Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
2000-01-27
2001-11-06
Trost, William (Department: 2683)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S452200, C455S453000, C455S509000, C455S422100, C379S133000, C379S134000
Reexamination Certificate
active
06314293
ABSTRACT:
BACKGROUND OF THE INVENTION
A. Field of the Invention
The present invention relates generally to communications systems. More particularly, this invention relates to the management of traffic in a wireless communication system by the probabilistic use of reserve channels.
B. Description of the Related Art
FIGS. 1A and 1B
illustrate two widely used cell patterns in a cellular telephony system. It is important to mention that the boundaries of each cell vary in reality, since they are defined by the radiation patterns of antennas corresponding to base stations in each cell (not shown). That is, the hexagonal shape of the cells represents an ideal concept that cannot be achieved when implementing the cellular telephony system.
Each base station (not shown) in a cell is assigned a number of channels (frequency channels are generally used in an analog cellular system while time slots could be used in a digital cellular system) for use by a group of mobile stations, being serviced by the base stations, in order to establish a communication link between the mobile stations and each base station. The communications link is used to establish a call between a mobile station and telephone terminal. The telephone terminal can be either a computer (via modem), a conventional telephone or another mobile station located either in the wireless communications system
etwork or being part of a conventional telephony network. A mobile station is a communication unit in the mobile communication system (e.g., cellular radio system) that is intended for use while it moves at unspecified locations. A mobile station is typically either a hand-held unit (portable telephone) or a mobile unit installed in a vehicle.
FIG. 2
shows base stations
204
and
206
, each covering a different cell, as well as a hand-held unit
214
and a mobile unit
208
.
The number of base stations per cell can be adjusted to comport with system design specifications such as the amount of traffic handled on a per cell basis, and signal to co-channel and signal to adjacent channel interference ratios. One technique that enables the use of multiple base stations in a given cell is called sectoring.
FIG. 1A
shows an example of cells
104
partitioned into three sectors. A base station (not shown) is placed in each of the three sectors in this figure. The sectoring pattern shown in
FIG. 1A
is known as 120 degree sectoring. Likewise,
FIG. 1B
shows cells
106
which are partitioned into six sectors, with each sector having a base station that covers the area defined by the sector. This second sectoring pattern is known as a 60 degree sectoring.
In a cell pattern such as that shown either in
FIGS. 1A
or
1
B, a given cell is assigned a number of channels, regardless of whether the cell has been sectored or not. When a cell is partitioned into sectors, each sector is assigned a subset of the channels that correspond to the cell, each channel subset being different for each sector. That is, if 12 channels are assigned to each cell
102
in the system of
FIG. 1A
, then each sector in the partitioned cells
104
might support 4 channels. Under similar circumstances, the cells
106
that are partitioned into sectors as shown in
FIG. 1B
have 12 channels to split among 6 sectors. Hence, each sector in cells
106
might support 2 channels. The important concept to keep in mind is that each sector has a collection of channels associated to it.
FIG. 2
illustrates a conventional hand-in process occurring in a cellular system environment. The system has been simplified by illustrating only two cells that are not partitioned in sectors. The system includes a mobile switching center (MSC)
218
, two base stations
204
and
206
, a mobile unit
208
, and a hand-held unit
214
. The function of a MSC
218
is to coordinate the routing of calls in a large area serviced by the mobile communications system. That is, the area for which radio coverage is provided by a group of base stations associated with the MSC
218
. In a cellular radio system, the MSC
218
connects the cellular base stations and the mobiles (or hand-held units) to the Public Switched Telephone Network (not shown).
FIG. 2
only shows a portion (i.e., two cells) of the service area supported by the MSC
218
.
The MSC
218
may manage admission of calls into each cell. Namely, a call is given or denied access to a channel of the channel assigned to each base station when the mobile unit enters an area in the cell corresponding to that base station. A person of ordinary skill would recognize that base stations may also manage the admission of calls into each cell. For different types of traffic, originating either from mobiles
208
or hand-held units
214
, the MSC prioritizes the assignment of a channel to a call requesting a channel. The prioritization depends on the type of call rather than the type of equipment (mobile unit or hand-held unit) from which the call originates. Also, not all MSC's implement a call prioritization procedure, as will be discussed below.
Two common traffic types are hand-in traffic and new traffic. Hand-in traffic refers to traffic that initiates from a mobile or hand-held unit in one sector of one cell and that subsequently would benefit from being handled by a different sector, either in the same cell or in another cell. This benefit might be due to an improved signal strength caused by the motion of the mobile or hand-held unit. On the other hand, new traffic refers to either traffic that is initiated by a caller in a cell (i.e., user of a mobile
208
or hand-held unit
214
) and that was not previously handled by a different sector or cell, or to traffic initiated by other callers which call a mobile in the cell.
A “hand-in” includes the process of transferring a call from one sector in one cell, supported by a first base station, to another sector in the same cell, supported by a second base station. Also, the use of the term hand-in applies in the situation where the transfer is from one sector in one cell to another sector in another cell, the transfer from one cell to another, or more generally, the transfer from an area supported by a first set of channels, to another area supported by a second set of channels. In more practical terms, a hand-in occurs, for example, when a wireless telephone call established between a mobile user and another user is handled by a first base station, and then transferred and handled by a second base station within that call period, without an interruption in the call, where each base station uses a different set of channels to communicate with the mobile unit. The term “hand-in call” refers to a call that experiences a hand-in.
Because it is less desirable for users to have a telephone call terminated than to attempt to make a telephone call without success, hand-in calls are desirably given preference over new calls at the time of assigning a base station channel to the call. A hand-in process and the preferential treatment of hand-in calls is explained in further detail with reference to FIG.
2
.
For simplicity's sake,
FIG. 2
illustrates a hand-in process that transfers a mobile call from one cell to another. None of these cells
102
is partitioned into sectors.
It is assumed that a call from mobile
208
is in progress as the mobile
208
moves towards base station
206
, and that the hand-in call is carried via a channel established between the mobile
208
and the base station
204
. The MSC
218
monitors the signal power received from the mobile
208
on the channel supporting the call. Graph
200
illustrates the monitored signal power level of a signal received at base stations
204
and
206
. These signal levels
201
and
202
correspond to the same signal, received at two different locations (i.e., base stations
204
and
206
). Although both base stations receive the signal, only one base station handles the call being carried by the signal. The decision as to which station handles the call depends, among other things, on the signal power level received at each base
Daley Daryl J.
Greene, Sr. Gregory A.
Hogg William E.
Nail Michael
Servi Leslie D.
Milord Marceau
Trost William
Verizon Laboratories Inc.
Weixel James K.
LandOfFree
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