Management of wireless control channel

Details Management of wireless control channel Management of wireless control channel

1998-12-10

2003-04-08

Zimmerman, Brian (Department: 2735)

Multiplex communications

Communication over free space

Combining or distributing information via time channels

C455S515000

Reexamination Certificate

active

06545996

ABSTRACT:

FIELD OF THE INVENTION
This invention is related to a control channel of a wireless telecommunications system, and more particularly to the scheduling of messages on the control channel.
BACKGROUND OF THE INVENTION
The radio spectrum assigned to a wireless telecommunications system is divided into radio channels. The radio channels are typically grouped into multiple traffic and control channels. The traffic channels are used for transmission of voice and user data information between a base station and mobile stations. The control channels are used for transmission of broadcast messages that convey system information, control messages, pages, and short user data messages between the base station and the mobile stations. Pages are messages that notify a mobile station that a base station needs to send further instructions to the mobile station. Pages include voice pages, notification of short messages, and message waiting messages.
The control channel's pages wake up a mobile station when the mobile station is in sleep mode. Typically, to conserve power, a mobile station operates in a sleep mode, where most of the mobile station's systems are in either off or operating in a power conservation mode. The mobile station wakes up, i.e. exits from sleep mode, for a predetermined short period of time to monitor the control channel to determine whether it needs to remain awake or whether it can return to the sleep mode. If a mobile station receives a page from the base station during the predermined time period, or if there is local action that requires the mobile station to wake up, the mobile station turns on some or all of the internal systems that were off during sleep mode.
The control channel also includes non-pages, such as acknowledgements including mobile station registration acknowledgements, and control messages that are used to set up a call including channel assignments. Additionally, depending on the system the control channel may also include other messages. Typically, the organization of the control channel and the information transmitted on the control channel is dependent on the type of air interface used.
Referring to
FIG. 1A
, for example, in a typical system using the North American Time Division Multiple Access (TDMA) system the radio spectrum is divided into 30 kHz radio channels
5
. Each radio channel
5
is divided into time slots having a duration of 6.67 milliseconds (ms). Three time slots comprise a TDMA Block and two consecutive TDMA Blocks or six time slots comprise a frame. As shown in
FIG. 1A
, every third time slot is used to create communication channel
10
. A communication channel can be either a control channel or a traffic channel. All time slots
1
and
4
are associated with one communication channel. All time slots
2
and
5
are associated with another communication channel, and all time slots
3
and
6
are associated with a third communication channel. When the control channel is used for sending information from the base station to the mobile station it is a downlink control channel, and when the control channel is used for sending information from the mobile station to the base station it is an uplink control channel. In a downlink control channel, 32 time slots comprise superframe
11
having a duration of 0.64 seconds, and as shown in
FIG. 1B
, two such superframes
11
,
14
comprise hyperframe
12
having a duration of 1.28 seconds. The first superframe in a hyperframe is referred to as the primary superframe (primary superframe
11
) and the second superframe is referred to as the secondary superframe (secondary superframe
14
). Each time slot has a time slot number that identifies the time slot's position in the superframe. Each hyperframe has a hyperframe number that identifies the position of the hyperframe in a cyclic repetition of hyperframes, which is typically 12 hyperframes.
In downlink control channel
10
, several of the time slots in each superframe are reserved for broadcasting. Broadcasting is the transmittal of generic system related information. The remaining time slots are used for all of the other messages carried by the control channel. As discussed above, in order to conserve power a mobile station only monitors the control channel during one assigned time slot and remains in sleep mode during the rest of the time slots. The mobile station is assigned to a particular time slot based on the mobile station's mobile identification number (MIN). In North American TDMA the MIN is the mobile station's area code and phone number. A hashing algorithm is used to determine which time slot is assigned to a particular MIN. A hashing algorithm is a function or table that pseudo-randomly assigns an output, such as a particular time slot, based on an input, such as the MIN.
Monitoring the control channel during one assigned time slot and remaining in sleep mode during the rest of the time slots results in the mobile station waking up for only one time slot in every superframe to check for pages such as voice pages or R-DATA SPACH notifications. A voice page is a brief page that informs the mobile station that there is a call to the mobile station, and an R-DATA SPACH notification is a brief message that informs the mobile station that there is a short message or SMS for the mobile station. If a mobile station receives a page, such as a voice page or a R-DATA SPACH notification, then the mobile station starts monitoring all of the time slots of the control channel to find further information, which can be in any time slot except the ones reserved for broadcast messages. In the case of receiving a voice page, the mobile station is waiting to receive a channel assignment in order to know what traffic channel to switch to to begin the voice call. In the case of receiving an R-DATA SPACH notification, the mobile station is waiting to receive a short message. If the mobile does not receive the further information within a certain period of time, for example 10 to 15 seconds, the mobile station goes back into sleep mode.
Pages are transmitted in the corresponding time slots of both superframes of a particular hyperframe. Referring to
FIG. 1B
, pages are transmitted once in a time slot of the first, or primary superframe
11
, and a second time in the corresponding time slot of the second, or secondary superframe
14
of the same hyperframe
12
. Non-pages are transmitted only once, and each message may require one or several time slots of the superframe. For example, if a channel assignment is transmitted in time slots
7
and
9
of primary superframe
11
of hyperframe
12
, a different non-page can be transmitted in time slots
7
and
9
of secondary superframe
14
. Typically, the priorities of pages are higher than that of the other messages, with voice pages having the highest priority. The priority of messages is typically fixed when the wireless communication system is designed and is based on the messages' characteristics, such as the messages' revenue generation potential, whether the message is assigned to a particular time slot (such as a voice page for a particular mobile station), and the timeout sensitivity of the message. A message's timeout sensitivity is determined by how quickly the message is dropped because the message had to wait to be transmitted for a longer time than allowed by the system for this type of message. A timed out message is one that had to wait longer than the time allowed by the system.
A mobile station registers with the wireless communication system using the uplink control channel. The base station that received the mobile station's registration message over the uplink control channel is identified as the base station having the mobile station within its cell. The wireless system may initially attempt to send pages to the mobile station using only the base station where the mobile last registered. If the mobile station is still in the cell where it last registered, the mobile station will receive pages. However, in most cases the mobile sta

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