Efficient Peer-to-Peer Communications in Bluetooth YounSuk KIM, KyungHun JANG, KyunHyon TCHAH IEICE TRANS. COMMUN. speaker ： jenchi

Outline  Introduction  Master-Slave Switching Mechanism  Dynamic Master Selection and Fast Master-Slave Switching Policies  Simulation  Conclusion

Introduction  Piconet  Communication master ： send packets in even slots slave ： send packets in odd slots point-to-point or point-to-multipoint  slaves can ’ t communicate directly with each other

Introduction (cont.)  Peer-to-peer communication A slave can communicate with other slaves as well as a master  But there is NO destination address field in the packet header sent by a slave

Master-Slave Switching Mechanism  Take place when a slave wants to become a master Tx and Rx timing is reversed Redefinition of the piconet ： piconet switch

Master-Slave Switching Mechanism (cont.) Unit 1 (Old Master) Unit 2 (New Master) Unit 3 (Slave) Unit 4 (Slave) Master-Slave Switch request Master-Slave Switch response Time alignment LMP message FHS packet FHS acknowledgement Time alignment LMP message FHS packet FHS acknowledgement Time alignment LMP message FHS packet FHS acknowledgement POLL Old hopping sequence New hopping sequence

Dynamic Master Selection and Fast Master-Slave Switching Policies  Why Dynamic Master Selection ？ Therefore, Dynamic master selection policy is needed in order to minimize the average slot occupancy per packet The switching is accomplished as fast as possible Master Piconet S1 S2 θ θ θ S1 → M → S2 ： 2θ S1 → S2 ： θ

Dynamic Master Selection and Fast Master-Slave Switching Policies (cont.)  Three policies Addressing policy Dynamic Master Selection Policy Fast Master-Slave Switching Mechanism

 The Motivation of Addressing Policy Each slave is assigned a 3 bits AM_ADDR (Active Member Address) by a master The AM_ADDR of the slave is used both in the master-to-slave and in the slave- to-master packets There is no destination address field in the packet header sent by a slave Dynamic Master Selection and Fast Master-Slave Switching Policies (cont.) -- Addressing Policy Header format AM_ADDRTYPEFLOWARQNSEQNHEC

Dynamic Master Selection and Fast Master-Slave Switching Policies (cont.) -- Addressing Policy  Addressing rules AM_ADDR  master ： “ 111 ”  slaves ： “ 001 ” ~ “ 110 ”  Broadcasing packet ： ” 000 ” The AM_ADDR field  is used only for destination address A 3-bits SRC-ADDR (source address) field  Carries the AM_ADDR of the source unit Bluetooth packet format with an added field in payload Access Code Header bits SRC-ADDR Payload

Dynamic Master Selection and Fast Master-Slave Switching Policies (cont.) -- Dynamic Master Selection Policy  Θ i occupancy parameter related with slaves ’ or master ’ s address by the number of the occupied slots,where i=1,2,…7  When a master receivers a packet It increases θ i=SRC  If received packet should be forward ， it increases θ i=DTS  If not ， it increases θ i=Master  When the master transmits a packet of which source address is its own It increases θ i=Master and θ i=DTS

Dynamic Master Selection and Fast Master-Slave Switching Policies (cont.) -- Dynamic Master Selection Policy Rx Tx i=src_addr of received packet =occupied slots of received packet Forwarding packet ？ j=dst_addr of received packet θ i ← θ i ＋△ θ j ← θ j ＋△ Tx θ i ← θ i ＋△ θ master ← θ master ＋△ Tx Yes No i=dst_addr of transmitting packet Forwarding packet ？ master NEW ＝ arg k maxθ k θ i ← θ i ＋△ θ master ← θ master ＋△ No Yes master New == master current Change master Rx Yes No

Dynamic Master Selection and Fast Master-Slave Switching Policies (cont.) -- Fast Master-Slave Switching Mechanism  Define an anchored master as a unit which creates a piconet a slave which takes over the master role from the anchored master by master-slave switching The temporary master still uses the channel parameters of the anchored master Only TDD switching of the anchored and temporary masters

Dynamic Master Selection and Fast Master-Slave Switching Policies (cont.) -- Fast Master-Slave Switching Mechanism Unit 1 (Anchored Master) Unit 2 (Slave) Unit 3 (Slave) Master-Slave Switch request Master-Slave Switch response Updated Piconet Information Master-Slave Switch request Piconet Information Master-Slave Switch request Master-Slave switch response Dynamic master selection policy Dynamic master selection policy Unit 2 (Temporary master) Master-Slave Switch response Piconet Information Dynamic master selection policy Hopping sequence of the anchored master

Simulation  A single piconet with up to six slaves  The TDD slot length in Bluetooth is equal to 625 μsec  Transmits single-slot DH1 packets every slot

Simulation (cont.)  Carrier frequency ＝ 2.4GHz  Symbol rate ＝ 1M symbol per sec  Modulation format ＝ non-coherent FSK  γ T (SNR threshold) ＝ 15dB  Mobile speed ＝ 2km/h

Simulation (cont.)

Conclusion  Addressing policy for L2 forwarding efficient peer-to-peer communications in Bluetooth Performs better than the conventional addressing policy  Dynamic master selection policy in order to minimize the average channel occupancy  Fast master-slave switching mechanism Minimize the switching delay