Multiuser detection for continuous phase modulation over Rayleigh fading channels

We study multiuser (MU) continuous phase modulation (CPM) over Rayleigh fading channels with a receiver antenna array. An optimum symbol-by-symbol MU detector is derived and its practical implementation with reduced-complexity is considered. According to the numerical results, the MU detector performs very close to a system free of interference by other users, when each user has more than one receiving antenna. For three receiving antennas, this difference is less than 0.25 dB, 0.4 dB, and 0.6 dB for two, three and four users, respectively. Moreover, the proposed system is bandwidth efficient as CPM is a bandwidth efficient modulation scheme, and the MU system only uses the single user CPM bandwidth.     

Bandwidth efficient constant-envelope digital signalling with phase-tree demodulation

A method is given for analysing constant-envelope signalling schemes with partial-response baseband pulses. We consider coherent phase-tree demodulation for the Gaussian channel. The results show that very good spectral properties can be obtained for systems with error probabilities equal to or better than for binary phase-shift keying.     

CPM—the effect of filtering and hard limiting

The attractive properties of the digital constant amplitude modulation scheme CPM (continuous phase modulation) have been demonstrated in a previous paper in this journal.¹ This concerned both the power and spectral efficiency of the large family of CPM schemes over the Gaussian channel. In this paper the considered channel can be both bandlimited or band- and amplitude-limited at the same time. Analytical results as well as simulations are presented for a number of selected CPM schemes. In today's increasing demand for bandwidth, CPM is an attractive candidate for future satellite applications because of its spectral efficiency. In addition to this comes the fact that the transmitted signal has a constant amplitude and good detection performance when optimal coherent detection is performed.     

Breadth-first maximum-likelihood sequence detection: geometry

SA(B, C) is an algorithm penetrating a tree (or trellis) breadth first. It performs maximum-likelihood sequence detection (MLSD) under that structural constraint, and also under the complexity constraints determined by the parameters B and C. First, C is the number of partitions into which the states are distributed, and B denotes the number of paths in each partition. Recursively selecting paths which are closest to the received signal in the Euclidean distance (Hamming distance) sense guarantees constrained MLSD for the additive white Gaussian (binary symmetric) channel. The previously presented vector Euclidean distance (VED) is an important tool for analyzing SA(B, C) over the additive white Gaussian noise (AWGN) channel. A geometric interpretation of the signals involved clarifies the basic properties of this VED and other relevant general results (invariance, monotonicity). These results also form a basis for the construction of an algorithm for the efficient and fast calculation of minimum VEDs (of interest for large signal-to-noise ratio, SNR, detection performance). This, in turn, reveals the necessary complexity requirements to meet specified performance requirements for concrete trellis-coded systems. Here, the simple example of convolutionally coded (rate 1/2) with Gray-coded quaternary phase-shift keying over the AWGN channel is considered. When C=1 and choosing B/spl sim//spl radic/S (S being the number of states in the code trellis) gives the same asymptotic detection performance (large SNR) as unconstrained MLSD (e.g., implemented using the Viterbi algorithm).     

Joint source-channel coding using combined TCQ/CPM: iterative decoding

An iterative decoding approach to joint source and channel coding (JSCC) using combined trellis-coded quantization (TCQ) and continuous phase modulation (CPM) is proposed. The channel is assumed to be the additive white Gaussian noise channel. This iterative procedure exploits the structure of the TCQ encoder and the continuous phase modulator. The performance in terms of the signal-to-distortion ratio (SDR) is compared with that of a combined TCQ/trellis-coded modulation (TCM) system. It is shown that the combined TCQ/CPM systems are both power- and bandwidth-efficient, compared with the combined TCQ/TCM system. For source encoding rate R=2 b/sample, it is observed that the combined TCQ/CPM systems with iterative decoding working at symbol level converge faster than the systems working at bit level. The novelty of this work is the use of a soft decoder and an iterative decoding algorithm for TCQ-based JSCC systems. The combined TCQ/CPM with iterative decoding is considered for the first time.     

Serially concatenated continuous phase modulation with convolutional codes over rings

In this paper, we investigate serially concatenated continuous phase modulation (SCCPM) with convolutional codes (CC) over rings. The transmitted signals are disturbed by additive white Gaussian noise. The properties for systems with both infinite and finite block lengths are investigated. For an infinite-length system, we check the convergence threshold using the extrinsic information transfer chart. For a finite-length system, we use union-bound techniques to estimate the error floors. In the union-bound analysis, we consider both the order and the position of nonzero permuted symbols. A simple method for determining a CPM error event through the sum of the input symbol sequence is shown. Thus, we can determine if the output symbol sequence of an error event in the ring CC can form an error event in CPM. Two properties concerning the interleaver gain (IG) are investigated. A recursive search algorithm for the maximal IG is shown. Compared with previous SCCPM with a binary CC, the proposed system shows an improvement concerning the convergence threshold or error floors.     

On forward-adaptive versus forward/backward-adaptive SISOalgorithms for Rayleigh fading channels

Two types of soft-input soft-output (SISO) algorithms have previously been proposed for iterative decoding of concatenated codes applied over fading channels; forward-adaptive algorithms exploit the dependency between the present symbol interval and past symbol intervals, while forward/backward-adaptive algorithms take both the past and the future into account. Numerical results presented for interleaved serially concatenated continuous phase modulation (CPM) over the Rayleigh fading channel indicate that the performance of forward-adaptive algorithms approaches the performance of forward/backward-adaptive algorithms when a long channel-memory depth is exploited     

On antenna array receiver principles for space-time-selectiveRayleigh fading channels

Optimum (in the sense of minimum-error probability) single-symbol diversity detection for fading, noisy channels is too complex for practical implementation. A simplified, near-optimum array receiver is proposed, which is based on the statistics (i.e., the covariance-function matrix) of the fading channel. This detector is then analyzed by calculating the exact error probability. When there is a spread of the direction of arrival of the incident radio waves, the proposed detector significantly gains over an adaptive antenna array (which forms a weighted sum of the received antenna signals). Also, for this adaptive array, a fundamental difference between maximum-likelihood weights and least-mean-square weights is observed     

Assessing Understanding of Planning and Scheduling Theory and Practice on Construction Projects

Abstract

Despite attention being paid to the development of planning and scheduling theory, it is unclear whether project stakeholders and practitioners have sufficient understanding about how it applies in practice. A study was conducted with the aim of assessing practitioners’ perceptions of planning and scheduling theory and practice on construction projects in Oman. Data were gathered through a questionnaire-based survey and analyzed using the relative importance index. Respondents were asked to consider: (1) the suitability and efficiency of existing planning methods; (2) scheduling development and performance control; and (3) knowledge-based planning and scheduling concepts. The analysis revealed no significant variations among respondents’ perceptions in regard to the above topics. The findings did, however, reveal a number of factors that are of equal importance to the development of project planning and scheduling. The overall findings imply that practicing managers should implement new management strategies that foster knowledge-based planning and scheduling concepts for a more effective construction process. Recommendations are made for improvement that include the need for practicing managers to professionalize project planning and scheduling based on a more proactive and knowledge-based planning approach, which is supported by management.     

Iterative diversity detection for correlated continuous-time Rayleigh fading channels

An antenna array is proposed as a means of achieving a space-diversity effect that partly overcomes the severity of continuous-time Rayleigh fading channels. The investigated channel is assumed to be frequency-nonselective with correlated diversity links, where the correlation is related to the array geometry and the spatial and Doppler dispersions. Further, the error performance is improved by bit interleaving and channel coding, where the encoders/channel is viewed as a serially concatenated system: a convolutional code constitutes the outer code, whereas a differential encoder and the fading channel (having truncated memory) form a joint inner code. In order to obtain a practical detector structure it is desirable to perform iterative decoding by applying some a posteriori probability (APP) algorithms. For this purpose, we propose a novel generalization of the well-known Bahl-Cocke-Jelinek-Raviv (1974) algorithm that calculates the APPs over channels having memory. Numerical results indicate that iterative decoding becomes more powerful when the exploited channel memory depth is extended. Also, the error performance is significantly improved by introducing multiple antennas. The interleaver gain is, however, seen to be quite moderate, in contrast to additive white Gaussian noise channels.