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1
Bottenfield, Joe, and Vern Moore. "SMALL VOLUME, FEHER-PATENTED QUADRATURE PHASE SHIFT KEYING, JR VERSION, TELEMETRY TRANSMITTER." International Foundation for Telemetering, 2003. http://hdl.handle.net/10150/606734.
Full textAbstract:
International Telemetering Conference Proceedings / October 20-23, 2003 / Riviera Hotel and Convention Center, Las Vegas, Nevada<br>This paper describes the implementation of a Feher-Patented Quadrature Phase Shift Keying (FQPSK) waveform variant that reduces overall design complexity, which in turn results in a telemetry transmitter that provides all the benefits of the existing FQPSK-B waveform, in a 3.0 x 2.0 x 1.0 volume. This variant is referred to the as the FQPSK-JR version. This waveform differs from the “near constant” envelop response of the qualified Herley airborne FQPSK-B telemetry transmitter in terms of the time domain wavelet transition functions and the amplitude scaling term associated with those functions. The end result is a “constant envelop” design, which employs simplified antialias filtering and more efficient digital design techniques.
2
Terziev, George, and Kamilo Feher. "ADAPTIVE FAST BLIND FEHER EQUALIZERS (FE) FOR FQPSK." International Foundation for Telemetering, 1999. http://hdl.handle.net/10150/607297.
Full textAbstract:
International Telemetering Conference Proceedings / October 25-28, 1999 / Riviera Hotel and Convention Center, Las Vegas, Nevada<br>The performance of novel experimental blind equalizers suitable for a large class of
applications including telemetry systems and other wireless applications is described.
Experimental hardware research of these adaptive patent pending Feher Equalizers (FE)
confirms computer simulated data [1]. A two-ray RF selective faded telemetry channel has
been simulated. A dynamically changing channel environment with a selective fade rate in
the 1Hz to 50Hz range has been constructed by laboratory hardware. The Test and
Evaluation (T&E) setup had RF frequency selective dynamic notch depth variations in the
Power Spectral Density (PSD) within the band of the signal of up to 15dB. As an
illustrative example of the adaptive equalizer capability we used a 1Mb/s rate Feher
patented FQPSK [1] Commercially Of The Shelf (COTS) product. Both hardware
experimental results as well as simulation indicate substantial performance improvement
with the utilization of the FE. It is demonstrated that the FE improves for a large class of
frequency selective faded systems the Bit Error Rate(BER) from 10^-2 to 10^-6. Similar
performance improvements are presented for the Block Error Rate (BLER).
3
Gao, Wei, Shih-Ho Wang, and Kamilo Feher. "TESTS AND EVALUATIONS OF ADAPTIVE FEHER EQUALIZERS FOR A LARGE CLASS OF SYSTEMS, INCLUDING FQPSK." International Foundation for Telemetering, 2000. http://hdl.handle.net/10150/606772.
Full textAbstract:
International Telemetering Conference Proceedings / October 23-26, 2000 / Town & Country Hotel and Conference Center, San Diego, California<br>Design and performance evaluation of a low-complexity equalizer for recently standardized spectral efficient Feher
patented quadrature phase shift keying (FQPSK) system [1] over multipath fading channel is presented. The
implementation based on a Feher patented equalizer (FE) [1] is of a structure with three branches, which are
individually used to compensate for a moving fade notch with different locations. These branches are switched by
the control signal that is generated based on pseudo-error on-line detection technique. It is demonstrated that for
typical aeronautical telemetry RF frequency selective fading channels, having delay spreads in 20 – 200 ns range,
the adaptive FE reduces the number of statistical outages by more than 60% without the need for training bits and
without increasing the receiver synchronization time.
4
Feher, Kamilo. "FQPSK Doubles Spectral Efficiency of Telemetry: Advances and Initial Air to Ground Flight Tests." International Foundation for Telemetering, 1998. http://hdl.handle.net/10150/607395.
Full textAbstract:
International Telemetering Conference Proceedings / October 26-29, 1998 / Town & Country Resort Hotel and Convention Center, San Diego, California<br>FQPSK is the abbreviation for Feher Quadrature Phase Shift Keying (FQPSK)
patented systems [1]. Digcom, Inc. licensed FQPSK products demonstrated significant
spectral saving and RF power efficient robust BER performance advantages. These bit
rate agile modems and Non Linearly Amplified (NLA) transceivers, DSP and hardware
implementations, and in some instances “software-radios” (20kb/s to more than 100Mb/s)
and RF frequency agile (from 150MHz to more than 40GHz) developments and systems
have recently been demonstrated and deployed. The spectral efficiency, i.e., data
throughput capability of the 1st generation of FQPSK, as demonstrated in initial Advanced
Range Telemetry (ARTM) flight tests, approximately doubles while 2nd generation
“FQPSK-2” systems have the potential to quadruple the spectral efficiency of operational
PCM/FM telemetry systems and be backward compatible with the 1st generation of
FQPSK technologies. It is also demonstrated that the spectral efficiency advantage of
FQPSK over that of NLA power efficient GMSK, OQPSK and QPSK modulated
transceivers is in the 50% to 300% range and that the potential spectral efficiency
advantage of FQPSK-2 over GMSK [1] is in the 200% to 500% range.
Based on extensive multi-year studies of alternative solutions for spectral and RF
power efficient, robust BER performance systems, several commercial US and
international organizations, AIAA, CCSDS, NASA, ESA, CCSDS and various programs
of the US Department of Defense (DoD) concluded that FQPSK offers the most
spectrally efficient high performance-high speed proven technology solutions and
recommended FQPSK standardization for several data links. Initial DoD-ARTM Program
Office Air-to-Ground L-band and S-band jet airborne telemetry Test and Evaluation
(T&E) data, obtained during the summer of 1998 are briefly highlighted. These include
simultaneosly tested FQPSK and PCM/FM. In these tests the following ARTM objectives
have been demonstrated: (a) FQPSK approximately doubles the spectral efficiency of
currently operational PCM/FM; (b) The Data Link Performance of these two systems is
comparable. The American Institute of Aeronautics and Astronautics (AIAA) draft
modulation standard recommended to the DoD, NASA and CCSDS, was approved by
the AIAA [23]. The AIAA standard recommends “that FQPSK modulation be
immediately adopted as the interim increment–1 standard.”
5
Feher, Kamilo, Robert Jefferis, and Eugene Law. "Spectral Efficiency and Adjacent Channel Interference Performance Definitions and Requirements for Telemetry Applications." International Foundation for Telemetering, 1999. http://hdl.handle.net/10150/607340.
Full textAbstract:
International Telemetering Conference Proceedings / October 25-28, 1999 / Riviera Hotel and Convention Center, Las Vegas, Nevada<br>Organizations such as the National Telecommunications and Information Administration
(NTIA), Federal Communications Commission (FCC), International Telecommunications
Union (ITU) and various commercial entities use a wide range of spectral efficiency
criteria in different broadcast and wireless system applications. These criteria and related
specifications have significant differences. This paper briefly reviews some common
adjacent channel interference (ACI) definitions as well as issues surrounding the
definition of spectral efficiency. The impact of these parameters on system bit error rate
(BER) performance and closely "packed" adjacent signals is described. ACI criteria and
spectral efficiency definitions considered appropriate for existing telemetry applications
and deployment of new generations of spectrally efficient systems are illustrated. Specific
ACI and spectral efficiency performance requirements adopted by the Department of
Defense (DoD) and Advanced Range Telemetry (ARTM) project are highlighted.
6
Aflatouni, Katayoun, and Kamilo Feher. "SMART DIVERSITY RECEIVERS FOR DYNAMIC, MULTIPATH, FREQUENCY SELECTIVE FADED FQPSK AND OTHER SYSTEMS." International Foundation for Telemetering, 2001. http://hdl.handle.net/10150/606440.
Full textAbstract:
International Telemetering Conference Proceedings / October 22-25, 2001 / Riviera Hotel and Convention Center, Las Vegas, Nevada<br>Design, performance Test and Evaluation (T&E) of a novel smart diversity receiver, based on Feher
Diversity (FD) patents over multipath, fast dynamic frequency selective fading channels is
presented. A hardware simulator for construction of a frequency selective fading channel has been
implemented in laboratory to resemble a telemetry aeronautical channel model, namely the two-path
channel model. As an illustrative example, the block error rate (BLER) of a 1 Mb/s rate IRIG 106-00 and CCSDS standardized Feher’s patented quadrature phase shift keying (FQPSK) [1][2] with
and without diversity in multipath frequency selective fading channels has been tested and evaluated.
The experimental results clearly indicate significant performance improvement with the proposed
diversity technique even in cases of severely distorted channels.
7
Lin, Jinsong, and Kamilo Feher. "BANDWIDTH EFFICIENCY AND BER PERFORMANCE OF ENHANCED AND FEC CODED FQPSK." International Foundation for Telemetering, 2000. http://hdl.handle.net/10150/607727.
Full textAbstract:
International Telemetering Conference Proceedings / October 23-26, 2000 / Town & Country Hotel and Conference Center, San Diego, California<br>Bit error rate (BER) and bandwidth efficiency of several variations of enhanced Feher patented quadrature phase shift keying (FQPSK) [1] are described. An enhanced FQPSK increases the channel packing density of that of the IRIG 106-00 standardized FQPSK-B by approximately 50% in adjacent channel interference (ACI) environment. As the bandwidth efficiency of FQPSK-B DOUBLES (2×) that of pulse code modulation/Frequency modulation (PCM/FM) [5], the enhanced FQPSK, with a simpler transceiver than FQPSK-B, has a channel packing density of TRIPLE (3×) that of PCM/FM. One of the other enhanced FQPSK prototypes has an end to end system loss of only 0.4 dB at BER=1x10^(-3) and 0.5 dB at BER=1x10^(-4) from ideal linearly amplified QPSK theory. The enhanced FQPSK has a simple architecture, thus is inexpensive and has small size, for ultra high bit rate implementation. With low redundancy forward error correction (FEC) coding which expands the spectrum by approximately 10%, further improvement of about 3-4.5dB E N b o is attained with NLA FQPSK-B and enhanced FQPSK at BER=1x10^(-5) .
8
Lin, Jin-Son, and Kamilo Feher. "NONCOHERENT AND DIFFERENTIAL DETECTION OF FQPSK WITH MAXIMUM-LIKELIHOOD SEQUENCE ESTIMATION IN NONLINEAR CHANNELS." International Foundation for Telemetering, 2002. http://hdl.handle.net/10150/606381.
Full textAbstract:
International Telemetering Conference Proceedings / October 21, 2002 / Town & Country Hotel and Conference Center, San Diego, California<br>This paper presents noncoherent limiter-discriminator detection and differential detection of FQPSK
(Feher quadrature phase-shift-keying) with maximum-likelihood sequence estimation (MLSE)
techniques. Noncoherent FQPSK systems are suitable for fast fading and cochannel interference
channels and channels with strong phase noise, and they can offer faster synchronization and reduce
outage events compared with conventional coherent systems. In this paper, both differential detection
and limiter-discriminator detection of FQPSK are discussed. We use MLSE with lookup tables to
exploit the memory in noncoherently detected FQPSK signals and thus significantly improve the bit
error rate (BER) performance in an additive white Gaussian noise (AWGN) channel.
9
Troublefield, Robert C. "DIGITAL RECEIVER PERFORMANCE." International Foundation for Telemetering, 2000. http://hdl.handle.net/10150/606794.
Full textAbstract:
International Telemetering Conference Proceedings / October 23-26, 2000 / Town & Country Hotel and Conference Center, San Diego, California<br>Bit errors often occur in a wireless communications link when impairments alter the transmitted signal.
It is advantageous to be able to predict how well a system will tolerate transmission problems. This
paper details laboratory performance measurements and comparisons in terms of evaluating
configurations of a digital receiver for Feher patented Quadrature Phase Shift Keying (FQPSK-B)
demodulation. The transmitted signal is subjected to calibrated levels of impairments while the receiver
performance is monitored in real-time.
10
Jefferis, Robert P. "EVALUATION OF CONSTANT ENVELOPE OFFSET QUADRATURE PHASE SHIFT KEYING TRANSMITTERS WITH A SOFTWARE BASED SIGNAL ANALYZER." International Foundation for Telemetering, 2004. http://hdl.handle.net/10150/605762.
Full textAbstract:
International Telemetering Conference Proceedings / October 18-21, 2004 / Town & Country Resort, San Diego, California<br>Off-line software based signal analysis can be a valuable tool for detailed examination of transmitter signal characteristics. This paper describes the Advanced Range Telemetry (ARTM) Constant Envelope (CE) offset quadrature phase shift keying (OQPSK) modulation analyzer. It was developed expressly for evaluation of FQPSK-B^(1), FQPSK-JR and shaped OQPSK transmitter signals. Rationale for its creation, underlying assumptions, computation methods, and examples of its data products are presented.
11
Temple, Kip. "MODULATOR IMBALANCE EFFECTS ON THE FQPSK AIRBORNE TELEMETRY LINK." International Foundation for Telemetering, 2000. http://hdl.handle.net/10150/607721.
Full textAbstract:
International Telemetering Conference Proceedings / October 23-26, 2000 / Town & Country Hotel and Conference Center, San Diego, California<br>When designing transmitters for quadrature modulation schemes, the designer always tries to achieve good balance and symmetry of the in-phase (I) and quadrature (Q) branches of the modulator in terms of amplitude, phase, and offsets. Perfect balance between modulators is ideal but rarely if ever achieved. The Advance Range Telemetry (ARTM) program has placed indirect specifications on the remnant carrier and sideband levels which are controlled by modulator imbalance. These specifications will govern the ARTM programs first generation of Feher’s patented quadrature phase shift keying, version B (FQPSK-B) [9] airborne telemetry transmitters. The ARTM Program has also adopted test procedures for quantifying these modulation imbalances. This paper looks at the effects of modulator imbalances on spectral occupancy and bit error probability of the airborne telemetry link. It also outlines how these imbalances influence the levels in one of the ARTM specifications. Recommendations are presented based on the measured data for higher bit rate telemetry systems.
12
Martin, Warren L. "FQPSK DEVELOPMENTS RECOMMENDED FOR CCSDS STANDARDIZATION BY NASA JPL." International Foundation for Telemetering, 2000. http://hdl.handle.net/10150/607720.
Full textAbstract:
International Telemetering Conference Proceedings / October 23-26, 2000 / Town & Country Hotel and Conference Center, San Diego, California<br>In 1992, international space agencies became concerned that increasing frequency band congestion, together with attempts by the mobile telephone industry to obtain additional bandwidth, would result in substantially more interference incidents. The CCSDS undertook a technical study to identify and recommend more bandwidth efficient modulation schemes, which would permit more users to co-exist in a frequency band while reducing interference incidents. This paper describes the contribution of the Jet Propulsion Laboratory (JPL) to that effort.
13
Chen, Dijin, James A. McCorduck, and Kamilo Feher. "FQPSK ANALOG/DIGITAL IMPLEMENTATIONS FOR LOW TO ULTRA HIGH DATA RATES IN 1Gb/s RANGE SYSTEMS." International Foundation for Telemetering, 2003. http://hdl.handle.net/10150/606735.
Full textAbstract:
International Telemetering Conference Proceedings / October 20-23, 2003 / Riviera Hotel and Convention Center, Las Vegas, Nevada<br>For simpler implementations of ultra high bit rate systems, combined analog/digital techniques, described here in, provide implementations with the smallest number of component count utilizing minimal “real-estate” and smallest DC power. While digital implementations with tradition Read Only Memory (ROM) and Digital to Analog Converters (DAC’s) have been proven in several commercial, NASA -CCSDS recommended, and U.S. DoD-IRIG standardized Feher’s QPSK (FQPSK) [2,3] products, such implementations can be further simplified, and in particular for ultra high bit rate product applications. Several waveform generating techniques such as linear approximation, analog approximation and mixed analog and linear approximations are investigated using preliminary simulation results.
14
Lee, Dennis, Marvin Simon, and Tsun-Yee Yan. "ENHANCED PERFORMANCE OF FQPSK-B RECEIVER BASED ON TRELLIS-CODED VITERBI DEMODULATION." International Foundation for Telemetering, 2000. http://hdl.handle.net/10150/607724.
Full textAbstract:
International Telemetering Conference Proceedings / October 23-26, 2000 / Town & Country Hotel and Conference Center, San Diego, California<br>Commercial FQPSK-B receivers traditionally use symbol-by-symbol detection and have a 2 dB Eb=No loss relative to ideal QPSK at a bit error rate (BER) of 10^(-5). An enhanced FQPSK-B receiver using a Viterbi algorithm (VA) to perform trellis decoding is simulated and shown to have a 1.2 dB Eb=No improvement over symbol-by-symbol detection for 10^(-5)5 BER at the cost of increased complexity. A simplified Viterbi receiver with a reduced trellis and significantly less complexity is introduced with only a slight BER degradation compared to the full Viterbi receiver. In addition, a theoretical bit error probability expression for the symbol-by-symbol FQPSK-B receiver is derived and compared with simulation results.
15
Temple, Kip. "ADVANCED RANGE TELEMETRY (ARTM) TIER I COMPATIBLE DEMODULATOR TESTING AND RESULTS." International Foundation for Telemetering, 2002. http://hdl.handle.net/10150/606309.
Full textAbstract:
International Telemetering Conference Proceedings / October 21, 2002 / Town & Country Hotel and Conference Center, San Diego, California<br>The Nova HYPERMOD demodulator operates in three modes, the classic pulse-code
modulation/frequency modulation (PCM/FM), sometimes known as continuous phase frequency shift
keying (CPFSK) mode, shaped offset quadrature phase shift keying (SOQPSK) mode, and continuous
phase modulation (CPM) mode. Of interest to this paper is SOQPSK mode which is a waveform similar
to the Advanced Range Telemetry (ARTM) Tier I waveform, Feher’s Quadrature Phase Shift Keying, B
version (FQPSK-B) revision (Rev) A1. Also considered is another variant, FQPSK-JR. This paper
will outline the cross compatibility and resynchronization speed of these waveforms based upon
ARTM-adopted demodulator performance tests. The results of these laboratory tests comparing the
HYPERMOD demodulator, the enhanced Tier I demodulator, and the current Tier I reference
demodulator, both from RF Networks, will be presented.
16
Lee, Tong-Fu, Shih-Ho Wang, Chia-Liang Liu, and Liu Bao. "FQPSK-L: An Improved Constant Envelope Modulation Scheme for QPSK." International Foundation for Telemetering, 1998. http://hdl.handle.net/10150/609210.
Full textAbstract:
International Telemetering Conference Proceedings / October 26-29, 1998 / Town & Country Resort Hotel and Convention Center, San Diego, California<br>A new constant envelope modulation scheme and architecture for QPSK by cubic spline interpolation methods which increase spectral efficiency and power efficiency, named FQPSK-L, is presented. This modulation technique is an extension of the Feher Quadrature Shift Keying (FQPSK) patented technologies, see Ref [1]. Being a constant envelope modulation, FQPSK-L can operate with class C power amplifier without spectrum regrowth. We achieve a more compact spectrum with comparable bit error rate performance. For example, FQPSK-L is about 20% more spectral efficient than GMSK BTb=0.3 from 40 to 70 dB attenuation point. Moreover, FQPSK-L intrinsically has spikes at fc ± 0.5fb, fc ± 1.0fb, fc ± 1.5fb, ... which are useful for carrier recovery, symbol time recovery and fading compensation. In Rayleigh fading channel, FQPSK-L outperform GMSK BTb=0.3 by 0.8 dB. FQPSK-L is an excellent scheme for wireless and satellite communications which require high spectral and power efficiency.
17
Horcher, Gregg. "DESIGN CONSIDERATIONS FOR DEVELOPMENT OF AN AIRBORNE FQPSK TRANSMITTER." International Foundation for Telemetering, 1999. http://hdl.handle.net/10150/607301.
Full textAbstract:
International Telemetering Conference Proceedings / October 25-28, 1999 / Riviera Hotel and Convention Center, Las Vegas, Nevada<br>This paper describes the design considerations used by Aydin Telemetry in the
development of its high data rate Feher Patented Quadrature Phase Shift Keying
(FQPSK) [1] frequency agile transmitter. We will address several key areas of interest to
the Telemetry community, such as the use of commercially available VLSI parts to
minimize parts count while maximizing reliability, adaptive filtering to accommodate a
wide range of data rates, and user selectable features to achieve a universal transmitter
design. User selectable features include differential encoder, 15 stage IRIG randomizer,
and 1/2 rate convolutional FEC coding. This paper also addresses the spectral efficiency
that can be achieved using a Class-C amplifier with FQPSK and the measured bit error
rate (BER) performance versus Eb/No.
18
Lee, Tong-Fu, Shih-Ho Wang, and Chia-Liang Liu. "FQPSK-O: An Improved Performance Constant Envelope Modulation Scheme for OQPSK." International Foundation for Telemetering, 1998. http://hdl.handle.net/10150/607387.
Full textAbstract:
International Telemetering Conference Proceedings / October 26-29, 1998 / Town & Country Resort Hotel and Convention Center, San Diego, California<br>A new constant envelope modulation scheme for OQPSK, called FQPSK-O, is
presented. This modulation technique is an extension of the Feher Quadrature Shift
Keying (FQPSK) patented technologies, see Ref[l]. This scheme uses cubic spline
interpolation to generate very smooth baseband waveforms in order to increase the
spectral and power efficiency. Being a constant envelope modulation, FQPSK-O can
operate with class C power amplifier without spectrum regrowth. We achieve a more
compact spectrum with comparable bit error rate performance. For example, the spectrum
of FQPSK-O is 25% narrower than that of GMSK with BT(b)=0.3 and FQPSK-1 with
hardlimiter [2] at -40 dB attenuation point. For coherent demodulation under AWGN
channel, FQPSK-O has almost the same BER performance as FQPSK-1 with hardlimiter.
Both of them are better than GMSK with BT(b)=0.3 for BER < 10^-4. In Rayleigh fading
channel, FQPSK-O outperforms GMSK with BT(b)=0.3 by 2 dB. FQPSK-O is an excellent
scheme for wireless and satellite communications which require high spectral and power
efficiency.
19
Feher, Kamilo. "SPECTRAL EFFICIENCY OF COMMERCIAL WIRELESS AND TELEMETRY SYSTEMS IS DOUBLED WITH IRIG 106-00 STANDARDIZED FQPSK AND IS QUADRUPLED WITH FQAM." International Foundation for Telemetering, 2000. http://hdl.handle.net/10150/606757.
Full textAbstract:
International Telemetering Conference Proceedings / October 23-26, 2000 / Town & Country Hotel and Conference Center, San Diego, California<br>Advances in spectrally efficient Feher’s Quadrature Phase Shift Keying (FQPSK) and Feher‘s
Quadrature Amplitude Modulation (FQAM) patented technologies, commercial and government
“dual-use” FQPSK products and Test & Evaluation (T&E) results are highlighted in this overview
paper. US and international customer requirements/systems, programs and recent deployments and
standardization programs are also described. FQPSK doubles the spectral efficiency of PCM/FM
Telemetry and of Feher patented Gaussian Minimum Shift Keying (GMSK or FGMSK) and of
alternatives, while FQAM quadruples the spectral efficiency of these systems. The predominant focus
of this presentation is on an overview and advances of IRIG 106-00 standardized FQPSK technologies.
FQAM systems will also be described. Use of FQPSK for applications such as telemetry, data links,
clear mode, TDMA ,CSMA and CDMA, OCDMA, WCDMA as well as OFDM – COFDM will be
included in the presentation.
20
Law, Eugene, and Kamilo Feher. "FQPSK VERSUS PCM/FM FOR AERONAUTICAL TELEMETRY APPLICATIONS; SPECTRAL OCCUPANCY AND BIT ERROR PROBABILITY COMPARISONS." International Foundation for Telemetering, 1997. http://hdl.handle.net/10150/609732.
Full textAbstract:
International Telemetering Conference Proceedings / October 27-30, 1997 / Riviera Hotel and Convention Center, Las Vegas, Nevada<br>The aeronautical telemetry community is investigating alternative modulation methods to the commonly used non-return-to-zero (NRZ) pulse code modulation (PCM)/frequency modulation (FM). This paper outlines the important characteristics being investigated. Measured data comparing the spectral occupancy and bit error probability (BEP) performance of PCM/FM with that of a prototype constant envelope Feher’s quadrature phase shift keying (FQPSK) modulator and demodulator will also be presented. Measured results in several radio frequency bands demonstrate that the 99.99% and -60 dBc bandwidths of filtered FQPSK are only approximately one-half of the corresponding bandwidths of optimized PCM/FM even when the signal is non-linearly amplified. The signal energy per bit to noise power spectral density (E /N ) required for a BEP of 1×10 b 0 -5 for non-optimized FQPSK was approximately 12 dB which is approximately the same as limiter discriminator detected PCM/FM.
21
Taylor, Fall Bernard. "Simulation study of digitized enhanced Feher quadrature phase shift keying (EFQPSK)." 2006. http://etd.utk.edu/2006/TaylorFall.pdf.
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