dynamic guard bandwidth scheme for wireless broadband networks ieee infocom 2001

Dynamic Guard Bandwidth Scheme for Wireless Broadband Networks

IEEE INFOCOM 2001

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Outline

Introduction Framework

Boundary approximation Estimation functionality based on GPS Dynamic guard bandwidth adaptation

Simulation Results Conclusion

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Introduction

Guard bandwidth / guard channel scheme Fixed Dynamic Proposed Scheme: Dynamic Guard Bandwidth Adaptation.

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Irregular Cell Boundary

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Approximating the Cell Boundary

Boundary Approximation Points (BAP). When a MT makes a handoff request, it is required to report

its position and its target handoff cell to the BS. The region around each BS is divided into M sectors, and the

reported handoff request positions within each sector are reduced to a single BAP, associated with a most likely target handoff cell .

The BAPs and their corresponding are stored in a table located at each BS.

The table could be updated based on handoff-request positions collected over a certain period.

nT

nT

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Estimating the Remaining Time to Handoff / the Target Handoff Cell

The trajectory of each MT is predicted to estimate the BAP that is likely to be closest to the actual handoff request location (Closest BAP, CBAP).

Each MT obtains its own position information at a regular time interval from its GPS receiver, and keeps track of its previous positions over the last (Q-1) intervals.

The current position of the MT is labeled as , and the previous (Q-1) points are labeled as … .

The MT’s direction of travel is estimated using linear regression over these Q points.

1 1,x y 1 1,Q Qx y

0 0,x y

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Method for the search of the CBAP: The M BAPs are divided into four quadrants, where points

(ag, bg), g = M(i-1)/4, M(i-1)/4 + 1, …, M(i-1)/4 – 1, lie in the ith quadrant.

Once the quadrant containing the CBAP is determined, a bisection search method is performed within that quadrant recursively until we obtain two BAPs that enclose the CBAP, and then we choose the closer BAP as CBAP.

O(log2 M) complexity.

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Important Points

The location information obtained from the GPS receivers are only used to estimate Tremain and Ctarget.

Actual handoff requests are still initiated based on received signal strength measurements, error rates, interference, and handoff protocols used.

The remaining time to handoff as well as the target handoff cell estimations are to be performed by individual MTs.

Distributed. The BS would not be overloaded with these computations.

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Important Points

This scheme has reasonable tolerance for prediction errors.

While the MTs could change direction and speed as it approaches the cell boundary, the target handoff cell prediction is erroneous only if the trajectory of the MT changes so much that it enters a different cell from the one predicted.

Predictions are made periodically and alternative reservations would be attempted if the previous decision has become invalid.

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Dynamic Guard Bandwidth Adaptation

Adaptation of wireless guard bandwidth: When a new call request arrives at a BS, the network shall

classify it into one of the I traffic classes that is supported. MTs make periodic predictions of Tremain and Ctarget every .

If Tremain is shorter than a threshold time (the remaining time to handoff threshold, RTHT), the MT will inform the target BS about its prediction, and the BS will increase BG accordingly.

T

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BG is only increased by a fraction of the actual bandwidth requirement.

Reservation ratio (RR). For a MT that belongs to traffic class i, with bandwidth

requirement Bi, and is anticipated to handoff to neighboring cell j within RTHT, the BG in cell j should be increased by RR(i,j) x Bi.

0 < RR(i,j) < 1, and it is dynamically adjusted based on measured values of PF(i, j).

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When to decrease of BG: The MT has entered the cell The call ends before the handoff The MT is no longer expected to handoff into the cell.

The BG for the cell is reduced if a handoff is not expected to occur within RTHT consistently over a number of prediction time intervals (the release Reservation Threshold Time, RRTT).

Typically the RRTT is set to a few .sT

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Adaptation of backbone guard bandwidth While handoffs into a radio cell could only originate from its

neighboring cells, handoff rerouting through a wired backbone link is dependent on network topology and the rerouting scheme used.

With the ability to predict the most likely handoff cell, the links whose BG need to be increased are limited to those between the COS and the target handoff cell.

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Admission control of new calls A new call of traffic class i is admitted only if

,

: spare bandwidth in link

: B in link G

: The set of linnks comprising the entire end-to-end connection, inclusive of the wireless link.

: The ba,

for all l l l i

S l Ll

G l Ll

L

Rl i

S G R l L

ndwidth requirement of a connection belonging to traffic class .i

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Admission control of handoff calls A common BG pool that is shared by different traffic classes

would favor those with smaller bandwidth requirements. A handoff call of traffic class i is only admitted if it satisfies

the following conditions:

, , ,1, 1

,,

,1

, if

, otherwise

: The set of links between the target handoff cell and the COS, inclusive of the wireless

I I

l l q l i l l qq q i q

l il l iI

l qq

S G R S G

GS R

G

L

link.

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Simulation Results

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Simulation Results

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Simulation Results

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Simulation Results

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Conclusion

Measurement-based approach. Suitable for heterogeneous bandwidth requirements. High scalability due to the distributed operation.

dynamic guard bandwidth scheme for wireless broadband networks ieee infocom 2001

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