Quality of service based CDMA broadcast scheduler

Details Quality of service based CDMA broadcast scheduler Quality of service based CDMA broadcast scheduler

1999-08-25

2002-09-10

Trost, William (Department: 2683)

Telecommunications

Radiotelephone system

Auxiliary data signaling

C455S503000, C370S335000, C340S007300

Reexamination Certificate

active

06449488

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to the field of telecommunications and, more particularly to a method and apparatus for providing a quality of service (QoS) based broadcast message scheduler for a CDMA wireless telecommunications system.
2. Description of the Related Art
FIG. 1
illustrates a schematic diagram of a portion of a typical wireless telecommunications system
100
and in particular, a code division multiple access (CDMA) wireless telecommunication system. The system
100
provides wireless communication service to a number of wireless terminals
101
-
1
,
101
-
2
,
101
-
3
that are situated within a graphical region. The heart of a typical wireless telecommunications system
100
is the Mobile Switching Center (MSC)
120
, which may also be known as a Wireless Switching Center (WSC) or Mobile Telephone Switching Office (MTSO). Typically, the MSC
120
is connected to a plurality of base stations
103
-
1
,
103
-
2
,
103
-
3
,
103
-
4
,
103
-
5
that are dispersed throughout the geographic area serviced by the system
100
and to at least one Public Switched Telephone Network (PSTN)
130
. The MSC
120
is responsible for, among other things, establishing and maintaining calls between wireless terminals and between a wireless terminal and a wireline terminal (not shown), which is connected to the system through local and/or long distance networks.
The geographic area serviced by the system
100
is partitioned into a number of spatially distinct areas called “cells.” In
FIG. 1
each cell is schematically represented by a hexagon; in practice, however, each cell usually has an irregular shape that depends on the topology of the terrain serviced by the system
100
. Typically, each cell contains a base station, such as for example base station
103
-
1
, which includes the radios and antennas that the base station uses to communicate with the wireless terminals in that cell and also comprises the transmission equipment that the base station uses to communicate with the MSC
120
.
For example, when wireless terminal
101
-
1
desires to communicate with wireless terminal
101
-
2
, wireless terminal
101
-
1
transmits the desired information to base station
103
-
1
, which relays the information to MSC
120
. Upon receipt of the information, and with the knowledge that the information is intended for wireless terminal
101
-
2
, the MSC
120
returns the information back to base station
103
-
1
, which relays the information to the wireless terminal
101
-
2
.
The MSC
120
is also connected to a short message service (SMS) message center (MC)
125
. The SMS MC
125
provides SMS and broadcast short message service (BSMS) to the system
100
. As known in the art, the BSMS allows the transmission of short text messages to multiple users within the system
100
. When received, the text message is displayed on the user's wireless terminal. Typically, the BSMS is used by the service provider for applications such as traffic and weather advisories, news and sports reports and mass advertisements.
In a CDMA telecommunications system information is transmitted over a traffic channel in fixed units of time referred to as frames. Each frame is typically twenty milliseconds long. Speech information is coded by a vocoder and transmitted in units referred to as speech frames, which have the same duration as the traffic frames on the CDMA traffic channel. The voice process of a user comprises alternating talk-spurt and silence periods, which are respectively reflected as voice data and breaks (i.e., no data) in the voice data of the speech frames. A BSMS message is transmitted on the forward traffic channel, i.e., base station to wireless terminal channel, along with voice information.
Each BSMS message is limited in size and delivered to a user in the form of data burst messages. Typically, the BSMS message is multiplexed into the traffic frame with the voice data by what is commonly referred to as a “dim and burst” method (i.e., where, depending upon the user's vocoder mode, a minute portion of the voice data is chopped off or dimmed and the BSMS message information is used to fill in the breaks of the frame). It should be appreciated that the multiplexing of the BSMS message with speech information may be carried out in several ways depending upon the user's service requirements.
It is desirable for the service provider to transmit BSMS messages to its users. It is also desirable for the users to receive the BSMS messages from the service provider. Unfortunately, the transmission of BSMS messages in a CDMA telecommunications system is not without its shortcomings. For example, signal interference between users of the CDMA system increases when the BSMS messages are multiplexed with the voice data. That is, since the breaks in the frame are now filled with the BSMS message information, extra radio frequency (RF) transmissions are required to transmit the traffic frames with the BSMS message in comparison to the RF transmission that would have been required to transmit the frame without the BSMS message. The extra RF transmissions are further compounded by the fact that the BSMS message is being transmitted to each user in the system. The extra RF transmissions to each user causes interference with the other users in the system. This interference dramatically effects the voice quality of the CDMA system.
Moreover, system capacity is also reduced by the transmission of BSMS messages. As is known in the art, in a CDMA wireless telecommunications system a base station process commonly referred to as “power control” regulates the transmitting power of wireless terminals communicating with the base station. The power control process also regulates the number of users that a cell can support at any one time based on the amount of noise or interference present within the cell. Since a CDMA wideband channel is reused in every cell, self interference caused by other users of the same cell and interference caused by users in other cells is the most limiting factor to the capacity of the cell and thus, the CDMA system. Due to fading and other channel impairments, maximum capacity is achieved when the signal-to-noise ratio (SNR) for every user is, on the average, at the minimum point needed to support an acceptable channel performance. Based on these and other principles, power control determines whether a new user (i.e., wireless terminal) or call can be added to a cell within the system. If power control determines that a new user or call cannot be added to a cell, it prevents the user from gaining access to the cell. Thus, the increased interference associated with the transmissions of the BSMS messages can also reduce the capacity of the CDMA telecommunications system.
Ensuring that a CDMA system operates to its full capacity while maintaining a high voice quality is extremely important for a CDMA service provider in terms of its revenue, customer satisfaction and reputation. As noted above, it is also desirable for the service provider to transmit BSMS messages and for the users to receive the BSMS messages. Accordingly, there is a desire and need to reduce the adverse impact on voice quality and system capacity attributable to the transmission of BSMS messages in a CDMA wireless telecommunications system.
SUMMARY OF THE INVENTION
In view of the foregoing shortcomings, and for other reasons, the present invention is directed to scheduling broadcast short message service (BSMS) messages in a manner that reduces the adverse impact on voice quality and system capacity, attributable to the transmission of the BSMS messages, in a wireless telecommunications system. The present invention comprises a computer implemented method and apparatus utilizing a quality of service (QoS) based broadcast message scheduler to negotiate and schedule the transmission times of the BSMS messages to the individual users in the system. The present invention also allows a user to tradeoff voice quality for broadcast capacity.

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