適用於雙耳助聽器之皮膚通道的通訊系統的研究與實現

Abstract

在現今的雙耳助聽器中，許多先進功能的實現都取決於雙耳助聽器進行參數及數據資料的交換。遺憾的是，如此必然會面臨到傳輸率、傳輸方式的問題。相較單耳助聽器，雙耳通訊助聽器會有著較高的功率消耗，而目前市面上販售的助聽器為了要滿足其通訊需求仍使用高功耗的射頻技術。然而，助聽器是電池供電的醫療器材，且使用者幾乎是全天配戴，若需要時常更換電池，將會大大影響到助聽器的實用性。因此，若要延長電池的使用時間，勢必要發展出一個低功耗的通訊系統。由人體通道頻率響應的量測結果發現，低功耗的基頻調變技術可運用在皮膚通道上，再加上配戴助聽器時助聽器會自然的和皮膚接觸，綜上所述，我們可知人體通道技術非常適合應用在雙耳助聽器的通訊需求上。

在此我們設計了一個皮膚傳導的通訊系統，而為了符合雙耳助聽器的需求，在系統的設計上將會有以下三個考量點:第一，群體延遲時間。根據研究，人類對於超過10毫秒的影音不同步現象，容易產生言語認知上的混亂[1]，而對於需要長時間配戴助聽器的患者而言，此現象將對他們產生更大程度的影響，因此這會是我們的最優先的考量點。第二，通訊系統的同步能力。無論是雙耳時間差(Interaural Time Difference，ITD)或雙耳強度差(Interaural Level Difference，ILD)的雙耳雜訊消除演算法，都需要將雙耳的資訊做一定程度的同步才能獲得預期的效果。三、功率消耗。 以下為章節排序，第一章簡介會介紹助聽器的架構及人體通道特性，評估建立此通訊系統的可行性並訂定設計目標。第二章以個人區域網路IEEE 802.15.4為例子，分析建立一個通訊系統需要訂定哪些協定及規範。第三章雙耳助聽器通訊系統設計，在這一章節提出我們針對助聽器的通訊系統設計，並討論基於雙耳助聽器的需求及實用性限制下，會有哪些需要取捨的部分。第四章電路實現，說明如何實現第三章所提出的雙耳通訊系統。第五章總結與未來展望，總結本論文的設計結果以及未來發展方向。

In modern binaural hearing aids, the realization of many advanced functions depends on reliable exchange of information for both sides. Commercially available hearing aids often use RF technologies to meet the communication needs, despite the relatively high power consumption associated with them. However, most advanced hearing aids are battery-operated, and with their small sizes the capacity of the accompanied batteries is quite limited. Therefore, in view of the practicality of binaural hearing aids, it is necessary to develop a low-power communication system. On the other hand, experiments are conducted to verify the channel characteristics of the waveguide type are good enough to support the proposed binaural communication system. And, due to the facts that skin contact naturally happens in binaural hearing aids and baseband modulation techniques with low power consumption can be used in transmission over skin, the skin communication system is found to be perfectly suited for the needs of binaural hearing aids.

This thesis presents a communication system with skin channel technology. To meet the needs of binaural hearing aid systems, we follow the following design guidelines. First, the group delay time is strictly limited. According to [1], if the audio and visual cues have delays more than 10 milliseconds, human beings are prone to sense the confusion in verbal cognition. So, this is the top-priority consideration. Second, the communication should have synchronization capability. It is important for applications where the cues of Interaural Time Difference (ITD) or Interaural Level Difference (ILD) are used to extract desired speech signal from the mixture of speech signal and noises from different directions. And last, the power consumption should be as low as possible.

This thesis is organized as follows. Chapter 1 introduces the structure of hearing aids and the feasibility study of a body channel communication system for binaural hearing aids. Chapter 2 presents a case study of IEEE 802.15.4 WPAN, and I try to learn from the analysis what kinds of protocols and specifications are needed for a body channel communication system. Chapter 3 discusses the trade-offs of designing a communication system for binaural hearing aids, particularly from the aspect functions and practicality demanded by hearing aids. Chapter 4 presents the design/implementation details of the binaural communication system. Chapter 5 summarizes this thesis and proposes future directions of further development.