基於人體通道傳輸之正交分頻多工基頻處理器設計

Abstract

近年來，另一項新技術–人體通訊傳輸的產生，使無線近身網路又擴展到新的領域，並已列入 IEEE 802.15.6的標準之中。由於人體可藉由手指觸碰來選擇並啟動傳輸，因此不再限於傳統的醫療照護應用，而能在多媒體影音傳輸、門禁、付款等使日常生活更加便利。目前在人體通道傳輸上的研究，傳感器的最高傳輸速率可到達 10 Mbps，但仍不足以支援多媒體傳輸等服務。為了適用於高傳輸速率的應用，我們採用了正交分頻多工調變技術，能夠在有限頻寬的人體通道中達到高頻譜效益和高傳輸速率的需求。 由於目前各文獻中人體通道量測結果有所出入。我們將影響通道環境的傳輸模式進行多次量測，並進行比較探討。在我們的環境設定下，對於單人通道傳輸的距離，合適的傳輸頻帶落於 30 – 50 MHz並以電容耦合方式較佳。另外，也藉由消除外部干擾與儀器雜訊下，建立不同傳輸距離的人體通道響應以供基頻系統之模擬。 在基頻處理器設計上，因為人體通道的特性，我們著重在通道等化並選擇較強的序列來提升偵測率。在通道等化的部分，採用較高精準度時域通道估計的方式來提升傳輸可靠度。至於偵測率的提升，則以 Zad-off Chu 序列加上 ZFS 的相關方式來支援在人體天線效應下之高雜訊傳輸環境。 為了驗證基頻處理器設計，人體通道傳輸的原型機以 FPGA 加上整合在 PCB 板上的類比元件完成實際傳輸。透過我們基頻處理器的設計，偵測率可提升超過 9 個百分點至約 98% 的平均性能，而 BER 則可提升 0.3 等級。因為現有商用晶片規格並沒有完全針對 BCC 的低頻帶設計，原型機並無法操作在高取樣率，但是目前已能在資料量 13 Mbps時達到 10-2 的 BER。 在晶片實現上，我們提出的人體通道傳輸處理器可達到29.1Mbps的高傳輸速率，並且藉由低功耗技術如電壓調降，時脈閘控等，更能達到與現今各傳送機相比擬的能量/位元比。

Recently, a new technique - body channel communication (BCC) emerges to extend the field of application, and is already included in standard IEEE 802.15.6. In BCC, a simple touch can be used to enable the transmission such that it can be applied to multimedia transmission application, payment system or entry access control system to improve convenience in our daily life. Recent work about BCC in the literature has data rate up to 10 Mbps which is not allowable for multimedia transmission application. To support that, OFDM modulation technique is adopted with high data rate and high spectral efficiency for band-limited BCC channel. To develop an OFDM baseband system for BCC, the measurement of transmission schemes influencing the channel is conducted. In our environment settings, the capacitive coupling approach is more suitable in the transmission distance on a single person and the proper transmission band is 30 – 50 MHz. By reducing the external wireless interference and the instrumental noise, a body channel impulse response is built with respect to 3 transmission distances on the body for the system simulation. In baseband processing, due to the character of BCC channel, high accuracy time domain equalizer is applied with little overhead of hardware complexity to enhance transmission reliability. And Zad-off Chu sequence is selected accompanied with ZFS detection scheme to combat noisy environment about body antenna effect. To verify the baseband processor design, the BCC prototype composed of FPGA and PCB is built for real transmission on human body. With proposed baseband processor design, there are over 9 percentage point enhancement and 98% detection rate in average, and BER performance is also improved in 0.3 order. And the operating speed of the prototype is limited by imperfection of the analog components, but it is still achieved that 10-2 BER performance in 13 Mbps throughput rate. In the chip implementation, the proposed BCC processor could reach 29.1 Mbps data rate, which is the highest one compared to state-of-the-art. With low power technique such as voltage scaling and clock gating, the energy per bit performance is also comparable.