Joint symbol detection and synchronization design for ultra high speed wireless data networks in the terahertz band
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Ongoing research in graphene-based nano-devices points to the Terahertz (THz) band (0.1-10∼THz) as the communication frequency range for nano-devices. We define an entire network which can be built using these nano-devices as nano-networks. Nanonetworks will enable to us achieve vast applications in the field of biomedical, military, environmental safety and many other industries. Femtosecond-long pulse-based modulation schemes have been proposed to enable ultra-broadband communication among nano-devices. While working in terahertz frequency, we cannot use the exisiting receiver models that are used in an RF system or a microwave devices. Hence, we need to look into an alternate receiver design that can be implemented successfully in our system. In addition to this, we also need a strong synchronization scheme which will help the receiver to detect pulses every one pico second. Hence, one of the main challenges with ultra-high-speed pulse-based communications is the need for tight symbol synchronization between transmitter and receiver. In this thesis, a synchronization scheme for pulse-based THz-band communications is designed and analyzed. The proposed scheme is aimed at iteratively estimating the symbol start time and reducing the observation window length for the symbol detector. The proposed scheme is fully analog and can be implemented with a combination of voltage-controlled delay (VCD) lines and Continuous-Time Moving-Average (CTMA) symbol detectors. Closed form expressions are obtained for the number of preamble symbols needed to achieve synchronization as well as the maximum number of bits that can be transmitted before requiring re-synchronization in the presence of clock skew. Similarly, the symbol error rate of the CTMA receiver is analytically modeled as a function of the resulting observation window length. Finally, the synchronization and symbol detection impact on the achievable throughput is studied. The developed scheme is experimentally tested with measured THz pulses and its performance is numerically investigated. The results show how the proposed scheme can successfully estimate the symbol start time and minimize the symbol error rate with less than ten synchronization preamble bits.