Performance of optical asynchronous code-division multiple-access (CDMA) systems with double optical hard-limiters is analyzed in the presence of avalanche photodiode (APD) noise and thermal noise. The following effec...
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Performance of optical asynchronous code-division multiple-access (CDMA) systems with double optical hard-limiters is analyzed in the presence of avalanche photodiode (APD) noise and thermal noise. The following effects on the optimal thresholds of double optical hard-limiters and on-off keying (OOK) decoder are clarified: sequence codes, the number of users, the received laser power, and the modulation extinction ratio. The results show that the optical asynchronous CDMA systems with double optical hard-limiters have good performance in the presence of the APD noise and the thermal noise even when the number of simultaneous users is large. Moreover the optical asynchronous CDMA systems with double optical hard-limiters are shown to be practical in the respect of setting optimal thresholds.
We address the problem of improving the performance of asymmetric M-PAM signal constellations in Euclidean space by embedding them in hyperbolic space when the communications system designer is bounded to using this m...
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We address the problem of improving the performance of asymmetric M-PAM signal constellations in Euclidean space by embedding them in hyperbolic space when the communications system designer is bounded to using this modulation. We derive the probability density function of the additive noise in one dimensional hyperbolic space by showing that it is a log-normal random variable. From this, we determine the optimum receiver for the M-PAM signal constellations in one dimensional hyperbolic space, and show that it is equivalent to the optimum receiver in the Euclidean space. Finally, we compare the performance of the communication system using M-PAM signal constellations in one dimensional hyperbolic space with the corresponding system in the Euclidean space. We show that the symmetric M-PAM signal constellations in one dimensional hyperbolic space derived from the corresponding asymmetric M-PAM in the Euclidean space have asymptotic coding gains.
Summary form only given. Electroabsorption (EA) modulators were primarily intended for high-speed coding as an alternative to LiNbO/sub 3/ Mach-Zehnder modulators. Beyond this application, EA modulators have been incr...
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ISBN:
(纸本)1557525293
Summary form only given. Electroabsorption (EA) modulators were primarily intended for high-speed coding as an alternative to LiNbO/sub 3/ Mach-Zehnder modulators. Beyond this application, EA modulators have been increasingly used for various optical processing functions thanks to specific properties. We focus in this paper on the use of multiple EA modulators, either in series or in parallel, for optical processing.
This paper describes modeling and simulation of candidate AM subcarrier systems to determine their relative performance. Based on the simulation results, a prototype system is designed that was successfully tested on ...
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This paper describes modeling and simulation of candidate AM subcarrier systems to determine their relative performance. Based on the simulation results, a prototype system is designed that was successfully tested on the air. A data rate of 200 bits per second was achieved without introducing main channel audio distortion; the digital data was recovered in an automobile over 200 miles from the transmitter site well beyond the Continental Divide through the Colorado Rocky Mountains. For the simulation study, the primary goals were to determine the level of interference between the digital baseband spectrum and the main channel audio spectrum, and to identify effective subcarrier modulation schemes. In early systems, the phase shifts modulating the main carrier were limited to +/-15 degrees to avoid significant audio program distortion during AM detection. This paper explores the possibility of applying other digital modulation techniques including BPSK, QPSK, GMSK and QAM. Sample speech segments are used to create the AM portion of the composite signal. Effects of the secondary RBDS signal on the voice program output signal-to-noise ratio are assessed. Conversely, the effect of the AM sidebands on the RBDS bit-error rate is measured. Finally, a prototype system is described using off the shelf components to demonstrate this technology on the air. Low rate digital data is digitally modulated onto the main carrier of a commercial AM radio station. A conventional car radio is modified to extract the soft bit stream, which is subsequently processed in real time within a laptop computer hosting a DSP board. The performance of this system during field trials, transmitting from commercial AM station KTLK in Denver, Colorado, is summarised.
The concept of spectrum efficient, anti-jam (A/J), high frequency (HF) communications is discussed. The HF concept is intended for mobile, beyond line of sight (BLOS) military communications for use in the 21st centur...
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The concept of spectrum efficient, anti-jam (A/J), high frequency (HF) communications is discussed. The HF concept is intended for mobile, beyond line of sight (BLOS) military communications for use in the 21st century. Spectrum efficiency and fast frequency hopping offer opportunities for high data rates and A/J capability. This system concept is referred to as HF 4 21. The concept employs a new high density modulation waveform-discrete trellis-coded modulation (d-TCM), Reed-Solomon code, and fast frequency hopping (3 or 6 kilohops/s), to achieve: high spectrum efficiency, frequency reuse, and A/J. These features are desirable for future army tactical communications, but unachievable in a single system with current HF technology. The technical feasibility and system performance are also presented.
Co-channel interference is a major impairment limiting the capacity of cellular radio systems. In order to mitigate its effect, a trellis-coded co-channel interference canceller (TCC) has been proposed which makes use...
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Co-channel interference is a major impairment limiting the capacity of cellular radio systems. In order to mitigate its effect, a trellis-coded co-channel interference canceller (TCC) has been proposed which makes use of trellis-coded modulation (TCM) in resolving the ambiguity that has been a problem with the conventional approach. This canceller uses TCM with maximum-likelihood sequence estimation (MLSE) of both the desired signal and co-channel interference, and outperforms conventional cancellers over static channels. In flat fading channels, however, the performance improvement owing to TCM cannot be obtained due to burst errors. An effective method for dealing with burst error channels is to interleave the coded data. In this paper, a novel algorithm which incorporates a block interleaving into the TCC is proposed to offer increased interference suppression capability over flat Rayleigh fading channels. This algorithm is a combination of interference cancellation, equalization, TCM decoding and deinterleaving, and also can be combined with a channel estimation technique. The BER performance of this algorithm is evaluated through computer simulations.
This paper presents the selection criteria for trellis codes used with the simple transmit diversity scheme proposed in Alamouti (1998) and reviewed in this paper. The optimum metrics for soft decision Viterbi decodin...
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This paper presents the selection criteria for trellis codes used with the simple transmit diversity scheme proposed in Alamouti (1998) and reviewed in this paper. The optimum metrics for soft decision Viterbi decoding are derived and the asymptotic coding gains are calculated. The design method achieves both coding gain and a diversity order of 2 using 2 transmit antennas and 1 receive antenna. It is also demonstrated that trellis codes optimized for AWGN are also optimal for use in conjunction with the transmit diversity scheme in Rayleigh fading.
Simulation results of product codes used in a group of typical mobile channels are reported. Compared with interleaved BCH codes, product codes can improve the BER of channels by a factor of ten times that of interlea...
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Simulation results of product codes used in a group of typical mobile channels are reported. Compared with interleaved BCH codes, product codes can improve the BER of channels by a factor of ten times that of interleaved codes.
A self-concatenated code with interleavers is a concatenated coded scheme based on only one recursive convolutional code. An upper bound on bit error probability, averaged over all possible interleavers, using maximum...
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A self-concatenated code with interleavers is a concatenated coded scheme based on only one recursive convolutional code. An upper bound on bit error probability, averaged over all possible interleavers, using maximum-likelihood decoding is obtained. Design rules for the single convolutional code, that maximize the interleavers gain and the effective free distance are presented. Design rules are extended to nonbinary modulation for the design of self-concatenated trellis coded modulation. A low-complexity self-iterative decoding algorithm for the self-concatenated code for binary and nonbinary modulation is proposed.
We discuss the application of iterative, decoding algorithms (turbo equalizer) to GSM data channels (TCH/F9.6). Although the turbo equalizer under realistic time-variant channel scenarios has a high potential, we only...
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We discuss the application of iterative, decoding algorithms (turbo equalizer) to GSM data channels (TCH/F9.6). Although the turbo equalizer under realistic time-variant channel scenarios has a high potential, we only get a minor performance gain when compared to conventional soft-decision algorithms. Certain constraints of the GSM coding scheme prevent better results. We discuss the transition from a very simple data transmission model to a full GSM-compatible system and compare the resulting bit error rates (BER). We introduce a modified turbo equalizer structure which adapts to the pipelining interleaver.
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