Highly power/bandwidth efficient digital transmission with selectedENCAP-OQPSK modulation schemes

The use of encoded-amplitude-and-phase offset quaternary phase-shift keying (ENCAP-OQPSK) signal encoding techniques are considered for power/bandwidth efficient transmission systems. It is shown that a coding gain is achievable. Connections with trellis-coded offset quadrature amplitude modulation (OQAM) schemes previously proposed by the authors are established     

A novel approach to modeling of OQPSK-type digital transmissionover nonlinear radio channels

Offset quaternary PSK-type (OQPSK) digital modulation schemes are often recommended for radio transmission systems employing grossly nonlinear amplifiers, and have found widespread use in land mobile and/or satellite communications. Most of the recommended OQPSK-type schemes-also called MSK-type schemes-jointly exhibit the following features: a constant envelope or, at least, a low envelope fluctuation; a compact spectrum after a power-efficient, saturated amplifier, and a high detection efficiency obtained with simple, low-cost receivers. We introduce a novel approach to computer-aided modeling of OQPSK-type digital transmission over nonlinear radio channels. By taking into account the specific nature of OQPSK-type modulations, when using the Volterra approach as proposed by Benedetto et al. (1987), we conclude that two signal representations (“parallel” and “serial”) can be achieved which are similar to the conventional Laurent (1986) representation of binary CPM signals with h=1/2. With the proposed approach, the OQPSK-type signals have an invariant structure along the transmission path (which is supposed to include, at least, one nonlinearity) in the sense that they are all made of several linear components of the same type. Some examples are given, including signal representation and power spectrum results. The proposed unified signal representations can be very useful for design and performance evaluation of radio communication systems (mobile and/or satellite applications). They combine flexibility, accuracy, and simplicity, and allow high computational efficiencies     

A class of nonlinear signal-processing schemes for bandwidth-efficient OFDM transmission with low envelope fluctuation

This work presents a wide class of digital signal-processing schemes for orthogonal frequency-division multiplexing (OFDM) transmission which combine a nonlinear operation in the time domain and a linear filtering operation in the frequency domain. The ultimate goal of these schemes is to reduce the envelope fluctuation of ordinary OFDM, while keeping its high spectral efficiency and allowing a low-cost, power-efficient implementation. An appropriate statistical model concerning the transmitted frequency-domain blocks is developed, which is derived from well-established results on Gaussian stochastic processes distorted by memoryless nonlinearities. This model can be employed for performance evaluation by analytical means, with highly accurate results whenever the corresponding conventional OFDM signals exhibit quasi-Gaussian characteristics. Cases where the signal-processing scheme is repeatedly used, in an iterative way, are treated through an extension of the proposed statistical modeling. A set of numerical results is presented and discussed so as to show the practical interest of both the proposed schemes and the analytical methods for evaluation of their performance. For the sake of comparisons, this paper includes numerical results concerning the partial transmit sequence technique, which is an alternative peak-to-mean envelope power ratio-reducing technique of higher complexity, often recommended due to its distortionless nature. The superior performance/complexity tradeoffs through the proposed class of nonlinear signal-processing schemes is emphasized.     

Design of TC-OQAM schemes using a generalised nonlinear OQPSK-type format

It is demonstrated that it is possible to design trellis-coded OQAM schemes on the basis of a signal format recently proposed for describing nonlinearly distorted OQPSK-type signals, by appropriately selecting the set of modulation pulses within that format. In some cases, these signal representations are closely related to the well-known TCM concept as proposed by Calderbank and Mazo (1984). Some examples are given and several relevant features of the proposed class of trellis-coded OQAM schemes are emphasised.     

On frequency-domain equalization and diversity combining for broadband wireless communications

This paper is concerned with the use of frequency-domain equalization (FDE) and space diversity within block transmission schemes for broadband wireless communications. The expected performance with both multicarrier (MC) and single-carrier (SC) modulations is emphasized, when a cyclic prefix, long enough to cope with the maximum relative channel delay, is appended to each transmitted block. A set of numerical results is presented and discussed, with the help of appropriate, analytical performance bounds which are conditional on a given channel realization. These bounds are used to explain the performance advantage of the SC/FDE option, the benefits of space diversity, and the impact of the criterion for computing the FDE parameters.     

A Turbo FDE Technique for Reduced-CP SC-Based Block Transmission Systems

For conventional cyclic-prefix (CP)-assisted block transmission systems, the CP length is selected on the basis of the expected maximum delay spread. With regard to single-carrier (SC)-based block transmission implementations, a full-length CP is recommendable, since it allows good performances through the use of simple frequency-domain equalization (FDE) techniques. In this letter, a soft-decision-directed correction (SDDC)-aided turbo FDE technique is presented for reduced-CP SC-based block transmission systems using conventional frame structures. The relations with some already known iterative FDE techniques are established, and a set of performance results is reported and discussed. The advantages of the proposed approach are emphasized, namely, the possibility of approximately achieving (besides the obvious bandwidth efficiency gain) the maximum power efficiency gain that a strong CP reduction allows     

A Reduced-CP Approach to SC/FDE Block Transmission for Broadband Wireless Communications

For conventional cyclic prefix (CP)-assisted single-carrier/frequency-domain equalization (SC/FDE) implementations, as well as for orthogonal frequency-division multiplexing (OFDM) implementations, the CP length is known to be selected on the basis of the expected maximum delay spread. Next, the data block size can be chosen to be large enough to minimize the CP overhead, yet small enough to make the channel variation over the block negligible. This paper considers the possibility of reducing the overall CP assistance, when transmitting sequences of SC blocks, while avoiding an excessively long fast Fourier transform window for FDE purposes and keeping good FDE performances through low-complexity, noniterative receiver techniques. These techniques, which take advantage of specially designed frame structures, rely on a basic algorithm for decision-directed correction (DDC) of the FDE inputs when the CP is not long enough to cope with the time-dispersive channel effects. More specifically, we present and evaluate a novel class of reduced-CP SC/FDE schemes, which takes advantage of a special frame structure for replacing "useless" CP redundancy by fully useful channel coding redundancy, with the help of the DDC algorithm. When using the DDC-FDE technique with these especially designed frame structures, the impact of previous decisions, which are not error-free, is shown to be rather small, thereby allowing a power-efficiency advantage (in addition to the obvious bandwidth-efficiency advantage) over conventional block transmission implementations under full-length CP. Additionally, the DDC algorithm is also shown to be useful to improve the power efficiency of these conventional implementations     

Coherent detection of multiamplitude MSK under imperfect phase synchronisation

Simple formulas for the BER performance achieved through coherent detection of MAMSK signals, under a carrier phase error, are presented. It is shown that MAMSK schemes are much less sensitive to imperfect carrier recovery than the corresponding QAM schemes, this advantage being especially clear when serial detection is employed. Possible applications to future TDMA satellite systems are emphasised.<>     

Effects of Growth Hormone Receptor Ablation in Corticotropin-Releasing Hormone Cells

Corticotropin-releasing hormone (CRH) cells are the dominant neuronal population responsive to the growth hormone (GH) in the paraventricular nucleus of the hypothalamus (PVH). However, the physiological importance of GH receptor (GHR) signaling in CRH neurons is currently unknown. Thus, the main objective of the present study was to investigate the consequences of GHR ablation in CRH-expressing cells of male and female mice. GHR ablation in CRH cells did not cause significant changes in body weight, body composition, food intake, substrate oxidation, locomotor activity, glucose tolerance, insulin sensitivity, counterregulatory response to 2-deoxy-D-glucose and ghrelin-induced food intake. However, reduced energy expenditure was observed in female mice carrying GHR ablation in CRH cells. The absence of GHR in CRH cells did not affect anxiety, circadian glucocorticoid levels or restraint-stress-induced corticosterone secretion and activation of PVH neurons in both male and female mice. In summary, GHR ablation, specifically in CRH-expressing neurons, does not lead to major alterations in metabolism, hypothalamic–pituitary–adrenal axis, acute stress response or anxiety in mice. Considering the previous studies showing that central GHR signaling regulates homeostasis in situations of metabolic stress, future studies are still necessary to identify the potential physiological importance of GH action on CRH neurons.