In the above-stated drawing the centralized option is represented. The TsKPS major function is identification the EXPERT and her detection in the roaming mode. Except that TsKPS carries out all operations necessary for mutual settlements between the operator and the user.
If the number working the EXPERT is great, Pci sum will change at addition several more EXPERT a little and, respectively, h Thus will decrease a little, we change deterioration of communication for increase in capacity. Other way consists in a transfer speed exchange for number of subscribers.
Size D decides proceeding from cross hindrances between honeycombs on an identical set of frequencies. Thus operate not with absolute value of D, but D/Rc ratio, where Rc – radius honeycombs. From a ratio find the necessary power of the transmitter.
Casual access to the channel has a negative side. At big activity of subscribers when the probability of collision of packages of Ra exceeds 18%, time of a delay of transfer of a package in relation to length of a package begins is inadmissible grow.
Here it is important to choose correctly R0 and D value taking into account requirements of high capacity and restrictions for speed of a control system of a network and for power opportunities of the equipment intended for transfer on a radio channel.
The choice of methods of coding is defined by nature of grouping of mistakes in the channel. At independent mistakes it is enough to use the powerful correcting code (the block code or is more often svertochny to. At the correlated mistakes it is necessary to apply the codes correcting packages of mistakes, however these codes have big redundancy therefore apply a combination of block and svertochny codes, using a svertochny code for correction of single mistakes, and block – for detection of uncorrected mistakes.
Analog standards, where the main service – a speech transmission, and in an analog form belong to the 1st generation at a WC and frequency division of channels. Standards of the 1st generation were developed independently in the different countries and intended for use by each country of the standard. Main standards of the 1st generation: NMT-450 (Scandinavian countries) and AMPS (SSh.
1st generation; the analog; speech transmission of 300 - 3000 Hz; WC; deviation of 5 of kHz; strip of 25 kHz; step of a grid of 25 kHz; strip of system of 4,5 MHz; 180 duplex frequency channels; FDMA; management of access from outside the EXPERT – self-governed access.
Standards of the 2nd generation – digital, that is the speech is transferred in a digital form, besides data with low speed can be transferred (to 9600 bits/sec.), use temporary division of channels, FM and its options, the roaming mode is provided. Standards: GSM-900 (Pan-European) (GSM-180 with division of TDMA-FDMA channels; D-AMPS (America (DCS-180, IS-54, IS-13 with division of TDMA-FDMA channels; IS-95 (America, South Korea, China, Gonkon with division of CDMA channels; Japanese standard.
The above advantage was the reason of that for commercial mobile communication cellular principle is used. Trunking systems exist and develop, but, mainly, are applied to so-called corporate communication.
Each sota has to serve lmax of subscribers. For this purpose Fsoty=lmaxfa is required. For all system – F=k lmaxFa, where k – coefficient of a reuse of frequencies of k1/3 (D/R2; total number of subscribers of N=lmaxL, where L – number of honeycombs in the territory of service, L1,21(R/R2; frequency efficiency of cellular =N/F3,6(R/R2 system / (Fa (D/R
Now it is considered that uniform, the general for all, the standard of the 3rd generation will not be, and there will be a set of various standards defining the recommended directions of development of already existing most advanced standards.
The first option – the systems working at one frequency used the POCSAG code with a speed of 1200 bits/sec., transferred 126000 voice-frequency calls an hour. The principle of construction – cellular, with synchronous division.
For control of an equalizer as a part of each package the training sequence known on the reception end is transferred, and control is made by criterion of the minimum error of reception of this sequence.