Full Rate L2-Orthogonal Space-Time CPM for Three Antennas

To combine the power efficiency of Continuous Phase Modulation (CPM) with enhanced performance in fading environments, some authors have suggested to use CPM in combination with Space-Time Codes (STC). Recently, we have proposed a CPM ST-coding scheme based on L2-orthogonality for two transmitting antennas. In this paper we extend this approach to the three antennas case. We analytically derive a family of coding schemes which we call Parallel Code (PC). This code family has full rate and we prove that the proposed coding scheme achieves full diversity as confirmed by accompanying simulations. We detail an example of the proposed ST codes that can be interpreted as a conventional CPM scheme with different alphabet sets for the different transmit antennas which results in a simplified implementation. Thanks to L2-orthogonality, the decoding complexity, usually exponentially proportional to the number of transmitting antennas, is reduced to linear complexity

L2 Orthogonal Space Time Code for Continuous Phase Modulation

To combine the high power efficiency of Continuous Phase Modulation (CPM) with either high spectral efficiency or enhanced performance in low Signal to Noise conditions, some authors have proposed to introduce CPM in a MIMO frame, by using Space Time Codes (STC). In this paper, we address the code design problem of Space Time Block Codes combined with CPM and introduce a new design criterion based on L2 orthogonality. This L2 orthogonality condition, with the help of simplifying assumption, leads, in the 2x2 case, to a new family of codes. These codes generalize the Wang and Xia code, which was based on pointwise orthogonality. Simulations indicate that the new codes achieve full diversity and a slightly better coding gain. Moreover, one of the codes can be interpreted as two antennas fed by two conventional CPMs using the same data but with different alphabet sets. Inspection of these alphabet sets lead also to a simple explanation of the (small) spectrum broadening of Space Time Coded CPM

Web Audio Guitar Tube Amplifier vs Native Simulations

We propose to present a tube guitar amplifier simulation we’ve been designing using the Web Audio API with the aim to faithfully reproduce the main parts of the Marshall JCM 800 amplifier schematics. Each stage of the real amp has been recreated (preamp, tone stack, reverb, power amp and speaker simulation). We’ve also added an extra multiband EQ. This “classic rock” amp simulation we’ve been building has been used in real gigs and can be favorably compared with some native amp simulation both in terms of latency, sound quality, dynamics and comfort of the guitar play. The amp is open source and can be tested online, even without a real guitar plugged-in. It comes with an audio player, dry guitar samples and a wave generator that can be used as inputs. Figure 1 shows the current GUI, with some optional frequency analyzers and oscilloscopes that we’ve been using to probe the signal at different stages of the simulation. One purpose was to evaluate the limits of the Web Audio API and see if it was possible to design a web-based guitar amp simulator that could compete with native simulations

L2 OSTC-CPM: Theory and design

The combination of space-time coding (STC) and continuous phase modulation (CPM) is an attractive field of research because both STC and CPM bring many advantages for wireless communications. Zhang and Fitz [1] were the first to apply this idea by constructing a trellis based scheme. But for these codes the decoding effort grows exponentially with the number of transmitting antennas. This was circumvented by orthogonal codes introduced by Wang and Xia [2]. Unfortunately, based on Alamouti code [3], this design is restricted to two antennas. However, by relaxing the orthogonality condition, we prove here that it is possible to design L2-orthogonal space-time codes which achieve full rate and full diversity with low decoding effort. In part one, we generalize the two-antenna code proposed by Wang and Xia [2] from pointwise to L2-orthogonality and in part two we present the first L2-orthogonal code for CPM with three antennas. In this report, we detail these results and focus on the properties of these codes. Of special interest is the optimization of the bit error rate which depends on the initial phase of the system. Our simulation results illustrate the systemic behavior of these conditions

Separable Implementation of L2-Orthogonal STC CPM with Fast Decoding

In this paper we present an alternative separable implementation of L2-orthogonal space-time codes (STC) for continuous phase modulation (CPM). In this approach, we split the STC CPM transmitter into a single conventional CPM modulator and a correction filter bank. While the CPM modulator is common to all transmit antennas, the correction filter bank applies different correction units to each antenna. Thereby desirable code properties as orthogonality and full diversity are achievable with just a slightly larger bandwidth demand. This new representation has three main advantages. First, it allows to easily generalize the orthogonality condition to any arbitrary number of transmit antennas. Second, for a quite general set of correction functions that we detail, it can be proved that full diversity is achieved. Third, by separating the modulation and correction steps inside the receiver, a simpler receiver can be designed as a bank of data independent inverse correction filters followed by a single CPM demodulator. Therefore, in this implementation, only one correlation filter bank for the detection of all transmitted signals is necessary. The decoding effort grows only linearly with the number of transmit antennas

WebAudio Virtual Tube Guitar Amps and Pedal Board Design

International audienceIn this paper are exposed our latest experiments with the WebAudio API to design different types of gears for guitarists: real-time simulations of tube guitars amplifiers, fx pedals, and their integration in a virtual pedal board. We have studied different real guitar tube amps and created an interactive Web application for experimenting, validating and building different amp designs that can be run in browsers. Blind tests have been conducted with professional guitar players who compared positively our real-time, low-latency, realistic tube guitar amps simulations with state-of-the-art native equivalents. We also created a set of "virtual audio fx pedals" that implement popular audio effects such as flanger, chorus, overdrive, pitch shifter etc. These amps and pedals simulations can be packaged as "WebAudio plugins" and stored in plugin repositories (REST endpoints or local folders). We also developed a "host" application-a virtual pedal board-that allows us to scan repositories for plugins and to chain/assemble them.

Semi-Blind Cancellation of IQ-Imbalances

International audienceThe technical realization of modern wireless receivers yields significant interfering IQ-imbalances, which have to be compensated digitally. To cancel these IQ-imbalances, we propose an algorithm using iterative blind source separation (IBSS) as well as information about the modulation scheme used (hence the term semi-blind). The novelty of our approach lies in the fact that we match the nonlinearity involved in the IBSS algorithm to the probability density function of the source signals. Moreover, we use approximations of the ideal non-linearity to achieve low computational complexity. For severe IQ-mismatch, the algorithm leads to 0.2 dB insertion loss in an AWGN channel and with 16-QAM modulation

A 2 Million Commercial Song Interactive Navigator

International audienceIn this paper, we present a web-based interactive tool for exploring a collection of two million commercially released songs. It gathers song information from a large number of heterogeneous sources, web-based and audio-based, and integrates work from multiple research groups. The resulting tool can be used to request information about a specific song such as lyrics, metadata and chords; to navigate further on to linked external resources such as Discogs, AllMusic, Mu-sicBrainz or a number of streaming providers; or to browse the collection by artist's discographies or band membership. Several Web Audio applications are integrated and use the dataset to enrich the experience

Emerging W3C APIs opened up commercial opportunities for computer music applications

International audienceIn 2018, with a group of researchers and developers (some of whom are members of the W3C WebAudio WG) we proposed a WebAudio Plugin standard (WAP) and gave birth to a growing ecosystem for the development of computer music applications in the browser [1]. These plugins can be seen as a transposition of what exists in the native world, adapted to be web-aware (i.e. a plugin can be remotely included in any host web audio application by a URI). Since then, many contributions have been made and many plugins have been developed. Not only several "host" applications have appeared, including commercial ones, but also tools to help developers, including an online IDE coded as a Progressive Web App (PWA) to write and publish plugins from A to Z, the audio DSP core of the plugins being compiled into WebAssembly. Some of the plugins we developed during the French research project WASABI are now sold as add-ons to an online Digital Audio Workstation (Amped Studio), showing the new opportunities that these emerging APIs have created