TDMA System Research Articles

Performance of trellis-coded 16-QAM/TDMA system for land mobile communications

The digital cellular telephone system is considered in various countries. It is a system which is more attractive than the conventional analog transmission system in the sense that various data can be transmitted using the same transmission band. In practice, it is very difficult to realize composite transmission of various data or the data transmission of the ISDN terminal. For such a situation, this paper proposes the trellis-coded, 16-QAM, six-channel TDMA system. The proposed system includes various elaborations to improve the transmission characteristics, e.g., the fading distortion estimation by inserting the pilot symbol, the space diversity with maximum ratio combining, the symbol interleaving, and the two-frequency hopping. A computer simulation is executed for such a system to examine its performance. It is seen as a result that the spectral efficiency is improved greatly and the high-quality transmission is realized, compared to the systems considered in the United States and in Europe.

An experimental TDMA transmission system using 1.5 GHz-band π/4 shifted QPSK

The π/4-shift QPSK transmission system with TDMA scheme is constructed and an experiment is conducted, aiming at the digital cellular automobile telephone system. Various detection methods are first compared and it is decided that differential detection is advantageous, considering the operation in TDMA system where the burst modulated wave must be demodulated. Then, by varying the bandwidth of the receiving filter in the differential detection demodulator, the biterror rate and the adjacent channel emission are examined using simulation. The optimal receiver bandwidth is determined. In the differential detection, the bit-error rate depends greatly on the carrier frequency drift. A highspeed automatic frequency control (AFC) circuit is newly proposed to solve this problem. The post-detection, two-branch selection diversity demodulator is experimentally constructed and a satisfactory performance is obtained, with the deviation from the theoretical value being 2.3 dB under the static condition, and the diversity gain is 6 to 7 dB. Based on those results, it is experimentally verified that the π/4-shifted QPSK differential detection with TDMA scheme is practically useful.

Carrier recovery and inter-burst interference in a symbol-synchronous tdma system

ESA is studying future communications satellite systems involving switching and processing on board the satellite. One concept uses a symbol-synchronous MF-TDMA system with very short data bursts. This paper investigates QPSK carrier phase estimation for coherent demodulation in such a system. The Viterbi and Viterbi algorithm is used to produce one phase estimate separately for each data burst. The algorithm and its properties are reviewed and computer simulation results are presented to show its performance. It offers excellent performance under the conditions planned for the MF-TDMA system and is robust against distortions and interference. One potential problem in such a system, with no interburst guard-time and possible level differences between adjacent bursts, is interburst interference. It is found that clear-weather level differences of several dB can be tolerated easily. Atmospheric attenuation of the wanted burst may result in major level differences between adjacent bursts, but the interburst interference itself does not increase with respect to the thermal noise environment and so does not contribute any new problems. Any requirement for power control, for instance, will be determined by considerations of noise rather than interference. The burst timing accuracy in such a system is set by normal intersymbol interference considerations, rather than by the interburst interference or the needs of the phase estimator.

Message delay and queue-size analysis for circuit-switched TDMA systems

A multiple-access communications channel which is shared among network stations using a circuit-switched time-division multiple-access (CS-TDMA) scheme is examined. Each station is allocated a fixed number of slots (N) during each frame. The authors carry out queue-size message delay analysis for CS-TDMA systems. They derive the generating function of the queue size and of the waiting time distribution for a discrete-time Geom/sup (x)//Geom/N queuing system. This result is used to obtain the generating function of the system size for the CS-TDMA scheme. The associated computation requires the solution of (N+1)2/sup N/ linear equations. To derive a more computationally effective procedure, tight lower and upper bounds are obtained, requiring the solution of at most 3N linear equations. The authors prove that a slot allocation scheme which distributes station slots uniformly over the frame yields a message delay lower bound. The application of the results to the analysis of demand-assigned CS-TDMA systems is also discussed. >

Performance of a decision feedback equalizer under frequency‐selective fading in land mobile communications

AbstractSome means to cope with frequency‐selective fading is indispensable to the realization of a wideband digital mobile communication, and various investigations have been made to this end. For example, the decision feedback equalizer (DFE) is considered promising, since it requires smaller‐scale equipment and is versatile in applications.The application of DFE to mobile communication requires tracking to the time‐varying channel as well as the fast initial adaptation. Thus, comprehensive investigations, including the construction of the equalizer and tap‐updating algorithm are needed.The Kalman algorithm is employed as the tap‐updating algorithm. By introducing the memory factor into the algorithm, the tracking performance to the time‐varying channel is improved as well as the speed of the initial adaptation.A computer simulation is made for the proposed method based on the model of 256 kbit/s TDMA system with QPSK modulation. It is verified that DFE is useful in compensating for the frequency‐selective fading in mobile communication.

Performance analysis of buffered slotted‐ALOHA/TDMA systems

Abstract The behavior of a hybrid ALOHA/TDMA protocol with a buffer at each of the user terminals is studied. An approximate expression for the average gueueing delay is derived as a function of the system input parameters (i.e. the number of users, the input traffic, the transmission and retransmission probabilities). In comparison with Kamal's model, the analysis carried out in the paper reveals that the reduction in the average queueing delay is quite significant, especially under heavy traffic conditions.

On the sensitivity of particle size to relative humidity for Los Angeles aerosols

A TDMA system (Tandem Differential Mobility Analyzer; Rader D.J. and McMurry P.H. J. Aerosol Sci. 17, 771–787, 1986) was used to measure the sensitivity of particle size to relative humidity for monodisperse Los Angeles aerosols. Measurements were made at Claremont, CA on 13 days between 19 June and 3 September 1987, in conjunction with the Southern California Air Quality Study (SCAQS). The particle sizes that were studied ranged from 0.05 μm to 0.5 μm diameter at ambient relative humidity (typically 45–65%). The data provide clear evidence that these atmospheric aerosols were externally mixed. Monodisperse ambient aerosols were often found to split into nonhygroscopic (no water uptake) and hygroscopic portions when humidified. An average of 30% of the particles in the 0.2–0.5 μm range were nonhygroscopic. However, the proportion of the particles that was nonhygroscopic varied considerably from day to day and was, on occasion, as high as 70–80% of the particles. There was no clear evidence for nonhygroscopic 0.05 μm particles, but the data are not definitive on this point. The data also show that for the hydrophilic aerosol fraction, the larger particles (0.4–0.5 μm) grew more when humidified than did smaller particles (0.05–0.2 μm). As relative humidities were increased from 50% to 90%, particle diameters grew by average factors of 1.46 ±0.02 (for 0.5 μm particles), 1.49 ± 0.08 (0.4 μm), 1.19 ± 0.08 (0.2 μm) and 1.12 ± 0.05 (0.05 μm). Similarly, when particles were dried from 50% RH to 6–10% RH, particle diameters changed by factors ranging from 0.94 ± 0.03 (0.5 μm) to 0.98 ± 0.01 (0.05 μm).

On‐board processing for communication satellites: Technologies and implementations

AbstractThis paper presents technologies which are key candidates for advanced on‐board processing for future communication satellites. Satellite switching centres for microwave and baseband signals, on‐board coherent modems for 120Mb/s burst‐mode TDMA systems and their technologies are discussed. A brief description of on‐board demultiplexing and demodulation of low bit rate carriers is offered and study results on investigation of on‐board unique word detectors and large buffers are presented.

Satellite communication systems for domestic/business services

AbstractThis paper is composed of two parts.The first part addresses some topics associated to the implementation of FDMA/TDM systems for ‘business’ services applications, operating at Ka band.A modular regenerative and processing satellite repeater, each module capable of handling up to 16 up‐link carriers in the 2 Mb/s range is considered. Available coding techniques were reviewed; concatenated codes seem highly interesting because of the high coding gains achievable with two simpler co‐decoding processes in series, and also because they lead to an implementation wherein the internal coder is installed on board the satellite, while the external one is installed in the user terminals.The problem of keeping stable the up‐link carriers in the satellite demodulators is discussed and a compensation method is proposed.Finally, simulation results of co‐decoding and carrier extraction performance are illustrated.The second part concerns the implementation of a multifrequency TDMA system. This is a hybrid system whereby the access for up‐links uses time and frequency slots in a time‐frequency map. The adoption of a clock synchronous network allows a frame for which no preamble and guard time are inserted between the burst.The error contributions and the performance of the clock synchronous network are assessed. A solution to the problem of fast phase/frequency estimation is proposed.For a clock synchronous network fast algorithms suitable for frequency demultiplexing and detecting of the FDM signal could be adopted; a modular solution to the implementation of the demultiplexer and detector is proposed based on the use of an optimized matched filter; a multistage scheme minimizes the number of multiplications.

Selection of gold and kasami code sets for spread spectrum CDMA systems of limited number of users

AbstractSpread spectrum code‐division multiple‐access (CDMA) systems are currently considered as very attractive alternatives to the more familiar FDMA and TDMA systems, especially in the presence of multipath fading and external interference. The problem of code selection in a CDMA system with a finite number of users is addressed in this paper. A simple and efficient method for the selection of finite code sets with relatively high processing gain from Gold and Kasami code families of relatively large sizes is described in detail. Selected code sets of period 63 are presented along with their overall average performance parameters for different number of users.

A feedforward tracking filter. Part 1: Principle and tracking behaviour

Conventional tracking filters using feedback control encounter a hang-up problem when fast acquisition is required in high-speed TDMA systems. This paper introduces a feedforward tracking filter (FTF) which solves the hang-up problem. Using two identical bandpass filters (BPF5) and feedforward control to compensate both phase and frequency variations, this FTF provides fast acquisition and unconditional stability. Different BPF configurations used in the FTF scheme are evaluated and it is found that, for the same noise bandwidth of the BPF, the FTF using two identical double-tuned BPFs provides the best performance. The fast acquisition of the FTF is not degraded by the inter-burst-interference encountered in TDMA applications. The effects of misaligned BPFs on the tracking performance are studied analytically and experimentally.

A channel estimation and synchronization technique for wide-band TDMA systems

This paper describes a novel synchronization technique for wide-band TDMA systems. The technique employs a complex matrix operation to detect the start of the sounding or synchronizing signal. The matrix operation can be used for both channel estimation and synchronization. The matrix technique not only enables a substantial reduction in computational processes to be achieved relative to that of the correlation method, but also improves the SNR in channel estimation.

A Compact 4-GHz Linearize for Space Use

A compact and lightweight 4-GHz linearizer for satellite TWTA's has been developed by using MIC packages with chip devices. The linearize is composed of a preamplifier, a predistortion Iinearizer, and a limiting ampfifier, consisting of two, three, and three 25x12.5-mm packages, respectively. It improves the noise power ratio for an FM system by 3 dB and the required C/N for a TDMA system by 4.5 dB compared with the conventional satellite TWTA. A space environmental test and an aging test were successfully performed on the equipment.

Design of a selective FEC subsystem to counteract rain fading in ku‐band TDMA systems

AbstractA major concern in satellite communications systems operating at frequencies above 10 GHz (e.g. Ku band) is the performance degradation caused by rain fading. In this paper, an effective method for combatting this phenomenon in TDMA systems is described. This method is based on the application of additional FEC coding protection on a dynamic basis to faded traffic terminals. Selective (adaptive) forward error correction (S‐FEC) coding permits the fixed fade margins used by the network earth‐stations to be substantially reduced, while a desired outage probability is maintained. This paper deals primarily with the implementation of the monitoring and control subsystems required in a practical S‐FEC network.

The acquisition and synchronization control procedures for the intelsat tdma system

AbstractControl of all bursts in the TDMA system is achieved by the use of complementary controlled and controlling procedures. Controlled procedures operate in traffic terminals and reference terminals alike, whereas controlling procedures operate only in reference terminals. Controlling procedures are the subject of this paper. These procedures govern the acquisition, synchronization and monitoring of all bursts, including reference bursts, in the TDMA system.To perform the acquisition and synchronization control function, each reference burst contains a control and delay channel (CDC) in which control information is transmitted to controlled terminals on a constant repetitive basis. The structure and timing of this control cycle will be discussed, assuming that the basic control frame and multiframe structure is familiar.Acquisition and synchronization control is performed only on the principal burst transmitted by each terminal; all other bursts are monitored by the reference terminals and controlled by the SDNTX (selective do not transmit) message which is transmitted in the reference burst service channel on an as‐needed basis. The procedure which governs the generation of these messages will also be discussed.

Reference terminal equipment for the intelsat tdma system

AbstractOne of the distinctive features of the INTELSAT TDMA system is that the role of the reference station is completely separated from the ordinary station. For this reason, the reference station (called a TDMA reference and monitor station (TRMS)) needs special facilities: reference terminal equipment (RTE) and a TDMA system monitor (TSM). NEC corporation has developed and produced the RTE/TSM facilities necessary for the INTELSAT TDMA/DSI system.In November 1984, the first RTE/TSM equipments were installed at the first two TRMS sites for the major path 2 in the Atlantic Ocean region. Since that time, several field tests have been successfully conducted.In this paper, the signal processing equipment (SPE) of the RTE is described in detail.

Intelsat tdma/dsi system: implementation and system management

AbstractThis paper presents an overview of the concepts underlying the implementation of the TDMA/DSI technique in the INTELSAT satellite system, together with a description of preliminary ideas on the system management of TDMA networks. The TDMA project is an INTELSAT response to steady growth in international services, and the TDMA system uses digital techniques for enhancing capacity on a satellite. The establishment of the system requires international co‐operation on an extensive scale; all the decision‐making components in INTELSAT's structure have contributed to the planning and implementation of the system. Preliminary ideas on network management are discussed. The methods used for establishing internationally agreed procedures and for orchestrating the maintenance of reference stations are described.

Nec's traffic terminal equipment for the intelsat tdma system

AbstractThe traffic terminal equipment (TTE) for the INTELSAT TDMA System handles the actual traffic of the network and operates under control of the reference terminal equipment (RTE) installed at the reference station.The required function and performance for the TTE are specified in detail by the INTELSAT TDMA/DSI specification, but there may be many approaches to actual equipment design. NEC's TTE has been designed based on NEC's extensive experience and field‐proven circuit techniques. In addition, the TTE design has been affected by the fact that NEC has been engaged in the development and production of the RTE for INTELSAT.NEC's TTEs have been delivered to customers since the summer in 1984, with the first test with the RTE through the satellite having been successfully performed at COMSAT's Etam station at the end of 1984.This paper describes the capabilities of the traffic terminal equipment, developed and manufactured by NEC Corporation, together with the design approach used in its fabrication.

Intelsat tdma system monitor

AbstractThe INTELSAT 120 Mb/s TDMA/DSI system consists of reference stations and traffic terminals which access the INTELSAT V satellites as a multiple beam network. Two reference stations located within each satellite beam serve the network by controlling the acquisition and synchronization of the traffic terminals and by performing TDMA system monitoring. Within the reference stations, the acquisition and synchronization control functions are performed by the reference terminal equipment and the monitoring functions are performed by the TDMA system monitor. This paper provides a discussion of the TDMA system monitor, including its configuration, measurement techniques, and an assessment of its measurement.

Discriminator with partial response detection of nrz. fsk signals

AbstractIn the TDMA subscriber loop radio communication system, large carrier frequency deviation exists in burst signals from subscribers to a base station. A modulation/demodulation technique, which is suitable for the burst transmission with large frequency variation, is studied in this paper. First, problems in the terrestrial TDMA system and clarified and it is shown that the use of conventional FSK‐discriminator detection causes large CNR degradation due to the variation. Next, differential FSK‐Partial Response Detection (DFSK), which can cope with the frequency variation and has a simple structure, is proposed and its principle and structure are described. Furthermore, the intersymbol interference and adjacent channel interference characteristics are evaluated theoretically and the bit error rate (BER) characteristics are evaluated experimentally. As a result, the optimum modulation index and IF‐band reception band path filter are obtained. Finally, the optimum transmission system of DFSK designed for wide‐band Digital Radio Subscriber Loop System using 26‐GHz band is described. DFSK is shown to be a practical and promising modulation/demodulation system for a terrestrial TDMA communication system, on which a large demand is expected in the future.