Operating Manual Vol 1 - ES Documentation

Digital Standard 3GPP W-CDMA (FDD)SMIQ2.14.3.4 Effects on Crest FactorThe crest factor of the signal is mainly influenced by the following parameters:• Link directionBy modifying the Q component of the scrambling code in the uplink, it is possible to avoid everysecond zero crossing. In contrast to the downlink, the crest factor is reduced by approx. 1.8 dB.(Standard case DPCCH + 1DPDCH, the effect decreases with increasing number of channels.)• Timing offset (see 2.14.3.3.5)In the case of more than 10 channels, an increment of 1 (i.e. the first channel is assigned 0, thesecond 1, etc.) causes a low crest factor. With a small number of channels, an increment of 3 or 5permits to obtain even better values.• Sequence length if timing offset is activeLonger sequences cause higher peak values and hence higher crest factors since the probability ofeven higher peak values increases.• Number of channelsMore channels cause higher crest factors.• Selection of channelization codesNeighbouring channelization codes usually cause higher crest factors than numbers distributed overthe full range of available values.• Example: 16 channels with channelization codes 0 to 15: 16.7 dB16 channels with channelization codes 0, 4, 8, to 60: 12,45 dB• Value of clipping level (see section 2.14.2.10)2.14.3.5 Orthogonality of ChannelsTo enable a 3GPP W-CDMA demodulator to restore the information of the individual channels from thesum signal, only certain combinations of• scrambling code sequences,• channel power and• symbol rate and channelization codesare allowed.2.14.3.5.1 Ideal ScenarioIn an ideal scenario the measured channel power (with code domain power analyzers) is equal to thetransmitted power (setting value in the channel configuration table), Even with great differences betweenthe channel powers the information of the channels can be restored 100%. For this purpose howeverorthogonality of the channels is required. Orthogonality is given in all cases described in section 2.14.3.3Orthogonality is given for instance if DPCH channels are used only and all of them have the samesymbol rate but different channelization codes. In addition, identical scrambling code values have to beset for all channels, i.e. all channels have to belong to a base station.In this case the bit streams SC i and SC q ' are identical for all channels. Since the channelization codesequences of two channels are orthogonal, the chip sequences Si and Sq of two channels are alsoorthogonal.2.14.3.5.2 Real ScenarioA real scenario usually consist of signals from different base/mobile stations that are operated atdifferent scrambling codes and have different delays. In this case there is no orthogonality, the channelpowers overlap and the bit error rates increase with decreasing channel power (therefore power controlis extremely important for all CDMA systems).1125.5555.03 2.230E-9