Contents Telektronikk - Telenor

116
class 1
class 2
class 3
[1,1,1] [2,1,1] [3,1,1] [4,1,1] 5,1,1]
[1,2,1] [2,2,1] [3,2,1] [4,2,1] 5,2,1]
Base stations in layer 1 have 8 resource
units allocated to each of them. 12
resource units have been allocated to
each of the base stations in layer 2.
Some data for the mobile station classes
are given in Table 2. Both the space element
dwelling times and the total call
holding times are negative exponentially
distributed. Every space element has the
same mean dwelling time. The process of
initiating new calls is equal for all the
classes and in each of the space elements.
New calls are initiated according to a
Poisson process and the rate is used as
the free variable in the results given.
Five different cases of the configuration
have been compared. These cases are
defined in Table 3. Case I is the one pre-
(2,1) (2,2) (2,3)
(1,1) (1,2) (1,3)
[3,3,1] [4,3,1]
Figure 14 Schematic illustration of the example: 12 space elements, 3 classes of base stations
and 6 base stations (arranged in two layers). The space element routing is “wrapped”
Table 1 Coverage list for the space elements in Figure 14
Space elements Coverage list
[1,1,1], [1,2,1] {(2,1)}
[2,1,1], [2,2,1], [2,3,1] {(1,1), (2,1)}
[3,1,1], [3,2,1], [3,3,1] {(1,2), (2,1), (2,2)}
[4,1,1], [4,2,1], [4,3,1] {(1,3), (2,2), (2,3)}
[5,1,1], [5,2,1] {(2,2), (2,3)}
Table 2 Relevant times and radio capacity usage for mobile station classes
sented so far. This is used as reference
for the other cases, i.e. only modifications
compared to case I are described in
the following. In case II the class 1
mobile stations are allowed to use base
stations in both layers. An additional
base station (3,1) is introduced in case
III. This base station covers all the space
element and is reserved for mobile stations
of class 3. Then, these mobile stations
are not allowed to use base stations
in layer 2. Base station (3,1) is capable of
handling three mobile stations of class 3
simultaneously (6 resource units allocated).
The number of resource units in the
layer 2 base stations is reduced by 2 each
(that is, 10 in each of layer 2 base stations).
In case IV a hybrid capacity allocation
scheme is introduced. Each of the
base stations is allocated 4 resource units
as fixed. A maximum amount of resource
units possible to allocate a base station
has been set. A layer 1 base station cannot
have more than 12 resource units and
a layer 2 base station cannot have more
than 20 resource units. The capacity is
allocated in groups of 4 resource units.
There are 9 groups of resource units that
can be allocated dynamically. An interference
matrix is defined. This matrix
states that a resource unit cannot be allo-
mobile station mean space mean total call available base number of
class element dwelling holding time stations (layers) resource unit
time per call
1 1 8 2 1
2 5 8 1 and 2 1
3 2 8 1 and 2 2
cated to more than one base station at a
time (that is, one base station interferes
with all the others). Queuing of handover
calls are allowed for in case V. Every
base station has a queuing capacity of 2
calls. The allowed time in a queue is negative
exponentially distributed with a
mean value of 0.1, a maximum queuing
time of 0.2 is set. A handover call is allowed
to wait in the queue for up to 5
base stations at the same time (this is a
non-effective limit as no space element is
covered by so many base stations).
The space element blocking probability
is considered to be the main service quality
variable for this example. The blocking
probabilities that mobile stations of
class 1 experience in space element
[4,1,1] are depicted in Figure 15. We see
that the different cases influence the
blocking probability. The most significant
effect results for case V (queuing of
handover calls is allowed). In this case,
the blocking of handover calls is the
resulting effect of the queue being full
upon arrival and that the time-out interval
ends before the call can be served by
any of the base stations it has placed in
the queue. As seen from the mobile station,
the effect of each of these events
will be similar. For case V, the new class
1 calls get reduced blocking while the
handover calls of class 1 get an increased
blocking. An explanation to the latter is
that some class 1 handover calls may
face a situation where a class 3 handover
call is located in front of them in the
queue. As this class 3 call requires 2
resource units, it is more likely that it
stays in the queue until the time-out
interval is ended. Therefore, the class 1
handover calls are experiencing a higher
blocking, which again would allow for
more new calls to be handled by the base
stations. We also see that introducing
hybrid allocation of capacity, case IV,
does not seem to improve the situation
much in this example compared to case I.
Allowing the class 1 calls to use base stations
in both layers, case II, gives lower
blocking for this class. This was expected.
In case III, the class 3 calls are not
competing with class 1 and 2 calls for
capacity of base stations in layer 2. For
the results depicted in Figure 15, we see
that this results in lower blocking for
class 1 calls for lower load, when compared
to case III. However, for higher
load the result is the opposite. An explanation
of the latter may be that each of the
base stations in layer 2 has got reduced
capacity in case III compared to case II
and this effect is more significant when
the traffic load is high.