Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W68/00—User notification, e.g. alerting and paging, for incoming communication, change of service or the like

Definitions

• the invention relates generally to radio communication systems, and particularly to those systems whose radios are subjected, from time to time, to undesirable levels of co-channel interference.
• Radio communication systems are well known in the telecommunications art. Such radio communication
• 1 5 systems e.g., Motorola's Advanced Mobile Phone System, or
• AMPS use many radio sites to provide radio service to a large metropolitan or rural area.
• the coverage area i.e., site
• the communication unit i.e.,
• Radio 20 radio can be reached to initiate (i.e., transmit) or terminate (i.e., receive) a call.
• Site identification can be accomplished by employing a number of techniques: e.g., requiring the radio to report its location each time it roams into a new coverage area; or alternatively, requiring
• FIG. 1 shows a graphical representation of a simple cellular communications system.
• the system of FIG. 1 is commonly referred to as a "3/3 re-use system" (i.e., having a system coverage pattern comprising a plurality of adjacent reuse patterns, each reuse pattern having three sites, and each site having three distinct, 120 degree coverage areas).
• 3/3 re-use system i.e., having a system coverage pattern comprising a plurality of adjacent reuse patterns, each reuse pattern having three sites, and each site having three distinct, 120 degree coverage areas.
• local reuse pattern i.e., having a system coverage pattern comprising a plurality of adjacent reuse patterns, each reuse pattern having three sites, and each site having three distinct, 120 degree coverage areas.
• local reuse pattern i.e., having a system coverage pattern comprising a plurality of adjacent reuse patterns, each reuse pattern having three sites, and each site having three distinct, 120 degree coverage areas.
• local reuse pattern i.e., having a system coverage pattern comprising a plurality of
• 101 denoted by a heavy, solid line— comprises equally partitioned hexagonal shaped sites 103-105, each site being further divided into three coverage areas. At each site, e.g., site 103, there are three directional antennas that provide the three coverage areas within the site.
• each of the coverage areas use different radio frequencies, denoted in FIG. 1 by the numbers 1-9.
• each frequency is used only once, so there is no source of co-channel interference within that region.
• co-channel interference can be a problem throughout service area 100.
• FIG. 1 shows that coverage areas
• FIG. 1 shows 4 occurrences where frequency 'V is used (of course, the pattern is repeated throughout service area 100).
• Re-use occurrences located equi-distant from an operating site e.g., coverage area 1 1 1
• first tier co-channel interferes are called first tier co-channel interferes.
• the pattern recurs outwardly from each site, there are higher order interferes (i.e., second, third, etc.) at greater distances.
• the first tier of interferes is closest to the site in question, they are generally the strongest interferes. Accordingly, only first tier interferes will be discussed here.
• the frequencies are commonly a duplex set of frequencies, one for land-to-mobile, and another for mobile-to-land direction, as in the case of typical cellular communication systems used today.
• re-use patterns from which to choose, but that choice substantially determines both the system capacity and radio performance. For example, choosing a large re-use factor (i.e., the total number of coverage areas within a re-use pattern) produces a system with minimal co-channel interference, but a limited number of communication channels available. Further, it limits the number of frequencies that may be deployed at a given site.
• a 3/3 re-use pattern i.e., re-use factor of 9
• 21 i.e. 189/9
• a 3/7 re-use pattern i.e., re-use factor of 21
• a 3/7 re-use pattern is able to deploy only nine (i.e., 189/21 ) frequency pairs at each coverage area, thus serving fewer simultaneous users.
• radio communication systems must also be designed to provide an acceptable level of performance to the users (i.e., radio operators).
• a commonly used indicator of performance for such systems is referred to as carrier-to-interference (C/l) ratio, which generally quantifies the effect of co- channel interference on a particular channel. That is, the C/l must exceed a minimum threshold to ensure adequate system performance.
• C/l carrier-to-interference
• increasing the C/l through reduced re-use factors results in reduced system capacity, as earlier described. Accordingly, the system designer strives to find a re-use pattern that provides an acceptable C/l ratio, while simultaneously providing adequate user capacity. Doing so, however, normally results in a re-use pattern which exhibits only marginal C/l performance on the borders of adjacent coverage areas, as herein described.
• One possible solution available for conventional analog cellular systems is to choose one re-use pattern for the control frequencies, and a second re-use pattern for the bearer/voice channels.
• a larger re-use factor for the control channel By using a larger re-use factor for the control channel, additional C/l margin and larger hysteresis loops (lower C/l threshold before acquisition, and higher thresholds afterwards) can be designed into the system, allowing the mobile to remain longer on a particular control channel. Under this scenario, since the control channel constitutes only a fraction of the total number of channels, the penalty of less efficient frequency re-use is minimized.
• TDM time division multiplex
• the control channel information and voice channel information are interleaved on different time slots within the same carrier, separated temporally within recurring time frames. Since one frequency pair in each coverage area carries both the control and voice traffic, selecting different re-use patterns for control and voice channels is impossible in a TDM system. Accordingly, there exists a need for a method of reducing control channel traffic, which at least partially results from co-channel interference in a radio communication system.
• FIG. 1 shows a graphical representation of a radio communication system coverage pattern, as is well known in the art
• FIG. 2 shows a graphical representation of a radio commun ication system coverage pattern , whose operational parameters are determined in accordance with the present invention.
• FIG. 3 shows a flow diagram depicting the operation of a radio, in accordance with the present invention.
• the present invention provides a method of reducing the effect of undesirable "chatter" between a mobile attempting to register while near the border between two or more adjacent location areas. That is, the present invention provides for the reduction in the volume of location reports (i.e. registration requests) that would otherwise occur while roaming near the border between location areas.
• location reports i.e. registration requests
• FDM frequency division multiplex
• communication service area 200 comprises a plurality of location areas, e.g., location area 210 (denoted by solid, heavy lines).
• Location area 210 includes coverage areas 212-215. These four coverage areas might be embodied using a "site" in the center of the hexagonal coverage area, which site might comprise an omni-directional antenna.
• the location area identifiers are broadcast to the mobiles via the control channels for each of the coverage areas (212 - 215).
• a new sub-region e.g., paging area 240
• paging area 240 is defined for each location area that includes the coverage areas associated with the corresponding location area, as well as a plurality of other coverage areas (e.g., as denoted by the dashed outer boundaries of coverage areas 250-259).
• These coverage areas referred to herein as supported coverage areas, might share a common border (i.e., neighbors), or other predetermined amount of geographical area with the coverage areas associated with the corresponding location area (e.g., location area 210) .
• FIG. 2 shows only one such paging area, there are, in a preferred embodiment, a plurality of paging areas defined throughout service area 200.
• the present invention employs a scheme by which the paging areas-each associated with a location area as defined earlier-overlap one another. Such a scheme ensures that the outer edges (i.e., boundaries) of coverage areas for each location area do not coincide with each other. [Note that in prior art systems, coinciding boundaries occurred, by definition, at the "borders" between adjacent location areas. The problems mentioned earlier are a principal result of this condition]. Accordingly, the mobile is able to communicate (i.e., transmit and receive) throughout a larger area without having to re-register when traveling outside of his last- registered location area.
• a record (i.e., list) having one or more elements, is kept in memory at the fixed end (e.g., master site controller) corresponding to each coverage area.
• the fixed end e.g., master site controller
• the first element identifies the location area logically associated with the coverage area of interest.
• Successive elements include identities of adjacent, supported location areas, e.g., those location areas that are associated with coverage areas adjacent to the coverage area of interest.
• Table 1 provides a representative list showing associated location areas, and supported location areas for three coverage areas shown in FIG. 2; namely coverage areas 213, 214, and 253: CA213 CA214 CA253
• FIG. 3 shows a flow diagram depicting the operation of a mobile (i.e., radio), in accordance with the present invention.
• a mobile i.e., radio
• the radio While registered with a current location area (whose identification is stored in memory at the mobile) and monitoring the control channel affiliated with a first coverage area, the radio might determine that another control channel has a greater signal level (e.g., as determined by well known received signal strength indication (RSSI) techniques). Accordingly, the mobile selects (302) the stronger control channel to facilitate subsequent communication. Having acquired a new control channel, the mobile must determine if it has roamed outside of its previous paging area. To accomplish this, the mobile must retrieve (304), from the information broadcast on the control channel, the list of associated and supported location areas.
• RSSI received signal strength indication
• a decision (306) is reached to determine whether or not the identity of the stored (i.e., mobile's last-registered) location area is included in the retrieved list. If the stored location area identification (ID) has no match in the retrieved list, the mobile must register (308) in the new location area using the current control channel. In addition, the mobile updates (310) the stored location area ID with the ID corresponding to the new location area. By contrast, if the stored ID matches one of the elements in the retrieved list, the mobile is still within the same paging area, and the routine is exited. That is, even though the mobile may have roamed into the boundaries of a new location area, it is still able to be reached without having to register with the new location area.
• ID stored location area identification
• an alternate embodiment of the present invention can be described, which embodiment has many of the same characteristics as the aforementioned implementation.
• a primary distinction lies in the affiliation between the elements of the location area ID list. That is, unlike the first embodiment, the first ID in the list has no special meaning.
• the elements in the list simply define the size and shape of the paging area corresponding to the location area associated with that coverage area. Accordingly, the paging areas can be made in a variety of shapes and sizes, depending on the system requirements and typical usage patterns (i.e., they need not be defined by a particular location area, plus selected peripheral coverage areas).
• a mountainous region between two coverage areas may not be traversed frequently enough to warrant the provision of a paging area which includes both coverage areas, (i.e., and hence providing a transparent hand-off between them).
• the system designer is afforded the capability of providing as much, or as little, overlap between paging areas as the application requires.
• the operation of the mobile is substantially the same as in the first embodiment, except that the stored location area identifier might preferably be provided as part of the registration process (i.e. , since the notion of a home location area is no longer relevant).
• the operation of the fixed end equipment is also substantially the same, except that the response to a registration request (i.e.
• transmitted to a single radio must transmit a single location area ID that is found in the list, which is also being transmitted. That is, the fixed end tells the mobile which ID should be stored for future comparison with elements in the received list. There are many possible methods of selecting which of the location area ID's to return to the mobile, but it is generally adequate to randomly select the location area ID.
• the present invention provides for a reduction in the amount of undesirable registration traffic without compromising system capacity (i.e. , through increased C/l margin).
• this reduction in control channel traffic is the result of a system that seeks to reduce co-channel interference, and the accompanying tendency of mobiles to chatter among two, or more, control channel frequencies.

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• Engineering & Computer Science (AREA)
• Computer Networks & Wireless Communication (AREA)
• Signal Processing (AREA)
• Mobile Radio Communication Systems (AREA)

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Citations (4)

• 1993
  • 1993-12-27 WO PCT/US1993/012589 patent/WO1994016529A1/en not_active Ceased
  • 1993-12-27 IL IL10818193A patent/IL108181A0/xx unknown
  • 1993-12-27 AU AU59864/94A patent/AU5986494A/en not_active Abandoned
• 1994
  • 1994-01-11 CN CN94100619.0A patent/CN1094202A/zh active Pending
  • 1994-01-18 TW TW083100370A patent/TW237586B/zh active

Patent Citations (4)

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