Multiplex communications – Communication over free space – Having a plurality of contiguous regions served by...
Reexamination Certificate
1997-07-29
2001-04-17
Nguyen, Chau (Department: 2663)
Multiplex communications
Communication over free space
Having a plurality of contiguous regions served by...
C370S468000
Reexamination Certificate
active
06219343
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to cellular telephone network data transmission, specifically to techniques for rate control used by a code division multiple access (CDMA) network to control the data rate allocations to packet data users in the network.
BACKGROUND OF THE INVENTION
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.
The cellular telephone industry has experienced an explosive growth in the last decade. This growth has driven many communication systems near capacity, particularly in major metropolitan areas. As a communication system's capacity is reached, users experience longer delays. Thus, innovative techniques are required to optimize system throughput and minimize delays.
In conventional circuit switched communication networks, users are offered a traffic channel based on a first-come, first-served basis. If the communication network reaches its maximum capacity, calls are blocked. In order to serve a predicted amount of user traffic while maintaining an acceptable level of blocking, the network must reserve sufficient capacity, i.e. traffic channels. The number of channels reserved to ensure sufficient capacity may be calculated from the Erlang B formula.
In contention based packet data networks, packet data requests are also served on a first-come, first-served basis. However, blocking levels are reduced by setting a limit on the maximum transmitted packet length. Thus, traffic channels are shared by the packet data users in a time multiplexed fashion. As the input load increases within the packet data network, users start to experience longer delays. Rate control for the packet data networks operating in a time multiplexed fashion is straightforward. The efficiency of the packet data network is determined by the speed at which the network allocates and releases traffic channels. Based on the nature of packet data transmissions, packet data networks can be quite stable and efficient, as long as the average input load is below a specified level.
When CDMA networks based on the TIA/EIA/IS-95A, Mobile Station-Base Station Compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular System, hereinafter simply referred to as IS-95A, offer packet data services they offer circuit switched call setup. Therefore, a CDMA network employing IS-95A can not offer the function of fast traffic channel allocation or releasing as needed for the packet data traffic. Using the conventional circuit switched Erlang B formula, the network is inefficient since the call duration for a packet data transmission is normally much shorter than a switched call.
Thus, a rate control strategy is needed in CDMA networks which improves channel utilization for packet data users while it reduces delays due to blocking.
Objects and Advantages of the Invention
It is a first object and advantage of this invention to provide an efficient technique 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 define techniques of rate control used by a code division multiple access (CDMA) network to control the data rate allocations to packet data users in the network.
Another object and advantage of this invention is to define techniques of rate control used by a CDMA network to optimize total system throughput, minimize user delay, and to offer more user traffic capacity per cell.
SUMMARY OF THE INVENTION
The foregoing and other problems are overcome and the objects of the invention are realized by methods in accordance with embodiments of this invention. More particularly, this invention is directed to solving the problem of inefficient packet data transmission in CDMA based mobile communication networks.
The present invention applies to, by example, IS-95A based CDMA networks which are planned for circuit switched traffic, i.e. speech, which at the same time, offer packet switched data services via circuit switched call setup procedures. In the present invention, the entire CDMA carrier may be dedicated for packet data services, or speech and data services can be mixed on the same carrier. However, the rate control algorithms as defined by the present invention are intended to be applicable to the packet data services.
In accordance with the present invention, a base station (BS) of a CDMA based mobile communication network defines a certain number of traffic channels for packet service within a cell. Additionally, a certain radio capacity is defined for packet services. In the CDMA network, the radio capacity is measured by the transmission power needed for the service. The number of traffic channels and radio capacity, referred to collectively as network resources, are increased or decreased from time to time in order to maintain a certain level of service.
Currently, under conventional methods of packet data service in IS-95A, when a packet arrives from the interworking function (IWF), e.g. internet, it is put into a buffer. A circuit switched call setup procedure is then triggered which evaluates the network resources in order to allocate a traffic channel for the transmission from the BS to a mobile station (MS), or from the MS to the BS. At the time the traffic channel is allocated a certain data rate is also determined for the transmission. At the end of the packet transmission, the traffic channel is either released immediately or else is released upon the expiration of an inactivity timer.
In the preferred embodiment of the present invention, two rate control algorithms may be employed to determine the most efficient data rate allocation for a packet data transmission. First, the transmission power of the BS for packet data service is evaluated in order to control the sharing of available network resources among the users. Second, the current system load of the cell is evaluated in order to control the peak data rate allocated per user transmission. Note that, in both algorithms, the amount of total transmit power from one BS for packet service is directly proportional to the radio capacity used by the packet service in that cell on the forward link. Thus, the network controls the capacity occupied by a packet data user by limiting the transmit power needed to provide a specific data rate to that user. The transmit power is dependent upon the location of the user within the cell. That is, the transmit power is determined by the path loss from the user to the serving BS. For the same data rate, the larger the path loss the higher is the required transmit power from the BS, and thus the radio capacity consumed by the user is greater. As such, the maximum data throughput is achieved when the MS with the smallest path loss is given the highest data rate.
In the present invention, the second technique for rate control evaluates the current system load level in order to determine a suitable data rate. This technique determines the current system load level by evaluating several parameters including, for example, the current load measured as the number of network resources already allocated, the maximum system load measured as the total number of network resources which may be allocated within the cell for packet data services, and data rate requests from the current packet data connections.
In accordance with the present invention, the total data throughput of the BS is monitored. The monitoring is required because the network has a theoretical upper bound of total throughput. For example, the network may become unstable as it approaches 50% to 75% of the maximum load. Thus, the existing load is used so that the peak user rate allocated is inversely proportional to the current load. For example, a light load means that a high peak rate is allocated, while a heav
Honkasalo Zhichun
Ma Lin
Parantainen Janne
Boakye Alexander
Gnuschke Jerald J.
Nguyen Chau
Nokia Mobile Phones Ltd.
Shaw Steven A.
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