Pulse Width Modulation with feedback stabilizing loop
Data di pubblicazione
Data di priorità
Italian Patent granted; European and US patent application
Politecnico di Milano
Department of Electronics, Information and Bioengineering
Umberto Spagnolini; Lorenzo Combi
Excessive bandwidth expansion of signals’ digitalization is a major constraint to the development of Cloud-RAN, a new paradigm allowing for dense wireless network with high data-rate (>20Mbps) and massive use of multiple antennas (∼32 per site) and MIMO processing.
Accurate analog pulse width modulation (PWM) is suitable for low-cost transmission over optical fiber, simultaneously avoiding the bandwidth expansion typical of digital transmission (in the order of 32x) and reducing the impairments introduced by the conventional PW-modulators. Furthermore, PWM is also energy efficient.
The present invention provides a device and method to achieve accurate PWM enabling the use of low-cost, low-precision devices without affecting overall system performances. Specifically, Sigma-Delta PWM (ΣΔ-PWM) modulation is achieved through a feedback loop including filtering, low-precision internal modulation and de-modulation in the feedback. The input signal is analog; the output is a two-level signal carrying information about the sample values of the input signal, thus implicitly sampling the input. The sampling clock is given by a timing signal that controls both the waveform generator and the de-modulator, and it can be either originated by a local oscillator or reconstructed starting from an external probing signal. As an example to illustrate the advantages of ΣΔ-PWM it is considered the application to antenna remotization for cellular system, since the invention avoids the bandwidth expansion that is a significant issue in deploying dense access networks (as in 5G and beyond). The ΣΔ-PWM is valid for any application of signals’ transport where a signal is to be analogically transmitted from a transmitter to a receiver, with its information content encoded in the duration of a predefined waveform.
Campo di applicazione
Inexpensive, precise pulse width modulation.
Centralized radio access networks (C-RAN) in future generation mobile networks (5G).
The invention solves the problem of reducing the noise in PW-modulator as the closed loop presents noise rejection capability with respect to any error introduced at the internal modulator. The analog transmission allows to avoid the digitization of the signal, and the resulting bandwidth expansion, simultaneously allowing the implementation of low-cost devices instead of expensive high-performance modulators. In addition, PWM is energy efficient