Showing papers on "Pulse-position modulation published in 1972"

Pulse position modulation communication system

Abstract: A pulse position modulation communication system which elminates the need for generating independent synchronizing pulses at transmitter facility. Numerical data is generated sequentially and is temporarily stored. The next occurring data is summed with the previously stored data, and the sum is transmitted in a position within a time frame representative of the numerical value. Simultaneously therewith this resultant sum replaces the previously stored data for summation with the next received data. Addition is performed by a modulo-M summing operation (i.e., ignoring any carry) where the value of M is the same as the number of time slots in each time frame. Subtraction of received pulse position data is performed in a similar manner at the receiver to restore the data to its original form.

The Effect of Timing Errors in Optical Digital Systems

Abstract: The use of digital transmission with narrow light pulses appears attractive for data communications, but carries with it a stringent requirement on system bit timing. The effects of imperfect timing in direct-detection (noncoherent) optical binary systems are investigated using both pulse-position modulation (PPM) and on-off keying for bit transmission. Particular emphasis is placed on specification of timing accuracy and an examination of system degradation when this accuracy is not attained. Bit error probabilities are shown as a function of timing errors from which average error probabilities can be computed for specific synchronization methods. Of significance is the presence of a residual or irreducible error probability in both systems, due entirely to the timing system, which cannot be overcome by the data channel.

Error performance bounds for two receivers for optical communication and detection.

Abstract: Two different receiver strategies for use with photoelectron emitting optical detectors are evaluated. Upper bounds on error probability are derived both for optical communication with pulse position modulation and for the general problem of detecting the presence of a pulsed optical signal in background light. The Poisson statistics of photoelectron emissions are used to find simple, easily evaluated, but tight upper bounds on error probability for these two problems. These receiver performance bounds illustrate several basic principles in optical communication and signal detection. These basic principles are then discussed in detail.

Synchronization using pulsed edge tracking in optical PPM communication system

Abstract: A pulse position modulated (PPM) optical communication system using narrow pulses of light for data transmission requires accurate time synchronization between transmitter and receiver. The presence of signal energy in the form of optical pulses suggests the use of a pulse edge tracking method of maintaining the necessary timing. The edge tracking operation in a binary PPM system is examined, taking into account the quantum nature of the optical transmissions. Consideration is given first to pure synchronization using a periodic pulsed intensity, then extended to the case where position modulation is present and auxiliary bit decisioning is needed to aid the tracking operation. Performance analysis is made in terms of timing error and its associated statistics. Timing error variances are shown as a function of system signal to noise ratio.

Pulse-Position Modulation for Signal Identification

Abstract: : The use of pulse position modulation (PPM) to code N signals has been investigated. The following three coding schemes were considered: (1) identical pulse periods with synchronization, (2) distinct pulse periods without synchronization, and (3) position modulation of alternate pulses. The theoretical performance of these methods was considered with respect to the probability of overlapping signals, the average frequency of such overlaps, and the generation of false signals. This investigation was concerned primarily with performance limitations due to signal design rather than receiver characteristics; thus, only the properties of the signal in an infinite signal- to-noise ratio; thus, only the properties of the signal in an infinite signal- to-noise ratio environment were considered. The false signal was found to be nonexistent in coding method (1); and for each of the other two schemes, false signals were found to occur less frequently than pulse overlap. For any given set of parameters, the performance of each coding scheme as measured by the frequency of overlaps was found to be the same.

Comments on "Codest: A New Pulse-Code Modulation System for Telegraph and Data Transmission"

Abstract: It is shown that it is incorrect to state that the coding method "Codest" for either synchronous transmission or time multiplexing of asynchronous data is more efficient than the sliding index method.