Cyclic Shift Diversity (CSD)
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Cyclic Shift Diversity (CSD)
- Cyclic shift diversity (CSD) is transmit diversity technique specified in the 802.11n standard.
- Unlike STBC, a signal from a transmitter that uses CSD can be received by legacy 802.11g and 802.11a devices.
- For mixed mode deployments, where 802.11n coexists with 802.11g and 802.11a devices, there is a need to have a way of transmitting the symbols in the legacy OFDM preamble over multiple transmit antennas.
- CSD is used and a cyclic delay is applied to each of the transmitted signals.
- The delays are calculated to minimize the correlation between the multiple signals.
- A conventional legacy system would treat the multiple received signals as multipath versions of the same signal.
- The cyclic delay is chosen to be within the limits of the guard interval (GI) so that it does not cause excessive intersymbol interference (ISI).
- An 802.11n system has no problem using the multiple signals to improve the overall SNR of the preamble.
Reference:
Coleman, David D.,Westcott, David A. CWNA: Certified Wireless Network Administrator Official Study Guide: Exam CWNA-106 Wiley.
Coleman, David D.,Westcott, David A. CWNA: Certified Wireless Network Administrator Official Study Guide: Exam CWNA-106 Wiley.
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