As Bluetooth and Wi-Fi begin to take theirrightful places in the world, Bluetooth as a Wire-less Personal Area Network (WPAN) technologyand Wi-Fi as a Wireless Local Area Networking(WLAN) technology, the situation has started tochange. Wi-Fi has become the network of choicefor wireless Internet connectivity in offices,homes and public hot spots. Bluetooth hasbecome the network of choice for cable replace-ment enabling wireless voice headsets, keyboardsand mice. These logical applications of Wi-Fiand Bluetooth technologies are leading to thenatural convergence of the two into handhelddevices such as PDAs and smartphones.

With the migration of these two wireless net-working technologies into handheld devices, thecoexistence of the two can no longer be achievedby depending on distance or limited usage mod-els. In fact, there are key applications that willrequire both networks to operate simultaneous-ly. Fortunately, solutions exist to enable simulta-neous operation of these two networks whenembedded in the same device.

Keying in on the problem Both Wi-Fi and Bluetooth operate in the unli-

censed 2.4 GHz industrial, scientific and medical(ISM) band. This band is 83.5 MHz wide, begin-ning at 2.4 GHz and ending at 2.4835 GHz.Because Wi-Fi and Bluetooth approach spec-trum use in different ways, they can cause con-siderable interference for one another.

Wi-Fi uses wideband stationary signals thatuse direct sequence spread spectrum (DSSS),single tone modulation, such as CCK (comple-mentary code keying) and PBCC (packet binaryconvolutional coding), and now OFDM (orthog-onal frequency division multiplexing) as addedin the new IEEE 802.11g standard. Bluetoothuses a frequency-hopping spread-spectrum

(FHSS) tech-nique. WhileWi-Fi devicesoccupy aboutone quarterof the 83.5MHz avail-able, Blue-tooth deviceshop acrossalmost theentire bandwith aninstantaneousbandwidth ofabout 1 MHz.

D i s t a n c ebetween Wi-Fi and Blue-tooth tends toprevent themfrom interfer-ing, but in aPDA this isnot possible.When Blue-tooth and Wi-Fi are put intothe samedevice, thetransmitted

signals from one network appear on the receiverof the other making them interfere with the eachother. When one transmits while the other isreceiving, it is nearly impossible to decode theincoming message, which can cause networkconnections to drop if left unmitigated.

The problem is similar to a room full of peo-ple talking. There may be a lot of noise in theroom from all of the conversations, but as long apeople are spread out and not too loud, two peo-ple in reasonable proximity can hear one anoth-er and successfully carry on a conversation.However, if one individual were to decide to talkloudly right next to your ear, you would find itvery difficult to continue a conversation withsomeone else.

Achieving coexistence To alleviate the general coexistence problem,

various solutions have been considered includ-ing Adaptive Frequency Hopping (AFH), Trans-mit Power Control (TPC) and Time DivisionMultiplexing (TDM). Using these mechanismsin whole are in part enables Bluetooth and Wi-Fito enjoy simultaneous operation in handhelddevices.

Adaptive frequency hopping, while not on themarket today, allows Bluetooth and Wi-Fi net-works to share frequency. When using AFH theBluetooth device no longer hops across thewhole band, but restricts its hop channels tothose frequencies not occupied by the Wi-Fi net-work. TDM techniques allow for both Bluetoothand Wi-Fi to provide simultaneous operation.And last but not least, each network can use TPCto lessen the degree of interference it generates.

Returning the room full of people talking andone rather loud individual near your ear, there isan analogy for each of the coexistence techniquesmentioned above. If you were able to politely askthe loud individual to speak at a higher frequen-cy that you could not hear, you would not carehow loud he was talking. This is analogous toAFH. Likewise, if you could reach an agreementwhereby the loud individual traded time speak-ing with you so you could still carry on anotherconversation, is analogous to TDM. And if youcould ask the individual to lower his volumewhen near your ear, you could also continueyour conversation without interruption, which isanalogous to TPC.

Reaching the goalIn handheld devices with Bluetooth and Wi-

Fi, coexistence can be achieved by using themechanisms described above. In practice, Blue-tooth and Wi-Fi devices must be designed inconjunction with each other to make sure theyhave the required degree of interference rejec-tion. In addition they must be able to commu-nicate with one another to enable mechanismssuch as TDM and AFH.

Bluetooth and WLAN block diagrams areshown in Figures 1 and 2, respectively. In coex-istence enabled solutions, collaborative coexis-tence mechanisms are typically enabled by com-munication between the Wi-Fi Media AccessController (MAC) and the Bluetooth link man-ager. Texas Instruments has designed its Blue-tooth and Wi-Fi solutions to allow the use of

coexistence mechanisms and enable simultane-ous operation for the next generation of hand-held communications devices. All this to ensurethat the first time you use your PDA to carry ona VoIP phone call over your Wi-Fi connectionthat is bridged to your Bluetooth wireless head-set your call will maintain high quality due todesign for coexistence.TEXAS INSTRUMENTS,Tel+1-214-4807976 • Fax+1-214-4803386

enter 3001 at www.epn-online.com

Bluetooth and Wi-Fi coexistence has found its quintessential form factor, and it is small enough to fit in the palm of your hand.For years companies and standards bodies have worked on making Wi-Fi (IEEE 802.11b) and Bluetooth (IEEE 802.15.1) coexist,because there was a fear that these devices would generate catastrophic interference with one another. Although the concern was

justified, the reality was that very little agony occurred in solving this problem. The usage scenarios and proximities of devicesresulting in detectable performance degradation on either network were few and far in between.

Bluetooth, Wi-Fi and Coexistence Mastered in Handheld DevicesBy Matthew B. Shoemake, Texas Instruments

WIRELESS ELECTRONICS

Wi-Fi Block Diagram

Bluetooth Block Diagram

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