Constant envelope (CE) precoding is an appealing transmission technique which enables the realization of high power amplifier (PA) efficiency. For CE precoding in a single-user multiple-input single-output (MISO) channel, a desired constellation is feasible at the receiver if and only if it can be scaled to lie in an annulus, whose boundaries are characterized by the instantaneous channel realization. Therefore, if a fixed receiver constellation is used for CE precoding in a fading channel, where the annulus is time-varying, there is in general a non-zero probability of encountering a channel that makes CE precoding infeasible, thereby causing a high probability of error. To tackle this problem, this paper studies the adaptive receiver constellation design for CE precoding in a single-user MISO flat-fading channel with an arbitrary number of antennas at the transmitter. We first investigate the fixed-rate adaptive receiver constellation design to minimize the symbol error rate (SER). Specifically, an efficient algorithm is proposed to find the optimal amplitude-and-phase shift keying (APSK) constellation with two rings that is both feasible and of the maximum minimum Euclidean distance (MED), for any given constellation size and instantaneous channel realization. Numerical results show that by using the optimized fixed-rate adaptive receiver constellation, our proposed scheme achieves significantly improved SER performance over CE precoding with a fixed receiver constellation. Furthermore, based on the family of optimal fixed-rate adaptive two-ring APSK constellation sets, a variable-rate CE transmission scheme is proposed and numerically examined.
This paper is concerned with spectrum sharing for wireless communication, where a secondary or cognitive radio (CR) link communicates over the same bandwidth that has been assigned to an existing primary radio (PR) link. It is assumed that the CR transmitter has perfect channel state information (CSI) on the channels from it to both the PR and CR receivers (as usually assumed in the literature), as well as the channel from the PR transmitter to PR receiver (a new assumption made). With known PR CSI, we study the optimal power control for the CR fading channel to maximize its ergodic capacity subject to the CR's transmit power constraint as well as the constraint on the maximum ergodic capacity loss of the PR link due to the CR transmission. It is shown that the new power-control policy performs better than the conventional one that does not depend on the primary user CSI, but is based on the average interference-power constraint at the PR receiver, in terms of both the PR and CR channel ergodic capacities.
Abstract In this paper, a low-profile broadband circularly polarized flat-top metasurface antenna is proposed. The array patch forms a diamond-shaped metasurface structure. It is fed by the stepped rotated microstrip line at the bottom through the slot of the ground plane. The design of the stepped rotated microstrip line does not require additional layers to achieve circular polarization as reported in other literature, and it cooperates with the metasurface to obtain good impedance bandwidth and axial ratio bandwidth, making the design simpler and easier to manufacture. The final design has an overall size of 1.76 × 1.76 × 0.07 λ 0 at 5 GHz. The simulation results compare well with the measured results. The maximum gain of the left-hand circular polarization gain is 8.5 dBic, the impedance bandwidth is 4.3–6 GHz (33%), the 3 dB axial ratio bandwidth is 4.6–5.6 GHz (20%), the flat-top bandwidth is 4.6–5.6 GHz (20%). The 3 dB flat-top beam bandwidth in the xoz plane and yoz plane of 4.6–5.0 GHz is stable greater than 90° and 91°, and the 3 dB flat-top beam bandwidth in 5.1–5.6 GHz is stable greater than 72° and 68°. Compared with other works, this antenna has the advantages of broadband circular polarization, low profile, and wide beam. The stable flat-top radiation pattern makes it more popular in the field of microwave power transmission.
For more than a thousand years, Chinese people were aware of the transmitted sensations by the application of needles on the body surface. This practice is called acupuncture. Acupuncture had been recorded and transcribed in writings and in drawings, until finally the acupoints were inscribed onto a bronze statue. The bronze statue was called the Meridian Figure. Deeply embodied in the bronze statue is a tripartite confrontation-prism representation of the humans body. This concept was a great scientific achievement in ancient China. The author traces the history of Meridian science described in traditional Chinese medical terms. Then he explores a clear analogy of the meridian pathway (MP) phenomenon. In a model system, by using a simple segmental in vertebrate, certain parallels can be demonstrated with the meridian concept. For example, the author demonstrated a clear correlation rule among the central mechano-sensory channels, and characteristics of positional discrimination in individual nerve cells from different receptive field inputs. The evidence suggests that the MP phenomenon is an objective neurobiological response. To clarify the research objective in this paper, the author suggests that the MP is a bi-directional pathway along which a positional message signal is transmitted. This phenomenon is evoked by physical stimulation, transmitted linearly across the human body segments, and is perceived by the brain. The MP consists of low resistance paths, is connected by the liquid media contained in the apposite membranous structure. At the cellular level, the regulation functions of MP must pass through along this low resistance path. Two aspects of the modern Meridian research are the functional regulation and the mechanism of intercellular liquid modulation at the nanometer level.
This article provides an overview of the state-of-art results on communication resource allocation over space, time, and frequency for emerging cognitive radio (CR) wireless networks. Focusing on the interference-power/interference-temperature (IT) constraint approach for CRs to protect primary radio transmissions, many new and challenging problems regarding the design of CR systems are formulated, and some of the corresponding solutions are shown to be obtainable by restructuring some classic results known for traditional (non-CR) wireless networks. It is demonstrated that convex optimization plays an essential role in solving these problems, in a both rigorous and efficient way. Promising research directions on interference management for CR and other related multiuser communication systems are discussed.
Intelligent reflecting surface (IRS) can bring promising advantages to enhance the communication system performance by reconfiguring wireless channels dynamically. The design of passive IRS reflection has attracted high attention and most existing works have considered continuous phase shift for IRS reflection. However, this is difficult to realize in practice due to hardware limitations and discrete phase shifts are applied for practical IRSs instead. In this letter, the information multicast beamforming problem in an IRS-aided multi-user system is considered, where the minimum receive signal-to-noise-ratio among the users is maximized by optimizing the IRS reflections with discrete phase shifts. By leveraging semi-definite relaxation (SDR) and gradient descent/ascent (GDA), two solutions are presented with high/low computational complexity, respectively. Simulation results show the efficacy of the proposed GDA-based algorithm as compared to the SDR-based and other benchmark schemes.
