1. LMDS

LMDS is a broadband wireless point-to-multipoint communication system operating above 20 GHz (depending on country of licensing) that can be used to provide digital two-way voice, data, Internet, and video services.

The acronym LMDS is derived from the following:
L (local)-denotes that propagation characteristics of signals in this frequency range limit the potential coverage area of a single cell site; ongoing field trials conducted in metropolitan centres place the range of an LMDS transmitter at up to 5 miles
M (multipoint)-indicates that signals are transmitted in a point-to-multipoint or broadcast method; the wireless return path, from subscriber to the base station, is a point-to-point transmission
D (distribution)-refers to the distribution of signals, which may consist of simultaneous voice, data, Internet, and video traffic
S (service)-implies the subscriber nature of the relationship between the operator and the customer; the services offered through an LMDS network are entirely dependent on the operator's choice of business.

There is a variety of ways in which LMDS is implemented (all decision involving bandwidth usage are left to the licensee), however there are many features common to all LMDS systems because of the way signals in that frequency band behave as they go through the atmosphere. LMDS can provide a distribution of services through a variety of multiple access techniques, such as Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), and Adaptive Time Division Duplexing (ATDD). There are new transport platforms on the horizon, such as Wireless Asynchronous Transfer Mode (W-ATM) and Wireless IP, which will have the capability to consolidate services on an end-to-end network basis.

LMDS is essentially a line-of-sight system. Radio frequency (RF) coverage is a critical issue because signals are easily obstructed at this frequency. Point-to-point systems have the advantage of two fixed end points allowing for confirmation of line of sight. The primary benefit associated with line-of-sight operation is that, when coupled with directional antennas and varying polarization, the service are can be highly sectorised, allowing for reuse of the valuable spectrum resource within the area.

LMDS frequencies operate on allocated spectrum and a licence is absolutely necessary to operate an LMDS frequency. Licensing fees could be a significant portion of the expense of an LMDS system, but do insure the there will not be unexpected interference from other systems.

One problem with this system is the rainfall attenuation of the signal; this issue can be solved through back up systems or a configuration that takes into account the historical weather conditions.

The network topology that is envisioned by most LMDS vendors is fiber fed hub and spoke network. However the majority of current deployments are point-to-point.

The total network bandwidth for an LMDS system can vary greatly from system to system however it will be limited to around 2 Gbps. In the point-to-multipoint configuration this can be reasonably broken down into at most 45 Mbps connection for each customer with most customers receiving less than 10 Mbps.

In conclusion, LMDS provides an effective last-mile solution and can be used by competitive service providers to deliver services directly to end-users. Benefits can be summarized as follows:

• Lower entry and deployment costs
• Ease and speed of deployment (systems can be deployed rapidly with minimal disruption to the community and the environment)
• Fast realization of revenue (as a result of rapid deployment)
• Demand-based build out (scalable architecture employing open industry standards ensuring services and coverage areas can be easily expanded as customer demand warrants)
• Cost shift from fixed to variable components (with traditional wire line systems, most of the capital investment is in the infrastructure, while with LMDS a greater percentage of the investment is shifted to customer-premise equipment [CPE], which means an operator spends dollars only when a revenue paying customer signs on)
• No stranded capital when customers churn
• Cost-effective network maintenance, management, and operating costs

• Purchase of expensive radio frequency
• Weather conditions could be an obstacle to reliable service
• Line of sight are a problem in city centres where high buildings are on the way
• Although a connection with health problems has not been found, health issues have been raised with all the wireless applications.