13.9 Link Budget

The link budget process, as defined in previous sections of this book, is essential for the establishment of a valid RF design to take place. The link budget helps define the cell-size spacing. The cell-site spacing is determined by the link budget using a signal level that is exceeded by 50 percent of the time.

There are two links that need to be determined in the establishment of a link budget: forward and reverse. The forward and reverse links utilize different coding and modulation formats. The first step in the link budget process is to determine the forward before the reverse links maximum path losses. The link budget is defined previously in an earlier chapter.

CDMA2000-1X has a better link budget than IS-95A/B at the same traffic loading therefore offering a high overall capacity at the same traffic load due to vocoder improvements as well as utilizing a coherent demodulation for the reverse link. However, for the link budget that will be used for the design, the link budget parameters primarily associated with IS-95 are utilized due to the prevalence of the RC1 and RC2 subscriber units in the market.

Regarding packet-data services, due to the improved modulation and coding scheme (resulting in a lower target Eb/No), the 38.4-Kbps packet data rate for CDMA2000-1x has approximately the same link budget as IS-95 13K voice vocoder, but at higher data rates the service coverage will shrink due to a variety of factors that include process gain as well...