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francês para inglês: Multi-standard Receiver for Medical IoT Sensor Networks General field: Outra Detailed field: TI (Tecnologia da Informação)
Texto de origem - francês Récepteur Multinormes pour les Réseaux de Capteurs de l’IoT Médical
4.1. Introduction
La norme IEEE 802.15.6 [IEE 12a] est dédiée aux communications sans fil, à très faible consommation énergétique et à faible couverture (portée de 3 m) opérant à proximité du corps humain pour offrir en particulier en temps réel des services médicaux fiables tels que la mesure de paramètres vitaux et des services non-médicaux comme les services de divertissement.
Contrairement au mode UWB de la norme 802.15.6, le mode bande étroite [LEE 09] aspire à devenir la norme de référence de l’internet des objets (IoT) pour l’industrie médicale [CHE 15]. C’est pour cette raison, et différemment des travaux [LEE 09], [CHO 10], [MAT 15], [PRI 14] et[LIA 13], que ce chapitre se concentre sur ce mode. Néanmoins, le mode bande étroite de la norme IEEE 802.15.6 doit coexister dans la bande ISM des 2.4 GHz avec des concurrents de taille tels que notamment IEEE 802.11a/b/g/n (WiFi) [IEE 12b], IEEE 802.15.1 (Bluetooth) [IEE 05a], IEEE 802.15.4 (ZigBee) [IEE 05b].
Pour favoriser l’essor du mode bande étroite de la norme IEEE 802.15.6, nous proposons un récepteur OFDM à l’instar de [Mic 01] (à multiples sous-porteuses orthogonales) pouvant par exemple être utilisé par un récepteur WiFi classique, et qui servirait alors de récepteur multi-standards.
Ce chapitre est organisé comme suit. Dans la section suivante, nous rappelons le contexte général et nous décrivons les caractéristiques des différentes normes WiFi 802.11a/n/ac. La section 4.3 rappelle les spécificités du signal de la norme WBAN. La section 4.4 détaille la conception de la couche physique proposée pour la norme 802.15.6 en mode bande étroite. La section 4.5 discute les résultats de simulations. Enfin, diverses conclusions sont données à la fin de ce chapitre.
4.2. Contexte général
4.2.1 OFDM
Les techniques multi-porteuses furent inventées en 1957 [DOE 57]. L’idée de base est de deviser le spectre du signal à transmettre en N_c sous canaux afin de simplifier l’égalisation et de profiter de diversité en fréquence.
Considérons une séquence de N_c données c_0, c_1,….c_(N_c-1), avec c_k est un symbole réel ou complexe.Le principe de modulation est d’envoyer chaque donnée c_k sur une porteuse f_k. Le signal modulé s’écrit donc :
s(t)=∑_(k=0)^(N_c-1)▒〖c_k e^(j2πf_k t) 〗.[4.1]
Malheureusement, la complexité des modulateurs/démodulateurs, rendirent la méthode difficile à appliquer et il faudra attendre une vingtaine d’années pour que les circuits de traitement soient capables des techniques multi-porteuses orthogonales grâce à la transformée discrète de Fourier [WEI 71].
En remarquons que le multiplexage [4.1] est orthogonal si l’espace entre les fréquences est Δ_f=1/T_s , oùT_s est la période symbole, le signal modulé devient :
s(t)=e^(j2πf_0 t) ∑_(k=0)^(N_c-1)▒〖c_k e^j2π(k/T_s )t 〗, [4.2]
où f_0est la fréquence centrale.
Il est simple de remarquer que le second terme de [4.2] est à bande limitée et sa fréquence maximale est F_max=N/(2T_FFT ).Nous pouvons donc l’échantillonner aux instantst_n=(nT_FFT)/N_c . Ces échantillons s’écrivent :
s(t_n )=s(n)=∑_(k=0)^(N_c-1)▒〖c_k e^2πk(n/N) 〗.[4.3]
[4.3] montre que les échantillons du signal à émettre ne sont que la transformée de Fourier inverse de la séquence c_0, c_1,….c_(N_c-1).
Les échantillons aux instants t_n=(nT_FFT)/N_c ,n=0,…,N_c-1du signal reçu en absence de bruit s’écrivent :
z(t_n )=z(n)=∑_(k=0)^(N_c-1)▒〖c_k 〖H_k e〗^2πk(n/N) 〗.[4.4]
où H_k est le gain de du canal sur la porteuse n°k.
Il suffit donc de faire la transformée de Fourier et d’égaliser pour obtenir la séquence c_0, c_1,….c_(N_c-1).
Cette technique de modulation/ démodulation est abondamment utilisée en Wifi.
Tradução - inglês Multi-standard Receiver for Medical IoT Sensor Networks
4.1. Introduction
The IEEE 802.15.6 standard [IEE 12a] is dedicated to wireless communications, with very low energy consumption and coverage (range of 3 m) operating close to the human body to particularly provide, in real time, reliable medical services such as the measurement of vital parameters and non-medical services such as entertainment.
Unlike the UWB mode of 802.15.6 standard, the narrow band mode [LEE 09] aims to become the Internet of Things (IoT) reference standard for the medical industry [CHE 15]. It is for this reason, and differently from research by [LEE 09], [CHO 10], [MAT 15], [PRI 14] and[LIA 13], that this chapter focuses on this mode. Nevertheless, the narrow band mode of the IEEE 802.15.6 standard must coexist in the 2.4 GHz ISM band with large competitors such as the IEEE 802.11a/b/g/n (Wi-Fi) [IEE 12b], IEEE 802.15.1 (Bluetooth) [IEE 05a], IEEE 802.15.4 (ZigBee) [IEE 05b].
In order to promote the development of the narrow band mode of the IEEE 802.15.6 standard, we propose an OFDM receiver like [Mic 01] (with multiple orthogonal subcarriers) that can for example be used by a conventional Wi-Fi receiver, and which would then serve as a multi-standard receiver.
This chapter is structured as follows. In the next section, we shall revisit the general context and describe the characteristics of various Wi-Fi standards 802.11a/n/ac. Section 4.3 shall revisit the specificities of the WBAN standard signal. Section 4.4 shall detail the physical layer design proposed for 802.15.6 standard in narrow band mode. Section 4.5 shall discuss simulation results. And finally, various conclusions shall be presented at the end of this chapter.
4.2. General context
4.2.1 OFDM
Multi-carrier techniques were invented in 1957 [DOE 57]. The basic idea was to devise the spectrum of the signal to be transmitted in N_c sub-channels in order to simplify the equalization and to take advantage of frequency diversity.
Consider a sequence of N_c data c_0, c_1,….c_(N_c-1), with c_k is a real or complex symbol. The modulation principle is to send each data c_k on a carrierf_k. The modulated signal can therefore be written:
s(t)=∑_(k=0)^(N_c-1)▒〖c_k e^(j2πf_k t) 〗.[4.1]
Unfortunately, the complexity of modulators/demodulators made the method difficult to apply and it will take twenty years for the processing circuits to be capable of performing orthogonal multi-carrier techniques thanks to the discrete Fourier transform [WEI 71].
Note that the [4.1] multiplexing is orthogonal if the space between the frequencies is Δ_f=1/T_s , whereT_s is the symbol period, the modulated signal becomes:
s(t)=e^(j2πf_0 t) ∑_(k=0)^(N_c-1)▒〖c_k e^j2π(k/T_s )t 〗, [4.2]
where f_0is the central frequency.
It is easy to notice that the second term of [4.2] is bandlimited and its maximum frequency is F_max=N/(2T_FFT ).We can therefore sample it at timest_n=(nT_FFT)/N_c . These samples are written as follows:
s(t_n )=s(n)=∑_(k=0)^(N_c-1)▒〖c_k e^2πk(n/N) 〗.[4.3]
[4.3] shows that the samples of the signal to be transmitted are only inverse Fourier transform of the sequence c_0, c_1,….c_(N_c-1).
The sampling instants t_n=(nT_FFT)/N_c ,n=0,…,N_c-1of the signals received in the absence of noise are written thus:
z(t_n )=z(n)=∑_(k=0)^(N_c-1)▒〖c_k 〖H_k e〗^2πk(n/N) 〗.[4.4]
where H_k is the gain of the channel on the carrier n°k.
Therefore, it is only necessary to make the Fourier transform and equalize it to get the sequence c_0, c_1,….c_(N_c-1).
This modulation/demodulation technique is widely used on Wi-fi
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Formação educacional em tradução
Master's degree - ASTI, University of Buea
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Anos de experiência em tradução: 13 Registrado no ProZ.com: Feb 2016. Tornou-se associado em: Oct 2018
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I am a Portuguese/French>English freelance translator
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