Design and implementation of intracell reverse link using approximately synchronized CDMA

We have proposed an intracell reverse link of an SS-CDMA flexible wireless network based on an approximately synchronized (AS) CDMA. The AS-CDMA features no co-channel interference during a guard-chip duration. A sequence with the guard-chip duration can be designed using the pseudo periodic method and the orthogonal frequency multi-channel method. The reverse link without co-channel interference does not require the sophisticated transmission power control, which is indispensable in the conventional systems such as IS-95. The AS-CDMA modem has been designed and implemented for the Japanese 2.4 GHz SS band. An AS-CDMA sequence of length 48 is designed. The number of orthogonal frequency multi-channel method is 2. One of the features of the implemented reverse link modem is the use of surface-acoustic-wave convolver as a correlator for rapid synchronization. The effects of frequency offset on stability have been evaluated using computer simulation. The simulation results have shown that the degradation of E_b/N₀ at a BER of 10^-4 is 1.4 dB, when the carrier frequency offset of an undesired signal is ±1 ppm and the desired-undesired signal power ratio is -30 dB. In the implemented AS-CDMA reverse link modem, the measured degradation of E_b/N₀ has been found to be 3.0 dB at a BER of 10^-4.