For radio communication systems, powerful error correction codes are necessary to operate in noisy and
fading channel conditions. Iterative forward error correction schemes like Turbo codes can achieve near
Shannon capacity performance on memory-less channels and also perform well on correlated fading
channels. The key to the excellent decoding performance of the Turbo coding systems is the BCJR
algorithm in conjunction with the iterative processing of soft information. A very popular modulation
technique is Differential Phase Shift Key (DPSK) which is not only a simple non-coherent modulation and
demodulation technique; it is also a recursive rate one code. Combining DPSK with a single convolutional
code structure as an iterative inner outer forward error correction system can provide excellent Turbo like
performance. Bit Interleaved Coded Modulation with Iterative Demodulation (BICM-ID), another powerful iterative technique achieves near Turbo code performance with significantly less mips. We will also introduce and compare with the latter systems yet another novel iterative scheme that utilizes coherent demodulation in conjunction with convolutional codes. This new system can easily be extended to higher order modulations such as 16 and 64 Quadrature Amplitude Modulation (QAM) while only requiring modest amounts of processing power. Monte Carlo simulation results will be shown for the Additive White Gaussian Noise (AWGN) channels.
For radio communication systems, powerful error correction codes are necessary to operate in noisy and
fading channel conditions. Iterative forward error correction schemes like Turbo codes can achieve near
Shannon capacity performance on memory-less channels and also perform well on correlated fading
channels. The key to the excellent decoding performance of the Turbo coding systems is the BCJR
algorithm in conjunction with the iterative processing of soft information. A very popular modulation
technique is Differential Phase Shift Key (DPSK) which is not only a simple non-coherent modulation and
demodulation technique; it is also a recursive rate one code. Combining DPSK with a single convolutional
code structure as an iterative inner outer forward error correction system can provide excellent Turbo like
performance. Bit Interleaved Coded Modulation with Iterative Demodulation (BICM-ID), which is a
similar iterative coding system that allows full coherent processing, will be analyzed and compared to the
DPSK BCJR iterative system. Monte Carlo simulation results will be shown for the Additive White
Gaussian Noise (AWGN) and Rayleigh fading channels.
For radio communication systems powerful error correction codes are necessary to operate in noisy and
fading channel conditions. Iterative forward error correction schemes like Turbo codes can achieve near
Shannon capacity performance on memory-less channels and also perform well on correlated fading
channels. The key to the excellent decoding performance of the Turbo coding systems is the BCJR
algorithm in conjunction with the iterative processing of the soft decision information. A very popular
modulation technique is Differential Phase Shift Key (DPSK) which is not only a simple non-coherent
modulation and demodulation technique, it is also a recursive rate one code. Combining DPSK with a
single convolutional code structure as an iterative inner outer forward error correction system can provide
excellent Turbo like performance. Monte Carlo simulation results will be shown for the Additive White
Gaussian Noise (AWGN) and Rayleigh fading channels for 1, 2, 3 and 4 bits per symbol DPSK.
For real world communication systems that operate in correlated fading channels, perfect channel state
information is not always available. In the literature, performance curves for error correction codes are
usually plotted from either closed form equations or simulations which assume perfect channel state
information. While these methods of measuring the capabilities of error correcting codes do serve a
theoretical purpose, they do not necessarily demonstrate how well a code will perform under non-ideal
conditions. The goal of this paper will be to compare LDPC and Turbo codes and determine how well they
perform when perfect channel state information is not available at the receiver. Bit error rate and some
block error rate performances will be provided for the AWGN, Rayleigh and 1Hz 1ms multipath fading
channel. The results of this paper may provide communication systems designers some useful insight into
the actual performance of error correcting codes in real-world scenarios.
High Frequency (HF) radio communication channels provide unique challenges to digital communication
systems. Typical HF communication systems propagate electromagnetic energy in the 2-30MHz radio
spectrum using the earth's ionosphere and surface as both refractors and reflectors for non line of sight
communications. Constantly changing ionosphere conditions result in multipath and severe fading channel
characteristics. Through numerical simulation, short block length block length (9e+3) Low Density Parity
Check (LDPC) forward error correction codes used in conjunction with Orthogonal Frequency Division
Multiplexing (OFDM) will be shown to provide excellent communication performance across the HF
channel. Average bit error rate performance results will be shown for a 2ms, 1Hz and 2Hz Watterson HF
channel model for both regular and irregular LDPC parity check matrices. Some results will also be shown
for imperfect channel estimation and its effects upon the performance of the LDPC decoder.
This paper will investigate the use of an enhanced rate one Alamouti Space Frequency (SF) multiple antenna
Orthogonal Frequency Division Multiplex (OFDM) radio communication system. A two transmit, single receive
antenna system will be simulated to operate under conditions of multipath fading with noise. A simple modification to
the standard coherent Alamouti receive combiner will be applied and shown to improve bit error rate (BER)
performance on rapidly fading multipath HF channels. Orthogonal Frequency Division Multiplexing frequency domain
techniques will be utilized to effectively eliminate the Inter-Symbol Interference (ISI) resulting from the effects of
multipath. Numerically simulated results will be shown for several multipath fading High Frequency (HF) radio
channels. Inner convolutional error correction coding will be applied in addition to the Alamouti coding and
numerically simulated BER results presented. Various HF channel conditions will be simulated including the 2 ms, 10
Hz, 2 ms, 5 Hz, CCIR poor (2 ms, 1 Hz) and extra poor (2 ms, 2 Hz) channel conditions. Performance under conditions
of correlated transmit antennas will also be investigated.
This paper will investigate the performance of a dual transmit antenna, single receive antenna, Alamouti differential Space Frequency (SF) Coded Orthogonal Frequency Division Multiplexed (COFDM) system on a multipath fading High Frequency (HF) radio channel. Prior work demonstrated that the multi-antenna Alamouti system without forward error correction did not perform as well on the HF Channel as a novel uncoded single antenna Code Division Multiple Access (CDMA) system. By adding additional convolutional or Low Density Parity Check (LDPC) error correction coding, the Bit Error Rate (BER) performance will be shown to improve and exceed that of a similar single antenna COFDM differential system. Numerical results will be shown for the CCIR poor (2ms, 1Hz) and extra poor (2ms, 2Hz) channel conditions for both a constraint length 7 convolutional code and a 7680 block length regular LDPC code. BER behavior for the SF-COFDM system will be plotted as a function of channel fade rate and interleaver size. BER comparisons will also be made between the coded system and a coded single transmit and receive antenna HF COFDM CDMA scheme.
KEYWORDS: Orthogonal frequency division multiplexing, Antennas, Receivers, Computer programming, Modulation, RF communications, Telecommunications, Transmitters, Signal to noise ratio, Binary data
This paper will investigate differential space frequency coding and its applicability to multipath fading High Frequency (HF) radio channels. Orthogonal Frequency Division Multiplexing (OFDM) will be combined with differential Alamouti space frequency codes to measure performance on the Watterson HF channel model. Differential coding facilitates non-coherent reception and can thus also reduce receiver complexity. Numerical results will be shown for the CCIR poor (2ms, 1Hz) and extra poor (2ms, 2Hz) channel conditions for a system comprised of 2 transmit antennas and a single receive antenna. For comparison, performance will also be shown vs. a new single transmit and receive antenna HF OFDM Code Division Multiple Access (CDMA) scheme.
High Frequency (HF) radio communication channels provide unique challenges to digital communication systems. Typical HF communication systems propagate electromagnetic energy in the 2-30MHz radio spectrum using the earth’s ionosphere and surface as both refractors and reflectors for non line of sight communications. Constantly changing ionosphere conditions result in multipath and severe fading channel characteristics. Through numerical simulation, small block length (520) Low Density Parity Check (LDPC) forward error correction codes used in conjunction with Orthogonal Frequency Division Multiplexing (OFDM) and Space-Time (ST) channel coding are shown to provide excellent communication performance across the HF channel. Average bit error rate performance results will be shown for a 2ms, 2Hz Watterson HF channel model as well as results for the independent Rayleigh fading channel. The space-time simulation parameters were chosen to model an Alamouti dual antenna transmit, single antenna receive communication system utilizing practical data and sampling rates.
This paper demonstrates through numerical simulation the performance of moderate (8E+3) block length Low Density Parity Check (LDPC) codes on a High Frequency (HF) multipath fading channel utilizing Orthogonal Frequency Division Multiplexing (OFDM). Some results are also shown for the Additive White Gaussian Noise (AWGN) and Rayleigh channels. The simulation parameters were chosen to compare results with the standard OFDM 39-tone HF waveform. LDPC codes are linear block codes that have outstanding error correction and detection capabilities.
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