A new construction for multilevel coded modulation with multistage decoding and unequal error protection is proposed and analyzed for both symmetric and asymmetric 16-QAM constellations. It is shown that the conventio...
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A new construction for multilevel coded modulation with multistage decoding and unequal error protection is proposed and analyzed for both symmetric and asymmetric 16-QAM constellations. It is shown that the conventional upper bound originally derived for PSK signaling is loose when applied to QAM. A new tight approximated upper bound is proposed for 16-QAM and the partitioning considered. The proposed multilevel codes provide a larger proportion of most important bits (MIB) than in previous constructions.
Incoherent direct-sequence spread-spectrum code-division multiple-access (CDMA) with differential phase-shift keying (DPSK) modulation is a promising approach for wireless portable communications. The pre-RAKE system ...
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Incoherent direct-sequence spread-spectrum code-division multiple-access (CDMA) with differential phase-shift keying (DPSK) modulation is a promising approach for wireless portable communications. The pre-RAKE system is also attracting attention for wireless portable communication in time division duplex applications due to achieving the same multipath diversity of the RAKE receiver but using an ordinary matched filter receiver at the portable unit. In this paper, we study the pre-RAKE system with DPSK modulation for multi-user communications in a Rayleigh fading channel. The system performance is analyzed in a generalized Rayleigh fading multipath channel. Two diversity-combining techniques, namely, maximal ratio combing (MRC), equal gain combing (EGG) and zero forcing equalization (ZFE) are considered Both diversity types are supplemented by selection diversity for the strongest paths in gain. We also consider the effect of imperfect channel estimation on the system performance and compare the results with the case of coherent QPSK pre-RAKE system.
The underwater acoustic communication system (UACS) is an important part of an AUV. We developed an underwater acoustic communication system for a AUV: IASS-1, which is based on both MFSK and MPSK. Generally a AUV sen...
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The underwater acoustic communication system (UACS) is an important part of an AUV. We developed an underwater acoustic communication system for a AUV: IASS-1, which is based on both MFSK and MPSK. Generally a AUV sends a large amount of data to the host vessel, and MPSK modulation is adopted. The receiver on the host vessel adopts space diversity (SD), a decision feedback equalizer (DFE), and fast self-optimized LMS phase estimator (FOLMSPE) techniques jointly. The fast self-optimized LMS (FOLMS) algorithm is implemented in the DFE. A short vertical hydrophone array is suspended or towed on the host vessel for signal reception. The separation between each hydrophone is far larger than the wavelength. The MFSK modulation and convolution code are adopted when the host vessel sends a message to the AUV. The receiver on AUV adopts the Viterbi algorithm. This well-known mechanism, using MFSK and convolution code, performs well when the transmission rate is low. Compared with MPSK modulation, it has the advantage of being very resistant to the most difficult multipath propagation, and is less sensitive to the vessel scattered wave. IAAS-1 was tested in a lake and was successfully operated at ranges over 100-4000 m (constrained by the test area). The symbol rate for QPSK is 2.5 ks/s and 5.0 ks/s. The bit error rate (BER) is between 10/sup -4/ and 10/sup -5/.
When the systems evolved from analog to digital, the performance was improved by the use of power control on the one hand and different modulations and coding schemes on the other. Condensing the available information...
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When the systems evolved from analog to digital, the performance was improved by the use of power control on the one hand and different modulations and coding schemes on the other. Condensing the available information we are able to propose a new concept of power control. The concept is applicable to real systems, since it uses the available measurements for estimating parameters necessary for the power control. It also supports the use of an adequate quality measure together with a quality specification supplied by the operator. We use frequency hopping GSM as an example and the resulting control algorithm is ready for implementation in the software in the base stations where the output powers are computed. No modifications are needed in the GSM standard, the mobile terminals, the radio interfaces or in the base station transmitters. Finally we provide simulation results confirming the benefits of using the new concept for power control.
Polynomial cancellation coding (PCC) is a coding method for orthogonal frequency division multiplexing (OFDM) in which the information to be transmitted is modulated onto weighted groups of subcarriers rather than ont...
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Polynomial cancellation coding (PCC) is a coding method for orthogonal frequency division multiplexing (OFDM) in which the information to be transmitted is modulated onto weighted groups of subcarriers rather than onto individual subcarriers. It has previously been shown that PCC substantially reduces the sensitivity of OFDM to carrier frequency offset. In this paper, it is shown that PCC also reduces the intercarrier interference (ICI) due to Doppler spread. Results are presented for a frequency non-selective i.e. flat fading channel, subject to classical Doppler spread. By using weighted pairs of subcarriers the ICI due to Doppler spread can be reduced by approximately 15 dB. By using weighted groups of three subcarriers a further 15 dB reduction in ICI can be achieved.
Coded modulation schemes based on convolutional codes as well as block codes, in particular turbo codes, are considered on AWGN and flat Rayleigh fading channels. It turns out that codes based on Gray mapping are robu...
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Coded modulation schemes based on convolutional codes as well as block codes, in particular turbo codes, are considered on AWGN and flat Rayleigh fading channels. It turns out that codes based on Gray mapping are robust to channel variations, whereas Ungerbock mapping is suitable only if the channel is a-priori known. The most power efficient scheme based on convolutional codes is multilevel coding with parallel decoding. For block codes, however, bit interleaved coded modulation gains by increased codeword length and outperforms the other schemes.
Two multilevel modulation systems are compared in terms of capacity, under the condition that the average energy per channel use is the same for the two systems. We consider the suboptimal multistage receiver for the ...
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Two multilevel modulation systems are compared in terms of capacity, under the condition that the average energy per channel use is the same for the two systems. We consider the suboptimal multistage receiver for the Gaussian channel. We conclude that, under these conditions, the capacity for the hexagonal system is close to 1 dB better than the capacity for the rectangular system.
This paper presents a new algorithm for the integrated design of digital communication systems. In order to design the system as a whole, all the restrictions and key subsystems of a communication system are taken int...
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This paper presents a new algorithm for the integrated design of digital communication systems. In order to design the system as a whole, all the restrictions and key subsystems of a communication system are taken into consideration. The algorithm produces appropriate design parameter values for the source coding, channel coding and modulation functions. Several design examples are provided to illustrate the utility of the approach. This algorithm is quite general and not application-oriented, as was the case in prior work in joint source-channel coding. A large variety of existing methods for source coding, channel coding and modulation may be utilized in achieving a practical system design.
Binary parallel concatenated recursive convolutional codes termed turbo-codes have received great attention due to their amazing error correcting capabilities. Nevertheless, reaching near Shannon limit performance is ...
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Binary parallel concatenated recursive convolutional codes termed turbo-codes have received great attention due to their amazing error correcting capabilities. Nevertheless, reaching near Shannon limit performance is only possible with very large interleavers prohibiting an application in speech-transmission. This paper presents simulation results for a short-frame data transmission system based on DS-CDMA (direct-sequence code division multiple access) employing turbo-codes. Furthermore, the performance of a turbo-coded modulation scheme is investigated with respect to the typical conditions of DS-CDMA systems. As a result, it is shown that turbo-codes are no longer superior to classical convolutional codes if the same decoding costs are assumed. Additionally, simulation results illustrate that coded modulation schemes are not well suited for the application in CDMA systems. Finally, it is proved that an accurate channel estimation is necessary for allowing high coding gains.
Wireless LANs (WLANs) offer an alternative to conventional wired LANs in modern organisations that require a flexible network. However, present-day WLANs yield low capacity compared to conventional wired LANs. In a pr...
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Wireless LANs (WLANs) offer an alternative to conventional wired LANs in modern organisations that require a flexible network. However, present-day WLANs yield low capacity compared to conventional wired LANs. In a previous study, we showed that the capacity of a WLAN can be increased by space division multiple access (SDMA). The implementation of a SDMA receiver requires a channel estimation algorithm. Therefore, we compared both a blind and training-based algorithm for channel estimation in an SDMA WLAN. In this paper we present the semi-analytic simulations based on a ray-tracing channel model. For both algorithms we determine (a) the number of symbols needed to obtain a frequency re-use factor of four, (b) compare their robustness and (c) calculate their complexity. As it turns out, the capacity reduction from training can be reduced to a negligible number of symbols (30 in our case study), the training-based algorithm is more robust and the complexity of the blind algorithm exceeds the complexity of the training-based algorithm by one order of magnitude.
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