I. Field of the Invention
The present invention relates to communications. More particularly, the present invention relates to a novel and improved method and apparatus for increasing the available data rate to and from a wireless station by multiplexing signals onto multiple carriers, multiple spread spectrum code channels and/or from multiple base stations.
II. Description of the Related Art
The present invention is concerned with transmitting data at rates which are higher than the capacity of a single CDMA channel. Many solutions to this problem have been proposed. One solution is to allocate multiple channels to the users and allow those users to transmit and receive data in parallel on the plurality of channels available to them. Two methods for providing multiple CDMA channels for use by a single user are described in co-pending U.S. Pat. No. 6,005,855, entitled xe2x80x9cMETHOD AND APPARATUS FOR PROVIDING VARIABLE RATE DATA IN A COMMUNICATIONS SYSTEM USING STATISTICAL MULTIPLEXINGxe2x80x9d, issued Dec. 21, 1999, and U.S. Pat. No. 5,777,999, entitled xe2x80x9cMETHOD AND APPARATUS FOR PROVIDING VARIABLE RATE DATA IN A COMMUNICATIONS SYSTEM USING NON-ORTHOGONAL OVERFLOW CHANNELSxe2x80x9d, issued Jul. 7, 1998, both of which are assigned to the assignee of the present invention and are incorporated by reference herein. In addition, frequency diversity can be obtained by transmitting data over multiple spread spectrum channels that are separated from one another in frequency. A method and apparatus for redundantly transmitting data over multiple CDMA channels is described in U.S. Pat. No. 5,166,951, entitled xe2x80x9cHIGH CAPACITY SPREAD SPECTRUM CHANNELxe2x80x9d, which is incorporated by reference herein.
The use of code division multiple access (CDMA) modulation techniques is one of several techniques for facilitating communications in which a large number of system users are present. Other multiple access communication system techniques, such as time division multiple access (TDMA), frequency division multiple access (FDMA) and AM modulation schemes such as amplitude companded single sideband (ACSSB) are known in the art. However, the spread spectrum modulation technique of CDMA has significant advantages over these modulation techniques for multiple access communication systems. The use of CDMA techniques in a multiple access communication system is disclosed in U.S. Pat. No. 4,901,307, entitled xe2x80x9cSPREAD SPECTRUM MULTIPLE ACCESS COMMUNICATION SYSTEM USING SATELLITE OR TERRESTRIAL REPEATERSxe2x80x9d, assigned to the assignee of the present invention and incorporated by reference herein. The use of CDMA techniques in a multiple access communication system is further disclosed in U.S. Pat. No. 5,103,459, entitled xe2x80x9cSYSTEM AND METHOD FOR GENERATING SIGNAL WAVEFORMS IN A CDMA CELLULAR TELEPHONE SYSTEMxe2x80x9d, assigned to the assignee of the present invention and incorporated by reference herein.
CDMA by its inherent nature of being a wideband signal offers a form of frequency diversity by spreading the signal energy over a wide bandwidth. Therefore, frequency selective fading affects only a small part of the CDMA signal bandwidth. Space or path diversity is obtained by providing multiple signal paths through simultaneous links from a mobile user through two or more cell-sites. Furthermore, path diversity may be obtained by exploiting the multipath environment through spread spectrum processing by allowing a signal arriving with different propagation delays to be received and processed separately. Examples of the utilization of path diversity are illustrated in copending U.S. Pat. No. 5,101,501 entitled xe2x80x9cSOFT HANDOFF IN A CDMA CELLULAR TELEPHONE SYSTEMxe2x80x9d, and U.S. Pat. No. 5,109,390 entitled xe2x80x9cDIVERSITY RECEIVER IN A CDMA CELLULAR TELEPHONE SYSTEMxe2x80x9d, both assigned to the assignee of the present invention and incorporated by reference herein.
The present invention is a novel and improved method and apparatus for the transmission of high speed data in spread spectrum communication systems. In the present invention, high speed data is provided by transmitting data on multiple carrier frequencies, multiple code channels and/or from multiple base stations. In a first embodiment of the present invention, multiplexed code symbols are transmitted on a plurality of carrier frequencies from the same base station. In second embodiment, code symbols are transmitted on multiple carrier frequencies with at least one corner frequency providing the code symbols is a multiple code channels. In a third embodiment, a subset of the multiplexed code symbols are redundantly provided on a different carrier from at least one additional base station. In a fourth embodiment, multiplexed symbols as transmitted on different carriers from the same base station and are redundantly transmitted on another set of carriers from a different base station. In a fifth embodiment, code symbols are multiplexed onto carriers from a plurality of base stations for increased throughput. In a sixth embodiment, code symbols are transmitted on carriers from a first base station and redundantly provided on at least one additional base station on the same carriers as used by the first base station.
The present invention further describes a method wherein a receiver can demodulate data on a plurality of channels and can allocate a demodulator or set of demodulators to search for other available systems, while maintaining the current level of data throughput. In addition the present invention describes a method for receiving multiple paging channels on a plurality of frequencies and code channels.