6.4Isolated performance for narrowband TDMA

Due to the lower bit rate, narrowband TDMA systems are able to provide a lower capacity for a single carrier but with lower power threshold level as well. In fact the useful bit rate provided by narrowband TDMA system is, as a reference value, 0,32 Mbit/s. By means of relationship (11), it is possible to obtain the power threshold level for a narrowband TDMA system based on 0,32 Mbit/s basic rate. By means of table 9 it is possible to verify the gain on power threshold level with respect broadband TDMA stated in subclause 4.4.

Table 9: Threshold power level for narrowband TDMA based on 0,32 Mbit/s the basic rate (e.g. five channels at 64 kbit/s)

6.5Cellular deployment performance for broadband TDMA

As stated in subclause 4.5, cellular deployment means that a certain number of frequencies are reused in other cells (or sectors) properly distanced. This means that a certain amount of co-channel interference has to be taken into account during link budget calculation. The presence of co-channel interference causes an increment of the power threshold level because it acts like an additional noise power at the input of the receiver. In this context, relation (4) can be evaluated by adding a contribution for each cell (or sector) working at the same frequency on the basis of subclause 4.5 rules. Supposing the interference as a gaussian noise, a general figure on power threshold level with co-channel interference can be evaluated by means of the following equation:

I TOT

bandwidth of the receiving filter.

At any rate, the best way to evaluate this figure is by means of measured sensitivity curves provided by the manufacturers.

6.6Cellular deployment performance for narrowband TDMA

In cellular deployment for narrowband TDMA the same approach as for broadband TDMA can be assumed even though some differentiation are necessary. As stated in subclause 4.4, the use of narrowband TDMA systems neither allows to improve system's capacity nor to reduce the cluster size. However, such systems introduce a very important degree of freedom which means a higher number of available frequencies. Such a feature has a great impact on frequency management due to the fact that the network designer is able to obtain a better trade off between the number of deployed frequencies and user penetration. In fact, to use a broadband TDMA system to cover a low populated area with a small degree of penetration means to obtain a coverage with a low spectral efficiency. On the other hand, the possibility to deploy a number of frequencies closer to the required capacity allows to obtain a better coverage of the whole area and, perhaps, a lower amount of bandwidth occupation.

As for broadband TDMA systems, a general figure on power threshold levels with co-channel interference can be obtained from relationship (20).

ETSI