Problem 1/1: 1. The design of handoff algorithms depends to a large extent on th

Question

Problem 1/1:

1. The design of handoff algorithms depends to a large extent on the user mobility pattern defined by the speed and direction of movement. For a fast moving MT, the speed is the dominant parameter in determining the cell boundary crossing.

(a) Explain why, with fast moving mobiles, speed is more dominant in characterizing the use mobility pattern than direction?

(b) Consider the situation in which, when the MS initiates and establishes a connection, its current location is 10 km from the cell boundary along the direction it is currently traveling. Also, the mobile is moving at a speed uniformly distributed between 40 km/hr and 60 km/hr. Calculate the mean time for the mobile to reach the cell boundary.

(c) In an MAHO scheme, the mobile sends profiles containing the signal strengths received from all neighboring BSs in the same MSC. If a profile is sent every three minutes on average, what is the mean number of profiles sent before the mobile crosses the boundary?

Explanation / Answer

Several handoff decision algorithms exist and can be utilized to make the correct decision to handoff the ongoing connection
Measurement phase: The measurement of the overall link or communication quality is measured either by the base station, the mobile station or both. The measurement data is processed and evaluated again by one or both of them and appropriate action is taken according to the result of the evaluation; perform handoff or don’t. The measured parameters could be: Received useful and total power in up- and downlink, interference levels in up- and
downlink, received signal levels from the neighboring reference BS/AP, bit error rates in both up- and downlink, estimate of the distance between the terminal and the BS/AP, and estimate of the terminal velocity.

Initiation and resource allocation phase: This phase includes the decision whether a handoff is needed, regardless of the actual availability of a new channel on a target (or on the serving) base station; it is based on processed measurement results or network variables, including offered traffic. Once the need for the handoff is determined, the new channel is selected taking the actual radio resource availability and network load into account.
Execution phase: Once the new channel is selected, the handoff is executed. The measurement results, which thedecision phase is based upon, may be incorrect or exposed to noise, thus making the decision inappropriate for the situation. Handoff decision algorithms, that execute the aforementioned handoff phases,
can be categorized based on the form of input that the algorithm exploits when making the handoff decision.
Quality-driven algorithms are those considering bit error ratio (BER), packet error ratio (PER) or frame error ratio (FER) as input for the decision to be made.
Mobility-driven algorithms rely on the estimates of link distance and mobilespeed. The connection of a fast-moving vehicle may be switched from small cells to larger cells to avoid frequent handoffs. In reality this class of
algorithms is by far the most challenging, as accurate location information is hard to come by, even though location estimation accuracy is rapidly increasing thanks to ongoing research in this area.
Traffic-driven algorithms: The initiation and decision phases take estimates of traffic load (channel occupancy) into account. This type of handoff initiation is essential for equal load sharing among different serving points of
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