The guard period after each rectangular pulse carrying the modulated data symbol is a simple and efficient method to deal with multi-path reception. The cyclic prefix (CP) simply consists of the last part of the following symbol. The size of the cyclic prefix field depends on the system and can even vary within one system. … Read more
The radio waves are distributed in 3Hz ~ 3000GHz. This spectrum is divided into 12 bands, as shown in the above table. The frequencies in each specific band present unique propagation features: The lower the frequency is, the lower the propagation loss will be, the farther the coverage distance will be, and the stronger the … Read more
Diversity technology means that after receiving two or more input signals with mutually uncorrelated fading at the same time, the system demodulates these signals and adds them up. Thus, the system can receive more useful signals and overcome fading. A mobile communication channel is a multi-path fading channel and any transmitted signal reaches a receive … Read more
Rake Receiver Instead of trying to overpower or correct multipath problems, CDMA takes advantage of the multipath to improve reception quality in fading conditions. CDMA does this by using multiple correlating receivers and assigning them to the strongest signals. This is possible because the CDMA mobile is synchronized to the serving base station. The mobile’s … Read more
Multi-path combination in the BSC during soft handoffMulti-path combination in the BTS during softer handoffs Soft handoff means that during the handoff of a mobile station at the coverage edge areas of two or multiple base stations, the mobile station receives the signals from multiple base stations (two in most cases) at the same … Read more
Eb/No corresponds to energy per bit over interference plus noise density for a given target FER (typical FER target is 1%). In digital communications, it is customary to designate one-sided noise density with No. In CDMA, interference is dominated by the noise generated due to other users in the system. Here No, is refers to … Read more
Time diversity is a technique common to most digital transmission systems. The Rake Receiver is used to find and demodulate multipath signals that are time delayed from the main signal. Rake Receiver to Find and Demodulate Multipath Signals. Data is Interleaved : Spreads Adjacent Data in time to Improve Error Correction Efficiency Convolutional Encoding : … Read more
If it is available, the second cell site returns the Walsh Code that will be assigned for the soft handoff. At this point, the original base station orders the soft handoff by using a handoff direction message on the traffic channel using one of the two types of signaling: dim and burst or blank and … Read more
Once a call is established, the mobile is constantly searching for other possible cell sites that might be good candidate for soft handoffs. Most of the search time is limited to looking for those PN offsets specified in the neighbor list found on the paging channel. The rake receiver’s searcher is the device that scans … Read more