Time-division multiplexing | EPFL Graph Search

Time-division multiplexing (TDM) is a method of transmitting and receiving independent signals over a common signal path by means of synchronized switches at each end of the transmission line so that each signal appears on the line only a fraction of time in an alternating pattern. It can be used when the bit rate of the transmission medium exceeds that of the signal to be transmitted. This form of signal multiplexing was developed in telecommunications for telegraphy systems in the late 19th century, but found its most common application in digital telephony in the second half of the 20th century. History Time-division multiplexing was first developed for applications in telegraphy to route multiple transmissions simultaneously over a single transmission line. In the 1870s, Émile Baudot developed a time-multiplexing system of multiple Hughes telegraph machines. In 1944, the British Army used the Wireless Set No. 10 to multiplex 10 telephone conversations over a microwave

Resource Sharing in Dataflow Circuits

Andrea Guerrieri, Paolo Ienne, Lana Josipovic, Axel Marmet

To achieve resource-efficient hardware designs, HLS tools share (i.e., time-multiplex) functional units among operations of the same type. This optimization is typically performed together with operation scheduling to ensure the best possible unit usage at each point in time. Dataflow circuits have emerged as an alternative HLS approach to efficiently handle irregular and control-dominated code. Yet, these circuits do not have a predetermined schedule-in its absence, it is challenging to determine which operations can share a functional unit without a performance penalty. Furthermore, although sharing seems to imply only some trivial circuitry, time-multiplexing units in dataflow circuits may cause deadlock by blocking certain data transfers and preventing operations from executing. In this paper, we present a technique to automatically identify performance-acceptable resource sharing opportunities in dataflow circuits and we describe a sharing mechanism that achieves deadlock-free dataflow designs. On benchmarks obtained from C code, we show that our approach effectively implements resource sharing: it results in significant area savings (i.e., a DSP reduction of up to 81%) compared to dataflow circuits which do not support this feature and matches the sharing capabilities of a state-of-the-art HLS tool.

IEEE2022

Advanced OFDM systems for terrestrial multimedia links

Renzo Posega

Recently, there has been considerable discussion about new wireless technologies and standards able to achieve high data rates. Due to the recent advances of digital signal processing and Very Large Scale Integration (VLSI) technologies, the initial obstacles encountered for the implementation of Orthogonal Frequency Division Multiplexing (OFDM) modulation schemes, such as massive complex multiplications and high speed memory accesses, do not exist anymore. OFDM offers strong multipath protection due to the insertion of the guard interval; in particular, the OFDM-based DVB-T standard had proved to offer excellent performance for the broadcasting of multimedia streams with bitrates over ten megabits per second in difficult terrestrial propagation channels, for fixed and portable applications. Nevertheless, for mobile scenarios, improving the receiver design is not enough to achieve error-free transmission especially in presence of deep shadow and multipath fading and some modifications of the standard can be envisaged. To address long and medium range applications like live mobile wireless television production, some further modifications are required to adapt the modulated bandwidth and fully exploit channels up to 24MHz wide. For these reasons, an extended OFDM system is proposed that offers variable bandwidth, improved protection to shadow and multipath fading and enhanced robustness thanks to the insertion of deep time-interleaving coupled with a powerful turbo codes concatenated error correction scheme. The system parameters and the receiver architecture have been described in C++ and verified with extensive simulations. In particular, the study of the receiver algorithms was aimed to achieve the optimal tradeoff between performances and complexity. Moreover, the modulation/demodulation chain has been implemented in VHDL and a prototype system has been manufactured. Ongoing field trials are demonstrating the ability of the proposed system to successfully overcome the impairments due to mobile terrestrial channels, like multipath and shadow fading. For short range applications, Time-Division Multiplexing (TDM) is an efficient way to share the radio resource between multiple terminals. The main modulation parameters for a TDM system are discussed and it is shown that the 802.16a TDM OFDM physical layer fulfills the application requirements; some practical examples are given. A pre-distortion method is proposed that exploit the reciprocity of the radio channel to perform a partial channel inversion achieving improved performances with no modifications of existing receivers.

EPFL2005

Tunable fiber bragg grating filters

Hill et al. reported for the first time in 1978 the formation of refractive-index gratings in germanium doped silica fibers exposed to UV laser radiation. Since then many studies have been performed on fiber gratings and a widespread range of applications has been found. For example, gratings are today used as sensors, for the measurement of strain, temperature and pressure, or in telecommunications, as multiplexers, filters, dispersion compensators, mode converters and fiber laser mirrors. The aim of this work is to conceive and to realize a fast and broadband tunable optical filter device for telecommunications. Up to now, no in-fiber filters combining wide tuning range and high tuning speed have been reported in literature. The main elements of the realized filter are two piezoelectric stack actuators permitting to push and/or pull the optical fiber exploiting the Bragg grating strain sensitivity. Two independent control loops are used to control and to adjust the actuators position. To minimize bending problems during compression, the fiber is inserted in a specially conceived guiding system. Any kind of fiber grating, e.g. Bragg, chirped, ... could be strained. However, the tuning range is inversely proportional to the strained length. A prototype, integrating the piezoelectric stack actuators, the control loops, the guiding system and the fiber grating, was realized. It operates both in reflection and in transmission. Maximum tuning speeds are around 19 nm/ms with setting times less than 1.5 ms. A tuning ranges of ∼45 nm was obtained for a grating of 2.5 mm length. The repeatability in the wavelength selection is better than 0.3 nm. This prototype is tunable over the Erbium Doped Fiber Amplifier range without spectral, reflectivity and bandwidth changes. This device is designed to work with a channel spacing of 100 GHz according to the International Telecommunications Union specifications for Wavelength Division Multiplexing systems. In addition this filter has been successfully used to continuously tune the output mirror of a cw praseodymium doped all fiber laser emitting in the 1.3 μm region. This device is of potential use in telecommunication networks for wavelength multiplexing, switching and routing or as wavelength selective filter.

EPFL1999

Advanced OFDM systems for terrestrial multimedia links

Renzo Posega

EPFL2005

Tunable fiber bragg grating filters

EPFL1999