Time-Reversal Wireless Paradigm for Green Internet of Things: An Overview <s> B. Data Transmission Phase-Downlink <s> The use of RDF data published on the Web for applications is still a cumbersome and resource-intensive task due to the limited software support and the lack of standard programming paradigms to deal with everyday problems such as combination of RDF data from dierent sources, object identifier consolidation, ontology alignment and mediation, or plain querying and filtering tasks. In this paper we present a framework, Semantic Web Pipes, that supports fast implementation of Semantic data mash-ups while preserving desirable properties such as abstraction, encapsulation, component-orientation, code re-usability and maintainability which are common and well supported in other application areas. <s> BIB001 </s> Time-Reversal Wireless Paradigm for Green Internet of Things: An Overview <s> B. Data Transmission Phase-Downlink <s> The Internet of Things (IoT) is the logical further development of today’s Internet. Technological advancements lead to smart objects being capable of identifying, locating, sensing and connecting and thus leading to new forms of communication between people and things and things themselves. Ambient Assisted Living (AAL) encompasses technical systems to support elderly people in their daily routine to allow an independent and safe lifestyle as long as possible. Keep In Touch (KIT) uses smart objects and technologies (Near Field Communication and Radio Frequency Identification) to facilitate telemonitoring processes. Closed Loop Healthcare Services take use of KIT technology and are capable of processing relevant data and establishing communication channels between elderly people and their environment and different groups of care-givers (physicians, relatives, mobile care providers). The combination of KIT technology (smart objects) and Closed Loop Healthcare Services results in an applied IoT infrastructure for AAL scenarios. Already applied IoT and AAL applications in telemonitoring and medication intake compliance projects show that these applications are useful and accepted by the elderly and that the developed infrastructure enables a new form of communication between people and people, people-to-people (P2P) communication. The personal communication between elderly people, their environment and relevant groups of care givers is an important aspect in AAL. Through the combination of KIT and Closed Loop Healthcare, a central AAL paradigm can be realized through the IoT, where the elderly live in their homes with smart objects, thus smart homes, communicating to the outside world in an intelligent and goal-orientated manner. <s> BIB002
After the channel recording phase, the system starts its data transmission phase. We first introduce the downlink scheme in this part. In the downlink scheme, at the BS, each of represents a sequence of information symbols that are independent complex random variables with zero mean. As shown in Fig. 8 , we allow different users to adopt different rate backoff factors to accommodate the heterogeneous QoS requirement of the applications of IoT. To implement the rate backoff, the th sequence is first upsampled by a factor of at the BS, and the th up-sampled sequence can be expressed as Then the up-sampled sequences are used to modulate the signature waveforms , by calculating the convolution of the th up-sampled sequence and the TR waveform as shown in Fig. 8 . After that, all the signals are combined together, and the combined signal to be transmitted is given by Z Z Fig. 8 . Basic diagram of the TRDMA downlink. BIB001 In this paper, users and devices are interchangeable. BIB002 In general, the probing period depends on how fast the channel may vary.  As we mentioned in Section II, we use the effective channel response for finite-bandwidth system. In essence, by convolving the information symbol sequences with TR waveforms, the TR structure provides a mechanism of embedding the unique location-specific signature associated with each communication link into the transmitted signal for the intended user. The signal received at user is represented as follows: Z which is the convolution of the transmitted signal and the channel response , plus an AWGN sequence with zero mean and variance . Thanks to the temporal focusing effect, the th receiver (user ) simply samples the received signal every seconds at , ending up with given as follows: where , and ⩽ ⩽ ⩽ < Thanks to the spatial focusing effect, in (16), when , the power of is typically very small compared to the power of the , which suppresses the inter-userinterference (IUI) for the TRDMA downlink. Consequently, based on (15), the resulting SINR for user in the TRDMA downlink is given by where and