 for some ten years. HALES require very reliable flight operations (perhaps solar powered) but could have high-density urban applications. Although full systems are unlikely, HALES could have emergency disaster area applications, offering instant infrastructure deployment, especially INFRASTRUCTURE TO 2030: TELECOM, LAND TRANSPORT, WATER AND ELECTRICITY - ISBN 92-64-02398-4 © OECD 2006 2. TELECOMS INFRASTRUCTURE TO 2030 for big cities, by replacing destroyed cellular mobile, or more easily, WiFi and WiMax networks. Signal identification from handsets at low power designed for terrestrial networking would be a challenge but not insoluble. Possible use power line carrier (PLC): Systems employing signalling to home/ office infrastructure has been around since the mainsborne signalling projects of the United States and others including the United Kingdom's DTI initiative in the 1970s. So far little has been achieved. Problems of noise, interference with attached appliances, including military equipment and the cost of the premises equipment have kept PLC back. Without enormous progress in signal propagation and noise processing algorithms, there seems to be little future for a local loop technology and less as long distance trunk technology over high voltage networks (except via fibre optics inside the national distribution power lines which has been proposed as a bypass technology). The level of investment - impacts of the new infrastructure model Over the past decade telecommunications spending has varied according to the economic conditions with a boom in the mid 1990s and then a reduction, from the "telecoms bust" from 2000 onwards, as shown below. Figure 2.17. OECD average of public telecommunication investment as a percentage of gross fixed capital formation (GFCF) 1990-2003 1990 1991 1992 1993 (1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 Source: OECD Communications Outlook, 2005 (1990 1996 are 3 year averaged figures). Thus, although the number of subscribers to all telecommunications services grew at th