A WLAN connects mobile and portable stations to the network using an access point device. Mobile nodes communicate within its range via wireless medium (radio waves). Requires a fixed permanent infrastructure.
Bluetooth was designed as a low-cost, low-power wireless networking technology . Bluetooth is a short-range (up to 10 m) . Radio transmission uses FHSS technique. Communication of Bluetooth devices follows a strict master-slave scheme.
Piconet : Group of Bluetooth devices which use the samefrequency hopping channel.Scatternet : A group of Piconet in which connections consists between different PiconetThe Bluetooth specification defines two distinct types of links : SCO ACL
Bluetooth is a radio technology for WPAN. It is much likely that Bluetooth devices and WLAN stations operating in the 2.4 GHz frequency band should be able to coexist as well as cooperate with each other, and access each other’s resources. These cooperative requirements have encouraged an intuitive architecture, called BlueStar. BlueStar nodes access WLAN through Bluetooth Wirelss Gateways which are 802.11 enabled.
Interference generated by integration : Persistent interference Intermittent interferenceSolution to combat with both these interferences Adaptive frequency hopping (AFH) Bluetooth carrier sense (BCS)
A new scatternet formation protocol for Bluetooth ad- hoc networks . BlueStars produces a mesh-like connected scatternet with multiple routes between pairs of nodes . The protocol proceeds in three phases :1. Topology discovery2. Piconet formation3. Piconet interconnection
Bluetooth wireless gateways (BWGs): possess both a WLAN interface and a Bluetooth interface The interaction between the Bluetooth network and the outside world is managed by the BWGs. IP packets over Bluetooth : Bluetooth network encapsulation protocol (BNEP) wherein IP packets are encapsulated in Ethernet packets which are then carried over Bluetooth links.
Proposed BluestarArchitectureProtocol stack for each entity
The crucial challenges in the design of BlueStar IP address of bluetooth device To combat the interference sourcesBlueStar employs a unique hybrid approach of an adaptive frequency hopping (AFH) and Bluetooth carrier sense (BCS).
Carrier sensing is efficient interference mitigation among Bluetooth piconets . BCS is incorporated Bluetooth without any modifications to the current slot structure . Before starting packet transmission, the next channel is sensed in the turn around time of the current slot. An ARQ packet will be sent when the slot is clear.
Nature of intermittent interference depends upon :Bluetooth packet slot lengthNumber of piconet
IEEE 802.11 DATA frame has a maximum size of up to 2346 byte so it can overlap with up to 30 Bluetooth slots . Two potential cases of packet collisions :1. When the Bluetooth packet is ahead of the WLAN packet.2. When the WLAN packet is ahead of the Bluetooth packet.
Implementation of AFH : A bitmap comprising of 79 bits where a one indicates that a frequency can be used for transmission. Each Bluetooth devices scan every ‘T-scan’ seconds for each of the 79 channels used by Bluetooth and collect PER statistics.
If the PER is above a threshold ‘PER-thres’, it is labeled as “bad”; otherwise it is labeled as “good”. When the piconet master request this, the slaves send their measured channel marks. The master conducts a referendum process and construct final mapping sequence. The overall effect on Bluetooth is that the total number of available channels decreases.
All functionalities of BlueStar implemented in the network simulator (ns-2) and BlueHoc A hybrid Bluetooth-802.11 model has been incorporated into the BWGs. Two simulation environment: Bluetooth-only simulation environment Combined Bluetooth and WLAN simulation environment
The topology used for this evaluation : Bluetooth with BCS greatly reduces the number of collisions and defers packet transmission until a safe channel is found .
Require implementations of both BCS and AFH . TCP/IP traffic simulation : WLAN packet is of total size of 1.5 KByte (approx) . Bluetooth stations to be stationary .
Four possible scenarios : Scenario A: Bluetooth devices downloading contents from the WAN . Scenario B: Bluetooth devices uploading information to the WAN . Scenario C: A BWG simultaneously receives data packets from both the WLAN AP and the Bluetooth devices . Scenario D: BWG simultaneously transmits data packets to both the Bluetooth devices and the WLAN AP.
Scenarios B and D: High persistent interference in the Bluetooth network causing a high PER . Scenario B suffers higher PER than scenario D. AFH is effective for a larger number of piconets until it reaches a point where the intermittent interference levels becomes significant.
Scenarios A and C : In scenario A the WLAN transmissions have been corrupting the Bluetooth ACK packets . In scenario C Bluetooth data packets are more impacted. Scenario A performs slightly better due to the shorter and less frequent duration of the ACK packets .
Scenarios C and D : A higher PER for scenario D In all scenarios, BlueStar achieves the lowest PER by taking advantage of both AFH and BCS than ordinary implementation. AFH outperforms BCS when most of the interference is of persistent type, but degrades as the number of piconets increases.
The topology of interconnection has influence on the number of resulting BWGs. A BWG serve as bridge node between exactly two neighboring piconets Proposition : For a scatternet comprised of n (n > 0) piconets, the maximum number of BWGs needed is [7n/2] − 2[4√n − 4] .
This paper introduces a novel architecture called BlueStar, which employs a combination of adaptive frequency hopping and Bluetooth carrier sensing to take advantage of the existing installed base of IEEE 802.11 wireless networks by assigning selected Bluetooth devices, called BWG, with IEEE 802.11 capabilities . The incorporation of BlueStar into Bluetooth is simple, does not incur much overhead, and hence is an excellent enabler for co-existence and cooperation of Bluetooth and IEEE 802.11.
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2. A scatternet operation protocol for Bluetooth ad hoc networks. Wireless Personal Multimedia Communications, 2002 27-30 Oct. 2002, pages: 223 – 227, Volume: 1 Authors: Tadashi Sato, Kenichi Mase3. Bluetooth scatternet models December 2004/ January 2005, pages : 36 – 39 Author: Patricia McDermott-Wells