When simultaneous wireless information and power transfer is carried out, a fundamental tradeoff between achievable rate and harvested energy exists because the received power is used for two different purposes. The tradeoff is well characterized by the rate-energy region, and several techniques have been proposed to improve the achievable rate-energy region. However, the existing techniques still have a considerable loss in either energy or rate and thus the known achievable rate-energy regions are far from the ideal one. Deriving tight upper and lower bounds on the rate-energy region of our proposed scheme, we prove that the rate-energy region can be expanded almost to the ideal upper bound. Contrary to the existing techniques, in the proposed scheme, the information decoding circuit not only extracts amplitude and phase information but also combines the extracted information with the amplitude information obtained from the rectified signal. Consequently, the required energy for decoding can be minimized, and thus the proposed scheme achieves a near-optimal rate-energy region, which implies that the fundamental tradeoff in the achievable rate-energy region is nearly eliminated. To W. Choi is with 2 practically account for the theoretically achievable rate-energy region, we also present practical examples with an M -ary multi-level circular QAM with Gaussian maximum likelihood detection. I. INTRODUCTIONEnergy efficient transmission is one of key considerations in recent wireless networks, such as wireless sensor networks, due to a limited lifetime of fixed energy supplies, e.g., batteries.In parallel, high costs and difficulty of frequent battery replacing motivates remote energy recharging technologies. Remote energy charing entials wireless power transfer (WPT)-enabled communications where wireless information transfer is combined with WPT. The WPT-enabled communication is in general classified into categories: simultaneous wireless information and power transfer (SWIPT) where energy harvesting and information decoding are simultaneously carried out at the receiver, and wireless powered communication networks (WPCN) where wireless information is transmitted with the harvested energy.SWIPT has been studied as a unified approach to energy harvesting and information decoding[1], [2]. In SWIPT, generally, there exists a fundamental tradeoff between achievable rate and harvested energy, which is characterized by the rate-energy region. With a constraint on the amplitude of the transmit signal, finding the rate-energy region is known to be non-trivial according to input distributions [1], while with an average power constraint on the transmit signal, the achievable rate-energy region can be identified [2]. To expand the achievable rateenergy region, several approaches in receiver design have been investigated [3]- [6]. Typically, the rate-energy tradeoff is optimized by either power split or time division between battery charging and information decoding. However, even with either opportunistic switching between WPT...
To improve diversity gain in an interference channel and hence to maximize diversity multiplexing tradeoff (DMT), we propose on-off switched interference alignment (IA) where IA is intermittently utilized by switching IA on/off. For on-off switching, either IA with symbol extension or IA with Alamouti coding is adopted in this paper. Deriving and analyzing DMT of the proposed schemes, we reveal that the intermittent utilization of IA with simultaneous non-unique decoding can improve DMT in the 2-user X-channel with two antennas. Both the proposed schemes are shown to achieve diversity gain of 4 and DoF per user of 4 3 . In particular, the on-off switched IA with Alamouti coding, to the best of our knowledge, surpasses any other existing schemes for the 2-user X-channel with two antennas and nearly approaches the ideal DMT.
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