Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1999-11-23
2001-05-29
Maung, Nay (Department: 2681)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S432300, C455S436000, C370S331000
Reexamination Certificate
active
06240292
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to wireless telecommunication systems. More particularly, the present invention relates to a method and system for providing handoff of a mobile telephone from a CDMA cellular telecommunication system to an analog cellular telecommunication system.
BACKGROUND INFORMATION
Wireless telecommunication systems provide information services traditionally provided by land-line or copper wire systems. Examples of wireless communications applications include Advanced Mobile Phone Service (AMPS) analog cellular service and AMPS-D digital cellular service in North America, and Group Speciale Mobile (GSM) cellular service in Europe.
Although the particular application may vary, the components of a wireless communication system are generally similar. For example, a wireless communication system usually includes a radio terminal or mobile station, a radio base station, a switch or network control device, often referred to as a mobile telephone switching office (MTSO), and a network to which the wireless communications system provides access, such as the Public Switched Telephone Network (PSTN).
The various wireless communication applications use different modulation techniques for transmitting information to more efficiently utilize the limited available frequency spectrum. For example, frequency division multiple access (FDMA), time division multiple access (TDMA) and code division multiple access (CDMA) modulation techniques are used to build high-capacity multiple access systems. Telecommunication systems designed to communicate with many mobile stations occupying a common radio spectrum are referred to as multiple access systems.
For example, in an FDMA analog cellular system, such as an AMPS analog cellular radio system, the available frequency spectrum is divided into a large number of radio channels, e.g., pairs of transmit and receive carrier frequencies, each of which corresponds to a message transmission channel. The bandwidth of each transmit and receive frequency channel is narrowband, generally 25-30 kHz. Thus, the FDMA system permits information to be transmitted in a bandwidth comparable to the bandwidth of the transmitted information, such as a voice signal. The cellular service area in the FDMA system is generally divided into a plurality of cells, each cell having a set of frequency channels selected so as to minimize co-channel interference between cells.
Frequency division is often combined with time division so that transmission circuits are trunked in both the frequency and time domain, e.g., a FD/TDMA system. In a digital FD/TDMA (commonly referred to as TDMA) cellular system, a narrowband frequency channel is reformatted as a digital transmission path which is divided into a number of time slots. The data signals from different calls are interleaved into assigned time slots and sent out with a correspondingly higher bit rate, the time slot assigned to each mobile station being periodically repeated. Although the TDMA bandwidth may be somewhat larger than the FDMA bandwidth, a bandwidth of approximately 30 kHz is generally used for AMPS-D digital TDMA cellular systems.
A very different approach to cellular multiple access modulation is CDMA. CDMA is a spread spectrum technique for transmitting information over a wireless communication system in which the bandwidth occupied by the transmitted signal is significantly greater than the bandwidth required by the baseband information signal (e.g., the voice signal). Thus, CDMA modulation spectrally spreads a narrowband information signal over a broad bandwidth by multiplex modulation, using a codeword to identify various signals sharing the same frequency channel. Recognition of the transmitted signal takes place by selecting the spectrally-coded signals using the appropriate codeword. In contrast to the narrowband channels of approximately 30 kHz used in FDMA and TDMA modulation techniques, a CDMA system generally employs a bandwidth of approximately 1.25 MHz or greater.
Regardless of the modulation technique used in a cellular telecommunication system, when a mobile station is in communication with its base station, for example to provide telephone service between a mobile station and a calling party, the cellular system must maintain uninterrupted service for the call despite movement of the mobile station through the cellular system. For example, in an analog cellular system, when the mobile station transitions from one cell to another cell, the mobile station must change frequencies because each cell supports a different set of frequencies. The process by which a cellular telecommunications system enables a mobile station to maintain an established connection when moving through cells of a cellular system is referred to as “handoff,” and is generally controlled by the MTSO.
In a conventional analog cellular system, a handoff is triggered when the base station currently providing the link between the mobile station and the MTSO detects that the received signal strength from the mobile station has dropped below a predetermined level. The low signal strength from the mobile station usually indicates that the mobile station is approaching the boundary of the cell. When the received signal strength is below the predetermined value, the base station requests the MTSO determine whether another base station, e.g., a neighboring base station, is receiving a stronger signal from the mobile station than the current base station.
In response to the request from the current base station, the MTSO sends a message to the appropriate neighboring base stations to measure the received signal strength from the mobile station. The neighboring base stations, using a scanning receiver, monitor the frequency channel of the mobile station and measure the received signal strength, if possible. The measurements made by the neighboring stations are reported to the MTSO. If one of the neighboring base stations receives the mobile station signal above a predetermined level, then the MTSO directs a handoff of the mobile station from its current base station to a new base station in an adjoining cell. In particular, the MTSO informs the mobile station of a new frequency to be used with the new base station, while the MTSO also switches the call from the current base station to the new base station. If the handoff is unsuccessful, however, the call will be lost, e.g., terminated. This type of handoff is often referred to as a system-assisted handoff because the cellular system controls the detection of the need for, and the execution of, the handoff.
Another type of handoff is referred to as a mobile-assisted handoff (MAHO). For example, in a digital CDMA cellular system, each base station transmits a CDMA pilot signal on a common frequency, each pilot signal being differentiated by its phase offset compared to other pilot signals. A mobile station located in a digital CDMA cellular system regularly monitors the pilot signal strength received from the various pilot signals of neighboring base stations. The mobile station detects when the received signal strength of a pilot signal from its current base station has dropped below a predetermined level and the received signal strength of a neighboring base station pilot signal exceeds a predetermined level. The mobile station transmits these signal strength measurements to the MTSO via the base station with which the mobile station is in communication. The MTSO directs a handoff from one base station to another base station based on the signal strength measurements made by the mobile station.
A conventional narrowband analog cellular system, such as an AMPS FDMA cellular system, cannot support MAHO because in the analog system there is no pilot signal, the mobile station does not take measurements of the signals transmitted by the analog base station, and the handoff is controlled by the base stations and MTSO. Moreover, a 30 kHz analog cell base station cannot transmit a 1.25 MHz CDMA pilot signal.
Similar to the CDMA system MAHO, in a digit
Haberman Michael
Pierson Glenn
Cellco Partnership
Maung Nay
McDermott & Will & Emery
LandOfFree
Method and system for providing a handoff from a CDMA... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and system for providing a handoff from a CDMA..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and system for providing a handoff from a CDMA... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2506959