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In many disciplines a greenfield is a project that lacks any constraints imposed by prior work. The analogy is to that of construction on greenfield land where there is no need to remodel or demolish an existing structure.
Cellular networks 
In wireless engineering jargon, a greenfield is a project which lacks any constraints imposed by prior networks. An example of a greenfield network is the second generation of cell phone networks. The first cellular telephone networks were built primarily on tall existing tower structures or on high ground in an effort to cover as much territory as possible in as little time as possible and with a minimum number of base stations. They were developed with no regard for future capacity considerations or frequency reuse. These early wireless telephone network designs were later augmented with additional base stations and antennas to handle the growing demand for additional voice traffic and higher network capacity. As wireless networks quickly evolved, it was evident that the earlier designs constrained the growth of the network. As governments made more radio spectrum available for licensed wireless telephone operators in the late 1980s, entirely new networks were built that performed better than legacy networks because their designs were free from the constraints of existing systems. They were termed "greenfield networks" or "greenfield projects". Today, any new network designed from scratch to enable new Radio Access Network technologies, such as 3G, 4G, and WiMAX are also referred to as greenfield projects.
Computer networking 
Greenfield carries a similar meaning with modern wireless LAN networks. 802.11n Wi-Fi networks have an optional greenfield mode that improves efficiency by eliminating support for 802.11a/b/g devices.
Greenfield land 
||It has been suggested that Greenfield land be merged into this article. (Discuss) Proposed since December 2012.|
Greenfield investment 
Greenfield investing is usually offered as an alternative to another form of investment, such as mergers and acquisitions, joint ventures, or licensing agreements. Greenfield Investing is often mentioned in the context of Foreign Direct Investment
A related term to greenfield investment which is becoming popular is brownfield investment, where a site previously used for business purposes, such as a steel mill or an oil refinery, is expanded/upgraded to achieve superior return.
A form of foreign direct investment where a parent company starts a new venture in a foreign country by constructing new operational facilities from the ground up. In addition to building new facilities, most parent companies also create new long-term jobs in the foreign country by hiring new employees.
Developing countries often offer prospective companies tax-breaks, subsidies and other types of incentives to set up greenfield investments. Governments often see that losing corporate tax revenue is a small price to pay if jobs are created and knowledge and technology is gained to boost the country's human capital.
Other uses 
Examples of greenfield projects are new factories, power plants, airports which are built from scratch on greenfield land. Those facilities which are modified/upgraded are called Brownfield land projects (often the pre-existing site/facilities are contaminated/polluted.)
In transportation industries (e.g. automotive, aircraft, engines) the equivalent concept is called "clean sheet design".
Greenfield also has meaning in sales. A greenfield opportunity refers to a marketplace that is completely untapped and free for the taking.
From an Information Technology Service Management (ITSM) perspective, an IT organization that is being set up from scratch is said to start from a 'greenfield' situation. This is because, it would have no live services or practices in place to start with.
See also 
- Broadcom. "802.11n: Next-Generation Wireless LAN Technology White Paper". Retrieved 2010-03-20.