Re: [STDS-802-16] Query regarding RS encoding in 802.16a
Hello Sridhar,
As you correctly observed, the RS encoder in OFDM mode sends the check bytes
first, and only then the data. This is related to the implementation
assumption that the zero tail byte (needed for the convolutional encoding)
is added prior to RS encoding, and in this manner it stays at the end. The
other alternative (which was not chosen) was to shorten the last RS block by
one data byte and add the tail byte in the convolutional encoder.
In the OFDMA mode the CC encoder is of Tail Biting type, therefore there in
no issue with the zero byte at the end of the message. Therefore the RS is
implemented in a more traditional way. This is not relevant any more,
however, since the RS was removed from the OFDMA spec and the example will
be adjusted accordingly soon.
Naftali Chayat
Alvarion.
-----Original Message-----
From: Sridhar [mailto:sridhar@isofttech.com]
Sent: Friday, April 30, 2004 4:02 PM
To: STDS-802-16@listserv.ieee.org
Subject: [STDS-802-16] Query regarding RS encoding in 802.16a
> Hi all,
> Here i have a query regarding RS encoding procedure in 802.16a-2003. In
> 802.16a standard document one
> "Example OFDM UL RS-CC encoding" was given under 8.4.3.5. In that, the
> randomized data was given as
> D5 0E A4 AA EF E4 DB 51 88 91 6B 00 DF AA 1E E7 02 A8 0E 70 4F 7F C9 D8 66
> 1D 9D F0 E7 20 E4 9D 7A 32 91
> and the Reed-solomon encoded data as
> 95 CE 22 76 D5 0E A4 AA EF E4 DB 51 88 91 6B 00 DF AA 1E E7 02 A8 0E 70 4F
> 7F C9 D8 66 1D 9D F0 E7 20 E4 9D 7A 32 91 00
> where 95 CE 22 76 are the parity bits that we get after encoding the
> randomized data. That means the parity bits were sent first and then the
> actual data part. That means one should have a buffer for the data part so
> that we send the parity bits first and then data part.
>
> But in the same standard, for OFDMA case there is another example. In
> 8.5.9.4.4, "Example of OFDMA UL RS-CC encoding" the randomized data
> was given as
> 5B 23 80 44 35 82 06 07 47 67 CB 37 1F 1A 9D 44 0B 62 3A CC F4 F4 50 E1 30
> 8A 6A 80 D4 00 4E 5E 84 BA 96 57
> and RS encoded data as
> 5B 23 80 44 35 82 06 07 47 67 CB 37 1F 1A 9D 44 0B 62 3A CC F4 F4 50 E1 30
> 8A 6A 80 D4 00 4E 5E 84 BA 96 57 3A CE 4E 81 36 AB DA 26 13 3E D1 3B
> That means the parity bits 3A CE 4E 81 36 AB DA 26 13 3E D1 3B were added
> after the data part. In this case, we may not need storage to buffer the
> data part.
> Can some one tell me why there is a difference like that?
> Which one is correct? I will be greatful if some one throgh some light on
> this.
>
> Thanks and Regards,
> Sridhar Nandula
> Sr Design Engineer
> Isofttech Pvt Ltd,
> Chennai, +91-44-24364915 ext 54
> India
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