1. Field
The present invention relates to point-to-multipoint services, in a wireline or a wireless communication system. More specifically, the present invention relates to a method and an apparatus for channel management in such a point-to-multipoint services in a communication system.
2. Background
Communication systems have been developed to allow transmission of information signals from an origination station to a physically distinct destination station. In transmitting information signal from the origination station over a communication channel, the information signal is first converted into a form suitable for efficient transmission over the communication channel. Conversion, or modulation, of the information signal involves varying a parameter of a carrier wave in accordance with the information signal in such a way that the spectrum of the resulting modulated carrier is confined within the communication channel bandwidth. At the destination station the original information signal is replicated from the modulated carrier wave received over the communication channel. Such a replication is generally achieved by using an inverse of the modulation process employed by the origination station.
Modulation also facilitates multiple-access, i.e., simultaneous transmission and/or reception, of several signals over a common communication channel. Multiple-access communication systems often include a plurality of remote subscriber terminals requiring intermittent service of relatively short duration rather than continuous access to the common communication channel. Several multiple-access techniques are known in the art, such as time division multiple-access (TDMA), frequency division multiple-access (FDMA), and amplitude modulation multiple-access (AM). Another type of a multiple-access technique is a code division multiple-access (CDMA) spread spectrum system that conforms to the “TIA/EIA/IS-95 Mobile Station-Base Station Compatibility Standard for Dual-Mode Wide-Band Spread Spectrum Cellular System,” hereinafter referred to as the IS-95 standard. The use of CDMA techniques in a multiple-access communication system is disclosed in U.S. Pat. No. 4,901,307, entitled “SPREAD SPECTRUM MULTIPLE-ACCESS COMMUNICATION SYSTEM USING SATELLITE OR TERRESTRIAL REPEATERS,” and U.S. Pat. No. 5,103,459, entitled “SYSTEM AND METHOD FOR GENERATING WAVEFORMS IN A CDMA CELLULAR TELEPHONE SYSTEM,” both assigned to the assignee of the present invention.
A multiple-access communication system may be a wireless or wire-line and may carry voice and/or data. An example of a communication system carrying both voice and data is a system in accordance with the IS-95 standard, which specifies transmitting voice and data over the communication channel. A method for transmitting data in code channel frames of fixed size is described in detail in U.S. Pat. No. 5,504,773, entitled “METHOD AND APPARATUS FOR THE FORMATTING OF DATA FOR TRANSMISSION”, assigned to the assignee of the present invention. In accordance with the IS-95 standard, the data or voice is partitioned into code channel frames that are 20 milliseconds wide with data rates as high as 14.4 Kbps. Additional examples of a communication systems carrying both voice and data comprise communication systems conforming to the “3rd Generation Partnership Project” (3GPP), embodied in a set of documents including Document Nos. 3G TS 25.211, 3G TS 25.212, 3G TS 25.213, and 3G TS 25.214 (the W-CDMA standard), or “TR45.5 Physical Layer Standard for cdma2000 Spread Spectrum Systems” (the IS-2000 standard).
In a multiple-access communication system, communications between users are conducted through one or more base stations. A first user on one subscriber station communicates to a second user on a second subscriber station by transmitting data on a reverse link to a base station. The base station receives the data and can route the data to another base station. The data is transmitted on a forward link of the same base station, or the other base station, to the second subscriber station. Likewise, the communication can be conducted between a first user on a mobile subscriber station and a second user on a landline station. A base station receives the data from the user on a reverse link, and routes the data through a public switched telephone network (PSTN) to the second user.
The above described wireless communication service is an example of a point-to-point communication service. In contrast, a point-to-multipoint service is a service where information provided by a source of the information is intended for a plurality of users. The basic model of a point-to-multipoint communication system comprises a set of users on subscriber stations, a group of which receives information from one or more sources of information via a wireline or wireless network. In a point-to-multipoint service, in which the source fixedly determines the information content, e.g., news, movies, sports events and the like, the users are generally not communicating back. To save resources, in general, each user's subscriber station participating in the point-to-multipoint service (a member subscriber station) monitors a shared channel modulated by the information. Such a point-to-multipoint service is also referred to as broadcast or multicast, examples of common usage of which comprise TV broadcast, radio broadcast, and the like. Alternatively, the source of information is a user, a member of the group, which transmits information intended for the remaining members of the group. If the user wishes to talk, he presses a push to talk (PTT) button. Typically, the talking user's voice is routed from the subscriber station to the network on a dedicated reverse link channel. The network then transmits the talking user's voice over a forward link shared channel. As in case of the point-to-point communication system, such a communication system allows both landline and wireless subscriber station to access the system. Such a point-to-multipoint service is also referred to as a group service. Examples of the group service communication system use is in dispatch services, such as local police radio systems, taxicab dispatch systems, Federal Bureau of Intelligence and secret service operations, and general military communication systems.
The above-mentioned point-to-multipoint service communication systems are generally highly specialized purpose-build communication systems. With the recent, advancements in wireless cellular telephone systems there has been an interest of utilizing the existing infrastructure of the—mainly point-to-point cellular telephone systems—for point-to-multipoint services. As used herein, the term “cellular” system encompasses system operating on both cellular and personal communication system (PCS) frequencies.
As discussed, to save resources, in general, the point-to-multipoint services rely on assigning a shared forward link channel to be monitored by all the member users. In contrast, the wireless cellular telephone systems assign a dedicated forward and reverse link channels between a base station or sector whose coverage area contains users wishing to communicate. Because of the limited number of such dedicated forward and reverse link channels that can be supported by a wireless cellular telephone system, the number of members who could participate in a point-to-multipoint service provided over dedicated forward and reverse link channels is limited. Furthermore, it is required that both group services and telephone services are enabled in a wireless cellular telephone systems. Therefore, there is a need in the art for a method and apparatus for such a channel management that enables both group services and telephone services utilizing an existing infrastructure of a wireless cellular telephone system.