載荷長度對(duì)藍(lán)牙數(shù)據(jù)傳輸吞吐量的影響

藍(lán)牙協(xié)議提供了多種不同長度的數(shù)據(jù)包類型，以提高在不同的信道條件下的數(shù)據(jù)傳輸性能。針對(duì)這一特性，該文建立了噪聲環(huán)境下藍(lán)牙數(shù)據(jù)傳輸系統(tǒng)的數(shù)學(xué)模型，分析了藍(lán)牙高斯頻移鍵控(GFSK)調(diào)制方式和2.0+EDR規(guī)范新增加的π/4-DQPSK與8DPSK調(diào)制方式，根據(jù)在加性高斯白噪聲信道(AWGN)下的比特錯(cuò)誤率(BER)與平均接收信噪比的關(guān)系，推導(dǎo)了ACL數(shù)據(jù)分組的重傳概率與平均接收信噪比的函數(shù)表達(dá)式，進(jìn)而分析了在不同的信噪比條件下載荷長度對(duì)藍(lán)牙數(shù)據(jù)傳輸吞吐量的影響。仿真分析結(jié)果對(duì)如何提高藍(lán)牙數(shù)據(jù)傳輸性能的研究提供了有益的參考。
關(guān) 鍵 詞 藍(lán)牙; 信噪比; 載荷長度; 數(shù)據(jù)傳輸吞吐量

There are several kinds of packet types in Bluetooth specification to enhance the data transmission performance in different noisy channels. In this paper, a Bluetooth data transmission mathematical model in noisy environments is presented. The relations between bit error rate and average received signal-to-noise ratio(SNR)in additional white gaussian noise (AWGN) channel are derived for gaussian frequency shift keying (GFSK) modulation and newπ/4-DQPSK and 8DPSK modulations adopted in Bluetooth 2.0+EDR specification. The function expressions of packet retransmission probability and average received SNR of asynchronous connection-oriented (ACL) data packets are put forward. The impact of payload length on Bluetooth data transmission throughput is obtained at last. Simulation results contained in this paper can be severed as a good benchmark against researches on how to enhance Bluetooth data transmission throughput.
Key words Bluetooth; signal-to-noise ratio; payload length; data transmission throughput

藍(lán)牙技術(shù)作為無線個(gè)域網(wǎng)(wirelee person area network，WPAN)的典型代表，由于其低成本、低功耗、抗干擾能力強(qiáng)等優(yōu)點(diǎn)，在近年來得到了越來越廣泛的應(yīng)用。藍(lán)牙工作在2.4 GHz的ISM頻段，當(dāng)同一區(qū)域有別的藍(lán)牙散射網(wǎng)(scatternet)或者無線局域網(wǎng)(802.11b)同時(shí)工作時(shí)，會(huì)對(duì)藍(lán)牙數(shù)據(jù)傳輸產(chǎn)生干擾，導(dǎo)致有的數(shù)據(jù)分組不能正確接收，產(chǎn)生一定的丟包率，進(jìn)而影響藍(lán)牙數(shù)據(jù)傳輸性能。影響丟包率的因素有：產(chǎn)生干擾的設(shè)備數(shù)量和其傳輸載荷量、干擾源的距離、藍(lán)牙收發(fā)系統(tǒng)的功率、藍(lán)牙數(shù)據(jù)分組的長度等[1-2]。
文獻(xiàn)[3-7]對(duì)噪聲環(huán)境下藍(lán)牙數(shù)據(jù)傳輸性能進(jìn)行了分析和研究。對(duì)藍(lán)牙數(shù)據(jù)傳輸性能的研究都是對(duì)藍(lán)牙數(shù)據(jù)分組作為一個(gè)整體來進(jìn)行研究的，忽略了載荷長度對(duì)數(shù)據(jù)傳輸吞吐量的影響。針對(duì)這一方面的不足，本文研究了在噪聲環(huán)境下藍(lán)牙數(shù)據(jù)分組長度與數(shù)據(jù)傳輸吞吐量之間的關(guān)系，以加性高斯白噪聲(additional white gaussian noise，AWGN)信道為信道模型，分析了在不同信噪比的干擾狀態(tài)下，藍(lán)牙數(shù)據(jù)載荷長度對(duì)數(shù)據(jù)傳輸吞吐量的影響。
1 藍(lán)牙2.0+EDR不同調(diào)制方式下的位錯(cuò)誤率分析
藍(lán)牙新規(guī)范Bluetooth2.0+EDR(增強(qiáng)數(shù)據(jù)速率)提高了數(shù)據(jù)傳輸速率并降低了功耗。新規(guī)范增加了六種新的ACL分組格式：2-DH1、2-DH3、2-DH5、3-DH1、3-DH3、3-DH5。其中，2-DH與3-DH類型分組與DH類型分組格式基本相似，但載荷部分分別使用π/4-DQPSK(相對(duì)四相相移鍵控)與8DPSK(八相差分相移鍵控)調(diào)制方式[2]，其接入碼和分組頭還是使用跟藍(lán)牙1.2協(xié)議相同的高斯頻移鍵控(gaussian frequency shift keying，GFSK)調(diào)制方式。其分組特性如表1所示。