藍(lán)牙和IEEE802.11無線局域網(wǎng)共存問題探析

摘要:使用WiFi(Wireless Fidelity) IEEE 802.11b/g協(xié)議的無線局域網(wǎng)(WLAN)技術(shù)已經(jīng)成為PC和筆記本電腦的標(biāo)準(zhǔn)而正在快速擴(kuò)散到PDA(Personal Digital Assistant)和其它便攜式設(shè)備。與此同時(shí)，藍(lán)牙作為耳機(jī)，麥克風(fēng)連到各種個(gè)樣的無線設(shè)備的串口線的替代品已經(jīng)越來越普遍。這兩種無線協(xié)議都工作于2.40至2.48GHz ISM(工業(yè)，科學(xué)和醫(yī)療)射頻帶。WiFi使用12個(gè)帶寬為22MHz重疊的頻道其中一個(gè)，而藍(lán)在帶寬為79MHz范圍跳頻[3]。因此，無論WiFi正在使用哪個(gè)頻道兩個(gè)系統(tǒng)間會(huì)存在互相干擾和共存的問題導(dǎo)致數(shù)據(jù)吞吐量的降低。實(shí)現(xiàn)IEEE802.11 WLAN協(xié)議的設(shè)使用FEC(Foward Error Correction)糾錯(cuò)技術(shù)來減輕于其它無線網(wǎng)的干擾。在該文中，我們將對RS(Reed Solomon)編碼與BS(Binary Convolutional) 編碼使用于解決WLAN于BT共存問題的相對有效性進(jìn)行一個(gè)調(diào)查并作出結(jié)論。

關(guān)鍵詞:無線局域網(wǎng);藍(lán)牙;RS;BS;干擾;共存

中圖分類號(hào):TP393文獻(xiàn)標(biāo)識(shí)碼:A文章編號(hào):1009-3044(2009)14-3635-01

An Analysis of the Coexistence Problem between Bluetooth and IEEE802.11 Wireless Local Area Networks

Chiphazi Banda

(South China University of Technology， Guangzhou 510640， China)

Abstract: WLAN(Wireless Local Area Network) devices that implement the Wifi(Wireless Fidelity) IEEE802.11b/g protocol have already become standard additions to Desktop and Laptop computers and are spreading to Personal Digital Assistants(PDA) and other portable devices at a rapid rate. At the same time， ear phones and microphones that use BT(Bluetooth) as a wireless replacement for the serial cable when connecting to all sorts of wireless devices are becoming increasingly common.These two wireless protocols both operate in the 2.4-2.48GHz ISM(Industrial， Scientific Medical) radio frequency band. WiFi uses one of 12 overlapping frequency bands each of having a bandwidth of 22MHz whereas BT frequency hops over a 79MHz band. Regardless of which channel currently being used by WiFi， there is a chance of mutual interference between the WiFi network and the BT network and this in turn can lead to a drop in the throughput of both systems. IEEE802.11. WLAN employs Forward Error Correction(FEC) codes to mitigate the effects of interference from other systems. In this paper we examine the relative effectiveness of using RS(Reed Solomon) coding versus BS(Binary Convolutional) coding in addressing the problem of BT and WiFi coexistence.

Key words: WLAN; bluetooth; reed solomon; binary convolutional; interference; mitigation

1 引言

WLAN和BT共存問題產(chǎn)生了大量的研究和電子工程業(yè)的興趣。不同的解決方案被提出，例如在文獻(xiàn)[1]有4種不同的解決方案被建議:

1) 自適應(yīng)分割而動(dòng)態(tài)調(diào)整WLAN數(shù)據(jù)包大小以便盡量減少與BT的網(wǎng)絡(luò)時(shí)間碰撞的機(jī)會(huì);

2) Adaptive Frequency Hopping(AFH) 或自適應(yīng)跳頻)用于減小WLAN與BT頻率碰撞的機(jī)會(huì);

3) 第3層流控制，修改WLAN驅(qū)動(dòng)程序使能快速切換而實(shí)現(xiàn)時(shí)間分享;

4) MAC層的協(xié)調(diào)，讓W(xué)LAN與BT的MAC層交換信令以便分享時(shí)間。所有這些方案使用BS FEC編碼方案，但在文獻(xiàn)[2]建議使用RS作為前向糾錯(cuò)方案。我們將用MATLAB進(jìn)行仿真并對這兩種WLAN糾錯(cuò)方案在BT與AWGN(Additive White Gaussian Noise)環(huán)境下的性能進(jìn)行比較。

2 仿真

先用MATLAB程序來模擬在BT和AWGN環(huán)境下WLAN的性能。MATLAB程序的輸入?yún)?shù)包括WLAN數(shù)據(jù)傳輸率，Eb/No范圍，數(shù)據(jù)包錯(cuò)誤率限制，數(shù)據(jù)包長度(以字節(jié)為單位)，SIR(Signal to Interference Ratio)范圍，RS輸入?yún)?shù)其中包括bits per symbol(2～16范圍之內(nèi))和可修改錯(cuò)誤數(shù)量(1～2m-1范圍之內(nèi))。BT干擾源的數(shù)量也是必要的參數(shù)。MATLAB程序的輸出是數(shù)據(jù)包錯(cuò)誤率(PER)和每比特能源與噪聲密度比(Eb/No)。關(guān)于使用MATLAB做通信方面的仿真或?qū)嶒?yàn)請參考文獻(xiàn)[4]。仿真結(jié)果收集、繪制如圖1。

3 結(jié)果解釋

從圖中的曲線可以看出藍(lán)牙干擾的影響。該曲線不是編碼通常的“瀑布”或凸曲線而因受BT的影響變?yōu)榘蓟蛟「仔螤?。還注意到對前四種數(shù)據(jù)傳輸速率就是6Mbps， 9Mbps， 12Mbps和18Mbps。在這底數(shù)據(jù)傳輸速率BS編碼表現(xiàn)明顯優(yōu)于RS編碼，但在更高的數(shù)據(jù)速率時(shí)BS編碼有明顯的惡化而未能實(shí)現(xiàn)基準(zhǔn)性能。

從圖1.1、圖1.2和圖1.3可以看出，使用BC能在底SIR(分別等于-16dB和-8dB) 和半碼速率條件下達(dá)到基準(zhǔn)PER=0.01性能標(biāo)準(zhǔn)而3/4碼速率在SIR=0dB也達(dá)到基準(zhǔn)性能。因此可以得出結(jié)論:半碼速率的BS編碼比3/4碼速率BS編碼強(qiáng)一些。

RS編碼在底數(shù)據(jù)傳出率顯的比較差，當(dāng)SIR在最低值時(shí)未能達(dá)到基準(zhǔn)性能(見圖1.1～圖1.4)。

4 結(jié)論

總體來說如果WLAN設(shè)備目標(biāo)環(huán)境是高數(shù)據(jù)速率(比如超過54Mbps)環(huán)境而很可能要與BT共存，則設(shè)備制造商應(yīng)該考慮使用RS coded OFDM來替代通常使用的BS coded OFDM。

參考文獻(xiàn):

[1] Ophir， L.， Y. Bitran， and I. Sherman. WI-FI (IEEE802.11) and bluetooth coexistence: Issues and solutions. 2004. Barcelona， Spain: Institute of Electrical and Electronics Engineers Inc.， Piscataway， NJ 08855-1331， United States.

[2] Anyaegbu， M.， Performance of Reed Solomon Coded IEEE 802.11g Wireless LAN in a Bluetooth Environment， in School of Electronic and Electrical Engineering. 2006， University of Leeds: Leeds.

[3] Performance of IEEE 802.11 WLANs in a Bluetooth environment Chiasserini， C.F. Rao， R.R.， Wireless Communications and Networking Conference， 2000. WCNC. 2000 IEEE

[4] MATLAB communications toolbox: http://www.mathworks.com/products/communications/.