Method and apparatus for achieving data rate variability in orthogonal spread spectrum communication systems

Abstract

A CDMA communication system is disclosed offering a near continuum of data rates up to a maximum rate. The disclosed CDMA communication system increases the data rate variability, without disturbing the orthogonality between users. An increased number of data rates is obtained by time multiplexing the data rates achievable with conventional CDMA systems to provide additional data rates for various multimedia applications. If a user is assigned a specific orthogonal code sequence, such as a Walsh sequence, which permits a maximum data rate, nR, with conventional systems, the user can obtain additional desired data rates up to the maximum rate nR, by time multiplexing the specific orthogonal code set. Desired bit rates are achievable for applications requiring bit rates that are not an integer multiple of the rates provided by conventional techniques. A fundamental rate of R or “fat pipe” rates of powers-of-two multiples of the fundamental rate can be achieved in a conventional manner. A desired rate up to the maximum “fat pipe” rate is achieved by time multiplexing the codes w to achieve rates between R and nR, where w , denotes the first nth of the spread spectrum code w . The transmitter of the present invention achieves a rate conversion to match the appropriate codeword to the appropriate data rate, by employing buffering and reclocking of the data, with time multiplexing of the orthogonal Walsh codes corresponding to the available lower and upper rates. The rate conversion must be synchronized with the selection of the orthogonal Walsh code (corresponding to the lower and upper rates).