IT2200 Reader System with Multimode Capability Installation & Maintenance/Service Guide
2-14
Each sequence is equal to one valid transaction, and is composed of six RF data
packets. If the amount of time it takes to complete one transaction is equal to the total
length of the RF payment zone, then, because of a 95% effective RF link coverage, the
probability of completing that transaction is 73.51% (.95
6
). The probability of
obtaining each transaction if the RF footprint is greater than the time for one
transaction is shown in Table 2-1.
Table 2-1 Time and Distance Required to Complete Payment Zone
The value of 95% RF effective coverage is derived from variables such as nulls and
multipath in the RF field because of reflections and various forms of interference. A
properly mounted tag in a vehicle exhibits at least this 95% value. A 95% coverage for
a 3m (10-ft) zone would mean that 0.15 m (0.5 ft) of the 3 m (10 ft) is a null or no RF.
As shown in Table 2-1, the minimum footprints or payment zones for each lane to
achieve an accuracy of 99.97% are 1.7 m (5.6 ft) at 64 kph (40 mph), 2.8 m (9.2 ft) at
105 kph (65 mph), and 4.3 m (14 ft) at 161 kph (100 mph).
Figure 2-6 illustrates that a minimum of four transactions must be allowed to occur to
achieve the required accuracy. The minimum time for these four transactions is 96 ms.
Figure 2-6 Four Transactions Can Occur Within 96 Milliseconds
Figure 2-7 shows a timeline for a sample read-only transaction using the IT2200
reader system with Multimode Capability operating in ATA mode and an ATA-type
tag.
Number of
Transactions
Time to
Complete
Payment Zone
Distance to Complete Payment Zone (in
meters (feet))
Probability (%)
64 kph (40
mph)
105 kph (65
mph)
161 kph
(100 mph)
1 24 ms 0.4 (1.4) 0.7 (2.3) 1.1 (3.5) 73.5092
2 48 ms 0.8 (2.8) 1.4 (4.6) 2.1 (7.0) 98.5093
3 72 ms 1.3 (4.2) 2.1 (6.9) 3.2 (10.5) 99.9250
4 96 ms 1.7 (5.6) 2.8 (9.2) 4.3 (14) 99.9963
5 120 ms 2.1 (7.0) 3.5 (11.5) 5.3 (17.5) 99.9998
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