Gokul Dridharan

Postdoctoral fellow (Now at Qualcomm)


Ivan Seskar

Associate Director for Information Technology


Narayan B. Mandayam

Distinguished Professor


Nazmul Islam

Now at Qualcomm


Advisors and collaborators at WINLAB

Research Projects

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    NC-OFDM communication system

    Implementation of NC-OFDM system using software defined radios.

    Non-contiguous OFDM (NC-OFDM), is well suited to enable spectrum usage in such dynamic environments. NC-OFDM is similar to OFDM, except that the transmission is restricted to certain sub-carriers. Non-contiguous sub-carrier access may arise either due to the presence of Primary users, or due to the frequency selective nature of the channel, or to ensure fair allocation of spectrum. Enabling the use of NC-OFDM for dynamic spectrum access requires two key challenges to be addressed first. First, NC-OFDM requires an agreement between transmitter receiver about the set of subcarriers being used in that link (i.e. frequency synchronization), andsecond, timing and frequency offset estimation must be established to ensure successful data detection.

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    Underlay Control channel

    Control channel design for NC-OFDM enabled communication system

    Although there are several techniques for detecting the start of a OFDM frame (timing synchronization) and to estimate frequency offset, they are not directly applicable to NC-OFDM due to concurrent nature of transmissions. We therefore propose a low data rate CDMA-like underlay control channel to address the above two issues. Such a control channel is envisioned to be low power and to span all available bandwidth. Multiple point-to-point links access this control channel by using different spreading codes. A two stage timing and frequency offset estimation technique is proposed using this channel. Once synchronization is established, channel is used to transmit control information such as sharing the active sub-carrier indices. Forsuch a control channel we study the accuracy of timing synchronization, data rates achieved in control channel and effect on the performance of NC-OFDM-based data transmission.

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    Security features of NC-OFDM transmission

    NC-OFDM as an LPE solution

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    Coexistence in CBRS band

    Coexistence between LTE-U/LTE-LAA and Radar in CBRS band