Mumbai university > Comp > SEM 8 > Mobile Communication

Marks: 5M

Year: Revised 2012

A. Cell dragging:

i. Cell dragging results from pedestrian users that provide a very strong signal to the base station.

ii. In urban areas when there is line of sight radio path between the subscribers and the base station as the user travel away from the base station at very slow speed, the average signal strength does not decay rapidly. Even when the user has travelled well beyond the designed range of the cell, the received signal at the station is above the handoff threshold, thus handoff is not made. But this creates a potential interference and traffic management problem, since the user has travelled deep within a neighbouring cell. This problem is called as cell dragging.

iii. This problem can be solved by adjusting handoff threshold and radio coverage parameters carefully.

B. Dwell time:

i. The time over which a call is maintained within a cell without handoff is called as dwell time.

ii. The dwell time of a particular user is governed by a number of factors like propagation, interference, distance between the subscriber and the base station and the other time varying factors.

iii. For stationary mobile user motion in the vicinity of base station and mobile produce fading, hence even stationary subscriber has finite and random dwell time.

iv. Dwell time vary depending on speed of user and type of radio coverage. For example cells which provide coverage to highway users with relatively constant speed, fixed well-defined path and good radio coverage dwell time is random variable highly concentrated at mean dwell time while for users in dense, cluttered microcell areas dwell time has large variation about dwell time and dwell time shorter than cell geometry is suggested.