Spectrum resource
Date: 2015-10-07; view: 442.
Intel-working Units (IWU)
The transmission of information to end users beyond the DECT link requires additional protocols that are outside the DECT specification. Thus to interface a DECT link with, say, a GSM fixed part will require an appropriate IWU to establish proper unambiguous message transfer and in the process influence the service standard to be offered. Clearly the IWU concept will play a very important role in the full exploitation of the DECT specification.
Throughout Europe the band 1880MHz to 1900MHz has been set aside for use by the DECT system. This 20MHz of spectrum must however be used efficiently and flexibly if it is to meet the requirements of high capacity business systems. It is the main purpose of the Physical Layer to bring this about by ensuring that adequate capacity radio channels are created in a manner that permits high orders of radio channel re-use. The DECT spectrum resource has been distributed in space, frequency and time.
Spatial distribution is brought about because DECT supports the use of the well-known concept of cellular radio channel re-use. In this process the area to be served is covered by a number of base stations, each of which provides radio coverage over a limited radius. This radius is typically of the order 20-50 metres depending partly on the construction nature of the building being served but more likely on the density of telecommunications traffic to be catered for. In this latter case each small cell is able to offer a certain number of radio channels and the smaller the cell the shorter the distance away the same channels can he re-used with acceptable co-channel interference ratio. This is the classical cellular frequency re-use concept that gives very high orders of spectrum efficiency, expressed in terms of Erlangs per MHz per sq. km.
Frequency distribution is achieved by segmenting the available band into ten carrier frequencies from 1881. 792MHz to 1897. 344MHz and separated by 1728 kHz.
Time distribution has been achieved by employing time division multiple access (TDMA) coupled with time division duplex transmission (TDD) to provide two-way communication on the same carrier frequency.
Exercise 1 Learn the following words and word combinations
| to interface | согласовывать, состыковывать | |
| back-end interface | интерфейс (для связи) с базами данных; внутренний интерфейс | |
| baseband interface | сопряжение по частоте модулирующего сигнала | |
| bit-serial interface | последовательный интерфейс; последовательный стык | |
| front-end interface | входное устройство сопряжения; внешний интерфейс | |
| PHL (the physical layer) | физический уровень | |
| MAC (the medium access control layer) | Промежуточный уровень управления доступом | |
| NWK (the network layer) | уровень сетевой иерархии | |
| spatial (space) distribution | пространственное распределение | |
| frequency distribution | частотное распределение | |
| time division | распределение по времени; временное распределение | |
| TDMA (time division multiple access) | многостанционный доступ с временным разделением каналов | |
| multi-carrier TDMA | мультичастотный многостанционный доступ с временным разделением каналов | |
| common spectrum | совместная спектральная плотность | |
| radio access | радиосвязь с абонентами | |
| bearer | 1 носитель 2 Однонаправленный канал, передача данных | |
| collision detection | обнаружение столкновений (в сети) |
Exercise 2 Read the text
Exercise 3 Give the Russian equivalents for the following English ones:
| around the mid 1980's | |
| a digital cordless telecommunication standard | |
| multi-carrier time division multiple access | |
| eventually | |
| the coexistence interface specification | |
| ISDN-based applications | |
| to conserve spectrum for other users | |
| the GSM digital cellular fixed network | |
| public intelligent telecommunication networks | |
| to multiplex and demultiplex all information | |
| to provide very reliable data links | |
| in support of | |
| the transparent unprotected service | |
| to meet the requirements of | |
| the density of telecommunication traffic | |
| the smaller the cell the shorter the distance | |
| the available band | |
| in this latter case |
Exercise 4 Answer the following questions:
| What led to DECT? | |
| What levels of standardisation does DECT have? | |
| What do you know about the application areas of DECT? | |
| How can you prove that DECT has the capability to become an access technology that is integrated with the network? | |
| What can you tell about the DECT protocol architecture, its four layers and their functions? | |
| Why do IWUs play a very important role in the full exploitation of the DECT specification? | |
| How has the DECT spectrum resource been distributed in space, frequency and time? | |
| Does the DECT system meet the requirements of high capacity business systems? |
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