C. Rapp

Bio: C. Rapp is an academic researcher. The author has contributed to research in topics: Phase-shift keying & Transmission (telecommunications). The author has an hindex of 2, co-authored 7 publications receiving 75 citations.

Performance of an RCPC-coded OFDM-based digital audio broadcasting (DAB) system

Abstract: A system proposal for DAB is investigated. The kernel is orthogonal frequency division multiplexing (OFDM) with 4-DPSK (differential phase shift keying) modulation, rectangular pulse-shaping, and a guard interval to reject multipath distortions. Emphasis is on the use of source-adapted channel coding with rate-compatible punctured convolutional (RCPC) codes. Based on analytical and simulated BER (bit error rate) curves for several propagation conditions and on preliminary source significance information (SSI), a static code design with unequal error protection (UEP) is presented that also takes auxiliary data services into account. The gain due to UEP is on the order of 8dB in signal power or 25% in bandwidth. >

Solacos YAG Communication System-YKS Implementation of the Syncbit-Concept

Abstract: The syncbit system is a new type of an optical homodyne transmission system. In the syncbit system the phase synchronisation information to maintain the receivers phase lock is time -multiplexed into the transmitter data stream. Compared to the Costas-Loop-system this concept avoids the 90° hybrid and the Q-channel for the expense of increased complexity in the digital signal processing unit. During the acquisition process two subsequent acquisition steps have to be carried out: In the first step the receiver is tuned to a low-IF and held there fore the subsequent acquisition phase. In the second step the position of the syncbits in the incoming datastream are located. Sampling the syncbits yields the error signal to pull the optical PLL into homodyne operation mode. To achieve reliable operation of such a system a very robust syncbit detection algorithm must be implemented. In the present work schemes for channel and syncbit coding are investigated. First results from computer simulations are presented.

DLR Experimental Systems for free Space Optical Communications

Abstract: The DLR experimental systems for coherent free space optical communications are presented. These systems have been designed for experimental studies in the laboratory and in a stationary free space testbed. The aim is to demonstrate the suitability of high bit rate coherent optical data transmission schemes for future space applications. A very high sensitive breadboard system uses PSK modulation with homodyne reception. A new synchronization technique made it feasible to build up a low complexity receiver allowing a power efficient transmission 3.5 dB above the shot noise limit at a data rate of 565 MBit/s. A second PSK homodyne system, which is now in construction, uses a smaller bit rate of about 1–5 MBit/s and allows further optimization of the time and frequency synchronization methods with smaller hardware effords. This work is sustained by a simulation program, which has been designed to simulate the whole optical communication system, enabling BER and signal analysis with different noise sources. In parallel, an earlier constructed DPSK heterodyne system has been embedded in a stationary test facility, which allows free space communication and PAT experiments between two buildings (720m).

Recent developments in phase synchronization techniques for optical space communication PSK homodyne receivers

Abstract: By allowing phase synchronization of the local oscillator and BPSK demodulation and by using only a simple "in-phase" demodulator front-end with a 180-degree hybrid the "Syncbit" method relocates the problem of optical complexity (90 deg. hybrid) into additional electronic circuitry. This has been advantageous, as long as the transmitted data rates are reasonable. In the optical ISL systems envisaged today, transmission rates of several Gigabit per second are used. The problems arising from the high data rates and from the implicit band limitations by electronic and electrooptic components initiated a further search for alternative and simple phase error detection schemes. All of these alternatives make use of the inherent nonlinear characteristic of the electrooptic phase modulator and in-phase demodulator combination.

Channel Capacity for Optical Space Communication Systems.

Abstract: In this paper, discrete and continuous channel models of free-space optical channel have been described. The discrete channel model is used to determine the channel capacity with photon counter for single-mode and multimode laser beams. The channel capacities with preamplified PIN photodiode direct detection receiver, heterodyne receiver, homodyne receiver and preamplified threshold detection receiver for m-PPM signalling scheme are determined from the continuous channel model.

BER sensitivity of OFDM systems to carrier frequency offset and Wiener phase noise

Abstract: In this contribution the transmission of M-PSK and M-QAM modulated orthogonal frequency division multiplexed (OFDM) signals over an additive white Gaussian noise (AWGN) channel is considered. The degradation of the bit error rate (BER), caused by the presence of carrier frequency offset and carrier phase noise is analytically evaluated. It is shown that for a given BER degradation, the values of the frequency offset and the linewidth of the carrier generator that are allowed for OFDM are orders of magnitude smaller than for single carrier systems carrying the same bit rate. >

Transmission techniques for digital terrestrial TV broadcasting

Abstract: The authors discuss the potential of OFDM signaling, with its limitations and inherent problems, as well as another potential technique that has so far been overlooked: single-carrier transmission with frequency-domain equalization. The carrier synchronisation issue is dealt with before the authors introduce coded-OFDM (COFDM), which makes use of channel coding and frequency-domain interleaving. >

Method and apparatus for multiple access between transceivers in wireless communications using ofdm spread spectrum

Abstract: A method for allowing a number of wireless transceivers to exchange information (data, voice or video) with each other. A first frame of information is multiplexed over a number of wideband frequency bands at a first transceiver, and the information transmitted to a second transceiver. The information is received and processed at the second transceiver. The information is differentially encoded using phase shift keying. In addition, after a pre-selected time interval, the first transceiver may transmit again. During the preselected time interval, the second transceiver may exchange information with another transceiver in a time duplex fashion. The processing of the signal at the second transceiver may include estimating the phase differential of the transmitted signal and pre-distorting the transmitted signal. A transceiver includes an encoder for encoding information, a wideband frequency division multiplexer for multiplexing the information onto wideband frequency voice channels, and a local oscillator for upconverting the multiplexed information. The apparatus may include a processor for applying a Fourier transform to the multiplexed information to bring the information into the time domain for transmission.

Source-controlled channel decoding

Abstract: Source and channel coding have been treated separately in most cases. It can be observed that most source coding algorithms for voice, audio and images still have correlation in certain bits. Transmission errors in these bits usually account for the significant errors in the reconstructed source signal. This paper proposes a modification of the Viterbi decoding algorithm (VA) for binary trellises which uses a priori or a posteriori information about the source bit probability for better decoding in addition to soft inputs and channel state information. Analytical upper bounds for the BER of convolutional codes for this modified VA (APRI-VA) are given. The algorithm is combined with the soft output viterbi algorithm (SOVA) and an estimator for the residual correlation of the source bits to achieve source-controlled channel decoding for framed source bits. The description is simplified by an algebra for the log-likelihood ratio L(u)=log(P(u=+1)/P(u=-1)) which allows a clear definition of the "soft" values of source-, channel-, and decoded bits as well as a simplified description of the traceback version of the SOVA. Applications are given for PCM transmission and the full rate GSM speech codec. For an PCM coded oversampled bandlimited Gaussian source transmitted over Gaussian and Rayleigh channels with convolutional codes the decoding errors are reduced by a factor of 4 to 5 when the APRI-SOVA is used instead of the VA. A simple dynamic Markov correlation estimator is used. With these receiver-only modifications the channel SNR in a bad mobile environment can be lowered by 2 to 4 dB resulting in the same voice quality. Further applications are briefly discussed. >

Multicode direct sequence spread spectrum

Abstract: In this patent, we present MultiCode Direct Sequence Spread Spectrum (MC-DSSS) which is a modulation scheme that assigns up to N DSSS codes to an individual user where N is the number of chips per DSSS code. When viewed as DSSS, MC-DSSS requires up to N correlators (or equivalently up to N Matched Filters) at the receiver with a complexity of the order of N2 operations. In addition, a non ideal communication channel can cause InterCode Interference (ICI), i.e., interference between the N DSSS codes. In this patent, we introduce new DSSS codes, which we refer to as the "MC" codes. Such codes allow the information in a MC-DSSS signal to be decoded in a sequence of low complexity parallel operations which reduce the ICI. In addition to low complexity decoding and reduced ICI. MC-DSSS using the MC codes has the following advantages: (1) it does not require the stringent synchronization DSSS requires, (2) it does not require the stringent carrier recovery DSSS requires and (3) it is spectrally efficient.