Multiplex communications – Channel assignment techniques – Using time slots
Reexamination Certificate
2000-05-19
2004-10-12
Qureshi, Afsar (Department: 2667)
Multiplex communications
Channel assignment techniques
Using time slots
C370S437000, C370S321000, C370S441000, C455S450000
Reexamination Certificate
active
06804252
ABSTRACT:
BACKGROUND
Continued growth in the electronics and computer industries, and indeed in the economy in general, is increasingly driven by the demand for access to the Internet and the myriad of services and features that it provides. The proliferation in the use of portable computing equipment, such as laptop computers, hand-held Personal Digital Assistants (PDAs) and Internet-enabled cellular telephones have resulted in a corresponding increase in demand for wireless access to computer networks. However, at the present time, existing wireless networks, such as the cellular telephone network, are not optimum for data communications. This is at least in part due to the architecture of such networks as originally designed. In particular, these networks were intended to support voice communications, as compared to the digital communication protocols needed for Internet packet-oriented communications. For example, voice grade services typically require access to a communication channel bandwidth of approximately 3 kilohertz (kHz). While techniques do exist for communicating data over such radio channels at a rate of 9.6 kilobits per second (kbps), such low bandwidth channels do not lend themselves directly to efficient transmission of data at the typical rates of 56.6 kbps or higher that are now commonly expected using wireless modems.
In addition, the very nature of Internet traffic itself is different from the nature of voice traffic. Voice communication requires a continuous duplex connection, that is, a user at one end of a connection expects to be able to transmit and receive to a user at the other end of a connection, while at the same the user at the other end is also transmitting and receiving.
However, the usage patterns of Internet data transmission systems are quite different from voice. For example, consider that access to Web pages over the Internet in general is burst-oriented. Typically, the user of a remote client computer first specifies the address of a Web page to a browser program. The browser program at the client computer then sends the request as a Transmission Control Protocol (TCP)/Internet Protocol (IP) message packet, which is typically about 100 bytes in length, to a network Web server. The Web server then responds with the content of the requested Web page, which may include anywhere from approximately 10 kilobytes to several megabytes of text, image, audio or video data. The user may thereafter spend several seconds or even several minutes reading the contents of the page before specifying a next Web page to be downloaded.
The result is that a typical Internet connection remains idle for a relatively long period of time. However, once a request is made, the user expects the information to be transmitted to the client at a relatively rapid rate. Therefore, making available channels only on an instantaneous “as needed” basis makes sense and indeed is a requirement if wireless data transfer services are to efficiently co-exist with the existing wireless voice communication systems. Therefore, dynamic traffic channel allocation schemes are required to increase the efficiency of high performance wireless data communication systems in an effort to more efficiently utilize available channel resources.
Furthermore, in most wireless systems, there are typically many more potential users or subscribers than available radio channel resources. Therefore, some type of demand-based multiple access technique is therefore typically required to make maximum use of the available radio channels. Multiple access is often provided in the physical layer, such as by Frequency Division Multiple Access (FDMA) or by schemes that manipulate the radio frequency signal such as Time Division Multiple Access (TDMA) or Code Division Multiple Access (CDMA). In any event, the nature of the radio spectrum is such that it is a medium that is expected to be shared. This is quite dissimilar to the traditional environment for data transmission, in which a wired medium such as a telephone line or network cabling is relatively inexpensive to obtain and to keep open all the time.
SUMMARY OF THE INVENTION
A particular problem exists with efficiently adapting communication systems which use on-demand multiple access techniques in the physical layer to efficiently handle the TCP/IP message traffic which is prevalent in Internet communications. Consider that the TCP/IP protocol is a frame-based protocol requiring the acknowledgment of the receipt of message frames. Thus, for example, when a user requests that a Web page be transmitted, the initial message requesting the Web page is sent on a reverse link communication channel from a client computer towards a Web server computer. The sending of the request message also requires allocation of a forward link connection to allow the acknowledgment message to return from the server to the client.
Unfortunately, in a wireless communication environment in which demand access is granted to wireless radio channels, opening up a new reverse link channel for the acknowledgment message is a time consuming process. For example, to allocate a channel in the reverse link direction may indeed end up taking longer than the time necessary to simply transmit the very short acknowledgment message.
The present invention seeks to overcome these difficulties. The invention is used in a time division multiplex (TDM) communication system supporting duplex operations whereby multiple users share forward and reverse channels. The system makes use of time slots to allocate specific channels on a demand basis. Thus, for example, a given forward link channel is allocated for only a predetermined time slot duration and only upon user request.
To minimize overhead in the allocation of channels, forward and reverse link time slots are automatically assigned in pairs. In particular, rather than requiring a separate process for allocating reverse link channels for the sending of acknowledgment messages in response to receipt of a forward link packet, a different scenario takes place. At the receiving end, such as for valid reception of data on a forward link channel at a central base station site, a reverse link time slot is automatically allocated in a time slot which depends upon the time slot allocation on the forward link.
This scheme assists with the rapid return of acknowledgment messages in a reverse link direction which is the predominant direction for such messages in a wireless system wherein most data traffic is Web page oriented.
The invention has several other advantages. Among these include the avoidance of the need to set up and tear down channels, especially reverse link channels, for the limited purpose of sending acknowledgment messages.
Minimizing the amount of reverse link traffic on shared frequency channels, such as in a CDMA system, in turn increases the data handling capacity of the entire system. The reverse link messages may also include other types of anticipated short messages, depending upon the type of forward link messages sent. For example, these may include link layer acknowledgment messages, or higher layer GET messages for links embedded in a Web page.
While the invention provides particular advantages in not explicitly allocating reverse link traffic channels for the anticipation of acknowledgment and other short messages, dedicated reverse link channels may still be explicitly allocated for long message traffic.
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Hamilton Brook Smith & Reynolds P.C.
IPR Licensing Inc.
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