DIFFS: A Low Power, Multi-Mode, Multi-Standard Flexible Digital Front-End for Sensing in Future Cognitive Radios

Cognitive Radios provide communication devices with the flexibility to adjust to varying network and channel conditions. For this to be fully realizable spectrum sensing and signal reception have to happen simultaneously and have to require as little power as necessary to function in handheld devices. This work argues for the need of flexible digital-front ends as indispensable building block, able to perform control operations over the analog front-end and to perform sensing and synchronization procedures without the need of power consuming baseband processors. A low power, reconfigurable digital front-end that supports concurrent synchronization and sensing of high-throughput wireless standards is presented. Multiple operating modes, useful for various communication standards, such as LTE, WLAN and DVB-T are introduced and analyzed. The digital front-end has been implemented in 65 nm CMOS technology resulting in a chip area of 6.4 mm2. Fine grain clock gating allows synchronization at 4 mW and sensing at 7 mW power consumption. Experiments in combination with a reconfigurable analog front-end show that a 1.7 GHz wide frequency band can be scanned based on energy detection in an exceptionally low time window of 10 ms while consuming 13 mW power and that coarse energy detection can speed-up the sensing process. Furthermore, advanced feature detection for DVB-T and LTE signals is implemented and measured. Low power sensing of DVB-T signals shows that a target false alarm rate of 10 % and a detection probability of 90 % at an input power level of−106 dBm while consuming 7 mW power are possible. Synchronization-aided FFT-based LTE sensing with leakage cancellation was experimentally validated for various bandwidths showing a power consumption of maximum 20 mW.