C O - EXISTENCE BETWEEN W I -F I & B LUETOOTH. SIDDHESH KARNAD.

INTRODUCTION This presentation is about the Wi-Fi and Bluetooth devices and the co existence between them. Both Wi-Fi and Bluetooth use same Unlicensed 2.4Ghz Band. As both of them use the same Frequency band the interference between the to is bound to happen. So we study the problem and try to find the best solution on it.

W I -F I AND B LUETOOTH B ANDWIDTH UTILIZATION Bluetooth and Wi-Fi works in 2.4 GHz range. Wi-Fi is based on DHSS and Bluetooth is based on FHSS. Bluetooth Devices hopes over 79 frequencies that are 1Mhz wide. Thus Bluetooth occupies 79MHZ of frequencies. Wi-Fi network uses a subset of 83.5Mhz frequency. Each channel is defined by its center frequency. Centre frequencies are 5MHz apart from each other. Wi-Fi channels are numbered from it uses 1,6 and 11 to avoid interference. So the frequency used is 48Mhz out of the 83.5 Mhz.

F REQUENCY OCCUPANCY OF THE 2 NETWORKS. BluetoothWi-Fi

PROBLEM By the help of different figures we will go through how the coexistence of this two products effect the throughput. The figure will explain the throughput : o With normal setup of Wi-Fi and Bluetooth. o With setup of Wi-Fi with Bluetooth interfering. o With setup of Bluetooth with Wi-Fi interfering.

S ETUP COMPONENTS.

W I -F I & B LUETOOTH COEXISTENCE SETUP.

W I -F I SETUP WITH B LUETOOTH I NTERFERENCE.

S IMILAR CASE WITH W I -F I INTERFERENCE.

C OEXISTENCE M ETHODS : Collocated Method: MEHTA: is a technique for managing packet transmission requests. It grants permission to transmit a packet based on parameters including signal strength and the difference between and Bluetooth center frequencies. MEHTA is a “Hebrew” word for conductor.

W HAT IS MEHTA? MEHTA involves the use of a centralized controller, that monitors the and the traffic and allows exchange of information between the two radio systems. The controller works at the MAC layer and allows precise timing of packet traffic, thus avoiding interference between the two devices voice traffic has priority over WLAN packets, otherwise WLAN traffic is transmitted first. When there is voice traffic pending, WLAN packets are queued.

O VERALL S TRUCTURE OF M ECHANISM :

S TRUCTURE D ETAILS : The MAC and LM + LC entities provide status information to the TDMA control and MEHTA control entities. The TDMA control entity provides a transmit enable ( Tx Enable ) signal to each stack. This is a continuous signal that gates whether each stack can start a new packet transmission. The MEHTA control entity receives a per-transmission transmit request ( Tx Request ) and issues a per-transmission transmit confirm ( Tx Confirm ) to each stack to indicate whether the transmission can proceed. The Tx Confirm carries a status value that is one of: allowed or denied. The Tx Request and Tx Confirm are discreet signals exchanged for every packet transmission attempt.

S TRUCTURE OF M EHTA :

S IMPLIFIED D IAGRAM :

C ONTROL E NTITY D ETAILS : MEHTA uses its knowledge of the duration of activity and future activity a number of slots into the future to predict collisions. When a collision would occur, MEHTA prioritizes transmissions based on simple rules that depend on packet types. Each stack has a corresponding control entity to which it submits its transmit requests. This control entity allows or denies the request based on the known state of both stacks. The purpose of the Control entity is to allow or deny transmit requests from the MAC. The Tx Request signal is sent when the MAC has determined that it can transmit according to its own protocol – i.e. after any required backoff has completed. On receipt of a Tx Request signal, the Control immediately generates a Tx Confirm signal containing a status value that is either allowed or denied. In response to a Tx Request signal, the control immediately generates a Tx Confirm signal containing a status value that is either allowed or denied. The effect of the denied result on the stack is to prevent transmission during the whole slot (or slot half in the case of scan sequences).

L OGIC FOR W I -F I TX REQUEST

B LOCK D ETAILS :

L OGIC F OR B LUETOOTH T X R EQUEST

B LOCK D ETAILS :

P RIORITIES. A SCO packet should have a higher priority than DATA MPDUs. A ACK MPDU should have a higher priority than all packets.

C ONCLUSION : In this presentation we have went through the effects of interference caused to throughput and discussed the coexistence mechanism technique MEHTA in detail.

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