Cognitive radio system (CRS) is a radio system which is aware of its operational and geographical environment, established policies, and its internal state. It is able to dynamically and autonomously adapt its operational parameters and protocols and to learn from its previous experience. Based on software-defined radio (SDR), CRS provides additional flexibility and offers improved efficiency to overall spectrum use. CRS is a disruptive technology targeting very high spectral efficiency. This paper presents an overview and challenges of CRS with focus on radio frequency (RF) section. We summarize the status of the related regulation and standardization activities which are very important for the success of any emerging technology. We point out some key research challenges, especially implementation challenges of cognitive radio (CR). A particular focus is on RF front-end, transceiver, and analog-to-digital and digital-to-analog interfaces which are still a key bottleneck in CRS development.
Cognitive radio system (CRS) is a disruptive technology targeting very high spectral efficiency. This paper presents an overview of CRS and summarizes the related regulation and standardization status. We point out some key research challenges, especially implementation challenges of cognitive radio and deduce research directions in CRS. Despite numerous challenges, the timeframe for the success of CRS is more linked to the economical and business model than real technological issues.
A fully integrated multi-band, 0.25 um BiCMOS direct-conversion transmitter for wide-band code division multiple access (WCDMA) is described. A new approach based on a cascaded attenuator and amplifiers creates the full necessary power range in RF and successfully suppresses the carrier leakage without any calibration needs. The transmitter uses also an optimized power control feature that allows current saving while meeting linearity requirements. The chip provides more than 85 dB power control range in both bands and it is designed to deliver +7 dBm in at 800-900 MHz and +5 dBm at 1700-1900 MHz with 70 mA and 79 mA respectively at nominal supply and temperature. It also provides an error vector magnitude (EVM) of 2.5% and an adjacent channel leakage ratio (ACLR) of -53 dBc in high band and 4.4% EVM with -48 dBc ACLR in low band.Index Terms -Carrier leakage, direct-conversion transmitter, mobile communication, wide-band code division on multiple access (WCDMA), power control
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