Peak to Average Power Minimization
Co-developed a patent pending technique to combine multiple OFDM waveforms without expected growth in Peak to Average Power Ratio (PAPR). Acted as the glue between the consultant who originally conceived the algorithm, the engineer who developed the simulation, and the engineer who is currently implementing the algorithm in FPGA technology. As a result, Clarcona Technology has the most comprehensive and detailed understanding of the fundamentals and operation of this algorithm.
Wideband Digital Pre-Distortion of Power Amplifiers
Linearization of power amplifiers has until recently been limited to bandwidths of 10-30 MHz even when the power amplifier is much wider. Clarcona Technology has been investigating methods to push this limit to 200 MHz and beyond. There are several challenges with wide bandwidth linearization. Short (passband roll off) and long (bias circuit interactions) term memory effects demand a more complicated pre-distortion algorithm and calibration algorithm. Digital pre-distortion is the algorithm of choice for wideband linearization. Most system specifications imply linearization to 5th order intermodulation products. This requires an expansion bandwidth of 5X the information bandwidth. For a 200 MHz waveform, this requires an expansion bandwidth of 1 GHz. Even when accounting for I/Q sampling, this is challenging for the digital signal processing ASIC. The DAC, I/Q modulator, and driver amplifiers are all very challenging, but a powerful algorithm will correct for some minor imperfections. The fundamentally weak link is the adaptation feedback path. This path comes from the output of the PA and is used to periodically calculate new DPD coefficients. Any imperfections in this path get “corrected”, and forwarded to the output. Of course, this actually leads to imperfections in the output. Mr. Horine is working towards using high dynamic range ADCs using superconducting technology to sample directly at RF frequencies. This approach will eliminate analog errors and make wide bandwidth linearization feasible.
Mr. Horine has simulated many state of the art techniques from the literature, including advanced models incorporating various degrees of non-linearity and memory effects. He has surveyed commercially available chips and understand their limitations. He is currently working with Optichron’s digital pre-distortion chip, which supports bandwidths up to 65 MHz. Moving to wider bandwidths will require new chips from vendors such as TI and Optichron or polyphase implementations of algorithms on high speed FPGAs.
OFDM Transceiver based upon Direct Sampling, High Dynamic Range ADC
Digital superconductor company Hypres develops high dynamic range ADCs that use superconducting technology to sample signals directly at RF frequencies. Mr. Horine has served as the system architect to use this technology for a high capacity 4G basestation. This system digitizes the entire 194 MHz band at 2.6 GHz and channelizes it into multiple baseband OFDM (LTE/WiMAX) waveforms.
A particular challenge is in the polyphase processing of the 2 GHz multibit data from the ADC. Although this work is delegated to an experienced FPGA designer, he is responsible for the overall design.
Multi-GHz Bandwidth Radar Receive Array Based Upon True Time Delay
Mr. Horine rewrote and consolidated some previous proposals and won a Missile Defense Agency SBIR for a wide band, multi-beam radar receive array using true time delay. This requires direct sampling ADCs at X and S band and picosecond level time control. He adapted phased array Matlab code for true time delay to analyze the array performance. He conceived of a technique achieve sub-clock sample delay adjustments. Mr Horine developed the overall system architecture is awaiting a decision on Phase II.
Chaos Based SATCOM Waveform
Clarcona Technology collaborated with Terry Consultants Inc. on an Army Phase I SBIR to develop and analyze a chaos based communication waveform for SATCOM applications with an emphasis on low probability of detection/interception (LPD/LPI). Mr. Horine was responsible for developing the simulation environment and in particular, the chaos sequence generation, modulation, and reception. He has a library of Matlab codes including many chaos sequences and modulation schemes.
Mr. Horine is the principle investigator for an Air Force Phase I SBIR about to start on chaos communications for inter-satellite communications for low data rate navigation and control information. He will be designing at a high level the chaos sequence generator chip. He will also predict the effects of radiation damage on the quality of the chaos sequence, develop techniques to monitor the chaos sequence (for limit states which can impair the LPD characteristics), and develop an overall waveform suitable for the application.
Blind Link Rendezvous Using Frequency Domain Probe Signal
Many link rendezvous algorithms rely upon a pilot channel, sometimes broadcasting available channels, other times, serving as the call up channel. Unfortunately, a pilot channel(s) represent a single point of failure. An adversary need only jam this channel in order bring down an entire network. Furthermore, this channel can also be a bottleneck. Clarcona Technology’s approach eliminates the need for a pilot channel. A radio node that wishes to establish a network, broadcasts a predefined pattern composed of spaced sinusoids on one or more channels, which it perceives as being clear of primary users. Other nodes monitor the spectrum for this probe signal. They perform wide band FFTs and correlate in the frequency domain for this pattern. When found, they respond back in kind on the intersection of the received channels with the channels that it senses are clear.
The initial probe starts with a short and low powered signal, with the goal of minimizing interference to ongoing communications, in the case of imperfect sensing. If a connection is not achieved during the first round, the power and duration is increased. The idea that point sensing is imperfect, and rendezvous techniques must consider the risk to interfering with ongoing communications guide all of my link rendezvous techniques. Another possible approach is to use a LPI/LPD waveform (based upon chaos based communications) for the probe/rendezvous signal.