Showing papers on "Spectral efficiency published in 1987"

Highly Efficient Digital Mobile Communications with a Linear Modulation Method

Abstract: Although linear modulation methods can achieve high spectrum efficiency, very little attention has been directed to their use in mobile radio systems. This is mainly due to the fact that the nonlinearity of the transmitter power amplifier tends to spread the spectrum and thus eliminate any spectrum efficiency advantage gained through the use of linear modulation methods. In this paper, a linear modulation system is proposed, which solves the above difficulty and which gives higher spectrum efficiency than conventional digital FM. The modulation/demodulation method is \pi /4 shift QPSK and phase-shift detection with a limiter-discriminator and an integrate-and-dump filter. By introducing a cartesian coordinate negative feedback control, 35 percent power efficiency at 10 W output power and - 60 dB relative out-of-band radiation are simultaneously achieved with a class "AB" amplifier, owing to the 29 dB feedback gain. The receiver configuration is easy to realize and gives immunity against fast fading through the use of noncoherent detection with limiter-discriminator. By using a novel decision method, bit error rate performances under both nonfading and fading condition are comparable to those obtained by digital FM. These results make it possible for linear modulation methods to achieve higher spectrum efficiency than is possible with conventional digital FM methods in mobile radio communications.

Cellular Efficiency with Slow Frequency Hopping: Analysis of the Digital SFH900 Mobile System

Abstract: The new digital cellular SFH900 mobile system, based on "mixed" slow frequency hopping (SFH) combined with time division, is described in detail. The system includes Viterbi quasi-coherent demodulation of GMSK for which performance measurements in multipath conditions are presented. A concatenated coding scheme that takes full benefit of built-in frequency diversity and interference diversity is introduced. A model for SFH cellular performance evaluation is presented and the quality-versus-capacity tradeoff for SFH900 is given for various frequency reuse patterns. With advanced 16 kbit/s speech coding techniques, and including a 25 percent overhead for management and signaling, the spectrum efficiency of a many-celled SFH900 network is around 3.5 users/cell/MHz, a significant increase in comparison to conventional analog systems. SFH provides intrinsic adaptability to varying traffic conditions and enhanced flexibility for multiservice operation. The SFH900 principles, which have been recently validated through field tests, are very promising for second generation cellular systems.

Hybrid channel assignment and reuse partitioning in a cellular mobile telephone system

Abstract: Radio bandwidth for mobile communications is very scarce. Therefore, attempts are made to increase spectrum efficiency. Investigations of these attempts have so far concentrated mainly on systems with small reuse patterns containing a relative small number of channels, and few comparisons between these systems and systems with larger number of channels have been performed. In this paper, hybrid channel allocation and reuse partitioning are investigated with respect to blocking probabilities and channel utilization. It is shown that the effects of hybrid allocation are less pronounced in small reuse patterns than in large. This is true for the advantages at low load as well as the disadvantages at high load. Reuse partitioning can on the other hand give substantial capacity increase, and the usual and unwanted side effect of unequal service over the system area can be decreased by the introduction of state protection.

New cellular schemes for spectral efficiency

Abstract: Assuming the constraint of an allocated frequency spectrum, two new schemes are suggested to increase spectral efficiency. Furthermore, the two new schemes can be integrated to become a hybrid system and offer greater performance which takes advantage of the merits and performance of each individual scheme.

Analysis for spectrum efficiency in single cell trunked and cellular mobile radio

Abstract: Spectrum efficiencies for single-cell trunked and cellular mobile radio systems are analyzed, taking into consideration fading circumstances and call blocking probability. Two kinds of transmit power control methods are considered. One retains area mean power at the receiver constant and the other retains local mean power constant. For single-cell trunked systems, it has been shown how spectrum efficiency is limited by the required traffic quality or permitable adjacent channel interference. A narrower channel spaced system shows superiority to wide-band systems, if an adjacent channel interference protection ratio is lower than about -40 dB and a few percent interference probability is permitted. On comparing cellular systems, superiority in spectrum efficiency is determined by the product of protection ratio and channel spacing. Call blocking probability and interference have little effect on spectrum efficiency comparison. For both systems, the two kinds of transmit power control and the two interchannel interference criteria show no significant difference between their effects on spectrum efficiency.

Transmission of log-PCM via QAM over Gaussian and Rayleigh fading channels

Abstract: The digital noise power due to transmission errors is determined for 8-bit μ-law PCM, μ = 255, signals transmitted via M-level QAM, M = 16, 64 and 256, over Gaussian and Rayleigh fading channels. The analytical results apply for various laws that map the 8-bit μ-law PCM signal into the QAM format, and for different binary Gray codes used to represent the QAM signal points. In addition to the theoretical results expressed as overall speech signal/noise ratio (SNR) as a function of channel SNR for different input speech signal levels, simulations for Gaussian and mobile radio channels using speech signals are also presented. From our deliberations we can conclude that the 256-level QAM system employing the best mapping law and Gray code has a gain of about 6dB in overall speech SNR compared to transmission without co-ordination of the speech bits over a Gray-coded link. Corresponding gains for 16-level and 64-level QAM are marginally smaller. By increasing the number of QAM levels from 4 to 256, the required increase in channel SNR per bit to maintain an overall speech SNR of 30 dB is approximately 12 dB. The bandwidth efficiency increases by a factor of four. The theoretical analysis in the paper is approximate. Only the effect of the most likely channel errors (single errors) has been taken into account. The theoretical results coincides well with the simulations, where such approximations were made.

1024-QAM and 256-QAM Coded Modems for Microwave and Cable System Applications

Abstract: Low redundancy FEC coded 1024-QAM modems, staggered 1024-QAM, and 256-QAM modems for spectrally efficient (up to 8.84 bits/s/Hz) microwave and cable systems applications are described. Such a high spectral efficiency is required for CEPT-1 (2.048 Mbit/s) rate digital transmission in a single analog supergroup (SG` band as well as for other emerging systems applications. Practical constraints of operational analog FDM systems are presented and taken into account in the choice of the low redundancy FEC codec and the coded 1024-QAM modem. Theoretical, computer simulation and experimental results of 256QAM modems have been extended to the feasibility study of 512-QAM, 961-QPRS, and 1024-QAM modems. Our experience with 256-QAM modems which have a T-1 (1.544 Mbit/s) rate in a 240 kHz analog supergroup (SG) band, i.e., an efficiency of 6.66 bits/s/Hz, demonstrates that a regenerative span over 1000 km is feasible over FDM radio systems. A significantly increased spectral efficiency of 8.84 bits/s/Hz is required for CEPT-1/SG system applications. Our R&D results, presented in this paper, demonstrate the feasibility of FEC coded 1024QAM modems, equipped with powerful digital adaptive equalizers, carrier phase noise, and symbol clock jitter cancellation subsystems, for the transmission of CEPT-1 rate signals in a single SG band.

Performance of Reduced-Bandwidth 16 QAM with Decision-Feedback Equalization

Abstract: This paper presents and investigates the performance of a reduced-bandwidth 16 QAM (RB-16 QAM) signaling technique which employs severe narrow-band filtering and decision-feedback equalization in the receiver to compensate for the resulting intersymbol interference The overall filtering is designed so as to provide the spectral efficiency of 64 QAM RB-16 QAM is compared to 64 QAM in terms of its performance on additive white Gaussian noise channels, in multipath fading environment, as well as in terms of its sensitivity to modem imperfections including carrier and timing phase errors, filter imperfections, nonlinear distortion and sinusoidal interference The results show that depending on the spectral shaping filters and the equalizer used, RB16 QAM can be significantly more advantageous than 64 QAM A most interesting finding is that while RB-16 QAM is comparable to 64 QAM in terms of its spectral efficiency, its robustness against system imperfections is very much like that of conventional 16 QAM

Transmission of Digital Speech in Highway Microcells

Abstract: Digital transmission of speech over highway microcellular channels is investigated and theoretical results of bit error rate (BER) as a function of channel SNR and co-channel interference are presented. MSK modulation is used and the co-channel interferer has both a carrier phase difference and data stream time offset from the wanted signal.Transmissions over Rayleigh fading and AWGN channels are studied, and the theoretical and simulation results are in close agreement. Simulations were also performed using log-PCM, ADPCM and SBC speech. It was found that for toll quality speech it was necessary to operate with a channel SNR and co-channel SIR that both exceeded 30 dB for a BER of 5×10−4. No channel coding or equalization was used. For free flowing vehicular traffic conditions where the average vehicular speed was 112 km/h, a three-cell cluster yielded a cell length of 2·13 km, assuming an allotted duplex bandwidth of 10 MHz, a channel spacing of 25 kHz and 133 mobile users per microcell. The spectral efficiency for 2% and 10% blocking was found to be 36·1 and 42·1 erlang/MHz/base station, while the corresponding erlang/MHz/km2 for a cell length of 2·13 km was 807·1 and 941·2.

On the use of repetition coding with binary digital modulations on mobile channels

Abstract: Repetition code, diversity and single error correcting codes are examined for use with binary modulation techniques over the faded mobile channel. Both bit-error performance and bandwidth efficiency are considered for PSK, DPSK and FSK modulations. The error correction capability of repetition coding is first considered and optimum repetitions is found. M-tuple diversity with maximum-ratio-combining MRC is then compared with repetition coding both with a single error-correcting code and without coding.

Orthogonal Cochannel Operation for High Spectrum Efficiency Based on the Example of 16 QAM-140 Mbit/s Systems Using Rolloff 0.19

Abstract: In view of the rapidly increasing demands for transmission capacity of public networks and the limited number of radio frequencies available, the band efficiency of existing systems in general will become insufficient for future high-capacity requirements. This fact is becoming increasingly evident for 16 QAM-140 Mbit/s radio systerns at 3.9, 6.7, and 11.2 GHz which are in widespread use in todays long-haul transmission networks. Conceptual and technological measures for making cochannel operation feasible and practical are presented using the example of a system family. By these means, even the capacity of existing 16 QAM-140 Mbit/s radio routes with 40 MHz interleaved channel arrangements can be doubled with the particular advantage of reutilizing the existing antennas and radio equipment with only minor modifications. A progressive filter concept makes orthogonal cochannel transmission possible with negligible adjacent channel spectrum interference. Surface acoustic wave IF filters are used to convert existing systems from 0.5 rolloff to 0.19 rolloff. Special RF channel/antenna arrangements were developed for the transmission of all RF channels in both directions, including space diversity and using only two antennas. A field experiment verified the feasibility of the concept and indicated that a crosspolar interference canceller is generally not necessary for 16 QAM140 Mbit/s cochannel operation.

A DBTV System for Optimum Bandwidth Efficiency

Abstract: A system for direct broadcasting by satellite is described which allows both a doubling of capacity without significant loss of quality compared with conventional broadcast TV and the option of trading the increased capacity in a compatible manner for enhanced definition and aspect ratio in the future. In order to achieve the necessary increase in bandwidth efficiency, two processes which exploit the redundancy in typical TV pictures are employed. Firstly, a relatively simple non-linear pre and post-filtering process is used to allow the time compression to be increased without significantly reducing the S/N. Secondly, subsampling and adaptive interpolation is used to limit the increase in time compression and the reduction in baseband bandwidth. One possible way of implementing compatible extension is described.

Worst case cochannel interference and spectrum efficiency of GMSK in cellular mobile radio systems

Abstract: A general theoretical analysis of GMSK in cellular mobile radio system is presented. A closed form expressions for the probability of error is derived in fast Rayleigh fading and in the presence of Gaussian noise and worst case cochannel interference. The spectrum efficiency is evaluated for some cases of interest and compared with the results presented in [1]. It is shown that the spectrum efficiency is lower under fast fading environment than that presented in [1] because higher protection carrier to interference ratio is required in fast fading.

Narrowband digital modems for land mobile radio

Abstract: The modems operate in the 900 MHz band and with a channel spacing of 25 kHz. Each transmitted signal from a mobile is a four-level QAM signal, with an element rate of 12,000 bauds and a total bandwidth of 24 kHz. 20% redundancy is allowed for retraining and synchronization purposes, giving a useful transmission rate of 19,200 bit/s for each QAM signal. Coherent demodulation together with a new technique of combined signal-detection and channel-estimation are used at the receiver, for more accurate tracking of the rapidly fading signal. Two four-level QAM signals can be transmitted simultaneously over each separate frequency band, giving a resultant bandwidth efficiency of just over 1·5 bit/s per Hz for useful data. The independent fading of the two signals, together with the particular detection and estimation processes employed at the receiver, prevent any undue interference between the two signals.The signals fed from the base station to the mobiles are 16-level QAM signals, that are frequency division multiplexed, with a channel spacing of 25 kHz. Each signal has an element rate of 12,000 bauds and a total bandwidth of 24 kHz. Two mobiles are fed from any one 16-level QAM signal, and the bandwidth efficiency for useful data is again just over 1·5 bit/s per Hz.The base station/mobile receiver uses two antennas, in an arrangement of space diversity, together with the maximum-likelihood combining of the two signals. The channel estimator is regularly retrained, so that it is not subject to catastrophic failure, and the detector achieves near-maximum-likelihood detection of the received data signal.

Numerical analysis of intermodulation interference in an optical coherent multichannel system

Abstract: Coherent optical transmission techniques have a potential for use in ultra-wide-band coherent optical lans (UCOL's) in addition to long distance applications. They offer the possibility of extremely high total bandwidth by making simultaneous transmission of multiple wide-band signals possible. This paper reports on the numerical simulation of the performance of a heterodyne optical FDM system as a function of channel spacing. The channel interference due to intermodulation noise is discussed. A possible channeling arrangement with a spectral efficiency of 45 percent is described.

A Comparison of Digital Modulation Techniques for Meteor Burst Communications

Abstract: This paper compares candidate modulation schemes for meteor burst communications (MBC) using average information throughput over the meteor scatter channel as the principal performance measure. Average throughput is shown to depend upon both the bandwidth efficiency and the required energy per bit to noise power spectral density ratio (i.e., E b /N o ) of a modulation scheme through the latter parameter's influence on the channel duty cycle. It is shown that among coherent modulation schemes, 8-ary biorthogonal FSK and QPSK have the best performance while among noncoherent herent modulation schemes, 8-ary orthogonal FSK has the best performance.

Orthogonal Cochannel Operation for High Spectrum Efficiency Based on the Example of 16 QAM-140 Mbit/s Systems Using Rolloff 0.19

Abstract: In view of the rapidly increasing demands for transmis- sion capacity of public networks and the limited number of radio fre- quencies available, the band efficiency of existing systems in general will become insufficient for future high-capacity requirements. This fact is becoming increasingly evident for 16 QAM-140 Mbit /s radio sys- tems at 3.9, 6.7, and 11.2 GHz which are in widespread use in todays long-haul transmission networks. Conceptual and technological measures for making cochannel op- eration feasible and practical are presented using the example of a sys- tem family. By these means, even the capacity of existing 16 QAM-140 Mhit /s radio routes with 40 MHz interleaved channel arrangements can be doubled with the particular advantage of reutilizing the existing antennas and radio equipment with only minor modifications. A pro- gressive filter concept makes orthogonal cochannel transmission pos- sible with negligible adjacent channel spectrum interference. Surface acoustic wave IF filters are used to convert existing systems from 0.5 rolloff to 0.19 rolloff. Special RF channellantenna arrangements were developed for the transmission of all RF channels in both directions, including space diversity and using only two antennas. A field experi- ment verified the feasibility of the concept and indicated that a cross- polar interference canceller is generally not necessary for 16 QAM- 140 Mbit /s cochannel operation.