The C- network ( wireless telephone network -C) was an analog cellular mobile radio network of the German DeTeMobil (formerly German Federal TELEKOM ). It was the third and at the same time last analog generation of mobile communications, which was used as a system only in Germany, Portugal and South Africa. Other countries in Europe ( such as the C- grid in Austria or the Natel C in Switzerland) used other standards, such as NMT and TACS. This heterogeneity prevented an international roaming of users and was one of the main motivations to start with the development of GSM. The C-net was primarily designed for telephone communication applications (car phone network ) with access to the telephone network and ISDN.
The C-Net was founded in 1984 ( officially: 1985 ) introduced in Germany and replaced the cumbersome handling of the B- and B2 - network. The C network was limited to Germany, Portugal and South Africa, however, a higher diffusion rate initially as the digital networks in their introduction to the D network in 1991. Due to the initially better accessibility especially in rural areas was the C-net in the car phone area still until the mid- 90s first choice. Also on ships near the coast of Germany was a C network device remain on board de facto standard. During the time of German reunification in 1990, West German owners of C-network phones could use when staying in East Berlin her phone and be spared the time-consuming assignment of a telephone call in the GDR landline.
A wide coverage (about 15-20 km radius) and small cells (2-3 km ) realized in large cell in the metropolitan areas. With the introduction of the C- net, the net of two mobile switching centers and 175 wireless zones or base stations existed. The C network could accommodate approximately 800,000 participants ( in the final ). Capitalized radio links were when changing the radio cell passed (handover). The C-Net participants was within the coverage area under a uniform access code ( 0161 ) and pager number accessible. On 31 December 1988, there were already 98 762 nationwide and in the state of Berlin 2076 C network participants. In addition to the limited number of C network were also the comparatively small voice quality and the high risk of eavesdropping criticisms of the C network. The so-called speech scrambling was enabled by default, but was merely an inversion of the speech band, which could be reversed with low technical means. In poor connections the user could even turn off this, and thus improve clarity.
The C- grid system is the first system supported the separation of subscriber identity and terminal. The subscriber identity and access rights were encoded on a magnetic card. This means that any mobile phone a user has been assigned by inserting this card. 1988, the magnetic strip is replaced by the calling card with an integrated microcontroller. In order for this concept was the forerunner of today's known SIM card.
For that time unusual were the functionally well-stocked listeners who possessed all controls, LCD display and LEDs. The button set was constructed according to the CCITT recommendations, and other man-machine interface was controlled by a FTZ guideline for all manufacturers, so that the user had no device-specific adjustment problems, but basically states such as " booked ", " connected " or " speech scrambling on" got in a well known form.
The C-Net offered in comparison to the previously known analog cellular networks, a handover function, which was not controlled by the field strength, but by the relative distance to the base station. This handover was possible even under the best radio conditions, which was a very useful feature in network planning and the compression of frequency reuse. Even so, the Gleichkanalstörwahrscheinlichkeit was significantly reduced. In order to support the relative distance measurement, however, additional technical effort for a time synchronization of all base stations was required, namely one another. In order to realize this nation or across the network, having each base station specific transmitter and receiver for synchronization signals.
Compared to the A- and B- mains power there was in the C network many " breakthrough " innovations that have long taken for granted today, for example:
- Common prefix ( 0161 -) for all mobile subscribers, you did not have to know where the participants resided in contrast to the A- and B network
- Seamless handover from one radio station to another (handover)
- Concealment of the ( analog ) radio signal difficult eavesdropping
- Next fixed-mounted devices and removable or even portable devices (mobile phone) possible.
- " Huge" capacity up to 850,000 subscribers (A - Net: 10.500, B network: 27,000 )
- Since the end of 1990 voicemail and call forwarding as a network feature ( until then only as a hardware accessory).
The operation of the C network, which was launched on 1 May 1985, was discontinued on 31 December 2000, except for some radio cells at the German -Dutch border, which were further operated for several months. Until the last years of the network, the German Telekom sold nor contracts for the now "C -Tel " mentioned system. Rates were generally more favorable than those in the digital mobile communications.
Railnet ( German Rail / T-Mobile)
The frequencies of the C network to be used in the future for Railnet ( Internet on the train ). The Telekom, which operated the C- network until 2000, is represented with her daughter Telekom Germany at Railnet. For the supply train in the WLAN is used, the connection between Zugserver and stationary antennas is made using Flarion. As a backup, UMTS and GPRS can be used, where GPRS is no longer used for transmitting Internet traffic. For the further expansion ( speeds over 300 km / h) but UMTS is inappropriate, because the transfer rate decreases with increasing speed rapidly. The data transfer rates of FLASH-OFDM are a maximum of 3.2 Mbit / s cumulative, thereby arise for the downlink about 2.5 Mbit / s and uplink 800 Kbit / s The big advantage over UMTS are the low latency of less than 50 milliseconds and an integrated Quality-of- service support. Thus, every user is in train a broadband connection. The North American company Flarion Technologies, developer of the FLASH-OFDM technology was bought in August 2005 from the competitors Qualcomm. A total of about 150 stations nationwide are on the air, there are investments from Qualcomm, type RR2000. Thus, a cover of the railway lines Dortmund and Munich and Frankfurt -Hamburg is guaranteed (as of November 2010).
- Frequency range:
- Transmitting power:
- 222 radio channels
- 287 radio channels from 1991 through frequency step change from 20 kHz to 12.5 kHz and 10 kHz
- Transmission of signaling data by dividing the audio signal ms in each 12.5 long audio blocks and their 10%, temporal compression to insert into the thus formed, 1.25 ms long gaps 4 -bit data telegrams
- Audio Modulation: Phase modulation 14F3
- Data modulation: binary frequency shift keying