. About 15 FOLs will be used to transfer event data to the Data Merger (event builder) over a distance of 200 metres. The FOL has a very simple interface and is capable of transmitting data at a rate of over 10Mbyte/s while performing error detection. The optical part of the FOL uses industry standard components. This, combined with its simplicity of use, makes the FOL suitable to be reused in a wide range of applications, which is shown by its use outside the NA48 experiment.