In the UL, BPSK symbols are used which give you a 1:1 ratio between symbols and bits.
In the DL, QPSK symbols are used which give you a 1:2 ratio between symbols and bits. As such you can get double the data rate for the same spreading factor.
In the UL, BPSK symbols are used which give you a 1:1 ratio between symbols and bits.
In the DL, QPSK symbols are used which give you a 1:2 ratio between symbols and bits. As such you can get double the data rate for the same spreading factor.
Hi Wolverine,
Would you please share a reference document.Thanks
Hi dear Friend,
For WCDMA (after Rel.4) in HSDPA and HSUPA you can refer to page 19&20 of attached file.
As we know, in DL (HSDPA) SF of every code is fix (equal 16).
For WCDMA Rel.99, wolverine's description is enough, I think.
I hope it can help you,
Originally Posted by electron
Hi all,
Can anybody explain why for same air rate for UL we have lesser spreading factor as compare to DL in WCDMA ?
In WCDMA R99:
In DL we have SF = 4 to 512.
For UL, the SF = 4 to 256.
The essence is to bring parity between uplink and downlink speeds as far as the standards go.
The user symbol rate = chip rate/SF. Since, the DL employs QPSK (where each symbol represents 2 bits), and UL employs BPSK (where each symbol represents 1 bit). If you check the data rates for DL with SF 512 and UL with SF 256, you would arrive at the same user throughput. On a sidebar, BPSK is used on UL, rather than QPSK, due to biomedical compatible reasons.
Bookmarks