Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1999-05-19
2002-09-03
Trost, William (Department: 2683)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S436000, C455S437000, C455S439000, C455S522000, C370S331000, C370S332000
Reexamination Certificate
active
06445917
ABSTRACT:
FIELD OF THE INVENTION
The field of the invention is wireless communications. The present invention uses a mobile radio station as a measurement tool for a radio access network.
BACKGROUND AND SUMMARY OF THE INVENTION
In a typical cellular radio system, a geographical area is divided into cell areas served by base stations which are connected to a radio network. Each user (mobile subscriber) in the cellular radio system is provided with a portable, pocket, hand-held, or car-mounted mobile station which communicates voice and/or data with the mobile radio network. Each base station includes a plurality of channel units including a transmitter, a receiver, and a controller and may be equipped with an omnidirectional antenna for transmitting equally in all directions or with directional antennas, each directional antenna serving a particular sector cell. Each mobile station also includes a transmitter, a receiver, a controller, and a user interface and is identified by a specific mobile station identifier.
In a cellular radio communications system, a handover operation allows an established radio connection to continue when a mobile radio participating in that connection moves between cells in the system. Handover is typically initiated when the signal strength or signal quality of the radio connection with an origination base station falls below a predetermined threshold value. Often, a low signal strength or a poor signal quality indication means that the mobile station is near a border between the two cells. If the mobile station moves closer to a destination cell or to a clearer line of unobstructed sight, handover of the radio connection to the destination cell usually results in improved radio transmission and reception.
In some cellular systems, a handover operation requires physically breaking the connection with the origination cell and then reestablishing the connection with the destination cell, i.e., a “break-before-make” switching operation. Such hard handover techniques are typically employed in Time Division Multiple Access (TDMA) and Frequency Division Multiple Access (FDMA) type cellular systems. On the other hand, “soft” handover techniques may be employed in Code Division Multiple Access (CDMA) type cellular systems. CDMA is an increasingly popular type of access for cellular communications because a higher spectrum efficiency is achieved compared to FDMA and TDMA techniques which means that more cellular users and/or services can be supported. In addition, a common frequency band allows simultaneous communication between a mobile station and plural base stations. Signals occupying the common frequency band are discriminated at the receiving station through spread spectrum CDMA waveform properties based on the use of a high speed, pseudo-noise (PN) code. These high speed PN codes are used to modulate signals transmit from the base stations and the mobile stations. Transmitter stations using different PN codes (or a PN code offset in time) produce signals that can be separately demodulated at a receiving station. The high speed PN modulation also allows the receiving station to advantageously generate a received signal from a single transmitting station by combining several distinct propagation paths of the transmitted signal.
In CDMA, therefore, a mobile station need not switch frequency when handoff of a connection is made from one cell to another. As a result, a destination cell can support a connection to a mobile station at the same time the origination cell continues to service the connection. Since the mobile station is always communicating through at least one cell during handover, there is no disruption to the call. Hence, the term “soft handover.” In contrast to hard handover, soft handover is a “make-before-break” switching operation.
Deciding which cells to involve in handover often requires coordination between the mobile station and the radio network. The mobile station monitors base station control or broadcast channels from adjacent cells to determine if these cells are suitable handover candidates. When suitable cell candidates are identified, the mobile station notifies the radio network of this fact which then may initiate handover operations. Of course, other handover procedures may be employed.
Power control is also important in radio communications systems, and particularly so in third generation, wideband CDMA systems (WCDMA). Before transmitting over an “uplink” channel, a mobile station must set its transmission power level. Similarly, the radio access network must set base station transmit power on “downlink” channels, e.g., a paging channel, a forward access channel, traffic channels. While the actual power level set for mobile station and base station radio transmission and the interference levels that result therefrom are significant concerns in all mobile radio communications systems, such interference is particularly problematic in CDMA systems where large numbers of radio transmit and receive on the same frequency. If one station transmits at a power output that is too large, the interference it creates degrades the signal-to-interference ratio of signals received from other radio stations to the point that a receiving station cannot correctly demodulate transmissions from other radios. Another power related problem is the so-called “party effect.” If a mobile transmits at too high of a power level, the other mobiles increase their respective power levels so that they can “be heard” thereby compounding an already serious interference problem.
In order to effectively manage handover, power control, and other important operations in a cellular radio communications network, the network should know the current status of the network. That status can be measured reasonably well by detecting the current values of various radio-related parameters at different locations in the network. In the handover example, the radio network should know which particular cells are appropriate candidates for handover for a particular mobile station connection. With respect to another example, i.e., controlling the interference levels in a particular cell, the radio network needs to know the transmit power levels of various radios in that cell, the received power levels, interference levels, etc. Other parameters may also be desirable for the network to monitor.
While these parameters could be measured by suitably located sensors or other monitoring equipment, the cost and installation of such equipment to make it effective and worthwhile would be prohibitive. On the other hand, the mobile stations themselves could be used (secondarily) as measurement tools to provide the radio network with important measurements reflecting the stations radio environment. Those measurements could then be used to facilitate radio network operations like handover, power control, resource management, etc.
The mobile radios could periodically provide measurement reports to the radio network for a standard set of radio-related parameters. The drawback, however, with periodic measurement reports is that if the period is too long, the reports may be outdated with the radio network responding too late or too slowly to changing conditions. On the other hand, if the reporting time period is reduced to improve the relevance of the information and appropriate responsiveness of the network to changing conditions, the amount of signaling from mobile stations increases significantly. This is disadvantageous for several reasons. First, the radio bandwidth is limited, and this kind of administrative signaling creates interference and reduces capacity for user communications. Second, much of the information that is transmitted in these frequent mobile station measurement reports will likely contain the same information as in recent reports. Third, frequent reporting also drains the mobile station's battery.
It is an object of the present invention to address the needs and overcome the problems identified above.
It is an object of the present invention to use mobile radio stations as f
Bark Gunnar
Bergström Joakim
Müller Walter
Nixon & Vanderhye PC
Telefonaktiebolaget LM Ericsson (publ)
Tran Congvan
Trost William
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