- •49 Cordless telecommunications
- •49. 1 Introduction
- •49. 1. 1 Analogue technology
- •49. 1. 2 H. F. /V. H. F. Analogue ct
- •49. 1.3 European 900 mHz analogue standard
- •49. 2 Digital technology
- •49. 2. 1 Areas of application
- •49. 2. 2 Main service principles
- •49. 2. 3 Traffic capacity
- •49. 2. 4 Digital cordless standards
- •49. 3 Ct2/cai digital specification
- •49. 3. 1 Radio aspects
- •49. 3. 2 Frame multiplex structure
- •49. 3. 3 Protocol structure
- •49.3. 4 Transmission plan and digital codec
- •49. 3. 5 Implementation
- •49. 4 Dect digital specification
- •49. 4. 1 Dect protocol architecture
- •49. 4. 2 Intel-working Units (iwu)
- •49. 4. 3 Spectrum resource
- •49. 4. 4 Detail radio aspects
- •49. 4. 5 Radio operational features
- •49. 4. 6 Frame structure
- •49. 4. 7 Transmission plan and digital codec
- •49. 4. 8 Implementation
49. 3. 1 Radio aspects
With only forty channels available to support the high traffic demands it was clear that the benefit of dynamic channel selection would be needed. Thus both handset and base are required to operate on any of the forty channel pairs through selection of the channel with the lowest co-channel and/or adjacent channel interference. This technique is more than adequate to meet the traffic capacity needs of residential and small business operations, but other techniques need to be exercised to raise the effective capacity to meet the requirements of larger business systems.
To increase the frequency re-use ability of the system in large buildings cordless business systems will need to use the multi-cell coverage techniques employed by cellular mobile systems. However, in a building the cells will be used on each floor consequently the cell structure has three dimensions to it and allowance must be made for signals passing through the floors as well horizontally through the walls of the building.
To ensure good and even coverage both antennae and radiating cables may be used to provide service in a large building complex as in Figures 49. 2 and 49.3 (Holmes and Swain, 1990).
A typical example for CT2/CAI coverage from an antenna is shown in Figure 49.4 (Swain, 1984) where measured signal levels and computed bit error ratios are indicated.
The detail parameters of the radio interface are given in ETSI (1991) but it specifies two level frequency shift keying with Gaussian filter shaping and a frequency deviation of 14. 4kHz to 25. 2kHz above carrier frequency to represent a binary 1 and equal shifts below the carrier frequency for binary 0. This represents a modulation index range of 0. 4 to 0. 7. As previously noted time division duplex transmission is used with 1ms for each transmit and receive packet. A dead time between transmit and receive bursts has been created to allow transmitters to ramp up and ramp down their power in a way designed to limit spectral splatter across adjacent channels. This period also permits oscillators to settle between bursts.
Exercise 1 Learn the words and word combinations
1 |
cordless |
с батарейным питанием |
2 |
handshaking |
подтверждение (установление) связи |
3 |
randomly selected binary codes |
хаотично отобранные бинарные коды |
4 |
radiated (radiation, radiant) power |
мощность излучения |
5 |
channel selection |
переключение каналов |
6 |
interference |
интерференция, взаимное влияние |
7 |
co-channel interference |
внутриканальная помеха, помехи совмещенного канала |
8 |
common channel interference |
помехи совмещенного канала |
9 |
acceptable interference |
допустимая помеха |
10 |
adjacent channel interference |
помеха соседнего канала, межканальная помеха |
11 |
burst mode |
1) режим пульсирующего трафика (при передаче информации); 2) режим ускоренной обработки (путем одновременного выполнения пересылки и обработки данных) |
12 |
handover |
переключение, переход; затягивание (сигнала) |
13 |
traffic density |
плотность трафика |
14 |
good |
необходимое качество |
15 |
splatter |
искажение речи |
16 |
binary code |
двоичный код |
17 |
allowance |
поправка (при изменении); допуск, норма |
18 |
ramp up |
линейно нарастающая характеристика |
19 |
ramp down |
линейно снижающаяся характеристика |
20 |
transmission capacity |
передаваемая мощность |
21 |
radio spectrum |
спектр радиочастот |
22 |
cordless telephone |
переносной радиоприемопередатчик, работающий в качестве телефонного аппарата, телефонная трубка |
23 |
ubiquitous |
вездесущий, повсеместный |
24 |
traffic capacity |
пропускная способность информационных потоков |
25 |
time interleaved burst mode |
режим пульсирующего трафика с чередованием времени |
26 |
radio link |
радиотракт, радиосвязь, линия радиосвязи |
27 |
coding algorithm |
алгоритм кодирования |
28 |
frequency shift keying |
частотная манипуляция |
29 |
carrier requency |
несущая частота, частота несущей |
Exercise 2 Read the text
Exercise 3 Give the Russian equivalents for the following English ones:
1 |
an instant success |
2 |
the quantity of illegal imports |
3 |
to be on the verge of |
4 |
to increase the basic production cost |
5 |
a handshake process |
6 |
the CEPT standard |
7 |
to use any available radio channel |
8 |
the benefits of DCS |
9 |
a major step forward |
10 |
consequently |
11 |
without incurring the costs |
12 |
limited traffic carrying capabilities |
13 |
in-call handover between cells |
14 |
a wired telephone |
15 |
traffic capacity |
16 |
the multi-cell coverage techniques |
17 |
a dead time between transmit and receive bursts |
18 |
to limit spectral splatter |
Exercise 4 Answer the following questions:
1 |
When and where did cordless telephone products first appear? |
2 |
What European countries was the cordless telecommunication successfully exported to? |
3 |
What are the basic technical characterics of the UK version of h.f. / v.h.f analogue CT? |
4 |
Is this technology the same in France and in America? |
5 |
What are the four general characteristics of the CEPT standard? |
6 |
What do you know about the benefits of DCS? |
7 |
What are the main areas of application and the main service principles of digital cordless technology? |
8 |
Do the two digital cordless standards (DECT and CT2/CAI) have much in common? Whose demands do they meet? |
9 |
What advantages does the duplex transmission have? |
10 |
How can cordless business systems increase the frequency re-use ability of the system in large buildings? |
Part II (49.3.2 – 49.3.5)