Method, systems, and terminals for assigning control channel...

Details Method, systems, and terminals for assigning control channel... Method, systems, and terminals for assigning control channel...

1999-05-10

2003-03-11

Bost, Dwayne (Department: 2681)

Multiplex communications

Communication over free space

Having a plurality of contiguous regions served by...

C370S314000, C370S329000, C370S442000

Reexamination Certificate

active

06532224

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to the field of communications and more particularly to radiotelephone communications methods and systems.
BACKGROUND OF THE INVENTION
Conventional cellular communications systems (such as systems operating according to the IS-136 standard) generally provide one-to-one communications from one mobile terminal to another mobile terminal or to a landline telephone coupled to a public switched telephone network. A conventional cellular communications system is illustrated in FIG.
1
. This system includes a mobile switching center (MSC)
31
and a home location register
33
.
The MSC is coupled to a plurality of radio base stations (RBS)
32
wherein each RBS
32
defines a cell
35
. In addition, the MSC can be coupled to a public switched telephone network (PSTN)
36
. As will be understood by those having skill in the art, the conventional cellular communications system of
FIG. 1
can provide cellular radiotelephone communications for one or more cellular mobile terminals (MT)
37
. More particularly, the cellular radiotelephone communications can be provided using conventional cellular standards wherein a telephone is dialed to place a call to another communications device.
Each RBS provides radio frequency transmit and receive functions and supports low level protocol functions. Moreover, a RBS can be considered a dumb peripheral of the MSC
31
wherein the MSC provides central intelligence for the system. Each RBS can be coupled to the MSC
31
via communications links
39
. These communications links can be T1 links provided, for example, via landline or microwave. The MSC
31
provides voice path switching between two cells or a cell and the PSTN
36
. The MSC
31
provides central system intelligence to control the radio base stations and to process high level protocol messages from mobile terminals
37
relayed by the radio base stations. In other words, the MSC handles call setup, paging, handoff, and call connection.
The home location register
33
keeps track of the current status of the mobile terminals. For each mobile terminal, for example, the home location register can record whether that terminal is on, off, or busy, as well as the location area (including a group of cells) within which the mobile terminal is located. The home location register can also include a database of restrictions and allowed service features for each mobile terminal. The home location register can also be considered a portion of the MSC.
The setup of a call between mobile terminals
37
using the system of
FIG. 1
is illustrated in FIG.
2
. As shown, the originating mobile terminal
37
a
issues an origination message which is received by the radio base station
32
a
for the cell
35
a
in which the mobile terminal
37
a
is located. The radio base station
32
a
checks the origination message for errors, and if no significant errors are detected, the radio base station
32
a
forwards the message to the mobile switching center. The mobile switching center authenticates the originating mobile terminal
37
a
and analyses the called number. If the originating mobile terminal and the called number are valid, the mobile switching center instructs the radio base station
32
a
to assign a Digital Traffic Channel (DTC) to the originating mobile terminal. Origination and channel designation messages are discussed, for example, in TR45, TIA, EIA-136-123-A Draft Text, Digital Control Channel Layer 3, Aug. 31, 1998, the disclosure of which is hereby incorporated herein in its entirety by reference.
Because the called party is another mobile terminal, the mobile switching center checks the HLR to determine the current location area (LA) for the called mobile terminal
37
b
if the called mobile terminal is active. A plurality of cells is assigned to a location area, and a mobile terminal updates its location with the cellular system only when the mobile terminal enters a new location area. Accordingly, location area updates are not needed every time a mobile terminal enters a new cell. While Digital Control Channel (DCCH) traffic may be reduced, pages for a called mobile terminal may need to be transmitted in all cells assigned to the location area.
The mobile switching center then issues a page message to all radio base stations supporting cells in the location area of the called mobile terminal
37
b.
Each of these radio base stations issues a page message on an appropriate paging subchannel. Because of the DCCH paging structure, however, a period of time as long as 1.28 seconds may pass before the page message can be issued. The page message wakes the called mobile terminal from its battery sleep mode, and the called mobile terminal
37
b
responds to the appropriate radio base station (now referred to as the called radio base station
32
b
) with a page response message to indicate the same.
The page response message is relayed from the called radio base station
32
b
to the mobile switching center, and the mobile switching center instructs the called radio base station
32
b
to assign a digital traffic channel to the called mobile terminal
37
b.
The mobile switching center then completes a communications path between the originating mobile terminal
37
a
and the called mobile terminal
37
b
using the two digital traffic channels.
Pages transmitted from the cellular communications system to a mobile terminal can be transmitted over a digital control channel (DCCH) as shown in FIG.
2
B. For example, the page transmitted by the radio base station to the terminal
37
b
of
FIG. 2A
can be transmitted over the digital control channel of FIG.
2
B. In particular, the digital control channel can be a time division multiple access (TDMA) control channel including a plurality of time slots T
0
to T
31
grouped into time frames so that each time frame includes a plurality of sequential time slots. According to the IS-136 standard, each super frame can include 32 time slots. Moreover, the time frames can be organized into a hyperframe structure with a primary superframe and a secondary superframe included in each hyperframe with each secondary superframe repeating the information transmitted during the preceding primary superframe. Accordingly, a mobile terminal typically has two opportunities to receive information transmitted over the digital control channel of FIG.
2
B.
A page can thus be transmitted to a mobile terminal during one of the 32 time slots of the primary superframe and then retransmitted during the corresponding time slot of the secondary superframe. To save power at the mobile terminal, the mobile terminal is assigned a time slot over which pages for the mobile terminal will be transmitted. Accordingly, the mobile terminal need only monitor the assigned time slot in each superframe, and the mobile terminal receiver can be powered down during the other time slots. In the example of
FIG. 2B
, the mobile terminal
37
is assigned time slot T
12
so that pages for the mobile terminal are transmitted during the twelfth time slot of a frame. The mobile terminal receiver can thus be turned off during time slots T
0
-T
11
and T
13
-T
31
of each time frame thereby reducing power consumption and increasing battery life. Moreover, if a page for the mobile terminal is correctly received during the assigned time slot of a primary superframe, the mobile terminal receiver can be turned off during the entirety of the subsequent secondary superframe.
A control channel paging time slot is typically assigned to the mobile terminal within a cell of a cellular communications system using a hashing algorithm based on a mobile identification number (MIN) for the mobile terminal. According to the IS-136 standard, this hashing algorithm is independently executed by both the mobile terminal and the radio base station for the cell so that the assignment of the time slot is not communicated between the mobile terminal and the radio base station. The hashing algorithm typically is designed to distribute mobile terminals within a cell across the

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