A CDMA format is used within a network to permit communication between members of a network. Network members are synchronized to each other and are each aware of a predetermined set of code words which has been established. A member desiring to transmit data selects a code word from the predetermined set. If there are unused code words, one of the unused words is randomly selected. If all words are being used, the code word of the farthest user is selected. Since all members are synchronized in time to stable clocks, the range of each user is known. All members of the network are always listening and keeping track of detections of other users and code words. Transmitted signals are a series of pulses with a jitter or sync pulse inserted within each series. The number and location of sync pulses is unique for each code and defines the CDMA code of the signal. A pseudorandom noise generator synchronized to the clock is gated with coded data pulsed with appropriate jitter insertion and transmitted over a frequency determined by the pseudorandom number at any instant in time.
Subtractive CDMA demodulation optimally decodes a coded information signal embedded in many other overlapping signals making up a received, composite signal. A radio receiver correlates a unique code corresponding to the desired signal to be decoded with the composite signal. Moreover, after each information signal is successfully decoded, it is recoded and removed from the composite signal. Subtractive CDMA demodulation is enhanced by decoding the composite signal in the order of strongest to weakest signal strength. The individual information signals are spread using block error correction codes which are correlated with the composite signal using Fast Walsh transforms. Correlated signals identified as the largest transform component are removed from the composite signal and the remaining composite signal is reformulated using an inverted Fast Walsh transform. Any residual error or interference caused during the extraction of a transform component is removed by recorrelating the composite signal using the index of that transform component.
A transmission method in a predetermined transmission bandwidth with a predetermined transmission format for a multiple access includes coding a signal at a position for managing a multiple access and transmitting a coded signal to base stations, modulating the coded signal at the base stations, respectively; and transmitting an output signal obtained by modulating the base stations.
A low-cost data communication system and method using modems to provide high speed multi-class services to subscribers is disclosed. In the present invention, an n-bit orthogonal modulating code is uniquely partitioned into several subsets whereas each subset is assigned to a particular class of services. When data streams from different classes of services go through an encoding modem equipped with the partitioned orthogonal codes, they can be split based on their classes, encoded, modulated through a multilevel phase modulation simultaneously. Thereafter, since the encoded streams are orthogonal to each other, they can be combined as a composite modulated outgoing data stream and transmitted through a wired communication channel such as a cable or optical fiber channel. At a receiving end, a decoding modem can receive the encoding scheme from the encoding modem, and appropriately decode the transmitted information. This method enables sharing the same communication channel by multiple classes of services and processing different classes of information separately but simultaneously, and thus enhancing the overall performance of the shared communication channel.
A cellular digital radio transmission system wherein messages are transmitted from a base station to a plurality of mobile stations assigned to it by time-division multiplexing of time slots in respective TDM time frames, each mobile station being assigned by the base station to a respective time slot constituting a channel for receiving and transmitting information. In order to fully utilize the channel capacity of the TDM time frames for users having different bandwidth requirements the base station divides each TDM time frame into time slots of different durations, whereby a mobile station can be assigned by the base station to a time slot of a duration corresponding to the bandwidth required by such mobile station.
A cellular communications system is provided having both surface and satellite nodes which are fully integrated for providing service over large areas. A spread spectrum system is used with code division multiple access (CDMA) employing forward error correction coding (FECC) to enhance the effective gain and selectivity of the system. Multiple beam, relatively high gain antennas are disposed in the satellite nodes to establish the satellite cells, and by coupling the extra gain obtained with FECC to the high gain satellite node antennas, enough gain is created in the satellite part of the system such that a user need only use a small, mobile handset with a non-directional antenna for communications with both ground nodes and satellite nodes. User position information is also available. A digital data interleaving feature reduces fading.
