Multiplex communications – Communication over free space – Having a plurality of contiguous regions served by...
Reexamination Certificate
1999-12-08
2003-07-15
Urban, Edward F. (Department: 2685)
Multiplex communications
Communication over free space
Having a plurality of contiguous regions served by...
C370S437000, C370S464000, C455S450000, C455S464000, C455S509000
Reexamination Certificate
active
06594241
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to data packet communications, and in particular, to controlling switching between communication channels of different types.
BACKGROUND AND SUMMARY OF THE INVENTION
In current and future mobile radio communications systems, a variety of different services either are or will be provided. While mobile radio systems have traditionally provided circuit-switched services, e.g., to support voice calls, packet-switched data services are also becoming increasingly important. Example packet data services include e-mail, file transfers, and information retrieval using the Internet. Because packet data services often utilize system resources in a manner that varies over the course of a data packet session, the flow of packets is often characterized as “bursty.” Transmitted packet bursts are interspersed with periods where no packets are transmitted so that the “density” of packets is high for short time periods and often very low for long periods.
Mobile communications systems must be able to accommodate both circuit-switched services and packet-switched services. But at the same time, the limited radio bandwidth must be used efficiently. Consequently, different types of radio channels may be employed to more efficiently accommodate different types of traffic to be transported across the radio interface.
The Global System for Mobile communications (GSM) is one example of a mobile communications system that offers circuit-switched services via a Mobile Switching Center (MSC) node and packet-switched services via a General Packet Radio Service (GPRS) node. For circuit-switched, guaranteed service, dedicated traffic channels are employed. A radio channel is dedicated (for the life of the mobile connection) to a particular mobile user and delivers frames of information as received without substantial delay. Typically, a dedicated channel provides a high data throughput. For packet-switched, best effort service, common channels are employed where plural mobile users share the common channel at the same time. Typically, a common channel delivers packets of information at a relatively low data throughput. Thus, when the quality of service parameter(s) requested is (are) relatively high, e.g., for a speech or synchronized communication, soft/softer handover, etc., a dedicated, circuit-switched channel is well suited to handle this kind of traffic. When the quality of service requested is relatively low, e.g., for an e-mail message, or if the user only has a small amount of data to transmit, a common, packet-switched channel is well suited to handle this kind of traffic. However, there is no “switching” between different types of channels in GSM/GPRS. All dedicated traffic is GSM circuit-switched, and all common traffic is GPRS packet-switched.
The selection of the appropriate channel type and channel type switching are prominent features to be included in third generation mobile systems that employ Wideband Code Division Multiple Access (W-CDMA). The third generation wideband CDMA systems must support a variety of circuit-switched and packet-switched services over a wide range of bit rates, e.g., kilobits per second to megabits per second. Two of the most critical radio resources in wideband CDMA needed to support such services are channelization codes and transmission power. Channelization codes are used to reduce interference and to separate information between different users. The more channel capacity required, the more channelization codes that must be allocated. The other critical radio resource is transmission power/interference level. Dedicated channels employ closed loop transmit power control which provides more accurate power assignments resulting in less interference and lower bit error rate. Common channels usually employ open loop power control which is less accurate and not as well suited for transmitting large amounts of data.
There are additional challenges in wideband CDMA systems to offering new and diverse services while at the same time effectively and efficiently distributing the limited system resources. For example, while data traffic is by nature “bursty,” as described above, traffic patterns are also affected by the particular transmission protocol employed. For example, the most commonly used transmission protocol on the Internet today is Transmission Control Protocol (TCP). TCP provides reliable, in-order delivery of a stream of bytes and employs a flow control mechanism and a congestion control mechanism. The amount of data delivered for transmission is regulated based on the amount of detected congestion, i.e., packets lost due to overflow in routers caused by traffic greater than the network capacity. To accomplish this regulation, when TCP senses the loss of packets, it reduces the transmission rate by half or more and only slowly increases that rate to gradually raise throughput. Another factor to consider is the use of different Quality of Service (QoS) classes. For example, three different priority classes may be provided to users in a network: low priority would include users with small demands in throughput and delays (e.g., an e-mail user), medium priority users that demand a higher level of throughput (e.g., Web service), and high priority users requiring high throughput with low delays (e.g., voice, video, etc.).
Because of the bursty nature of packet data transmissions, congestion-sensitive transmission protocols, QoS parameters, and other factors, (collectively “dynamic aspects” of packet data transmissions), the channel-type best-suited to efficiently support a user connection often changes during the life of that user connection. At one point, it might be better for the user connection to be supported by a dedicated channel, while at another point it might be better for the user connection to be supported by a common channel. The problem addressed by the present invention is determining if, when, and how often to make a channel-type switch during the course of a particular user connection.
One way of determining when to switch a user connection from a dedicated channel to a common channel is to monitor the amount of data currently being stored in a transmission buffer associated with that user connection. When the amount of data stored in the buffer is less than a certain threshold, that smaller amount of data may not justify the use of a dedicated channel. On the other hand, the decrease in the amount of data to be transmitted for that user may only be temporary, given the dynamic aspects of data transmission, and the amount of data in the buffer may quickly accumulate because of the load on the common channel or increased capacity needs for the connection. As a result, the connection may need to be switched right back to a dedicated channel.
Consider the situation where a user connection is currently assigned a dedicated radio channel having a higher data transmission rate/capacity than the current incoming rate of the user data to be transmitted over that channel. This situation might arise if there is congestion at some part of the Internet, e.g., Internet congestion causes TCP to dramatically reduce its transmission rate as described above. A slower incoming rate may also be the result of a “weak link” in the connection external to the radio network, e.g., a low speed modem. In such situations, the radio transmit buffer is emptied faster than the data to be transmitted arrives. As a result of the slow incoming data rate, which may very well only be temporary, the user connection is switched to a common channel, even though soon thereafter, the user has a large amount of data to transmit. Consequently, shortly after the user connection is transmitted to the common channel, the buffer fills up rapidly due to lower throughput on the common channel, and the user connection is switched right back to a dedicated channel. These conditions may ultimately result in rapid, prolonged switching back and forth between a common channel and a dedicated channel as long as such conditions persist. Such “ping-p
Nixon & Vanderhye P.C.
Telefonaktiebolaget LM Ericsson (publ)
Trinh Sonny
Urban Edward F.
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