Predictive and adaptive bandwidth reservation for hand offs in cellular networks
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Predictive and Adaptive Bandwidth Reservation for Hand-Offs in Cellular Networks Goal: provide a probabilistic guarantee on connection hand-off drops as mobile user moves from one cell to another

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Predictive and adaptive bandwidth reservation for hand offs in cellular networks l.jpg
Predictive and Adaptive Bandwidth Reservation for Hand-Offs in Cellular Networks

  • Goal: provide a probabilistic guarantee on connection hand-off drops as mobile user moves from one cell to another

  • Naïve solution: for no hand-off drops, reserve bandwidth in all cells a mobile/connection might pass through

  • Problem: bandwidth quickly consumed and new connection blocking probability increases

  • Proposed solution: a cell estimates aggregate bandwidth for hand-offs from adjacent cells, to be reserved and used solely for hand-offs, not new connection requests

  • Predictive: estimate directions and hand-off times of ongoing connections in each cell

  • Adaptive: dynamically adjust amount of reserved bandwidth to account for estimation inaccuracies and varying traffic/mobility conditions


System model l.jpg
System Model in Cellular Networks

  • Cellular infrastructure with a wired backbone and base stations as access points to mobiles in their cells

  • A hand-off fails if new cell does not have sufficient bandwidth

  • Solution: reserve bandwidth in each cell for possible hand-offs from its adjacent cells

  • Simple admission control of new connection requests:

    sum of current bandwidths + new bandwidth <=

    cell capacity – reserved handoff bandwidth

  • Reserved handoff bandwidth can be static, but then can not effectively handle varying conditions

  • Want to update it in a predictive and adaptive way before performing the admission test

  • Note reserved handoff bandwidth is a target, not actual reserved bandwidth

  • A base station needs to communicate its hand-off load to other other base stations


Hand off estimation l.jpg
Hand-Off Estimation in Cellular Networks

  • A cell’s base station maintains quadruplets:

    Time when mobile moved from current cell

    Previous cell before entering current cell

    Next cell to which mobile moved

    Residence time in current cell

  • Give less weight to quadruplets observed long ago

  • For a given previous cell, compute probability of going to some next cell given residence time in current cell


Bandwidth reservation l.jpg
Bandwidth Reservation in Cellular Networks

  • Given current time and time elapsed in current cell, estimate probability of connection handing off to some next cell within a time (estimation) window

  • A cell can then estimate the bandwidth required in some next cell for its hand-offs, and inform this adjacent cell

  • A cell computes its total bandwidth to be reserved for hand-offs from all its adjacent cells

  • Large (small) estimation window may lead to over-reservation (under-reservation)

  • Keep track of the proportion of hand-off drops to total observed hand-offs

  • If it exceeds target, increase estimation window

  • Otherwise, decrease estimation window


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Admission Control in Cellular Networks

  • AC1: simple admission control done in current cell only

  • Problem: cell overloaded with hand-offs from adjacent cells

  • Solution AC2: check available bandwidths of adjacent cells as well as current cell

  • Cheaper solution AC3: consider some adjacent cells only; those which “appear” to be overloaded


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Simulations in Cellular Networks

  • 1-dimensional system (e.g. cars on a highway)

  • Voice and video connections

  • Poisson arrivals and exponentially-distributed cell residence times

  • Static reservation is not effective under varying conditions (voice ratio, mobile speed, offered load)

  • AC3 is effective in meeting target hand-off dropping probability

  • Reserved bandwidth increases with offered load, video ratio and user mobility speed increase

  • As hand-off drops increase, estimation window increases

  • AC1 gives the most hand-off drops

  • AC2 and AC3 perform similarly and are fair (i.e. almost same new connection blocking probability in all cells)

  • AC3 is a better choice since it is less complex


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Conclusions in Cellular Networks

  • Meet connection-level hand-off dropping requirements by predicting hand-offs and adapting the estimation interval

  • Robust admission control of new connections

  • Higher dimensional systems, more realistic mobility patterns, use of readily available path/direction information, routing/re-routing over the wired backbone, …

  • Hierarchical architecture?


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