Predictive and Adaptive Bandwidth Reservation for Hand-Offs in Cellular Networks

1
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

2
System Model

• 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 lt
  
• 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

3
Hand-Off Estimation

• A cells 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

4
Bandwidth Reservation

• 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

5
Admission Control

• 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

6
Simulations

• 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

7
Conclusions

• 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?