Introduction

Excessive bandwidth expansion of signals digitalization is a major constraint to the development of Cloud-RAN, a new paradigm allowing for dense wireless network for 5G development with high data-rate (>20Mbps) and massive use of multiple antennas (∼32 per site) and MIMO processing. The proposed analog pulse width modulation (PWM) is suitable for low-cost transmission over optical fiber, simultaneously avoiding the bandwidth expansion typical of digital transmission.

Technical features

The 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. 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.

Possible Applications

• Inexpensive, precise pulse width modulation;
• Centralized radio access networks (C-RAN) in future generation mobile networks (5G).

Advantages

• Noise reduction in PW modulators;
• The analogue transmission allows to avoid the digitalization of the signal, which leads to a higher band occupation;
• It allows to avoid the in-band expansion linked to digitization, and, together, to develop low devices instead of expensive high-performance modulators.