超寬頻人體區域網路之無線電通道探討與建構

Abstract

應用於超寬頻單輸入單輸出人體區域網路通道建構，由時間響應可觀察出在空曠的環境中繞射波為主要的傳播路徑，但在有許多散射體的環境下，接收端擺放在身體後面，散射體所引起的散射波成為主要的傳播機制。收到的信號強度也會比在沒有散射體的環境下來得強。因此在有許多散射體的空間中，路徑散逸指數會比空曠環境小。赤池信訊息量準則 (Akaike Information Criterion) 指出對數常態分佈是最適合用來模擬小尺度衰減。 應用於超寬頻多輸入多輸出人體區域網路通道量測，接收端天線陣列放置於身體背部的通道容量會高於接收端放置在身體的前端。是因為身體擋掉接收端的訊號，減少接收端天線的相關性。多輸入多輸出人體區域網路系統的容量受環境影響不大。但是，接收端放置在身體前端比起放置在後端比較容易受當地的環境影響。我們可以發現當天線空間增加時通道容量減少，是因為即使傳送端與接收端的天線空間增加也許會使得相關性降低導致容量增加，但是由於繞射波大幅降低使得次通道的訊號強度會被削弱，次通道沒有貢獻。因此，天線之間的空間增加也許不會對通道容量有所貢獻。

For channel modeling of UWB SISO BAN, it is found that the diffracted wave is the dominant propagation path in the open space observed from the temporal response. However, when the Rx places on the back of the body that is surrounded by dense local scatterers, the scattering due to the local scatterers becomes the dominant propagation mechanism and the received signal strength is much larger than that of without local scatterers. Therefore, the path loss exponent in the room with dense local scatterers is smaller than that in open space. The AIC indicates that the Lognormal distribution is the best one in modeling the small scale fading distribution. For MIMO BAN measurement, the capacity of Rx antenna array elements placed on the back of the body is higher than that placed on the front of the body. This is due to the received signal obstructed by the body, which yields reduction of the spatial channel correlation at the Rx antenna. The influence of environment on the capacity of BAN MIMO system is not significant. However, the capacity of Rx placed on the front of the body is more easy affected by the local environment than that placed on the back of the body. It is found that the capacity of the MIMO BAN decreases as the element spacing increases. It is because that although the increasing element spacing may reduce the correlation of Rx or Tx and leads capacity increase, the signal strength of the subchannel decreases a lot due to large diffraction loss and yields little contribution of the subchannel. Therefore, element spacing increases may not contribute to the MIMO channel capacity.