The newly emerging wireless powered communication networks (WPCNs) have recently drawn significant attention, where radio signals are used to power wireless terminals for information transmission. In this paper, we study a WPCN where one multi-antenna access point (AP) coordinates energy transfer and information transfer to/from a set of single-antenna users. A harvest-then-transmit protocol is assumed where the AP first broadcasts wireless power to all users via energy beamforming in the downlink (DL), and then the users send their independent information to the AP simultaneously in the uplink (UL) using their harvested energy. To optimize the users'throughput and yet guarantee their rate fairness, we maximize the minimum throughput among all users by a joint design of the DL-UL time allocation, the DL energy beamforming, and the UL transmit power allocation plus receive beamforming. We solve this non-convex problem optimally by two steps. First, we fix the DL-UL time allocation and obtain the optimal DL energy beamforming, UL power allocation and receive beamforming to maximize the minimum signal-to-interference-plus-noise ratio (SINR) of all users. This problem is shown to be in general non-convex; however, we convert it equivalently to a spectral radius minimization problem, which can be solved efficiently by applying the alternating optimization based on the non-negative matrix theory. Then, the optimal time allocation is found by a one-dimension search to maximize the minimum rate of all users. Furthermore, two suboptimal designs of lower complexity are proposed, and their throughput performance is compared against that of the optimal solution. Index TermsWireless power transfer, energy beamforming, wireless powered communication, non-negative matrix theory.
Energy harvesting is a promising solution to prolong the operation of energy-constrained wireless networks. In particular, scavenging energy from ambient radio signals, namely wireless energy harvesting (WEH), has recently drawn significant attention. In this paper, we consider a point-to-point wireless link over the narrowband flat-fading channel subject to time-varying co-channel interference. It is assumed that the receiver has no fixed power supplies and thus needs to replenish energy opportunistically via WEH from the unintended interference and/or the intended signal sent by the transmitter. We further assume a single-antenna receiver that can only decode information or harvest energy at any time due to the practical circuit limitation. Therefore, it is important to investigate when the receiver should switch between the two modes of information decoding (ID) and energy harvesting (EH), based on the instantaneous channel and interference condition. In this paper, we derive the optimal mode switching rule at the receiver to achieve various trade-offs between wireless information transfer and energy harvesting. Specifically, we determine the minimum transmission outage probability for delay-limited information transfer and the maximum ergodic capacity for no-delay-limited information transfer versus the maximum average energy harvested at the receiver, which are characterized by the boundary of so-called "outage-energy" region and "rate-energy" region, respectively. Moreover, for the case when the channel state information (CSI) is known at the transmitter, we investigate the joint optimization of transmit power control, information and energy transfer scheduling, and the receiver's mode switching. The effects of circuit energy consumption at the receiver on the achievable rate-energy trade-offs are also characterized. Our results provide useful guidelines for the efficient design of emerging wireless communication systems powered by opportunistic WEH. Index TermsEnergy harvesting, wireless power transfer, power control, fading channel, outage probability, ergodic capacity.
It has long been recognized that the allergy to mites of the genus Dermatophagoides is associated with diseases such as asthma, rhinitis, and atopic dermatitis (1, 2). In this regard, the species D. pteronyssinus and D. farinae predominate and many studies have been performed to identify the allergens they produce. Studies on D. pteronyssinus have, for example, demonstrated that at least six major allergens are of clinical importance (3, 4). One of the major mite allergens, designated Derp l, has been purified and shown to react with anti-mite IgE antibodies in up to 80% of allergic sera (3-5). This allergen, reportedly a glycoprotein of mol wt 27 x 1Os , appears to be an excretory product associated with fecal particles (6).Currently, the diagnosis and immunotherapy of the house dust mite allergy is based on the use of crude mite preparations (7). Developments in this field have been hampered by the small or variable quantities of mite allergens present in the extracts . To help overcome these limitations, and to facilitate further studies, the molecular cloning of mite allergens is being investigated in our laboratory . To date, a cDNA clone coding for the allergen Der p 1 has been isolated and shown to contain a 0 .8-kb cDNA insert (8) . We now report the sequence analyses of the Der p 1 cDNA clone and the similarity between its inferred amino acid sequence and the group of cysteine proteases.
The efficacy of an "allergen-gene immunization" protocol in altering allergic response was examined. Intramuscular injection of rats with a plasmid DNA encoding a house dust mite allergen into the muscle results in its long-term expression and the induction of specific immune responses. Significantly, this approach prevents the induction of immunoglobulin E synthesis, histamine release in bronchoalveolar fluids, and airway hyperresponsiveness in rats challenged with aerosolized allergen. Furthermore, this suppression is persistent and can be transferred into naive rats by CD8+ T cells from gene-immunized rats. These findings suggest that allergen-gene immunization is effective in modulating allergic responses, and may provide a novel therapeutic approach for allergic diseases.
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