than the same-cell Mbb contribution. As an example, consider a system with two omnidirectional cells 1 and 2 with the ma- trix in Eq. (28.22): (28.22) Cell 1 serves 1 users, cell 2 serves O2 users, and we are assuming for this example that the radio path gain for all users to their nonserving cells is times lower than to their serving cells. We are going to add k users in the serving area of cell 1. Thus their radio signal path gains to cell 2 are times lower than to cell 1. Adding k users to cell 1 increases first-column components of M1(k) as shown in Eq. (28.23): (28.23) The upper-left coefficient of M1(k) reflects the full value of k extra users being served by base station 1, whereas the lower-left coefficient reflects the extra contribution of their interfering path to base station 2. However, for some reason, we may decide to serve the same k users with antenna face 2 instead. This increases the second-column components of M2(k) as shown in Eq. (28.24): (28.24) The lower-right coefficient of M2(k) reflects the extra user being served by base station 2, but in this example the upper-right coefficient increases by k/B, a number greater than k, because the interfering path has greater path gain than the serving signal path. We can solve the CDMA equations using matrices M1(k) and M2(k) and notice that matrix M2(k) gives higher power levels or, even worse, negative power levels that in- dicate system overload. A simpler approach to see the same effect is to realize that the Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. CDMA Principles for Multicellular Systems Capacity and Quality Principles system becomes overloaded when the determinant of matrix M is zero. The determinant for a two-by-two matrix is given in Eq. (28.25):4 (28.25) If we start with a well-behaved CDMA system, a matrix M with positive determinant D, then we can ask how ma