Multiplexing

In MPEG coding, there are three types of encoded pictures. Since these picture coding types have different importance of data content, the cell loss of each picture coding type affects the video quality differently in MPEG video transmission through ATM networks. This paper analyzed the per-session cell loss properties of MPEG video traffic in an ATM switching node in both the steady-state case and the transient case considering each picture type. In the analysis, a 3-state Markov modulated Bernoulli process (MMBP) is proposed as a traffic model for MPEG video which is tractable analytically. Numerical results revealed the influence of the picture transmission pattern on the cell loss properties of each picture coding type

I N THE first part of this two-part paper, a structure and hierarchy were developed for tracing the key signal processing steps of a typical digital communications system. With the structure as a guide, formatting, source coding, and modulation transformations were examined. Also treated were potential trade-offs for power-limited and bandwidth-limited systems. In Part II, the signal processing overview continues with channel coding, multiplexing and multiple access, frequency spreading, encryption, and synchronization. To complete the overview, fundamental link analysis relationships are reviewed in the context of a satellite repeater channel.

Modern radar systems often have the conflicting requirements of a large phased array antenna for increased power-aperture product and/or angular resolution versus wide instantaneous signal bandwidth for fine range resolution. Pulse-to-pulse diversity may also be desired as a countermeasure against coherent repeater jammers. Using the multicarrier nature of orthogonal frequency-division multiplexing to encode wide instantaneous bandwidth pulses we propose a novel digital phased array architecture which mitigates dispersion effects experienced when the array main beam is electronically steered off broadside. The result is the ability to transmit and receive wideband pseudo-random phase coded pulses with a phased array antenna. Simulation results are used to quantify the benefit of the architecture. An overview of digital orthogonal frequency-division multiplexing waveform generation is also provided.

Orthogonal frequency division multiplexing (OFDM) is a multicarrier modulation technique which is deployed in modern communication systems because of its immunity to channel’s harsh affects. Radix-2 ifft butterfly algorithm is used to implement the IFFT block. The system is designed using VHDL and simulated using MODELSIM Altera.

We evaluate the performance of three direct-detection orthogonal frequency-division multiplexing (OFDM) schemes in combating multipath distortion in indoor optical wireless links, comparing them to unipolar M-ary pulse-amplitude modulation (M-PAM) with minimum mean-square error decision-feedback equalization (MMSE-DFE). The three OFDM techniques are DC-clipped OFDM and asymmetrically clipped optical OFDM (ACO-OFDM) and PAM-modulated discrete multitone (PAM-DMT). We describe an iterative procedure to achieve optimal power allocation for DC-OFDM. For each modulation method, we quantify the received electrical SNR required at a given bit rate on a given channel, considering an ensemble of 170 indoor wireless channels. When using the same symbol rate for all modulation methods, M-PAM with MMSE-DFE has better performance than any OFDM format over a range of spectral efficiencies, with the advantage of (M-PAM) increasing at high spectral efficiency. ACO-OFDM and PAM-DMT have practically identical performance at any spectral efficiency. They are the best OFDM formats at low spectral efficiency, whereas DC-OFDM is best at high spectral efficiency. When ACO-OFDM or PAM-DMT are allowed to use twice the symbol rate of M-PAM, these OFDM formats have better performance than M-PAM. When channel state information is unavailable at the transmitter, however, M-PAM significantly outperforms all OFDM formats. When using the same symbol rate for all modulation methods, M-PAM requires approximately three times more computational complexity per processor than all OFDM formats and 63% faster analog-to-digital converters, assuming oversampling ratios of 1.23 and 2 for ACO-OFDM and M-PAM, respectively. When OFDM uses twice the symbol rate of M-PAM, OFDM requires 23% faster analog-to-digital converters than M-PAM but OFDM requires approximately 40% less computational complexity than M-PAM per processor.

We present experimental and numerical investigations of Kerr nonlinearity compensation in a 400-km standard single-mode fiber link with distributed Raman amplification with backward pumping. A dual-pump polarization-independent fiber-based optical parametric amplifier is used for mid-link spectral inversion of 5 × 28-GBd polarization-multiplexed 16-QAM signals. Signal quality factor (Q-factor) improvements of 1.1 dB and 0.8 dB were obtained in the cases of a single-channel and a five-channel wavelength-division multiplexing (WDM) system, respectively. The experimental results are compared to numerical simulations with good agreement. It is also shown with simulations that a maximum transmission reach of 2400 km enabled by the optical phase conjugator is possible for the WDM signal.