Implementation

Date: 2015-10-07; view: 451.

Transmission plan and digital codec

DECT is subject to the same constraints as applied to CT2/CAI in terms of transmission performance. It is notable that both use the same codec standard and hence offer the same basic speech quality level. However, since DECT employs TDMA working the inevit­able consequence is that DECT loop delay amounts to about 25ms. Such a delay cannot he tolerated in the local public network in the presence of speech echoes from the DECT handset. At present two approaches are being taken towards the amelioration of this effect:

1. By designing handset with virtually zero echo return. This calls for high orders of acoustic coupling loss between handset ear and mouth pieces approaching 46dB.

2. A combination of good handset design combined with the use of acoustic echo cancellation or control.

The latter seems to be preferred. Unfortunately the problem of echo cancellation and control in terminal equipment is not an independent design exercise as care needs to be taken to ensure that there are no unfavourable reactions with similar devices already in place on long distance connections, e. g. over a satellite link.

To achieve success the basic production cost of DECT must be low. Thus the same objectives that were seen to he important to CT2/CAI's cost basis are equally applicable to DECT, i.e. the adoption of common components and large scale production to achieve the full cost benefits of scale.

Furthermore, equipment installation practices must be developed that can guarantee standards of communication quality that the customer has come to expect from the more conventional wired terminal equipment.

Exercise 1 Learn the following words and word combinations

Exercise 2 Read the text

Exercise 3 Give the Russian equivalents for the following English ones:

Exercise 4 Answer the following questions: