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Minimal CDMA Recoding Strategies in Power-Controlled Ad-Hoc Wireless Networks. Honglei Miao [email protected] Centre for Wireless Communications University of Oulu, Finland. Outline. Introduction Problem statement and previous work New recoding strategies Simulation Results - PowerPoint PPT Presentation
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© Honglei Miao: Presentation in Ad-Hoc Network course 13.01.2004 1(19)
Minimal CDMA Recoding Strategies in Power-Controlled Ad-Hoc Wireless
Networks
Honglei Miao
Centre for Wireless CommunicationsUniversity of Oulu, Finland
© Honglei Miao: Presentation in Ad-Hoc Network course 13.01.2004 2(19)
Introduction Problem statement and previous
work New recoding strategies Simulation Results Conclusions
Outline
© Honglei Miao: Presentation in Ad-Hoc Network course 13.01.2004 3(19)
Introduction
• Transmitter Oriented Code Assignment (TOCA) in CDMA based Ad-Hoc wireless network− Each node is assigned one code to be used to transmit it’s message.− Two kinds of collisions can be happened to damage the
transmission. • Primary collision where an incoming transmission is damaged by a
simultaneous outgoing transmission from the receiving mobile.• Secondary collision where two incoming transmissions garble each other.
− Correct and efficient TOCA algorithms should be:• Eliminate all the collisions including primary and secondary collisions.• Minimize the maximum code index assigned to any network node.
− Several centralized and distributed heuristics have been proposed for static multihop networks.
• Why recoding in Ad-Hoc network?− In a dynamic ad-hoc network, nodes are free to
• move about. • connect or disconnect from the network.• Increase or decrease transmission ranges.
− These events may introduce new collisions, Recoding is needed to eliminate these new collisions.
© Honglei Miao: Presentation in Ad-Hoc Network course 13.01.2004 4(19)
• Existed code assignment algorithms are inappropriate for recoding− Centralized code assignment algorithms determine a
new code assignment for every node on each event. (costly)
− Distributed heuristics assume a static network. (inappropriate)
• Minimum recoding algorithms are proposed in this paper.− Distributed, only need communication local to the
event.− Minimal recoding, minimize the number of the nodes to
be recoded on any network. − Least increase in the maximum code index assigned to
the network.
Introduction (2)
© Honglei Miao: Presentation in Ad-Hoc Network course 13.01.2004 5(19)
• A power controlled ad-hoc network is modelled as a dynamic directed graph G=(V,E).− V = {v1,v2,….,vn} is set of nodes in the network. ri is the
transmission range of node vi. ci is the code assigned to node vi.
− E = {(vi, vj): i !=j, and dij<=ri} is the set of the directed edges.
• TOCA is to assign a code to each node in the network so that the following two constraints are satisfied. − CA1-(Primary) collision avoidance 1: For every edge
− CA2-(Secondary) collision avoidance 2: For every pair of edges
Problem statement and previous work
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© Honglei Miao: Presentation in Ad-Hoc Network course 13.01.2004 6(19)
• Assumption of the events or reconfiguration in the dynamic ad-hoc network− Events occur one after another and not simultaneously.− Nodes move and change their ranges in discrete steps.− Minimal connectivity: A node v can change its configuration iff
it has both from-neighbour and to-neighbour.
• The goals of an efficient recoding strategy− Minimize the maximum code index used by any node in the
network. (hardware consideration) − Minimize the number of nodes that change their codes. − Minimize the overhead of the recoding− Keep the recoding strategy distributed and local.
Problem statement and previous work (2)
© Honglei Miao: Presentation in Ad-Hoc Network course 13.01.2004 7(19)
• Previous strategy: CP strategy− The new node and its 1-hop neighbours exchange the
information about their old codes and constraints.− Ordering by identities
• The new nodes and it’s 1-hop neighbours need to be recoded continuously check if they are the highest (or lowest)-identity node in its vicinity that has not been assigned a code.
− Respect for the constraints• If it is the highest (or lowest)-identity node. The lowest
available code (not taken by any 1-hop and 2-hop neighbours) is selected.
Problem statement and previous work (3)
© Honglei Miao: Presentation in Ad-Hoc Network course 13.01.2004 8(19)
• Handling Node Join
New recoding strategies
© Honglei Miao: Presentation in Ad-Hoc Network course 13.01.2004 9(19)
New recoding strategies (2)
• From CA1 and CA2, all nodes in 1n, 2n, {n} each need to have codes different from each other. Nodes in 3n need not change their codes since n will be assigned a new code anyway and this will need to be different from any of the codes in 3n.
• If a K-sized subset of nodes in 1n U 2n have the same old code, only K-1 nodes need to be changed.
• More generally, if they are K nodes in 1n U 2n , and m different codes in 1n U 2n, then only K-m nodes need to be changed to different codes.
© Honglei Miao: Presentation in Ad-Hoc Network course 13.01.2004 10(19)
• Algorithm for recoding on a node join
New recoding strategies (3)
© Honglei Miao: Presentation in Ad-Hoc Network course 13.01.2004 11(19)
• Example of recoding on a node join
• 1n = {7}, 2n = {1 2 3 6}, 3n = {}, 4n = {4 5}
New recoding strategies (4)
© Honglei Miao: Presentation in Ad-Hoc Network course 13.01.2004 12(19)
• Handling Node Power Increase
New recoding strategies (5)
© Honglei Miao: Presentation in Ad-Hoc Network course 13.01.2004 13(19)
• No new constraints are induced among 1n U 2n U 3n U 4n.
• All constraints due to CA1 and CA2 added by the new edges involve node n.
• Minimum recoding only change the code of n if the old code of n can not satisfy the new constraints.
• However, the proposed algorithm may not be the optimal among all minimal recoding strategies. For example, n only have one new constraint with another node m. If n has lots of old constraints and m very few, recoding only m might be more optimal in terms of maximum code index assigned to the network while achieving the minimal recoding bound.
New recoding strategies (6)
© Honglei Miao: Presentation in Ad-Hoc Network course 13.01.2004 14(19)
New recoding strategies (7)
• Handling Node Leaves and Power Decreases− No recoding since no new conflicts are introduced.
• Handling Node Movement− Node movement is treated as a pair of consecutive
events where the moving node n leaves and joins the network.
− Recoding strategy on a node move is similar to that on a node join.
© Honglei Miao: Presentation in Ad-Hoc Network course 13.01.2004 15(19)
Simulation results
• The different algorithms are simulated for a long sequence of events.
• The proposed algorithms are compared to− BBB algorithm: centralized colouring heuristic, recolor
all the nodes at every event.− CP strategy
• The performance metrics to be concerned− Maximum code index assigned in the network (the
lower the better).− The number of nodes recoded (recoded with a new
code different from its old one).
© Honglei Miao: Presentation in Ad-Hoc Network course 13.01.2004 16(19)
Simulation results (2)
© Honglei Miao: Presentation in Ad-Hoc Network course 13.01.2004 17(19)
Simulation results (3)
© Honglei Miao: Presentation in Ad-Hoc Network course 13.01.2004 18(19)
Simulation results (4)
© Honglei Miao: Presentation in Ad-Hoc Network course 13.01.2004 19(19)
• A set of recoding strategies Minim for TOCA CDMA recoding in a dynamic ad-hoc network are proposed.
• Given an event, the strategy change the codes of the minimum number of mobiles needed to eliminate all collisions in the network.
• Simulation results reveal that the Minim approaches trade off a relatively small loss in terms of maximum code index assigned in the network to obtain a significant gain in terms of the total number of instances where a node has to change its code.
• The proposed strategies can be very practical in scenarios such as hard real-time systems and high data rate applications running on an ad-hoc network.
Conclusions