Neighborhood list assimilation for cell-based microsystem

Details Neighborhood list assimilation for cell-based microsystem Neighborhood list assimilation for cell-based microsystem

1998-05-28

2002-07-16

Rao, Seema S. (Department: 2661)

Multiplex communications

Communication over free space

Having a plurality of contiguous regions served by...

C370S438000, C370S343000, C455S434000, C455S444000, C455S450000, C455S511000

Reexamination Certificate

active

06421328

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to microcellular radio transmission systems, and is particularly directed to dynamic radio frequency scanning, planning, and channel allocation for microcellular systems coexisting in a macrocellular environment.
DESCRIPTION OF THE RELATED ART
The last decade has witnessed an explosion in the deployment of analog and digital cellular radio communication systems across the globe. Such systems provide spectrum efficient, low-power wireless communication between mobile or fixed communications terminals (“mobiles”) and fixed radio transceivers (“base stations”) dispersed throughout the service area of a macro cellular system (“macrosystem”). Typically, each macrosystem base station maintains a permanent communications link with a mobile telephone exchange (MTX), which is responsible for wireless call processing as well as interfacing the mobiles to the Public Switched Telephone Network (“PSTN”).
In narrowband cellular macrosystems, such as defined in the IS-136, IS-54B, and GSM standards, RF spectrum efficiency is realized through geographic distribution and reuse of a finite number of signal-bearing carrier frequencies within the macrosystem service area. Conventionally, this is accomplished through geographically segmenting the service area into a number of macrocells, each containing at least one base station. Within each macrocell, wireless communications are established between mobiles within the macrocell and the macrocell base station(s) using only a portion of the radio frequency spectrum or operational band allocated to the macrosystem. In so doing, each macrocell may be statically or dynamically allocated a subset from the pool of more than 400 defined frequency pairs within the macrosystem's operational band. Adjacent macrocells are assigned non-overlapping frequency channels to maximize traffic loading without producing co-channel interference. However, at or beyond the reuse distance of a given macrocell (which is dictated by such factors as base station/mobile transmitter power and receiver sensitivity specifications, macrocell size, and terrain), a set of partially or fully overlapping frequency pairs may be allocated.
Narrowband cellular radio is inherently scaleable, and has proven to be a reliable, wireless communications system offering relatively low fixed-end and infrastructure costs when smaller geographical areas are to be serviced. Network communications companies have also recognized the market need for private wireless communications having network functions tailored to the specific requirements of individual businesses, government, and private institutions. Hence, it has become popular to deploy a private microcellular radio communication system or “microsystem” within the macrosystem service area. Such a microsystem will typically be integrated into a private branch exchange (“PBX”) as part of a private communications network and can be conveniently deployed within an office building, campus or worksite to enable wireless communications among the occupants thereof. Potentially each subscribing mobile positioned within the microsystem's service area can register with this private network through the microsystem's base station(s) and emulate a desktop terminal served by the PBX.
Representative private microcellular networks have been developed by Northern Telecom Limited, the assignee of the present invention. See, for example, U.S. Pat. Nos. 4,771,448 to Koohgoli, et al. and 5,537,610 to Mauger, et at One of the hallmarks of these and other known microsystem approaches is the ability for both the microsystem and macrosystem to utilize the same mobile unit. Another is the nearly seamless handoff operation a subscribing mobile undergoes when moving from the macrosystem to the microsystem (such as when a mobile's user walks into the office building) and vice versa. Yet another feature is the ability for the mobile to remain registered on the macrosystem and potentially make and receive macrosystem calls while in the microsystem's coverage area but not registered on this microsystem.
To accommodate these features while conserving scarce frequency spectrum resources, a microsystem must be able to re-use some of the traffic and control frequencies allocated to the overlying macrosystem. But, in order for the microsystem to “peacefully” coexist with the macrosystem, the microsystem must be able to quickly obtain and relinquish frequency resources without inducing co-channel interference or otherwise disrupting macrosystem operations. Traditionally, macrosystem spectrum resources were statically assigned to the macrocells, and so microsystem planners could routinely predict and reserve frequencies allocated to the macrosystem but left unassigned to the macrocell(s) in which the microsystem was located. However, as macrosystem traffic demands increasingly strain capacity, macrosystem planners have responded by all-too-frequently adapting macrocell frequency allocations to varying use patterns, thereby making cooperative microsystem resource planning difficult, if not impossible to implement.
In response, an automatic frequency allocation system has been proposed in laid-open PCT application WO 96/31075. The disclosed system will enable the microsystem to scan the uplink subrange of frequencies allocated to the overlying macrosystem through periodically placing an idle microcell base station transceiver in a locate receiver mode. Once the frequency subrange is scanned, measurement data associated with each scanned frequency is evaluated by the microsystem and a set of available frequencies is determined for use in microsystem communications.
However, in this system, no provision has been made to efficiently apprise registered mobiles within range of the microsystem of backup control channel information as well as control information for the overlying cells of the macrosystem and any competing Microsystems, particularly when such mobiles are being actively serviced by the microsystem. This is so even though the microsystem is attempting to cooperatively share a common operational band with the overlying macrosystem and any competing microsystems.
Therefore, it would be desirable for a microsystem to manage such control information at a local level which can be made conveniently accessible to all registered mobiles being serviced by the microsystem. Furthermore, it would be advantageous if, in so doing, the microsystem would be able to exploit yet remain compatible with existing planning information issued by the overlying macrosystem, including, but not limited to macrosystem neighbor list communications. Finally, it would be advantageous if microsystem-centric control channel information could be presented and assimilated by the registered mobiles without substantial modification to the mobiles themselves.
SUMMARY OF THE INVENTION
In light of the above shortcomings and desires, the present invention is directed to a method for assembling a microsystem neighbor list to define control channel usage within the operational band being used by the microsystem, the overlying macrosystem, and any competing Microsystems. The present invention is also directed to a frequency planning controller and microsystem utilizing this method, as well as a computer program product defining the same.
Preferably, assembly of the microsystem neighbor list includes defining preferred and non-preferred members. In the below-described embodiments, the preferred member(s) of the microsystem neighbor list will include at least one control channel defined within the common operational band which is determined to be available for use by the microsystem. In the typical case, more than one preferred member will be defined in order to provide backup control channels should interference be detected.
According to one embodiment of the invention, potential preferred members (and suitable control channel candidates) of the microsystem are identified through scanning a set of control channel candidates to obtain measured RSSI signa

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