Signal Processing Worksystem Research Articles

An adaptive code position modulation scheme for wireless sensor networks

In this letter, an energy-efficient adaptive code position modulation scheme is proposed for wireless sensor networks to provide the relatively stable bit error ratio (BER) performance expected by the upper layers. The system is designed with focus on the adaptive control of transmission power, which is adjusted based on the measured power density of background noise. Interfaces among the modulation module, packet scheduling module and upper layer are provided for flexible adjustments to adapt to the background noise and deliver expected application quality. Simulations with signal processing worksystem (SPW) validate the effectiveness of the scheme.

An adaptive code position modulation scheme for wireless sensor networks

In this letter, an energy-efficient adaptive code position modulation scheme is proposed for wireless sensor networks to provide the relatively stable bit error ratio (BER) performance expected by the upper layers. The system is designed with focus on the adaptive control of transmission power, which is adjusted based on the measured power density of background noise. Interfaces among the modulation module, packet scheduling module and upper layer are provided for flexible adjustments to adapt to the background noise and deliver expected application quality. Simulations with signal processing worksystem (SPW) validate the effectiveness of the scheme.

A Link-Level Simulator of the cdma2000 Reverse-Link Physical Layer.

The cdma2000 system is an evolutionary enhancement of the IS-95 standards which support 3G services defined by the International Telecommunications Union (ITU). cdma2000 comes in two phases: 1XRTT and 3XRTT (1X and 3X indicates the number of 1.25 MHz wide radio carrier channels used and RTT stands for Radio Transmission Technology). The cdma2000 1XRTT, which operates within a 1.25 MHz bandwidth, can be utilized in existing IS-95 CDMA channels as it uses the same bandwidth, while 3XRTT requires the commitment of 5 MHz bandwidth to support higher data rates. This paper describes a software model implementation of the cdma2000 reverse link and its application for evaluating the effect of rake receiver design parameters on the system performance under various multipath fading conditions. The cdma2000 models were developed at the National Institute of Standards and Technology (NIST), using SPW (Signal Processing Worksystem) commercial software tools. The model has been developed in a generic manner that includes all the reverse link six radio configurations and their corresponding data rates, according to cdma2000 specifications. After briefly reviewing the traffic channel characteristics of the cdma2000 reverse link (subscriber to base station), the paper discusses the rake receiver implementation including an ideal rake receiver. It then evaluates the performance of each receiver for a Spreading Rate 3 (3XRTT) operation, which is considered as a true “3G” cdma2000 technology. These evaluations are based on the vehicular IMT-2000 (International Mobile Telecommunication 2000) channel model using the link budget defined in cdma2000 specifications for the reverse link.

Shared buffer implementations of signal processing systems using lifetime analysis techniques

There has been a proliferation of block-diagram environments for specifying and prototyping digital signal processing (DSP) systems. These include tools from academia such as Ptolemy and commercial tools such as DSPCanvas from Angeles Design Systems, signal processing work system (SPW) from Cadence, and COSSAP from Synopsys. The block diagram languages used in these environments are usually based on dataflow semantics because various subsets of dataflow have proven to be good matches for expressing and modeling signal processing systems. In particular, synchronous dataflow (SDF) has been found to be a particularly good match for expressing multirate signal processing systems. One of the key problems that arises during synthesis from an SDF specification is scheduling. Past work on scheduling from SDF has focused on optimization of program memory and buffer memory under a model that did not exploit sharing opportunities. In this paper, we build on our previously developed analysis and optimization framework for looped schedules to formally tackle the problem of generating optimally compact schedules for SDF graphs. We develop techniques for computing these optimally compact schedules in a manner that also attempts to minimize buffering memory under the assumption that buffers will be shared. This results in schedules whose data memory usage is drastically lower than methods in the past have achieved. The method we use is that of lifetime analysis; we develop a model for buffer lifetimes in SDF graphs and develop scheduling algorithms that attempt to generate schedules that minimize the maximum number of live tokens under the particular buffer lifetime model. We develop several efficient algorithms for extracting the relevant lifetimes from the SDF schedule. We then use the well-known first-fit heuristic for packing arrays efficiently into memory. We report extensive experimental results on applying these techniques to several practical SDF systems and show improvements that average 50% over previous techniques, with some systems exhibiting up to an 83% improvement over previous techniques.

Simulation of Optical Fiber Transmission Systems Using SPW on an HP Workstation

In this article, an intensity modulation-direct detection (IM-DD) optical fiber transmission system is simulated and investigated using a signal processing worksystem (SPW) on a Hewlett-Packard (HP) workstation. The optical fiber transmission system simulated includes a laser diode source, a single-mode fiber and a positive-intrinsic-negative (p-i-n) photodiode receiver model. Simulation methods are pre sented on the optical source waveforms, fiber attenuation and dispersion, and receiver noise. The end-to-end performance of a typical trans mission system is also presented. In the simula tion, models can be made as detailed as neces sary and computer waveforms can be compared directly to measured waveforms. Measured data can be used to accurately characterize functional components, such as sources, fibers and detectors. The impact of noise on the per formance of the transmission system can be observed. SPW software and its usage on HP workstations are introduced.

OFDM performance in amplifier nonlinearity

The activities of the current European RACE and ACTS projects have led to an increasing interest in OFDM (orthogonal frequency division multiplexing) as a means of combating impulsive noise and multipath effects and making fuller use of the available bandwidth of the system. This paper analyses the performance of OFDM signals in amplifier nonlinearity. In particular, bit error rate (BER) degradation as a result of amplitude limiting or clipping are analysed. In the presence of both nonlinear distortion and additive Gaussian noise, optimized output power back off is provided to balance the requirements of minimum BER and power amplifier efficiency. For this purpose, an OFDM system has been built using the SPW (Signal Processing Worksystem) simulator.

Performance of digital collective antenna systems in the presence of phase noise and clock jitter

SMATV (satellite master antenna television) systems can be considered as an optimal distribution network for a fast and effective introduction of digital TV to the end users in several European countries and is an alternative in those which can be used countries their that are developing infrastructures. This paper studies the performance of digital collective systems in the presence of a noisy phase reference (phase noise) and a noisy clock reference (clock jitter). For this purpose, an attempt has been made to characterize the performance of this digital transmission system through the bit error rate (BER) or symbol error rate (SER) as a function of the Eb/No ratio. The Eb/No ratio has been parametrised by phase noise and clock jitter, obtained through computer simulations. It is shown that these effects produce a significant increase in the BER/SER performance. The simulator used was the SPW (Signal Processing WorkSystem) by means of which the BER/SER has been estimated using a quasianalytical (semianalytic) approach and the Monte Carlo method, so that the results can be compared and checked.

EDFA Custom-Coded Simulation Block for Use in WDM Optical Fiber Communication System Studies

An Erbium-doped fiber amplifier (EDFA) custom-coded block (CCB) for simulation of multichannel amplification has been created in the COMDISCO Signal Processing Worksystem. The resultant model can achieve accurate results with reasonable speed and can be used readily for a wide range of different situations. In the EDFA CCB both forward and backward amplified spontaneous emission (ASE) are considered. Practical application of the block is demonstrated in the analysis of a four node wavelength division multiplexed (WDM) optical fiber ring network using EDFAs to compensate the section losses. We find that for such a system non-uniform sampling of the ASE spectrum offers an advantage for reducing storage requirements and running time of the simulation compared with uniform sampling. The CCB is also used in the simulation of a WDM optical fiber communication system using 9 cascaded EDFAs, which are highly saturated, to compensate for the transmission loss of the fiber. We find that the simulation results of the output signal level and ASE spectrum exhibit the same general pattern as previously published results, demonstrating the applicability of the EDFA CCB for such highly saturated cases.