CC1200: DSSS PN mode

Hi,

My customer is using CC1200 with GFSK 100kbps.
He wants to improve sensitivity and wonders DSSS PN mode can be used.
According to User's guide (SWRU346B) section 5.2.5 "DSSS PN Mode", the mode can be enabled by setting MODCFG_DEV_E.MODEM_MODE=10b.

After changing the mode, he found below behaviors.
a) Up to 16 octets data (exclude PHY header and FCS), data are received properly at receiver side and FCS is matched.
b) More than 16 octets data (exclude PHY header and FCS), FCS does not match.
c) He tried to change configurations, like 802.15.4g mode, data whitening, auto FCS disable, etc. but results were the same.

Here are examples of sent data. data size 16/32/64/128 octets were tried.
Leading 2 bytes (0x18, 0x12) or (0x18, 0x22) are PHY header.
Data with yellow are matched. Results are the similar with different data.

16 octets
send: 0x18,0x12,
0x92,0x3f,0x0c,0xb3,0xd5,0xff,0x24,0x6c,0x7f,0xff,0xed,0x07,0x17,0xff,0x24,0xcc,
recv: 0x18,0x12,
0x92,0x3f,0x0c,0xb3,0xd5,0xff,0x24,0x6c,0x7f,0xff,0xed,0x07,0x17,0xff,0x24,0xcc,

32 octets
send: 0x18,0x22,
0x92,0x3f,0x00,0xb3,0xd5,0xff,0x24,0x6c,0x7f,0xff,0xed,0x07,0x17,0xff,0x24,0xcc,
0x7f,0xff,0xed,0x07,0x17,0xb0,0x00,0x00,0x00,0x80,0x00,0xe0,0x7d,0x74,0x26,0x48,

recv: 0x18,0x22,
0x92,0x3f,0x00,0xb3,0xd5,0xff,0x24,0x6c,0x7f,0xff,0xed,0x07,0x17,0xff,0x24,0xcc,
0x7f,0xff,0xed,0x07,0x17,0xb8,0x8f,0x74,0x8b,0xb1,0x40,0xeb,0xc0,0x9f,0xa2,0xfc,

64 octets
send: 0x18,0x42,
0x92,0x3f,0xf4,0xb3,0xd5,0xff,0x24,0x6c,0x7f,0xff,0xed,0x07,0x17,0xff,0x24,0xcc,
0x7f,0xff,0xed,0x07,0x17,0xb0,0x00,0x00,0x00,0x80,0x00,0xe0,0x7d,0x74,0x26,0x48,
0xb9,0xc5,0xf3,0xd9,0xa8,0xc4,0xb1,0xd5,0x91,0x11,0x01,0x42,0x0c,0x39,0xd5,0xb0,
0x97,0x9d,0x28,0xd4,0xf2,0x9b,0xa4,0xfd,0x64,0x65,0x06,0x8c,0x29,0x96,0xfe,0xa2,

recv: 0x18,0x42,
0x92,0x3f,0xf4,0xb3,0xd5,0xff,0x24,0x6c,0x7f,0xff,0xed,0x07,0x17,0xff,0x24,0xcc,
0x7f,0xff,0xed,0x07,0x17,0xb0,0x00,0x00,0x00,0x80,0x00,0xe0,0x7d,0x74,0xca,0x05,
0xf8,0x77,0x1f,0xc5,0xee,0x4c,0xb0,0x53,0x2d,0x35,0x29,0x80,0xac,0xef,0x7b,0x72,
0x86,0xb6,0x76,0x78,0x7c,0x80,0x4f,0xda,0xda,0x28,0xe4,0x0a,0x42,0xda,0x10,0x49,

128 octets
send: 0x18,0x82,
0x92,0x3f,0x4c,0xb3,0xd5,0xff,0x24,0x6c,0x7f,0xff,0xed,0x07,0x17,0xff,0x24,0xcc,
0x7f,0xff,0xed,0x07,0x17,0xb0,0x00,0x00,0x00,0x80,0x00,0xe0,0x7d,0x74,0x26,0x48,
0xb9,0xc5,0xf3,0xd9,0xa8,0xc4,0xb1,0xd5,0x91,0x11,0x01,0x42,0x0c,0x39,0xd5,0xb0,
0x97,0x9d,0x28,0xd4,0xf2,0x9b,0xa4,0xfd,0x64,0x65,0x06,0x8c,0x29,0x96,0xfe,0xa2,
0x71,0x4d,0xf3,0xf8,0x2e,0x58,0xdb,0x0d,0x5a,0x5f,0x15,0x28,0xf5,0x74,0x07,0xce,
0x25,0xaf,0x2b,0x12,0xe6,0xd0,0xdb,0x2c,0xdc,0xc3,0x7f,0xf0,0x3e,0x3a,0x13,0xa4,
0xdc,0xe2,0xf9,0x6c,0x54,0xe2,0xd8,0xea,0xc8,0x88,0x00,0x21,0x86,0x9c,0x6a,0xd8,
0xcb,0x4e,0x14,0x6a,0xf9,0x4d,0xd2,0x7e,0xb2,0x32,0x03,0xc6,0x14,0x4b,0x7f,0xd1, 

recv: 0x18,0x82,
0x92,0x3f,0x4c,0xb3,0xd5,0xff,0x24,0x6c,0x7f,0xff,0xed,0x07,0x17,0xff,0x24,0xcc,
0x7f,0xff,0xed,0x07,0x17,0xb0,0x00,0x00,0x00,0x80,0x00,0xe0,0x7d,0x74,0x26,0x48,
0xb9,0xc5,0xf3,0xd9,0xa8,0xc4,0xb1,0xd5,0x91,0x11,0x01,0x42,0x0c,0x39,0xd5,0x7b,
0x8f,0xa7,0x46,0x9c,0x5c,0x76,0x8d,0x1b,0x49,0x0d,0x2e,0xbf,0x5b,0xd4,0x5e,0xcd,
0xea,0x6c,0xb7,0xac,0xad,0x17,0x2b,0x2a,0xe8,0xa5,0x3a,0xd4,0x96,0xdc,0x51,0x73,
0x87,0xcf,0x29,0x48,0x3c,0xfe,0x56,0x9d,0xa9,0x1f,0xbd,0x24,0x08,0xa0,0x6d,0xa8,
0x94,0x6d,0xfd,0xdc,0xaf,0x61,0x59,0x5e,0xf5,0x00,0x87,0x14,0x7a,0x88,0xd2,0x6d,
0x06,0x96,0x3a,0x5d,0x2a,0x72,0xb4,0x09,0x18,0xf6,0xcc,0x1e,0xaf,0x82,0xbd,0x7b,

Could you tell me how to use DSSS PN mode properly?

Thanks and regards,
Koichiro Tashiro