A Survey on M2M Systems for mHealth: A Wireless Communications Perspective <s> IR-UWB Transmitter <s> Given the trend towards a user-centric concept in mobile communications, body area networks have received increasing attention within the wireless personal area community. Researchers and designers have been investigating radio propagation characterisation and modelling owing to its importance in developing and designing efficient and reliable radio systems. The paper presents an experimental investigation of ultra-wideband (UWB) on-body radio propagation. Channel models with respect to large scale and delay analysis have been derived from measured parameters. Effects of different antenna types on channel behaviour are also demonstrated. Results and analyses highlight the consequences of changes in body postures and positions in addition to antenna orientations on the communication channels. Measurement data are also used in predicting the performance of potential UWB wireless systems and their applications in body-centric networks. It is indicated that bi-phase modulation for UWB body-centric networks performs better than pulse position modulation systems. The study also concludes that the use of hybrid antenna types for different on-body links will provide better system performance. <s> BIB001 </s> A Survey on M2M Systems for mHealth: A Wireless Communications Perspective <s> IR-UWB Transmitter <s> In this paper, we propose an ultra wide band (UWB)-based full-body motion capture system for gait analysis. The system is designed to reduce the implementation complexity and cost of current gait analysis setups, which require expensive locomotion laboratories and equipment. The solution exploits recent developments in wearable computing (i.e., electronic textiles) and relies on estimating the relative distance between body-worn sensors through time-of-flight measurements. While such a system may find application in several areas, substantial research is still required to prove its feasibility and accuracy. From this perspective, the present contribution addresses two key aspects to enable its development: i) the interaction between UWB electromagnetic pulses and the human body is analyzed and, by contrast to most results in the literature, the body- induced pulse distortion is characterized in terms of an equivalent channel impulse response, and ii) by explicitly taking into account that body-induced distortion, the accuracy of various time-of- flight-based ranging algorithms is investigated. <s> BIB002 </s> A Survey on M2M Systems for mHealth: A Wireless Communications Perspective <s> IR-UWB Transmitter <s> UWB technology is an attractive technology for Wireless Body Area Networks. There are many advantages of using ultra-wideband (UWB) as both a sensing and a communication standard for biomedical applications: very low radiated power (-41.3 dBm/MHz), low power consumption, good coexistence with other existing wireless technologies, robustness to interference and multipath. Moreover, one specific UWB technology, namely Frequency Modulated (FM)-UWB, has also an important advantage, which make it even more convenient for biomedical applications, such as lower power consumption than IR-UWB. The main issue that is addressed in this paper is the integration of sensing and communication devices using FM-UWB so that a single device can be obtained for two different operational modes. A preliminary feasibility study shows that an integrated sensing and communication device based on FM-UWB can meet the requirements, both for the sensing and the communication points of view, of typical biomedical applications such as non-invasive heart rate monitoring. <s> BIB003 </s> A Survey on M2M Systems for mHealth: A Wireless Communications Perspective <s> IR-UWB Transmitter <s> Ultra wideband (UWB) communication is a very promising candidate for the use in wireless body area networks (BAN). The high UWB peak data rate allows for medium average data rates in combination with a very low duty cycle, which is the key for a very low power consumption. Devices in a wireless BAN require low complexity. Hence, mainly non-coherent receivers such as energy detector and transmitted-reference receiver are suited. In this paper, the symbol-wise maximum-likelihood (ML) detectors for pulse position modulation (PPM) and transmitted reference pulse amplitude modulation (TR PAM) are derived assuming partial channel state information (CSI) at the receiver. Additionally, also the ML detectors for a combination of PPM and TR PAM are presented. The performance of the derived receiver structures is evaluated using a novel BAN channel model not distinguishing line-of-sight and non line-of-sight situations. This simple channel model is based on 1100 channel measurements in the frequency range between 2 and 8 GHz, which were measured in an anechoic chamber. Using the BAN channel model, performance of the derived receiver structures is evaluated showing that the knowledge of the average power delay profile (APDP) at the receiver improves performance substantially. Requiring only slightly more complexity such receivers are a well suited alternative to non-coherent receivers for the use in a BAN. <s> BIB004 </s> A Survey on M2M Systems for mHealth: A Wireless Communications Perspective <s> IR-UWB Transmitter <s> In the current scenario, where it is becoming very important for many Health Care Monitoring System to provide non-invasive and non-contact measurements, this paper presents a novel monitoring system for vital signs based on the Frequency Modulated-Ultra Wide Band (FM-UWB) technology. First of all, an analysis of the error introduced by each block of the transceiver device is performed in order to better understand the achievable resolution under no ideal working conditions. Then, a comparison with an IR-UWB monitoring system is performed in terms of sensitivity. As it is expected, the FM-UWB radar, which is a continuous wave radar, can achieve the same resolution also working much lower SNRs than IR-UWB systems. This means that proposed system can work also with lower power levels than an IR-UWB device. Moreover, our simulation confirms that the FM-UWB system can achieve the desired resolution (of the order of mm) for the context of interest (heart-beat, respiration rate monitoring). <s> BIB005 </s> A Survey on M2M Systems for mHealth: A Wireless Communications Perspective <s> IR-UWB Transmitter <s> Wireless technology has been developing fast for years and is spreading to new areas of everyday life. One of the newest areas is healthcare and welfare sector where it can be a significant way to save costs and improve existing procedures. The coming years are going to be challenging as the population, in the developed countries especially, is aging fast and more patients are going to need treatment but with the same or even smaller number of nursing staff than nowadays. Therefore there is a clear need for both improvement of methods and cutting down the costs. In this paper, the performance of different ultra wideband (UWB) receivers implemented following the IEEE 802.15.4a requirements are being compared in different hospital environments. Wireless body area network (WBAN) radio channel models used in the simulations are based on the measurements carried out in a real hospital environment in Oulu, Finland. <s> BIB006 </s> A Survey on M2M Systems for mHealth: A Wireless Communications Perspective <s> IR-UWB Transmitter <s> In this paper, the performances of two singleband ultra wideband (UWB) systems, i.e., direct sequence UWB (DS-UWB) and UWB frequency modulation (UWB-FM) are studied in two different channel models to reveal an impact of a channel model on the system's performance. The applied channel models are the experimental wireless body area network (WBAN) channel model developed at the Centre for Wireless Communications (CWC), Finland, and the IEEE 802.15.6 channel model. The simulation results indicate that the choice of the WBAN channel model applied in the simulations has a major impact on the performance of UWB-FM, whereas it is not such a crucial in the case of DS-UWB. <s> BIB007 </s> A Survey on M2M Systems for mHealth: A Wireless Communications Perspective <s> IR-UWB Transmitter <s> In this paper we present receiver design considerations and performance analysis for the physical layer of low data-rate non-coherent Ultra--Wideband Impulse Radio (UWB--IR) communication systems. Such UWB--IR systems are of particular interest in wireless medical Body Area Networks (BAN); in medical BAN the amount of traffic is relatively low, however, reliability of communication under body-shadowing and interference conditions is of utmost importance. Two non-coherent modulation/detection schemes are treated analytically and numerically through noise and interference performance studies. Particular attention is given to the performance enhancement achieved by compression of the received signal by methods previously introduced by the authors. <s> BIB008
IR-UWB can support many of the well known modulation schemes that are usually employed in NB systems  , resulting to a wide range of achieved data rates. In order to demodulate IR-UWB signals, coherent, differentially coherent, and non-coherent detection schemes can be applied. A performance study of an IR-UWB system for WBANs is presented in BIB001 , where the impact of two different modulation techniques on the Bit Error Rate (BER) of different on-body radio links is analyzed. The authors in BIB006 have studied different (coherent and non-coherent) UWB receivers, implemented according to the IEEE 802.15.4a requirements in different hospital environments, showing that both receivers yield equivalent performance in short-distance LOS links. The authors in BIB002 have investigated the problem of pulse distortion due to the interaction between UWB electromagnetic pulses and the human body. By studying the performance of various detection algorithms in the presence of pulse distortion and receiver noise, it has been shown that non-coherent receivers, such as energy detectors and Transmitted-Reference (TR) receivers (In TR systems, two signals-a reference and a data signal-are transmitted per bit. The information is contained in the sign difference of the transmitted signals.), are suitable for WBANs, due to the fact that they do not require any explicit channel estimation (thus consuming less power and reducing complexity). In BIB008 , two non-coherent modulation/detection pairs for IR-UWB systems with and without chirp pulse compression have been investigated. The authors strongly recommend the usage of chirp pulse compression in medical IR-UWB WBAN devices that are expected to use low data rates. Non-coherent detectors for Pulse Position Modulation (PPM) and TR Pulse Amplitude Modulation (TR-PAM) are proposed in BIB004 . The authors verify via simulations that the knowledge of the average power delay profile at the receiver can substantially improve the system performance. FM-UWB: FM-UWB is a low-complexity, constant envelope, low data rate UWB communication technology with good interference robustness at very low data rates and lower power consumption with respect to IR-UWB. FM-UWB is typically an analog implementation of a spread-spectrum system using double FM: digital Frequency Shift Keying (FSK), followed by high modulation index analog FM to create a constant envelope UWB signal. A typical FM-UWB transceiver architecture is presented in Figure 3 . The data signal modulates a low-frequency subcarrier using NB FSK techniques. Then, the subcarrier signal modulates the RF oscillator using analog FM with high modulation index. The receiver demodulates the FM-UWB signal without requiring local oscillator and carrier synchronization (as in the case of IR-UWB), which makes the device both simpler and cost-efficient. The main characteristics of FM-UWB are: (i) simple and straightforward transmitter implementation; (ii) no need for carrier synchronization at the receiver; and (iii) system operation with a variety of antennas, adding robustness against NB jamming. A novel system for the monitoring of vital signs based on the FM-UWB technology is presented in BIB005 . The authors study the error introduced by each block of the transceiver, in order to understand the achievable resolution under non-ideal working conditions. A comparison with an IR-UWB system is also conducted, showing that the FM-UWB system can achieve the same performance, working with lower power levels. The authors in BIB003 propose the implementation of a device which integrates both sensing and communication capabilities by using the same FM-UWB technology. Finally, the authors in BIB007 compare the performance of IR-UWB and FM-UWB transceivers in various channel models, showing that while the selection of the channel model has a has a major impact on the FM-UWB performance, the performance of the IR-UWB transceiver is not significantly affected. MB-OFDM UWB: MB-OFDM UWB is a technique based on the simultaneous transmission of data over multiple carriers spaced apart at precise frequencies. A typical architecture of an MB-OFDM UWB transceiver is illustrated in Figure 4 , where the carrier and sampling synchronization is performed after the analog front end. In the specific architecture shown in the figure, time and frequency synchronization (carrier and sampling offset estimation and compensation) are performed in the time domain, while channel estimation and equalization are performed in the frequency domain. Nevertheless, different transceiver designs can be implemented, depending on the adopted algorithms for synchronization, channel estimation and signal detection. 