Discussion:

1.2 Determining the Time of Handoff Requests Reservation

 

The handoff request reservations takes place prior the actual acceptance of handoff calls. The acceptance of handoff calls means that the new BS should allocate bandwidth for the calls. Here, an enhanced scheme to determine the Reservation Deadline (RD) is proposed. Thus, a time instance limit for the bandwidth assignment of the arriving handoff call is expected to be completed.

 

To avoid the blind selection of the start point of Bandwidth reservation for handoff requests and reducing the signaling traffic overhead, the concept of Non-Reservation-Zone (NRZ) with a radius of size Threshold Distance (TD) in the current cell is defined in this research (Fig.1).

abc

 

Fig 1- Time of handoff requests reservation[12]

In NRZ, there is a high probability for the MS to make a dramatic change in its direction and speed. However, if the MS moves beyond NRZ, the chances of sudden change of direction are reduced. In this paper, the radius of NRZ is the value should be large enough so that once the MS moves beyond NRZ, which is very close to the cell boundary the change are reduced.

 

The relationship between the Received Signal Strength (RSS) and distance d from the transmitter in the BS is determined by the following equation [11]:

 

RSS dB = −10γ × log (di),

Where γ is the propagation path-loss coefficient [typically, γ = 2 for highways and γ = 4 for micro-cells in a city] and di represents the distance (of the transmitter to the MS) between the MS and base station of celli. This can be further expressed in terms of the MS’s position (x(t), y(t)) at time t and the location of base station (ai , bi ) as follows:

 

     di = [(x(t) − ai )2 + (y(t) − bi )2]1/2

The MT’s position (x(t), y(t)) at time t can estimated by GPS or RSS.

To determine the value of RD, the following two criteria are considered:

a. The RSS level of current BS. If the level drops below a threshold RSS2, it indicates the difficulty to maintain communication with MT.

b. The RSS level of next BS cell is stronger than that of the current BS by a given hysteresis margin ∆.

 

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