Showing papers on "Bit error rate published in 1970"

An analysis of the effectiveness of hybrid transmission schemes

Abstract: A comparison is made of the performance of pure retransmission, forward error correction and hybrid (error detecting/ correcting) schemes for data transmission in a noisy (probability of error, P > 10-4) binary symmetric channel. The performance calculations are based on the use of BCH codes for error detection and correction up to the full correction capability of the code. It is shown that a probability of undetected error of less than 10-9 error/bit, can be achieved by correcting only a few errors while retaining a reasonable throughput and a very low retransmission rate. The best codes in the class considered are specified and the complexity of instrumentation is estimated. Finally, various combinations of possible systems employing half duplex and reverse channel operation are used in a comparison of the transmission schemes. For line error rate worse than 10-4 error /bit, a hybrid system operating with a reverse channel is superior to the other possibilities.

Adaptive pulse code modulation system

Abstract: An adaptive pulse code modulation system useful for increasing the channel capacity of a fixed bandwidth communication link by reducing the redundancy characteristic of nonadaptive systems. In the subject system, the transmitter allocates space in a fixed bit length sample field amongst multiple channels on a frame by frame basis. Each channel is assigned space in the sample field only when that channel is active. The activity status of each channel is determined by averaging the sample amplitudes from that channel over a specified number of frames and if that average exceeds a specified threshold, then that channel is defined to be active. The activity status of each channel is monitored at a very high rate so that when a user begins speaking, his voice will be detected and assigned space soon enough to prevent his speech from being noticeably clipped. Each frame includes at least three fields; (1) an active channel sample field, (2) an activity status field and (3) an activity sync field. The activity status field is used to represent the activity status of a different channel each frame. Thus, in a typical 30 channel system, the activity status of each channel will be reported once every 30 frames. The activity sync field is comprised of one bit which enables the receiver to assign each received activity status field to the proper channel. In constructing a frame, the transmitter samples each voice channel and allocates a portion of the adaptive sample field to each active channel leaving vacant space if the complete sample field is not required and ''''rounding off'''' the samples to ''''fit'''' them in the sample field if an unusually large number of channels are active. To process each incoming frame, the receiver counts the total number of active channels, determines the number of bits per sample, and then rescales the received samples back to full magnitude if they were rounded off.

Character bit error detection and correction

Abstract: Method and apparatus for detecting and correcting single bit errors in a bit pattern recorded on a two-track magnetic recording medium, the bit pattern including a parity bit. The bits corresponding to binary ones are recorded as flux transitions on one track and the bits corresponding to binary zeros are recorded as flux transitions on the other track. An error is defined if a flux transition is not detected in both tracks for a particular bit location or if flux transitions are detected in both tracks for a particular bit location. A detected error is shifted into an error register at the associated bit location as the bit pattern is shifted into a binary storage register. If established parity is not lost and the number of errors in the bit pattern which ended with the parity bit is not greater than one, the bit detected to be in error is complemented in the binary storage register.

Analysis and Simulation of a PN Synchronization System

Abstract: This paper analyzes the synchronization error which results when a pseudonoise synchronization signal in a coherent communication link is degraded by both additive white Gaussian noise and amplitude jitter produced by the reference carrier phase error. A synchronization system similar to a phase-locked loop is presented and simulated on a digital computer in order to find the distribution of the synchronization error. It is shown that the error is made up of two Gaussian components: one produced by the additive noise and one produced by the amplitude jitter. An approximate solution is also derived by appropriately bounding the reference phase error. The results are shown to be applicable to several similar systems found in the literature.

Error correcting and detecting systems

Abstract: A single error correcting system for correcting messages of any number of data bits comprises encoding means and decoding means. The encoding means adds r check bits, each check bit representative of at most r-1 data bits and, on the average, each check bit representative of >r/2 data bits; each check bit is representative of no more than one common data bit; and each data bit is represented by exactly two check bits. The decoding means for each data bit has an error correcting circuit receiving three inputs from input circuitry, one input being the data bit itself and the other two inputs being combinations, respectively, of one of the two check bits and other data bits representative of the received data bit. The error correcting circuit is capable of producing an output correctly corresponding to the data bit if no more than one input thereto was in error. A double error detecting system, useful with this single error correcting system, inputs syndrome bits representative of each check bit and of an added parity bit to an OR circuit and to an ADDER circuit, and compares the output from these circuits.

Digital data decoder with data rate recovery

Abstract: A decoder circuit is disclosed for decoding digital signals having frame end transitions, for example, on bits of value ''''1'''' and mid-frame transitions for the second one of two sequential ''''0''s'''' and for each ''''0'''' thereafter. Sequential transitions alternatingly trigger two oscillators of similar frequency which is at least twice the bit rate frequency. The oscillations overlap to ensure phase coherency. The oscillator outputs are combined and counted down to the bit rate frequency for bit rate recovery. The frame ends are strobed to detect absence or presence of a transition for bit value recovery.

Digital demodulation with data subcarrier tracking

Abstract: Digital demodulator is based on early-late bit timing scheme coupled with Costas data tracking loop. System is successful in enhancement of weak signals from space where atmospheric and other interference media cause bit error rate to reach excessive level.

Mitigation of Non-linear Distortion Using PTS and IDAR Method for Multi-Level QAM-OFDM System

Abstract: The future satellite communication systems are required to support the higher transmission data rate for providing the multimedia services by employing the efficient modulation method such as multi-level QAM. The employment of single carrier transmission with multi-level QAM would cause the fatal degradation of signal quality due to the non-linear amplifiers located at the earth station and satellite. To overcome this problem, we have proposed the multilevel QAM-OFDM technique with IDAR (Improved Decision Aided Reconstruction) method designed for non-linear satellite channel. However, the proposed method could not mitigate the non-linear distortion sufficiently when modulation level becomes higher such as 64QAM. This paper proposes the combined scheme of partial transmission sequence (PTS) and OFDM-IDAR methods so as to enable the usage of higher multi-level QAM method, which can achieve the higher transmission data rate with keeping the better bit error rate performance in the non-linear satellite channel. The various computer simulations are conducted in this paper to verify the effectiveness of proposed method in the non-linear satellite channel.

The Bit Error Rate analysis of Direct Sequence Ultra Wide Band System in Mine Channel

Abstract: The necessity for wireless communications in underground mines is well understood. Some companies have started to deploy modern wireless networks in mine galleries with the objective of increasing safety and productivity. This paper presents the Bit Error Rate (BER) analysis of Direct Sequence Pulse Amplitude Modulation (PAM) Ultra Wide Band (UWB) system for underground mine environment. Discrete time channel impulse response is used to build up revised channel model for underground mine which is based on the UWB channel model proposed by IEEE802.15.3a.With the revised channel model, we compare the performance of IEEE channel and mine channel by considering Mean Excess Delay, Root Mean Square (RMS) delay and Number of significant Paths with in 10 dB of peak (NP 10dB) and observe the significant increase in the parameter. We evaluated the BER performance using RAKE receiver employing maximal ratio combining (MRC) for different data rate, repeat bit and number of RAKE figure in underground mine channel. Simulation results shows that DS-PAM-UWB system can sustain in the dense multipath environment of underground mine and provide acceptable BER.

Estimation of Bit Probability of Error Using Sync Word Error Rate Data

Abstract: Assuming bit errors are independently distributed with a constant probability of error p e , it is shown that a simple estimator is highly efficient for estimation of p e . The estimator is based on a simple function of the number of sync words containing no bit errors. The estimator is shown to be maximum likelihood, minimum chi-square, and modified minimum chi-square when the quality index reported is simply the percent of frames containing zero errors. An approximate confidence interval for p e is obtained, and a determination of the number of sync words to observe in order to obtain an approximate confidence interval of fixed length is indicated. The method of scoring which can be used to obtain a more efficient estimator of p e is described.

Error detection and correction equipment

Abstract: 1,175,866. Digital transmission systems. STANDARD TELEPHONES & CABLES Ltd. 30 May, 1968 [6 June, 1967], No. 26061/67. Heading H4P. To reduce the effects of error bursts the bits of a group of digital data words, each consisting of a multi-bit character and a corresponding error-correcting multi-bit check signal, are rearranged so that no two adjacent input bits are adjacent when transmitted. As described, the words consist of 5-bit characters and 5-bit check signals. Five such words are passed to a 50-bit shift register which has each stage connected via a gate to a corresponding stage of a second 50-bit register. The interconnection is such that when the second register is read out for transmission all the first bits of the 5-bit characters are transmitted first, followed by the first bits of the 5-bit check signals. Then the second bits of the characters and check signals are sent, then the third, and so on. This ensures that any error burst less than 6 bits long will not effect more than one bit in any one character or check signal, the check signal being such that single bit errors can be corrected. At the receiver the transmitted signals are reformed to their original order by apparatus similar to that at the transmitter.

The Upper Bounds of the Confidence Intervals of Bit Error Probabilities Based on a Markov Chain Bit Error Model

Abstract: Confidence intervals for the bit error probability of an actual PCM telemetry data can be determined based on the analysis of received redundant bits. The procedure usually requires the assumption of independence of bit errors. However, bit errors may occur in clusters under various conditions of multipath, injection of nonthermal noise of long duration, and bit jitters. As a representation of bit errors in clusters, a Markov chain model is introduced. Some results on the confidence interval of bit error probability are obtained as functions of a Markovian parameter, which designates the degree of departure from the binomial model. The computations are quite laborious compared to the case of the binomial model. This paper gives step-by-step instructions for computing the probabilities that r error bits occur among mn received bits which can then be used for the derivation of the confidence interval.

Comparison of SCM and Rayleigh Channel Models by Exploitation of Diversity in Time and Spatial Domain Using OpportunisticCommunication Technique

Abstract: This paper exploits the concept of diversity using adaptive antenna at BS, where different users are communicating with BS from different locations but at same frequency in flat fading and frequency selective environments. In this paper in the simulations it is assumed that there is one jammer whose direction is known in advance. Therefore it uses the known direction of the jammer to calculate the interference plus noise correlation matrix Rii€«n so that it can place a null in the direction of jammer. When user-1 is communicating with the BS a composite signal is received using the optimal beamformer that forms main beam towards user-1, while placing a null towards user-2 considering it as a jammer. The interference plus noise correlation matrix Rii€«n is used to find the weight of an optimal beamformer. The opportunistic communication method has been implemented using Matlab Rayleigh and Spatial channel model (SCM) developed by 3rd generation partnership project (3GPP). The main focus is on comparison of results using SCM and Matlab Rayleigh channel and is shown with the help of simulations that SCM provides an improvement in terms of bit error rate (BER) as compared to Matlab Rayleigh Channel. The BER performance of SCM systems is much better thereby showing an improvement of about 5dB in flat fading environment which is achieved because of exploitation of spatial diversity offered by SCM. In case of frequency selective fading environment there is an improvement of 2-3 dB for two users while using SCM as compared to Matlab Rayleigh channel by exploitation of diversity in both spatial and time domains.