1. Field
The present invention relates generally to communications, and more specifically, to decoding signals received on wireless communication systems.
2. Background
The field of wireless communications has many applications including, e.g., cordless telephones, paging, wireless local loops, personal digital assistants (PDAs), Internet telephony, and satellite communication systems. A particularly important application is cellular telephone systems for mobile subscribers. As used herein, the term “cellular” system encompasses both cellular and personal communications services (PCS) frequencies. Various over-the-air interfaces have been developed for such cellular telephone systems including, e.g., frequency division multiple access (FDMA), time division multiple access (TDMA), and code division multiple access (CDMA). In connection therewith, various domestic and international standards have been established including, e.g., Advanced Mobile Phone Service (AMPS), Global System for Mobile (GSM), and Interim Standard 95 (IS-95). IS-95 and its derivatives, IS-95A, IS-95B, ANSI J-STD-008 (often referred to collectively herein as IS-95), and proposed high-data-rate systems are promulgated by the Telecommunication Industry Association (TIA) and other well known standards bodies.
Cellular telephone systems configured in accordance with the use of the IS-95 standard employ CDMA signal processing techniques to provide highly efficient and robust cellular telephone service. Exemplary cellular telephone systems configured substantially in accordance with the use of the IS-95 standard are described in U.S. Pat. Nos. 5,103,459 and 4,901,307, which are assigned to the assignee of the present invention and incorporated by reference herein. An exemplary system utilizing CDMA techniques is the cdma2000 ITU-R Radio Transmission Technology (RTT) Candidate Submission (referred to herein as cdma2000), issued by the TIA. The standard for cdma2000 is given in the draft versions of IS-2000 and has been approved by the TIA, and the 3rd Generation Partnership Project 2 “3GPP2”. Another CDMA standard is the W-CDMA standard, as embodied in 3rd Generation Partnership Project “3GPP”, Document Nos. 3G TS 25.211, 3G TS 25.212, 3G TS 25.213, and 3G TS 25.214.
The telecommunication standards cited above are examples of only some of the various communications systems that can be implemented. Within these various communications systems, multiple users must share limited system resources. In accordance with the actual system implementation, resources such as frequency bandwidth, time, transmission power, or spreading code assignments are typically shared by multiple users within the system. In a FDMA system, the system bandwidth is divided into many frequency channels and each frequency channel is allocated to a user. In a TDMA system, the system bandwidth is divided into many time slots and each time slot is allocated to a user. In a CDMA system, the system bandwidth is simultaneously shared among all users by using spreading codes, wherein each user is assigned a spreading code.
User demand drives the development of higher transmission data rate systems. In systems that can transmit data traffic in packetized formats, such as TDMA and CDMA systems, control information is transmitted containing essential information, such as the identity of the addressee, the modulation format, the coding format, the transmission timing, and the orthogonal codes used to cover the data. Receivers that cannot decode this control information correctly will fail to receive the packet data. Furthermore, receivers that cannot decode this information in a timely manner will have to store portions or all of the possible orthogonal codes with sufficient resolution in a memory element, whereupon the stored codes can be used to de-modulate data information at a later time. Such an implementation would increase the complexity and cost of the receiver.
It is therefore desirable to provide means for the control information to be decoded with a high probability of success and in a timely manner. Possible methods of increasing the probability of correctly decoding the control information are to increase the transmission power at which the control information is transmitted or to increase the duration of the transmission. However, these methods are undesirable due to the increased consumption of system resources, which in turn, decreases the amount of available resources for the transmission of data. Methods to increase transmission data rates are useless without the ability to quickly and accurately decode received information. Hence, there is a current need for improving the speed and accuracy at which decoders operate.