Method and apparatus for encoding data for transmission in a communication system

#The present invention relates generally to radio communication systems, and more particularly to a method and apparatus for encoding data for transmission in a radio communication system.

#Radio communication systems rely on modulating carrier frequencies in a finite portion of the electromagnetic spectrum to wirelessly transmit and receive signals. Modulation can be performed on the amplitude, frequency, and/or phase of the carrier frequency to separate the signal from unwanted noise. The signals typically convey various types of information such as audio, video, and data to and from transceiving devices such as cellular base stations, cellular subscriber units, and personal computers.

#In code division multiple access communication systems, a plurality of transmissions, each with its own code, can share the same band of frequencies. Each transmission is spread over the available bandwidth by mixing the signal to be transmitted with that signal's unique code. For a CDMA system, spreading gain is defined as the ratio of chip rate to information data rate. This ratio also quantifies the redundancy for any particular user. Typically, information data stream is first encoded by a forward error correction (FEC) code such as a convolutional code. The FEC encoded data stream then is further spreaded by a code from an orthogonal codeword set.

#These and other features and advantages of the present invention will become more apparent from a detailed consideration of the following detailed description of certain preferred embodiments when taken in conjunction with the drawings in which:

#FIG. 1 is a schematic illustration of a communication system capable of utilizing the teachings of the present invention;

#FIG. 2 is a block diagram of a typical code-division multiple access transmitter and receiver;

#Although for simplicity of explanation the following description focuses primarily on encoding data for transmission in a communication system having one or two transmitters, persons of ordinary skill in the art will readily appreciate that the techniques of the present invention are in no way limited to communication systems with only one or two transmitters. On the contrary, a communication system having any number of transmitters sending data streams representing different uses and/or services (e.g., audio, video, pocket data) may employ the techniques shown herein. Further, although for ease of discussion, the following description focuses on a method and apparatus for encoding data for transmission wherein one of the data stream employs a first subset of orthogonal codes for encoding and another data stream employs a second subset of orthogonal codes for encoding; persons of ordinary skill in the art will appreciate that any number of orthogonal code subsets may be employed without departing from the scope of the present invention.

#A representative communication system capable of utilizing the teachings of the present invention is shown in FIG. 1. A base station 10, such as a cellular communications base station or a satellite, is used to transmit and receive a plurality of radio signals 12 to and/or from a plurality of terminals 14, such as voice terminals (e.g., cellular subscriber units) and/or data terminals (e.g., computers). The base station 10 is optionally coupled to a network 16, such as a public switched telephone network (PSTN), the Internet, and/or any other analog or digital network. Signals 12 transmitted to the terminals 14 by the base station 10 could originate from a device connected to the network 16. Similarly, radio signals 12 transmitted to the base station 10 by the terminals 14 could be destined for a device connected to the network 16. The radio signals 12 are transmitted by modulating a carrier frequency. The radio signals 12 could be representative of audio signals (e.g., voice signals), video signals (e.g., television signals), data messages (e.g., computer data), and/or any other signals or combinations of signals. Preferably, the terminals 14 share the available electromagnetic spectrum by using code-division multiple access (CDMA), a well known multiple access technique.

#A typical code-division multiple access communication system is shown in FIG. 2. A transmitter 18 (integral to the base station 10 or terminal 14) spreads 24 a data signal 20, representing a message to be sent, and mixes the result with a carrier 22 to produce the radio signal 12. The radio signal 12 is captured by a receiver 26 (integral to the terminal 14 or base station 10) which recovers an estimate 28 of the data signal 20 by mixing the radio signal 12 with a local carrier 30 and despreading the signal 32.