CDMA in the systems 3G

1) spectral Efficiency:

It is the relationship between the demanded binary rhythm in a cell and the band to disposition of the service, in order to increase it it can or be reduced the dimensions of the cell or to increase of to the K ability that is the number of simultaneously servibili customers for cell.

 

2) Advantages of the CDMA:

The CDMA concurs to re-use all the band in an adjacent cell, that is the cluster it is composed of a single cell, of it derives greater a spectral efficiency since in the formula of same dimension m of the cluster it appears to the denominator.

 

3) Probability outside service:

The system capacity K can be increased in indiscriminate way sin when the offered service continuous to maintain to a advanced quality to a level limit, this is determined from the interferences that they grow simultaneously to growing of the number of connected customers determining therefore a Hard-Blocking or a Soft-Blocking.

 

4) Hard-Blocking and Soft-Blocking:

Hard-Blocking is had when the system once caught up the number of the maximum customers does not concur the access with new customers while the Soft-Blocking is had when the quality of the service decreases gradually until to the block of the income per new customers, is the case of the CDMA in which the income of new customers ago that you increase the interference, until arriving to an inferior relationship S/I to that one demanded for one quality of the acceptable service.

 

5) coherent Reception:

The coherent reception is a reception assisted from a pilot who concurs to extract of the parameters of synchronization like pure of the information on the power, such coherent reception in the IS-95 is possible in reduction in how much in climb only has difficulty sincronizzare the receivers between they.

 

6) inner and external Interference:

The inner interference is that due to the other present customers of the service in the same cell, evidently if it marks them that it reaches from a determined customer is the much widest one regarding what reaches from an other customer, will be a soffocamento effect and therefore will come received the solo marks them more fort, is therefore important that the SRB executes a power control is it to chain sluice that to open chain so that they reach to it all almost marks having them the same level. The external interference is instead due to the adjacent cells and is approximately par to the half of the inner interference.

 

7) Synchronization of the SRB:

The synchronization of the SRB is much complex and expensive, in system IS-95 it is carried out leaning itself to system GPS, it concurs to manage the soft handover in optimal way in how much can be carried out a comparison between the various ones marks them receipts in correspondence of a same emission is in band base but above all to radio frequency by means of a receiver RAKE who couples itself to various you walk multiple.

 

8) Sequence PN overlapped to weft CDM:

Every station radiobase adds to the CDM a sequence PN that identifies it, in system IS-95 the sequence is only for all the SRB but sfasata while in the UMTS a sequence for every SRB is had, this between the other it concurs I re-use of the codes in adjacent cells.

 

9) Techniques CDMA:

to)       DS-CDMA

b)       W-CDMA

c)       TD-CDMA

d)       MC-CDMA

and)       OFDM-CDMA

 

10) Techniques in order to improve the performances radio:

The scope of these techniques is to reduce the interference in the channel, to such purpose can be adopted two strategies:

to)       limiting the amount of interference generated in the channel with strategies like the activity and power control

b)       to improve the quality of the systems of transmission by means of techniques of time diversity (codes), space (handover), frequency (rake).

11) Control of power:

The technique of the power control concurs to reduce the inner interference, in particular the IS-95 uses an control system to cycle opened in the sense that the receiver currency marks received them from the BTS, assumes that it marks them from emitted it endures the same attenuation and therefore it deduces the level of power with which transmitting, the made assumption is however enough rough in how much uplink and downlink they happen to various frequencies. The control instead comes made from the SRB that it carries out of the measures of marks received them from a data finishes them mobile, and communicates to same the eventual modifications of the emission power. In the comparisons of the external interference that is worth the half of that inner one, no sagacity cannot be taken.

 

12) Control of transmission activity:

In a vocal conversation, there are of the pauses of the spoken one that they last approximately 60% of the time, can be reduced the interference of 60% simply recognizing these pauses and avoiding to transmit during the same ones.

 

13) Settorizzazione of the cell:

The settorizzazione of the cell improves the ability to a system CDMA is in downlink that in uplink, in uplink in fact the SRB it picks up power from minor a number of finishes them interfering while in downlik the same one smaller power regarding the case of omnidirezionale antenna can be allowed to irradiate one.

 

14) Codifica of channel:

It codifies of channel is time to the improvement of the performances of the system, it is but best adapted to characterize of the errors scatters to you that of the burst of errors therefore it always does not come associated to a interleaving that it can be is simple that convoluzionale.

 

15) Receiver RAKE:

Is multiple receiver thought so as to to take advantage of the way rather than to endure them, in particular 3 correlatori that demodular mark them from the 3 more way multiple to elevated power, in the IS-95 are had are then a fourth tooth of the receiver who takes care itself to try between all the other way multiple if ce n' it is one to such power to enter in the group of the 3.

 

16) Soft Handover:

Verification when they finishes that she must pass from a cell to an other in a narrow within spaces receives them the same one marks them from both the BTS, is fundamental therefore that it is equipped of Rake receiver. Once that the handover has been taken place, the BTS of the cell of origin must stop to transmit towards that piece of furniture in how much otherwise generates interference.

 

17) Softer Handover:

It is the handover soft carried out between two various fields of a partizionata cell, comes true thanks to the lobes of cancellation not perfectly selective of the antennas.

 

18) Codes to tree:

They are to the base of the W-CDMA and of the TD-CDMA, they concur to make that various give-installments produce always the same binary rhythm in escape, as an example are associated a shorter code to give-installments discs of a valve and a longer code to fast give-installments.

 

19) intelligent Antennas:

Draft of antennas in a position to realizing a cancellation lobe much strait that goes centered around the customer who agrees to serve, in such a way reduces the interference is in uplink that in downlink.

 

20) Detections multicustomer:

The SRB knows all the codes of marks them to it addresses to you therefore can execute a combined demodulation of all marks them with the scope to reduce the inner interference

 

21) Characteristics IS-95:

It is a system based on the CDMAone, draft of a DS-CDMA that implies a band of 1,2MHz. It introduces characteristic following:

to)       soft handover

b)       Rake receiver in finishes them

c)       settorizzazione

d)       power control

and)       control of transmission activity