 (MSC), and we enlarge the backhaul network to provide this increase in transport. Once the base station reaches its maximum configuration, the growth of the backhaul network is continuing growth in the number of backhaul network nodes rather than a continuing increase in the capacity of the existing backhaul links. We have discussed how to set up a backhaul network for a wireless telephone sys- tem. We wrote about mathematical global optimization techniques in Sec. 26.1 and then explained in Sec. 35.2 how an incremental-improvement heuristic can get a near- optimal calculation for a minimum-cost backhaul network. The heuristic has us form list of candidate backhaul routes from each base station and has us repeatedly eval- uate each base station's choices until no improvement is found. Since the backhaul 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. Adding Transport Increasing Capacity network grows by adding nodes, we have to think of its cost minimization as an ongo- ing optimization in the backhaul planning process. Each new cell has subscriber demand to be served, so each new base station has a backhaul requirement. The new base station is a new node in the network flow opti- mization. Thus we can continue the heuristic by forming a candidate list for backhaul hops from the new base station to the MSC and to all the nearby base stations within three cells. Let us examine some of the issues that make backhaul growth different from the initial cost minimization we described earlier. Incremental growth on the existing transport links is almost certainly cheaper than forming new links because transport costs are typically concave. This means that they have decreasing incremental cost as the quantity increases. The exception to this rule is when incremental demand pushes the transport requirement past a small number of big units so that the