Advanced Video Distribution for Wireless E-Healthcare Systems - E-Healthcare Systems and Wireless Communications - page 356

both systems. A new approach to the definition
of handoff is required.
This section presents these schemes and clas-
sifies them into categories based on the concepts
they adopt (Katzela & Naghshineh, 1996).
Non-Prioritised Handoff schemes do not al-
locate priorities to handoff calls over originating
calls for this scheme. The forced termination
probability is relatively higher than normally
anticipated (Yi-Bing & Mohan, 1994; Anderssen,
2005). The scheme does not differentiate handoff
and initial (originating) calls. An initial call or a
handoff call will be served, as long as there is a
channel available in the cell. Otherwise, if there
are no free channels, the request is blocked im-
mediately. This non-prioritised scheme is able to
minimise the call rejection and has the advantage
of efficient utilisation of the available frequency
spectrum. However, this scheme is not suitable
for multi-service environments like healthcare
information systems (Vegados, 2007).
Prioritised Handoff Schemes provide improved
performance at the expense of a reduction in the
total admitted traffic and an increase in the block-
ing probability of new calls (Katzela, 1996). All
handoff prioritisation approaches can provide
handoff requests precedence over the new session
requests (Diederich & Zitterbart, 2005), but the
improvement in the performance is related with
the way each scheme gives priorities to handoff
calls. Several handoff prioritisation schemes,
that support different services and different traf-
fic requirements, can be found in the literature
(Lee, 2005; Ye, Law & Krishnamurthy, 2006;
Ojesanmi, 2009; Weithoelter & Hoene, 2003).
These handoff prioritisation schemes can be
further classified into:

• Handoff queuing schemes which give pri-

ority to handoff attempts by permitting
them to queue instead of denying access, if
the potential new base station is busy,

• Channel transferred schemes which in the

case of unavailable channels accommodate
a handoff call request, e.g. a channel from
a neighbouring cell may be transferred,

• Subrating schemes for certain channels are

allowed to be temporarily divided into two
channels at half of the original rate to ac-
commodate handoff calls,

• Genetic schemes use genetic algorithms in

order to assign the channels by local state-
based call admission double-threshold
policies,

• Hybrid schemes which are combinations

of channel reservation, handoff queuing,
channel transferred, genetic and subrating
schemes, the key idea is to combine the
different prioritisation policies to further
decrease the blocking probabilities or to
improve the channel utilisation) (Vergados,
2007).

Priority Schemes for e-Health Services: Within
the e-Health environment it is possible to define
three types of calls based on the level of urgency:

• The highest priority, calls from ambulanc-

es and emergency calls,

• Secondly, calls from seriously ill patients

(for example with chronic diseases, etc),

• Finally other calls which do not use real-

time applications (request to a database or
some statistical data, etc.).

These are summarised in (Hu & Kumar, 2003)
where three types of medical services for the
sensor-based telemedicine network are introduced:

• Channel reservation schemes which offer a

method to increase the number of accepted
handoff requests by reserving a number of
channels exclusively for handoff requests,
in a predictive or non-predictive manner,

1. Real-time calls from Ambulance Patients .
These calls are given the highest priority
because the level of urgency is the highest