Synchronous multipoint-to-point CDMA communication system
First Claim
1. A synchronous multipoint-to-point CDMA communication system, comprising:
- a plurality of CDMA transmitting stations and a single CDMA receiving station, all of which are intercoupled to each other over one CDMA channel and one feedback channel;
said CDMA transmitting stations each including a respective modulator which modulates data signals with a respective spreading code to generate CDMA signals that are added together on said CDMA channel and sent to said CDMA receiving station;
said CDMA receiving station including an error detection circuit which detects respective time differences between a reference clock signal and said spreading codes in said CDMA signals as received at said CDMA receiving station, and an error sending circuit which sends respective error signals that indicate said time differences over said feedback channel to each of said CDMA transmitting stations; and
,said CDMA transmitting stations each including a respective error receiver circuit which receives a respective error signal on said feedback channel, and a respective error correction circuit which responds to the received error signal by time shifting said CDMA signals to said CDMA channel such that said spreading code in said CDMA signals arrive at said receiving station in synchronization with said reference clock signal.
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Abstract
A multipoint-to-point CDMA communication system comprises a plurality of CDMA transmitting stations and a single CDMA receiving station, all of which are intercoupled to each other over one CDMA channel and one feedback channel. On the one CDMA channel, the plurality of CDMA transmitting stations simultaneously send respective CDMA signals to the receiving station. In the receiving station, respective time differences are measured between a reference clock signal and the spreading codes in the CDMA signals from each of the CDMA transmitting stations; and these time differences are indicated in respective error signals which the CDMA receiving station sends on the feedback channel to each of the CDMA transmitting stations. Each CDMA station responds to its error signals by time shifting its spreading code such that it arrives in the receiving station in synchronization with the reference clock signal. This synchronization enables interference between the spreading codes at the receiving station to be reduced by using codes which have minimal cross-correlation when their time difference is zero; and consequently, the maximum number of stations that can simultaneously transmit is increased.
181 Citations
19 Claims
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1. A synchronous multipoint-to-point CDMA communication system, comprising:
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a plurality of CDMA transmitting stations and a single CDMA receiving station, all of which are intercoupled to each other over one CDMA channel and one feedback channel; said CDMA transmitting stations each including a respective modulator which modulates data signals with a respective spreading code to generate CDMA signals that are added together on said CDMA channel and sent to said CDMA receiving station; said CDMA receiving station including an error detection circuit which detects respective time differences between a reference clock signal and said spreading codes in said CDMA signals as received at said CDMA receiving station, and an error sending circuit which sends respective error signals that indicate said time differences over said feedback channel to each of said CDMA transmitting stations; and
,said CDMA transmitting stations each including a respective error receiver circuit which receives a respective error signal on said feedback channel, and a respective error correction circuit which responds to the received error signal by time shifting said CDMA signals to said CDMA channel such that said spreading code in said CDMA signals arrive at said receiving station in synchronization with said reference clock signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19)
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Specification