Showing papers on "Bit error rate published in 1992"

8-PSK trellis codes for a Rayleigh channel

Abstract: A suboptimal trellis coding approach based on the concept of combining a good convolutional code and bit interleavers is presented. The aim is to improve the reliability of digital radio communication over a fading channel. It is shown that over a Rayleigh channel and for a fixed code complexity the proposed system is superior to the baseline system. Its performance is analyzed using the generalized R/sub o/ and the upper bound on the bit error rate. The results suggest that on a Rayleigh channel, the standard trellis codes may not be the correct approach for improving the reliability of the communication channel. The discussion is restricted to a rate 2/3 coded system with 8-PSK modulation. >

Polarization multiplexing with solitons

Abstract: It is shown both analytically and with numerical simulation, and confirmed experimentally in transmission over distances up to approximately 10000 km, that solitons maintain a high degree of polarization over an ultra-long distance transmission system consisting of birefringent dispersion-shifted fiber segments and erbium amplifiers. Based on that fact, the authors propose a polarization/time division multiplexing technique which should allow the single-wavelength bit-rate capacity of an ultra-long distance soliton transmission system to be doubled with little or no significant increase in bit error rate. >

Bandlimited quasi-synchronous CDMA: a novel satellite access technique for mobile and personal communication systems

Abstract: Recent trends in digital communications are opening commercial applications to code division multiple access (CDMA). A novel access technique based on bandlimited quasi-synchronous CDMA (BLQS-CDMA) is described, showing all the advantages of synchronizing conventional direct sequence CDMA to drastically reduce the effect of self-noise. Bandlimitation is achieved with no detection loss by means of Nyquist chip shaping, leading to a simple all-digital demodulator structure. Detection losses due to imperfect carrier frequency and chip timing synchronization are analytically derived and numerical results are checked by computer simulations. Impairments due to satellite transponder distortions are evaluated. The full digital modem structure is presented, together with possible applications to mobile and very small aperture terminal (VSAT) satellite communications. >

Subband image coding using entropy-coded quantization over noisy channels

Abstract: Under the assumption of noiseless transmission the authors develop two entropy-coded subband image coding schemes. The difference between these schemes is the procedure used for encoding the lowest frequency subband: predictive coding is used in one system and transform coding in the other. After demonstrating the unacceptable sensitivity of these schemes to transmission noise, the authors also develop a combined source/channel coding scheme in which rate-compatible convolutional codes are used to provide protection against channel noise. A packetization scheme to prevent infinite error propagation is used and an algorithm for optimal assignment of bits between the source and channel encoders of different subbands is developed. It is shown that, in the presence of channel noise, these channel-optimized schemes offer dramatic performance improvements. >

Digital communication system using superposed transmission of high speed and low speed digital signals

Abstract: A digital communication system using superposed transmission of high and low speed digital signals capable of transmitting superposed high and low speed digital signals through an identical frequency band efficiently by increasing a simultaneously transmittable number of channels in the low speed digital signals, while achieving the practically reasonable bit error rate performances for both the high speed digital signals and the low speed digital signals. In this system, the low speed digital signals are transmitted in a form of spread spectrum signals and the high speed digital signals are cancelled out from the superposed transmission signals in obtaining the output low speed digital signals by using the phase inverted replica of the high speed digital signals to be combined with the superposed transmission signals, so that it becomes possible to increase a number of channels for the low speed digital signals, while achieving the practically reasonable bit error rate performances for both the high speed digital signals and the low speed digital signals.

Combined effects of phase sweeping transmitter diversity and channel coding

Abstract: A novel transmitter diversity scheme that generates forced fading to improve the performance of channel coding is proposed and investigated. Since the required phase sweeping frequency is much smaller than the transmission bit rate, bandwidth expansion is negligible. A sinusoidal phase sweeping function Delta Theta sin(2 pi f/sub H/t) is employed in laboratory experiments using 32 kbit/s quarternary differential phase shift keying (QDPSK) with differential detection and BCH(23,12) code. It is shown that Delta Theta =200 degrees and f/sub H/=67 Hz can be used when m (interleaving depth)=10 b. Hence, excessively long interleaving is not required by the use of transmitter diversity. Under very slow Rayleigh fading (f/sub D/=1 Hz), a measured improvement of 4.8 dB is obtained at a word error rate of 10/sup -2/ without receiver diversity. Applications include paging systems that require very simple receivers. >

Channel modeling and simulation in satellite mobile communication systems

Abstract: An analog model describing signal amplitude and phase variations on shadowed satellite mobile channels is proposed. A linear combination of log-normal, Rayleigh, and Rice models is used to describe signal variations over an area with constant environment attributes while an M-state Markov chain is applied to represent environment parameter variations. Channel parameters are evaluated from the experimental data and utilized to verify a simulation model. Results, presented in the form of signal waveforms, probability density functions, fade durations, and average bit and block error rates, show close agreement with measurements. >

Qam system in which the constellation is modified in accordance with channel quality

Abstract: A radio system is so designed as to allow each of a pair of transceivers to assess the quality of the link, and to modify the signal constellation accordingly. Each transceiver monitors the quality of the channel by assessing the strength of the received signal, or the bit error rate, or both. The system is specifically adapted to time division duplex (TDD) transmission over fast fading channel. In each block of data, the first bit is a QPSK (4QAM) signal, which indicates which constellation is to be used.

Bit error rate of binary and quaternary DPSK signals with multiple differential feedback detection

Abstract: A differentially coherent detection scheme with improved bit error rate (BER) performance is presented for differentially encoded binary and quaternary phase shift keying (PSK) modulation. The improvement is based on using L symbol detectors with delays of 1, 2, . . ., L symbol periods and on feeding back detected PSK symbols. Exact formulas for the bit error probability are derived for the case that correct symbols are fed back. The effect of symbol errors in the feedback path on the BER is determined by computer simulations. >

On the implementation and performance of single and double differential detection schemes

Abstract: A variety of schemes for performing differential detection in environments characterized by frequency offset are discussed. All of the schemes involve encoding the input phase information as a second-order difference and performing an analogous second-order differential detection at the receiver. Because of the back-to-back differential detection operations at the receiver, The performance of most of the schemes is considerably degraded relative to that of first-order differential detection schemes. However, the latter are quite sensitive to frequency offset and, in many instances, cannot be used at all. It is demonstrated that via a simple enhancement of using a 2 T s (instead of T s) delay in the second stage of the encoder and first stage of the decoder, the performance degradation can be significantly reduced. This result is significant in view of the fact that it comes without any penalty in implementation complexity. >

Demonstration of error-free soliton transmission over more than 15000 km at 5 Gbit/s, single-channel, and over more than 11000 km at 10 Gbit/s in two-channel WDM

Abstract: By transmitting trains of 213 bit pseudorandom words in a recirculating loop, we demonstrate ‘error-free’ (measured BER ≥10−10) soliton transmission at 5 Gbit/s, single channel, and at 10 Gbit/s in a two channel WDM, over paths as great as 15 400 km and 11 250 km, respectively.

Image coding system using an orthogonal transform and bit allocation method suitable therefor

Abstract: A bit allocation method which facilitate control of the number of bits to be assigned to transform coefficients and block of image data with a deviation from the functional form. An image coding system which can implement an optimal bit allocation that minimizes quantization error under a predetermined information content or amount, in carrying out bit allocations of block-adaptive type and transform coefficient-adaptive type.

Matched filter performance bounds for diversity combining receivers in digital mobile radio

Abstract: By employing the technique known as the matched filter bound, the authors derive analytical expressions for the distribution and average of the bit-error-rate in an ideal space diversity mobile radio receiver. Each diversity branch receives from a frequency-selective Rayleigh fading channel of arbitrary delay profile, and is subjected to additive Gaussian noise of arbitrary spectral shape. Numerical results calculated from the analytical expressions give insight into the relative benefits of antenna diversity and wideband transmission over the mobile radio channel. >

Uncoded and coded performance of MFSK and DPSK in Nakagami fading channels

Abstract: The author presents uncoded and coded performance results for noncoherent M-ary frequency-shift keying (MFSK) and differentially coherent binary phase-shift keying (DPSK) in a slow nonselective Nakagami-m (1960) fading channel. He gives simple expressions for the asymptotic slopes of probability of bit error for large signal-to-noise ratio and shows that the effective order of diversity compared to an uncoded Rayleigh channel is the product of two parameters, one for the channel and one for the code. He also compares the uncoded Nakagami-m results to those of the Rician channel in order to show performance differences between these two generalized fading channel models. >

Symbol-aided plus decision-directed reception for PSK/TCM modulation on shadowed mobile satellite fading channels

Abstract: The symbol-aided (SA) synchronization concept developed by Moher and Lodge (1989) is applied to the MSAT channel modeled with a shadowed Rician process. Simulation data demonstrate that it can track the severe phase jitter encountered on the fading channel free of the false lock which plagues conventional techniques. The algorithm multiplexes known symbols into the data stream, establishing an absolute reference free of decision errors that is used to estimate the fading phase. An improvement to the SA algorithm which extracts phase information from the data-bearing symbols is proposed. It is found that the new technique is more effective for larger K. The improved algorithm is referred to as symbol-aided plus decision-directed (SADD) phase estimation. A system employing SADD phase estimation, trellis-coded modulation, interleaving, and amplitude weighting within the Viterbi decoder yielded the best BER performance on the shadowed MSAT channel considered. >

Digital transmission of acoustic signals over a noisy communication channel

Abstract: The performance of digital communication over a noisy communication channel is improved. An encoder combines bit modulation with error control encoding to allow the decoder to use the redundancy in the error control codes to detect uncorrectable bit errors. This method improves the efficiency of the communication system since fewer bits are required for error control, leaving more bits available for data. In the context of a speech coding system, speech quality is improved without sacrificing robustness to bit errors. A bit prioritization method further improves performance over noisy channels. Individual bits in a set of quantizer values are arranged according to their sensitivity to bit errors. Error control codes having higher levels of redundancy are used to protect the most sensitive (highest priority) bits, while lower levels of redundancy are used to protest less sensitive bits. This method improves efficiency of the error control system, since only the highest priority data is encoded with the highest levels of redundancy. The effect of uncorrectable bit errors is reduced by adaptively smoothing the spectral parameters in a speech decoder. The amount of smoothing is varied depending upon the number of errors detected during the error control decoding of the received data. More smoothing is used when a large number of errors are detected, thereby reducing the perceived effect of any uncorrectable bit errors which may be present.

A Bayesian maximum-likelihood sequence estimation algorithm for a priori unknown channels and symbol timing

Abstract: It is shown that the optimum demodulator for the case of an a priori unknown channel and symbol timing can be approximated using a modified Viterbi algorithm (VA), in which the branch metrics are obtained from the conditional innovations of a bank of extended Kalman filters (EKFs). Each EKF computes channel and timing estimates conditioned on one of the survivor sequences in the trellis. It is also shown that the minimum-variance channel and timing estimates can be approximated by a sum of conditional EKF estimates, weighted by the VA metrics. Simulated bit error rate (BER) results and averaged-squared channel/timing error trajectories are presented, with estimation errors compared to the Cramer-Rao lower bound. The BER performance of the modified VA is also shown to be superior to that obtained using a decision-directed channel/timing estimation algorithm. >

Wireless communication system compulsively turning remote terminals into inactive state

Abstract: A wireless communication system containing at least one transmission apparatus and at least one communication terminal. The transmission apparatus transmits a wireless signal representing a bit sequence containing at least a predetermined number of bit errors, to the communication terminal. The communication terminal receives the wireless signal to regenerate the bit sequence. The communication terminal then examines the bit sequence represented by a received wireless signal to determine whether or not the number of bit errors contained in the bit sequence is equal to or greater than a predetermined number. When it is determined that at least the predetermined number of bit errors are contained in the bit sequence represented by a received wireless signal, the operation of the communication terminal is made inactive. Further, the transmission apparatus may transmit a wireless signal representing a bit sequence containing no pattern coinciding with a predetermined frame synchronization pattern, to the communication terminal. The communication terminal receives the wireless signal to regenerate the bit sequence. The communication terminal then examines the bit sequence represented by a received wireless signal to determine whether or not the bit sequence contains the predetermined frame synchronization pattern. When it is determined that the bit sequence does not contain the predetermined frame synchronization pattern, the operation of the communication terminal is made inactive.

Modulation and filtering control of soliton transmission

Abstract: Two methods of controlling the temporal diffusion of solitons in long-distance transmission are investigated theoretically. One, pursued experimentally by Nakazawa et al. [ Electron. Lett.27, 1270 ( 1991)] uses amplitude modulation synchronized with the bit rate. The other method, first proposed recently, uses filtering. The latter is better adapted to wavelength division multiplexing. It is shown that the so-called Gordon-Haus limit of soliton propagation can be extended significantly.

Performance analysis of various 16 level modulation schemes under rayleigh fading

Abstract: The average bit error rate (BER) performances of 16 square/star QAM and 16 CPSK/DPSK under Rayleigh fading are theoretically analysed and compared. 16 star QAM is inferior to 16 square QAM, which achieves the best performance, by ∼4 dB in the required average Eb/N0; however, when compared with differentially encoded square QAM, the performance inferiority is less than 2 dB.

Simulation and performance of the pan-European land mobile radio system

Abstract: The introduction of the European Telecommunications Standards Institute/Groupe Special Mobiles (ETSI/GSM) digital land mobile radio system has required the study and application of advanced transmission techniques, necessary to meet the quality objectives in very demanding environments. In particular, the authors consider the performance of the compact-spectrum constant-envelope modulation chosen by ETSI/GSM, together with concatenated block and convolutional coding, Viterbi adaptive equalization, and soft-decision Viterbi decoding to cope with the severe time- and frequency-selective distortions caused by propagation phenomena, properly modeled for computer simulation. Channel coding and adaptive equalization techniques, supported also by frequency hopping and diversity reception, are fundamental to operate the system with the required quality. >

Error probabilities of fast frequency-hopped FSK with self-normalization combining in a fading channel with partial-band interference

Abstract: Error probability analysis is performed for a binary orthogonal frequency-shift-keying (FSK) receiver using fast frequency-hopped (FFH) spread-spectrum waveforms transmitted over a frequency-nonselective slowly fading channel with partial-band interference. Diversity is performed using multiple hops per data, bit. A nonlinear combination procedure referred to as self-normalization combining is used by the receiver to minimize partial-band interference effects. Diversity is found to completely negate degradation of the self-normalized receiver caused by partial-band interference and offers definite receiver performance improvement when the direct signal component is weak. The self-normalized receiver is sensitive to fading channels. For severe channel fading, the performance of a conventional noncoherent binary FSK receiver is generally either equivalent or superior to that of the self-normalized receiver. >

Hybrid DS/SFH spread-spectrum multiple access with predetection diversity and coding for indoor radio

Abstract: The authors derive close upper and lower bounds on the average bit error probability for hybrid direct-sequence/slow-frequency-hopped spread-spectrum multiple-access (DS/SFH-SSMA) systems with noncoherent DPSK demodulation, using predetection diversity (selection combining and equal gain combining) in conjunction with interleaved channel coding (Hamming

Increased CDMA system capacity through adaptive cochannel interference regeneration and cancellation

Abstract: Asynchronous code division multiple access (CDMA) systems using digital matched filtering (DMF) reception techniques suffer from poor multiple access spectral efficiency. This is due entirely to the lower bound on the mean square crosscorrelation levels which exist between the orthogonal codes allocated to each system subscriber. This interference can be estimated through channel measurement, and it is then possible to regenerate and subsequently cancel crosscorrelation components from individual interfering channels, thereafter increasing the effective signal-to-interference ratio on the desired channel for a given subscriber activity level. This paper suggests a technique to exploit this ability in order to gain an increase in the number of multiple access channels available within a particular bandwidth. Theoretical analysis of the proposed cancellation scheme shows an upper bound on the spectral efficiency approaching 130% or 1.3 normalised channels per hertz for successive cascaded cancellation stages. Simulation results for CDMA systems show that, for the traditional DMF receiver without dynamic cancellation, the CDMA efficiency is approximately 10% for a bit error rate of 10−4. Analysis is presented for single and two stage cancellation receivers showing 40% and 50% capacity, respectively, for the same error rates derived from a receiver whose complexity is linear in the number of supported active subscribers.

Bounds on the error performance of coding for nonindependent Rician-fading channels

Abstract: New upper bounds on the error performance of coded systems for Rician channels are presented. The fading channels need not be fully interleaved to obtain meaningful performance results. These bounds hold for coherent, differentially coherent and noncoherent demodulation of binary signals. They provide a useful analytical approach to the evaluation of the error performance of convolutional or block coding and they may be generalized to M-ary signals and trellis modulation. The approach allows for complex bounds using the fine structure of the code, for simpler bounds similar to those on memoryless channels and finally for a random coding bound using the cutoff rate of the channel. The analysis thus permits a step by step evaluation of coded error performances for Rician-fading channels. >

Performance of smart lightwave receivers with linear equalization

Abstract: Signal processing techniques can be used to reduce linear and nonlinear distortion in high-speed lightwave systems caused by fiber dispersion and nonideal responses of optoelectronic and electronic components. The improvement in the performance of 2.5 and 10 Gb/s intensity modulation, direct detection systems is assessed for receivers which utilize an analog taped delay line equalizer to compensate for signal distortion. Synchronous and fractionally spaced equalizers are evaluated. Smart receivers that jointly optimize the decision time, decision threshold, and equalizer tap weights under a minimum bit error ration criterion are considered. This yields the optimum system performance and allows consideration of both reduced distortion and enhanced noise arising from the signal processing. The effectiveness of the equalization is determined as a function of several important system parameters. Three-tap and five-tap synchronous equalizers yield virtually the same improvement in receiver sensitivity. Depending on the system, a five-tap fractionally spaced equalizer with half-bit-period tap spacing may or may not be significantly more effective than a three-tap synchronous equalizer. >

Hybrid DS/SFH-SSMA with predetection diversity and coding over indoor radio multipath Rician-fading channels

Abstract: The authors investigate the bit-error-rate (BER) performance of hybrid direct-sequence/slow-frequency-hopped spread-spectrum multiple-access (DS/SFH-SSMA) systems operating over a multipath Rician-fading channel (which models indoor radio propagation in factories). They consider both phase-shift-keying (PSK) modulation with coherent demodulation and differential phase-shift-keying (DPSK) modulation with noncoherent demodulation. Predetection multipath diversity (maximal ratio combining for coherent reception and equal gain combining for noncoherent reception) and simple interleaved channel coding are employed for improving the BER performance. The BER of both coherent and noncoherent hybrid systems is obtained using a Gaussian interference approximation. >

OFDM for data communication over mobile radio FM channels. II. Performance improvement

Abstract: For pt.I see ibid., vol.39, no.5, p.783-93 (1991). The performance of an orthogonal frequency-division multiplexing (OFDM)/frequency modulation (FM) system for data communication over Rayleigh-fading mobile radio channels was analyzed in pt.I. The effects of forward error correction, switching diversity, automatic gain control (AGC), and squelch are studied. It is shown that OFDM/FM works well with switching diversity because OFDM can average out the transients created by switching between antennas. It is also found that the independent error assumption can be used to predict the distribution of the number of errors in a word. The use of squelch produced a small (about 1 dB) performance improvement, whereas the use of AGC provided negligible improvement. >

Apparatus and method for high speed flexible multiplexing for fibre optic data transmission

Abstract: Disclosed is a method and apparatus for flexibly converting an electrical parallel digital data signal to a serial optical digital data signal for transmission along a fiber optic cable and then subsequent conversion back to a parallel electrical digital data signal. An input conditioner circuit is used to set a ratio between a transmission link clock rate and a sample clock rate such that the ratio determines the number of bits being transmitted for a sample word thus enhancing the flexibility of the device to different sampling rates. Each individual sample word is a frame of data which includes a single frame bit set up in a 4-bit frame pattern. A first frame bit is a sync acquisition bit comprised of an alternating sequence of "0"s and "1"s, a second and fourth parity bit computed from the parity of the previous two words of data, and a third channel identification bit. An output conditioner circuit receives the serial stream of data bits to convert it back to a parallel data format. The output conditioner further must identify and remove the frame bits as discussed above for proper processing. By this, the system can transmit data at flexible sample rates.

Suppression of narrowband jammers in a spread-spectrum receiver using transform-domain adaptive filtering

Abstract: The author investigates the use of transform-domain adaptive filtering for the suppression of narrowband jammers in a direct-sequence (DS) spread-spectrum receiver. An input signal consisting of the DS signal, white Gaussian noise, and a narrowband jammer is transformed into the frequency domain where adaptive filtering acts to suppress the jammer. Weight leakage is used to allow jammer suppression while preserving the desired DS signal. Bit error rate (BER) results obtained by computer simulation are presented to illustrate performance for a single-tone jammer and for a jammer consisting of a second DS signal with a lower chip rate. These results are compared to those for a transform-domain exciser. Expressions for the converged tap weights are derived and the results are verified via the simulation. Finally, the convergence properties of the adaptive suppressor are illustrated. >