A coded transponder was developed for operation in C-band and verified using the SAR sensor of the Active Microwave Instruments (AMI) on the ERS-1 and ERS-2 satellites. The coded transponder uses signal modulation tec...
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A coded transponder was developed for operation in C-band and verified using the SAR sensor of the Active Microwave Instruments (AMI) on the ERS-1 and ERS-2 satellites. The coded transponder uses signal modulation techniques which affect the SAR signal in both range and azimuth and decouples the transponder signal from the background signal. Encoding adds additional features without losing any of the advantages transponders have over passive targets.
In this work, system adaptation under measurement uncertainty is considered for environments where there exist accurate statistical models of how the desired parameter depends on the available measurements. First, pre...
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In this work, system adaptation under measurement uncertainty is considered for environments where there exist accurate statistical models of how the desired parameter depends on the available measurements. First, previous work on robust adaptive coded modulation using outdated multipath fading estimates is reviewed. The same ideology is then applied to power control when there is statistical uncertainty in the measurement of the path loss and log-normal shadowing. For a single-user system, a closed form power control rule is found, and numerical results are presented which suggest a moderate gain over systems which employ traditional power control functions with an energy margin to compensate for measurement uncertainty. The analogous multi-user power control problem is straightforward to pose, but it has not been amenable to closed form solution to this point.
Summary form only given. The combination of jointly optimized rate compatible punctured convolutional (RCPC) codes and channel-matched tree-structured vector quantizers (CM-TSVQ) is shown to provide improved performan...
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Summary form only given. The combination of jointly optimized rate compatible punctured convolutional (RCPC) codes and channel-matched tree-structured vector quantizers (CM-TSVQ) is shown to provide improved performance, in some cases, compared to the use of CM-TSVQ. The embedded nature of the RCPC codes and CM-TSVQ is inherited by the jointly optimized combination so that the resulting coder is itself progressive. The joint design algorithm allows unequal error protection to be applied to each bit of the CM-TSVQ output. When refinement bits are sent they may be used either to: (1) provide new source coding bits; (2) provide protection to new source coding bias; or (3) provide further protection to previous source coding bits. Soft decoding is used for the RCPC codes and, to allow equitable comparisons to be made, q-bit soft-decision BPSK modulation is used for the baseline CM-TSVQ (to which we make comparisons). The codebook size of the q-bit soft-decision based CM-TSVQ is 2/sup qrk/ where r is the rate in bits per sample and k is the vector dimension. An illustration of the results obtained for a Gauss-Markov source with correlation coefficient /spl rho/=0.9 and a channel SNR=0 dB is shown below. In this case, k=4 and end-to-end distortion is given in dB. In the cases marked "x", the system complexity precluded calculation of reliable results. Each row of the table shows the performance of a single embedded quantizer, with incremental rates of 0.5 bits per sample provided at each refinement. Our results show that the joint combination of soft-decoded RCPC codes and CM-TCVQ provides little rate-distortion advantage over soft CM-TSVQ at the first step of refinement. The same conclusion may be made about the joint combination of soft-decoded RCPC codes and COVQ versus soft COVQ.
The soft-input soft-output (SISO) module is the basic building block of any iterative receiver for a system consisting of a network of finite state machines (FSM). It is a trellis based algorithm that provides soft in...
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The soft-input soft-output (SISO) module is the basic building block of any iterative receiver for a system consisting of a network of finite state machines (FSM). It is a trellis based algorithm that provides soft information on the input and output of an FSM, with linear complexity on the decision delay D (or the observation length N). When parametric uncertainty is present, the need for adaptive SISOs arises. The proposed solutions either oversimplify the parameter model, or result in exponential complexity on D. In this paper, the exact expression for the soft metrics in the presence of parametric uncertainty modeled as a deterministic constant is rederived in a novel way. Based on this expression, suboptimal algorithms with linear complexity on D and N are presented. The applicability of the proposed algorithms is demonstrated with two examples, namely serially concatenated convolutional codes (SCCC) with carrier phase tracking, and trellis coded modulation (TCM) in frequency-selective fading channels.
We consider space-domain interference suppression for reverse-link IS-95 and wideband DS-CDMA (W-CDMA) based on the minimum mean square error (MMSE) cost criterion. An adaptive algorithm for estimating the MMSE combin...
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We consider space-domain interference suppression for reverse-link IS-95 and wideband DS-CDMA (W-CDMA) based on the minimum mean square error (MMSE) cost criterion. An adaptive algorithm for estimating the MMSE combining coefficients for each path is presented which is compatible with IS-95 orthogonal modulation and long spreading codes. The relative performance of noncoherent, maximal ratio (max-ratio), and MMSE combining are compared with mixed (high and low) data rates, where received power is proportional to data rate. Our results show that MMSE combining can offer a significant increase in capacity relative to max-ratio combining. Analytical performance results for W-CDMA based on a large system limit are also presented, and are shown to be accurate even with relatively few combining coefficients.
Link adaptation and incremental redundancy are two link level techniques proposed to enhance data rate and increase throughput in wireless data networks. Link adaptation pro-actively adjusts the modulation and coding ...
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Link adaptation and incremental redundancy are two link level techniques proposed to enhance data rate and increase throughput in wireless data networks. Link adaptation pro-actively adjusts the modulation and coding scheme based upon estimated channel conditions. Incremental redundancy, on the other hand, adjusts the code rate to actual channel conditions by incrementally transmitting redundancy information until decoding is successful. In this study, we investigate the system performance of these two techniques. Our results show that incremental redundancy achieves significantly higher throughput compared to link adaptation, especially under high traffic loading conditions. This gain is achieved at the expense of higher terminal and base station complexities, as well as a higher packet delay. On the other hand, in contrast to link adaptation, incremental redundancy does not require any channel quality measurements, and can operate based solely upon ACKs and NACKs.
Selection of modes, i.e. coding and modulation schemes against the current channel is a way to increase the degree of service to individual users as well as improving system capacity in a wireless packet data system. ...
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Selection of modes, i.e. coding and modulation schemes against the current channel is a way to increase the degree of service to individual users as well as improving system capacity in a wireless packet data system. By proper selection of trellis coded modulation schemes, all modes can use a common receiver structure without sacrificing error performance. Apart from a low receiver complexity, this also enables code combining of different modes, which is useful when ARQ is used. Through system level simulations on correlated Rayleigh fading channels it is found that a simple way of selecting the proper mode gives excellent performance.
It is essential to find suitable modes (combinations of alphabet sizes and code rates) for transmission in cellular systems. Bad choices result in low spectrum efficiency. An analytical method is proposed to find the ...
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It is essential to find suitable modes (combinations of alphabet sizes and code rates) for transmission in cellular systems. Bad choices result in low spectrum efficiency. An analytical method is proposed to find the modes which give the highest spectrum efficiency when using adaptive modulation. It is demonstrated that data rates considerably higher than 271 and 384 kbps are feasible in GSM and EDGE systems by using adaptive modulation. It is further demonstrated that the spectrum efficiency can be improved more than 100% by using three modes in a GSM system.
The Envelope Constrained Filter (ECF) concept seems to be a useful tool in filter response shaping applications. There are several applications in radar techniques where the ECF concept can be utilised, such as the ra...
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The Envelope Constrained Filter (ECF) concept seems to be a useful tool in filter response shaping applications. There are several applications in radar techniques where the ECF concept can be utilised, such as the range sidelobe suppression in the receiver filter design or the antenna pattern sidelobe suppression in the antenna design. However, the nonfeasible solution case is almost always encountered with these applications. Moreover, a minimax feature of the filter designed is desired then. The original algorithms did not prove successful in such a scenario. The paper presents a novel approach to the ECF design, the main feature of which is the minimax behaviour in the nonfeasible solution case.
Parallel Decision-Feedback Decoders (PDFD) use a joint equalization and channel decoding scheme that performs decision-feedback equalization based on each survivor path in the channel decoder. In this paper, we propos...
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Parallel Decision-Feedback Decoders (PDFD) use a joint equalization and channel decoding scheme that performs decision-feedback equalization based on each survivor path in the channel decoder. In this paper, we propose novel efficient computation methods to implement the PDFD. We show that, contrary to the belief that PDFD is too complex to implement, standard Viterbi decoders can be modified to implement the PDFD and achieve very high bit-rates.
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