Home automation systems rely on wireless sensor networks to transfer data between the nodes. However, in indoor environments, the wireless communication reliability is deteriorated due to channel fading. To mitigate the effect of prolonged fades, phase sweep amplify-and-forward (PSAF) cooperative diversity is proposed in this work.

PSAF is a novel cooperative diversity technique that relies on a repeater to apply dynamic phase modulation and amplify the signal with negligible delay. At the destination, the signal received from the repeater and from the source combine such that the equivalent channel fade duration is shortened. Then, through time diversity, the communication performance of channel coded transmissions is improved.

At the repeater, the re-radiated signal is amplified by applying microwave reflection between the antenna and an active load. The active reflector is developed using low-cost 0.13-μm CMOS technology and a cross-coupled transistor pair serves as the active load. To account for process variations and network uncertainty, an all-analog dual automatic gain control (DAGC) circuit is responsible for adjusting the device operating frequency and gain.

The active reflector is differentially interfaced to a discrete dipole antenna for operation at 4 GHz. In an anechoic chamber, a 22.3-dB wireless gain and phase modulation are demonstrated at the repeater. An ultra-low power consumption on the order of 120-μW is achieved constrained on device nonlinearity.

Realistic indoor channel measurements between the source and destination when the repeater is activated confirm that PSAF can be used to reduce the duration of deep fades. By including the measured channel impulse response in system level simulations, it is demonstrated that the coverage area of an indoor wireless network can be increased by a factor of four for a 10⁻⁴ target bit error rate.