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Method and apparatus for determining coverage and switching between overlay communication systemsMethod and apparatus for determining coverage and switching between overlay communication systems description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20090163209, Method and apparatus for determining coverage and switching between overlay communication systems. Brief Patent Description - Full Patent Description - Patent Application Claims
The present Application for patent is a Continuation of U.S. application Ser. No. 10/366,101 entitled “Method and Apparatus for Determining Coverage and Switching Between Overlay Communication Systems” filed Feb. 12, 2003. The present invention relates generally to communication, and more specifically to techniques for determining coverage for a terminal and switching between overlay communication systems. I. Field II. Background Wireless communication systems are widely deployed to provide various types of communication such as voice, packet data, and so on. These systems may be multiple-access systems capable of supporting communication with multiple users by sharing the available system resources. Examples of such multiple-access systems include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, and frequency division multiple access (FDMA) systems. A CDMA system may be designed to implement one or more standards such as IS-2000, IS-856, IS-95, W-CDMA, and so on. A cdma2000 system is a CDMA system that may implement IS-2000 and/or IS-856. A TDMA system may be designed to implement one or more standards such as Global System for Mobile Communications (GSM) and so on. A GSM system may implement General Packet Radio Service (GPRS) for packet data transmission. These various standards are well known in the art. Some communication systems (e.g., such as those that implement IS-2000 W-CDMA, and GSM/GPRS) are capable of supporting voice and packet data services. Each type of service is characterized by a set of requirements. For example, voice service typically requires a fixed and common grade of service (GOS) for all users as well as relatively stringent and fixed delays. In contrast, packet data service may be able to tolerate different GOS for different users and may further be able to tolerate variable amounts of delays. To support both types of service, a communication system may first allocate system resources to voice users and then allocate any remaining system resources to packet data users whom can tolerate longer delays. Some communication systems (e.g., such as those that implement IS-856) are optimized for packet data transmission, which is typically characterized by long periods of silence punctuated by large bursts of traffic. For an IS-856 system, a large portion of the system resources may be allocated to one user at a time, thereby greatly increasing the peak data rate for the user being served. A service provider/network operator may deploy multiple communication systems to provide enhanced services for its subscribers. For example, a service provider may deploy one system capable of supporting both voice and packet data services for a large geographic area and may deploy another system capable of supporting packet data service for “hot spots” where packet data usage is expected to be high. The coverage areas of the two systems would typically overlap at least partially, and these systems would then be considered as “overlay” systems. A multi-mode/hybrid terminal may be able to receive service from one of the systems depending on its location and the desired service. Some of the challenges in such overlay systems include (1) determining the coverage bounds of the individual systems and (2) deciding when a terminal should switch between the systems. There is therefore a need in the art for techniques to determine coverage for a terminal and to switch between overlay communication systems. Techniques are provided herein to determine whether or not a terminal is under the coverage of a current system (e.g., a packet data system) and to switch from the current system to another system (e.g., a voice/data system) if and when appropriate. Various schemes to determine coverage and to switch between multiple overlay systems may be implemented based on a metric, a metric threshold, a timer, other factors, or a combination thereof. The metric may be a parameter or a function of one or more parameters. An exemplary parameter is signal quality, which may be quantified by a signal-to-noise ratio (SNR). An exemplary metric is a Switch metric that is a function of SNRs of signals (e.g., pilots) received from base stations in one or more sets (e.g., selected from an active set, a candidate set, and a neighbor set described below). The metric threshold may be a fixed value or an adaptive value that is dependent on operating condition. The metric threshold is selected such that (1) the coverage bounds of the current system may be accurately determined and/or (2) the terminal does not switch from the current system too early or too late. The timer may be used to provide hysteresis so that (1) the terminal does not intermittently indicate that it is within/outside the coverage of the current system and (2) an out-of-coverage indication is not erroneously declared too frequently because of noisy measurements. The timer may be for a fixed duration or a variable duration that is dependent on operating condition. In one specific method of switching a terminal from a first communication system to a second communication system, at least one measurement of at least one parameter for at least one base station in the first communication system is initially obtained. The at least one measurement may be SNR measurements. A metric is then derived based on the at least one measurement and is used (typically along with a metric threshold and a timer) to determine whether or not the terminal is within the coverage of the first communication system. A switch to the second communication system is initiated if the terminal is deemed to be outside the coverage of the first communication system. The first and second communication systems provide at least one common service (e.g., packet data service). The first system may be, e.g., an IS-856 system, and the second system may be, e.g., an IS-2000 system. The switch from the first system to the second system may be based on one switching scheme, and the switch from the second system back to the first system may be based on another switching scheme. Two different switching schemes may be used, for example, if the coverage areas of the first and second systems are different. Various aspects and embodiments of the invention are described in further detail below. The features, nature, and advantages of the present invention will become more apparent from the detailed description set forth below when taken in conjunction with the drawings in which like reference characters identify correspondingly throughout and wherein: Continue reading about Method and apparatus for determining coverage and switching between overlay communication systems... Full patent description for Method and apparatus for determining coverage and switching between overlay communication systems Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Method and apparatus for determining coverage and switching between overlay communication systems patent application. 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