METHOD FOR SCHEDULING PACKET
DATA TRANSMISSION
This application is a divisional of Ser. No. 08/851,368, May 5, 1997.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to cellular telephone network data transmission, specifically to a method of scheduling packet data transmission for a connection-less packet service.
2. Prior Art
Packet data communication is known in cellular telephone systems, as is evidenced by, for example, commonly assigned U.S. Pat. No. 5,257,257, issued Oct. 26, 1993, entitled "Method of Controlling the Operation of a Packet Switched CDMA Communication Network for Controlling the Operation of Transmitters and Receivers", by X. H. Chen and J. Oksman.
One further example is defined in TIA/EIA/IS-657, Packet Data Service Option for Wideband Spread Spectrum Cellular System. IS-657 is used along with TIA/EIA/IS95A, Mobile Station-Base Station Compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular System, and, TIA/EIA/IS- 99 Data Services Option Standard for Wideband Spread Spectrum Digital Cellular System. The current IS-657 based packet data scheme for code division multiple access (CDMA) does not allow the traffic channel to be shared between more than one user. The IS-657 scheme is based on a make-and-break of multiple traffic channel connections during the life of a packet data session. In the worst case, a packet may suffer a call set-up delay which can range from tens of milliseconds to a few seconds. Also, it is possible for a mobile station (MS) to transmit idle (eighth rate) frames for a user defined time if there are no packets to send. This results in wasted bandwidth, especially in high-speed data systems, because the traffic channel capacity is reserved for this user and cannot be utilized by any other user. Thus, an access scheme that allows two or more users to share traffic channels, and allows the network to control the packet delay is needed.
In connection-less packet data transmission in mobile communication systems, discrete packets are transmitted on a packet-basis, that is, no dedicated end-to-end connection is set up. Sharing of traffic channels in connection-less packet data transmission has generally been supported via random access or random reservation media access control (MAC) protocols. Under these MAC protocols, multiple mobile stations compete for traffic channels in order to receive packet data service from a base station (BS). The number of available traffic channels for packet service within a cell is defined by the BS.
Random reservation protocols are generally believed to offer high channel utilization. However, in a CDMA based system that is approaching the system's maximum capacity, random access attempts are more likely to be unsuccessful due to higher interference levels. Thus, as a cell approaches its maximum capacity of available traffic channels, multiple MSs compete for fewer and fewer available traffic channels. This normally leads to even further access attempts by the MSs. Often, the random attempts themselves increase the communications load in the cell and reduce traffic channel capacity.
OBJECTS AND ADVANTAGES OF THE
INVENTION
It is a first object and advantage of this invention to provide an efficient method for transmitting packet data over
a cellular communication network that overcomes the foregoing and other problems.
Another object and advantage of this invention is to maintain scheduled traffic channel sharing among multiple 5 packet data users who are attached to a cell of a mobile communication network.
Another object and advantage of this invention is to provide the base station of a cellular communication network with control over which mobile station(s) may attempt 10 access to the system during a specified period of time.
Another object and advantage of this invention is to provide the base station of a cellular communication network the ability to preemptively control priority and duration of mobile station access by employing a scheduling method which considers one or more parameters including priority access service, quality of service, and a maximum number of bytes per transmission.
SUMMARY OF THE INVENTION
20
The foregoing and other problems are overcome and the objects of the invention are realized by methods and apparatus in accordance with embodiments of this invention. More particularly, this invention is directed to solving the
25 problem of inefficient packet data transmission in CDMA based mobile communication systems.
Scheduled packet access, as taught by this invention, leads to more stable load conditions, offers higher channel utilization, and enables determination and control of a
3Q maximum delay in packet data transmission experienced by users. According to the teachings of this invention, the BS divides access to the traffic channel(s) allocated for packet data services into time slots. The right to access a given traffic channel for a specific time slot is referred to as a
35 packet token, hereinafter simply a token. One or more token(s) are allocated to the MSs from time slot to time slot, in a pre-defined manner. The token allocation schedule is determined at the BS, which may employ a variety of schemes to determine how the token is assigned. This
4q pre-defined, scheduled token allocation is distinguishable over conventional random access and random reservation protocols. Token allocation, as taught by this invention, is accomplished by granting transmission access to an available traffic channel to each packet data MS in the cell
45 according to specific, scheduled time intervals. This scheduled approach allows the BS to preemptively control traffic channel access among packet data MSs. Random access protocols, on the other hand, allow access to an available traffic channel as a packet data MS requests it. Thus, the
5q conventional random protocols employ a first-come-firstserve method of traffic channel access assignment.
Allocating the right to access an available traffic channel may not always result in a transmission from the packet data MS. If, at the end of a time slot, the BS has not received a
55 valid transmission from the MS(s) who are allocated the token(s), either because the MS has nothing to send or an access preamble did not reach the BS successfully, then the BS allocates the token to the next MS(s) in the cell. In this way, the MSs share the packet traffic channels in a time
60 multiplexed fashion, and the BS schedules and controls the allocation of the traffic channels at all times. This technique eliminates the problems associated with conventional MS random access attempts to gain a traffic channel for transmitting a packet.
65 This invention preferably employs a technique in which a BS transmits at least one dedicated MAC channel on the forward link. When transmitting the MAC channel messages
