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(a)
(b)
F IG . 3. Two allocation schemes. (a) Flat broadcast allocation. (b) Hierarchical broadcast allocation.
ure 3 is intended to distinguish this scheme from the flat broadcast allocation scheme
discussed in Section 3.1.1 . Assume six data items to be allocated to two broadcast
channels. Figure 3 (a) shows the flat broadcast allocation of the data items of two
broadcast channels of the same speed. Alternatively, Fig. 3 (b) depicts the allocation
of the aforementioned data items on two broadcast channels where the first channel
is twice faster than the second one.
3.1.1.4 Square-Root Based Allocation. Acharya et al. [1] made an
observation that in a broadcasting scenario minimum overall mean access time is
achieved when the instances of hot data items are equally spaced. Based on this
observation, Vaida and Hameed [62] proposed the so called square-root based allo-
cation algorithm that based on the demand probability (access frequency), the length
of the data item, and location of the broadcast data items in the past, determines what
data item from the data base should be broadcast next. Assume M , p i , and l i , respec-
tively stand for the number of the data items in the data base, demand probability of
item i , and the length of the item i . Furthermore, let R i stand for the time at which
an instance of item i was most recently appeared on the broadcast. Then
(Q − R i ) 2 ∗ p i
MAX (G i ) =
/l i ,
1 i M,
determines the next data item to be broadcast ( Q is the present time).
Assume the database is composed of three data items with (p 1 ,l 1 ) , (p 2 ,l 2 ) , and
(p 3 ,l 3 ) of ( 1 / 2 , 1 ) , ( 3 / 8 , 2 ) , and ( 1 / 8 , 4 ) . Figure 4 depicts the broadcast schedule
 
 
 
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