A microcellular local area network (LAN) for indoor communications is proposed using code division multiple access (CDMA) and DPSK for data modulation. The pseudonoise (PN) codes in the transmitters of the base station are mutually synchronized. For this purpose, sets of Gold code sequences having low cross correlation have been found by an exhaustive computer search. Together with wideband measurements of the indoor radio channel at 900 MHz, a fivepath RAKE receiver was designed to combat fading effects and to process the time diversity by using multipath signal reception. Each receiver path is demodulated independently. Several methods of diversity combining of these paths have been investigated. Acquisition and tracking of the spreading code in the receiver are controlled by a digital signal processor (DSP). Experimental results of the CDMA system are presented, showing the behavior in a multipath environment.
The TIC is an 8 channel, 33MHz digital timeintegrating correlator chip. As the key component of a spread-spectrum receiver it calculates the correlation between an input signal @bit) and a reference sequence (lbit) of length up to 2047.
We present the design and performance measurements of a digital direct-sequence spread-spectrum (DSSS) receiver for a wireless indoor communication system. The system operates at a chip rate of 16.36840' chips/s with a processing gain of 30 dB. A RAKE-structure is used to resolve the time diversity due to multipath propagation. The received signal is despread in 8 arms at the baseband using a digital time-integrating correlator (TIC). All algorithms for synchronization and data demodulation are implemented as software modules on a general purpose digital signal processor (DSP). We give the derivation of these digital algorithms, a description of the hardware implementation, and results of the first measurements. 1038 0-7803-0673-2/92 $3.00 1992 IEEE
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