High throughput channel tracking for JTRS wireless channel emulation

Many future airborne networks will be built around the software-defined joint tactical radio system (JTRS). Because of the programmability of JTRS, planners of these networks will have a great deal of flexibility in their selection of waveforms. There can be a wide variation in the properties of the candidate waveforms, such as data rate, spectral efficiency, latency, and protection against jamming. In order to choose those waveforms which best meet mission needs, these capabilities must be understood. Because of the nodes' high altitudes and use of omnidirectional antennas, airborne networks can be particularly susceptible to jamming. In this paper, we investigate the performance of three representative waveforms in the presence of hostile jamming. One waveform is based on orthogonal frequency division multiplexing (OFDM), a multicarrier modulation technique. The second uses single-carrier direct-sequence spread-spectrum modulation. Finally, a waveform based on the legacy Link 16 system, which uses a combination of frequency-hop and direct-sequence spread spectrum, is considered. Quantitative results comparing the performance of these waveforms against several jamming threats, including tone, partial-band, and frequency-follower jamming, are presented, and techniques to improve their robustness to the interference are considered.

Carrier generation and IF signal up-conversion using optical injection locking and stimulated Brillouin scattering

The noise simulation circuit of noncoherent spread-spectrum system intermediate frequency (IF) signal simulator is designed based on FPGA and DSP. This circuit generates white Gaussian noise (WGN), calculates coefficients of signal-to-noise ratio (SNR) refer to the specified SNR of each channel and according to these coefficients to generate spread-spectrum IF signal for transmitting to simulate the actual receive signal of responder beacon (RSP). It has been verified that the result of test meets the requests of system.

Phase-locked loops (PLL's) may be used to implement signal combiners which coherently sum multiple signals from an array of sensors. In each combiner channel, the sensor signal is simultaneously downconverted to an intermediate frequency (IF) signal and phase-locked to an appropriately generated reference signal by a "long-loop" PLL. This loop maintains a nominal 90° phase difference between the IF signal and the reference signal irrespective of phase of the channel input (sensor output) signal. The channel IF signals are summed to generate the combiner output signal. The reference signal may be a locally generated sine wave or a delayed version of the combiner output signal. Imperfect phase control and, thus, imperfect signal combining results when noise voltages are associated with the channel signals. In this paper, a lincarized model of a PLL coherent combiner is developed. This model applies when the desired channel signals are equal amplitude and angle modulated; the channel noise voltages are equal level, Gaussian distributed, and independent; and the combiner phase errors are appropriately small. This model is then used to derive equations for the variance of differential phase errors associated with combiner operation and to show the effect of these phase errors on the average power in the combiner output signal. Relevant experimental results from a four-channel combiner are compared with the performance predicted by the linear model.

We propose a photonic mixer with image rejection capability using a broadband optical source (BOS) and polarization processing. Intermediate frequency (IF) signals with image rejection are generated from the local oscillator-modulated and the time-delayed radio frequency (RF)-modulated BOS light. The RF operating frequency is flexibly tunable over a wide range by simply adjusting the time delay. In addition, the proposed system is free from dispersion-induced mixing power fading and bias drift problem. Experimental results exhibit an image rejection ratio of more than 44.6 dB for RF signals from 2 to 18 GHz, while the IF signal is fixed at 800 MHz. Image rejection mixing operation at different IF frequencies and signal power is also confirmed.

An image-rejected multi-band frequency down-conversion scheme is proposed and experimentally demonstrated based on photonic sampling. The multi-band radio-frequency (RF) signals to be processed are copied into two replicas in quadrature, which are then sampled by an ultra-short optical pulse train via a polarization-multiplexed modulator. After polarization demultiplexing and detection using a pair of low-speed photodetectors, the multi-band RF signals are simultaneously down-converted to the intermediate frequency (IF) band. The image components can be suppressed by quadrature coupling the two generated IF signals via an electrical 90° hybrid coupler (HC). In the experiment, multi-band RF signals in the frequency range of 6 GHz to 39 GHz are down-converted to the IF band below 4 GHz using a local oscillator (LO) signal at 8 GHz to generate the ultra-short optical pulse train. Image rejection is achieved in the digital domain using digital signal processing to compensate for the amplitude and phase mismatch between the two IF signals and to implement quadrature coupling. In addition, through using an electrical phase shifter, an electrical attenuator, and an electrical 90° HC to achieve quadrature coupling of the two IF signals, image-rejected multi-band frequency down-conversion is also verified in the analog domain.

We propose and experimentally demonstrate a photonic millimeter-wave frequency divider based on a super-harmonic injection-locked optoelectronic oscillator (OEO) and an optical frequency comb. The optical frequency comb generator is incorporated into an OEO loop to create broadband comb lines with low noise. By injecting a millimeter-wave with frequency around N times of the fundamental oscillating frequency f0 of the OEO, the injection signal can be down-converted to an intermediate frequency (IF) signal close to the oscillating frequency of the OEO. The free running OEO is synchronized with the IF signal via an injection locking mechanism. Consequently, it forms an injection-locked frequency divider as the frequency ratio between the injection signal and OEO's output signal is precisely equal to N. We carry out an experiment to divide the 45 GHz signal into 7.5 GHz and the experimental results agree well with the theoretical analysis. By changing the frequency of the injection signal, division ratio from 2 to 5 is also demonstrated on one setup. Due to the broadband spectra of the optical comb and low phase noise characteristics of the OEO, it is potential to realize very large division ratio and low phase noise for multiple input frequencies mf 0 .

Wideband photonic microwave channelization and image-reject down-conversion

The performance of bulk InSb mixers is investigated, A heterodyne experiment has been performed at 69 GHz with IF's varying from 0.4 to 20 MHz. In this experiment the conversion loss was measured as a function of the intermediate frequency (IF) for ambient temperatures in the range 1.5 to 20°K. The IF at which the conversion loss increased by 3 dB determined the response time. Using an electron temperature model, expressions for the conversion loss and the response time are derived by making a small-signal expansion of an energy balance equation. Good agreement between theory and experiment is shown. In this theory the InSb mixer is viewed as a bolometer mixer. An evaluation of mixer performance, stressing operation at ambient temperatures in the 1.5 to 20°K range, is presented. The available tradeoffs between conversion loss and response time as a function of ambient temperature and applied fields are given. Values as low as 11 dB for the minimum conversion loss can be obtained at 1.5°K, where the maximum useable IF is 1 MHz. To obtain a substantially higher IF, such as 10 MHz, the temperature must be increased to 16°K. However, the optimum conversion loss increases at a rate of 1 dB/°K and is 27 dB at 16°K. It is also shown that the device performance of InSb mixers can be predicted satisfactorily from static I-V characteristics and that the best mixer material can be determined by making simple dc measurements.

In the new 4K/8K satellite broadcasting, the maximum intermediate frequency (IF) is proposed to be changed from 2071 MHz to 3224 MHz. The coaxial cable has been widely used for IF signal transmission, but the attenuation is significant with a high signal loss when a high-frequency signal is transmitted. With the increasing number of 4K/8K channels and the development of broadcasting technology, the frequency used for the IF signal will keep increasing. Therefore, the coaxial cable may not meet the future ultra-high-definition satellite broadcasting requirements anymore. Compared to the all-electrical signal transmission, the Radio-over-Fiber (RoF) system can achieve signal transmission with lower loss and reduce noise sensitivity by transmitting the signal through an optical fiber. In this work, we propose a system that uses the RoF technology to reduce the signal loss during high-frequency transmission while adopting the Power-over-Fiber (PoF) technology to generate electric power for Low-Noise Block (LNB) and RoF unit on the antenna side. A method that combines the RoF technology and PoF technology into one Double-clad Fiber is also reported. With the comparison between the signal transmitted through an RoF system and that through a coaxial cable, it can be clearly shown that the advantage of the RoF technology in the signal loss performance. The experimental results of signal transfer demonstrate that by using the RoF technology, the average amplitude of the effective signal containing TV channels increases by 8.89 dB in the range of 2224-3224 MHz, while the average amplitude increases by 5.7 dB for the effective signal in the range of 1032-2071 MHz.

Design of a low cost Schottky diode based single-balanced mixer (SBM) in full V-band with an ultra-wide intermediate frequency (IF) bandwidth is presented here. By loading multiple quarter-wavelength short-ended stubs at both radio frequency (RF) and local oscillator (LO) frequency on the multistage stepped impedance matching networks, a broadband grounding circuit is provided for IF signal and thus output power nulls are eliminated over an ultra-wide IF band. The hybrid network is constructed by a 3 dB branch coupler and a 90-degree delay line, which enables the required balanced outputs with equal amplitude and 180-degree phase difference. A prototype of the SBM is designed, fabricated and tested. Measured results demonstrate that, for RF and LO frequency over entire V-band, the mixer has a conversion loss from 6.8 to 11.4 dB with an ultra-wide IF range of 0.01–22 GHz.

The first, to the best of our knowledge, implementation of optical single-sideband modulation (OSSBM) in coherent Doppler lidar (CDL) is demonstrated for use with short pulse widths. It is shown that by providing more bandwidth through a higher intermediate frequency (IF), the OSSBM CDL addresses cross talk between the IF and baseband spectra, reducing spectral distortion. Ultimately, a 4-ns pulse width with a 1-GHz IF is achieved and the effectiveness of the OSSBM CDL is confirmed through velocimetry experiments. This represents a several fold improvement over current fiber-based CDL implementations.

A front‐end MMIC working at 37–43.5 GHz for 5G high‐performance channel emulator is presented in this paper. The chip is fabricated in a 0.1‐μm commercial GaAs pHEMT process and integrated with a passive star mixer and a local oscillator (LO) chain, which is composed of a frequency tripler, a bandpass filter, a power amplifier, and an LO filter. The 10.5 GHz intermediate frequency (IF) signal is upconverted with the high frequency LO signal of 48–54 GHz through a passive double‐balanced star mixer, which can output 37–43.5 GHz radiofrequency signal. The high frequency LO can avoid the increase of bit error rate caused by the frequency band of input signal covering IF frequency. The conversion gain of −11.2 to −9.7 dB, the OP1‐dB of −0.26 to 1.7 dBm are achieved and the front‐end chip occupies an area of 2.78 × 0.9 mm2.

In this paper, the design of a continuous-time baseband sigma-delta modulator with an integrated mixer for intermediate-frequency (IF) analog-to-digital conversion is presented. This highly linear IF modulator digitizes a GSM channel at intermediate frequencies up to 50 MHz. The sampling rate is not related to the input IF and is 13.0 MHz in this design. Power consumption is 1.8 mW from a 2.5-V supply. Measured dynamic range is 82 dB, and third-order intermodulation distor- tion is 84 dB for two 6-dBV IF input tones. Two modulators in quadrature configuration provide 200-kHz GSM bandwidth. Active area of a single IF modulator is 0.2 mm in 0.35- m CMOS.

In this paper, the design of a continuous-time baseband sigma-delta (/spl Sigma//spl Delta/) modulator with an integrated mixer for intermediate-frequency (IF) analog-to-digital conversion is presented. This highly linear IF /spl Sigma//spl Delta/ modulator digitizes a GSM channel at intermediate frequencies up to 50 MHz. The sampling rate is not related to the input IF and is 13.0 MHz in this design. Power consumption is 1.8 mW from a 2.5-V supply. Measured dynamic range is 82 dB, and third-order intermodulation distortion is -84 dB for two -6-dBV IF input tones. Two modulators in quadrature configuration provide 200-kHz GSM bandwidth. Active area of a single IF /spl Sigma//spl Delta/ modulator is 0.2 mm/sup 2/ in 0.35-/spl mu/m CMOS.