Land Mobile Communication Systems Research Articles

Frequency‐offset compensation for MPSK differential detection by using double differential encoding

AbstractAlthough differential detection methods having superior fading resistance and, in general are effective in digital land mobile communications systems, phase shifts due to frequency offsets become a major factor that deteriorates the error rate in these differential detection methods. Although various frequency‐offset compensating methods have been studied and developed, the maximum amount of frequency offset that can be compensated is limited due to the ambiguity of the phase, which has become a problem in estimating the phase shift due to a frequency offset.In this paper, a method for compensating frequency offset by double differential encoding of transmission data sequences, which allows a resolution of the forementioned problem even when a large frequency offset occurs, is proposed and the error rate performance in the application of a /4‐shift QPSK scheme is evaluated by computer simulation. As a result, it is shown that the proposed method has superior compensating performance on land mobile communications channels.

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

Trellis-coded 16QAM/TDMA systems are proposed that have a high spectral efficiency and high transmission quality and that can support a wide variety of services. A digital pilot-symbol-aided channel sounding scheme, as well as diversity reception with maximal ratio combining, are used to compensate for fading. To further improve transmission quality, symbol interleaving and two-frequency hopping are used in the trellis-coded 16QAM/TDMA system. Computer simulation demonstrates that the bit error rate (BER) performance and the spectral efficiency of the trellis-coded 16QAM/TDMA cellular system are superior to those of /spl pi//4-QPSK/TDMA used in the American and Japanese digital cellular standards. It is also demonstrated that the trellis-coded 16QAM/TDMA with diversity, symbol interleaving, and frequency hopping can achieve a BER of about 10/sup -4/ if the delay spread is 0.1 T/sub s/. >

An evolutionary role for small comsats

A review of orbit and constellation options is presented for regional and global coverage in real time for voice-based communication and for intermittent or delayed messaging. An evolutionary trend to increasing spacecraft size and cost is explained in terms of increasing productivity. A viewpoint is presented that small satellites do not have unique technical capabilities but do promise lower unit costs to build and launch. These features coupled with orbit and constellation characteristics make smallsats attractive in start up, low capacity and experimental missions and particularly in global systems requiring many satellites. Comments are made on the system features of some of the current mobile system filings before the FCC which rely on small satellites for communications and position location. Two additional applications of small satellites are presented, one for a medium capacity GEO satellite for domestic or regional fixed satellite service at C or Ku-band. The other is for a constellation of 3 medium altitude polar orbit satellites to provide high latitude mobile service as a complement to a global geosynchronous-based system for aeronautical, maritime and land mobile communications.

Rayleigh fading compensation for QAM in land mobile radio communications

A pilot symbol-aided Rayleigh fading compensation is investigated for M-ary quadrature amplitude modulation (QAM) to achieve highly spectrally efficient land mobile communication systems. The optimum parameters for fading compensation, bit error rate (BER) performance against E/sub b//N/sub 0/ (energy per bit to the noise power spectrum density), adjacent channel interference, and cochannel interference for 16-QAM, 64-QAM, and 256-QAM, and the spectral efficiencies for these modulation schemes in Rayleigh fading environments are investigated by computer simulation. To further verify the effect of pilot symbol-aided fading compensation from a a practical point of view, a 16-QAM modem is implemented, laboratory experiments are executed, and the impact of the dynamic range limitation due to the resolution of the analog-to-digital (A/D) converters is evaluated, along with the imperfection of the analog circuits. It is demonstrated by computer simulation and laboratory experiments that the pilot symbol-aided fading compensation can sufficiently compensate for fast varying Rayleigh fading, and 16-QAM gives the highest spectral efficiency in the case of cellular systems. >

A frequency scanning satellite system for land mobile communications

AbstractA frequency scanning system for mobile applications has been assessed for a European mission at L‐band. Feasibility evaluations, electrical design and analysis have been performed for both the antenna and the entire repeater. Efforts have also been made to solve accommodation, thermal and mechanical problems, so as to demonstrate the actual feasibility of the frequency scanning concept in user‐oriented applications. The very promising results obtained are presented in this paper.

Land mobile satellite communication system using the geostationary platform

If the geostationary platform (GPF) is available in the first decade of the 21st century, the demand on a voice communication base is expected to be about 800,000 Land Mobile Satellite Service (LMSS) terminals. To improve the frequency use of an LMSS over Japan, it is important to reuse the frequencies allocated to the Tokyo metropolitan area in the Osaka-Kobe-Kyoto region. An onboard multibeam antenna with beam intervals of 0.468 deg (L band 30-m class) for each of the 11 beams covering the main Japanese islands, cluster power feeding, and dual polarization can enable the reuse of frequencies at one-beam intervals. A deployable antenna is under development that is lightweight and has a high storage efficiency for launching. This will form the basis for an antenna with an aperture diameter of 30 m. Such a large antenna will be a key factor in reducing ground terminal size. This paper estimates the weight and power requirements of the mission payloads onboard the GPF, which include an LMSS, a millimeter wave personal satellite communication system, and a high-definition television/regional television satellite broadcasting service system. The total weight of this GPF would be approximately 4-5 tons.

A detector diversity system for land mobile communications

AbstractThe land mobile communication is affected by fading when the mobile station moves in the multipath transmission environment. On the other hand, there are cases where there is no fading as in the communication with the standing or transported mobile station. It has been understood that the coherent detection using PLL is better in the nonfading environment and the differential detection is better in the fading environment.From such a viewpoint, this paper proposes a detector diversity system for mobile communication which can cope with the complicated states of the transmission path by switching between the coherent detection (PLL) and the differential detection using the error‐detection code. The proposed system uses a simple error‐detection code, and the two detectors are switched by selecting the detector with a fewer number of detected errors. The feature of the system is that it is simple, being constructed by the existing PLL and the differential detector. The effectiveness of the proposed system is verified by computer simulation.

Error control for low-bit-rate speech communication systems

The incorporation of low-bit-rate speech coders into emerging land and satellite mobile communication systems presents problems which previous communication systems have never encountered. One of the most important of these problems is the degradation experienced in speech quality as a result of corruption of the transmitted speech information by channel errors. This paper presents a systematic survey of the various techniques that are being adopted to mitigate this condition.

Field experiments on pilot symbol aided 16 QAM modems for land mobile communications

Field experimental results of the pilot symbol aided 16 QAM for land mobile communication are reported. Its performance is evaluated by determining the 50% value of the bit error rate (BER). The obtained performances are almost the same as the theoretically expected values. These results verify that 16 QAM is a practical modulation scheme for land mobile communication systems.

Fully digital M-ary psk and M-ary qam demodulators for land mobile satellite communications

A fully digital implementations of digital modems is the preferred option of system designers because high performance can be achieved at reasonable cost. The paper explains the beneficial features inherent in fully digital demodulator implementations. Other features which are required for land mobile satellite communication systems are also discussed. Recently reported techniques for the synchronisation and detection of M-ary PSK and M-ary QAM modulation schemes are reviewed with emphasis placed on those which are well suited to digital implementation.

A new millimetre wave satellite system for land mobile communications

AbstractCellular systems are gaining wide acceptance. In Europe the GSM system is expected to provide service to more than 10 million users by the year 2000. Assuming that a demand for additional services at 64 kbit/s or so will not easily be satisfied either by the present GSM system or by advanced satellite systems at L‐band, this paper proposes a new satellite system at EHF (40150 GHz) to be integrated at the end of the decade with the GSM system or its descendants. First, the paper describes the main obstacles for the new system, in terms of channel characteristics and technology developments, and then illustrates a preliminary system design to show the technical feasibility in the proposed ten years time scale.

Digital transmission through a land mobile satellite channel

An analytical derivation of the probability of bit error noncoherent frequency-shift keying (FSK) and coherent phase-shift keying (PSK) signals transmitted through a land-mobile satellite channel is described. The channel characteristics used in the analysis are based on a recently developed model which includes the combined effects of fading and shadowing. Analytical expressions for the probability of bit error of FSK and coherent phase-shift keying (CPSK) signals are obtained. The results show that large amounts of signal-to-noise ratio (SNR) are required to compensate for the combined effect of fading and shadowing. An analytical expression for the irreducible probability of bit error of a CPSK signal due to phase variations caused by fading and shadowing is derived. The results described should be useful in the design of land mobile satellite communication systems. >

Land mobile communications in Ku‐band. Results of a test campaign on eutelsat I‐F1

AbstractThis paper presents and discusses the results of technical tests on land mobile communications conducted in June and July 1989 in Europe using a EUTELSAT satellite. The land mobile communication system under test was that already operated by QUALCOMM in the U.S.A. under the registered name OmniTRACS.The field trial was organized in conjunction with the Signatories who expressed to EUTELSAT an interest in a full‐scale technical investigation of the system. The aim of the field trial was to evaluate the technical characteristics of the system and test its performance in different operating conditions.The results establish the relationship between transmission performance (i.e. essentially the required number of transmission attempts in order to get a message through the communication channel), and the environment of the land mobile, the satellite transponder's mode of operations and the interference conditions.

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. >

A Continuum Vibrational Analysis for a Tetrahedral Space Platform

Antennas over 50 metres diameter are being considered for use in land mobile communication systems. As the satellite in geostationary orbit has an angular velocity equal to that of the earth, no tracking systems are necessary and low cost fixed ground antennas can be used. In addition, a typical early truss platform could possibly be a geostationary communication one of size up to 300m × 300m. In this paper structural stiffness, strength and dynamic characteristics of large skeletal frameworks for space applications are investigated by analysing the tetrahedral truss which is idealised as an equivalent continuum. Appropriate analytical relationships are presented in terms of the truss member properties which are taken as slender graphite/polyethersulphone composites. Fundamental and harmonic frequencies have been calculated and have been compared with those from a finite element skeletal analysis and a finite element plate analysis. It has been shown that the results of the simplified analysis technique are accurate to within 10 per cent of those of the analytical solutions provided the system is both large and flexible. In addition, the analysis provides a simple methodology for the preliminary assessment of vibration frequencies for large space structures.

Channel hand-off strategies in cellular mobile communication systems

This paper describes a computer simulation study of a cellular, land-mobile radio communication system with and without frequency hand-off strategies. The authors assume that cell boundary crossings for calls-in-progress exist. In the hand-off procedure, they have studied several strategies where channels are specifically reserved for hand-offs. These strategies have been evaluated in terms of the new-call rejection rate and the rate of premature terminations of calls-in-progress. In a second method the authors have found the additional base station transmitter power required to service all the calls in progress without switching them to new channels. In addition, the cochannel interference introduced by this method has been evaluated and studied as a function of the additional transmission distance, with different partitions of channels, while maintaining a blocking probability of 2% or less.

Optimal design for cellular mobile systems

Cellular zone design parameters for a land mobile communication system are clarified. System parameters having a strong influence on cellular system performance are discussed and some problems encountered when system parameters are changed are examined.

Design and test of a spectrally efficient land mobile communications system using LPC speech

A communication system was built and tested to operate in the land mobile VHF band (150-174 MHz) at a channel separation of only 6 kHz. The audio source was digitally encoded at 2.4 kbits/s using linear predictive coding (LPC). The speech data stream was transmitted by frequency shift keying (FSK) which allowed the use of class-C transmitters and discriminator detection in the receiver. Baseband filtering of the NRZ data resulted in a narrow transmitter spectrum. The receiver had a 3 dB bandwidth of 2.4 kHz which allowed data transmission with minimal intersymbol interference and frequency offset degradation. A 58 percent eye opening was found. Bit error rate (BER) performance was measured with simulated Rayleigh fading at typical 150 MHz rates. Additional tests included capture, ignition noise susceptibility, adjacent channel protection, degradation from frequency offset, and bit error effects upon speech quality. A field test was conducted to compare the speech quality of the digital radio to that of a conventional 5 kHz deviation FM mobile radio.

Design and Test of a Spectrally Efficient Land Mobile Communications System Using LPC Speech

A communication system was built and tested to operate in the land mobile VHF band (150-174 MHz) at a channel separation of only 6 kHz. The audio source was digitally encoded at 2.4 kbits/s using linear predictive coding (LPC). The speech data stream was transmitted by frequency shift keying (FSK) which allowed the use of class-C transmitters and discriminator detection in the receiver. Baseband filtering of the NRZ data resulted in a narrow transmitter spectrum. The receiver had a 3 dB bandwidth of 2.4 kHz which allowed data transmission with minimal intersymbol interference and frequency offset degradation. A 58 percent eye opening was found. Bit error rate (BER) performance was measured with simulated Rayleigh fading at typical 150 MHz rates. Additional tests included capture, ignition noise susceptibility, adjacent channel protection, degradation from frequency offset, and bit error effects upon speech quality. A field test was conducted to compare the speech quality of the digital radio to that of a conventional 5 kHz deviation FM mobile radio.

The monopole slot as a two-port diversity antenna for UHF land-mobile radio systems

Urban land-mobile communication systems designed to operate over the upper portion of the UHF band are very susceptible to frequent wide signal variations. Deep fades arise due to the presence of many obstructions in the propagation path between the transmitter and receiver. One way to combat the effects of Rayleigh fading due to multipath propagation is to provide a diversity combiner in the mobile receiving system with two signals, each containing the same information, which fade independently of one another. Such a system can virtually eliminate deep fades from the receiver output. Described herein is a method of obtaining two diversity branches, with independent signals if so desired, from a single two-port antenna which is both well matched to the transponder and efficient over the land-mobile frequency band from 820- 890 MHz. A directive pattern is associated with each port. When operating with a direct wave, signal gain over an omnidirectional antenna is therefore possible.