DSCDMA

DS-CDMA, direct-sequence code-division multiple access, is a spread-spectrum communication method that lets multiple users share the same radio channel. Each user is assigned a unique direct-sequence spreading code, which multiplies the data before transmission, spreading it over a wide bandwidth. The receiver uses the same code to de-spread the signal, recovering the data. This process provides resistance to interference and eavesdropping and enables concurrent multi-user access on the same spectrum.

Implementation typically combines orthogonal codes for channelization with independent pseudo-random sequences for user separation. Modulation is usually BPSK, though higher-order schemes may be used. The spreading factor (chip rate divided by data rate) determines processing gain and resilience to interference; higher factors improve interference tolerance but lower data throughput. The near-far problem is addressed with network power control, adaptive coding, and soft handoffs.

DS-CDMA was central to early CDMA cellular systems, notably IS-95 and CDMA2000. It uses rake receivers to exploit multipath and provides soft handover between cells. Its interference robustness and QoS capabilities supported multi-rate service, but it requires sophisticated receivers and careful power management.

Today it has largely been superseded by OFDM-based technologies such as LTE and 5G, but DS-CDMA remains part of legacy CDMA2000 networks and is of historical and interoperability interest.