l1/xch_dc12: Add channel coding for various channel types over DC12 bursts

Used in GMR-1 3G

Signed-off-by: Sylvain Munaut <tnt@246tNt.com>

1 files changed, 107 insertions, 0 deletions

diff --git a/src/l1/xch_dc12.c b/src/l1/xch_dc12.c
new file mode 100644
index 0000000..26c122e
--- /dev/null
+++ b/src/l1/xch_dc12.c
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+/* GMR-1 xCH over DC12 channel coding */
+/* See GMR-1 05.003 (ETSI TS 101 376-5-3 V3.3.1) - Section 6.1a */
+
+/* (C) 2011-2016 by Sylvain Munaut <tnt@246tNt.com>
+ * All Rights Reserved
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+/*! \addtogroup xch_dc12
+ *  @{
+ */
+
+/*! \file l1/xch_dc12.c
+ *  \brief Osmocom GMR-1 xCH over DC12 channel coding implementation
+ */
+
+#include <stdint.h>
+#include <string.h>
+
+#include <osmocom/core/bits.h>
+#include <osmocom/core/conv.h>
+#include <osmocom/core/crc16gen.h>
+
+#include <osmocom/gmr1/l1/conv.h>
+#include <osmocom/gmr1/l1/crc.h>
+#include <osmocom/gmr1/l1/interleave.h>
+#include <osmocom/gmr1/l1/punct.h>
+#include <osmocom/gmr1/l1/scramb.h>
+
+
+static struct osmo_conv_code gmr1_conv_xch_dc12;
+
+static void __attribute__ ((constructor))
+gmr1_xch_dc12_init(void)
+{
+	/* Init convolutional coder */
+	memcpy(&gmr1_conv_xch_dc12, &gmr1_conv_k9_13, sizeof(struct osmo_conv_code));
+	gmr1_conv_xch_dc12.len = 208;
+	gmr1_puncturer_generate(&gmr1_conv_xch_dc12, NULL, &gmr1_punct_k9_13_P1213, NULL, 0);
+}
+
+
+/*! \brief Stateless GMR-1 xCH over DC12 channel coder
+ *  \param[out] bits_e Data bits of a burst
+ *  \param[in] l2 L2 packet data
+ *
+ * L2 data is 24 byte long, and bits_e is a 432 hard bit array to be
+ * mapped on a burst.
+ */
+void
+gmr1_xch_dc12_encode(ubit_t *bits_e, const uint8_t *l2)
+{
+	ubit_t bits_u[208];
+	ubit_t bits_c[432];
+	ubit_t bits_ep[432];
+
+	osmo_pbit2ubit_ext(bits_u, 0, l2, 0, 192, 1);
+	osmo_crc16gen_set_bits(&gmr1_crc16, bits_u, 192, bits_u+192);
+	osmo_conv_encode(&gmr1_conv_xch_dc12, bits_u, bits_c);
+	gmr1_interleave_intra(bits_ep, bits_c, 54);
+	gmr1_scramble_ubit(bits_e, bits_ep, 432);
+}
+
+/*! \brief Stateless GMR-1 xCH over DC12 channel decoder
+ *  \param[out] l2 L2 packet data
+ *  \param[in] bits_e Data bits of a burst
+ *  \param[out] conv_rv Return of the convolutional decode (can be NULL)
+ *  \return 0 if CRC check pass, any other value for fail.
+ *
+ * L2 data is 24 byte long, and bits_e is a 432 soft bit array
+ * unmapped from a burst.
+ */
+int
+gmr1_xch_dc12_decode(uint8_t *l2, const sbit_t *bits_e, int *conv_rv)
+{
+	sbit_t bits_ep[432];
+	sbit_t bits_c[432];
+	ubit_t bits_u[208];
+	int rv;
+
+	gmr1_scramble_sbit(bits_ep, bits_e, 432);
+	gmr1_deinterleave_intra(bits_c, bits_ep, 54);
+
+	rv = osmo_conv_decode(&gmr1_conv_xch_dc12, bits_c, bits_u);
+	if (conv_rv)
+		*conv_rv = rv;
+
+	rv = osmo_crc16gen_check_bits(&gmr1_crc16, bits_u, 192, bits_u+192);
+
+	osmo_ubit2pbit_ext(l2, 0, bits_u, 0, 192, 1);
+
+	return rv;
+}
+
+/*! @} */