phone Demand mostly to make sure that they are not the limiting factor in our system design. How- ever, it is highly unlikely that the high-delay-tolerant data services are going to be a limiting factor in capacity planning. With an enumeration of data services, subscriber count estimates for those services, and usage pattern estimates, we can form estimates of the peak-time demand in er- langs e for each low-delay wireless data service. We need to focus on the busy hour hav- ing adequate data capacity for those services. For the other services, those that can tol- erate higher delay, we can ensure enough capacity for them by counting up the total requirement spread out over peak and nonpeak times. Motion increases the required Eb/No for the same bit error rate (BER), typically by about 2 dB, for data, just as it does for voice. Thus it is important to estimate the frac- tion of data subscribers who are moving while they are using wireless data service. We can use Eq. (31.1) to get the CDMA capacity needed to serve each data service. The value of y is a proxy value. While y does not represent the true number of chips, it does represent a measure of air-interface capacity required to deliver each type of data service, as we will see in Eq. (31.2). The Eb/No for each service should be adjusted to take into account the fraction of users who are stationary and the fraction who are moving. For each data service, we estimate the number of subscribers and the peak-hour us- age per subscriber. The product of the subscriber estimate and the peak-hour usage per subscriber gives us a total usage for each data service. Once we have that total for each data service, we use Eq. (31.1) to add up all these estimates for a gross number of chips per second y that we can use to estimate cell count later on in Sec. 31.4. We complete the estimation process for data service by creating a geographic picture of data service demand. The total demand gives us an estimate of air-interface capac- ity requirement, but the geographic informat